Blood clotting on foreign surfaces remains a major limitation in the clinical application of many devices, including cardiovascular bypass, stents, catheters, and glucose sensors. In many situations, platelets are the initiator of blood clotting on the biomaterial surface. Recent studies in our lab have identified a quantitative design criterion to eliminate platelet adhesion, namely the need to reduce fibrinogen adsorption to very low levels (less than 5 ng/cm2), far below that which occurs on most materials. Radio frequency plasma deposited tetraglyme materials we have made can often meet this criteria, but it remains to be shown whether this results in the perfectly blood compatible biomaterial that we seek. We also must establish that ultra-low fibrinogen uptake can be achieved consistently and that the materials are stable in this regard. Therefore, a series of studies to perfect the glyme technology and evaluate its blood compatibility is proposed.
The specific aims of the proposal are as follows: 1. Tetraglyme plasma treatment conditions will be optimized to achieve coating uniformity, durability and ultra low protein uptake and a new reactor to treat the inside surfaces of longer tubes will be made. A hypothesis about the role of tightly bound water in causing non-fouling of glyme coatings will be tested. Two new monomers for producing plasma deposited PEG- like surfaces will be evaluated. 2. Fibrinogen adsorption from plasma will be compared to ESCA and TOF-SIMS surface chemical data for a series of tetraglymes to establish the conditions that result in ultra-low fibrinogen uptake. The tetraglyme series will be made under varying reactor conditions which will cause variations in surface chemistry, and thus allow us to test the hypothesis that the criteria that must be met to achieve ultra- low fouling are high, optimized ether carbon content relative to non-ether carbon and prevention of delamination. Resistance to fouling by fibronectin, vitronectin, von Willebrand factor, and IgG will also be measured. Resistance to uptake of all proteins from plasma will be characterized with surface plasmon resonance and by two dimensional gel electrophoresis. 3. Blood interactions will be characterized using both in vitro and in vivo methodology. In vitro platelet adhesion and procoagulant activation on a series of glyme coated materials will be measured after their pre-exposure to blood plasma or fibrinogen. The role of non-platelet mediated clotting events will be assessed by measuring clotting times and clotting enzyme activity in recalcified plasma in contact with the tetraglymes. The effect of non-adhesive encounters on platelet activation and aggregation will be characterized using laser emboli detection. In vivo blood compatibility of materials exhibiting ultralow fibrinogen and platelet uptake will be assessed in dogs with tubular tetraglyme ex vivo shunts by measuring both acute phase and steady state indicators of clotting.
