Injectability and tissue compatibility of poly-(N-vinyl-2-pyrrolidone) in the skin of rats: A pilot study

BACKGROUND. Filling substances have been used in dermatologic surgery for d ecades, but an ideal agent has yet to be discovered. Poly-(N-vinyl-2-pyrrol idone) is a hydrogel that has been used in medical settings for more than 5 0 years, but not as a cutaneous filling agent. OBJECTIVE. We investigated the intracutaneous injectability and tissue comp atibility of this hydrogel in a rat model. Particular attention was paid to ease Of injection through small needles, volume retention of the implant, clinical course, and histocompatibility. METHODS. The shaved backs of 12 anesthetized Sprague-Dawley rats were injec ted with the sterilized hydrogel and the rats closely observed. The rats we re sacrificed in groups of four at 2, 4, and 12 weeks after implantation. I mplant size was measured, volume calculated, and biopsies taken at each tim e interval. RESULTS. Poly-(N-vinyl-2-pyrrolidone) is easily injected through 30-gauge n eedles. All rats tolerated the implants well clinically. Histopathology rev ealed well-circumscribed implants with pseudoencapsulation, neoangiogenesis , and mixed inflammatory cells predominating at the periphery. Volume calcu lations revealed an average of 33% reduction at 4 weeks and 35% reduction a t 12 weeks. CONCLUSION. Poly-(N-vinyl-2-pyrrolidone) is easy to inject intracutaneously and is well tolerated in the rat model. Shortterm volume retention is good . Histopathology suggests a subclinical inflammatory reaction expected with implantation of a synthetic substance into the skin. Additional studies ar e necessary to investigate the continued persistence of the hydrogel and it s long-term effects on surrounding tissue.