Objective To investigate the biological and biomechanical characteristics of acellular porcine aortic valve with dye mediated photo oxidation so that a new and better bioprosthetic valve materials can be obtained. Methods Thirty porcine aortic valves were divided into three groups with random number table. Acellular valves (n=10) were stabilized by dye mediated photo oxidation in dye mediated photo oxidation group; acellular valves (n=10) were stabilized by glutaraldehyde in glutaraldehyde group; and acellular valves (n=10) were acellularized only in acellular valves group. Thickness, appearance, histology, water content, shrinkage temperature, breaking strength and soluble protein level of acellular porcine aortic in three groups were tested respectively. Results There were light blue, soft, flexible and unshrinking valves in dye mediated photo oxidation group. Compared to valves in glutaraldehyde group, valves in dye mediated photo oxidation group had lighter thickness（0.26±0.09mm vs. 0.38±0.08mm，Plt;0.05）, more water content（86.30%±4.03% vs. 71.10%±3.23%，Plt;0.05）, and lower shrinkage temperature （76.30±0.70℃ vs. 87.70±0.30℃，Plt;0.05）; while these indexes had no statistically significant differences compared to those in acellular valves group. At the same time, compared to valves in acellular valves group, valves in dye mediated photo oxidation group had more breaking strength（17.33±2.65 mPa vs. 9.11±0.95 mPa，Plt;0.05） and lower soluble protein level（0.039%±0.013% vs. 0.107%±0.024%，Plt;0.05）; while these indexes had no statistically significant differences compared to those in glutaraldehyde group. Conclusion Acellular porcine aortic valve stabilized by dye mediated photo oxidation has nice biological and biomechanical characteristics.
In order to understand how the biomechanical properties of rabbit cornea change over time after corneal ablation, 21 healthy adult rabbits were used in this study, with the left eye as experimental side and the right eye as the control side. Firstly, a lamellar knife was used to remove a portion of the anterior corneal surface tissue (30%~50% of the original corneal thickness) from the left eye of each rabbit, as an animal model simulating corneal refractive surgery. Secondly, postoperative experimental rabbits were kept for one, three, or six months until being euthanized. Strip specimens were produced using their corneas in vitro to perform a uniaxial tensile test with an average loading-unloading rate of approximately 0.16 mm/s. Finally, the visco-hyperelastic material constitutive model was used to fit the data. The results showed that there was a significant difference in the viscoelastic parameters of the corneas between the experimental and the control eyes at the first and third postoperative months. There was a difference in tangential modulus between the experimental and the control eyes at strain levels of 0.02 and 0.05 at the third postoperative month. There was no significant difference in biomechanical parameters between the experimental and the control eyes at the sixth postoperative month. These results indicate that compared with the control eyes, the biomechanical properties of the experimental eyes vary over postoperative time. At the third postoperative month, the ratio of corneal tangential modulus between the experimental and the control eyes significantly increased, and then decreased. This work lays a preliminary foundation for understanding the biomechanical properties of the cornea after corneal refractive surgery based on rapid testing data obtained clinically.
Focusing on the poor mechanical strength of porous bioceramics bone scaffold, and taking into account of the good mechanical properties of biodegradable magnesium alloy, we proposed a novel method to fabricate magnesium alloy/bioceramics composite bone scaffold with stereolithography double channels. Firstly, a scaffold structure without mutually connected double channels was designed. Then, an optimized bioceramics scaffold was fabricated according to stereolithography and gel-casing. Molten AZ31 magnesium alloy was perfused into the secondary channel of scaffold by low-pressure casting, and magnesium alloy/bioceramics composite bone scaffold was obtained when magnesium alloy was solidified. The compression test showed that the strength of bioceramics scaffold with only one channel and without magnesium alloy was (9.76±0.64) MPa, while the strength of magnesium alloy/bioceramics composite scaffold with double channels was (17.25±0.88) MPa. It can be concluded that the magnesium alloy/bioceramics composite is obviously able to improve the scaffold strength.
The pediatric cadaver impact experiments were reconstructed using the validated finite element(FE) models of the 3-year-old and 6-year-old children. The effect of parameters, such as hammer size, material parameters and thorax anatomical structure characteristics, on the impact mechanical responses of 3-year-old and 6-year-old pediatric thorax was discussed by designing reasonable finite element simulation experiments. The research results showed that the variation of thorax contact peak force for 3-year-old group was far larger than that of 6-year-old group when the child was impacted by hammers with different size, which meant that 3-year-old child was more sensitive to hammer size. The mechanical properties of thoracic organs had little influence on the thorax injury because of the small difference between 3-year-old and 6-year-old child in this research. During the impact, rib deformation led to different impact location and deformation of internal organs because the 3-year-old and 6-year-old children had different geometrical anatomical structures, such as different size of internal organs. Therefore, the injury of internal organs in the two groups was obviously different. It is of great significance to develop children finite element models with high biofidelity according to its real anatomical structures.
