RESUMO
Objective To investigate the phenomenon of amorphous carbon coating delamination during crimping and expansion of the vascular stent, and study how to avoid such phenomenon from both material selection and dimension design of the stent. Methods Amorphous carbon coatings were deposited onto a bare metal stent by chemical vapor deposition method, and then to simulate the crimping and expansion process of the stent. Coating delamination at different regions of the stent was observed by scanning with electron microscope, and the force mechanism and influencing factors related with amorphous carbon coating delamination during stent crimping and expansion were analyzed by finite element method. Results The finite element results could perfectly agree with the experimental results. The thickness of amorphous carbon coatings determined the complexity, as well as the formation pattern of coating delamination at different regions of the stent. Larger elastic modulus of amorphous carbon coatings could cause the formation of coating delamination much easier to occur. Besides, the stent modulus would also have some impact with different influencing patterns at different regions on coating delamination. Conclusions In order to avoid coating delamination, the thickness of amorphous carbon coatings should be carefully designed, and the elastic modulus of both amorphous carbon coatings and stents should be rationally selected.
RESUMO
Objective To design mechanical structure of exoskeleton which simulates physiological structure and kinematic characteristics of lower limbs according to kinematics analysis of human body, and investigate biomechanical properties of exoskeleton under two different phases of human gait period, so as to provide references for such exoskeleton design and optimization. Methods Based on clinical gait analysis of lower limbs, the mechanical structure of exoskeleton was first established by using 3D modeling software. Then the physical model was assembled, meshed and materialized by 3D modeling software, and surface to surface contact relationship between each component was also constructed to simulate and analyze the stress distributions of exoskeleton. Results Under the load of 1 kN, the maximum stress of double stance (calculating condition I) was 91.45 MPa and the maximum stress of vertical tibia (calculating condition II) was 154.55 MPa, occurring at the back support and hip, respectively, and such results were in accordance with the analysis results of force transmission mechanism got before design. Conclusions The stress distributions of exoskeleton under different calculating conditions were obviously different. Some uncertain factors such as some shock caused during the walking period, which have not been taken into account in the calculation, should be considered for the design and optimization of exoskeleton and multiplied by a certain safety coefficient.