Chemical and physical properties of collagen implants influence their fate in vivo as evaluated by light and confocal microscopy

Abstract

Porcine collagen membranes having a rough and a smooth side were used for subcutaneous implantation studies in rats. Two tanning protocols were used for the membranes, a new one involving microwaving and glutaraldehyde treatment (NEWGA), and the other, a conventional method using glutaraldehyde treatment at room temperature (OLDGA). Untreated membranes (NONGA) were also implanted. Sections of the implants were examined by light microscopy and with the confocal laser scanning microscope focusing on neovascularization and incorporation of the implant. At 64 days, the smooth sides of NEWGA and OLDGA implants were not well incorporated, with scarring subjacent to the surface and dystrophic calcification of that side of the membrane. At the same time, the rough sides of the NEWGA and OLDGA were not calcified with a giant cell reaction around the porcine collagen. The best incorporation was found in the NONGA membranes with no dystrophic calcification, excellent neovascularization of all layers, and complete remodeling at day 64. After 5 months, the completely remodeled NONGA membrane still could be identified, and the NEWGA and OLDGA membranes were calcified with a giant cell reaction having a dense fibrous capsule. It is concluded that if cross-linking is deemed necessary, the microwave cross-linking method is advisable because in the early stages there is less reactive inflammation around it, and the implant surfaces should be rough with an open structure, making calcification of cross-linked collagen unlikely.