Polyimides as biomaterials: preliminary biocompatibility testing

A number of commercially available polyimide materials were evaluated in vitro using a selected battery of levels I and II testing protocols prescribed by the National Institutes of Health Guidelines for Blood-Material Interactions. These procedures consisted of electron spectroscopy for chemical analysis and contact angle characterization surface studies, and protein adsorption, cell culture cytotoxicity, clotting time and haemolysis biocompatibility testing. The polyimide surfaces were invariant from the bulk composition with 60-80% C, 10-20% O and 2-5% N, producing advancing contact angles in the hydrophobic range (80-100 degrees). Consequently, they adsorbed significant amounts of albumin (2-3 micrograms/cm2) and fibrinogen (0.5-0.8 microgram/cm2). The polyimides also displayed an insignificant level of cytotoxicity and haemolysis, and clotting times ranged from 63 to 98% of normal. These clotting times and haemolytic index values were intermediate between the values observed for Teflon and Silastic controls. These factors, along with the strong adherence of polyimides to metal oxide substrates, indicate that polyimide materials are good candidates for further testing as encapsulants for implantable biosensors.