Evaluation of a Collagen-Hyaluronate Bilayer Matrix for Bone and Cartilage Repair
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Evaluation of a Collagen-Hyaluronate Bilayer Matrix for Bone and Cartilage Repair Lin-Shu Liu, Andrea Thompson, Robin Daverman, James W. Poser, and Robert C. Spiro Orquest, Inc. 365 Ravendale Drive, Mountain View, CA 94043, USA ABSTRACT We have developed a novel bilayer matrix composed of a porous type I collagen layer that transitions into a hyaluronate gel layer. This study evaluates the potential of the bilayer matrix to support the in vitro and in vivo formation of both bone and cartilage tissue. In the presence of recombinant human growth and differentiation factor-5, fetal rat calvarial cells cultured in the HA layer grew in a round, aggregated, chondrocyte-like morphology, while those in the collagen layer grew flattened and spread. Biochemical analysis demonstrated that cells in the collagen layer expressed higher levels of alkaline phosphatase activity, and lower levels of sulfated glycosaminoglycans and type II collagen when compared to cells in the HA layer. Intramuscular implants of the bilayer matrix with growth factor retrieved at 28 days revealed the presence of bone and cartilage tissue in the collagen and hyaluronate layers, respectively. These results demonstrate that the differentiation of cells in response to a single growth factor can be guided by specific compositional changes of the extracellular matrix.
INTRODUCTION Many of the current approaches to tissue repair and regeneration involve the implantation of extracellular matrix (ECM) either alone or in combination with recombinant growth factors or cultured cellular components. The role of the matrix in these strategies is to function not only as a delivery vehicle for the growth factor or cellular components, but also to support cellular differentiation events that result in the formation of proper reparative tissue. The chemical composition and physical organization of the extracellular matrix plays a key role in determining cellular differentiation events through direct cell-matrix communication [1]. The most common strategy in the design of a tissue graft matrix is to copy or mimic the composition and architecture of the damaged tissue [2,3]. In defects or wounds that involve more than one type of tissue, it would be ideal to have a graft matrix that can simultaneously support distinct tissue repair requirements. For example, in most osteochondral joint injuries, a matrix with the potential to support both bone and cartilage repair within distinct regions of the matrix would have a significant clinical impact. In the present study, a bilayer matrix was constructed by the covalent cross-linking of collagen (COL) and hyaluronate (HA) layers. The matrix was evaluated for the ability to support bone and cartilage tissue growth, both in vitro and in vivo, in combination with recombinant human growth and differentiation factor –5 (rhGDF-5), a member of the bone morphogenetic protein (BMP) family.
EXPERIMENTAL METHODS
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Materials Bovine type I collagen was purchased from Kensey-Nash (Extron, PA) and sodium hyaluronate was from Lifecor
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