Journal of the mechanical behavior of biomedical materials最新文献

Polyethylene glycol (PEG) hydrogels, renowned for their hydrophilicity, biocompatibility, and biodegradability, play a crucial role in a range of biomedical applications. Optimising their performance requires a quantitative and mechanistic understanding of time-dependent mechanical behaviour. This study investigates the effect of a clinically relevant gamma-sterilisation (GS) procedure on the time-dependent mechanical behaviour of PEG hydrogels. Multi-rate nanoindentation loading-creep tests were performed on non-irradiated and irradiated samples. An inverse poro-visco-hyperelastic finite element model, coupled with global optimisation, was used to simultaneously fit load-displacement and creep curves and to extract a consistent set of equivalent elastic, viscoelastic and poroelastic parameters. The results show that γ-irradiation not only increases Young's modulus but also shortens relaxation times and suppresses long-time poroelastic flow, suggesting an effective shift in the time-dependent response from fluid-flow effects towards solid-network mechanics over the investigated time scales. These findings clarify the role of GS in altering the time-dependent mechanical response of hydrogels and establish a general approach for the mechanical characterisation when designing PEG-based hydrogels for biomedical applications.

Bone fractures require the proper integration of fixation devices to ensure long-term biomechanical performance and accelerated recovery, while allowing for early load-bearing and equitable load-sharing. The primary objective of this research is to elucidate the effect of four different generations of fixation devices on synthetic tibiae with induced comminuted fractures. The fixation devices considered herein comprised an intramedullary nail, as well as various distal interlocking screws and plates. The overall biomechanical response was studied under quasi-static compressive loading, following cyclic testing to evaluate the overall system stiffness. More advanced generations (Gen III and IV) showed increased stiffness, reaching values of 1304.69 ± 2.90 kN/m and 1461.00 ± 2.98 kN/m, respectively. Cyclic compressive tests were performed before load-to-failure studies, with the biomechanical constructs being instrumented with strain gauges affixed to the intramedullary nail distally and full-field digital image correlation proximally at the superior flat part of the tibia, revealing the load-sharing capabilities of each fixation device configuration throughout the cyclic loading scenario. The digital image correlation analysis revealed that the proximal tibia exhibited higher strain levels in fixation configurations with only two medial-to-lateral screws, further substantiating the importance of incorporating additional components into the bone-implant system to provide greater stabilization. The distal strain gauges, which registered the deformation of the intramedullary nails, revealed that Gen IV, the only configuration including a medial plate, proved to reduce instabilities in that area, thereby enhancing load sharing between the bone and the intramedullary nail. Ultimately, this extensive experimental work elucidates the importance of comprehensive distal tibiae fixations, which are paramount for future interventions, providing biomechanical stability and bone-implant load sharing. These outcomes are clinically relevant, potentially accelerating load-bearing after surgery by selecting the optimal fixation configuration based on patient conditions and improving the quality of life thereafter.

Background: Hydraulic cements used in endodontic therapy interact with the clinical environment. In vitro testing requires the use of extracted human teeth to mimic the clinical environment. This introduces bias, ethical restrictions and a limited supply of natural teeth, so an alternative tooth replica is required to mimic the microstructure, morphology and the mineral content of natural dentine.

Methods: A slip-casting method was chosen to produce a tooth replica from a slurry of hydroxyapatite, porogen, binding and dispersing agent. μ-CT scanning was used to create an accurate 3D model of the root canal anatomy of extracted teeth. Plaster moulds were produced to accommodate the slip-casting process, and samples of variable hydroxyapatite-to-porogen ratio were created to study the effect of this ratio on the resulting microstructure and hardness and whether these values were comparable to natural dentine. All three compositions were analysed using a scanning electron microscope for the microstructural assessment and a Vickers indenter to determine the microhardness.

Results: All the tested compositions closely matched the pore diameter of that of the coronal and middle thirds of natural teeth while demonstrating significantly bigger pore diameters compared to the apical section except composition 3 which showed significantly bigger pore diameters compared to both middle and apical sections. Varying the wt.% of the constituent materials did not significantly affect the pore density/mm² (ranging from 8787 to 11,813). All compositions revealed hardness values higher than natural dentine, which shows potential as a suitable tooth substitute in research.

Conclusions: The slip casting method to manufacture hydroxyapatite tooth replicas is promising but requires further research to assess its suitability to test hydraulic cements in endodontics.

Hydrogels typically exhibit significant swelling in aqueous environments and fail to maintain stable mechanical properties underwater, which severely limits their practical applications. To address this critical challenge, we herein report the incorporation of tannic acid (TA) as a multifunctional crosslinker and the adoption of a facile one-pot synthesis method for the fabrication of chitosan-chitosan quaternary ammonium salt-tannic acid/poly(acrylic acid) (CS-QCH-TA/PAA) triple-network hydrogels. The optimized hydrogel (with 5% TA) demonstrates exceptional mechanical performance, including a tensile strength of ∼1900 kPa and a compressive strength of ∼6913 kPa, which outperforms previously reported dual-network hydrogels. Benefiting from multiple dynamic crosslinking interactions, the hydrogel can autonomously repair damage and retain mechanical strength even after swelling. As a proof-of-concept, flexible strain sensors fabricated from this hydrogel exhibit clear and repeatable signals when monitoring human finger and wrist movements. Furthermore, the reduced water swelling behavior of the hydrogel ensures stable performance under wet conditions. This work provides a novel strategy for preparing robust, self-healing hydrogels with enhanced water stability, thereby paving the way for their potential applications in wearable sensors, biomedical devices, and other fields requiring hydrogels to withstand aqueous environments.

Measuring the forces of individual muscles in a muscle group around a joint is non-trivial, and researchers have suggested using surrogates for individual muscle forces instead. Traditionally, experimentalists have shown that the force output of the skeletal muscle tissue can be correlated to the intra-muscular pressure (IMP) generated by the muscle belly. However, IMP proves difficult to measure in vivo, due to variations from sensor placement and invasiveness of the procedure. Numerical biomechanical simulations offer a tool to analyze muscle contractions, enabling new insights into the correlations among non-invasive experimentally measurable quantities, such as strains and the force output. In this work, we investigate the correlations between the muscle force output, the principal, shear and volumetric strains experienced by the muscle, as well as the pressure developed within the muscle belly as the tissue undergoes isometric contractions with varying activation profiles and magnitudes. It is observed that pressure does not correlate well with force output under higher sub-maximal and maximal activation levels, especially at locations away from the center of the muscle belly due to pressure relaxation effects. This study reveals strong correlations between force output and the strains at all locations of the belly, irrespective of the type of activation considered. This observation offers evidence for further in vivo studies using experimentally measurable principal and volumetric strains in the muscle belly as proxies for the force generation by the individual muscle and consequently enables the estimation on the contribution of various muscle groups to the total force.

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.