Studies were designed to demonstrate the need for standardization of shape of samples used as implants to evaluate histotoxicity of polymer materials. Six medical-grade polymers (polypropylene, polyethylene, polyurethane, silicone rubber, poly(vinyl chloride), and Teflon) were extruded as rods with circular-, triangular-, and pentagonal-shaped cross sections, and were implanted in rat gluteal muscles for 14 days. Evaluation of the tissue response was assessed by quantitating cellular lysosomal acid phosphatase enzyme activity by using microspectrophotometry. All triangular-shaped implants showed the highest enzyme activity and cellular response; pentagon shapes showed less, and circular rods showed the lowest activity. The results demonstrate the need for standard sample shape for valid comparative studies of tissue response to implanted polymers.

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Transmission electron microscopy was used to study the ultrastructure of cells at the interface with an implanted biodegradable polymer, Polyglactin 910. Various stages of implantation were observed from 1 day to 63 days, when absorption of the polymer was essentially complete. Events occurring at the interface include initial adhesion of macrophages on the implant surface; phagocytosis of wound debris; and subsequent erosion, invasion, and phagocytosis of the polymer by macrophages and giant cells. A vascular perfusion technique for fixation of the polymer sites implanted in soft tissue is also described.

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