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Collagen-based films and sponges are widely used as biomaterials. The rate of their biodegradation can be reduced by treating them with different cross-linking agents. The efficiency of different reticulation procedures on thermal stability (measured by differential scanning calorimetry) and susceptibility to bacterial collagenase digestion of the final material (films or sponges) is compared. The chemical agents used on collagen gels or directly on collagen sponges and films were glutaraldehyde (GTA), hexamethylene diisocyanate (HMDC), cyanamide, 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide (EDC) and the two acyl azide methods (with hydrazine or diphenylphosphorylazide (DPPA)) developed in the authors' laboratory. Under these experimental conditions, collagen stabilization by the different agents increased in the following order: cyanamide < EDC < HMDC < hydrazine < DPPA < GTA. Sponges with the highest thermal stability were obtained by treating collagen gel with 0.5% GTA for 1 h at pH 5.5 (initial T~=75.8°C; after 3 months, Ta=75.6°C). Direct treatment of collagen films with DPPA gave similar thermal stability (Ta=72.6 °C) and collagenase resistance when compared with treatment with 0.6% GTA for 96 h (Td =74.6 °C). It is demonstrated that collagen sponges and films can be prepared with a wide range of thermal stability (49-75.8 °C) and collagenase digestion resistance (10-100%). Recent biocompatibility studies show, however, that DPPA and EDC are the best choices for preparing cross-linked collagen sponges and films.

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