Soft Tissue Response to PHA and PLA in Hamsters

Two products were produced for a study on potential biodegradable materials in maxillofacial fixation. Polyhydroxyalkanoates (PHA) was produced from palm oil-utilizing bacteria. It is a natural product completely biodegradable to CO2 and water. Poly-L-Lactic Acid (PLA) was produced by polymerization of lactic acid and modified by crosslinking with an amino resin to improve mechanical strength. Objective: To determine the biocompatibility of PHA and PLA in a hamster model. Methods: Thin discs of each material were placed subcutaneously in antero-dorsal (PLA) and postero-dorsal (PHA) regions of the forelegs in twenty adult hamsters. The discs were allowed to heal undistrubed following primary closure of the incision. One animal per week was sacrificed from week 2 to week 21. The discs were carefully dissected away from the excised specimens and the soft tissues processed into 5µ sections for staining with H&E and PAS reagents. Results: Both materials exhibited fibroblastic response in the soft tissue around the implanted materials. However, there was a high extrusion rate of PLA resulting in superficial infection and early loss of the specimen. PHA was well accepted with no adverse reaction. Interestingly, in the case of PHA, small areas of osteoid formation were found adjacent to the fibroblastic lining. Conclusions: PHA demonstrated higher compatibility compared to PLA in the subcutaneous location in a hamster model. While the osteoid formation may represent dystrophic ossifying reaction of subcutaneous tissues to by-products released from the PHA, its nature remained conjectural and it warrants further investigations. This research was supported by a grant from Malaysia's Intensified Research in Priority Areas IRPA Vote 06-02-03-0169