Degradation of polyetherurethane by subcutaneous implantation into rats. II. Changes of contact angles, infrared spectra, and nuclear magnetic resonance spectra.

In vivo degradation of polyetherurethanes (PEUs) was studied using two kinds of PEUs, U-3 and U-8, coated on a base film of ethylene/vinyl alcohol copolymer (EVAL). U-3 is a nonsegmented PEU prepared from 4,4'-diisocyanatodiphenylmethane (MDI) and poly(tetramethylene oxide) (PTMO 1000). U-8 is a segmented PEU prepared from MDI, PTMO 1000, and 1,4-butanediol. Previous studies of PEUs were conducted using gel permeation chromatography and scanning electron microscopy. In this study, the explanted materials were examined with contact angle measurement, ATR-FTIR, and nuclear magnetic resonance (NMR) spectroscopies. All data obtained by these methodologies indicate that the PTMO/MDI oligomers diffused to the material surface in the early stage of implantation. Then, the low-molecular-weight fraction of the oligomers leached out from the surface to the exudate. Degradation became dominant after 2-4 weeks. In the case of PU-8, the PTMO fraction decreased approximately 35-40% from the surface at 24 weeks postimplantation. In the case of PU-3, the loss of coating material (U-3) on the base film (EVAL) was observed after 10 weeks. The PTMO fraction of the surface U-3 remained on EVAL at 6 weeks postimplantation, however, it was 64% of the initial material. The molecular weight of the U-3 remaining on EVAL also decreased. Degradation of U-3 occurred more rapidly than that of U-8. The data obtained with our materials were insufficient in determining evidence of oxidative degradation with IR or NMR spectra.