Modification of inflammatory response to implanted biomedical materials in vivo by surface bound superoxide dismutase mimics.

The healing response to implanted biomedical materials involves varying degrees and stages of inflammation and healing which in some cases leads to device failure. In this article, we describe synthetic methods and in vivo results of a novel surface treatment for biomedical materials involving covalent conjugation of a low molecular weight superoxide dismutase mimic (SODm), which imparts anti-inflammatory character to the material. SODm investigated in this study are a new class of anti-inflammatory drugs consisting of a Mn(II) complex of a macrocyclic polyamine ring that catalyze the dismutation of superoxide at rates equivalent to that of native enzyme. The SODms were covalently linked to small disks of ultra-high molecular weight polyethylene, poly(etherurethane urea), and tantalum metal at two concentrations and implanted in a subcutaneous rat implant model for 3, 7, 14, and 28 days. Histological examination of the implant tissue performed at 3 and 28 days revealed striking anti-inflammatory effects on both acute and chronic inflammatory responses. At 3 days, the formation of a neutrophil-rich acute inflammatory infiltrate seen in control implants was inhibited for all three materials treated with SODm. At 28 days, foreign body giant cell formation (number of FBGCs per field) and fibrous capsule formation (mean thickness of implant capsule) were also significantly inhibited over untreated control implants. A mechanism based on our current understanding of superoxide as an inflammatory mediator at implanted biomedical materials is proposed.