SURFACE ENGINEERING IN CONTACT ACTIVATION OF COAGULATION

血浆(一种细胞)凝固级联通过与材料接触而激活，被认为是通过将激活复合体的蛋白质直接组装到促凝血剂表面上的分子组装来启动的，导致酶原因子XII转化为解吸进入溶液相的蛋白酶形式FXIIa。这一机制与实验观察结果不符，即接触活化的效率严重依赖于促凝剂表面能，与蛋白质吸附能力的顺序相反，高表面能(可润湿的)表面是无效的蛋白质吸附剂，而中能和低能(可润湿较差的)表面是有效的吸附剂。此外，从表面能量学的角度很难解释促凝剂表面如何同时充当有效的FXII吸附剂(导致分子在表面组装)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之间的分子差异相对较小。提出的机制和实验之间的这些和其他差异可以通过另一个假设来合理化，该假设提出：接触激活复合体的蛋白质在邻近水区内的促凝剂表面附近组装，具有特殊的溶剂性质，这是高能表面水化的结果。自我放大的酶原-酶转化发生在这个邻近的水带内，但不是直接在表面上发生，并从那里传播到大块的等离子体相。水在中低表面能材料附近的溶剂性质不会引起FXII的激活，直接吸附到这些相对疏水的表面上也不会加强等离子体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这一命题和潜在引理的准确性，着眼于阐明表面工程路线，以获得血液接触应用中具有更好血液相容性的材料。这项拟议的工作是生物物理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，该问题将与蛋白质吸附的表面热力学、AFM直接测量的表面-蛋白质结合以及具有可变固定化因子的表面的促凝血剂效率有关。

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.