Hydroxyapatite (HAp) which is a main component of natural bone has the osteoinduction properties. Composites of HAp and Poly (L-lactic acid) (PLLA) have been expected for artificially-grafting materials. It is required that PLLA in the composites decomposes and is interchanged by osteoblast in vivo. Because of the weak interaction between HAp and PLLA, PLLA effluents instantly in vivo, and the mechanical strength degrades accordingly before being interchanged by osteoblast. In this study, polymeric diphenylmethane isocyanate (PMDI) was introduced as a linker between PLLA and HAp to improve the interfacial adhesive properties of HAp and PLLA in PLLA/HAp composites. The introduction effect of PMDI on the mechanical properties and biodegradability was investigated. L-lactic acid (LLA) oligomer (Mn : 3,800-4,020 g mol-1) was synthesized by ring-opening polymerization of L-lactide. The composites were fabricated by introducing PMDI and LLA oligomer into porous HAp ceramics (p-HAp: porosity is about 40%), followed by heating. The concentration of PMDI in THF solution was changed to 0.1 - 0.8 g mL-1 to prepare composites. Urethane bonds in obtained composites were confirmed by FT-IR measurements. The introduction ratios of PMDI-PLLA in the composites calculated from the residual weight at 500°C of the TG measurements were 16-19 wt %. The bending strength and elastic modulus of PMDI-PLLA/HAp composites were measured by three-point bending test. Compared to p-HAp, the bending strength of PMDI-PLLA/HAp composites was improved. The bending strengths of the composite increased with increasing concentration of the PMDI solution and reached a maximum value of 73.5 MPa, when the concentration of of PMDI solution was 0.6 g mL -1. The elastic modulus of the composite was 10.3 GPa. The biodegradability test of composites was conducted for 21 days. While PLLA flowed out within 3 days from the conventional PLLA/HAp composites, the PMDI-PLLA/HAp composite maintained PMDI-PLLA for 21 days.

Fabrication of PLLA/HAp composites with urethane bond (IV): Effect of introduction amount of urethane bonds

256th National Meeting (2018)

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