Injectable gels of anionic collagen:rhamsan composites for plastic correction: preparation, characterization, and rheological properties.

The present article describes the preparation and characterization of anionic collagen gels obtained from porcine intestinal submucosa after 72 h of alkaline treatment and in the form of rhamsan composites to develop injectable biomaterials for plastic reconstruction. All materials were characterized by SDS/polyacrylamide gel electrophoresis, infrared spectroscopy, thermal stability, potentiometric titration, rheological properties, and fluidity tests. Biocompatibility was appraised after the injection of anionic collagen: rhamsan composites at 2.5% in 60 North Folk rabbits. Independently of processing, the collagen's secondary structure was preserved in all cases, and after 72 h of hydrolysis the collagen was characterized by a carboxyl group content of 346+/-9, which, at physiological pH, corresponds to an increase of 106+/-17 negative charges, in comparison to native collagen, due to the selective hydrolysis of asparagine and glutamine carboxyamide side chain. Rheological studies of composites at pH 7.4 in concentrations of 2, 4, and 6% (in proportions of 75:1 and 50:1) showed a viscoelastic behavior dependent on the frequency, which is independent of concentration and proportion. In both, the concentration of the storage modulus always predominated over the loss modulus (G'>G'' and delta<45 degrees ). The results from creep experiments confirmed this behavior and showed that anionic collagen:rhamsan composites at pH 7.4 in the proportion of 50:1 are less elastic and more susceptible to deformation in comparison to gels in the proportion of 75:1, independent of concentration. This was further confirmed by flow experiments, indicating that the necessary force for the extrusion of anionic collagen:rhamsan composites, in comparison to anionic collagen, was significantly smaller and with a smooth flow. Biocompatibility studies showed that the tissue reaction of anionic collagen:rhamsan composites at 2.5% in the proportion of 75:1 was compatible with the application of these gels in plastic reconstruction. These results suggest that the association of collagen with rhamsan may be a good alternative in the replacement of glutaraldehyde to stabilize the microfibril assembly of commercial collagen gel preparations.