Tissue response to hydroxylapatite in induced diabetic and nondiabetic rats: histologic evaluation

This study evaluated the tissue response to the subcutaneous implantation of nonporous hydroxylapatite (HA) in 24 induced-diabetic (ID) and 24 nondiabetic (ND) rats. One cubic centimeter of HA was implanted subcutaneously in each rat's chest. Subgroups of 6 rats from the ID and ND groups were killed at 3, 6, 12, and 24 weeks postimplantation. The implants were removed with the surrounding soft tissues and processed for histologic evaluation. This revealed that soft tissue inflammation was mild at each time interval. There was a decreased response at 6 months in ND rats and a persistent inflammatory reaction in ID rats. Collagen maturity and fibroplasia increased within ND rats, whereas the ID rats showed a marked delay in collagen maturity and density. No osteogenesis was observed in any specimen. Dystrophic calcification was observed at the HA-tissue interface in 37% of ND and 59% of ID specimens. It was concluded that HA elicited a greater inflammatory response in ID than in ND rats when implated subcutaneously.