Towards sustainable diagnostics: assessing biodegradable lateral flow cassettes in real world conditions in Africa

1 Introduction

Lateral flow assays (LFAs) are rapid, portable diagnostic tests used in clinical, bedside, and home settings. They detect disease biomarkers and pathogens and have been applied widely in infectious disease diagnosis, including malaria, influenza, bacterial infections, and COVID-19 (Miller and Sikes, 2015; Larkins and Thombare, 2023). For instance, in low- and middle-income countries, the average medical expenses and income losses faced by tuberculosis (TB) patients over the course of treatment can amount to more than 50% of their average annual income, and half of this cost is incurred in the process of seeking diagnosis (Tanimura et al., 2014).

Despite their value, LFAs are single-use devices, and improper disposal of their plastic cassettes has become a growing environmental and health concern, particularly in low- and middle-income regions (Janik-Karpinska et al., 2022). Conventional diagnostic cassettes are usually made from non-biodegradable polymers such as polyethylene and polypropylene that persist in the environment for centuries, fragmenting into microplastics that threaten ecosystems and human health (Evode et al., 2021; Chen et al., 2020).

While access to testing continues to expand, waste management practices have not kept pace. The increasing volume of diagnostic waste from single-use devices highlights the urgent need for environmentally responsible alternatives (Street et al., 2022).

Biodegradable diagnostic cassettes have emerged as promising alternatives to conventional plastic formats. Produced from renewable, plant-based materials such as starch, cellulose, and polylactic acid (PLA), they can decompose through natural microbial activity into harmless by-products like water, carbon dioxide, and biomass. Their adoption presents a sustainable solution to diagnostic waste management, particularly in low-resource settings where disposal infrastructure is limited. Beyond their environmental advantages, biodegradable cassettes align with global sustainability targets by reducing the ecological footprint of point-of-care medical devices.

The growing global concern over plastic pollution and climate-related environmental impacts has accelerated the demand for biodegradable and bio-based materials across multiple sectors, including healthcare (Anthony et al., 2024). In response, innovations in sustainable polymers have extended to diagnostic technologies, enabling the development of plant-based alternatives to conventional plastic components. A notable example is the biodegradable lateral-flow cassette produced by Okos Diagnostics (Netherlands), which offers an eco-friendly replacement for petroleum-based diagnostic formats and contributes to global efforts to reduce medical waste and promote sustainable healthcare practices.

However, the true environmental performance of these alternatives remains uncertain without standardized validation methods. Factors such as soil composition, microbial diversity, and climate strongly influence degradation rates (Kale et al., 2007; Moshkbid et al., 2024). Rigorous field assessment is therefore necessary to confirm their real-world biodegradability and sustainability.

In response to these challenges, this study conducted at Helix Biogen Institute (Ogbomoso, Nigeria) evaluates the biodegradability of Okos’ plant-based diagnostic cassettes under field conditions using a 4-month simulated landfill model across loamy, sandy, and clayey soils.

The objective was to assess the degradation rate of biodegradable diagnostic cassettes under varying soil conditions, compare their environmental performance with conventional plastics, and identify factors influencing their breakdown. The findings aim to support the development of biodegradability standards and sustainable diagnostic waste management practices. This study contributes to the growing field of sustainable diagnostics by providing empirical data from real-world tropical environments, complementing existing laboratory-based biodegradation standards (Kale et al., 2007).

2 Materials and methods

Lateral flow cassettes used in this study were developed by Okos Diagnostics (Leiden, Netherlands) and manufactured by Sheng Feng Plastic (Figure 1). These plant-based cassettes maintained the structural integrity required for standard diagnostic testing while providing an eco-friendly alternative to petroleum-based plastics. They were produced from bio-based polymers derived from renewable sources such as corn starch and sugar cane, compliant with ASTM D6400 and EN 13432 compostability standards. Preliminary internal evaluations by Okos Diagnostics demonstrated comparable test performance to conventional plastic cassettes and showed measurable degradation within 3 months under controlled composting conditions. Diagnostics (2024 internal report) showed comparable test performance between biodegradable and plastic cassettes (MEDICA-tradefair.com, 2024) Detailed laboratory data, however, remain unpublished; therefore, this field-based experiment was conducted in collaboration with Helix Biogen Institute to validate and extend those findings under real-world tropical soil conditions.

