Journal of the Mechanical Behavior of Biomedical Materials最新文献

Elastography is an emerging diagnostic technique that uses conventional imaging modalities such as sonography or magnetic resonance imaging to quantify tissue stiffness. However, different elastography methods provide different stiffness values, which require calibration using well-characterized phantoms or tissue samples. A comprehensive, fast, and cost-effective elastography technique for phantoms or tissue samples is still lacking.

Therefore, we propose ultrasound Bessel-fit-based time harmonic elastography (B-THE) as a novel tool to provide rapid feedback on stiffness-related shear wave speed (SWS) and viscosity-related wave penetration rate (PR) over a wide range of harmonic vibration frequencies. The method relies on external induction and B-mode capture of cylindrical shear waves that satisfy the Bessel wave equation for efficient fit-based parameter recovery. B-THE was demonstrated in polyacrylamide phantoms in the frequency range of 20–200 Hz and was cross-validated by magnetic resonance elastography (MRE) using clinical 3-T MRI and compact 0.5-T tabletop MRI scanners. Frequency-independent material parameters were derived from rheological models and validated by numerical simulations.

B-THE quantified frequency-resolved SWS and PR 13 to 176 times faster than more expensive clinical MRE and tabletop MRE and have a good accuracy (relative deviation to reference: 6 %, 10 % and 4 % respectively). Simulations of liver-mimicking material phantoms showed that a simultaneous fit of SWS and PR based on the fractional Maxwell rheological model outperformed a fit on PR solely.

B-THE provides a comprehensive and fast elastography technique for the quantitative characterization of the viscoelastic behavior of soft tissue mimicking materials.

Background and objective

Different bone remodeling algorithms are used to predict bone adaptation and to understand how bones respond to the mechanical stimuli altered by implants. This paper introduces a novel micro-scale bone remodeling algorithm, which deviates from conventional methods by focusing on structure-based bone adaptation instead of density-based approaches.

Methods

The proposed model simulated cellular activities such as bone resorption, new bone formation, and maturation of newly formed bone. These activities were assumed to be triggered by mechanical stimuli. Model parameters were evaluated for the 3D geometries of trabecular bone from intact femur developed from micro computed tomography (CT) scan data. Two different hip implants, solid and porous were used, and two different bone remodeling methods were performed using the proposed and conventional methods.

Results

Results showed that micro CT scan-based finite element (FE) models accurately captured the microarchitecture and anisotropy of trabecular bone. The predicted bone resorption rate at the peri-prosthetic regions for the solid and porous implants was in the range of 17–27% and 4.5–7.3%, respectively, for a simulated period of four years.

Conclusions

The results obtained from FE analysis strongly align with clinical findings, confirming the effectiveness of the proposed algorithm. By emphasizing the structural aspect of bone adaptation, the proposed algorithm brings a fresh perspective on bone adaptation at the peri-prosthetic bone. This method can help researchers and clinicians to improve implant designs for better clinical outcomes.

Spider silk is a type of natural protein fiber with excellent toughness and tensile strength. The mechanical properties of chimeric silk have been improved by integrating the spider silk protein gene into the silkworm (Bombyx mori) genome, but this strategy requires a long time to produce genetically modified silkworms. In this study, to rapidly produce chimeric silkworms/spider silk with improved toughness and tensile strength, recombinant Autographa californica multiple nucleopolyhedrovirus (AcMNPV), AcMNPV-FHP-MaSp-G, harboring a full-length Trichonephila clavipes major ampullate spidroin G (MaSp-G) gene driven by the silkworm fibroin heavy chain (Fib-H) promoter, was constructed, in which the signal peptide sequence of the MaSp-G gene was replaced by the signal peptide sequence of the Fib-H gene. Western blot and LC–MS/MS results showed that MaSp-G was successfully expressed in the posterior silk gland of silkworm larvae infected with AcMNPV-FHP-MaSp-G and secreted into the cocoon. Mechanical property tests revealed that the average maximum breaking stress and the average maximum elastic strain of chimeric silkworms/spider silk were 497.867 MPa and 14.824%, respectively, which were 36.53% and 23.55% greater than those of silk produced by normal silkworms. Fourier transform infrared (FTIR) spectroscopy revealed that the proportions of β-sheets, α-helices, and β-turns in the chimeric silk increased by 18.22%, 16.92%, and 18.72%, respectively. These results indicate that the mechanical properties of the chimeric silk produced by silkworms infected with AcMNPV-FHP-MaSp-G were significantly improved, which provides a new method for rapid production of chimeric silk in a genetically modified/genome-edited silkworm-independent manner.

