The performance of silicone drains has been improved by coating their surfaces with a hydrogel polymer. This hydrogel is formed by reacting polyvinylpyrrolidone with an isocyanate prepolymer. By absorbing water, the hydrogel creates a drain surface with a low coefficient of friction. The results of this experimental study demonstrate that the surface coating reduces the adherence of blood clots to the drain and facilitates its removal from the wound. On the basis of these and other experiments, the Food and Drug Administration has allowed the use of hydrogel for coating surgical drains for use in patients.