The material is bio-based, derived from renewable sources such as corn starch and sugar cane, and compliant with ASTM D6400 and EN13432 compostability standards. It offers adequate mechanical stability for manufacturing and storage yet decomposes readily under environmental conditions.

2.1 Biodegradability testing protocol

Biodegradability testing followed soil burial protocols adapted from Kale et al. (2007), emphasizing field-based degradation rather than controlled laboratory conditions to capture realistic environmental responses.

2.2 Rationale for 4-month period

The 4-month monitoring period was chosen to capture early to mid-term degradation dynamics under tropical field conditions against the 3-month laboratory-controlled condition study by Okos Diagnostics and to align with initial operational timelines for post-use waste accumulation. This timeframe allows observation of microbial colonization and initial polymer weakening while remaining practical for seasonal fieldwork.

2.3 Preparation of the cassette sample prior to landfill

The biodegradable and plastic cassettes were categorized into four groups (Figure 2) representing monthly sampling intervals. Each group contained one single biodegradable cassette (no strip), one single biodegradable cassette with strip, and one combo (3-in-1) biodegradable cassette. Plastic single and combo cassettes were included in later months for comparison. A summary of the cassette group composition and sampling schedule is presented in Table 1.

TABLE 1. Summary of cassette grouping and sampling schedule.

2.4 Study location and site characteristics

The experiment was conducted at Helix Biogen Institute, Oke-Anu, Ogbomoso, Oyo State, Nigeria (8°08′N, 4°16′E). Three soil types sandy, clayey, and loamy were selected within a 500-m radius to ensure uniform climatic influence while enabling comparative assessment of degradation under different soil textures. These soil types were selected to represent distinct physical and microbial environments influencing degradation rates—high drainage (sandy), poor aeration (clayey), and balanced conditions (loamy).

2.5 Soil and site selection and preparation

At each site (A: sandy, B: clayey, C: loamy), a 508 mm-deep pit was dug for sample burial. Four cassette groups, each representing 1 month of exposure, were buried and retrieved sequentially at monthly intervals for 4 months. Physical appearance, weight, and dimensional changes were recorded upon retrieval (Figure 3) (Table 2).

TABLE 2. Summary of site characteristics.

https://maps.app.goo.gl/ZCQprtyQXRxAWLZm7.

2.6 Validation of the storage cassette

To assess storage stability, biodegradable cassettes were stored under four conditions: 1. open in a refrigerator, 2. sealed in a black nylon bag in a refrigerator, 3. sealed in polyethylene bags in a refrigerator, and 4. in a desk drawer at room temperature.

2.7 Biodegradability assessment

Biodegradability was assessed by monthly monitoring of cassette weight and physical appearance. A precision balance was used to measure weight change associated with microbial colonization, moisture absorption, and material breakdown. Qualitative degradation was also documented photographically for each site and time point (Kale et al., 2007).

2.8 Physical degradation

Physical degradation indicators such as bending, cracking, and colour change were recorded. Early microbial colonization was inferred from the appearance of black or purple patches, while advanced deformation (e.g., 45° bending) signified progressive weakening. Plastic controls served as negative references and remained stable throughout the experiment (Yao et al., 2024; Ślężak et al., 2023; Dintcheva, 2024).

2.9 Statistical validation of plant-based material degradation

Descriptive statistics (mean ± SD) were used to summarize monthly weight changes and assess consistency across soil types. Each mean and SD value was derived from duplicate measurements (n = 2) for each cassette type and soil condition per month. Site comparisons identified environmental factors influencing degradation, such as microbial activity and soil composition. Although only descriptive statistics were used, they provided adequate validation of observed biodegradation trends (Ornaghi et al., 2019).

