RESUMO
PURPOSE: The purpose of this study was to determine if the addition of calcium gluconate to gellan solution results in a stronger gel structure on initial exposure to tear fluid due to the displacement of calcium from the gluconate ion by tear monovalent cations (Na+, K+). METHODS: Test solutions of gellan and gellan-calcium gluconate were mixed thoroughly with simulated tear fluid (STF) at a 5:1 ratio. The resulting gel was measured for viscosity at 32°C-36°C. RESULTS: The addition of optimized amounts of calcium gluconate to gellan formulations resulted in gellan-calcium gluconate-STF gels of higher strength (statistically significant) than when gellan alone was mixed with STF. Gellan experimental preparations demonstrated thixotropic behavior both before and after addition of STF. CONCLUSIONS: It appears possible to enhance the initial in situ gel-forming properties of gellan by adding a divalent cation bound to an ion exchange molecule or resin. Optimal amounts of polyvinylpyrrolidone (PVP) appear to be effective in slowing timolol release when added to gellan and calcium gluconate solutions.