Resorbable structured porous materials in the healing process of hard tissue defects

The long-term goal of this research is to assist the resurfacing of damaged articular cartilage. Coralline hydroxyapatite (HA) was coated with a thin film of polylactide (PLa), maintaining pore structural characteristics. Cylindrical plugs (3 x 7 mm) implanted in non-load-bearing femoral and tibial diaphyses of the rabbit indicated substantial bone ingrowth at 3 weeks, with no significant difference between coated and uncoated HA in the amount and distribution of new bone. PLa-epsilon caprolactone polymeric negative replicas of coral Goniopora (G), inserted into the rabbit femur for 4 wks, showed newly formed bone grown deeply into the pores. Tight attachment of new bone to the implant and minimal inflammatory response suggested an osteocompatible reaction. In order to maintain the desirable pore structure of G while introducing controllable degradation rate and mechanical properties, a novel technique was employed to replicate G with PLa and its co-polymers. An intermediary negative replica of G was prepared with aspirin. A co-polymer positive replica of G was then prepared by solution or melt infusion into the negative replica; the aspirin was removed by methanol. A macro- (300-500 microns) and microporous (5-15 microns) structure was prepared by freeze-drying. This replica received appreciable bone ingrowth when implanted in the rabbit tibia for 3 wks. Our results demonstrate the feasibility of creating devices with interconnected pore structures and controlled porosity, elasticity, and mechanical strength sufficient for articular cartilage application, osteocompatibility, and controlled degradation rate.