Journal of the mechanical behavior of biomedical materials最新文献

The human amniotic membrane (hAM) is a collagen-rich tissue increasingly used as a natural scaffold in tissue engineering. A key step in these applications is decellularization, which extracts the extracellular matrix (ECM) as a biomaterial. In this study, native hAM was processed using two different protocols: peptide bond hydrolysis with EDTA-assisted trypsin (En) and cell membrane disruption using a nonionic detergent combined with reversible alkaline swelling (SD), along with nuclease activity. The effects of each protocol on the composition, structure, and tensile behavior of the processed hAM were evaluated. Additionally, the repopulation efficiency of epithelial cells on both surfaces of the decellularized hAM was assessed. Comparisons between decellularized and digested hAM and native tissue revealed residual DNA contents ranging from 0.14 to 30% for the En method and from 1.7 to 10% for the SD method. Meanwhile, sulfated glycosaminoglycans (sGAG) content varied from 1.5 to 30% and from 1 to 18%, respectively. The En method substantially reduces fibronectin levels, while the SD method reduces lumican in the leached components of decellularized hAM. En-treated specimens exhibit altered elastic and rupture properties, negatively impacting their mechanical behavior. The hAM-derived ECM materials were repopulated by human vaginal epithelial cells, adopting morphologies that depend on the surface characteristics provided by the anatomical portion of the native tissue. Overall, these results suggest that native tissue variability influences the final composition of hAM-derived materials, that tensile properties are influenced by the used decellularization method, and that surface characteristics play a critical role in epithelial cell repopulation.

Vital pulp therapy (VPT) is an established approach for preserving pulp vitality following direct exposure. Its success depends on the formation of a dentin bridge that seals the exposure site. This study investigated the localised mechanical properties of dentin bridges formed using different VPT materials and applied a quantitative protocol for their assessment. Dentin bridges induced by calcium hydroxide, mineral trioxide aggregates (MTA), or a bioceramic material were examined in a murine model of direct pulp capping. Nanoindentation load-hold-displacement data were interpreted using a generalized Kelvin-Voigt framework to resolve instantaneous elastic and delayed viscous deformation. Morphology and composition were assessed using scanning electron microscopy with energy-dispersive X-ray spectrometry and Raman spectroscopy, enabling correlation of mechanical parameters with mineral content and collagen-related features. Nanoindentation revealed material-dependent differences in the mechanical response of dentin bridges. The bioceramic-induced bridge exhibited elastic stiffness and viscous damping values most closely approximating those of native dentin under wet conditions. Conversely, bridges formed by calcium hydroxide showed significantly lower values for elastic stiffness. Mineral density was highest in native dentin, whereas Ca/P ratios were higher in the MTA and bioceramic groups, indicating that the elastic modulus was associated with the mineral density and the Ca/P ratio. The quantitative protocol applied in this study revealed that different VPT materials influenced the structure and mechanical properties of the resulting dentin bridges.

The stability and durability of ultra-high molecular weight polyethylene (UHMWPE) components are critical to the long-term success of total arthroplasty. Although radiation-induced degradation has been extensively studied and is recognized as a major issue, UHMWPE degradation by synovial lipids has garnered limited attention. Specifically, clinical evidence for lipid-induced degradation is lacking, and the validity of squalene as a model lipid remains unestablished. Therefore, this study was aimed at assessing UHMWPE degradation caused by lipids in clinical practice and developing a clinically relevant model. UHMWPE components and synovial fluid retrieved from revision surgeries were analyzed for lipid content. An in vitro lipid-induced degradation model was developed by introducing these lipids into UHMWPE. Degradation was evaluated using high-spatial-resolution mechanical testing and oxidation index (OI) measurements. Limited squalene was detected in either retrieved components or synovial fluid, whereas cholesterol esters and triglycerides were abundant. In vitro, all tested lipids elevated the OI of UHMWPE, but only lipids containing unsaturated bonds caused minor reductions in mechanical properties. Detailed analysis of retrieved components failed to detect evidence of lipid-induced degradation. These findings indicate that synovial lipids can increase OI without necessarily impairing mechanical properties. Consequently, OI alone is insufficient for evaluating degradation, and mechanical testing is essential. The extent of synovial-lipid-induced degradation was subtle compared with other degradation mechanisms. Squalene-based models do not quantitatively replicate clinical conditions, and their results must be interpreted with caution. These findings can guide the accurate assessment and prevention of lipid-induced degradation of UHMWPE in clinical settings and implant development.

