Surface integrity and biofunctional performance of AISI 316L stainless steel implants: the role of mechanical surface treatments, corrosion resistance, and tribocorrosion behavior

1 Introduction

Metallic biomaterials remain essential in contemporary medicine owing to their ability to provide the mechanical strength, structural reliability, and durability required for long-term clinical applications. Orthopedic, dental, cardiovascular, and trauma-related devices frequently operate under complex loading conditions while simultaneously interacting with physiological environments. Consequently, the selection and engineering of metallic biomaterials continue to pose significant challenges in the development of safe, durable, and biologically compatible implant systems, in which long-term clinical success depends on the interplay among mechanical reliability, corrosion resistance, and host biological response (Ratner et al., 2013; Hanawa, 2004; Chen and Thouas, 2015; Navarro et al., 2008; Geetha et al., 2009).

Among the metallic materials employed in biomedical applications, AISI 316L stainless steel has maintained a prominent position for several decades. The alloy combines satisfactory mechanical properties, good corrosion resistance, manufacturing versatility, widespread availability, and relatively low production costs. These characteristics have supported its extensive use in fracture fixation devices, spinal implants, cardiovascular components, temporary orthopedic systems, and surgical instruments (Disegi and Eschbach, 2000; Jawahir et al., 2011; M'Saoubi et al., 2008a). Despite these advantages, concerns regarding localized corrosion, tribocorrosion, wear-induced degradation, release of metallic ions, and long-term biological interactions continue to motivate the development of advanced surface engineering strategies.

The long-term performance of metallic implants depends not only on their bulk properties but also on the characteristics of the surface exposed to the biological environment. Following implantation, the surface becomes the primary region of interaction between the material and surrounding tissues. Proteins, cells, microorganisms, physiological fluids, and mechanical forces act directly on the surface, making it a critical region for both degradation processes and biological responses (Marcus, 2011; Revie, 2011). These interactions are dynamic and mutually dependent, making surface integrity a key determinant of both implant longevity and clinical performance.

The concept of surface integrity provides a comprehensive framework for understanding the interactions occurring at the implant–environment interface. Surface integrity encompasses the topographical, microstructural, mechanical, and physicochemical characteristics of the surface and subsurface regions generated during manufacturing and post-processing operations (Jawahir et al., 2011; M'Saoubi et al., 2008a). Parameters such as surface roughness, residual stress distribution, grain refinement, phase constitution, and deformation-induced microstructural changes can significantly influence corrosion behavior, wear resistance, fatigue performance, tribocorrosion mechanisms, and biological interactions (Jawahir et al., 2011; M'Saoubi et al., 2008a; Marcus, 2011; Revie, 2011; Mischler, 2008; Landolt et al., 2001; Moriarty, 2001; Valiev et al., 2000; Bagherifard et al., 2012). However, the relative contribution of each parameter remains dependent on the specific surface treatment, processing conditions, and physiological environment, highlighting the need for a critical comparison of available experimental evidence. The relationships among these factors and their contribution to implant performance are illustrated in Figure 1.

Although AISI 316L exhibits good corrosion resistance because of the formation of a chromium-rich passive film, degradation may still occur under physiological conditions (Schmutz and Virtanen, 2006). Localized corrosion, passive film instability, release of metallic ions, wear processes, cyclic loading, and microbial colonization have all been reported as factors affecting implant durability and clinical performance (Mischler, 2008; Landolt et al., 2001; Moriarty, 2001). In many biomedical applications, these mechanisms do not act independently but interact in complex ways throughout the device’s service life. Implant design, loading conditions, and patient-specific physiological factors strongly influence the clinical relevance of these degradation mechanisms.

Particular attention has been paid to tribocorrosion, a degradation phenomenon resulting from the simultaneous action of wear and corrosion. Recent studies have demonstrated that the magnitude of synergistic material loss varies considerably with contact conditions, electrochemical environment, passive film repassivation kinetics, and surface modification strategy, underscoring the need for standardized testing methodologies and quantitative comparisons. In orthopedic and dental systems, repeated mechanical contact may disrupt passive films, exposing fresh metallic surfaces to the physiological environment and accelerating material degradation. This interaction may increase material loss, influence electrochemical behavior, and modify biological responses occurring at the implant–tissue interface (Valiev et al., 2000).

In parallel with the growing understanding of degradation mechanisms, significant advances have been achieved in surface engineering technologies. Mechanical surface treatments such as shot peening, burnishing, deep rolling, ultrasonic surface modification, and laser shock peening have been shown to alter the near-surface microstructure without altering the alloy’s bulk composition. Although these treatments generally improve surface mechanical properties, their effects on corrosion resistance and biological performance are not universally consistent, requiring careful evaluation of processing parameters and service conditions. These treatments may induce grain refinement, residual compressive stresses, increased dislocation density, and phase transformations, thereby influencing both degradation resistance and biological performance (Bagherifard et al., 2012).

Recent investigations have suggested that surface integrity may influence biofunctional behavior. Surface features generated through mechanical processing can affect protein adsorption, cellular attachment, osteogenic activity, bacterial adhesion, tissue integration, macrophage polarization, immune modulation, angiogenesis, and early osteoimmunological events. However, the magnitude of these effects depends on the specific surface condition and biological environment (Marcus, 2011; Revie, 2011; Valiev et al., 2000; Bagherifard et al., 2012).

The principal degradation mechanisms affecting AISI 316L biomedical implants, together with their potential implications for long-term clinical performance, are summarized in Table 1 (Marcus, 2011; Revie, 2011; Mischler, 2008; Landolt et al., 2001). A comprehensive understanding of the interactions among corrosion, wear, tribocorrosion, fatigue-related damage, metallic ion release, and biological processes, and their influence on implant longevity and clinical reliability, is essential for the rational design of surface engineering strategies to improve both durability and biofunctional performance. Furthermore, establishing reliable correlations between laboratory observations and clinical outcomes remains a major challenge in the development of next-generation stainless-steel implants (Mischler, 2008; Landolt et al., 2001; Moriarty, 2001; Valiev et al., 2000; Bagherifard et al., 2012).

TABLE 1. Literature search strategy, eligibility criteria, information sources, and study-selection workflow adopted in this review according to the PRISMA 2020 reporting guideline.

Electronic searches identified 63 records, complemented by 7 records obtained through manual reference screening, resulting in 70 potentially relevant studies. After duplicate removal (n = 18), 52 records underwent title and abstract screening. Twenty-three studies were assessed for full-text eligibility, of which 11 satisfied all inclusion criteria and were incorporated into the qualitative evidence synthesis. PRISMA, Preferred Reporting Items for Systematic Reviews and Meta-Analyses.

The objective of this review is to critically evaluate the relationships among mechanical surface treatments, surface integrity, corrosion resistance, tribocorrosion behavior, and biological performance in AISI 316L stainless steel used for biomedical applications. The literature analyzed in this review was identified through a structured search strategy conducted via the CAPES Journal Portal and is reported in accordance with the PRISMA 2020 reporting guideline. Particular emphasis is placed on critically comparing the available experimental evidence, identifying current knowledge gaps and methodological limitations, and discussing the mechanisms by which different mechanical surface treatments influence corrosion behavior, tribocorrosion resistance, and biological performance. The review also examines emerging opportunities to integrate mechanically engineered surfaces with bioactive and multifunctional surface technologies to support the development of next-generation biomedical implants with improved long-term clinical performance.

2 Review methodology

This review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) guidelines to ensure transparency, reproducibility, and methodological rigor throughout the processes of literature identification, screening, eligibility assessment, and qualitative evidence synthesis (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019). The structured qualitative review conducted according to PRISMA 2020 focused on published studies addressing the influence of mechanical surface treatments on the surface integrity, corrosion behavior, tribocorrosion resistance, and biological performance of AISI 316L stainless steel for biomedical applications. Because the available literature exhibited substantial heterogeneity regarding surface-treatment parameters, experimental methodologies, electrochemical protocols, tribological conditions, biological evaluation methods, and reported outcome measures, a qualitative critical synthesis was considered more appropriate than a quantitative meta-analysis (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019). The methodological workflow adopted in this structured qualitative review, conducted according to PRISMA 2020, is illustrated in Figure 1, while the complete literature search strategy is summarized in Table 1.

2.1 Review protocol (PRISMA 2020)

This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA 2020) reporting guideline, which provides a transparent and reproducible framework for identifying, screening, assessing eligibility, and synthesizing published evidence (Page et al., 2021a; Page et al., 2021b). The review protocol was designed to ensure methodological consistency throughout the literature-search process and to minimize potential sources of selection bias by applying predefined search strategies and eligibility criteria (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019). Although this review was not prospectively registered in the International Prospective Register of Systematic Reviews (PROSPERO) because its scope is focused on biomaterials and surface engineering rather than clinical interventions, the methodological principles established by PRISMA 2020 were adopted throughout all stages of the review (Page et al., 2021a; Page et al., 2021b).

The review aimed to critically evaluate published evidence regarding the influence of mechanical surface treatments on the surface integrity, microstructural evolution, corrosion resistance, tribocorrosion behavior, and biological performance of AISI 316L stainless steel used in biomedical applications. Emphasis was placed on studies investigating the relationships between deformation-induced microstructural modifications and their effects on electrochemical, tribological, mechanical, and biological responses under conditions relevant to orthopedic, dental, cardiovascular, and surgical implants (Ratner et al., 2013; Hanawa, 2004; Chen and Thouas, 2015; Navarro et al., 2008; Geetha et al., 2009; Disegi and Eschbach, 2000; Jawahir et al., 2011; M'Saoubi et al., 2008a; Marcus, 2011; Revie, 2011; Mischler, 2008; Landolt et al., 2001; Moriarty, 2001; Valiev et al., 2000; Bagherifard et al., 2012).

The methodological workflow adopted in this structured qualitative review conducted according to PRISMA 2020 comprised six sequential stages: (i) definition of the research question and review scope; (ii) identification of relevant publications through structured database searches; (iii) removal of duplicate records; (iv) screening of titles and abstracts according to predefined eligibility criteria; (v) full-text assessment of potentially relevant studies; and (vi) qualitative extraction and critical synthesis of the selected evidence. The complete study-selection process is presented in the PRISMA flow diagram (Figure 1), while the literature search strategy, eligibility criteria, information sources, and study-selection workflow are summarized in Table 1 (Page et al., 2021a; Page et al., 2021b).

2.2 Information sources

The literature search was conducted through the CAPES Journal Portal (Coordination for the Improvement of Higher Education Personnel, Brazil), which provides institutional access to major international scientific databases. These databases cover biomaterials, materials science, corrosion engineering, tribology, surface engineering, and biomedical research (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

The databases accessed through the CAPES Portal included Web of Science Core Collection, Scopus, ScienceDirect (Elsevier), SpringerLink, Wiley Online Library, Taylor and Francis Online, IEEE Xplore, ACS Publications, Nature Portfolio, MDPI, and SAGE Journals, among other indexed scientific sources.

