Native bone tissue presents a mechanoelectrical microenvironment characterized by matrix viscoelasticity and intrinsic piezoelectricity. To reproduce these physical features, gelatin methacryloyl (GelMA) was used as the primary polymer network, and aldehyde-functionalized methacrylated hyaluronic acid (OHAMA) was introduced to form reversible Schiff base bonds and impart viscoelastic behavior. Barium titanate (BaTiO3, BTO) nanoparticles were incorporated to produce an ultrasound-responsive piezoelectric viscoelastic hydrogel, designated as PVE-Gel. PVE-Gel retained suitable compressive properties, exhibited a lower swelling ratio and slower degradation than GelMA, and generated periodic electrical signals during ultrasound stimulation. In vitro, ultrasound-stimulated PVE-Gel enhanced the spreading and migration of bone marrow mesenchymal stem cells (BMSCs), increased runt-related transcription factor 2 (RUNX2) and osteocalcin (OCN) expression and alkaline phosphatase activity, and enhanced matrix mineralization. In macrophages, ultrasound-stimulated PVE-Gel reduced CD86 expression and increased CD206 expression, producing a marker profile consistent with a shift toward a repair-associated phenotype. These findings indicate that PVE-Gel combines matrix viscoelasticity with ultrasound-induced piezoelectric stimulation and supports BMSC migration and osteogenic differentiation while altering macrophage marker expression in vitro. These in vitro findings support further evaluation of PVE-Gel in appropriate bone defect models to determine its potential for bone repair.
A uniaxial compression device adapted to very soft materials has been developed for characterizing the mechanical behavior of nineteen samples from five porcine pancreases. The mechanical responses obtained exhibited strong non-linearities and were first modeled analytically in the hyperelasticity framework. Several hyperelastic models have been considered and compared. This approach is carried out with the assumption that the geometry is cylindrical. As the specimens are particularly soft, ensuring a cylindric geometry after the cutting is not possible. The specimens have been scanned and a mean cylinder was used to fit their geometry. A Finite Element simulation of each test has been performed from the 3D scanned geometry. The constitutive parameters have been identified with a Finite Element Model Updating (FEMU) procedure. Whatever the approach followed, analytical or numerical, an equivalent elastic modulus is recalculated in domains of different maximum strains.The elastic modulus obtained with the FEMU have been found lower by a factor up to 2.5 compared to those obtained with the analytical approach. Unlike the analytical approach, the inter- and intra-pancreas values are close. This is explained by the simplifying assumptions made on the sample geometry in the analytical approach.This result reinforces the interest of numerical simulation for identifying the mechanical properties of very soft tissues, for which the geometry of the tested samples cannot be accurately controlled.The mechanical characterization methodology of pancreas samples developed in this study is well suited to the behavior of soft materials, and could therefore be applied to other biological tissues.
Magnesium alloys, such as WE43, have attracted considerable attention for temporary biomedical implant applications owing to their biodegradability, favourable mechanical properties, and inherent biocompatibility. Nevertheless, their practical implementation remains constrained by corrosion and mechanical wear accelerating material degradation. In this context, surface modification strategies have emerged as a promising approach to enhance the stability of WE43 while preserving its biodegradable characteristics. This study investigated the influence of environmental conditions on the wear behaviour of uncoated and Nb2O5-coated WE43 alloy under dry sliding in air, both without and following 1 h of pre-immersion in 0.01 mol L−1 NaCl solution. The results demonstrated that the Nb2O5 coating can improve the wear resistance of the WE43 alloy under both tested conditions, reducing wear depth by approximately 47% and wear volume by nearly 35% during tests performed in air. For the dry wear tests after 0.01 mol L−1 NaCl solution exposure, the coated samples exhibited an even more pronounced improvement in wear volume (nearly 36% reduction) and wear track width (approximately 44% reduction) compared with the uncoated alloy, although the reduction in wear depth was more modest (∼8%). Concomitantly, the coefficient of friction remained relatively stable for all conditions, indicating that the improved tribological performance was mainly associated with the protective character and load redistribution capacity of the Nb2O5 layer rather than with friction reduction. These findings demonstrate that Nb2O5 coatings can improve the tribological durability of WE43 and potentially enhance its lifespan as a temporary implantable device.
Developing low-cost, practical human surrogates is essential for understanding the health effects of kinetic threats and improving protective equipment. Accurate characterization of energy propagation through tissue during kinetic events is important for refining surrogate models and experimental methodologies. Most data collection detailing surrogate tissue responses to kinetic threats has been qualitative, with few internal quantitative measurements obtained. To address this, this study evaluated four tissue surrogate materials with embedded pressure sensors and strain gauges. Two surrogate bone materials were used to assess various density-gradient bone-tissue interfaces, with each configuration exposed to low- and high-velocity kinetic stimuli. Inconsistent responses were observed among the trials performed, evidenced by poor agreement across the time-pressure histories. This mainly occurred at shallow depths, where tissue-bone interfaces heavily influence internal pressure dynamics for each material (x‾±33% kPa at 1 cm). However, depth-based effects later become dominant, as tighter intra-material agreement was observed (x‾±17% kPa at 5 cm). The tissue-bone boundaries yielded opposing results between the experimental setups, as low-density bone pairings produced the highest peak pressures during high-velocity testing. In contrast, high-density bone pairings had higher peak pressures throughout low-velocity testing. This was observed in all surrogate tissues except one, where its low shear modulus allowed the projectile to become permanently embedded, resulting in peak pressures with no-bone to be 10.2 kPa higher than with high-density bone. These results demonstrate the need for precise representation of bone-tissue interfaces to describe internal pressure dynamics from kinetic threats.
Guided bone regeneration (GBR) relies on collagen membranes to stabilize grafted sites and prevent soft tissue ingrowth; however, the mechanical behavior of these membranes at pin-fixation sites where geometric discontinuity creates localized stress concentration remains poorly characterized. This in vitro study aimed to characterize and compare the tensile mechanical properties of five commercially available collagen membranes (Geistlich Bio-Gide®, Collprotect®, Jason®, BioCover™, and Ossix Agile™) when fixated with titanium pins to a standardized artificial cortical bone model, and to evaluate the effect of margin configuration (single-layer versus double-layer folding) on mechanical performance. Standardized specimens were wetted in physiologic saline and subjected to uniaxial tensile loading using a universal testing machine (Instron Model 4502). Maximal load (N), tensile strength (MPa), maximal extension (mm), and energy to failure (N·mm) were recorded. Physical parameters including thickness, cross-sectional area, volume, and density were measured and analyzed. Two-way ANOVA revealed that both membrane type and configuration significantly influenced all mechanical parameters (p < 0.001). The membrane × configuration interaction was significant for maximal load, nominal tensile strength and energy to failure, but not for maximal extension outcomes, indicating that the effect of folding was membrane-dependent. Double-layer margin folding significantly increased maximal load in Ossix Agile™ and Bio-Gide® only; energy to failure increased significantly in Ossix Agile™, Bio-Gide® and BioCover™, and maximal extension in Ossix Agile™ and BioCover™. Non-cross-linked membranes (Jason®, Collprotect®) showed unchanged or reduced values. Cross-linked membranes consistently exhibited superior tensile strength and energy absorption. Volume was the most consistent positive predictor of mechanical resistance across membrane types. Within the limitations of an in-vitro test performed on GBR membranes the clinical value of this technique remains to be established.