In order to improve the interfacial bonding strength of hydroxyapatite/polyurethane implanted material and dispersion of hydroxyapatite in the polyurethane matrix, we in the present study synthesized nano-hydroxyapatite/polyurethane composites by in situ polymerization. We then characterized and analyzed the fracture morphology, thermal stability, glass transition temperature and mechanical properties. We seeded MG63 cells on composites to evaluate the cytocompatibility of the composites. In situ polymerization could improve the interfacial bonding strength, ameliorate dispersion of hydroxyapatite in the properties of the composites. After adding 20 wt% hydroxyapatite into the polyurethane, the thermal stability was improved and the glass transition temperatures were increased. The tensile strength and maximum elongation were 6.83 MPa and 861.17%, respectively. Compared with those of pure polyurethane the tensile strength and maximum elongation increased by 236.45% and 143.30%, respectively. The composites were helpful for cell adhesion and proliferation in cultivation.
This study aims to investigate the range of motion (ROM) and the stress variation in the intervertebral disc and the vertebral body on adjacent segments and the influence of force transmission mode after the dynamic cervical implant (DCI) surgery. Two types of surgery, DCI implantation and interbody fusion were used to establish the finite element model of the cervical C5, 6 segment degeneration treatment. The ROM and the adjacent discs and vertebral body stresses of two procedures under flexion, extension, lateral bending and axial rotation working conditions were analyzed. The results showed that ROM of the surgical segment in DCI model was well preserved and could restore to the normal ROM distributions (reduction of the amplitude was less than 25%), and the kinetic characteristics of adjacent segments was less affected. In fusion surgery model, however, ROM of the surgical segment was reduced by 86%-91%, while ROM, disc stress and vertebral stress of adjacent segments were increased significantly, and stress of the C5 vertebral body was increased up to 171.21%. Therefore DCI surgery has relatively small influence on cervical ROM and stress. The study provides a theoretical basis for DCI and fusion surgery in clinic.
The effect of parasitic ions on the results of ultraviolet A (UVA) cross-linking in iontophoresis was still not clear. In this work, the porcine sclera was cross-linked by riboflavin lactate Ringer’s solution (group A) and riboflavin normal saline (group B) in vitro, respectively. The concentration of parasitic ions in the solution was calculated. In addition, the average fluorescence intensity, penetration depth and concentration after the introduction of riboflavin and the mechanical properties of cross-linked sclera tissue were measured. The ranges of diffusion coefficient of the two solutions were also calculated, respectively. The results showed that more kinds of parasitic ions were detected in group A compared with group B, while the average fluorescence intensity, penetration depth and concentration of riboflavin and scleral elastic modulus in group B were significantly higher than those in group A when the penetration time was 10 minutes. Besides, the diffusion coefficient of riboflavin in group B was about 1.5 times larger than that in group A. The results suggested that the species of parasitic ions has a great impact on the permeability of riboflavin, and affects the mechanical properties of cross-linked sclera. The above results could provide a reference for improving the efficiency of riboflavin introduction and optimizing the formula of riboflavin in iontophoresis scleral cross-linking.
Biodegradable stents (BDSs) are the milestone in percutaneous coronary intervention(PCI). Biodegradable polymeric stents have received widespread attention due to their good biocompatibility, moderate degradation rate and degradation products without toxicity or side effects. However, due to the defects in mechanical properties of polymer materials, the clinical application of polymeric BDS has been affected. In this paper, the BDS geometric configuration design was analyzed to improve the radial strength, flexibility and reduce the shrinkage rate of biodegradable polymeric stents. And from the aspects of numerical simulation, in vitro experiment and animal experiment, the configuration design and mechanical properties of biodegradable polymeric stents were introduced in detail in order to provide further references for the development of biodegradable polymeric stents.
Coronary artery diseases (CAD) have always been serious threats to human health. The measurement, constitutive modeling, and analysis of mechanical properties of the blood vessel wall can provide a tool for disease diagnosis, stent implantation, and artificial artery design. The vessel wall has both active and passive mechanical properties. The passive mechanical properties are mainly determined by elastic and collagen fibers, and the active mechanical properties are determined by the contraction of vascular smooth muscle cells (VSMC). Substantial studies have shown that, the two-layer model of the vessel wall can feature the mechanical properties well, and the circumferential, axial and radial strain and stress are of great significance in arterial wall mechanics. This study reviewed recent investigations of mechanical properties of the vessel wall. Challenges and opportunities in this area are discussed relevant to the clinical treatment of coronary artery diseases.
Objective To review the research progress of design of bone scaffolds with different single cell structures. Methods The related literature on the study of bone scaffolds with different single cell structures at home and abroad in recent years was extensively reviewed, and the research progress was summarized. ResultsThe single cell structure of bone scaffold can be divided into regular cell structure, irregular cell structure, cell structure designed based on topology optimization theory, and cell structure designed based on triply periodic minimal surface. Different single cell structures have different structural morphology and geometric characteristics, and the selection of single cell structure directly determines the mechanical properties and biological properties of bone scaffold. It is very important to choose a reasonable cell structure for bone scaffold to replace the original bone tissue. Conclusion Bone scaffolds have been widely studied, but there are many kinds of bone scaffolds at present, and the optimization of single cell structure should be considered comprehensively, which is helpful to develop bone scaffolds with excellent performance and provide effective support for bone tissue.