To maximize literature coverage and minimize the risk of publication bias, complementary manual searches were also performed by examining the reference lists of the selected articles and recent review papers. This additional screening enabled the identification of relevant publications that were not retrieved during the initial electronic database search, particularly highly cited classical studies and recently published articles available online ahead of print (Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

The literature search prioritized peer-reviewed journal articles published in English and covered publications from 2000 to June 2026, with particular emphasis on studies published between 2022 and 2026 in order to incorporate recent advances in mechanical surface treatments, corrosion science, tribocorrosion, surface integrity, and biological performance of AISI 316L stainless steel for biomedical applications. The principal information sources, search periods, and retrieved records are summarized in Table 1.

2.3 Search strategy

A comprehensive literature search was conducted using predefined Boolean expressions to identify studies examining the effects of mechanical surface treatments on the surface integrity and functional performance of AISI 316L stainless steel for biomedical applications. The search strategy combined keywords related to the alloy, degradation mechanisms, and surface engineering processes to maximize both the sensitivity and specificity of the retrieved records (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

The principal search expression adopted in this review was (“AISI 316L” OR “316L stainless steel”) AND (tribocorrosion OR corrosion OR wear) AND (surface treatment OR shot peening OR burnishing).

To improve literature coverage, complementary search combinations included the additional terms surface integrity, laser shock peening, deep rolling, ultrasonic surface treatment, severe shot peening, nanostructured surface, passive film, biofilm, osseointegration, fatigue, biomaterials, implant, and corrosion fatigue. These supplementary searches enabled the identification of studies addressing specific aspects of microstructural evolution, electrochemical behavior, tribocorrosion mechanisms, biological response, and multifunctional surface engineering that were not captured by the primary search expression.

The search was limited to peer-reviewed journal articles published in English between 2000 and June 2026, with particular emphasis on publications from 2022 to 2026 to ensure that the review incorporated the most recent advances in biomaterials, corrosion science, tribology, and biomedical surface engineering. The initial electronic search identified 63 records, which were subsequently screened according to the predefined eligibility criteria. The complete search strategy, information sources, search terms, publication period, and number of retrieved records are summarized in Table 1, while the study-selection process is presented in Figure 1 (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

2.4 Eligibility criteria

Eligibility criteria were established before the literature screening process to ensure methodological consistency and minimize selection bias throughout the review (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019). Studies were considered eligible when they met the following criteria: (i) investigated AISI 316L stainless steel or AISI 316L stainless steel-based biomedical devices; (ii) evaluated one or more mechanical surface treatments, including shot peening, severe shot peening, burnishing, deep rolling, ultrasonic surface treatment, laser shock peening, or related deformation-based surface-engineering techniques; (iii) reported experimental or review data concerning surface integrity, microstructural evolution, corrosion resistance, tribocorrosion behavior, fatigue performance, wear resistance, or biological response; (iv) were published as full-text articles in peer-reviewed scientific journals; and (v) were written in English.

Studies were excluded when they (i) focused exclusively on alloys other than AISI 316L without providing relevant comparative data; (ii) addressed surface modification techniques unrelated to mechanical surface engineering; (iii) consisted of conference abstracts, editorials, letters, patents, theses, dissertations, book chapters, or duplicate publications; (iv) did not provide sufficient methodological or experimental information for critical evaluation; or (v) were unrelated to biomedical applications or implant performance (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

When multiple publications reported substantially overlapping experimental datasets, only the most complete or most recent study was retained for qualitative synthesis to avoid duplicating evidence. The eligibility criteria were applied consistently during both the title-and-abstract screening stage and the subsequent full-text assessment, following the PRISMA 2020 recommendations (Page et al., 2021a; Page et al., 2021b). The application of these criteria during the study-selection process is summarized in Figure 1, whereas the overall screening results are presented in Table 1.

2.5 Study selection

The study-selection process was conducted in accordance with the PRISMA 2020 recommendations and followed a sequential procedure comprising identification, screening, eligibility assessment, and inclusion of relevant publications (Page et al., 2021a; Page et al., 2021b). Following the electronic database search, all retrieved records were imported into Zotero reference-management software, where duplicate records were identified and removed before the screening stage.

The remaining publications were initially screened by title and abstract to assess their relevance to this review’s objectives. Studies clearly unrelated to AISI 316L stainless steel, mechanical surface treatments, corrosion, tribocorrosion, surface integrity, or biomedical applications were excluded at this stage. The full texts of the potentially eligible articles were subsequently retrieved and independently evaluated according to the predefined eligibility criteria described in Section 2.4 (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

During the full-text assessment, publications were excluded when they did not provide sufficient experimental evidence, lacked methodological consistency, focused on non-biomedical applications, or did not address the relationships among mechanical surface treatments, surface integrity, corrosion behavior, tribocorrosion, or biological performance. Additional relevant studies identified through manual examination of the reference lists of selected articles were also considered for inclusion when they fulfilled all eligibility criteria (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

The complete study-selection workflow, including the number of records identified, screened, excluded, and included for qualitative synthesis, is presented in the PRISMA 2020 flow diagram (Figure 1). The numerical results obtained at each stage of the selection process are summarized in Table 1, providing a transparent description of the review methodology and ensuring reproducibility of the literature-selection procedure (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019).

2.6 Data extraction and qualitative synthesis

Data extraction was performed systematically using a standardized framework to ensure consistency during the qualitative analysis of the selected studies (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019). For each publication, information was collected regarding the authors, year of publication, biomedical application, mechanical surface treatment, processing parameters, characterization techniques, microstructural evolution, residual stress distribution, grain refinement, deformation-induced martensitic transformation, corrosion behavior, tribocorrosion performance, fatigue resistance, biological response, principal findings, and reported limitations. Particular attention was given to experimental variables that could influence the interpretation and comparison of the reported results.

Because the selected studies exhibited considerable heterogeneity in experimental design, surface-treatment parameters, electrochemical testing protocols, tribological conditions, biological evaluation methods, and reported outcome measures, a qualitative critical synthesis was adopted instead of a quantitative meta-analysis (Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019). The evidence was analyzed by comparing convergent and divergent findings, identifying methodological limitations, and evaluating the relationships among surface integrity, microstructural evolution, corrosion resistance, tribocorrosion behavior, and biological performance. This approach enabled a comprehensive assessment of the current state of knowledge while highlighting conflicting findings and unresolved scientific questions.

To facilitate comparison among studies, the extracted information was organized into thematic categories corresponding to the principal topics addressed throughout this review. Comparative data regarding metallic biomaterials, degradation mechanisms, mechanical surface treatments, multifunctional surface-engineering strategies, conflicting observations, and future research priorities were summarized in Tables 2–7, whereas the principal concepts and mechanistic relationships are illustrated in Figures 2–4. This integrated synthesis provided the basis for the critical discussion presented in the subsequent sections and the identification of current knowledge gaps and future research directions (Ratner et al., 2013; Hanawa, 2004; Chen and Thouas, 2015; Navarro et al., 2008; Geetha et al., 2009; Disegi and Eschbach, 2000; Jawahir et al., 2011; M'Saoubi et al., 2008a; Marcus, 2011; Revie, 2011; Mischler, 2008; Landolt et al., 2001; Moriarty, 2001; Valiev et al., 2000; Bagherifard et al., 2012; Page et al., 2021a; Page et al., 2021b; Higgins et al., 2019; Snyder, 2019).

TABLE 2. Principal degradation mechanisms affecting AISI 316L biomedical implants under physiological conditions, including corrosion, wear, tribocorrosion, fatigue-related damage, and biofilm-associated degradation.

Multiple degradation mechanisms frequently operate simultaneously under physiological conditions. The interactions among corrosion, mechanical wear, tribocorrosion, fatigue, metallic ion release, and biofilm formation govern the long-term structural integrity, electrochemical stability, and biological performance of AISI, 316 L biomedical implants. These degradation processes should therefore be evaluated as an interconnected system rather than as independent phenomena.

TABLE 3. Comparison of metallic biomaterials commonly used in implant applications, including AISI 316L stainless steel, Ti-6Al-4V alloy, and Co–Cr–Mo alloy, with emphasis on mechanical properties, corrosion resistance, biomedical applications, advantages, limitations, and representative literature.

Property ranges represent typical values reported for wrought biomedical alloys and may vary according to chemical composition, manufacturing route, thermomechanical processing, heat treatment, and testing methodology. The table is intended to provide a comparative overview of the principal metallic biomaterials currently employed in orthopedic, dental, and cardiovascular implant applications rather than absolute design values.

TABLE 4. Mechanical surface treatments applied to AISI 316L stainless steel for biomedical applications, including their principal deformation mechanisms, microstructural evolution, functional effects, limitations, and representative literature.

The effects summarized in this table represent the predominant trends reported in the current literature and may vary according to alloy composition, initial microstructure, manufacturing route, treatment intensity, processing parameters, surface preparation, and testing environment. For AISI, 316L stainless steel, surface roughness, grain refinement, deformation-induced martensitic transformation, dislocation density, passive-film stability, and residual stress distribution should be evaluated together when interpreting corrosion resistance, tribocorrosion behavior, fatigue performance, wear resistance, and biological response. Therefore, optimization of mechanical surface treatments requires balancing mechanical strengthening with electrochemical stability and biological compatibility rather than maximizing a single surface property.

TABLE 5. Opportunities, current limitations, and future directions for integrating mechanical surface engineering with bioactive surface functionalization strategies in AISI 316L biomedical implants.

Current evidence indicates that long-term implant performance depends on the combined optimization of surface integrity, corrosion resistance, tribocorrosion behavior, biological functionality, and antibacterial performance. Mechanical surface engineering and bioactive surface functionalization should therefore be regarded as complementary rather than independent strategies. Future developments are expected to focus on multifunctional surface architectures capable of integrating structural reliability, electrochemical stability, favorable host response, infection control, and intelligent design approaches.

TABLE 6. Principal conflicting findings reported for mechanically modified AISI 316 L stainless steel, possible causes of disagreement, current interpretation, and representative references.

The apparent contradictions reported in the literature do not necessarily represent inconsistent scientific evidence but frequently arise from differences in alloy condition, processing parameters, experimental methodologies, electrochemical protocols, tribological configurations, biological models, and surface characterization techniques. Consequently, mechanically induced surface modifications should be interpreted through an integrated assessment of surface integrity, microstructural evolution, electrochemical behavior, tribocorrosion performance, and biological response rather than by considering isolated variables.

