Tissue reactions to polypyrrole-coated polyesters: A magnetic resonance relaxometry study

The electrically conductive properties of polypyrrole (PPy) as a coating on polyester material are very attractive for the manufacture of small diamet er blood conduits. However, before these PPy-coated materials can be invest igated for their capacity to generate endothelialized luminal surfaces, the y must first be studied for their innocuousness in a living environment. Th e specific goal of the present study was to investigate the in vivo interac tions of PPy-coated and noncoated woven polyester materials implanted subcu taneously in rats for prescheduled periods of 2, 5, 10, 20, and 30 days. Th e in vivo magnetic resonance (MR) relaxation times were computed for a smal l area of muscle tissue adjacent to the implants. A correlation was concurr ently attempted with blood monocyte activation studies as well as histologi cal observations of the tissue-material interface. The progressive pattern of the slower transversal relaxation time (T-2s) values revealed a more per sistent tissue reaction for the most conductive PPy-coated materials and a shorter acute tissue response as the surface resistivity increased. Similar ly, the blood monocyte activation studies indicated that the thickness of t he PPy coating, which correlated with the conductivity, was directly relate d to tissue response. Furthermore, both the MR and biological studies showe d that the PPy-coated material with a high surface resistivity displayed th e lowest tissue reaction over the entire period of implantation. The result s obtained from the blood monocyte activation studies and histological obse rvations correlate well with the noninvasive MR measurements of the body's healing process. The conductive materials with high surface resistivities m ust be further investigated. Finally, the noninvasive nature of MR relaxome try reveals its outstanding potential for future in vivo investigations of the body's tissue interactions with polymers and nonferromagnetic biomateri als.