BIODEGRADATION OF POLYURETHANE FOAM, REVISITED, IN THE RAT MODEL

In a prospective, randomized, controlled animal study, we systematical ly analyzed implanted polyurethane foam to determine the rate of degra dation in the rat and to compare it to our previous human data. Sixtee n 1-cm(2) silicone-backed pieces of polyurethane foam were randomly im planted into dorsal subcutaneous pockets in each of 16 Sprague-Dawley rats. Eight animals had polyurethane implants removed at 3 and 6 month s and the remaining 8 animals at 9 and 12 months. Specimens were exami ned either by histology or by scanning electron microscopy of recovere d foam after collagenase digestion of the capsule. Histologically, the re was evidence of foam degradation and a multinucleated giant cell in flammatory response surrounding the implants. With the scanning electr on microscope, the strut width of the polyurethane foam upon implantat ion measured 51.4 +/- 1.3 mu m (mean + SEM). This progressively decrea sed to 29.1 +/- 1.3 mu m at 3 months, 16.6 +/- 0.6 mu m at 6 months, 1 4.9 +/- 0.5 mu m at 9 months, and 13.2 +/- 0.3 mu m at 12 months (P < 0.0001). Duration of implantation has a significant impact on polyuret hane degradation as measured by scanning electron microscopy in the ra t animal model. The rate of degradation in the rat is much faster than in our human study, indicating that the rat studies cannot be used to draw conclusions regarding rate of biodegradation in humans.