Effects of processing conditions on the rheological behavior of collagen dispersions.

Biomedical collagen preparations are mainly based on liquid aqueous preparations either used directly as injectables or transferred for example into solid implants or porous devices. In all cases the viscosity of the dispersion or solution has to be controlled or adjusted by pH, temperature, collagen concentration or crosslinking. We tested these effects on the rheological and structural properties of collagen fiber dispersions focusing on oscillatory rheometry. With increasing difference between pH and pI viscosity increased and went through a maximum with less rigidity of the fibers. The dispersions acted like a predominantly permanently linked network. This character changed to only partially linked at low collagen concentration due to isolation of the individual fibers. Up to 40 degrees C, temperature is a tool suitable for adjusting viscosity without changes in the network structure. At 50 degrees C, fourier transform - infrared spectroscopy (FT-IR) spectroscopy indicated the transition of the helical into random coil structure. Renaturation of the helices was found upon cooling but atomic force microscopy (AFM) indicated severe temperature induced damages of the fibers. Crosslinking with glutaraldehyde (GTA) leads to an increase in viscosity and the effect on the network structure depends on the processing conditions.