TABLE 7. Major research gaps and priorities for future development of mechanically engineered AISI 316L implant surfaces.

The research priorities summarized in this table reflect the principal knowledge gaps identified throughout the present review. Future progress will require multidisciplinary approaches integrating materials science, corrosion engineering, tribology, biomechanics, electrochemistry, surface engineering, biology, immunology, microbiology, computational modelling, and clinical validation. Particular emphasis should be placed on standardized methodologies, clinically relevant testing conditions, and multifunctional surface-engineering strategies capable of simultaneously improving structural integrity, electrochemical stability, biological functionality, and long-term implant performance.

3 AISI 316L stainless steel as a biomaterial

AISI 316L stainless steel remains one of the most widely used metallic biomaterials in orthopedic, dental, cardiovascular, and surgical applications owing to its favorable combination of mechanical strength, corrosion resistance, formability, commercial availability, and cost-effectiveness (Park and Lakes, 2007; Niinomi, 2002; Niinomi, 1998; Long and Rack, 1998). Although titanium- and cobalt-based alloys are increasingly employed in permanent implant systems, AISI 316L continues to play an important role in temporary implants, fracture fixation devices, surgical instrumentation, and components exposed to moderate service demands (Niinomi, 1998; Long and Rack, 1998; Hermawan, 2018). Its continued clinical use reflects not only its favorable balance of mechanical and economic characteristics but also its compatibility with advanced surface-engineering strategies that improve functional performance without altering the alloy composition.

The alloy belongs to the austenitic stainless-steel family and is characterized by low carbon content and significant additions of chromium, nickel, and molybdenum. The corrosion resistance of AISI 316L is primarily attributed to the formation of a chromium-rich passive film, whereas nickel stabilizes the austenitic structure and enhances toughness and ductility. Molybdenum plays an important role in improving resistance to localized corrosion, particularly pitting corrosion in chloride-containing environments similar to physiological fluids (Sedriks, 1996; Lo et al., 2009; Virtanen, 2008). The reduction in carbon content compared with conventional 316 stainless steel minimizes chromium carbide precipitation during thermal exposure and reduces susceptibility to sensitization-related corrosion phenomena. Nevertheless, passive film stability may be compromised under simultaneous mechanical loading, tribological contact, and aggressive physiological environments, conditions frequently encountered in biomedical applications.

Under conventional processing conditions, AISI 316L exhibits a predominantly austenitic microstructure. Owing to its relatively low stacking-fault energy, the alloy is highly sensitive to plastic deformation. It may undergo microstructural evolution involving dislocation accumulation, mechanical twinning, and strain-induced martensitic transformation, particularly under severe deformation conditions such as cold working and surface engineering processes (Lo et al., 2009; Talonen and Hänninen, 2007; Olson and Cohen, 1975). These phenomena play a central role in determining the alloy’s response to mechanical surface treatments and the subsequent effects on mechanical, electrochemical, and biological performance. However, the magnitude of these microstructural modifications depends strongly on the processing route, treatment parameters, and deformation intensity, leading to significant variability among experimental results reported in the literature.

The mechanical behavior of AISI 316L satisfies the requirements of numerous biomedical applications. The alloy combines good strength, high ductility, fracture toughness, and satisfactory fatigue resistance under physiological loading conditions. Furthermore, its widespread industrial use facilitates processing through conventional forming, machining, welding, and finishing operations. These practical advantages continue to support its use in applications where cost-effectiveness and manufacturing flexibility remain important considerations (Virtanen, 2008). These characteristics have also contributed to the widespread investigation of mechanical surface treatments as practical approaches for improving implant performance while maintaining established manufacturing routes.

Despite these advantages, AISI 316L is not without limitations. Compared with titanium alloys, stainless steel possesses a higher elastic modulus, resulting in a greater mismatch with the mechanical properties of cortical bone. This difference may contribute to stress shielding and altered load transfer in certain orthopedic applications. Furthermore, titanium alloys generally exhibit superior corrosion resistance because of the exceptional stability of their titanium oxide passive layer (Talonen and Hänninen, 2007). Nevertheless, the higher manufacturing cost of titanium alloys and the continued development of advanced surface-modification techniques have sustained the clinical and technological relevance of AISI 316L for several biomedical applications.

Cobalt–chromium alloys represent another important class of metallic biomaterials used in load-bearing environments. These materials typically offer higher hardness and wear resistance than AISI 316L, although they are associated with greater density, increased manufacturing complexity, and higher production costs. Consequently, the selection of metallic biomaterials often requires balancing mechanical performance, biological response, processing considerations, and economic factors rather than optimizing a single property (Olson and Cohen, 1975). Therefore, the choice of implant material should be based on the specific clinical application, expected service conditions, and the potential to enhance surface functionality through appropriate engineering strategies.

Although titanium- and cobalt-based alloys dominate many permanent implant applications, the combination of manufacturing versatility, cost-effectiveness, clinical familiarity, and adaptability to surface-engineering approaches continues to justify the widespread use of AISI 316L in biomedical systems (Park and Lakes, 2007; Niinomi, 2002; Niinomi, 1998; Long and Rack, 1998; Hermawan, 2018; Virtanen, 2008). Recent advances in mechanical surface modification have further expanded the potential of this alloy by improving surface integrity, corrosion resistance, tribological behavior, and biofunctional performance while preserving its favorable bulk mechanical properties.

The comparison presented in Table 3 highlights how targeted surface-modification strategies may further enhance the functional performance of AISI 316L (Jawahir et al., 2011; M'Saoubi et al., 2008a; Bagherifard et al., 2012; Lu K. and Lu J., 2004). The long clinical history of this alloy, combined with its susceptibility to controlled surface modification, explains its continued relevance in biomaterials research. At the same time, recent developments in surface engineering emphasize that the long-term performance of AISI 316L depends not only on its intrinsic properties but also on optimizing surface integrity for the intended biomedical application. Understanding its composition, microstructure, properties, and limitations provides the basis for evaluating the role of surface integrity in biomedical performance, as discussed in the following section.

4 Surface integrity concepts for biomedical implants

Surface integrity is a multidisciplinary concept encompassing the physical, mechanical, metallurgical, and topographical characteristics of a material’s surface and subsurface regions after manufacturing or surface-processing operations. Originally developed within manufacturing engineering to evaluate the quality of machined components, the concept has progressively gained importance in biomaterials research because many degradation and biological phenomena originate at the implant surface (Brinksmeier et al., 1982; Field and Kahles, 1971; M'Saoubi et al., 2008b). More recently, surface integrity has evolved into a fundamental framework for understanding how manufacturing-induced surface modifications influence the long-term electrochemical, tribological, mechanical, and biological performance of biomedical implants.

For biomedical devices, surface integrity extends beyond conventional measures of surface quality. The surface represents the first region of contact between the implant and the physiological environment. It therefore plays a fundamental role in determining corrosion behavior, wear resistance, fatigue performance, protein adsorption, cellular interactions, and bacterial colonization. As a result, surface integrity has become an important link connecting materials science, surface engineering, electrochemistry, tribology, and biology (Leach, 2013). Growing evidence indicates that immune modulation, early inflammatory events, and osteoimmunological responses are also strongly influenced by surface characteristics, underscoring the importance of integrating biological and engineering perspectives in evaluating implant performance.

Surface roughness is one of the most frequently investigated parameters of surface integrity. Variations in roughness influence the effective contact area between the implant and surrounding tissues, affect fluid transport near the surface, and modify local electrochemical conditions. Roughness also influences protein adsorption and cell attachment, thereby affecting subsequent biological responses. However, the influence of roughness is highly dependent on scale, geometry, and application-specific requirements, making universal optimization difficult (Whitehouse, 2010). Consequently, surface roughness should not be interpreted in isolation but rather in combination with microstructural evolution, residual stresses, surface chemistry, and the intended biomedical application.

Surface topography provides a broader description of the surface’s geometric characteristics. Unlike roughness parameters alone, topography incorporates spatial distribution, surface texture, directional features, and multiscale morphological characteristics. Recent advances in surface characterization have demonstrated that micro- and nanoscale topographical features can significantly influence both biological performance and degradation behavior (Leach, 2013; Fontana, 1986; Mathew et al., 2009; Ponthiaux et al., 2004; Wilson et al., 2005; Ratner and Bryant, 2004; Anselme, 2000; Campoccia et al., 2006; Gittens et al., 2011). In mechanically treated surfaces, topography interacts with microstructural evolution and residual stress development, collectively contributing to overall surface integrity (Jawahir et al., 2011; M'Saoubi et al., 2008a; Withers and Bhadeshia, 2001; Lu K. and Lu J., 2004). Modern characterization techniques, including electron backscatter diffraction (EBSD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), nanoindentation, focused ion beam (FIB) microscopy, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS), have substantially improved the understanding of these complex surface and subsurface modifications.

Residual stress constitutes another important element of surface integrity. These stresses are generated during manufacturing operations such as machining, grinding, polishing, forming, and mechanical surface treatments. Depending on their magnitude and distribution, residual stress may influence fatigue resistance, crack initiation, passive film stability, and susceptibility to localized corrosion. In biomedical applications, compressive residual stresses are often considered beneficial because they may delay crack nucleation and improve structural reliability under cyclic loading conditions (Withers and Bhadeshia, 2001). Nevertheless, excessive deformation or non-uniform residual stress distributions may also promote surface damage or adversely affect corrosion behavior, demonstrating that the beneficial effects of residual stresses depend on both processing parameters and service conditions.

Microstructural characteristics within the near-surface region also play a decisive role in implant performance. Grain size, crystallographic texture, dislocation density, deformation bands, twins, and phase transformations may alter both mechanical and electrochemical behavior. In metastable austenitic alloys such as AISI 316L, plastic deformation may produce significant microstructural modifications that extend several hundred micrometers below the surface. These modifications often become particularly important after mechanical surface treatments designed to improve functional performance (Morshed-Behbahani et al., 2024). The extent of these microstructural changes varies considerably across processing routes, underscoring the importance of correlating treatment parameters with the resulting mechanical, electrochemical, and biological responses.

Among the microstructural phenomena associated with surface deformation, strain-induced martensitic transformation has attracted considerable attention. The transformation of austenite into martensite may modify hardness, residual stress distribution, magnetic behavior, corrosion resistance, and wear performance. Although the influence of deformation-induced martensite on implant behavior remains an active area of investigation, its formation is frequently reported on mechanically treated AISI 316L surfaces (Angel, 1954). Recent investigations suggest that the effect of strain-induced martensite is not universally beneficial, since its influence on corrosion resistance and tribocorrosion depends on the balance between grain refinement, passive film stability, and the volume fraction of the transformed phase.

