In vitro and in vivo digestion of collagen covalently immobilized onto the silicone surface.

In order to study the in vivo digestion of immobilized collagen and gelatin, these proteins labeled with 125I or fluorescein isothiocyanate (FITC) were covalently immobilized onto silicone surfaces, which were grafted with acrylic acid to introduce carboxyl groups, and implanted subcutaneously in rats and mice. When the proteins were labeled with FITC, the amount of proteins immobilized decreased with the increase of the number of FITC molecules conjugated with the protein molecule. In the wet state, FITC conjugated with the proteins was less stable than 125I. Approximately half of the amount of the immobilized proteins was digested in vivo within the first week and until 5 weeks after implantation the proteins were gradually digested. At that time, the amount of the proteins remaining on the silicone surface ranged from 0.6 to 1.0 microgram/cm2, which was several times larger than the amount of an assumed monolayer adsorption of proteins. Even after 15 weeks, the amount of proteins remaining on the silicone was almost the same as after 5 weeks. No significant difference in digestion was observed between collagen and gelatin, regardless of the labeling agent. Because of less stability and easier handling of FITC and higher stability and more difficult handling of 125I, FITC seems more suitable for short-term and 125I for long-term studies.