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K.Y. Then, M. Ahearne, K.K. Liu, Y. Yang, E. Siamantouras, P.J. McDonnell, S. Shah, S. Rauz, A. El Haj; A New Technique for Mechanically Characterising Hydrogels for Tissue Engineering Cornea . Invest. Ophthalmol. Vis. Sci. 2005;46(13):2185.
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Purpose: One of the main difficulties in growing corneal tissue in–vitro is to replicate the physical characteristics of the cornea. This experiment looked into how the mechanical characteristic of a corneal construct can be monitored in vitro. Methods: Alginate and agarose are hydrogels that have similar mechanical properties to collagen gel and both have been used for engineering tissue. A novel ball loading indentation system has been set up. It consists of a computerised long–focal CCD microscope, image analyser and clamping system. The circular corneal equivalent is clamped around its outer diameter and a ball of known weight and size is placed on top of it causing a deformation. The CCD microscope allows the capture of a side–view deformation profile. A theoretical model was derived to correlate quantitatively the viscoelasticity to the time–dependent deformation profile of the stromal equivalent. The force required to cause a deformation to occur was measured by the force transducer. The elastic modulus of the hydrogel can be calculated from the deformation. Viscosity values can be calculated from the creep or relaxation curves Results: Alginate exhibits highly viscoelastic deformation and the determined viscosity decreased with the increase of alginate concentration. The presence of cells appears to initially weaken hydrogel. By day 3, it appears that the mechanical strength of the gel improves in the presence of the gel. Conclusions: This technique is capable of characterising the mechanical strength of the corneal equivalent construct. It can also be used to study the affect of cyclic strain on the cells in a 3D matrix.
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