SURFACE ENGINEERING IN CONTACT ACTIVATION OF COAGULATION

通过与材料接触激活血浆（细胞）凝血级联被认为是通过将激活复合物的蛋白质直接分子组装到促凝血剂表面上而引发的，导致酶原因子XII转化为解吸到溶液相中的蛋白酶形式FXIIa。 这种机制与实验观察不一致，即接触活化的效率以蛋白质吸附能力的相反顺序严重依赖于促凝血剂表面能，对于作为低效蛋白质吸附剂的高表面能（水溶性）表面具有非常有效的活化，而对于作为高效吸附剂的中间能量和低能量（水溶性差）表面具有低效活化。 此外，从表面能量的角度难以合理化促凝血表面如何能够同时充当有效的FXII吸附剂（导致表面上的分子组装）和无效的FXIIa吸附剂（导致从表面释放），尤其是鉴于酶原和蛋白酶形式之间的相对较小的分子差异。 提出的机制和实验之间的这些和其他差异可以合理化的替代假设，提出：蛋白质的接触活化复合物组装附近的促凝剂表面内的一个邻近的水区域具有特殊的溶剂性质，导致从高能量表面的水合作用。 自放大的酶原-酶转化发生在该邻近的水区域内，但不直接在表面上，并且从表面传播到本体血浆相中。在中低表面能材料附近的水的溶剂性质不会诱导FXII的活化，并且直接吸附到这些相对疏水的表面上不会增强血浆凝血级联的内在途径。本申请中概述的工作的总体目标是测试该命题和基本引理的准确性，着眼于阐明血液接触应用中具有改善的血液相容性的材料的表面工程路线。 拟议的工作是一个长期存在的生物工程问题，将涉及表面热力学的蛋白质吸附，表面蛋白质结合直接测量的AFM，和促凝剂的效率的表面吸附轴承固定化因子的生物物理和血液学方法的平衡组合。

Activation of the blood plasma (a cellular) coagulation cascade by contact with materials is thought to be initiated by molecular assembly of the proteins of the activation complex directly onto procoagulant surfaces, leading to conversion of the zymogen Factor XII to the protease form FXIIa that desorbs into the solution phase. This mechanism is at odds with the experimental observation that the efficiency of contact activation is critically dependant on procoagulant surface energy in reverse order of protein adsorbent capacity, with very efficient activation for high-surface energy (water wettable) surfaces that are inefficient protein adsorbents and inefficient activation for intermediate- and low-energy (poorly water wettable) surfaces that are efficient adsorbents. Furthermore, it is difficult to rationalize from a surface energetic perspective how procoagulant surfaces can simultaneously serve as efficient FXII adsorbents (leading to molecular assembly on a surface) and inefficient FXIIa adsorbents (leading to release from a surface), especially in view of the relatively minor molecular difference between zymogen and protease forms. These and other discrepancies between proposed mechanism and experiment can be rationalized by an alternative hypothesis proposing that: Proteins of the contact activation complex assemble near procoagulant surfaces within a vicinal water region having special solvent properties that result from the hydration of high-energy surfaces. Self-amplifying zymogen-enzyme conversion occurs within this vicinal water zone, but not directly on surfaces, and propagates into the bulk plasma phase therefrom. Solvent properties of water near intermediate-to-low surface energy materials does not induce activation of FXII and adsorption directly onto these relatively hydrophobic surfaces does not potentiate the intrinsic pathway of the plasma coagulation cascade. The overarching objective of the work outlined within this application is to test the veracity of this proposition and underlying lemma with an eye to elucidating surface-engineering routes to materials with improved hemocompatibility for blood- contact applications. The proposed work is a balanced mix of biophysical and hematological approaches to a long-standing bioengineering problem that will relate surface thermodynamics of protein adsorption, surface-protein binding directly measured by AFM, and the procoagulant efficiency of surfaces variably bearing immobilized factors.