Surface integrity should therefore be viewed as a combination of interconnected parameters rather than a collection of isolated characteristics. Modifications introduced into one aspect of the surface frequently influence several others simultaneously. For example, processes that refine grain size may also alter residual stresses, hardness, roughness, passive film stability, and biological response. Consequently, understanding implant performance requires considering the combined effects of multiple surface-integrity parameters rather than individual properties in isolation (Arifvianto, 2011). This integrated perspective provides a more reliable basis for comparing mechanical surface treatments and for identifying the mechanisms responsible for the improvements or limitations reported in the literature.

The growing relevance of surface integrity in biomedical engineering stems from the recognition that degradation mechanisms and biological responses are governed by interconnected phenomena in the near-surface region. Rather than acting independently, roughness, residual stresses, microstructural evolution, and physicochemical surface characteristics collectively determine implant performance under physiological conditions. Consequently, the effectiveness of mechanical surface treatments cannot be assessed through isolated parameters but must be interpreted within the broader framework of surface integrity discussed throughout this review (Omarov et al., 2023). Accordingly, the following sections critically compare how different mechanical surface treatments modify these interconnected parameters and how such modifications influence corrosion resistance, tribocorrosion behavior, and biofunctional performance in AISI 316L biomedical implants.

5 Mechanical surface treatments applied to AISI 316L

Mechanical surface treatments have emerged as effective approaches for improving the functional performance of metallic biomaterials without altering their bulk composition. Unlike coating technologies or thermochemical treatments, these processes modify the near-surface region through controlled plastic deformation, generating microstructural changes that may influence mechanical, electrochemical, tribological, and biological behavior. Because AISI 316L exhibits significant microstructural sensitivity to deformation, it responds particularly well to these surface-engineering strategies (Lu K. and Lu J., 2004). Recent investigations further demonstrate that the effectiveness of these treatments depends strongly on the processing parameters employed and the resulting modifications in surface integrity, rather than on the treatment category alone.

The fundamental objective of mechanical surface treatments is to introduce beneficial modifications to the surface and subsurface regions while preserving the material’s desirable bulk properties. Depending on the process parameters employed, these treatments may produce grain refinement, increased dislocation density, deformation twinning, strain-induced martensitic transformation, work hardening, and compressive residual stresses. The resulting changes often improve fatigue resistance and may influence corrosion behavior, wear resistance, and biological performance (Valiev et al., 2006). However, the magnitude of these improvements varies considerably across treatment conditions, underscoring the need to critically compare processing parameters, microstructural evolution, and functional performance reported in the literature.

Shot peening is among the most widely investigated mechanical surface treatments applied to stainless steels. The process involves repeated impacts of small spherical media against the surface, producing localized plastic deformation and compressive residual stresses. Numerous studies have demonstrated that shot peening can improve fatigue performance and alter corrosion behavior by modifying the near-surface microstructure (Guagliano, 2001). Nevertheless, excessive peening intensity may increase surface roughness and promote localized disruption of the passive film, indicating that improvements in fatigue performance are not always accompanied by enhanced corrosion resistance.

Severe shot peening is an extension of conventional shot peening, in which higher kinetic energies and greater deformation are intentionally introduced. Under appropriate processing conditions, severe shot peening may generate ultrafine-grained or nanostructured surface layers. These microstructural modifications have attracted considerable attention because they may simultaneously affect hardness, fatigue resistance, corrosion performance, and biological interactions (Valiev and Langdon, 2006). However, the available evidence indicates that the beneficial effects of severe shot peening are highly dependent on process optimization, since excessive deformation may increase surface defects or promote unfavorable electrochemical responses under certain physiological conditions.

Burnishing is another deformation-based surface treatment frequently applied to metallic components. During burnishing, a hard tool is pressed against the surface while moving under controlled conditions. The process reduces surface roughness, increases hardness, and generates compressive residual stresses. Because it can be integrated directly into manufacturing operations, burnishing has received increasing interest as a practical method for enhancing surface integrity in biomedical alloys (Altenberger). Compared with impact-based treatments, burnishing generally produces smoother surfaces while preserving favorable residual stress distributions, making it particularly attractive for applications where both corrosion resistance and fatigue performance are critical.

Deep rolling employs a similar principle but introduces deformation at greater depths beneath the surface. The process is particularly effective in generating compressive residual stress fields that extend significantly below the treated region. These characteristics make deep rolling attractive for applications where fatigue resistance and structural reliability are critical considerations (Altenberger et al., 2012). Its ability to generate deep compressive stress fields may also improve resistance to crack initiation and propagation under cyclic loading, although quantitative comparisons with other mechanical treatments remain limited.

Ultrasonic surface treatments utilize high-frequency mechanical vibrations to induce severe plastic deformation within the near-surface region. Techniques such as ultrasonic nanocrystal surface modification and related processes have demonstrated the ability to produce substantial grain refinement and surface nanostructuring. The resulting microstructures have been associated with improvements in hardness, wear resistance, and biological response (Tao et al., 2002). Recent studies further suggest that these treatments may enhance cellular adhesion and early osteogenic activity; however, the reported biological outcomes remain strongly dependent on the resulting surface morphology and physicochemical characteristics.

Laser shock peening differs from conventional mechanical treatments because deformation is generated through high-pressure shock waves induced by pulsed laser irradiation. The process can introduce deep compressive residual stress fields while minimizing direct mechanical contact with the surface. Because of its ability to modify subsurface stress distributions without substantial changes in surface geometry, laser shock peening has attracted growing interest in biomedical and aerospace applications (Lu J. and Lu K., 2004). Compared with conventional impact-based treatments, laser shock peening generally provides greater control over residual stress distribution while minimizing undesirable increases in surface roughness. However, equipment cost and process complexity remain important practical limitations.

Although these treatments differ in their operating principles, all seek to modify surface integrity through controlled deformation mechanisms. Their relative effects on roughness, residual stresses, grain refinement, work hardening, and phase transformation are summarized in Table 4. Table 4 also provides a quantitative comparison of the principal microstructural and functional changes reported for each treatment, facilitating the identification of their respective advantages and limitations. The choice of treatment depends on the desired balance among mechanical performance, corrosion resistance, tribological behavior, manufacturing feasibility, and application-specific requirements (Roland et al., 2006).

Current research increasingly recognizes that the performance of mechanically treated AISI 316L cannot be predicted solely from improvements in hardness, residual stress magnitude, or fatigue resistance. Instead, treatment-induced microstructural modifications influence a network of interacting phenomena involving passive-film stability, tribocorrosion processes, cellular response, and long-term structural reliability. Consequently, the assessment of mechanical surface treatments has evolved from a purely mechanical perspective toward a multifunctional approach that integrates electrochemical, tribological, and biological performance criteria (Guo et al., 2010). Accordingly, future optimization of mechanically treated AISI 316L should consider not only improvements in individual surface parameters but also the combined effects of microstructure, electrochemical stability, tribocorrosion resistance, and host biological response to achieve more reliable long-term clinical performance.

6 Microstructural evolution induced by surface deformation

The effectiveness of mechanical surface treatments is fundamentally associated with their ability to modify the microstructure of the near-surface region. The deformation introduced during these processes generates structural changes over multiple length scales, ranging from atomic defects to grain refinement and phase transformations. Because AISI 316L is a metastable austenitic alloy with relatively low stacking-fault energy, its microstructural response to deformation is particularly complex and strongly dependent on processing conditions (Sano et al., 2006). Consequently, similar surface treatments may yield markedly different microstructural features depending on processing parameters, deformation intensity, and the material’s initial condition, underscoring the need for critical interpretation of the available experimental evidence.

Plastic deformation initially promotes the multiplication and accumulation of dislocations within the austenitic matrix. As deformation progresses, interactions among dislocations increase local strain hardening and contribute to the development of heterogeneous deformation structures. The resulting increase in dislocation density represents one of the primary mechanisms responsible for the enhanced hardness frequently observed after mechanical surface treatments (Montross et al., 2002). However, excessive dislocation accumulation may also increase stored strain energy and affect passive film stability, demonstrating that increased hardness does not necessarily translate into improved electrochemical performance.

At higher deformation levels, mechanical twinning may become an important deformation mechanism. Twins act as effective barriers to dislocation motion and further strengthen the surface layer. In metastable austenitic stainless steels, the simultaneous operation of dislocation slips and twinning often produces highly refined deformation substructures that significantly alter the material’s mechanical behavior (Peyre and Fabbro, 1995). The relative contribution of deformation twinning varies with stacking-fault energy and deformation conditions, which partly explains the variability observed among mechanical surface treatments reported in the literature.

One of the most distinctive microstructural phenomena observed in mechanically deformed AISI 316L is strain-induced martensitic transformation. Under appropriate combinations of strain, strain rate, and temperature, metastable austenite may partially transform into martensitic phases. This transformation is influenced by alloy composition, stacking-fault energy, and processing history. Although the extent of martensite formation varies among different surface treatments, its presence may influence hardness, residual stress distribution, wear resistance, magnetic behavior, and corrosion performance (Sultana et al., 2024). Recent investigations indicate that the influence of deformation-induced martensite on corrosion and tribocorrosion remains controversial, as changes in passive film stability and local electrochemical behavior may counterbalance the beneficial effects of work hardening.

Severe plastic deformation may also lead to substantial grain refinement within the near-surface region. Under sufficiently intense deformation conditions, the progressive subdivision of grains through dislocation rearrangement and boundary formation may produce ultrafine-grained or nanocrystalline surface layers. Such microstructures are characterized by a high density of grain boundaries and interfaces, which may modify both mechanical and electrochemical behavior (Meyers et al., 2006). Although grain refinement generally improves hardness and fatigue resistance, its influence on corrosion resistance depends on the balance between enhanced passive film formation and increased grain-boundary diffusion paths.

The development of compressive residual stresses constitutes another important consequence of surface deformation. These stresses arise from non-uniform plastic deformation and are often superimposed on the microstructural modifications generated during treatment. As illustrated conceptually in Figure 3, grain refinement, dislocation accumulation, phase transformation, and residual stress development are interconnected phenomena that evolve simultaneously during mechanical surface processing. Their combined effects play a decisive role in determining subsequent corrosion, tribocorrosion, and fatigue behavior (Nalla et al., 2003). Accordingly, evaluating individual microstructural parameters in isolation may lead to incomplete or even misleading interpretations of implant performance under physiological conditions.

Characterization of deformation-induced microstructural evolution requires complementary experimental techniques. X-ray diffraction remains one of the most widely employed methods for evaluating residual stresses, phase transformations, and crystallographic changes. Diffraction-based approaches are particularly useful for quantifying deformation-induced martensite and assessing changes in lattice strain generated by surface treatments (Stachowiak and Batchelor, 2013). Recent advances in synchrotron X-ray diffraction have further improved the spatial resolution and quantitative analysis of residual stresses and phase evolution in mechanically treated biomaterials.

