Localization of bone morphogenetic protein-induced bone and cartilage formation on a new carrier: fibrous collagen membrane.

A fibrous collagen membrane (FCM) made of crosslinked reconstituted collagen fibers was applied as a carrier of BMP. The effectiveness of FCM as a BMP carrier was compared with conventionally used insoluble bone matrix (IBM). Partially purified BMP was obtained from a guanidine HCl extract of bovine bone after a three-step chromatographic procedure. The BMP fraction was combined with FCM or IBM and implanted subcutaneously in the back of rats. Bone and cartilage formation were determined by radiographic, histologic, and biochemical analyses after removal at 1, 2, 3 and 4 weeks. After 2 weeks, bone and cartilage formation were evident histologically in IBM-BMP and FCM-BMP. In IBM-BMP, cartilage was formed in the area of presumptive bone. On the other hand, in FCM-BMP, cartilage formation occurred in the space between the fibers of fiber-bundles, while on the surface of the fibers bone formation started independently. Biochemically, the most noteworthy difference between FCM-BMP and IBM-BMP was the marked increase in type II collagen content in FCM-BMP, which contrasted with its decrease in IBM-BMP at 3 weeks. This study demonstrated that FCM definitely functioned as a BMP carrier that led to bone and cartilage formation at distinct sites. Therefore, we conclude that BMP could induce differentiation of immature cells preferentially into either osteogenic cells or chondrocytes depending upon the nature of the carrier which provides the environment for cell differentiation.