Use of 2% hydroxypropyl methylcellulose to prevent the corneal swelling during the in vitro mechanical characterization

The aim of this study was to assess the use of 2% HPMC during in vitro uniaxial tensile tests, with corneal strips immediately obtained or after storing the eyes for 24 h in 0.9% NaCl solution at 4 celcius. The purpose was to establish a standardized procedure to prevent phenomena which can modify the mechanical properties of the tissue. Rabbit eyes were divided into four groups. Group A had seven eyes that were preserved in NaCl solution for 24 h before testing. Group B had seven eyes that were immediately tested. In both groups, to prevent both swelling and dehydration, 2% hydroxypropyl methylcellulose (2% HPMC) was applied. Group C had seven eyes that were preserved in NaCl solution for 24 h before testing. Group D had seven eyes that were immediately tested. In both groups, HPMC was not applied. Regarding the mechanical response, groups with HPMC showed similar Cauchy stress-stretch curves and there were no statistically significant differences at 5%, 10% and 15% strain between them, which mean that both showed similar mechanical behavior. The same result was obtained between groups without HPMC. However, for coupled groups with and without HPMC, statistically significant differences at 10% and 15% strain were observed. On the other hand, when grouped by storage time, statistically significant differences were found between groups that had eyes preserved for 24 h with and without HPMC, respectively, as well as between groups immediately tested with and without HPMC, respectively, at 15% strain. Nevertheless, if coupled groups were considered, between groups that were preserved for 24 h in NaCl before testing and groups that were immediately tested, no statistically significant differences were obtained. In addition, the Cauchy stress-stretch curves of groups without HPMC showed a decreasing slope of the linear part (strain > 8%) of the graph during the experiment. In summary, the use of HPMC during the handling of the tissue from excision to testing seems to prevent both swelling and dehydration.