Gelation of dilute collagen solutions by ultraviolet light

Dilute collagen and collagen–polymer solutions were irradiated at 4°C with UV light (254 nm) under a nitrogen atmosphere. The collagen had been recovered from native tissue by a process of simultaneous acid solubilization together with proctase treatment to remove telopeptides. In the range of concentrations studied (0.1% to 0.9% collagen), gelation occurs after a few minutes, and the dynamic mechanical properties are followed thereafter using a freely oscillating torsion pendulum. During the irradiation, crosslinking and scission reactions compete. Initially crosslinking reactions dominate and the storage modulus increases. However, with extensive irradiation, scission reactions become important, and the storage modulus passes through a maximum and finally decreases. Furthermore, the time for incipient gelation decreases with concentration and the maximum storage modulus increases with concentration to the 2.5 power for collagen solutions. As an example, the maximum storage modulus for a 0.5% solution is 1.1×104 dynes/cm2. The modulus–dose behavior can be reduced to a single relationship in which the ratio of modulus to maximum modulus is a function of dose divided by dose to reach the maximum modulus.