Abstract
Usage of the conventional bioabsorbable plastic bone fixation devices have been limited, because the mechanical characteristics of them are lower. In this study, poly-L-lactide(PLA) that is one of the bioabsorbable plastic was molded into the screw shape, and the mechanical characteristics of the PLA screw was investigated. A PLA bar was prepared by extruding a rectangular PLA block, and molding into the shape of the screw by forging. The molding conditions were varied to evaluate the formability of PLA. The mechanical properties, such as pulled out strength, shearing strength and the twist strength were measured. Decrease in shear strength and increase in twist strength for the screw extruded using lubricants were observed, which is due to lower extrusion ratio. Same tendency is observed for the screws molded at higher temperature. These results suggested the lubrication and higher molding temperature have similar effects. Decrease in shear strength at molding temperature of 120 ℃ was obtained, which was caused by crystallization.
