A small diameter cardiovascular prosthesis was developed that utilized compound coatings of a stable, three-dimensional, fluid-imbibing gel network having controlled and identified microstructure. Two types of polyethylene terephthalate (Dacron('(REGTM))) tubular substrates (USCI('(REGTM)) DeBakey('(REGTM)) Vasculour('(REGTM))-D and USCI('(REGTM)) Sauvage('TM) filamentous velour) were selectively coated with polyhydroxyethyl methacrylate (P-HEMA) using a two-stage polymerization process. The first stage of this process imparted a coating of P-HEMA having a heterogeneous macroporous structure and the second stage yeilded an internal surface coating of hydrogel with a homogeneous microporous structure;Preliminary investigations demonstrated that the morphology of P-HEMA on a colloidal level could be controlled by adjustment of the cosolvent ratios holding other fabrication parameters constant. The microstructural details of a family of hydrogel formulations were identified by scanning electron microscopy techniques. Both radiation and thermal initiation of HEMA polymerization were evaluated as methods to coat polymeric substrates. The tabulation of the resulting physical properties aided in matching a potential hydrogel coating for a desired function when applied to the prosthesis design;The rabbit paravertebral muscle implantation test was used to evaluate the tissue response to the hydrogel composite materials. Samples and surrounding muscle tissue were examined histopathologically at 10 days, one month, and three months. All the materials tested showed no cytotoxic activity. The polyethylene terephthalate hydrogel composite materials showed a considerable amount of tissue ingrowth up to 700 (mu)m. The P-HEMA bulk polymer exhibited a small amount of tissue ingrowth. Silicone rubber composites were surrounded by a thin layer of encapsulating collagen in the range of 10 to 30 (mu)m. Scanning electron microscopy (SEM) evaluation of microstructural details (e.g., the relationship of tissue penetration to the interconnecting pores of the hydrogel coating) indicated that a variety of microstructural features could be correlated to the fabrication variables;A compound prosthesis design was pursued whereby the microstructure of hydrogel impregnating a fabric substrate would be controlled to allow sufficient permeability to cellular ingrowth from the exterior and at the same time provide a smooth nonthrombogenic flow surface. Canine carotid artery replacements with these materials demonstrated high potency rates and the development of early luminal surface cellular organization over a 21-day implantation period.