Some Current Problems and new Dimensions of Polymeric Biomaterials for Blood-Contacting Applications

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Abstract
The biological performance of both impervious and porous polymeric coatings is profoundly influenced by substrate effects. “Antithrombogenic” behavior and lack of acute toxicological response are not necessarily indicative of blood compatibility or long-term tolerability in the physiological environment. Biomaterials should be tested whenever possible with donated human blood by in vitro and ex vivo procedures to augment in vivo evaluations in animals whose blood closely resembles humans. Such biological evaluation of candidate biomaterials should precede in vivo animal experiments with devices since otherwise it may be impossible to judge the relative performance of one material over another, leading to problems in establishing the causes of failure of medical devices and separating design parameters from the effects of biomaterials. An important area that is still not fully appreciated in cardiovascular applications involves the need to match the mechanical properties of tissues with anisotropic synthetic biomaterials. Several smooth-surfaced biomaterials have performed well in various flexing cardiovascular assist devices with a high degree of patient survival who otherwise may have died, and these are preferred over so-called “flocked” surfaces consisting of randomly oriented, tiny polyester microfibers embedded into polymeric substrates. “Flocked” surfaces are not to be confused with textured” surfaces and “biolized” materials. Intrinsic semiconduction and electronic conduction (as distinct from extrinsic conduction and ionic conduction) may play an important role in blood compatibility. Adsorption studies with single proteins while valuable, are not necessarily representative of the dynamic in vivo physiological events that influence the long-term biological performance of biomaterials.