Bale M D, Ferry J D
Department of Chemistry, University of Wisconsin, Madison.
Thromb Res. 1988 Dec 15;52(6):565-72. doi: 10.1016/0049-3848(88)90129-6.
Fine fibrin clots, prepared at pH 8.5, ionic strength 0.45, with minimal lateral aggregation of protofibrils, and ligated (cross-linked) by factor XIIIa, were subjected to constant static shear strain (gamma) with superposed small oscillating strains. The incremental shear modulus (dynamic storage modulus) measured in the oscillating deformations was strain-independent at small static strains (up to about 0.1) and approximately equal to the static modulus. At higher static strains, it increased rapidly, up by a factor of 5 to 8 at gamma = 0.35. Comparison with earlier data on unligated clots showed that the enhancement of stiffness was independent of ligation except at very high strains. The enhancement is attributed to additional forced contacts between network fibers as the strands are bent and oriented. When the static strain was maintained for up to one day, in a clot ligated by factor XIIIa the enhanced incremental modulus remained constant or decreased slightly, and after removal of stress the clot returned almost to its original shape. This contrasts with the behavior of unligated clots, where most of the enhancement was progressively lost as the incremental modulus fell toward its small-strain value, and there was a substantial permanent deformation after the removal of stress. The latter behavior has been attributed to gradual severance of network strands at high strains, followed by their rejoining in relaxed configurations, but leaving some structural damage that is only very slowly recovered in the resting state. Ligation of protofibrils evidently eliminates the possibility of strand rupture.
在pH 8.5、离子强度0.45条件下制备的、原纤维横向聚集最小且经因子XIIIa连接（交联）的精细纤维蛋白凝块，受到恒定静态剪切应变（γ）以及叠加的小振荡应变作用。在振荡变形中测量的增量剪切模量（动态储能模量）在小静态应变（高达约0.1）时与应变无关，且近似等于静态模量。在较高静态应变下，它迅速增加，在γ = 0.35时增加了5至8倍。与早期关于未连接凝块的数据比较表明，除了在非常高的应变下，刚度的增强与连接无关。这种增强归因于随着链的弯曲和取向，网络纤维之间额外的强制接触。当静态应变保持长达一天时，在经因子XIIIa连接的凝块中，增强的增量模量保持恒定或略有下降，去除应力后凝块几乎恢复到其原始形状。这与未连接凝块的行为形成对比，在未连接凝块中，随着增量模量向其小应变值下降，大部分增强逐渐丧失，并且在去除应力后存在大量永久变形。后一种行为归因于在高应变下网络链的逐渐断裂，随后它们在松弛构型中重新连接，但留下一些结构损伤，这些损伤在静止状态下恢复非常缓慢。原纤维的连接显然消除了链断裂的可能性。
