1. Faculty of Engineering and Health, HAWK University of Applied Sciences and Arts Hildesheim/Holzminden/Göttingen, Göttingen, Germany., 2. Institute of Clinical Pharmacology, University Medical Center Göttingen, Göttingen, Germany., 3. Medical Laser Center Lübeck, Lübeck, Germany., 4. Institute of Biomedical Optics, University of Lübeck, Lübeck, Germany.
Focused ultrasound (FUS) is being investigated as a non-invasive technique to modulate vascular barriers and improve therapeutic delivery to protected tissues, including the central nervous system. This study examined Lucifer Yellow transport across human cerebral microvascular endothelial hCMEC/D3 monolayers cultured on ThinCert inserts during and after a 60-second continuous-wave FUS exposure at 1.2 MHz and 80 Vpp, without added microbubbles.
The acoustic field was characterized using hydrophone measurements, and tracer accumulation was quantified before exposure, immediately afterward, and nine minutes later in eight independent paired experiments. During the exposure interval, FUS produced a mean control-adjusted increase in Lucifer Yellow transport of 0.283 nmol, with a 95% confidence interval of 0.185–0.380 nmol. All eight experiments showed an increase in the same direction. During the subsequent nine-minute interval, the additional control-adjusted accumulation was 0.035 nmol, which was not statistically significant.
Exploratory cell-free measurements and acute live/dead fluorescence imaging did not establish a consistent ultrasound-associated effect in those assessments. The findings demonstrate an increase in Lucifer Yellow transport during FUS exposure in the investigated endothelial monolayer–insert system. Further studies are needed to clarify the underlying acoustic mechanisms, characterize barrier recovery, and assess the applicability of these results to other vascular barrier models.
Sam Bleker, Kyra-Elisa M. Redeker, Gerrit Meußler, Ralf Brinkmann, Jürgen Brockmöller, Christoph Russmann
Focused ultrasound (FUS) is being investigated as a non-invasive approach to modulate vascular barriers and thereby facilitate drug delivery to the central nervous system and other protected tissues. However, interpretation of in vitro endothelial responses to FUS is complicated by culture-vessel acoustics and by the need to distinguish transport occurring during exposure from transport occurring afterward. We investigated Lucifer Yellow transport across hCMEC/D3 human cerebral microvascular endothelial monolayers cultured on ThinCert inserts during and after a 60-s continuous-wave FUS exposure at 1.2 MHz and 80 V pp (peak-to-peak voltage) without added microbubbles. Hydrophone measurements at 100 V pp identified 1.2 MHz as the frequency yielding the highest mean peak rarefactional pressure in the frequency scan at an axial distance of 5.0 mm from the lens apex. Separate axial scans at 1.2 MHz located the axial pressure maximum at the same distance; first-order voltage scaling of the corresponding peak rarefactional focal pressure (PRFP) yielded an estimated PRFP of 0.838 ± 0.054 MPa for the 80-V pp condition in the calibration geometry. Lucifer Yellow accumulation was quantified immediately before exposure, at the end of exposure, and 9 min later in eight independent paired experiments using sampling- and volume-corrected receiver amounts. During the 60-s exposure interval, the mean control-adjusted increase was 0.283 nmol (95% confidence interval, 0.185–0.380 nmol; Holm-adjusted P = 0.000475; Cohen’s d z = 2.43), and all eight experiments showed the same effect direction. During the subsequent 9-min interval, the additional control-adjusted accumulation was 0.035 nmol (95% confidence interval, −0.100–0.171 nmol; Holm-adjusted P = 0.555). In a separate preliminary cell-free session, three within-session FUS/control pairs did not reproduce the positive exposure-interval response seen in the cellular series; these observations were descriptive only. In five separate paired experiments, acute Calcein-AM- and ethidium homodimer-1-derived image metrics showed mixed FUS-minus-control differences without a reproducible FUS-associated direction. These findings demonstrate an exposure-associated increase in Lucifer Yellow transport across the hCMEC/D3 monolayer–insert system that arose predominantly during insonification, without statistically detectable continued differential accumulation during the observed post-exposure interval. Together, these results provide a controlled in vitro framework for temporally resolving FUS-associated transport in this monolayer–insert system.