The reconstruction of maxillofacial defects caused by anomalies, fractures, or cancer is challenging for dentofacial surgeons. To produce efficient, patient-specific implants with long-term performance and biological suitability, numerous methods of manufacturing are utilized. Because additive manufacturing makes it possible to fabricate complex pore structure samples, it is now recognized as an acceptable option to design customized implants. It is well recognized that a porous structure with proper design promotes accelerated cell proliferation, which enhances bone remodeling. Porosity can also be employed to modify the mechanical characteristics of fabricated implants. Thus, design and choice of rational lattice structure is an important task. The influence of the structure of jaw implants made of highly porous titanium-based materials on their mechanical properties and bone tissue growth was studied. Based on a 3D computer model of Wigner-Seitz lattice structure, the model samples were fabricated from Ti6Al4V powder by selective laser melting to characterize the mechanical properties of the samples depending on their macroporosity. Then two types of jaw bone implants were manufactured to conduct studies of bone tissue ingrowth when implanted in laboratory animals. The research was carried out in several stages: design and production of the implants for replacing incomplete defects of the lower jaw; implantation of SLM-printed implants in laboratory animals into an artificially produced defect of the lower jaw; analysis of the degree of fixation of the “implant - bone” connection (for implantation periods from 2 weeks to 9 months). During the research, Ti-alloy structures with cell diameters of 2–3 mm and macroporosity of 90–97% mimicking the spongy structure of trabecular bone tissue, were characterized by a compressive strength of 12.47–37.5 MPa and an elastic modulus of 0.19–1.23 GPa, corresponding to the mechanical properties of bone tissue. Active processes of tissue growth into implant cells were detected 2 weeks after implantation, the significant differences in the volume and types of filling tissue depending on the size of the cell were described. Recommendations for choosing the cell size depending on the type of bone tissue damage were given. When using SLM-printed implants with lattice structure (cell sizes from 1 to 3 mm), an active osteosynthesis processes occurred, which culminated in the formation of bone tissue inside the implant cells 9 months after implantation, with 68% of the samples characterized by the maximum degree of implant fixation. Implants with 3 mm cells with macropores diameters of 850 μm were recommended for replacing cavities after removal of perihilar cysts. To replace complete and partial defects, it was recommended to use implants with a cell size of 2 and 3 mm.

Transcatheter aortic valve replacement (TAVR) has become today the most attractive procedure to relieve patients from aortic valve disease. However, the procedure requires crimping biological tissue within a metallic stent for low diameter catheter insertion purpose. This step induces specific stress in the leaflets especially when the crimping diameter is small. One concern about crimping is the potential degradations undergone by the biological tissue, which may limit the durability of the valve once implanted. The purpose of the present work is to investigate the mechanical damage undergone by bovine pericardium tissue during compression and analyze how this degradation evolves with time under fatigue testing conditions. Pericardium 500 μm thick pericardium ribbons (5 mm large, 70 mm long) were crimped down to 12 Fr for 30 and 50 min within a metallic stent to replicate the heart valve crimping configuration. After crimping, samples underwent cyclic fatigue flexure and pressure loading over 0.5 Mio cycles. Samples were characterized for mechanical performances before crimping, after crimping and after fatigue testing in order to assess potential changes in the mechanical properties of the tissue after each step. Results bring out that the ultimate tensile strength is not modified through the process. However an increase in the modulus shows that the crimping step tends to stiffen the pericardium. This may have an influence on the lifetime of the implant.

Background and objective

Fatigue failure of the humeral stem is a severe long-term failure after shoulder arthroplasty, causing harm to patients and resulting in complex revision surgeries. However, there are few studies on humeral stem fatigue testing, and corresponding testing standards have not been established. Therefore, this study aims to investigate the fatigue performance of the humeral stem by establishing an efficient numerical simulation method.

Methods

Material properties are obtained by uniaxial tensile and fatigue tests. A parameterized static analysis program was written, and an automated fatigue numerical simulation platform was established using Abaqus, Fe-safe, and Isight in combination, enabling the establishment of a numerical simulation method for the fatigue performance of the humeral stem.

Result

Standard testing conditions include an 8 mm diameter humeral stem, a 40-21B humeral head, an 8° tilt angle, and a 2 mm fillet radius. Further research found that the fatigue life of the humeral stem decreases with increasing patient weight, and patients should control their weight after surgery.