Electron microscopy techniques provide additional information regarding grain refinement and deformation structures. Scanning electron microscopy and electron backscatter diffraction are frequently used to characterize grain morphology, crystallographic orientation, and deformation-induced microstructural heterogeneity. Transmission electron microscopy has also been extensively employed to investigate nanostructured surface layers produced by severe plastic deformation (Hutchings and Shipway, 2017). Complementary techniques such as atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), focused ion beam (FIB) microscopy, nanoindentation, Raman spectroscopy, and time-of-flight secondary ion mass spectrometry (ToF-SIMS) have further expanded the understanding of surface chemistry, passive-film characteristics, and nanomechanical properties associated with mechanically modified surfaces.

More recently, advanced diffraction-based approaches, including line-profile analysis and whole-powder-pattern modeling, have been applied to quantify dislocation density, crystallite size, and microstrain. These methodologies have improved the understanding of the relationships between processing parameters and microstructural evolution in mechanically treated stainless steels (Blau, 2008). The integration of these advanced characterization methods with electrochemical and tribological testing has enabled more reliable correlations between microstructural evolution and functional performance, supporting the optimization of mechanical surface treatments for biomedical applications.

The principal microstructural modifications associated with the surface treatments discussed in the previous section are summarized in Table 4. Collectively, these deformation-induced modifications establish the structural basis for many of the functional changes reported in mechanically treated AISI 316L. However, the same microstructural features that enhance hardness and wear resistance may also alter passive film formation, localized corrosion susceptibility, and tribocorrosion behavior. This dual effect explains why apparently similar surface treatments can produce different outcomes under physiological conditions and highlights the importance of correlating microstructural characterization with electrochemical performance (Teixeira et al., 2026a). Therefore, quantitative comparison of microstructural parameters, together with corrosion, tribocorrosion, and biological data, is essential for identifying the most effective surface-engineering strategies and improving the predictive assessment of long-term implant performance.

7 Corrosion behavior of mechanically modified AISI 316L

Corrosion resistance is one of the main factors governing the long-term performance of metallic biomaterials and must be considered together with fatigue resistance, wear behavior, tribocorrosion, and biological compatibility. In many applications, mechanical degradation mechanisms such as fatigue and fracture are closely related to surface conditions, often initiating at defects or stress-concentration sites and progressively compromising structural integrity during service (Gilbert et al., 1993). From a clinical perspective, corrosion-related degradation may reduce implant longevity, promote the release of metallic ions, and contribute to adverse biological responses, reinforcing the need for an integrated evaluation of mechanical, electrochemical, and biological performance.

While AISI 316L stainless steel exhibits good corrosion resistance under physiological conditions, its electrochemical behavior remains strongly influenced by the characteristics of the near-surface region. Because mechanical surface treatments intentionally modify microstructure, residual stress distribution, and surface morphology, understanding their influence on corrosion performance is essential for evaluating the suitability of these approaches for biomedical applications (Koch, 2007; Eliaz, 2019). However, the effects reported in the literature are not always consistent, since corrosion behavior depends on the combined influence of processing parameters, surface integrity, testing methodology, and physiological environment.

The corrosion resistance of AISI 316L is primarily associated with the spontaneous formation of a thin chromium-rich passive film. This oxide layer acts as a barrier between the metallic substrate and the physiological environment, reducing metal dissolution and limiting electrochemical degradation. However, passive films are not static structures. Their composition, thickness, stability, and self-healing capacity may be influenced by surface condition, microstructural heterogeneity, and environmental factors (Eliaz, 2019). Recent studies further demonstrate that passive film stability is strongly affected by local mechanical damage, cyclic loading, and tribological contact, conditions commonly encountered during implant service.

Mechanical surface treatments often indirectly alter the characteristics of the passive film by modifying the underlying substrate microstructure. Grain refinement, increased dislocation density, deformation-induced martensitic transformation, and residual stress redistribution may affect the kinetics, stability, and repassivation behavior of the passive film. Consequently, mechanically modified surfaces frequently exhibit electrochemical responses that differ from those of conventionally processed materials (Eliaz, 2019; Teixeira et al., 2026b; Gleiter, 2000; Suryanarayana, 1995).

The magnitude of these changes varies substantially across mechanical treatments, underscoring the importance of correlating microstructural characterization with quantitative electrochemical measurements.

Among the mechanisms responsible for these differences, grain refinement has attracted particular attention. The introduction of ultrafine-grained or nanostructured surface layers increases grain-boundary density and may accelerate diffusion processes involved in passive film formation. Several investigations have reported improved passivation kinetics and enhanced corrosion resistance following severe plastic deformation treatments, although the magnitude of these effects depends strongly on processing conditions and environmental parameters (Gleiter, 2000). Conversely, other studies have reported only limited improvements or even reductions in corrosion resistance when excessive deformation promoted surface defects or deformation-induced martensite, highlighting the need for critical interpretation of the available evidence.

Although compressive residual stresses generated by mechanical surface treatments are generally beneficial for fatigue resistance by delaying crack initiation and propagation, their influence on corrosion remains controversial. Their electrochemical effects are considerably more complex and depend on the characteristics of the surface treatment, the associated microstructural modifications, and the stability of the passive film. Under certain conditions, compressive residual stresses may enhance corrosion resistance by improving passive film integrity, whereas in other situations they may promote localized electrochemical heterogeneity and impair corrosion performance. Consequently, the relationship between residual stress state and corrosion resistance cannot be interpreted independently of the accompanying microstructural changes (Suryanarayana, 1995). This apparent contradiction explains why treatments producing similar residual stress levels may exhibit markedly different electrochemical responses under physiological conditions.

Localized corrosion remains one of the most significant concerns associated with stainless-steel implants. Physiological environments contain chloride ions that can destabilize passive films and promote corrosion pitting. Once initiated, pits may act as stress concentrators and preferential sites for further degradation. Surface defects, inclusions, microstructural heterogeneities, and deformation-induced phase transformations may all influence susceptibility to localized corrosion (Celis et al., 2006). From a clinical standpoint, localized corrosion may accelerate implant degradation, increase the release of metallic ions, and facilitate crack initiation under cyclic loading, thereby contributing to premature implant failure.

Strain-induced martensitic transformation also plays an important role in the electrochemical response of stainless steels. The formation of martensite during deformation can modify local surface conditions, influencing passive film stability and promoting galvanic interactions between different microstructural regions. Although this behavior has been widely examined, its effect on corrosion resistance still depends strongly on the microstructure developed during processing. Another important consideration is that microstructural heterogeneities and defects introduced by processes such as welding can increase the susceptibility of stainless steels to stress-corrosion cracking under aggressive environments (Sedriks, 1996; Barril et al., 2005). These findings demonstrate that phase transformation should be evaluated alongside grain refinement, residual stresses, and passive film characteristics, rather than as an isolated microstructural parameter.

The interactions among surface integrity, passive film stability, localized corrosion, and biological environment are summarized in Figure 4. The figure highlights how microstructural changes induced by mechanical surface treatments may influence electrochemical processes and ultimately affect implant performance. It also illustrates the interconnected nature of these mechanisms, emphasizing that corrosion resistance results from the combined effects of microstructure, surface chemistry, mechanical loading, and physiological conditions.

Metallic ion release constitutes an additional aspect of corrosion behavior with direct biological relevance. Corrosion processes may release iron, chromium, nickel, and molybdenum ions into surrounding tissues. Although the quantities released are often small, long-term exposure has been associated with inflammatory responses, hypersensitivity reactions, and local tissue effects in susceptible individuals (Yan et al., 2007). Recent evidence further indicates that corrosion-induced ion release may contribute to macrophage activation, chronic inflammatory signaling, and osteolytic processes, reinforcing the importance of minimizing electrochemical degradation in long-term implant applications.

The literature reviewed here suggests that corrosion performance cannot be predicted solely from surface roughness, hardness, residual stress state, or grain size considered individually. Instead, corrosion behavior arises from the simultaneous interaction of multiple surface-integrity parameters. This observation helps explain the variability frequently reported in the literature and reinforces the importance of comprehensive surface characterization (Stack and Abdulrahman, 2002). Accordingly, electrochemical characterization should ideally combine techniques such as potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), open-circuit potential monitoring, and complementary surface analyses to provide a more complete understanding of corrosion mechanisms.

The principal degradation mechanisms associated with corrosion-related processes in biomedical environments are summarized in Table 2. Understanding how mechanical surface treatments affect passive-film stability, localized corrosion, and metallic ion release is essential, as these mechanisms rarely occur in isolation in clinical service. In many biomedical applications, corrosion processes interact directly with mechanical contact and wear, creating synergistic degradation pathways that cannot be explained by electrochemical analysis alone. This interaction forms the basis of tribocorrosion, discussed in the following section (Mathew et al., 2014). Therefore, quantitative comparison of electrochemical performance, along with tribological and biological responses, is essential for identifying the most effective surface-engineering strategies for AISI 316L biomedical implants and for improving predictions of long-term clinical performance.

8 Critical assessment of conflicting findings

Although numerous studies have reported beneficial effects of mechanical surface treatments on the performance of AISI 316L stainless steel, the available literature does not always present consistent conclusions. Significant variability exists regarding the influence of grain refinement, residual stresses, strain-induced martensitic transformation, and surface roughness on corrosion resistance, tribocorrosion behavior, and biological performance. These discrepancies highlight the complexity of surface integrity and emphasize the need for careful interpretation of published results. They also demonstrate that differences in processing parameters, experimental methodologies, electrochemical testing conditions, and biological evaluation protocols often limit direct comparisons among studies.

One of the most debated topics concerns the influence of grain refinement on corrosion resistance. Several investigations have reported that ultrafine-grained and nanostructured surface layers promote faster passive film formation and improved corrosion resistance due to enhanced diffusion processes and increased grain-boundary density (Moriarty, 2001; Valiev et al., 2000; Morshed-Behbahani et al., 2024; Lu K. and Lu J., 2004; Teixeira et al., 2026b).

Conversely, other studies have suggested that the high density of grain boundaries and deformation-induced defects may increase electrochemical heterogeneity and facilitate localized corrosion under specific environmental conditions (Gilbert et al., 1993; Koch, 2007). Differences in electrolyte composition, chloride concentration, passive-film characterization methods, and surface preparation procedures further contribute to the variability of the reported results. Collectively, the available evidence suggests that these apparently contradictory observations arise primarily from differences in deformation intensity, passive-film characterization methods, and testing environments rather than from grain refinement itself.

