Fischell Department of Bioengineering, University of Maryland, College Park, Maryland, United States.
Department of Chemical and Biomolecular Engineering, University of Maryland, College Park, Maryland, United States.
Invest Ophthalmol Vis Sci. 2024 Nov 4;65(13):14. doi: 10.1167/iovs.65.13.14.
To quantify corneal cross-linking (CXL)-induced stiffening via mechanical testing to estimate the impact of changes in hydration levels (H) and evaluate depth-dependent tissue hydration after CXL.
Eighty-three porcine corneal buttons were divided into three groups: Standard protocol CXL (S-CXL), accelerated CXL (A-CXL), and untreated (nonirradiated riboflavin-only) controls. Samples were hydrated or dehydrated to modulate H and dynamic mechanical analyzer compression tests were performed to measure Young's modulus (E). To extract the solid tissue network modulus, the cornea was modeled as a biphasic material after measuring E at different H. Corneal hydration was correlated with depth-dependent tissue thickness characterized by confocal reflection microscopy (CRM).
Young's modulus increased fourfold after S-CXL (0.72 ± 0.1 MPa) and threefold after A-CXL E (0.53 ± 0.12 MPa) versus controls (0.17 ± 0.045 MPa). However, H decreased from 4.07 ± 0.35 in controls to 2.06 ± 0.2 after S-CXL and 2.79 ± 0.12 after A-CXL. After H modulation and biphasic mechanical modeling, Young's modulus for corneal solid tissue network showed only a 1.8-fold increase after S-CXL (2.25 MPa) and 1.5-fold increase after A-CXL (1.85 MPa) versus controls (1.22 MPa). With CRM, the overall thickness of the corneal tissue was found to linearly correlate to hydration H as expected. No appreciable depth dependence of hydration-induced thickness changes throughout the corneal buttons were observed.
Corneal tissue hydration changes significantly impact measured corneal stiffness after CXL using mechanical testing. Not considering H leads to major overestimation of the stiffening effect of the CXL procedure. Depth-dependence of corneal thickness because of changing hydration is strongly dependent on the integrity of the tissue.
通过力学测试量化角膜交联（CXL）诱导的硬度变化，以估计含水量（H）变化的影响，并评估 CXL 后组织深度依赖性的水化作用。
将 83 个猪眼角膜瓣分为三组：标准方案 CXL（S-CXL）、加速 CXL（A-CXL）和未处理（未辐照的仅核黄素）对照组。通过调节 H 使样本水合或脱水，并进行动态力学分析仪压缩测试以测量杨氏模量（E）。为了提取固体组织网络模量，在不同 H 下测量 E 后，将角膜建模为双相材料。通过共聚焦反射显微镜（CRM）测量组织厚度，将角膜水合作用与深度依赖性组织厚度相关联。
与对照组（0.17 ± 0.045 MPa）相比，S-CXL 后杨氏模量增加了四倍（0.72 ± 0.1 MPa），A-CXL 后增加了三倍（0.53 ± 0.12 MPa）。然而，H 从对照组的 4.07 ± 0.35 降至 S-CXL 后的 2.06 ± 0.2 和 A-CXL 后的 2.79 ± 0.12。经过 H 调节和双相力学建模后，S-CXL 后角膜固体组织网络的杨氏模量仅增加了 1.8 倍（2.25 MPa），A-CXL 后增加了 1.5 倍（1.85 MPa），而对照组为 1.22 MPa。通过 CRM，角膜组织的整体厚度被发现与预期的水合作用 H 呈线性相关。在整个角膜瓣中，没有观察到明显的水合诱导厚度变化的深度依赖性。
在使用力学测试时，角膜交联后的角膜组织水合变化会显著影响测量的角膜硬度。不考虑 H 会导致 CXL 程序僵硬效果的严重高估。由于含水量变化导致的角膜厚度的深度依赖性强烈依赖于组织的完整性。
