Biaxial mechanical testing of human sclera

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• 作者：Armin Eilaghi ; John G. Flanagan ; Inka Tertinegg ; Craig A. Simmons ; G. Wayne Brodl ; C. Ross Ethier
• 刊名：Journal of Biomechanics
• 出版年：2010
• 出版时间：18 June 2010
• 年：2010
• 卷：43
• 期：9
• 页码：1696-1701
• 全文大小：528 K

文摘

The biomechanical environment of the optic nerve head (ONH), of interest in glaucoma, is strongly affected by the biomechanical properties of sclera. However, there is a paucity of information about the variation of scleral mechanical properties within eyes and between individuals. We thus used biaxial testing to measure scleral stiffness in human eyes. Ten eyes from 5 human donors (age 55.4±3.5 years; mean±SD) were obtained within 24 h of death. Square scleral samples (6 mm on a side) were cut from each ocular quadrant 3–9 mm from the ONH centre and were mechanically tested using a biaxial extensional tissue tester (BioTester 5000, CellScale Biomaterials Testing, Waterloo). Stress–strain data in the latitudinal (toward the poles) and longitudinal (circumferential) directions, here referred to as directions 1 and 2, were fit to the four-parameter Fung constitutive equation W=c(e^Q−1), where and W, c’s and E_ij are the strain energy function, material parameters and Green strains, respectively. Fitted material parameters were compared between samples. The parameter c₃ ranged from 10⁻⁷ to 10⁻⁸, but did not contribute significantly to the accuracy of the fitting and was thus fixed at 10⁻⁷. The products cc₁ and cc₂, measures of stiffness in the 1 and 2 directions, were 2.9±2.0 and 2.8±1.9 MPa, respectively, and were not significantly different (two-sided t-test; p=0.795). The level of anisotropy (ratio of stiffness in orthogonal directions) was 1.065±0.33. No statistically significant correlations between sample thickness and stiffness were found (correlation coefficients=−0.026 and −0.058 in directions 1 and 2, respectively). Human sclera showed heterogeneous, near-isotropic, nonlinear mechanical properties over the scale of our samples.