The role of strain-induced martensitic transformation remains similarly controversial. Numerous studies have associated deformation-induced martensite with increased hardness and improved wear resistance (Talonen and Hänninen, 2007; Olson and Cohen, 1975; Sultana et al., 2024; Barril et al., 2005). However, the electrochemical consequences of martensite formation are less clear. Some authors have reported detrimental effects resulting from local galvanic interactions between martensitic and austenitic regions. In contrast, others have observed negligible or even beneficial effects depending on the fraction, morphology, and spatial distribution of the transformed phase (Talonen and Hänninen, 2007; Sultana et al., 2024; Barril et al., 2005). These findings suggest that martensite should not be evaluated in isolation from the surrounding microstructural environment. Instead, its influence should be interpreted alongside grain refinement, residual stress distribution, passive-film characteristics, and the electrochemical conditions under which corrosion tests are conducted.

Conflicting results have also been reported regarding the influence of residual stresses on corrosion behavior. Compressive residual stresses are generally recognized as beneficial for fatigue performance because they retard crack initiation and propagation (Whitehouse, 2010; Altenberger; Altenberger et al., 2012; Nalla et al., 2003). Nevertheless, their influence on passive-film stability and localized corrosion remains uncertain. Some studies have reported enhanced corrosion resistance in compressively stressed surfaces, while others have observed limited or inconsistent electrochemical improvements (Koch, 2007; Suryanarayana, 1995). Such variability indicates that the effects of residual stress are often coupled with concurrent changes in roughness, grain refinement, and deformation substructures generated during surface treatment. Consequently, residual stress magnitude alone cannot be considered a reliable predictor of corrosion performance without simultaneous microstructural and electrochemical characterization.

Surface roughness represents another parameter frequently associated with contradictory findings. Increased roughness may enhance osseointegration by promoting cell attachment and tissue anchorage (Celis et al., 2006; Barril et al., 2005; Yan et al., 2007). However, rougher surfaces may also increase bacterial adhesion, alter local electrochemical conditions, and facilitate the initiation of corrosion under certain circumstances (Sedriks, 1996; Koch, 2007; Stack and Abdulrahman, 2002; Mathew et al., 2014). Consequently, optimizing surface roughness often requires balancing biological and electrochemical requirements rather than maximizing a single performance criterion. This balance is highly dependent on the intended clinical application, since surface characteristics favorable for temporary fixation devices may differ from those required for long-term load-bearing implants.

Tribocorrosion studies also exhibit substantial variability. Improvements in hardness and wear resistance achieved through severe plastic deformation are often expected to improve tribocorrosion resistance. Nevertheless, tribocorrosion behavior depends simultaneously on wear mechanisms, passive-film stability, repassivation kinetics, electrochemical conditions, and contact mechanics (Mathew et al., 2014; Puthillam and Selvam, 2024; Landolt, 2007). As a result, improvements observed in isolated wear or corrosion tests do not necessarily translate into superior tribocorrosion performance. Moreover, differences in experimental configurations, applied loads, sliding conditions, counterbody materials, and electrochemical monitoring techniques make quantitative comparison among published studies particularly challenging. Standardized tribocorrosion testing protocols would therefore improve the reliability and reproducibility of future investigations.

Collectively, these conflicting findings demonstrate that implant performance cannot be predicted from individual surface-integrity parameters considered in isolation. Instead, corrosion resistance, tribocorrosion behavior, and biological response emerge from complex interactions among microstructure, residual stress distribution, surface topography, passive-film characteristics, and physiological conditions. Accordingly, future studies should prioritize integrated experimental approaches combining advanced microstructural characterization, quantitative electrochemical analysis, tribocorrosion testing, and biological evaluation to establish more reliable laboratory-to-clinical correlations. A synthesis of the principal conflicting observations reported for mechanically modified AISI 316L surfaces is presented in Table 6.

9 Tribocorrosion of AISI 316L implants

Tribocorrosion describes material degradation resulting from the simultaneous action of mechanical wear and electrochemical corrosion. Unlike conventional corrosion or wear processes considered independently, tribocorrosion involves continuous interactions between mechanical and electrochemical phenomena, often producing degradation rates that exceed the sum of their individual contributions. Because many biomedical devices operate under conditions involving cyclic loading, relative motion, and exposure to physiological fluids, tribocorrosion has become an important consideration in evaluating implant performance and longevity (Puthillam and Selvam, 2024). The synergistic interaction between wear and corrosion is therefore recognized as one of the principal degradation mechanisms limiting the long-term reliability of load-bearing biomedical implants.

In orthopedic and dental applications, implant surfaces are frequently subjected to repeated contact and micro-motion. These interactions may mechanically disrupt passive films that would otherwise protect the underlying metallic substrate. Once the passive layer is removed, freshly exposed metal surfaces become susceptible to electrochemical dissolution. Subsequent repassivation may occur, but repeated cycles of film removal and regeneration can significantly increase material degradation over time (Landolt, 2007). This degradation mechanism is particularly relevant in modular implant junctions and fretting contacts, where repetitive micro-motion accelerates passive-film disruption and increases both material loss and the release of metallic ions.

The tribocorrosion behavior of AISI 316L is strongly influenced by surface integrity. Surface roughness, residual stress, microstructural condition, hardness, and passive film characteristics all affect the balance between mechanical wear and electrochemical degradation. Consequently, the microstructural modifications produced by mechanical surface treatments may alter tribocorrosion resistance in ways that are not always predictable from conventional wear or corrosion tests alone (Jones, 1996). This complexity demonstrates that tribocorrosion performance should be evaluated through integrated electrochemical and mechanical analyses rather than by independently assessing wear resistance or corrosion behavior.

Grain refinement and surface hardening generally improve wear resistance by increasing resistance to plastic deformation and material removal. However, the beneficial effects of these modifications may be offset if the associated microstructural changes adversely affect passive film stability. Similarly, deformation-induced martensitic transformation may enhance hardness while simultaneously altering local electrochemical behavior. These observations illustrate the complex relationship between microstructure and tribocorrosion performance (Fontana, 1986). Consequently, improvements in hardness alone cannot be considered reliable predictors of tribocorrosion resistance, since electrochemical stability frequently governs the overall degradation process.

Experimental evaluation of tribocorrosion typically involves the simultaneous measurement of mechanical and electrochemical variables. Potentiodynamic polarization, open-circuit potential monitoring, electrochemical impedance spectroscopy, and friction measurements are frequently combined to investigate the interactions between wear and corrosion under simulated physiological conditions. Such approaches provide valuable information regarding material loss mechanisms, repassivation kinetics, and degradation pathways (Mathew et al., 2009). Current experimental protocols are commonly based on international standards, including ASTM G119 for evaluating the synergism between wear and corrosion. At the same time, electrochemical impedance spectroscopy (EIS) and open-circuit potential monitoring are widely employed to characterize passive-film stability and repassivation kinetics during tribocorrosion testing.

The interactions among wear processes, passive film disruption, electrochemical degradation, metallic ion release, and biological response are summarized in Figure 4. The figure highlights the multidirectional relationships that govern tribocorrosion behavior in biomedical environments and emphasizes the importance of considering mechanical and electrochemical processes as components of a single degradation system. It also illustrates how changes in surface integrity influence repassivation kinetics and the synergistic interaction between wear and corrosion throughout implant service.

The degradation mechanisms most commonly associated with tribocorrosion are also included within the broader framework presented in Table 2. In vivo, tribocorrosion rarely occurs in isolation and frequently coexists with fatigue damage, localized corrosion, and biological processes. Consequently, the long-term performance of implant materials depends on the collective influence of multiple degradation mechanisms operating simultaneously (Ponthiaux et al., 2004). According to the tribocorrosion framework widely adopted in the literature and consistent with the methodology described in ASTM G119, the total material loss can be expressed as the sum of mechanical wear, electrochemical corrosion, and their synergistic interaction, as given by Equation 1. This relationship provides a quantitative basis for evaluating the relative contribution of each degradation mechanism and facilitates comparison among different mechanical surface treatments performed under similar experimental conditions.where T is the total material loss during tribocorrosion, W is the material loss due exclusively to mechanical wear, C is the material loss due exclusively to electrochemical corrosion, and S is the synergistic material loss resulting from the interaction between wear and corrosion. The synergistic component (S) is particularly relevant because it represents the additional degradation arising from the interaction between mechanical and electrochemical processes, which often exceeds the sum of the individual wear and corrosion contributions. Consequently, improvements observed in isolated wear or corrosion tests cannot be directly extrapolated to tribocorrosion performance without accounting for the synergistic contribution described by Equation 1. This integrated approach provides a more reliable framework for interpreting tribocorrosion mechanisms and for comparing the effectiveness of different mechanical surface treatments under clinically relevant conditions.

T = W + C + S (1)

Tribocorrosion has become a major concern in the long-term performance of metallic implants because mechanical wear and electrochemical degradation occur simultaneously under physiological conditions. Mechanical surface treatments have attracted considerable attention as a strategy to improve tribocorrosion resistance by modifying hardness, residual stress state, and microstructural characteristics, while preserving the material’s bulk properties. Improvements in tribocorrosion performance have been reported following treatments that enhance surface integrity and alter near-surface microstructures (Puthillam and Selvam, 2024; Landolt, 2007; Jones, 1996; Fontana, 1986; Mathew et al., 2009; Ponthiaux et al., 2004; Wilson et al., 2005). However, the magnitude of these improvements varies considerably among different mechanical surface treatments, reflecting differences in microstructural evolution, passive-film stability, and electrochemical response.

Despite these advances, comparison among published studies remains challenging because tribocorrosion behavior is highly sensitive to experimental conditions. Variations in contact geometry, loading regime, counterface (or counterbody) material, electrolyte composition, and repassivation kinetics can substantially influence degradation mechanisms and measured performance. Consequently, greater consistency in testing methodologies and broader adoption of clinically relevant experimental conditions are needed to improve the reliability and practical relevance of tribocorrosion assessments for biomedical applications (Mischler, 2008; Landolt et al., 2001; Landolt, 2007). Future investigations should also prioritize standardized testing protocols, quantitative decomposition of material loss, and stronger correlations between laboratory tribocorrosion experiments and long-term clinical performance in orthopedic and dental implants.

10 Biological response to mechanically engineered surfaces

The biological performance of an implant is determined by a complex sequence of interactions that begin immediately after implantation. While mechanical integrity and corrosion resistance are essential, long-term clinical success ultimately depends on the surrounding biological environment’s response to the implant surface. Because surface engineering modifies the physical and microstructural characteristics of the near-surface region, it may influence biological processes ranging from initial protein adsorption to tissue integration and bacterial colonization (Ratner and Bryant, 2004). Current evidence further demonstrates that the biological response is regulated not only by surface morphology but also by the coordinated interaction between immune cells, inflammatory mediators, and tissue-regeneration pathways, making surface integrity a critical determinant of implant biocompatibility and long-term clinical performance.

