Abstract
A study has been made to determine the long-term effect of collagen-immobilized porous polyethylene on living body tissues as a result of reaction between them, and to clarify the ultramicrostructure in the interface between such a material and the tissues. Experiments were made using 70 Wister rats. Collagen-immobilized porous polyethylene pieces, in which immobilization was attained through covalent bouding, and virgin porous polyethylene pieces were implanted subcutaneously in the backs of the rats. These polyethylene pieces were removed from the rats together with surrounding tissue from one week to one year after implantation, and were studied histologically using a light microscope, a scanning electron microscope (SEM) and transmission electron microscope (TEM). The results were as follows:
1) Virgin Porous Polyethylene The rate of soft-tissue ingrowth into pores of these polyethylene pieces was very small, ranging from 13% to 18%, in all of the rats. The ingrown tissue was composed of granulation tissue having many inflammatory cells, and hyalinezation was observed in parts of the tissue. As far as SEM observation is concerned, it was found that the collagen fibers in the ingrowth tissue run in parallel to the surface of the pore in the polyethylene pieces, and irrespective of the differences of implanted period no contact between them was observed. One year after the implantation, tumorous growth was observed in nine (45%) of the 20 implanted virgin porous polyethylene pieces.
2) Collagen-immobilized Porous Polyethylene The rate of tissue ingrowth into the porous polyethylene pieces stood at 23.2% one week after the subcutaneous implantation, 32.4% after two weeks, 60.2% after four weeks, 69.3% after six weeks, 81.6% after 12 weeks and higher than 90% 20 weeks after implantation.
One year after implantation there was little change in the percentage, and by that time the ingrowth tissue and the porous polyethylene pieces had turned into biocomposite. The ingrowth formed loose connective tissue abounding in rete vasculosum containing a relatively low level of inflammatory cells. SEM observation found that the collagen fibers within the ingrown tissue were developing toward the pore surface of polyethylene material and coming in contact with the material surface. On the other hand, TEM observation of material-tissue interface found that one year after the implantation the living-body-originated collagen fibers were firmly anchored into the immobilized atero-collagen layer.
One year after implantation, tumor formation was found in only one (5%) of the 20 polyethylene pieces removed from the rats representing virgin porous polyethylene use. These results suggest that covalent bonding immobilization of collagen onto surface of porous polyethylene material is useful in promoting the ingrowth of soft tissue, tissue-adhesion, and inhibition of tumorigenesis, making porous polyethylene material more suitable for introduction into the living body.
