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R.A. Bergstrom, A. Hubel; Influence of Microstructure on the Biomechanical and Optical Properties of Corneal Stroma Equivalents . Invest. Ophthalmol. Vis. Sci. 2005;46(13):3565.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Increasing numbers of refractive surgeries and corneal replacements have fueled interest in the development of a tissue–engineered cornea. Replicating the functional properties of the cornea such as strength, low permeability, transparency, and refraction in vitro is an extremely challenging task. The microstructure of the cornea is known to influence its biomechanical and optical properties. We hypothesize that an improvement in biomechanical properties for stromal equivalents can be achieved without decreasing optical properties by altering the microstructure of the initial matrix. Methods: The biomechanical and optical properties of reconstituted, hydrated collagen films and spongers were measured through uniaxial testing and the fraction of transmittance. Uniaxial tests were conducted with 5% strain steps at 0.05 mm/sec up to 25% strain followed by loading at 0.1 mm/sec until failure, and the fraction of light transmitted through the constructs in relation to through the surrounding medium at 400 and 700nm was also measured. Results:The relaxed modulus and ultimate tensile strength of the dense films, 0.3 ± 0.1 MPa and 0.4 ± 0.2 MPa, were an order of magnitude greater than that of the porous sponges, 0.03 ± 0.02 MPa for both, yet still at least an order of magnitude less than that of the native cornea. The fraction of transmittance at 400 and 700nm was 0.77 ± 0.06 and 0.93 ± 0.03 for the film and 0.64 ± 0.07 and 0.80 ± 0.04 for the sponge, which is still less than that reported for the native cornea at 0.90 and 0.98 respectively. Further investigations into the effects of evenly spacing the collagen with the use of additives and physically aligning the collagen with directional solidification are being conducted. Conclusions: By increasing the density of collagen with the films rather than the sponges, the strength of the hydrated matrices was increased without compromising the optical properties. By understanding the relationships between microstructure, biomechanical properties, and optical properties, optimized stromal equivalents can be fabricated. Such a tissue–engineered stroma would be a major step toward reducing, if not eliminating, the need for donor corneas for transplantation.
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