RESEARCH FOR HA/ POLY-L-LACTIDE COMPOSITE AS BIORESORBABLE HIGH-STRENGTH OSTEOSYNTHETIC IMPLANTS

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The biodegradation behavior of the ultra-high-strength hydroxyapatite/poly(1-lactide) (HA/PLLA) composite rods for fracture repair was investigated both in subcutis and medullary cavity in rabbits. The bending strength of the composites implanted in the subcutis was maintained at more than 200 MPa at 25 weeks and at 150 MPa at 52 weeks. The molecular weight dropped to 45% of the initial values at S weeks and to approximately 10% at 52 weeks. SEM demonstrated that HA particles disappeared increasingly from the rod surfaces over time and that the spaces left by these HA particles formed many pores in the composite surfaces at 52 weeks. Histologically, a fibrous tissue layer was formed around the composite rod from 4 weeks in the subcutis and in the diaphyseal area of the medullary canal. In the medullary cavity, the affinity indices of all composite rods were significantly higher than those of unfilled PLLA rods during follow-up, (p < 0.01 ; two-way ANOVA). The maximum affinity index (4 1%) was attained at 4 weeks in c-HA40 rods. The only significant difference in affinity indices among the composites was that calcined HA40 had a higher affinity index than unsintered HA40 (p < 0.05 at 4 weeks). During the experimental period, there were no inflammatory cells such as mono- or multi-nuclear phagocytes. Although further long-term studies for degradation are needed, the composites have promising mechanical strength and no adverse tissue reaction for use as fracture-fixation devices during the experimental periods.