Just before the turn of this century, physicists were impressed with their abilities to explain many of the basic laws of the universe mathematically. However, the energy output spectrum of a heated black body resisted rigorous explanation, particularly at the shorter wavelengths. This failure of classical physics was referred to as the "ultraviolet catastrophe" and was ultimately resolved by Planck in 1900 with his concept of quantization of energy. We in the biomaterials field are faced with a contemporary intellectual crisis that I will refer to as the "blood compatibility catastrophe"-we lack some guiding principle that will permit us to analyze and explain blood compatibility.
At a recent NHLBI Device and Technology Branch (DTB)-sponsored meeting on cardiovascular devices and materials, a distinguished panel of experts on blood compatibility was challenged to name a bloodcompatible material. The group declined to do so (although pharmacologic approaches were suggested). This lethargic response is symptomatic of a crisis in understanding that is observed throughout the field of cardiovascular materials. For example, the literature is rife with controversy about what is "blood compatible," with widely differing classes of materials labeled "blood ~ompatible."'-~ Other commonly used, but ill-defined, terms include hemocompatible, antithrombogenic, thromboresistant, and nonthrombogenic. At the same time as the blood-compatible materials research literature continues to expand, we find few (perhaps no) promising new materials undergoing the critical transition from laboratory to clinic. Table I lists clinical observations suggesting that we do not yet have blood-compatible synthetic materials. After more than 25 years of steady funding of research in blood-compatible materials and blood compatibility testing by the DTB, why was this