3 Results, observations and findings

3.1 Visual disintegration and soil-type comparison

Biodegradable cassettes exhibited progressive surface and structural changes across all soil types. Early black discoloration, consistent with microbial colonization, appeared within the first month, while purple patches became more pronounced by the second month, especially in loamy soil (Site C). By the fourth month, some cassettes in Site C showed advanced deformation indicating substantial structural weakening illustrated in Figures 4, 5; Tables 3, 4 (Shah et al., 2008).

TABLE 3. Weight progression of biodegradable cassette types across four months.

Site A Sandy soil; Site B clay soil and Site C loamy soil; SBC, Single Biodegradable Cassette; SBCs, Single Biodegradable Cassette with strip; CBC, Combo Biodegradable Cassette; PSC, Plastics Single Cassette, Plastics Combo Cassette.

TABLE 4. Statistical summary of weight and percentage changes of biodegradable cassettes across soil types.

Statistical summary of initial and final weights, total percentage change, and monthly percentage changes of biodegradable cassette types across different soil conditions, with plastic cassettes serving as controls.

The rate and extent of degradation varied noticeably among soil textures. Loamy soil (Site C) demonstrated the most significant visual and structural degradation, followed by sandy (Site A) and clayey (Site B) soils. These variations align with differences in moisture retention, aeration, and microbial activity across soil types. Loamy soils, with their balanced composition and favourable moisture retention, typically support higher microbial diversity and activity, accelerating biodegradation. In contrast, sandy soils characterized by rapid drainage and low organic matter showed moderate degradation, while clayey soils, due to their dense structure and reduced aeration, exhibited the least microbial activity and therefore the slowest degradation (Liu et al., 2023; Coban et al., 2022; Urbanek et al., 2018).

The initial weight of the biodegradable cassettes ranged from 4.84 g (single cassette) to 11.06 g (combo cassette), while the plastic controls weighed 3.68 g (single) and 8.34 g (combo). Before burial, all biodegradable cassettes appeared off-white, whereas plastic controls were white with blue inscriptions (Figure 4). Subsequent changes in weight and physical appearance over the 4-month period are presented in Table 3.

3.2 Weight changes and progressive degradation patterns

Weight measurements taken monthly revealed an initial increase across all biodegradable cassettes, attributable to moisture uptake and microbial biomass accumulation rather than net material gain. Loamy soil showed the highest weight increase, while clayey soil exhibited the least. Plastic controls remained virtually unchanged throughout the experiment (Figure 6). Site A (sandy) +7.44% ± 0.12%, Site B (clayey) +7.02% ± 0.08%, and Site C (loamy) +11.36% ± 0.16%; plastic controls showed minimal change (+1.36% ± 0.04%) (Gómez and Michel, 2013). A consolidated summary of the weight progression and physical observations of biodegradable cassette types across all months and soil types is presented in Table 3.

The data show a consistent pattern of progressive deformation and microbial activity. The average percentage weight change reached +11.36% in loamy soil, +7.44% in sandy soil, and +7.02% in clayey soil by the fourth month, these differences in final weights across soil types are further illustrated in Figure 7, confirming that biodegradation proceeded most rapidly under loamy conditions. The monthly progression of all cassette types across soil types is shown in Figure 8.

3.3 Observed anomalies and edge effects

Some results deviated from simple mass-loss expectations: early weight increases (compare to the initial weight Table 4) occurred due to moisture uptake and biofilm formation, and degradation was spatially heterogeneous within cassettes (edge effects). Internal test strips remained comparatively intact while external cassette bodies degraded, suggesting protective microenvironments. Plastic controls exhibited no degradation, confirming the material-specific nature of observed effects.

These findings highlight the complexity of degradation processes, where factors such as moisture dynamics, microbial colonization, and material heterogeneity can lead to unexpected outcomes and spatial variability within samples. The preservation of internal components despite external degradation underscores the potential for edge effects and protective microenvironments within composite systems. The absence of degradation in plastic controls further supports the specificity and reliability of the experimental observations.

