Reactive capsule formation around soft-tissue implants is related to cell necrosis

Low-density polethylene disks with smooth or course surfaces were implanted in the abdominal wall of rats, and the tissue response was evaluated after 1, 6, or 12 weeks. Cell damage was detected by two different methods. Cell s with increased membrane permeability could be identified using fluorescen ce microscopy by injection of propidium iodide prior to the killing of the rats. Second, cell death was verified by detection of DNA fragmentation. At 1 week a considerable number of the interfacial cells was stained with pro pidium iodide. Propidium-iodide-positive cells also were enriched at the ed ges of the disks irrespective of surface texture. The numbers of positive i nterfacial cells decreassed markedly over time. Cells with DNA fragmentatio n initially displayed a scattered distribution; at later time points they a ppeared mainly in the outer portion of the enveloping capsule. The reactive capsule was thicker for the smooth surface, and there was a positive corre lation between capsule thickness and propidium-iodide-positive cells at ear lier implantation periods. The results suggest that the thickness of the re active capsule is related to the extent of cell necrosis. It is suggested t hat the major initiator for this cell necrosis is mechanical shear since ce ll necrosis was found mainly in areas where mechanical shear could be expec ted. (C) 1999 John Wiley & Sons, Inc.