title: Poly(carbonate urethane) and poly(ether urethane) biodegradation: in vivo studies.
abstract: Several strategies have been used to increase the biostability of medical-grade polyurethanes while maintaining biocompatibility and mechanical properties. One approach is to chemically modify or replace the susceptible soft segment. Currently, poly(carbonate urethanes) (PCUs) are being evaluated as a replacement of poly(ether urethanes) (PEUs) in medical devices because of the increased oxidative stability of the polycarbonate soft segment. Preliminary in vivo and in vitro studies have reported improved biostability of PCUs over PEUs. Although several studies have reported evidence of in vitro degradation of these new polyurethanes, there has been no evidence of significant in vivo degradation that validates a degradation mechanism. In this study, the effect of soft segment chemistry on the phase morphology, mechanical properties, and in vivo response of commercial-grade PEU and PCU elastomers was examined. Results from dynamic mechanical testing and infrared spectroscopy suggested that the phase separation was better in PCU as compared with PEU. In addition, the higher modulus and reduced ultimate elongation of PCU was attributed to the reduced flexibility of the polycarbonate soft segment. Following material characterization, the in vivo biostability and biocompatibility of PEU and PCU were studied using a subcutaneous cage implant protocol. The results from the cage implant study and cell culture experiments indicated that monocytes adhere, differentiate, and fuse to form foreign body giant cells on both polyurethanes. It is now generally accepted that the reactive oxygen species released by these adherent macrophages and foreign body giant cells initiate PEU biodegradation. Attenuated total reflectance-Fourier transform infrared analysis of explanted samples provided evidence of chain scission and crosslinking in both polyurethanes. This indicated that the PCU was also susceptible to biodegradation by agents released from adherent cells. These results reinforce the need to evaluate and understand the biodegradation mechanisms of PCUs.
authors.affiliation: Center for Applied Polymer Research, and Department of Macomolecular Science, Case Western Reserve University, Cleveland, Ohio 44106, USA.
authors.forename: Elizabeth M
authors.initials: EM
authors.lastname: Christenson
authors.forename: Mahrokh
authors.initials: M
authors.lastname: Dadsetan
authors.forename: Michael
authors.initials: M
authors.lastname: Wiggins
authors.forename: James M
authors.initials: JM
authors.lastname: Anderson
authors.forename: Anne
authors.initials: A
authors.lastname: Hiltner
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry / Q000378:metabolism*; D002448:Cell Adhesion; D002478:Cells, Cultured; D004987:Ethers / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D015847:Interleukin-4 / Q000378:metabolism; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D011108:Polymers / Q000737:chemistry / Q000378:metabolism*; D011140:Polyurethanes / Q000737:chemistry / Q000378:metabolism*; D017550:Spectroscopy, Fourier Transform Infrared; D013314:Stress, Mechanical
chemical_list: D001672:Biocompatible Materials; D004987:Ethers; D011108:Polymers; D011140:Polyurethanes; D015847:Interleukin-4