Lattice structures are increasingly being adopted for orthopaedic implant designs; however, questions remain about the long-term strength and risk of fatigue failure of porous titanium (Ti) and Ti-alloy structures. To provide a deeper understanding of this issue, this study conducted a comprehensive review of fatigue performance of latticed Ti/Ti-alloy parts, printed via laser powder bed fusion (PBF-LB), for orthopaedic applications, spanning studies over the past decade. Key lattice parameters were collected, including porosity, pore size, feature thickness, and lattice type, and their corresponding effect on fatigue performance of the end part. This review found that many Ti/Ti-alloy lattice structures can achieve comparable mechanical properties to trabecular bone (E of 0.01-3 GPa, fatigue strength of 0.3-3 MPa) while only one reviewed sample matched both the Young's modulus and fatigue strength of cortical bone (E of 15-20 GPa, fatigue strength 40-60 MPa). This review addresses the gap in having consolidated data describing the effects of various properties of Ti/Ti-alloy lattices on their compressive fatigue strengths, providing guidance on design considerations of such lattice structures for orthopaedic applications. Data provided in this review further highlights the need for continued development of implant latticing strategies and design parameter development to better mimic human cortical bone in orthopaedic implants.

Orthopaedic and dental implants, the majority of which are made from titanium alloys, face the crucial challenge of both inducing osteogenesis whilst inhibiting bacterial biofilm formation in an economical manner over the life of the implant. This study introduces an innovative strategy combining cost-effective alloying elements, selected due to their reported biological benefits, for developing new titanium alloys that achieve a tailorable mechanical, corrosion, and biological response. The combination of alloying and manufacturing results in homogeneous materials characterised by a lamellar microstructure. The developed low-cost Ti alloys have a maximum ultimate compression strength of 659 MPa, maximum tensile yield stress of 606 MPa, and maximum elongation of 8.3% without failing catastrophically. The alloys do not degrade as abiotic corrosion is significantly hampered by their intrinsic passivation behaviour (maximum corrosion rate of 8.9 μm/year), and have adjustable surface wettability with contact angles in the 60-81° range. Consequently, stomal cell attachment, cytotoxicity and cytokine production (IL-6 and TGF-β1), and antibacterial rate on S. aureus are consistent and comparable to those of current implnat materials. Based on these characteristics, the low-cost Ti alloys are promising materials for load-bearing biomedical devices.

Although the uniaxial tensile deformation of human hair has been extensively studied, the temperature response under tensile loading has not been directly measured, limiting insight into the entropic and enthalpic contributions. To address this gap, we developed a tensile apparatus equipped with a thermocouple capable of detecting temperature variations with ±50 μK precision. The temperature change exhibits a characteristic N-shaped profile during extension up to fracture at λ≈1.6. This behavior can be interpreted using the two-phase model in which crystalline α-helical filaments are embedded in an amorphous matrix. In the Hookean region (λ=1-1.05), stress increases linearly with strain while the temperature rises by several tens of mK, indicating an exothermic response dominated by the amorphous matrix. Cyclic extension-contraction tests reveal reversible thermal responses together with gradual accumulation of residual strain. In the transformation region (λ=1.05-1.3), the temperature response reverses and exhibits a pronounced endothermic decrease, reflecting the α-to-β structural transition. In the post-transformation region (λ=1.3-1.6), the temperature increases again, consistent with the progressive development of β-sheet structures.

