Department of Ophthalmology, Nara Medical University, Nara 634-8522, Japan.
J Phys Chem B. 2009 Dec 24;113(51):16314-22. doi: 10.1021/jp907232h.
The phase equilibrium property and structural and dynamical properties of pig cornea were studied by macroscopic observation of swelling behavior, dynamic light scattering (DLS), and small-angle X-ray scattering (SAXS) under various conditions. It was found that the corneal gel collapses into a compact state isotropically or anisotropically depending on the external conditions. The corneal gel collapses uniformly into a compact state at a temperature above 55 degrees C because of the denaturation of collagen, whereas it collapses along an axis parallel to the optic axis with increasing NaCl concentration. Anisotropic deswelling was also observed during desiccation. SAXS measurements revealed that the periodicity of the collagen fiber of the cornea does not change even at higher NaCl concentration, which indicates that hydration and dehydration resulting from changes in salt concentration simply cause swelling and deswelling of the glycosaminoglycan (GAG), which is located between the regular two-dimensional lattices of collagen fibers, which obliges the change in thickness. From observations of the dynamics of light scattered by the corneal gel, intensity autocorrelation functions that revealed two independent diffusion coefficients were obtained. Divergent behavior in the measured total scattered light intensities and diffusion coefficients with varying temperature was observed. That is, a slowing of the dynamic modes accompanied by increased "static" scattered intensities was observed. This is indicative of the occurrence of a phase transition as a function of temperature.
采用宏观溶胀行为观察、动态光散射（DLS）和小角 X 射线散射（SAXS）等方法研究了猪眼角膜的相平衡性质以及结构和动力学性质。结果发现，角膜凝胶在不同条件下会发生各向同性或各向异性的塌陷。由于胶原变性，角膜凝胶在 55 摄氏度以上的温度下会均匀地塌陷成紧凑状态，而随着 NaCl 浓度的增加，它会沿着与光轴平行的轴发生各向异性塌陷。在干燥过程中也观察到各向异性的收缩。SAXS 测量结果表明，即使在较高的 NaCl 浓度下，角膜胶原纤维的周期性也不会改变，这表明由于盐浓度的变化而导致的水合和脱水作用只是导致位于胶原纤维规则二维晶格之间的糖胺聚糖（GAG）的溶胀和收缩，从而导致厚度的变化。通过观察角膜凝胶散射光的动力学，获得了揭示两个独立扩散系数的强度自相关函数。随着温度的变化，测量的总散射光强度和扩散系数表现出不同的行为。也就是说，观察到动态模式的减缓伴随着“静态”散射强度的增加。这表明随着温度的变化发生了相转变。
