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This research work allows a direct comparison between collagen solutions of equal concentration derived from the two widely used collagen sources: bovine Achilles tendon (BAT) and rat tail tendon (RTT), and extraction methods: acid (AS) and pepsin (PS) solubilization on the properties of extruded collagen fibers. Scanning electron microscopy revealed that the substructure of the collagen fibers was the same independent of the treatment. Transmission electron microscopy revealed that the AS collagen-derived fibers were comprised of thick quarter-staggered fibrils, while the coexistence of thin nonbanded and thick banded fibrils was apparent for the PS collagen-derived fibers. The BAT-derived fibers demonstrated higher denaturation temperature than the RTT-derived ones (p < 0.05). The extraction method had no influence on the thermal characteristics of the fibers produced (p > 0.05). ASBAT collagen was of higher viscosity than both ASRTT and PSBAT (p < 0.002), and therefore larger diameter fibers were obtained (p < 0.001). An inversely proportional relationship between dry-fiber diameter and stress at break was observed within the treatments. The PS yielded 10 times more soluble collagen from BAT and the derived fibers were of similar tensile strength, stiffness, and elongation (p > 0.05) as those derived from the AS collagen. No significant difference was observed for the stress at break for the ASBAT and the ASRTT, while significant difference was observed for the elongation and modulus values (p < 0.005). Overall, reconstituted collagen fibers were produced with properties similar to native or synthetic fibers to suit a wide range of tissue engineering applications.

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Collagen is the most abundant protein in animals and because of its high mechanical strength and good resistance to degradation has been utilized in a wide range of products in industry whilst its low antigenicity has resulted in its widespread use in medicine. Collagen products can be purified from fibres, molecules reconstituted as fibres or from specific recombinant polypeptides with preferred properties. A common feature of all these biomaterials is the need for stable chemical cross-linking to control the mechanical properties and the residence time in the body, and to some extent the immunogenicity of the device. This can be achieved by a number of different cross-linking agents that react with specific amino acid residues on the collagen molecule imparting individual biochemical, thermal and mechanical characteristics to the biomaterial. In this review we have summarised the major techniques for testing these characteristics and the mechanisms involved in the variety of cross-linking reactions to achieve particular properties..