Material properties of polymerized NDGA-collagen composite fibers: development of biologically based tendon constructs.

Methods for stabilizing collagen-based materials with catechol containing monomers were developed in order to produce fibers with mechanical properties in tension comparable to those of normal tendon. Fibers produced from pepsin solubilized, bovine tendon type I collagen were polymerized with the di-catechol nordihydroguaiaretic acid (NDGA). Polymerization was based on the chemical oxidation of the constituent o-catechols to reactive o-quinone functionalities. NDGA caused a dose dependent increase in the tensile strength and stiffness of the type I collagen fibers. A second treatment with NDGA improved the tensile properties significantly. Comparison of the effects of NDGA with those of biologically relevant mono-catechols indicated that the bi-catechol functionality of NDGA was responsible for generation of the superior tensile properties. Elimination of unreacted intermediates from the treated fibers with ethanol increased the effectiveness of the cross-linking process while simultaneously sterilizing the material. Catalyzing oxidation by saturating the reaction buffer with oxygen increased the effectiveness of polymerization and the resulting tensile properties of the treated fibers. The ultimate tensile strength of the optimized NDGA-treated fibers averaged 90 MPa; the elastic modulus of these fibers averaged 580 MPa. Both values are comparable to native tendon. The material properties of the NDGA cross-linked fibers exceed the properties of collagen fibers treated with other cross-linking strategies such as glutaraldehyde and carbodiimide. These results indicate that NDGA cross-linking may provide a viable approach to stabilizing collagenous materials for use in repair of ruptured, lacerated or surgically transected tendons, as well as other biomaterial constructs for surgical repair of musculoskeletal injuries and disease.