Abstract
Metallic bone fixation devices have been used for treatment of bone fracture. After complete recovery, it is necessary to remove the fixation device. This re-operation is a burden for the patient economically, physically and mentally. Therefore, the adoption of bioabsorbable materials, which is resolved and absorbed in the body, to the bone fixation devices has been studied. Applications of conventional bioabsorbable bone fixations are limited to low loaded region, because of their lower mechanical characteristics. In this study, poly-L-lactide (PLA), which is known as bioabsorbable plastics, were used. Weight average molecular weights of PLA are 95000, melting point is 169℃ and glass-transition temperature is 73℃. PLA screws were prepared by extruding and forging. The screw is subjected to torque loading when it is inserted in the body. Then, it is subjected to shear loading after the operation. Therefore, the PLA were strengthened by extruding at extrusion ratio of 2, 4 and 8 to evaluate effects of extrusion ratio on the mechanical properties, such as torsional strength and shear strength. As a result, there were not the significant differences in shear strength and torsional strength between extension ratio 2, 4 and 8. This result suggested that orientation was considered to be saturated at extrusion ratio of 2.
