Mast cells and tissue reaction to intraperitoneally implanted polymer capsules.

The inflammatory reaction to implanted biomaterials often compromises the clinical usefulness of implantable devices. Dexamethasone, an anti-inflammatory agent, acts on macrophages to decrease production of inflammatory mediators, and on mast cells to prevent degranulation. Systemic administration of dexamethasone (dms) in rats decreases the tissue reaction to intraperitoneally implanted vinyl chloride-acrylic copolymer capsules. Local release of even smaller amounts of dms from a polymeric substrate placed inside an acrylic copolymer capsule may control the tissue reaction while avoiding the undesirable side effects of systemic treatment. Such a system also allows investigation of the local effect of soluble molecules on tissue-material interactions without altering the surface properties of the implant or adding the effect of a releasing material. In the present study, we investigated the effect of dms released from ethylene vinyl acetate (EVAc) rods placed in acrylic copolymer capsules and implanted in the peritoneal cavity of rats. In vitro the release of dms from EVAc rods was quasilinear for 5 weeks. When implanted intraperitoneally into rats, polymer capsules containing EVAc/dms rods generated a tissue reaction that was significantly thinner and featured fewer fibroblast and collagen layers than that around capsules containing pure EVAc rods at all time points studied. The tissue reaction layer was also thinner than that previously described in rats treated systemically with dms. The trabeculae of implants with dms-loaded EVAc rods contained significantly more intact mast cells than implants with EVAc alone, suggesting that degranulation of mast cells is involved in the tissue reaction to intraperitoneal polymer implants.