In-vivo degradation of polyurethanes: Transmission-FTIR microscopic characterization of polyurethanes sectioned by cryomicrotomy

A combination of cryomicrotomy and transmission Fourier transform infrared (FTIR) microscopy was used to investigate chemical changes in unstrained sheets of Pellethane® 2363-80A, Tecoflex® EG80A and Biomer® caused by biodegradation (18 month subcutaneous ovine implant). Cryomicrotomy was used to obtain thin sections (ca. 2.5 μm) from the surface into the bulk, parallel to the plane of the surface. FTIR microscopy was then used to obtain infrared absorbance spectra in the range 4000-600 cm^-1. Comparisons between the infrared spectra (by spectral subtraction) from implant surface, implant interior and non-implanted controls were used to detect chemical changes. Scanning electron microscopy was used to assess microstructural changes owing to biodegradation. Biodegradation in Biomer® was observed as uniform pitting and superficial fissuring (< 2.0 μm depth) over the implant surface. Biodegradation in Pellethane® 2363-80A and Tecoflex® EG80A was observed as severe localized embrittlement of the surface with fissures infiltrating up to 40 μm into the bulk. The chemical changes associated with biodegradation were observed as localized oxidation of the soft segment and hydrolysis of the urethane bonds joining hard and soft segments. Tecoflex® EG80A was also found to be susceptible to localized hydrolysis of the urethane bond within the aliphatic hard segment. Biomer® showed evidence of a significant non-specific degradation in the non-implanted wet control (37°C phosphate buffered saline at pH 7.3) samples and in the implant bulk.