Abstract
Much attention has recently been given to poly(lactic acid) (PLA) because it is degraded to nontoxic lactic acid through non-enzymatic hydrolytic degradation in the body. As one of the methods to improve mechanical properties of PLA, orientation of molecular chains by drawing has been investigated. In this study, PLA screws were made of drawn PLA rod to obtain high mechanical properties. Immersion in phosphate buffered solution was conducted to forecast mechanical properties of screw which inserted in the body. Weight measurement during the immersion suggested that degradation ratio of drawn screw is slower than undrawn screw. Shear test on screw after immersion showed that stiffness and strength of screw decrease by the immersion. Shear strength of screw increased by drawing and the maximum strength of 110 MPa was achieved at extrusion ratio 2. Shear strengths after immersion were 80 MPa at extrusion ratio 2 or more, while was 60 MPa at extrusion ratio 1. The result showed that the increase in shear strength by drawing is maintained after immersion.
