The aim of this study was to histologically evaluate the tissue reaction to implantation of polyurethane disks containing castor oil produced in premolded form, supplied commercially, and biomass molded at the moment of application; since a late tissue reaction may occur during the total hardening process of the biomaterial. Twenty female Wistar rats, about 3 months of age, weighing 300-350g, and polyurethane disks 0.8cm in diameter and 0.5cm in thickness were used. The premolded disk was implanted into the subcutaneous tissue at the right flank and the molded biomass disk at the left flank. Five rats each were submitted to euthanasia at 3, 7, 15 and 30 days after surgery, and the polyurethane disks and surrounding tissue were collected. The specimens were processed for HE staining and examined microscopically. A moderate inflammatory reaction was primarily composed of polymorphonuclear cells and macrophages. The lymphocytes varied from absent to discreet. The intensity of the inflammatory reaction decreased at the same time the formation of fibrous conjunctive tissue increased around the implants. However, the numbers of macrophages remained the same. In conclusion, both polyurethane disks induce the same type of inflammatory reaction that varies from slight to moderate according to evaluation time.
Castor oil; biomaterial; polyurethane; histology
