Studies on composites of collagen and a synthetic polymer. Second report - mode of reaction of a laminar composite with living tissue, and results of long-term implantation.

Abstract

We have been studying composites of synthetic polymers and proctase-treated bovine collagen (telopeptide-poor collagen). In a previous paper, it is described that one of our composites appears to have a high tissue affinity, because it was found under a scanning electron microscope, well bonding the living tissue 6 weeks after implantation in the rabbit subcutaneous tissue. In the present study, the composites were also implanted in the subcutaneous tissue in rabbits to observe the mode of its bonding to the living tissue, and at the same time the bonding force was measured at various intervals during a period of 1.5 years, to observe the degree and duration of the effect of the composition, and further to study the optimal conditions for preparation of such a composite. As a method of composition, ultraviolet radiation and glutaraldehyde treatment were also comparatively examined, besides gamma-radiation that had been employed in a previous study. As the results, it is revealed that the composite bonds to the living tissue in such a manner that a portion of the collagen part is digested and absorbed to be replaced by the invading connective tissue and a part of collagen near the surface of the synthetic polymers had escaped digestion to combine with the rabbit's own collagen fiber. From these results we like to insist that the mode of reaction of our composites may be similar to real organization and be different in natur from mere encapsulation which was shown by the artificial materials hitherto in use to be considered to have a good tissue affinity. Therefor we think now the encapsulation is pseudoorganization. It is also shown that the bonding force of the composite to the living tissue and its duration depend chiefly on the degree of swelling, that is, the degree of intermolecular cross-linking, of the composed collagen part. Out of the gamma-radiated composites, those radiated 1--3 Mrads proved desirable in both tissue affinity and duration of tissue bonding, with a potent bonding force remaining effective even 1.5 years later, while the composite radiated with 5 Mrads or more proved poorer in these properties because of destruction of the collagen part, vastly varying in the properties. By ultraviolet radiation, it was easy to control the degree of swelling of collagen part with the radiation dose, however, this method gave a lower bonding force and a shorter duration of the force than gamma-radiation. The glutaraldehyde method allowed the collagen to remain over a long time, but gave the composite less tissue affinity than the other two methods.