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Paulo Schor, Regina F Nogueira, Patrícia A Bersanetti; Mechanical and thermal characterization of corneas submitted to crosslink by Açai fruit (Euterpe orelacea) extract. Invest. Ophthalmol. Vis. Sci. 2014;55(13):4213.
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© ARVO (1962-2015); The Authors (2016-present)
To characterize rabbit corneas subjected to crosslinking by Açai extract (Euterpe orelacea) in comparation to riboflavin/UVA treatment by analyzing its Young modulus of elasticity (YM) and thermal denaturation (DSC) profile.
Ten rabbit eyes obtained from a local slaughterhouse (Granja dos Ipes, Salto de Pirapora, Brazil) were divided in three groups: 1. eyes treated with 0.1% comercial riboflavin (Ophthalmos, Sao Paulo, Brazil) and ultraviolet-A irradiation (365 nm) for 30 min, using a solid-state commercial device (X-Link; Opto Eletronica, Sao Carlos, Brazil); 2. corneas treated with 4% Açai extract by 2 hours; 3. control corneas (without treatment). After treatment corneas were deepithelialized and mantained in Optisol GS (Bausch&Lomb, New York, USA) or balanced saline solution (BSS) until characterization. YM was determined by the three point bend method by compressing corneal strips (2.0 mm x 7.0 mm) in an Universal Tester Shimadzu EZTest-SX (Kyoto, Japan) with a 1 N load cell at crosshead speed of 0.5 mm.min-1. Denaturation temperature was measured by differential scanning calorimetry (DSC). The DSC curves were obtained from 25 to 100oC using heating rate of 10oC.min-1 in a calorimeter (Shimadzu DSC-60, Kyoto, Japan).
YM value at 3% strain of group 1 was 0.118±0.001 MPa and 0.35±0.03 in group 2 (P<0.01). Control corneas (group 3) showed a YM of 0.038±0.008 MPa (p<0.01). DSC curves of control and treated corneas showed endothermic events that correspond to denaturation process of collagen. The results showed that the temperature of denaturation increased in the groups treated with agents that promote crosslinking (group 1= 64.5±0.9oC and group 2= 63.4±0.7oC) compared to control samples (60.8±2.2oC) (p<0.05).
The Açai extract was more effective in promoting the increase in mechanical resistance in rabbit corneas than the traditional treatment. This behaviour was confirmed by mechanical characterization that demonstrated a higher increase in YM in corneas treated with Acai extract than in riboflavin/UVA group. The thermal characterization by DSC analysis showed that crosslink leads to an increase in denaturation temperature of collagen that was similar for the two crosslink methodologies. The increase in denaturation temperature can be attributed to the denaturation of collagen fibrils that occurs during the crosslinking process.
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