Non-destructive mechanical characterisation of UVA/riboflavin crosslinked collagen hydrogels

Aims: To establish a non-destructive method of characterising the mechanical properties of collagen hydrogels to model corneal tissue and to examine the effect of photochemical crosslinking on their mechanical properties. Methods: Collagen hydrogels were manufactured, submerged in 0.1% riboflavin solution and crosslinked using two UVA tube bulbs with an intensity of between 2.8 and 3.2 mW/cm(2). The hydrogels were clamped around their outer edge and deformed using a sphere. The deformation was measured in situ using a long-working-distance microscope connected to a CCD camera, and the deformation displacement was used with a theoretical model to calculate the Young modulus of the hydrogels. Collagen hydrogels seeded with human corneal fibroblasts were used to examine cell viability after UVA irradiation. Results: There was an increase in Young modulus of the collagen hydrogels after UVA/riboflavin treatment that was dependent on the exposure time. UVA irradiation without riboflavin showed decreased mechanical integrity and strength. Cell viability was reduced with increased UVA exposure time. Conclusion: The non-destructive technique demonstrated a new methodology comparable with strip extensiometry for cornea or corneal model specimens but with more convenient features. This approach could be used as an initial step in developing new crosslinking treatments for patients with keratoconus.