All biodegradable cassettes showed weight gain over 4 months, indicating moisture absorption and microbial colonization. Loamy soil (Site C) showed the highest weight gain, while plastic controls remained essentially unchanged.

Clear distinction between biodegradable and plastic cassettes. Biodegradable materials show active environmental interaction, while plastic materials remain inert.

Comparison of all cassette types tested across the three soil types, showing consistent patterns of biodegradable material interaction with soil environments.

4 Discussion

This study provides critical insights into the biodegradability of plant-based diagnostic cassettes under real-world tropical soil conditions. The initial weight gain observed (Figure 5) across all sites, especially in loamy and sandy soils, indicates moisture absorption and early microbial colonization behaviour typical of biodegradable polymers such as PLA (Gómez and Michel, 2013). The observed colour changes (black and purple patches) and structural deformation indicate active microbial degradation. However, degradation occurred more slowly than in Okos Diagnostics’ laboratory tests, highlighting the need for field validation since laboratory composting accelerates degradation under optimized temperature and humidity (Kale et al., 2007; Emadian et al., 2017). Internal, unpublished laboratory tests by Okos Diagnostics showed substantial material breakdown within about 3 months under controlled composting conditions, whereas our field results demonstrated only partial degradation after 4 months. The slower rate reflects fluctuating soil moisture, temperature variation, and heterogeneous microbial colonization. These outcomes underscore how real-world conditions influence biodegradation kinetics and emphasize the importance of validating biodegradable materials beyond laboratory simulations.

Site-specific variations faster degradation in loamy soil (Site C) and slower in clayey soil (Site B) highlight the influence of soil composition and microbial diversity on biodegradation (Urbanek et al., 2018). The unchanged plastic controls confirm the persistence of conventional materials and reinforce the need for biodegradable alternatives.

The findings both align with and extend previous research on biodegradable materials The initial weight gain pattern corresponds to reports on PLA and starch-based composites that absorb moisture before decomposition begins (Gómez and Michel, 2013; Siracusa et al., 2008). Unlike studies showing immediate weight loss via hydrolysis (Tokiwa et al., 2009), this experiment suggests early microbial colonization precedes measurable degradation. Variations among sites further reveal the dependence of biodegradation kinetics on local environmental conditions, an aspect often minimized in controlled laboratory settings.

The black and purple discolorations observed are consistent with fungal and bacterial colonization reported in similar studies (Shah et al., 2008) but may also result from abiotic factors such as mineral oxidation. Future analyses of biofilms and soil chemistry are recommended to differentiate biological from abiotic staining and to assess ecosystem interactions. Isolating and characterizing site-specific microbes could inform bioaugmentation strategies for enhanced waste degradation (Urbanek et al., 2018).

The negligible weight change in plastic cassettes confirms that conventional plastics like polyethylene resist natural degradation (Barnes et al., 2009). Compared with composting studies, the slower field degradation underscores the gap between laboratory predictions and environmental performance, supporting the need for standardized field-testing protocols (Kale et al., 2007), Statistical analysis revealed differences in initial and final weights, as well as variations in total and monthly percentage changes among biodegradable cassette types across the three soil conditions compared to the plastic controls (Tziourrou et al., 2025).

The deformation and structural breakdown patterns observed align with PLA- and PHA-based material studies (Arrieta et al., 2014). While complete degradation has been reported under optimized conditions (Emadian et al., 2017), this work observed partial breakdown, highlighting environmental variability. Incorporating silver-coated polyethylene for strip protection may help balance biodegradability and product stability in future cassette designs.

