Injectability and Tissue Compatibility of Poly-(N-Vinyl-2-Pyrrolidone) in the Skin of Rats: A Pilot Study


  • This study was sponsored by Biomorphics Group, Inc., Lincoln, MA.

  • C.J. Arpey, MD, L.K. Chang, MD, and D.C. Whitaker, MD indicate no financial interest in Biomorphics Group, Inc., Lincoln, MA.

Address correspondence and reprint requests to: Christopher J. Arpey, MD, Department of Dermatology, University of Iowa College of Medicine, 200 Hawkins Dr., Iowa City, IA 52242, or e-mail:


Background. Filling substances have been used in dermatologic surgery for decades, but an ideal agent has yet to be discovered. Poly-(N-vinyl-2-pyrrolidone) is a hydrogel that has been used in medical settings for more than 50 years, but not as a cutaneous filling agent.

Objective. We investigated the intracutaneous injectability and tissue compatibility 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 injected with the sterilized hydrogel and the rats closely observed. The rats were sacrificed in groups of four at 2, 4, and 12 weeks after implantation. Implant size was measured, volume calculated, and biopsies taken at each time interval.

Results. Poly-(N-vinyl-2-pyrrolidone) is easily injected through 30-gauge needles. All rats tolerated the implants well clinically. Histopathology revealed well-circumscribed implants with pseudoencapsulation, neoangiogenesis, and mixed inflammatory cells predominating at the periphery. Volume calculations revealed an average of 33% reduction at 4 weeks and 35% reduction at 12 weeks.

Conclusion. Poly-(N-vinyl-2-pyrrolidone) is easy to inject intracutaneously and is well tolerated in the rat model. Short-term volume retention is good. Histopathology suggests a subclinical inflammatory reaction expected with implantation of a synthetic substance into the skin. Additional studies are necessary to investigate the continued persistence of the hydrogel and its long-term effects on surrounding tissue.