Regional Mechanical Properties of the Sclera / 医用生物力学

Objective To investigate the differences in mechanical properties of the sclera in different regions. Methods The sclera of sus scrofa was divided into 3 regions, namely, anterior, equatorial and posterior area. Local indentation was performed on different areas of the whole sclera. Strip specimens of different regions were circumcised along the equatorial direction, and subjected to uniaxial stretching by INSTRON 5544. Results Within the normal physiological stress range, the stiffness at anterior, equatorial, and posterior area of the sclera measured by local indentation was (0.91±0.21), (0.6±0.16), (0.39±0.13) MPa, respectively. The elastic modulus at anterior, equatorial, and posterior area of the sclera measured by uniaxial stretching was (1-28±0.37), (0.95±0.31), (0.72±0.28) MPa, respectively. Conclusions The local indentation could reflect regional mechanical properties of the sclera. The anterior sclera performed a higher stiffness than the equatorial and posterior areas. The results provide references for further study on the pathogenesis of ocular diseases including myopia.

The preliminary study on biomechanical properties of four synthetic implants for reconstructive surgery of pelvic floor dysfunction / 生物医学工程学杂志

This study aimed to investigate biomechanical properties of synthetic implants for reconstructive surgery of pelvic floor dysfunction. In this dissertation, we chose four synthetic implants, i.e. total pelvic floor repair system (PROLIFT), gynecone TVT obtutator system (TVT-O), intra-vaginal sling placement device (IVS) and acellular dermal matrix (Renov), for tensile test respectively. The biomechanical properties of four synthetic implants were measured and analyzed using a material testing machine (Instron 4302 versatile material testing machine). The biomechanical parameters included ultimate stress strength, modulus of elasticity, maximum load and maximum elongation. The results showed that the maximum load of the four symthetic implants was TVT-O > IVS > PROLIFT > Renov, and the maximum load of TVT-O was significantly higher than PROLIFT and Renov ( < 0.05). The ultimate stress strength was TVT-O > IVS > PROLIFT > Renov, with no significant differences among them ( > 0.05). The maximum elongation of the four implants was TVT-O > PROLIFT > IVS > Renov, and the maximum elongation of TVT-O and PROLIFT were both significantly higher than Renov ( < 0.05). The modulus of elasticity was IVS > Renov > TVT-O > PROLIFT, with no significant differences among them ( > 0.05). Taken together, the present study demonstrates that the modulus of elasticity of IVS was the highest in the four synthetic implants; TVT-O had the highest mechanical strength; The maximum load, ultimate stress strength and maximum elongation of Renov were all the lowest; The mechanical properties of PROLIFT was the most stable, and its modulus of elasticity was the lowest in the four synthetic implants, which had good extensibility and elasticity. Therefore, it is necessary to pay attention to the biomechanical properties of new pelvic reconstructive materials for the clinical pelvic reconstructive surgery.

An experimental study on anisotropic mechanical properties of porcine thoracic aorta / 医用生物力学

Objective To study the anisotropic mechanical properties of the thoracic aorta in porcine. Methods Twenty-one porcine thoracic aortas were collected and categorized into three groups. The aortas were then cut through in their axial directions and expanded into two dimensional planes. Then, by setting the length direction of the planar aortas (i.e., axial directions of the aortas) as 0°, each planar aorta was counterclockwisely cut into 8 samples with orientation of 30°, 45°, 60°, 90°, 120°, 135°, 150° and 180°, respectively. Finally, the uniaxial tensile tests were applied on three groups of samples at the loading rates of 1, 5 and 10 mm/min, respectively, to obtain the elastic modulus and ultimate stress of the aorta in different directions and at different loading rates. Results The stress-strain curves exhibited different viscoelastic behaviors. With the increase of sample orientations, the elastic modulus gradually increased from 30°, reached the maximum value at 90°, and then gradually decreased till 180°. The variation trend of ultimate stress was similar to that of elastic modulus. Moreover, different loading rates showed a significant influence on the results of elastic modulus and ultimate stress, but a weak influence on the anisotropic degree. Conclusions The porcine thoracic aorta is highly anisotropic. This research finding provides parameter references for assignment of material properties in finite element modeling, and is significant for understanding biomechanical properties of the arteries.

Effects of the Amount of Proximal Tibia Resection on the Bone Strength of Prepared Bone Surface: A FEM Study / 대한정형외과학회잡지

PURPOSE: We wanted to evaluate the mechanical strength of proximal tibia as resection distance increased from the joint surface. MATERIALS AND METHODS: We obtained the CT images of twenty knee osteoarthritis patients undergoing total knee arthroplasty. The finite element models were created based on the computed tomography images. The 8-node hexahedron element was made from BIONIX(TM) (CANTIBio. Co, Suwon, Korea), which is automatic mesh generation software program. The finite element model of the proximal tibia was resected at 6 mm, 8 mm, 10 mm, 12 mm, 15 mm and 18 mm from the lateral joint surface. A 1% strain rate was applied to a model by using HyperMesh(TM) software (Altair Engineering. Inc, Seattle, USA). The ultimate stress was calculated from the finite element analysis with using ANSYS 9.0 (ANSYS. Inc, Orlando, USA). RESULTS: The mean ultimate stress was 906.84 MPa, 877.22 MPa, 895.93 Mpa, 852.70 MPa, 742.90 Mpa and 585.51 Mpa at the 6 mm, 8 mm, 10 mm, 12 mm, 15 mm and 18 mm resection levels. As compare to the 6 mm resection level, the bone strengths at 15 mm and 18 mm were decreased with statistical significance (15 mm: p=0.005, 18 mm: p=0.000). CONCLUSION: The ultimate stress was decreased as the resection distance increased from the joint surface. But within a 12 mm resection distance from the lateral condyle articular surface of the tibia, the ultimate stress was not significantly decreased (p>0.05).

Strength of Surgical Wire by Different Wiring Technique / 대한정형외과학회잡지

The role of surgical wire in the bone and joint surgery is very important. To get a maximum effect of the surgical wiring, the orthopaedic surgeon should not only select appropriate wire diameter but also apply adequate wiring technique. When strong fixation is required, wire loops are frequently untrustworthy. These are due to insufficient caliber or inadequate technique of wire thightening and/or twisting. The theoretical background for effective wiring technique and useful diameter in cerclage wiring is poor. Ultimate stress and stress at breaking point of different diameter of the wire was higher in 16G than 18G or 21G. Twist knot was stronger than knot twist. Wire holder was more effect than tensioner(york). Tension tightening with twist knot by wire holder have been found most suitable for internal fixation by surgical wire.