Environmentally, the results demonstrate the potential of biodegradable cassettes to reduce medical plastic waste, supporting global efforts to mitigate pollution, especially in low-resource settings. However, site-specific degradation and colour changes suggest that breakdown products may interact differently with local ecosystems, warranting further ecotoxicity assessments. Industrially, biodegradable cassettes show strong potential as sustainable diagnostic components. Their sensitivity to moisture and microbial activity necessitates protective packaging and consideration of regional environmental conditions for optimal storage, performance, and disposal. These findings may encourage diagnostic manufacturers to explore sustainable materials and motivate policymakers to reduce single-use plastics through incentives for eco-friendly innovations.

4.1 Study limitations

The study’s interpretation is constrained by several factors. The 4-month observation period may not reflect long-term degradation trends, a common limitation in short-duration biodegradation studies (Blessy et al., 2014; Vranic et al., 2025). The lack of continuous temperature and humidity monitoring prevented precise attribution of site-specific degradation differences to environmental drivers, limiting mechanistic interpretation and reproducibility. Microbial activity was inferred only indirectly from colour and weight changes; no molecular or culture-based microbial analyses were performed, limiting insight into the biological agents responsible (Figures 6, 7).

Incomplete characterization of cassette composition and additives may have influenced degradation patterns and interpretation (Pagar et al., 2022). The limited number of samples per site reduced statistical robustness and may have introduced sampling bias (Yu and Tseng, 1999; Zhai and Ye, 2018). Overall, these constraints highlight the need for longer-term studies with environmental monitoring, microbial characterization, and larger sample sizes. Despite these gaps, this work provides the first field-based biodegradation evidence for plant-based diagnostic cassettes in tropical soils, bridging laboratory and real-world data.

4.2 Future directions

Future work should extend monitoring to 6–12 months to capture complete degradation cycles and potential microbial lag phases. Systematic measurement of soil moisture, temperature, and microbial diversity will allow stronger correlations between environmental conditions and degradation rates (Bhangare et al., 2022). Metagenomic and culture-based analyses should identify key degraders and enable bioaugmentation strategies, aligning with recent calls for mechanistic biodegradation studies (Vranic et al., 2025). Evaluating the ecotoxicity of degradation by-products is essential to ensure that breakdown products are environmentally safe (Blessy et al., 2014).

Collaboration with manufacturers should focus on optimizing material composition for faster, more uniform degradation across diverse environments (Bhangare et al., 2022; Xie et al., 2020). Field trials in compost or organic-waste environments are recommended to simulate real disposal scenarios and evaluate degradation efficiency. Collectively, these recommendations call for multidisciplinary, data-driven, and longer-term research integrating advanced analytical and environmental-monitoring methods (Blessy et al., 2014; Vranic et al., 2025; Xie et al., 2020).

5 Conclusion

Biodegradable cassettes degraded progressively under natural soil conditions but at a slower rate than observed in laboratory studies This may be due to the fact that the microorganisms responsible for biodegradation in the selected site used for the experiment are new to the material used in producing the biodegradable cassette. Adaptation or colonization of the microbes to degrade the materials will take a while compared to the laboratory set up experiment in which notable and desirable microbes, nutrients and environmental conditions to aid biodegradation will have been put in place or provided. Continued monitoring for an additional 4–6 months is recommended to capture full degradation patterns. Other sites like compost area, dunghills can be considered for this experiment. This study confirms that biodegradable alternatives to plastic diagnostic cassettes are viable and should be integrated into future manufacturing and waste management strategies.

After successful degradation, isolating, characterizing, and potentially patenting effective microbial strains from these sites could provide valuable biotechnological tools for pollution reduction and waste management. To prevent strip deformation or spoilage, a polyethylene bag coated with silver internally or externally is recommended for cassette packaging. Storage instructions should specify a cool, dry environment at room temperature; refrigeration is discouraged since condensation can deform or contaminate test strips.

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Footnotes

Edited by: Anne-laure Deman, Université Claude Bernard Lyon 1, France

Reviewed by: Collins Otieno Odhiambo, African Society for Laboratory Medicine, Ethiopia

Roshni Pattanayak, Central Institute of Plastics Engineering and Technology Laboratory for Advanced Research in Polymeric Materials, India