SURFACE ENGINEERING IN CONTACT ACTIVATION OF COAGULATION

通过与材料接触而激活血浆（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表面来引发的，导致酶原因子 XII 转化为蛋白酶形式 FXIIa，解吸到溶液相中。 这种机制与实验观察结果不一致，即接触活化的效率主要取决于促凝表面能，与蛋白质吸附能力相反，对于低效蛋白质吸附剂的高表面能（水可湿性）表面的活化非常有效，而对于高效吸附剂的中低能量（水可湿性差）表面的活化效率低。 此外，很难从表面能量的角度合理解释促凝血表面如何同时充当有效的 FXII 吸附剂（导致表面上的分子组装）和低效的 FXIIa 吸附剂（导致从表面释放），特别是考虑到酶原和蛋白酶形式之间相对较小的分子差异。 所提出的机制和实验之间的这些和其他差异可以通过另一种假设来合理化，该假设提出：接触激活复合物的蛋白质在具有由高能表面水合产生的特殊溶剂性质的邻近水区域内的促凝血表面附近组装。 自放大酶原-酶转化发生在该邻近水区内，但不直接发生在表面上，并从那里传播到本体等离子体相中。中低表面能材料附近的水的溶剂特性不会引起 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固级联的内在途径。本申请中概述的工作的总体目标是测试该命题的准确性和潜在引理，着眼于阐明表面工程路线，以获得具有改善的血液接触应用的血液相容性的材料。 拟议的工作是生物物理和血液学方法的平衡组合，解决了一个长期存在的生物工程问题，该问题将涉及蛋白质吸附的表面热力学、AFM 直接测量的表面蛋白质结合以及可变地承载固定因子的表面的促凝血效率。

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.