Devyani Gupta, Akash Chandra, Jagruti M. Patil, Karla P. Mercado-Shekhar
Polyvinyl alcohol (PVA) phantoms are used to evaluate shear wave elastography and viscoelastography systems. This study investigated how aluminum oxide and the cryoprotectants ethylene glycol (EG) and propylene glycol (PG) affect the microstructural, acoustic, and viscoelastic properties of PVA phantoms. Phantoms containing 10% PVA were fabricated with varying concentrations of aluminum oxide, EG, or PG. Their microstructure, density, longitudinal sound speed, acoustic attenuation, shear modulus, and viscosity were evaluated. Aluminum oxide increased acoustic attenuation, density, and shear modulus, while its effects on longitudinal sound speed and viscosity were not statistically significant. Increasing EG and PG concentrations increased sound speed and influenced attenuation. Their effects on shear modulus and viscosity were concentration-dependent and nonlinear. These findings demonstrate that additives can simultaneously alter several phantom properties, highlighting the importance of carefully controlling formulation parameters to improve the standardization, accuracy, and reproducibility of ultrasound elastography experiments.
Encapsulated microbubbles (EMBs) play important roles in biomedical ultrasound applications, including diagnostic imaging, targeted drug delivery, sonoporation, and mechanotransduction, yet existing Rayleigh-Plesset-type and potential-flow-based formulations remain limited in their ability to resolve the complex viscous fluid-structure interactions and nonspherical interfacial dynamics exhibited by EMBs. In the present study, a fully resolved computational fluid dynamics (CFD) framework based on immersed boundary-lattice Boltzmann coupling is developed to simulate ultrasound-driven EMB dynamics in biologically relevant environments. The proposed methodology combines an axisymmetric multicomponent multiphase lattice Boltzmann flow solver with an immersed boundary representation of the EMB viscoelastic shell, while incorporating shell rheology through the Boussinesq-Scriven constitutive law along with an exponential elasticity model. The framework is validated through Young-Laplace equilibrium tests and comparison with solutions of a modified Rayleigh-Plesset equation for acoustically-driven EMB oscillations. The results demonstrate accurate prediction of interfacial pressure jumps, physically relevant liquid-to-gas density ratios, and EMB oscillatory dynamics under both linear and nonlinear acoustic regimes. Higher-order interpolation-spreading stencils and higher-order advection schemes are shown to improve numerical accuracy, while further simulations reveal that shell elasticity strongly modifies nonlinear oscillatory behavior and that shell dilatational viscosity introduces substantial damping and dissipative effects. Beyond radial oscillations, the proposed solver accurately reproduces jet formation and nonspherical collapse of an ultrasound-driven EMB near a membrane, a problem of particular interest in sonoporation. Altogether, the present work establishes a robust and physically resolved CFD framework capable of capturing complex multiphase fluid-structure coupling in ultrasound-driven EMBs, thereby providing a versatile computational platform for further nonspherical EMB dynamics (e.g., EMB shape mode oscillations), fully bidirectional bubble-boundary interactions, cavitation-based tissue ablation, and other biomedical ultrasound phenomena.
Ran Wei, Zhiyu Sheng, Mengyue Chen, Huaiyu Wu, Edith Tzeng, Xuecang Geng, Xiaoning Jiang, Kang Kim
Ultrasound thermal strain imaging (US-TSI) exploits temperature-dependent changes in speed of sound (SoS) to monitor tissue temperature change and characterize tissue composition. However, quantitative relationships among composition, temperature, and thermal strain remain insufficiently characterized. We developed a quantitative framework using measured SoS–temperature relationships, Wood’s equation-based mixture modeling, Field II simulations, and experimental validation. Thermal strain was estimated using a slope-based displacement method. Thermal strain showed a linear dependence on temperature rise (simulation: R 2 = 0.975–0.996; experiment: R 2 = 0.868–0.968) and on oil mass fraction (simulation: R 2 = 0.998–0.999; experiment: R 2 = 0.925–0.993) within a temperature-rise range of 1 °C–4 °C. These results demonstrate strong agreement among theory, simulation, and experiment and support the use of US-TSI for quantitative tissue characterization.
