Journal of the Mechanical Behavior of Biomedical Materials最新文献

With the increasing prevalence of obesity worldwide, bariatric surgery is becoming increasingly common. However, the mechanic of the gastric wall related to bariatric surgery complications remains to be investigated. This study aims to understand mechanical behaviour of stomach by developing advanced material laws for gastric tissue incorporating microstructure. A multi-scale characterisation of the porcine stomach wall was performed in the fundus and corpus anatomical regions and in circumferential and longitudinal orientations The protocol included uniaxial tensile testing until damage, survival analysis to provide damage probability, comparison of phenomenological (Fung and Ogden order 1, 2 and 3) and structural (Holzapfel fibre-reinforced) computational models fitted to the experimental data, and quantitative analysis of elastin and collagen fibre structure from histological slides. All constitutive models fitted the experimental data well (r² > 0.988 and RSME<3.8 kPa). Longitudinal and circumferential elastic modulus in quasi linear phase were respectively 1.75 ± 1.2 MPa, 0.76 ± 0.35 MPa for fundus, and 2.30 ± 0.66 MPa, 1.36 ± 0.89 MPa for corpus, highlighting significant differences between orientations in fundus and corpus, with an overall softer fundus in the circumferential direction. Microstructure analysis illustrated collagen and elastin fibre orientation, dispersion and density. As microstructure appears to play an important role in stomach biomechanics, model incorporating fibre structure such as Holzapfel fibre-reinforced model, seem best suited to describe the material behaviour of the stomach wall. Future research should complement these findings with an expanded sample set in human models.

Zirconia and resin are the most commonly utilized materials in dental restorations. However, zirconia presents significant wear on opposing teeth, whereas resin materials have low wear resistance and mechanical performances. A zirconia-resin interpenetrating phase composite (IPC) dental restoration was designed and fabricated using 3D printing and vacuum infiltration processes, incorporating zirconia scaffolds with triply periodic minimal surfaces (TPMS) structures. The mechanical and tribological performances of the IPCs were investigated through compressive and tribological experiments and finite element analysis, elucidating the influence of zirconia volumetric fraction. Results showed that IPCs exhibit excellent mechanical and tribological compatibilities, which can reduce the damage and wear of the antagonistic teeth. This designing and manufacturing strategy enables the IPC restorations with promising applications in dentistry.

Purpose

To study the potential of viscoelastic parameters such as liver stiffness, loss tangent (marker of viscous properties) and viscoelastic dispersion to detect hepatic inflammation by in-vivo and ex-vivo MR elastography (MRE) at low and high vibration frequencies.

Methods

15 patients scheduled for liver tumor resection surgery were prospectively enrolled in this IRB-approved study and underwent multifrequency in-vivo MRE (30–60Hz) at 1.5-T prior to surgery. Immediately after liver resection, tumor-free tissue specimens were examined with ex-vivo MRE (0.8–2.8 kHz) at 0.5-T and histopathologic analysis including NAFLD activity score (NAS) and inflammation score (I-score) as sum of histological sub-features of inflammation.

Results

In-vivo, in regions where tissue samples were obtained, the loss tangent correlated with the I-score (R = 0.728; p = 0.002) and c-dispersion (stiffness dispersion over frequency) correlated with lobular inflammation (R = −0.559; p = 0.030). In a subgroup of patients without prior chemotherapy, c-dispersion correlated with I-score also in the whole liver (R = −0.682; p = 0.043). ROC analysis of the loss tangent for predicting the I-score showed a high AUC for I ≥ 1 (0.944; p = 0.021), I ≥ 2 (0.804; p = 0.049) and I ≥ 3 (0.944; p = 0.021). Ex-vivo MRE was not sensitive to inflammation, whereas strong correlations were observed between fibrosis and stiffness (R = 0.589; p = 0.021), penetration rate (R = 0.589; p = 0.021), loss tangent (R = −0.629; p = 0.012), and viscoelastic model parameters (spring-pot powerlaw exponent, R = −0.528; p = 0.043; spring-pot shear modulus, R = 0.589; p = 0.021).

Conclusion

Our results suggest that c-dispersion of the liver is sensitive to inflammation when measured in-vivo in the low dynamic range (30–60Hz), while at higher frequencies (0.8–2.8 kHz) viscoelastic parameters are dominated by fibrosis.

Young's modulus of elasticity (or stiffness, E) is an important material property for many applications of polymers and polymer-matrix composites. The common methods of measuring E are by measuring the velocity of ultrasonic pulses through the material or by resistance to flexure, but it is difficult for ultrasound to penetrate polymers that contain filler particles, and flexural measurements require large specimens that may not mimic the clinical case. Thus, it may be difficult to determine E using conventional techniques. It would be useful to have a relatively rapid technique that could be applied to small specimens, highly filled materials, and even specimens cured in situ. We suggest using a microhardness indentation technique that was originally developed for ceramic materials. We tested two unfilled rigid polymers, four resin composites, and four unfilled polymers with lesser hardness for this study. The study found that greater Vickers hardness loads yielded more consistent results than lesser loads. We developed a modified equation for E based on Knoop microhardness indentations. We concluded that laboratories may use a microhardness indenter to estimate the elastic moduli of polymers and resin composites. The results support our initial hypotheses that the slope of the equation relating the indentation parameter and the hardness/elastic modulus ratio was different for polymers and resin composites than for ceramics; however, the intercept is the same irrespective of the material tested.

