MINERALIZATION OF AN AXIALLY ALIGNED COLLAGENOUS MATRIX - A MORPHOLOGICAL-STUDY

Bone can be described as a highly ordered composite of type I collagen integrated with an inorganic mineral phase. In vitro models of bone m ineralization using collagenous substrates have been reported in the l iterature. This study reports an in vitro system of mineralized recons tituted collagen fibers, with aligned fibrillar substructure. The coll agen fibers were mineralized in a double diffusion chamber saturated w ith respect to calcium and phosphate. The morphology and ultrastructur e of the mineral precipitate were evaluated as a function of the pH of the incubating media. Brushite crystal was observed at acidic pH. Lar ge rectangular crystals formed at pH 5.15 and appear to associate with the collagen fibers. At neutral and alkaline pHs, hydroxyapatite crys tals were observed in association with the collagen fibers. Spherical aggregates of hydroxyapatite crystals were seen at neutral and alkalin e pHs, but these structures were reduced in size when formed on collag en at alkaline pH. On close examination these spherical structures wer e found to be hollow when viewed in cross section. The crystals precip itated within the interior of the collagen fiber at neutral and alkali ne pHs were comparable in both size and shape to crystals observed in mineralized turkey tendon and skeletal tissues. These preliminary obse rvations indicate that with further refinement the reconstituted colla gen fibers may prove useful in model systems for the study of collagen mediated mineralization in vitro. In addition, mineralization of coll agenous matrices may lead to the development of biomaterials for bone repair and replacement.