Effect of fiber crosslinking on collagen-fiber reinforced collagen-chondroitin-6-sulfate materials for regenerating load-bearing soft tissues.

Porous collagen-glycosaminoglycan structures are bioactive and exhibit a pore architecture favorable for both cellular infiltration and attachment; however, their inferior mechanical properties limit use, particularly in load-bearing situations. Reinforcement with collagen fibers may be a feasible route for enhancing the mechanical characteristics of these materials, providing potential for composites used for the repair and regeneration of soft tissue such as tendon, ligaments, and cartilage. Therefore, this study investigates the reinforcement of collagen-chondroitin-6-sulfate (C6S) porous structures with bundles of extruded, reconstituted type I collagen fibers. Fiber bundles were produced through extrusion and then, where applicable, crosslinked using a solution of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide/N-hydroxysuccinimide. Fibers were then submerged in the collagen-C6S matrix slurry before being lyophilized. A second 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-hydroxysuccinimide crosslinking process was then applied to the composite material before a secondary lyophilization cycle. Where bundles had been previously crosslinked, composites withstood a load of approximately 60 N before failure, the reinforcing fibers remained dense and a favorable matrix pore structure resulted, with good interaction between fiber and matrix. Fibers that had not been crosslinked before lyophilization showed significant internal porosity and a channel existed between them and the matrix. Mechanical properties were significantly reduced, but the additional porosity could prove favorable for cell migration and has potential for directing aligned tissue growth.