Melatonin-loaded hyaluronic acid (HA) and poly(vinyl alcohol) (PVA) gels were prepared by using freeze-thaw technique and an emulsion method followed by freeze-thaw technique to produce a new synergistic system for topical application. Freeze-thaw hydrogels and emulgels were characterized by means of Fourier transform infrared spectroscopy, rheology and swelling tests. The porous structure of the hydrogels was shown by scanning electron microscopy observations and thermal properties were tested by differential scanning calorimetry measurements. Bioadhesion and in vitro release characterization of formulations were performed by texture profile analysis and dialysis bag method, respectively. The pore size of both formulations was ranging from 900 nm to 30 μm. Melatonin showed a good compatibility with the polymeric matrices as the pores were smaller for the drug-loaded systems. In vitro release studies showed that the release was improved by emulgel formulations. After 24 h, the release percentage was found to be 13.240% ± 1.094 and 15.192% ± 2.270 for hydrogel and emulgel, respectively. Emulgels had better bioadhesion properties than simple freeze-thaw samples. As a conclusion, regarding the in vitro characterization studies HA and PVA hydrogel and emulgel formulations and their lyophilized forms could be promising systems for topical application of melatonin.
Keywords: Hyaluronic acid; emulgel; freeze–thaw; hydrogel; melatonin; poly(vinyl alcohol).