ABSTRACT
Objective To develop an in vitro vascular tensile stress loading device and study the distributions of tensile stress and tensile strain on the elastic basement membrane (silicone sheet). Method The in vitro vascular tensile stress loading device which simulated the human hemodynamic environment was developed based on the elastic basement membrane deformation loading technology. The images of grid points before and after the stretch of the silicon sheet were recorded by camera and transformed into the digital images. The characteristics for the location of the grid points were calculated by using Matlab software, so as to obtain the strain distribution on the silicon sheet. Experiments were conducted on the silicon sheet by using the universal material testing machine, so as to calculate the mechanical parameters of the silicon sheet. The finite element model was established according to the mechanical parameters, and the distribution of tensile stress and tensile strain on the silicon sheet was simulated and calculated. The experimental results and simulative results were then compared. Results The finite element results were basically in accordance with the experimental results. The maximum value of tensile stress and tensile strain appeared on the loading point, while the stress and strain in intermediate area were comparatively homogeneous. 60% of the intermediate area in the silicone sheet could be regarded as homogeneous strain fields Conclusions The research finding can provide experimental techniques for the dynamic culture of vascular endothelial cells and the research on cell mechanics in the future.
ABSTRACT
Objective To assess the biomechanical stability and vertebra strain distribution of asymmetrical posterior internal fixation for minimally invasive transforaminal lumbar interbody fusion ( MI-TLIF) . Methods Range of motion ( ROM) and strain distribution testing were performed in 8 fresh-frozen calf lumbar spine motion segments in flexion/extension, lateral bending, and axial rotation using 5. 0 Nm torques at the L4-5 motion segment. The sequential test configurations included intact motion segment, TLIF with unilateral pedicle screw ( UPS) , TLIF with UPS plus transfacet pedicle screws ( UPS+TFPS) , and TLIF with bilateral pedicle screw ( BPS) . The ROM was deter-mined to assess the construct stability. Strain distribution was recorded along with flexion and lateral bending configurations. Results In flexion/extension, lateral bending, and axial rotation, there was no significant difference in the ROM between BPS and UPS+TFPS fixation after TLIF. After TLIF, the UPS construct provided less segment stability than BPS and UPS+TFPS fixation in flexion, lateral bending. Strain distribution under UPS+TFPS fixation was respectively 21. 8% and 24. 2% higher than that under BPS fixation along with flexion and lateral bending. Conclusion UPS+TFPS fixation provides stability comparable to that of MI-TLIF with bilateral PS, with better load share with the vertebrae body.
ABSTRACT
Objective To compare the differences in biomechanical properties of embalmed and PMMA femurs under axial loads, so as to provide a more reliable and unified femoral model for replacement. Methods Ten embalmed femurs and ten PMMA femurs were selected, and each femur was instrumented with 49 strain gauges totally on the medial and lateral side. The axial load was applied dynamically up to a maximum of 1.2 kN, and the strain of each strain gauge and load displacement curve were recorded. Results The strain distributions on two types of femur were similar, and the load displacement presented a linear relationship, but the vertical displacements under different loads were significantly different (P<0.05). The axial stiffness value of PMMA femur and embalmed femur were (259.84±24.63) and (600.40±78.56) N/mm, respectively, showing significant difference (P<0.01). The strain concentration parts at the proximal part of two femurs were the same, but the average strain value of the PMMA femur was significantly different from that of the embalmed femur (strain gauge No. 1~5: PMMA femur (-3 420.63±373.31) με, embalmed femur (-1 289.42±417.89) με; strain gauge No. 26~27: PMMA femur (1 748.67±193.98) με, embalmed femur (673.42±104.49) με; strain gauge No. 7~10: PMMA femur (-4 028.25±267.27) με, embalmed femurs (-1 139.01±288.83) με; strain gauge No. 30~36: PMMA femur (1 599.02±194.68) με, embalmed femurs (590.52±153.18) με, P<0.01). The strain concentration parts at the distal part of the two femurs were different. The medial and lateral parts of strain transformation between positive and negative of PMMA femurs were similar to embalmed femurs. The strain-load curves of strain gauge No. 2, 26, 6, 29, 8 and 33 indicated a linear relationship, but the strain value of the two femurs had significant differences (P<0.05). Conclusions The PMMA femur can replace the embalmed femur to a certain degree in biomechanical experiments on the upper part of femur. Due to the difficulty of obtaining fresh femurs, the PMMA femurs provide a more reliable and unified femoral model for replacement.