Co-20Cr-15W-10Ni (mass%, CCWN) alloy is extensively used as a platform material for balloon-expandable stents. In this study, the mechanical properties of CCWN alloy are improved following the addition of Fe, and the effects of Fe addition on the mechanical and corrosive properties of the alloy are investigated. As-cast specimens were fabricated by adding pure Fe to a commercially available CCWN alloy (base alloy) such that the resulting alloys contained 4, 6, and 8 mass% Fe. The as-cast specimens were subjected to homogenization heat treatment at 1523 K for 7.2 ks and then hot-forged at 1473 K (as-forged specimens). The as-forged specimens were cold-rolled at a reduction rate of 30% and heat-treated at 1473 K for 300 s (recrystallized specimens). The matrix of the recrystallized base- and Fe-containing alloys consisted of a single γ (face-centered cubic)-phase. The Fe-added alloys revealed precipitates composed of the η-phase (M₆X-M₁₂X-type phase, M: metallic element, X: C and/or N). The average grain size of the recrystallized base and Fe-added alloy specimens was approximately 34 μm and the amount of added Fe had no significant effect on the static recrystallization behavior of the resulting alloys. Alloys containing 6 mass% or more Fe showed improvements in strength and ductility compared with the base alloy. When the Fe-added alloys were compared, their strength decreased whereas their ductility increased when the added Fe increased. Because Fe acts as a γ-phase-stabilizing element for Co, Fe addition increases the stacking fault energy of the base alloy, resulting in the formation of the ε (hexagonal close-packed)-phase owing to the suppression of strain-induced martensitic transformation (SIMT), and improvements in ductility. No deterioration in corrosion resistance was observed following the addition of up to 8 mass% Fe to the base alloy. Based on these results, the addition of Fe to CCWN alloy may be considered an effective method to improve its mechanical properties, especially ductility, without impairing its corrosion resistance. The results of this study will be useful for the future development of Ni-free Co-Cr alloys for next-generation, small-diameter stents.

Polydimethylsiloxane (PDMS) is an elastomer that has received primary attention from researchers due to its excellent physical, chemical, and thermal properties, together with biocompatibility and high flexibility properties. Another material that has been receiving attention is beeswax because it is a natural raw material, extremely ductile, and biodegradable, with peculiar hydrophobic properties. These materials are applied in hydrophobic coatings, clear films for foods, and films with controllable transparency. However, there is no study with a wide range of mechanical, optical, and wettability tests, and with various proportions of beeswax reported to date. Thus, we report an experimental study of these properties of pure PDMS with the addition of beeswax and manufactured in a multifunctional vacuum chamber. In this study, we report in a tensile test a 37% increase in deformation of a sample containing 1% beeswax (BW1%) when compared to pure PDMS (BW0%). The Shore A hardness test revealed a 27% increase in the BW8% sample compared to BW0%. In the optical test, the samples were subjected to a temperature of 80 °C and the BW1% sample increased 30% in transmittance when compared to room temperature making it as transparent as BW0% in the visible region. The thermogravimetric analysis showed thermal stability of the BW8% composite up to a temperature of 200 °C. The dynamic mechanical analysis test revealed a 100% increase in the storage modulus of the BW8% composite. Finally, in the wettability test, the composite BW8% presented a contact angle with water of 145°. As a result of this wide range of tests, it is possible to increase the hydrophobic properties of PDMS with beeswax and the composite has great potential for application in smart devices, food and medicines packaging films, and films with controllable transparency, water-repellent surfaces, and anti-corrosive coatings.

Background and aim

The present investigation explored the potential for recycling residual blocks obtained from the machining processes under hydrothermal conditions. Furthermore, the study examined the recycled samples’ various physical and mechanical properties to assess their viability for further use.

Materials and methods

In this in vitro study, Aman Girbach blocks were collected, half of which underwent a hydrothermal process, while the other half did not. The blocks were then subjected to ball milling. Uniaxial and isostatic pressed blocks were prepared, and 10 samples were obtained from each type of recycled block. These samples were compared to a commercial material, and four groups were formed based on the powder type and pressing method used. The quality control analysis of the recycled samples included assessing particle size distribution, identifying crystalline phases, analyzing color differences, examining microstructure, and evaluating mechanical properties. Statistical tests such as normal distribution calculations (k-s test), one-way ANOVA, Brown-Forsythe, Tukey HSD, and Games-Howell tests were used to compare the four groups and perform pairwise comparisons.

