Polyurethane (PU55D) and copolymer materials have low thermal stability and are highly susceptible to thermal damage during cautery. Implanting physicians should be aware of the lead insulation materials being used during implant procedures and their properties. The use of direct contact cautery on transvenous leads should be minimized to avoid damage to the lead, especially on leads with polyurethane or copolymer outer insulations.
Long term in vitro biostability of thermoplastic polyurethanes (TPUs) containing mixed polyisobutylene (PIB)/poly(tetramethylene oxide) (PTMO) soft segment was studied under accelerated conditions in 20% H(2)O(2) solution containing 0.1M CoCl(2) at 50 °C to predict resistance to metal ion oxidative degradation (MIO) in vivo. The PIB-based TPUs showed significant oxidative stability as compared to the commercial controls Pellethane 2363-55D and 2363-80A. After 12 weeks in vitro the PIB-PTMO TPUs with 10-20% PTMO in the soft segment showed 6-10% weight loss whereas the Pellethane TPUs degraded completely in about 9 weeks. Attenuated total reflectance Fourier transform infrared spectroscopy confirmed the degradation of Pellethane samples via MIO by the loss of the ∼1110 cm(-1) aliphatic C-O-C stretching peak height attributed to chain scission, and the appearance of a new peak at ∼1174 cm(-1) attributed to crosslinking. No such changes were apparent in the spectra of the PIB-based TPUs. The PIB-based TPUs exhibited 10-30% drop in tensile strength compared to 100% for the Pellethane TPUs after 12 weeks. The molecular weight of the PIB-based TPUs decreased slightly (10-15%) at 12 weeks. The Pellethane TPUs showed a dramatic decrease in M(n) and an increase in low molecular weight degradation product. Scanning electron microscopy (SEM) showed severe cracking in the Pellethane samples after 2 weeks, whereas the PIB-based TPUs exhibited a continuous surface morphology. The weight loss, tensile, and SEM data correlate well with each other and indicate excellent biostability of these materials.
Photooxidative degradation and stabilization of a polystyrene-block-polybutadiene-block-polystyrene thermoplastic elastomer using a polychromatic UV light in air at 60°C has been studied by monitoring the appearance of the hydroxyl and carbonyl groups in Fourier transform infrared spectroscopy. The extent of photooxidative degradation in different samples has been compared. The rate of photooxidation was also estimated in the presence of different concentrations of 2,6-di-tert-butyl-4-methylphenol [BHT], 2-(2Ј-hydroxy-5Ј-methylphenyl)benzotriazole [Tinuvin P] and tris(nonylphenyl) phosphite [Irgafos TNPP], and 1,2,2,6,6-pentamethyl piperidinyl-4-acrylate was grafted onto the surface of the SBS film. The kinetic evolution of the oxidative reaction was determined. The morphological changes upon irradiation in the solution cast SBS films were studied by scanning electron microscopy. Based on the experimental data a suitable photooxidative degradation mechanism also has been proposed.
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