Simplification of Molding Method by Drawing during Thread Molding of Self-reinforced Poly(lactic acid) Bone Fixation Screw

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  • 自己強化ポリ乳酸骨固定スクリューのネジ成形中の延伸による成形手法の簡易化

Abstract

<p>Poly(lactic acid) (PLA) is degraded to nontoxic lactic acid through non-enzymatic hydrolytic degradation. Thus, the foreign body reaction during PLA degradation is mild. PLA has attracted much attention as a material of bioabsorbable bone fixation screw which is used for fracture treatment. The purpose of this study is simplify a molding method of screw made from extrusion drawn PLA. PLA screws were prepared by three different molding methods : molding method A ; casting, molding method B ; extrusion drawing and forging, molding method C ; the draw screw molding. In molding method C, the draw screw molding was proposed for simultaneous with extrusion drawing and thread molding. Mechanical properties of PLA screw were investigated by shear and torsion tests. As a result, PLA screws could be molded by all molding method. The molding time of molding method C was shortened by about 30 minutes per molding compared to molding method B. As results of shear and torsion test, screws of molding method A was more ductile than molding method B and C. On the other hand, shear strengthes of molding method B and C were higher than molding method A. In comparison of molding method B and C, the shear strength of molding method C was slightly higher than molding method B. And, the torsional strength of molding method C was slightly lower than molding method B. Those results might be due to molecular orientation by extrusion drawing and subsequent disorder of orientation during forging.</p>

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