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J.E. Candiello, A. Feola, T.R. Friberg, H. Lin; Calcification Induced Changes in Bruch’s Membrane Elasticity . Invest. Ophthalmol. Vis. Sci. 2006;47(13):1398.
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The wet form of age related macular degeneration (AMD) has been associated with disruption of the Bruch’s membrane (BM). The Bruch’s membrane undergoes significant structural change over time, including membrane thickening and calcification of the membrane sublayers. We have investigated the biomechanical properties of the porcine Bruch’s membrane and changes in its elasticity due to calcification.
The structural and elastic properties of the unfixed cryo–sections of porcine retina/Bruch’s membrane/choroid have been studied using atomic force microscopy (AFM). The elastic modulus of Bruch’s membrane was measured by nano–indentation of BM/choroid cross–section. The elastic moduli were measured for tissue samples incubating in phosphate–buffer saline containing various amount of CaCl2 over a period of 24–48 hours.
The elastic (Young’s) modulus of the unfixed porcine BM ranges from 80 kPa to 160 kPa. The central regions (elastin sublayer) of BM is softer in comparison to the outer collagenous sublayers. The BM is significantly stiffer than the surrounding choroid and retina pigment epithelial areas. Light staining of RPE/BM/choroid with a diluted multi–stain dye solution that contains some ethylene alcohols in the solvent induced a nearly 10 fold increase in the BM Young’s modulus. Incubation of BM with 2 mM CaCl2 over a 24–48 hour period caused significant hardening of the BM: the Yong’s modulus of BM increased to 240–400 kPa, a more than 2 fold increase in stiffness. This stiffening has been observed in the central elastin sublayer as well as the outer collagenous sublayers.
This study demonstrates that elasticity of the Bruch’s membrane is very sensitive to its environment and calcification induces significant change to BM stiffness, which may have important implication for BM disruption in AMD.
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