Interaction between polymeric materials and tissue -- biodeterioration of polymeric materials.

Styrene-isoprene block copolymer/methyl methacrylate graft copolymer (SIS-MMA), styrene-butadiene block copolymers (SBS), polyethylene, 1,2-polybutadiene, polysulfone, polycaprolactone polyurethane (PU) and ethylene-vinyl acetate copolymer (EVA) were implanted subcutaneously in dogs for 1 year. The same materials were stored in physiological saline solution at 37 degrees C (in vitro) and in air at room temperature (in air) for 1 year for comparative purpose. Biodeterioration or biodegradation of these materials was studied by mechanical property testing, viscometry, x-ray diffractometry, infrared spectroscopy and microscopy. A little deterioration of the mechanical properties of all the implanted samples was noticed as compared with the samples stored in vitro and in air. The infrared spectrum and x-ray diffraction pattern of the implanted sample except SIS-MMA were practically identical with the control. The implanted samples of SIS-MMA and SBS showed a cracked surface under a differential interference microscope. Viscosity measurements suggested a possible main chain scission for SIS-MMA and cross-linking for SBS and showed that the molecular weight of the other materials was almost unchanged. The intactness was rather surprising in regard to the infrared spectrum and viscosity of PU and EVA, because they were supposed to be more biodegradable. Deterioration of the mechanical properties was not always due to the results of biodegradation, as is often believed, but it must be considered that it might also be due to the absorption of some constituents such as lipids, steroids and amino acid from the body fluids and/or leaching of low molecular weight substances from the implanted materials.