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. Cells with increased membrane permeability could be identified using fluorescence 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 propidium iodide. Propidium-iodide-positive cells also were enriched at the edges of the disks irrespective of surface texture. The numbers of positive interfacial cells decreased markedly over time. Cells with DNA fragmentation initially displayed a scattered distribution; at later time points they appeared mainly in the outer portion of the enveloping capsule. The reactive capsule was thicker for the smooth surface, and there was a positive correlation between capsule thickness and propidium-iodide-positive cells at earlier implantation periods. The results suggest that the thickness of the reactive capsule is related to the extent of cell necrosis. It is suggested that the major initiator for this cell necrosis is mechanical shear since cell necrosis was found mainly in areas where mechanical shear could be expected.