Results

The flexural strength and density of the control commercial group were significantly higher than the other experimental groups (P = 0.000). Linear shrinkage of recycled isostatic pressed experimental bodies was significantly lower than that of others (P = 0.000). Qualitative evaluation of microstructure and crystalline phase by FESEM and XRD showed no significant difference in grain size and crystalline phase between different groups.

Conclusion

The hydrothermal process is a promising way to recycle zirconia ceramic with lower energy consumption. Recycled waste demonstrates potential as a cost-effective and viable option for ceramic prostheses in situations with low to medium stress levels.

Ballistic gelatin has been extensively used in ballistics research for decades, but calibration standards were established on limited datasets, and only few studies have attempted to recreate these experiments with biological tissues. Recent studies have demonstrated better biofidelity with 20% ordnance ballistic gelatin, but researchers have discredited the use of synthetic gelatin claiming different behavior than ordnance gelatin. To investigate the use of synthetic clear gelatin as an acceptable surrogate of biological tissue, depth of penetration was compared between low-velocity impacts of various projectiles into porcine tissue (n = 192), post-mortem human subjects (n = 29), and Clear Ballistics synthetic gelatin (n = 39). The predicted depth of penetration of the 0.177" steel BB (38.1 mm) was consistent with the manufacturer's calibration standard (31.75–44.45 mm) and within calibration bounds of recently proposed empirical equations. Compared to impacts in biological tissue, synthetic gelatin demonstrated the least variability in depth of penetration (R² = 0.96). Using ANCOVA, velocity was a significant covariate (p < 0.001), and there were no significant differences in normalized depth of penetration over density between porcine tissue, post-mortem human subjects, and 20% synthetic gelatin (p = 0.22). Ultimately, this study confirmed the use of 20% synthetic gelatin as an acceptable tissue simulant using standard calibration methods for use in future ballistic studies.

The development of biomaterials such as synthetic scaffolds for peripheral nerve regeneration requires a precise knowledge of the mechanical properties of the nerve in physiological-like conditions. Mechanical properties (Young’s modulus, maximum stress and strain at break) for peripheral nerves are scarce and large discrepancies are observed in between reports. This is due in part to the absence of a robust testing device for nerves. To overcome this limitation, a custom-made tensile device (CMTD) has been built. To evaluate its reproducibility and accuracy, the imposed speed and distance over measured speed and distance was performed, followed by a validation using poly(dimethylsiloxane) (PDMS), a commercial polymer with established mechanical properties. Finally, the mechanical characterization of rodents (mice and rats) sciatic nerves using the CMTD was performed. Mouse and rat sciatic nerves Young’s modulus were 4.57 ± 2.04 and 19.2 ± 0.86 MPa respectively. Maximum stress was 1.26 ± 0.56 MPa for mice and 3.81 ± 1.84 MPa for rats. Strain at break was 53 ± 17% for mice and 32 ± 12% for rats. The number of axons per sciatic nerve was found to be twice higher for rats. Statistical analysis of the measured mechanical properties revealed no sex-related trends, for both mice and rats (except for mouse maximum stress with $p=0.03$). Histological evaluation of rat sciatic nerve corroborated these findings. By developing a robust CMTD to establish the key mechanical properties (Young’s modulus, maximum stress and strain at break) values for rodents sciatic nerves, our work represent an essential step toward the development of better synthetic scaffolds for peripheral nerve regeneration.

Purpose

Acute ischemic stroke is a leading cause of death and morbidity worldwide. Despite advances in medical technology, nearly 30% of strokes result in incomplete vessel recanalization. Recent studies have demonstrated that clot composition correlates with success rates of mechanical thrombectomy procedures. To understand clot behavior during thrombectomy, which exerts considerable strains on thrombi, in vitro studies must characterize the rate-dependent high-strain behavior of embolus analogs (EAs) with different formation conditions, which can be used to fit models of hyper-viscoelasticity.

Methods

In this study, the effect of collagen infiltration as a carotid-induced collagen-rich thrombosis surrogate is considered as a contributor to embolus analog high-strain stiffness, when compared to 40% hematocrit EAs.

Results

EA high-strain stiffnesses, characterized on a uniaxial load frame, increase by an order of magnitude for collagenous clot analogs. Chandler loop analogs show high-strain stiffnesses and clot compositions commensurate with previous reports of stroke patient clots, and collagenous clots show significant increase in stiffness when compared to stroke patient clots. Finally, hyper-viscoelastic curve fitting demonstrates the asymmetry between tension and compression. Nonlinear, rate-dependent models that consider clot-stiffening behavior match the high strain stiffness of clots fairly well. Furthermore, we demonstrate that the stability of the elastic energy needs to be considered to obtain optimal curve fits for high-strain, rate dependent data.

Conclusion

This study provides a framework for the development of dynamically formed EAs that mimic the mechanical and structural properties of in vivo clots and provides parameters for numerical simulation of clot behavior with hyper-viscoelastic models.