Long-term in vivo studies of poly(2-hydroxyethyl methacrylate).

Poly(hydroxyethyl methacrylate) (PHEMA) was implanted subcutaneously in rats, hamsters, and guinea pigs for up to 24, 23, and 13 months, respectively. The tissue response and tumorigenesis caused by PHEMA were compared among the three species of the animals. Thick fibrous capsule formation and tumor production were noted only in rats, while no tumorigenesis and thin fibrous capsule formation were observed in hamsters and guinea pigs. These results support our previous hypothesis that animals producing a thick and avascular capsule tend to develop tumors at the implant site. PHEMA retrieved was characterized by scanning electron microscopy and x-ray energy dispersive analysis. Calcium and phosphorus were the main elements detected on the surface of PHEMA implants. PHEMA is suggested to be not suitable for long-term implant material.