Structure–release rate correlation in collagen gels containing fluorescent drug analog

The paper examines the release properties of collagen gels that contain covalently bound fluorescent drug analogs. Collagen gels were prepared by fibrilogenesis. The gels were stabilized by cross linking with EDAC/NHS. SEM studies showed that increasing the cross-linking time with EDAC/NHS resulted in decreasing pore size and increasing gel density. Fluorescence spectroscopy measurements showed a clear correlation between decreasing pore size and increasing gel density, and lower release rate from the gels. Additives like chondrotitin-6-sulfate (CS) and amino acids altered the release properties of the cross-linked collagen gels. CS increased the stability of collagen gels to enzymatic degradation and non-enzymatic degradation. This was attributed to increasing gel rigidity due to carbohydrate–protein interactions. The amino acid lysine increased the stability of collagen gels which was attributed to increasing cross-linking level between the collagen fibrils and the primary amine group on the lysine side chain. The amino acid histidine decreased the stability of the gels, particularly to non-enzymatic degradation. These results correlated with increasing pore size following treatment with histidine. Our study shows, for the first time, a clear correlation between structure and release properties of collagen gels. It describes in detail the effect of additives on the structural and release properties of collagen gels. The study focused on gels that were prepared through fibrillogenesis and were therefore similar in structure to native collagen.