Biomimetic Mineralization of an Aligned, Self-Assembled Collagenous Matrix.
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Biomimetic Mineralization of an Aligned, Self-Assembled Collagenous Matrix.
DAVID CHRISTIANSEN AND FREDERICK H. SILVER Department of Pathology, UMDNJ - Robert Wood Johnson Medical School, Piscataway, NJ 08854
Abstract: An in-vitro method of mineralizing an aligned, self-assembled collagenous matrix is presented. Reconstituted collagen fibers were mineralized by exposure to saturated solutions of calcium and phosphate of varying pH in a double diffusion chamber for seven days at room temperature. Microscopic investigation of the mineral precipitate within the fibers indicate the formation of hydroxyapatite crystals with features comparable to mineral observed in bone and avian tendon. Mechanical test results indicate that tensile strength and tangent modulus increase after mineralization in comparison to unmineralized control fibers. These results suggest that mineralization of collagen fiber in-vitro may parallel some of the events seen in mineralization of bone and turkey tendon. In addition, mineralized collagen fibers may be useful in the design of composites for the replacement or augmentation of hard tissue. Introduction: A variety of organisms have developed structural materials based on the controlled nucleation and growth of inorganic crystals in association with an organic matrix [7]. In mammalian systems the structural bone material produced by the osteoblast can be characterized as a fiber reinforced composite consisting of a dense mineral phase intimately associated with a highly ordered collagenous matrix. Osteoblasts derived from undifferentiated primitive mesenchymal cells or differentiated chondrocytes [9], produce a collagenous matrix termed osteoid, and indirectly control mineralization through the release of matrix vesicles containing apatitic mineral. The vectorial sequence of mammalian mineralization has been studied in avian tendon via transmission electron microscopy [1]. The initial stage involves the localization of apatite within matrix vesicles, and the subsequent spread of mineral from the matrix vesicle to the extracellular space, then to the adjacent collagen fibrils. Once the mineral is deposited interfibrillarly, the mineral is observed to advance both laterally and axially. The role of collagen in the growth and nucleation of hydroxyapatite has been investigated in-vitro by Nakamura et al. [8]. In this study they grew osteogenic cells on a variety of collagenous substrates and discovered that the cells mineralized the matrix when the "intrinsic fibrillar architecture" of the collagenous matrix simulated a structure similar to the osteoid. In contrast, acellular in-vitro studies have failed to produce bone like mineralization of collagenous substrates [8]. In this study we have evaluated the influence of aligned, reconstituted collagen fibers with a fibrillar substructure mimicking tendon, on the nucleation and growth of hydroxyapatite crystals in-vitro. Materials and Methods: Reconstituted Collagen Fiber Production. The methods used to produce reconstituted collagen fibers were id
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