The first biological event following implantation is the adsorption of proteins from blood and interstitial fluids onto the material surface. This adsorbed protein layer mediates subsequent cellular interactions and therefore plays a critical role in determining biological outcomes. Surface roughness, surface energy, chemistry, and microstructural characteristics may all influence protein adsorption kinetics and conformation. Consequently, modifications introduced through mechanical surface treatments may indirectly affect cellular behavior by altering the nature of the adsorbed protein layer (Anselme, 2000). Recent studies have further demonstrated that the formation of a dynamic protein corona governs the initial recognition of the implant by immune and tissue cells, thereby influencing subsequent inflammatory signaling, cell adhesion, and tissue healing.

Surface characteristics strongly influence cell adhesion and proliferation. Numerous studies have demonstrated that micro- and nanoscale topographical features affect cellular attachment, morphology, migration, and differentiation. Mechanically engineered surfaces may provide favorable conditions for osteoblast adhesion and growth by modifying surface roughness and microstructural organization while preserving the substrate’s chemical composition. Such effects are particularly relevant for orthopedic and dental applications where rapid tissue integration is desirable (Campoccia et al., 2006). Beyond osteoblast activity, increasing attention has been directed toward fibroblast behavior, endothelial cell responses, and angiogenesis, as successful tissue integration depends on coordinated vascularization and extracellular matrix formation during the early stages of implant healing.

Surface nanostructuring generated by severe plastic deformation has attracted growing interest due to its potential biological benefits (Campoccia et al., 2006; Gittens et al., 2011). Nanostructured surface layers may enhance cellular activity through mechanisms associated with increased surface area, altered protein adsorption behavior, and modified cell–surface interactions (Anselme, 2000; Campoccia et al., 2006; Gittens et al., 2011). Emerging evidence further indicates that nanostructured surfaces influence osteogenic differentiation and mineralization, suggesting that mechanical surface treatments contribute to both structural performance and biological functionality. More recently, nanostructured surfaces have also been associated with modulation of macrophage polarization toward a pro-regenerative phenotype, highlighting the emerging role of osteoimmunology in the design of mechanically engineered implant surfaces.

The influence of surface integrity on biological performance extends beyond tissue integration. Bacterial adhesion and biofilm formation remain important concerns for implantable devices because implant-associated infections are among the most serious complications in clinical practice. Surface roughness, topography, wettability, and microstructural condition may affect the initial attachment of microorganisms and the subsequent development of biofilms. Although the relationships between surface characteristics and bacterial behavior remain complex, growing evidence suggests that carefully engineered surface structures may help reduce microbial colonization while maintaining favorable cellular responses (Gittens et al., 2011). However, biofilm maturation is governed by multiple physicochemical and biological factors, and surface modifications that reduce bacterial adhesion should also preserve host-cell compatibility and tissue integration to ensure long-term clinical success.

The interactions among surface integrity, corrosion processes, metallic ion release, protein adsorption, cellular response, and bacterial adhesion are illustrated in Figure 3. These interconnected phenomena demonstrate that biological performance cannot be considered independently of electrochemical and tribological behavior. Instead, implant functionality emerges from the simultaneous interaction of multiple processes occurring at the material–tissue interface. Beyond its electrochemical consequences, corrosion-induced release of metallic ions may influence inflammatory signaling, macrophage activation, and local immune regulation, further reinforcing the close relationship between electrochemical degradation and biological performance.

Current research increasingly emphasizes multifunctional surface engineering strategies that simultaneously improve mechanical performance, corrosion resistance, tribocorrosion behavior, and biological response. Mechanical surface treatments are an important component of this approach because they modify biological interactions without altering the bulk composition of the implant material. However, the biological consequences of deformation-induced microstructural modifications remain incompletely understood, particularly when long-term tissue remodeling, immune response, and microbial colonization are considered simultaneously. Establishing robust correlations between surface-integrity parameters and clinically relevant biological outcomes remains one of the principal challenges in translating laboratory-scale observations into reliable implant-design strategies (Boc et al., 2010). Future investigations should integrate advanced surface characterization with in vitro, in vivo, and clinical studies to clarify the relationships among surface integrity, osteoimmunological regulation, angiogenesis, biofilm development, and long-term implant survival. Such multidisciplinary approaches are expected to support the development of next-generation biomaterials that simultaneously optimize mechanical performance, electrochemical stability, and biological functionality.

11 Integration of mechanical surface engineering and bioactive surface functionalization

Mechanical surface treatments have demonstrated significant potential for improving the structural and functional performance of AISI 316L stainless steel. Through grain refinement, residual stress generation, surface hardening, and microstructural modification, these treatments can enhance fatigue resistance, wear performance, corrosion behavior, and, in some cases, biological response. Nevertheless, mechanical surface engineering alone may not fully meet the requirements imposed on modern biomedical implants, particularly those related to tissue integration, infection control, and long-term biological functionality (Dorozhkin, 2014). Consequently, increasing attention has been directed toward multifunctional surface-engineering strategies capable of simultaneously optimizing mechanical performance, electrochemical stability, and biological activity.

For this reason, increasing attention has been directed toward combining mechanical surface modification with bioactive surface functionalization strategies (Teixeira et al., 2023; Hanawa, 2011; Silva et al., 2024). In such approaches, mechanical treatments are employed to optimize the substrate’s microstructural condition, while additional surface layers or functional coatings are introduced to promote specific biological responses (Teixeira et al., 2023; Hanawa, 2011; Silva et al., 2024; de Lacerda et al., 2025). Rather than acting as competing technologies, mechanical and chemical surface modifications may be viewed as complementary components of an integrated surface-engineering strategy. This synergistic approach optimizes of both the substrate’s structural integrity and the implant surface’s biological, thereby addressing multiple degradation mechanisms simultaneously.

One of the most extensively investigated approaches involves depositing calcium phosphate- and hydroxyapatite-based coatings. These materials exhibit chemical similarities to the mineral phase of bone and have been widely studied because of their ability to support osteoconduction and tissue integration. When applied to mechanically engineered substrates, bioactive coatings may benefit from improved adhesion and enhanced structural stability resulting from the modified surface condition of the underlying alloy (Teixeira et al., 2023). Recent investigations have also explored multifunctional bioactive coatings that incorporate therapeutic ions, antibacterial agents, and controlled drug delivery to enhance implant performance further (Hanawa, 2011).

Oxide-based surface layers represent another important class of biofunctional modifications (Silva et al., 2024). Controlled oxidation processes may improve corrosion resistance while simultaneously modifying surface chemistry and biological interactions. In addition, oxide layers can serve as intermediate platforms for the subsequent incorporation of bioactive molecules, growth factors, or antibacterial agents. Such multifunctional oxide systems have demonstrated considerable potential for improving osseointegration while maintaining favorable electrochemical stability under physiological conditions (Silva et al., 2024; de Lacerda et al., 2025).

Antibacterial surface technologies have also become increasingly important in implant design (de Lacerda et al., 2025; Sha et al., 2024). Surface-associated infections remain among the most challenging complications in orthopedic and dental surgery. Consequently, considerable research has focused on incorporating antibacterial functionality through surface coatings, ion-releasing systems, immobilized bioactive agents, or multifunctional hybrid structures. These approaches seek to reduce bacterial colonization without compromising cellular compatibility and tissue integration. Recent developments include antibacterial nanotopographies and stimuli-responsive surface systems that reduce bacterial adhesion while preserving favorable host-cell interactions (Sha et al., 2024; Zhang et al., 2026).

The integration of mechanical surface treatments with bioactive and antibacterial functionalization strategies is illustrated in Figure 5. As shown, surface engineering may be viewed as a hierarchical process in which microstructural optimization, corrosion resistance, tribocorrosion control, biological response, and antibacterial performance are addressed simultaneously rather than independently. This integrated concept reflects the current transition from conventional surface modification toward multifunctional implant design based on complementary engineering and biological principles (Teixeira et al., 2023; Hanawa, 2011; Silva et al., 2024; de Lacerda et al., 2025; Sha et al., 2024).

A summary of the principal opportunities, limitations, and future research directions associated with integrated surface-engineering strategies is presented in Table 5. Current evidence suggests that multifunctional surfaces capable of simultaneously enhancing structural durability and biological performance are among the most promising directions for next-generation metallic implants (Teixeira et al., 2023; Hanawa, 2011; Silva et al., 2024; de Lacerda et al., 2025; Sha et al., 2024; Zhang et al., 2026). Particular emphasis has recently been placed on integrating mechanical surface treatments with smart coatings, bioactive nanostructures, and controlled therapeutic functionalities to improve both implant longevity and clinical outcomes (de Lacerda et al., 2025; Sha et al., 2024; Zhang et al., 2026).

Several challenges remain unresolved despite the advances reported in recent years. The long-term stability of multifunctional surfaces, the interaction between mechanical and biological degradation processes, the durability of surface coatings under tribocorrosion conditions, and the clinical relevance of laboratory-based observations remain insufficiently understood. These limitations complicate the interpretation of published results and highlight the need for experimental approaches that more closely replicate the conditions implants experience in service (Wilson et al., 2005; Wang et al., 2023). Additional challenges include the lack of standardized long-term testing protocols, limited implant retrieval data, and insufficient laboratory-to-clinical correlation for many emerging surface-engineering strategies.

Another recurring theme in the literature is the difficulty of simultaneously optimizing corrosion resistance, tribocorrosion resistance, antibacterial activity, and osseointegration. Improvements in one functional property do not necessarily result in equivalent gains in overall implant performance. For this reason, increasing attention has been paid to strategies that combine mechanical surface modification, control of surface chemistry, and bioactive functionalization. Such approaches provide a broader framework for improving the long-term performance and reliability of stainless-steel implants (Dorozhkin, 2014; Hrir et al., 2025). Emerging technologies, including laser surface texturing, gradient surface structures, self-healing coatings, artificial intelligence-assisted surface optimization, machine-learning-based materials design, and digital twins for implant performance prediction, are expected to expand the capabilities of integrated surface-engineering strategies further and represent promising directions for the next-generation of biomedical implants.

12 Research gaps and future perspectives

This review was conducted using a structured literature search strategy and reported in accordance with the PRISMA 2020 framework. Although the available evidence was critically analyzed through qualitative synthesis, the heterogeneity in experimental methodologies, surface-treatment parameters, electrochemical protocols, tribological conditions, and biological evaluation methods precluded a quantitative meta-analysis. Consequently, the conclusions presented here should be interpreted as a critical integration of the current evidence rather than as a statistical estimation of treatment effects.