Higher complication rates in reverse shoulder arthroplasty are commonly reported in patients receiving smaller humeral implants, potentially due to reduced bone stock and compromised implant stability. While bone-preserving hybrid onlay-Grammont humeral stems are thought to improve cortical engagement, comparative biomechanical evidence remains scarce, particularly in small humeri. A 2 × 2 factorial design was conducted in this exploratory study to evaluate the independent effects of implant size (large vs. small humerus) and implant placement (inlay vs. hybrid onlay-Grammont) on implant stability. Paired humeri from a male (large) and female (small) donor were implanted with inlay and hybrid onlay-Grammont designs. Specimens were tested under controlled physiological and compressive failure loading in a custom-built μCT-compatible rig. Implant stiffness, vertical displacement, and cortical failure were quantified using 3D μCT imaging and force-displacement data. Rigid co-registration and surface mesh segmentation were used to assess implant migration and bone deformation. In the large humerus, the hybrid onlay-Grammont implant showed greater stiffness (288 N/mm) and failure load (2800 N) than the inlay design, consistently causing cortical opening. In the small humerus, the inlay implant exhibited the highest distal migration (-12 mm) without cortical cracking, while the onlay design produced controlled radial cortical failure consistent with the large specimen. These results demonstrate that reduced peri-prosthetic bone stock can prevent the implant from fully loading the cortex causing a shift of the failure mechanism, particularly in the small humerus. They also support further larger studies on patient, surgical, and loading factors concerning implant stability.

Cortical fold development in the human brain progresses through various stages of wrinkling, primary folding and secondary folding, resulting in complex gyrus-sulcus formation. Differential growth in gray and white matter is a key driver of this morphological sequence. This process, modeled here in terms of a large scale mismatch in growth strain, gives rise to mechanical stress. An intrinsic residual stress is thus present in the fully developed brain structure. We describe a model for determining this growth induced residual stress and then examine its key features. This includes a focus on how tensile and compressive regions correlate with sulcus-gyrus formation, how sulcal wall self contact is affected by secondary folding, how wall self contact affects the stress, and which deep tissue surface orientations may be especially predisposed to microtear. This work considers a new paradigm for brain injury modeling by demonstrating how growth-induced residual stresses fundamentally influence trauma susceptibility, with tensile stress concentrations at gray-white matter interfaces creating preferential sites for injury initiation.

The repair of critical bone defects resulting from trauma, infection, tumors, and congenital malformations poses significant clinical challenges. The combination of medical-grade polycaprolactone (PCL) and β-tricalcium phosphate (β-TCP) is widely investigated for developing synthetic bone graft substitutes, attracting considerable interest in regenerative medicine. However, the material's inherent lack of osteogenic capacity remains a bottleneck to its widespread clinical application. This study synthesized a strontium oxide (SrO)-functionalized three-dimensional (3D)-printed polycaprolactone (PCL)/β-tricalcium phosphate (β-TCP) composite scaffold. Gradient SrO-doped (0-2.0 wt %) 3D printed scaffolds (3D PTSr) were fabricated by melt blending and direct ink writing (DIW) technology, and their physicochemical and biological properties were systematically characterized. Scanning electron microscopy (SEM) showed that the 3D PTSr scaffold had a precisely regulated macroscopic pore structure (pore size ∼ 1 mm) and uniformly distributed Sr element. When the doping amount of SrO was 1.5 wt %, the scaffold exhibited the best comprehensive performance: the surface contact angle was reduced to 64.78° ± 0.54°, and the weight loss rate was 42.83 ± 0.02 % after 4 weeks of in vitro degradation. At the same time, it showed the sustained release characteristics of Sr²⁺ for 56 days (cumulative release of 10.42 ppm). Mechanical tests showed that the compressive strength (5.64 ± 0.04 MPa) and tensile strength (2.75 ± 0.16 MPa) were significantly better than the control group (p < 0.05). In vitro biomimetic mineralization experiments confirmed that SrO functionalization facilitated dense calcium-phosphate composite layer formation. In vitro experiments demonstrated that the 3D PTSr1.5 scaffold significantly promoted the proliferation of MC3T3-E1 cells, and its osteogenic differentiation ability was verified by increasing alkaline phosphatase (ALP) activity and calcium nodule formation. Implantation of 3D PTSr1.5 scaffold into rat cranial defects significantly enhanced bone regeneration at 12 weeks versus controls. Histological analysis confirmed substantial regeneration of mature bone tissue and collagen fibers within the defect area. This study reveals the molecular mechanism of SrO functionalization promoting bone regeneration by regulating the synergistic effect of material degradation-ion release-topology, and provides a theoretical basis and technical reserve for the development of next-generation intelligent bone repair materials.