SURFACE ENGINEERING IN CONTACT ACTIVATION OF COAGULATION

与材料接触的血浆（细胞）凝血级联的激活被认为是由激活复合物蛋白的分子组装直接在促凝剂表面启动的，导致酶原因子XII转化为蛋白酶形式FXIIa，并解吸到溶液中。这一机制与实验观察结果不一致，即接触激活的效率严重依赖于促凝剂的表面能，与蛋白质吸附能力相反，对于高表面能（可湿性差）表面是低效的蛋白质吸附剂，而对于中低能量（可湿性差）表面是低效的吸附剂。此外，很难从表面能的角度来解释促凝剂表面如何同时作为高效的FXII吸附剂（导致分子在表面上的组装）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：接触活化复合物的蛋白质聚集在邻近水区的促凝剂表面附近，具有由高能表面水合作用产生的特殊溶剂性质。自扩增酶-酶转化发生在邻近的水区，但不直接发生在表面，并从水区传播到体浆相。中低表面能材料附近的水的溶剂性质不会诱导FXII的活化，直接吸附在这些相对疏水的表面上不会增强等离子体凝聚级联的固有途径。本应用程序中概述的工作的总体目标是测试该命题和潜在引理的准确性，并着眼于阐明具有改善血液相容性的材料的表面工程路线，以用于血液接触应用。提出的工作是生物物理学和血液学方法的平衡组合，以解决一个长期存在的生物工程问题，将涉及蛋白质吸附的表面热力学，由AFM直接测量的表面-蛋白质结合，以及不同承载固定因子的表面的促凝效率。

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.