Despite substantial advances in understanding the relationships among mechanical surface treatments, microstructural evolution, corrosion resistance, tribocorrosion behavior, and biological performance, several important challenges remain unresolved (Zhang et al., 2026; Hrir et al., 2025). Current knowledge is largely derived from experimental investigations conducted under controlled laboratory conditions, whereas the physiological environment is considerably more complex and dynamic. Consequently, translating laboratory observations into reliable predictions of long-term clinical performance remains a significant scientific challenge. Increasing the availability of long-term clinical studies, implant retrieval analyses, and standardized in vivo investigations will be essential for reducing the current gap between laboratory findings and clinical practice (Zhang et al., 2026; Hrir et al., 2025).

One of the principal limitations identified throughout the literature is the lack of standardization in experimental methodologies. Differences in surface preparation, treatment parameters, characterization techniques, simulated body fluids, electrochemical protocols, tribological conditions, and biological assays frequently hinder direct comparisons among studies. As a result, contradictory conclusions are often reported regarding the influence of grain refinement, residual stresses, and deformation-induced martensitic transformation on corrosion and tribocorrosion resistance. Future studies should prioritize standardized experimental protocols and quantitative reporting to improve reproducibility and facilitate direct comparison among different surface-engineering strategies (de Lacerda et al., 2025; Zhang et al., 2026).

Another important challenge concerns the multiscale nature of surface integrity. Mechanical surface treatments simultaneously modify roughness, topography, microstructure, residual stress distribution, and phase constitution. Because these variables evolve together, isolating the contribution of individual parameters remains difficult. Future investigations should therefore prioritize integrated characterization approaches that correlate microstructural, electrochemical, tribological, and biological phenomena within a unified framework (de Lacerda et al., 2025; Zhang et al., 2026; Hrir et al., 2025). Combining advanced characterization techniques with computational modeling may further improve the understanding of the relationships between processing parameters, surface integrity, and functional performance.

The long-term stability of mechanically engineered surfaces under physiological conditions also requires further investigation. Most available studies evaluate short-term corrosion or tribocorrosion performance, whereas biomedical implants may remain in service for years or decades. Understanding the evolution of residual stress, nanostructured surface layers, passive films, and mechanically induced microstructures during prolonged exposure to biological environments remains essential for predicting clinical durability (Sha et al., 2024; Zhang et al., 2026). Long-term degradation studies incorporating cyclic loading, corrosion-fatigue interactions, tribocorrosion, and biological aging are particularly needed to improve the prediction of implant service life.

Despite extensive investigation, the role of deformation-induced martensitic transformation in biomedical applications remains incompletely resolved. Although numerous studies have demonstrated its influence on hardness and wear resistance, its effects on corrosion behavior, tribocorrosion mechanisms, ion release, and biological response remain incompletely understood. Improved understanding of this phenomenon may help optimize surface treatments for biomedical alloys (Teixeira et al., 2023; Zhang et al., 2026). Future investigations should also clarify the interactions between deformation-induced martensite, passive-film stability, and local electrochemical heterogeneity using advanced microstructural and surface-sensitive characterization techniques (Teixeira et al., 2023; de Lacerda et al., 2025; Zhang et al., 2026).

From a biological perspective, the relationships among surface integrity, protein adsorption, cellular response, immune modulation, and bacterial colonization remain incompletely characterized (Sha et al., 2024; Zhang et al., 2026). Future research should increasingly incorporate multidisciplinary approaches that evaluate mechanical, electrochemical, microbiological, and biological responses simultaneously rather than independently. Such strategies would provide a more realistic representation of implant behavior in vivo. Particular attention should be directed toward macrophage polarization, osteoimmunological regulation, angiogenesis, endothelial-cell response, fibroblast activity, and biofilm maturation, as these processes have emerged as critical determinants of long-term implant success (Sha et al., 2024; Zhang et al., 2026).

The growing interest in multifunctional implant surfaces represents one of the most promising directions for future development (Zhang et al., 2026; Hrir et al., 2025). As summarized in Figure 5 and Table 5, the integration of mechanical surface engineering with bioactive and antibacterial functionalization strategies offers opportunities to simultaneously address structural reliability, degradation resistance, osseointegration, and infection control. Future advances will likely depend on the development of hierarchical surface architectures that provide multiple functionalities without compromising long-term stability. Additional opportunities include gradient surface structures, laser surface texturing, smart and self-healing coatings, antibacterial nanotopographies, and multifunctional bioactive systems that simultaneously promote tissue regeneration and reduce microbial colonization (Zhang et al., 2026; Hrir et al., 2025).

The principal knowledge gaps and research priorities identified throughout this review are summarized in Table7. These research priorities highlight the need for standardized experimental methodologies, integrated surface characterization, clinically relevant testing conditions, and multidisciplinary approaches to accelerate the translation of laboratory discoveries into clinical applications (Zhang et al., 2026; Hrir et al., 2025).

Taken together, the available evidence indicates that the convergence of advanced surface characterization techniques, computational modeling, additive manufacturing, and multifunctional surface engineering is expected to accelerate the development of next-generation AISI 316L biomedical devices (Zhang et al., 2026). Emerging technologies, including artificial intelligence-assisted surface optimization, machine-learning-based materials design, digital twins for implant performance prediction, and data-driven optimization of manufacturing parameters, are expected to further transform the design and optimization of mechanically engineered biomaterials (Wang et al., 2023; Hrir et al., 2025). Continued collaboration among materials scientists, corrosion engineers, tribologists, biologists, clinicians, and biomedical engineers will be essential for translating these advances into clinically effective implant technologies.

13 Conclusion

AISI 316L stainless steel remains a widely used metallic biomaterial because it combines adequate mechanical performance, corrosion resistance, manufacturing versatility, a long clinical history, and cost-effectiveness. Although titanium- and cobalt-based alloys are increasingly used, AISI 316L is still applied in orthopedic, dental, cardiovascular, and surgical devices, especially when reliability and cost are key considerations. Its continued clinical relevance is further supported by its excellent compatibility with mechanical surface-engineering strategies that improve functional performance without altering the alloy’s bulk composition.

The evidence reviewed in this work demonstrates that the long-term performance of AISI 316L implants is strongly influenced by surface integrity. Surface roughness, topography, residual stress distribution, microstructural condition, and deformation-induced phase transformations collectively affect corrosion behavior, tribocorrosion resistance, fatigue performance, and biological interactions. Consequently, surface integrity should be considered a key parameter in the design and optimization of biomedical devices rather than merely as a consequence of manufacturing operations. The qualitative synthesis performed in this review further demonstrates that these parameters should be interpreted as an interconnected system, since their individual effects cannot adequately predict implant performance under physiological conditions.

Mechanical surface treatments have emerged as effective tools for modifying the near-surface region of AISI 316L without altering its bulk composition. Processes such as shot peening, severe shot peening, burnishing, deep rolling, ultrasonic surface treatments, and laser shock peening can introduce beneficial microstructural modifications, including grain refinement, increased dislocation density, compressive residual stresses, and strain-induced martensitic transformation. These changes may improve mechanical performance and influence both electrochemical and biological behavior. However, the literature consistently demonstrates that the effectiveness of these treatments depends on the processing parameters employed and on the resulting balance between mechanical strengthening, passive-film stability, and biological compatibility.

The review also highlights the complex relationships among microstructural evolution, passive film stability, corrosion mechanisms, and tribocorrosion processes. Although numerous studies have reported improvements in corrosion resistance and wear performance following mechanical surface modification, the resulting behavior depends on the interplay among multiple surface-integrity parameters. This complexity reinforces the importance of comprehensive characterization strategies that can correlate structural, electrochemical, tribological, and biological phenomena. Accordingly, integrated characterization that combines advanced microstructural analysis with electrochemical, tribological, and biological evaluations is essential for identifying the mechanisms underlying the variability reported among different mechanical surface treatments.

From a biological perspective, mechanically engineered surfaces have demonstrated the potential to influence protein adsorption, cellular attachment, osteogenic activity, and bacterial adhesion. These observations support the growing recognition that surface engineering may contribute not only to implant durability but also to biofunctional performance. However, important questions remain regarding the long-term biological consequences of deformation-induced microstructural modifications and their interaction with physiological environments. Future studies should investigate immune modulation, macrophage polarization, osteoimmunological regulation, angiogenesis, and biofilm development to understand better of the biological mechanisms governing long-term implant success.

The integration of mechanical surface treatments with bioactive and multifunctional surface functionalization strategies represents a promising direction for future implant development. As illustrated by the framework proposed in Figure 5 and summarized in Table 5, the combination of microstructural optimization, corrosion control, tribocorrosion mitigation, antibacterial functionality, and enhanced biological response may provide a pathway toward more durable and biologically effective implant systems. Emerging approaches incorporating smart coatings, antibacterial nanotopographies, gradient surface structures, and controlled therapeutic functionalities are expected further to expand the capabilities of mechanically engineered implant surfaces.

Analysis of the available literature indicates that no single surface-integrity parameter can explain implant performance. Corrosion resistance, tribocorrosion behavior, and biological response result from the combined influence of microstructural evolution, residual stress distributions, surface topography, and passive-film characteristics. Studies reporting improved hardness, wear resistance, or corrosion behavior after mechanical surface treatment do not always demonstrate equivalent gains in overall biological or clinical performance, emphasizing the importance of evaluating these properties as an interconnected system rather than as isolated outcomes. The critical assessment presented in this review indicates that differences in processing parameters, characterization methods, electrochemical protocols, and biological evaluation procedures remain major sources of variability among published studies, highlighting the need for standardized methodologies and quantitative comparison of experimental data.

The literature reviewed suggests that the greatest improvements are likely to arise from combining deformation-induced surface modification with bioactive and multifunctional surface-engineering strategies. Further advances will require stronger correlations between surface-integrity metrics and long-term in-service behavior, supported by rigorous characterization and clinically relevant testing methodologies. Such efforts may contribute to the development of AISI 316L implants with improved durability, enhanced biological functionality, and more predictable long-term performance. Future progress will also depend on integrating advanced surface characterization, additive manufacturing, artificial intelligence-assisted materials optimization, machine-learning approaches, digital twins, and multidisciplinary collaboration to accelerate the translation of laboratory discoveries into clinically effective implant technologies.

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Footnotes

Edited by: Diana Petronela Burduhos Nergis, Gheorghe Asachi Technical University of Iaşi, Romania

Reviewed by: Ada Orlowska, Silesian University of Technology, Poland

Sudhir Mittal, Guru Kashi University, India