Conclusions

The established automated fatigue numerical simulation platform avoids repetitive operations and efficiently completes large-scale calculations, guiding preoperative humeral stem selection and testing.

Transcatheter arterial embolization is a minimally invasive intervention process in which the blood supply to a tumor or an abnormal area of tissue is blocked. One of the most commonly used embolic agents in clinics is microsphere (MS). In order to understand the flow behavior of microspheres in arteries, it is essential to study their mechanical properties systematically. In this work, calcium-alginate MSs with varying calcium concentrations were synthesized using a coaxial airflow method. Indocyanine green (ICG) was added as a fluorescent dye. The effect of ICG concentration change on microspheres was investigated by studying morphology, imageability, rheology, and swelling behavior. Then the effect of calcium chloride concentration change on microspheres was studied by conducting rheological tests, atomic force microscopy tests, hemolysis assay, and thrombogenicity assay. Results showed that microspheres with higher ICG concentrations have longer lasting fluorescence and lower storage modulus (G′). Higher concentrations of calcium chloride led to higher G′, while the local Young's modulus obtained by AFM test was not significantly affected. The MSs with and without ICG showed good hemocompatibility and thrombogenicity.

Tendon-bone fibrocartilaginous insertion, or enthesis, is a specialized interfacial region that connects tendon and bone, effectively transferring forces while minimizing stress concentrations. Previous studies have shown that insertion features gradient mineralization and branching fiber structure, which are believed to play critical roles in its excellent function. However, the specific structure-function relationship, particularly the effects of mineralization and structure at the mesoscale fiber level on the properties and function of insertion, remains poorly understood. In this study, we develop mesoscale computational models of the distinct fiber organization at tendon-bone insertions, capturing the branching network from tendon to interface fibers and the different mineralization scales. We specifically analyze three key descriptors: the mineralization scale of interface fibers, the mean, and relative standard deviation of the local branching angles of interface fibers. Tensile test simulations on insertion models with varying mineralization scales of interface fibers and structures are performed to mimic the primary loading condition applied to the insertion. We measure and analyze five representative mechanical properties: Young's modulus, strength, toughness, resilience, and failure strain. Our results reveal that mechanical properties are significantly influenced by the three key descriptors, with tradeoffs observed between mutually exclusive properties. For instance, strength and resilience plateau beyond a certain mineralization scale, while failure strain and Young's modulus exhibit monotonic decreasing and increasing trends, respectively. Consequently, there exists an optimal mineralization scale for toughness due to these tradeoffs. By analyzing the mesoscale deformation and failure mechanisms from simulation trajectories, we identify three fracture regimes closely related to the trends in mechanical properties, supporting the observed tradeoffs. Additionally, we examine in detail the effects of the mean and relative standard deviation of local branching angles on mechanical properties and deformation mechanisms. Overall, our study enhances the fundamental understanding of the composition-structure-function relationships at the tendon-bone insertion, complementing recent experimental studies. The mechanical insights from our work have the potential to guide the future biomimetic design of fibrillar adhesives and interfaces for joining soft and hard materials.

3D printing of materials which combine fracture toughness, high modulus and high strength is quite challenging. Most commercially available 3D printing resins contain a mixture of multifunctional (meth)acrylates. The resulting 3D printed materials are therefore brittle and not adapted for the preparation of denture bases. For this reason, this article focuses on toughening by incorporation of triblock copolymers in methacrylate-based materials. In a first step, three urethane dimethacrylates with various alkyl spacer length were synthesized in a one-pot two-step synthesis. Each monomer was combined with 2-phenoxyethyl methacrylate as a monofunctional monomer and a polycaprolactone-polydimethylsiloxane-polycaprolactone triblock copolymer was added as toughener. The formation of nanostructures via self-assembly was proven by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The addition of the triblock copolymer resulted in a strong increase in fracture toughness for all mixtures. The nature of the urethane dimethacrylate had a significant impact on fracture toughness and flexural strength and modulus of the cured materials. Most promising systems were also investigated via dynamic fatigue propagation da/dN measurements, confirming that the toughening also works under dynamic load. By carefully selecting the length of the urethane dimethacrylate spacer and the amount of block copolymer, materials with the desired physical properties could be efficiently formulated. Especially the formulation containing the medium alkyl spacer length (DMA2/PEMA) and 5 wt% BCP1 (block copolymer), exhibits excellent mechanical properties and high fracture toughness.