RHEOLOGICAL PROPERTIES OF HYDROGELS FORMULATIONS FOR OPHTHALMIC APPLICATIONS

Rheological behavior of materials has been shown to be essential for their characterization as drug-delivery systems and, especially in the case of ophthalmic formulations for the treatment of ocular conditions, such as dry eye syndrome (DES). Different polymers, Hydroxypropylmethylcellulose (HPMC, MW of 10 and 90 kDa), sodium alginate (SA) and gellan gum (GG) have been used as unique systems or in association hydrogels for ocular applications and were found to be suitable due to their biocompatibility and non-toxicity. The aim of this study was to characterize the rheological properties of different hydrogel formulations: HPMC (MW 10 kDa) and HPMC (MW 90 kDa) at 2%, SA at 1.5%, GG at 1.5% and the associations of HPMC 90 and 10 kDa. (both at 1%); and SA-GG (1.5-1.5%). The curve flow profiles, sol-gel transition temperature (Tsol-gel) and frequency sweep analysis were performed in order to calculate the hysteresis area, viscosity (η), viscous (G”) and elastic (G’) moduli. The temperature sweep analysis demonstrated that, at physiological temperature (35.5°C), the G'/G'' ratio of HPMC formulations (MW 90 kDa) and the association of HPMC 90 and 10 kDa exhibited values lower than 1, (0.357 and 0.373, respectively), indicating a predominant viscous behavior. Viscosity values were influenced by temperature increase, reaching values from 1.47 to 0.39 Pa*s, at 35.5°C. The GG formulation and the SA-GG association are well-structured at low temperatures, exhibiting G'/G'' greater than 1, 2.72 and 5.21, respectively, with a decrease in viscosity at elevated temperatures, reaching values equal to 49.55 and 30.61 Pa*s, respectively. G' values were close to G'' indicating that materials were thermosensitive. The HPMC 10 and 90 hydrogels and SA showed G'/G'' ratio greater than 1, 8.02 and 2.76, respectively, but with viscosity parameters lower than those expected for hydrogels (from 0.041 to 0.044 Pa*s, respectively, at 35.5°C). The results relating to temperature variation point to the structural susceptibility of the main components used for the formulations, however, some associations favor ocular application since they have reduced viscosity and ease of flow.