Types I and III collagen in the tissue capsules of titanium and stainless-steel implants

Collagen plays an important role in wound healing and as such is present in connective tissue capsules around implanted materials. The proportion of type I collagen to type III collagen is lower during wound healing than that found in normal dermis, but the amount of type I collagen gradually increases and type III decreases as healing continues. The intent of this research was to investigate a possible correlation between implant metals and type I and type III collagen formation in the ensuing soft-tissue capsules. Smooth implants of grade 4 commercially pure titanium and 316L stainless steel were placed via injection needle into the subcutaneous tissue of 12 rats for 6 weeks. The soft-tissue capsule that formed around each implant was evaluated histologically and by immunofluorescence. Although the two metal implant types differ in many respects, they were chosen for their differences in surface conductivity. Titanium oxide is semiconducting, whereas the oxide of stainless steel is conducting. Impedance spectroscopy was used for conductivity analysis of the surface. No qualitative differences were found in amount of type I or type III collagen in the capsules of the two metals. However, the capsules around titanium stained for type I collagen were thicker than capsules around stainless steel. In addition, type I collagen showed evidence of a greater association with densely packed, highly orientated collagen fibers.