Collagenous Biocomposites for the Repair of Soft Tissue Injury
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COLLAGENOUS BIOCOMPOSITES FOR THE REPAIR OF SOFT TISSUE INJURY DAVID CHRISTIANSEN*, GEORGE PINS*, MING CHE WANG*, MICHAEL G. DUNN**, AND FREDERICK H. SILVER* *Dept. of Pathology, UMDNJ-Robert Wood Johnson Medical School, Piscataway, NJ. 08854 **Orthopaedic Research Laboratory, Division of Orthopaedic Surgery, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ 08903
Abstract Results of implantation studies in a variety of animal tissue models demonstrate that the rate of biogradation of a collagen scaffold should parallel the rate of wound healing observed in particular anatomic sites. This rapid degradation maximizes tissue regeneration and minimizes encapsulation of the implant. The following paper reviews the effects of crosslinking on the rate of tissue ingrowth and regeneration. In addition, preliminary mechanical data on newly developed soluble type I collagen fibers is presented as a possible advance in the production of high strength collagen based tissue scaffolds. Introduction: Collagen is one of the major scaffolding elements produced by nature. It is found in various biochemical forms and in different tissue architectures. Tendon/ligament contains quarter-staggered collagen molecules that are laterally bundled into fibrils, bundles of fibrils and fibers (1). In comparison, skin contains a wavy "biaxial' array of collagen fibers that are found within a plane almost parallel to the surface. Peripheral nerve contains collagenous sheaths or tubes that surround groups of axons. Dura mater is a bilayer containing collagen fibers parallel to the midline of the brain that is sandwiched on top of a layer of collagen fibers perpendicular to the midline. Collagenous biocomposites that mimic the structural components found in the tissues listed above have been investigated including: (a) a collagen tendon/ligament prosthesis consisting of parallel aligned type I collagen fibers in an amorphous type I collagen matrix; (b) a dermal replacement consisting of collagen fibers freeze dried into a planar open pore sponge; (c) a dural replacement composed of a collagen film containing planar collagen fibers; and (d) a collagen fiber substrate for axon elongation in peripheral nerve. In all of these applications the degradation rate of the implant should match the rate of tissue repair to optimize the rate of wound healing and at the same time it should act as a scaffold that mimics normal tissue architecture. It has been known since the 1950s that collagen molecules can be self assembled in neutral salt solutions to form fibrils that are identical to those found in tissues. Our laboratory has developed collagenous biocomposites, using the self assembly technique, that mimic connective tissue found in tendons/ligaments, skin, nerve and dura mater. In all cases the reconstituted collagen biocomposite has been stabilized through crosslinking processes. These crosslinking processes consist of one of either of two methods. The first method involves exposing the collagen to a water soluble carbodiimide, resulting in the
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