Aloe vera based bigels: Synthesis, characterization and investigation of their effectiveness on bioactive agent release

This study was supported by Hacettepe University Scientific Research Coordination Unit (FHD-2022-19944), titled " Synthesis, Characterization of Aloe vera-Based Bigels and Development of PLGA Nanoparticle-Loaded Transdermal Melatonin Release Systems ". In the first stage of the presented thesis, it was aimed to create an innovative bigel system using Aloe vera oil organogel and ĸ-carrageenan/Aloe vera hydrogel. In the second stage, it is aimed to carry out characterization studies of the bigels. In the last stage, it is aimed to examine the potential of the hybrid structure formed by loading melatonin, an amphiphilic hormone, into the produced bigels, as a transdermal release system. For these purposes, firstly, organogel production was carried out using ĸ-carrageenan/Aloe vera based hydrogel and Aloe vera oil organogel. Then, bigels with stable structure were produced by mixing the hydrogel and organogel at room temperature with hydrogel/organogel ratios (H:O) of 90:10, 70:30, 50:50, 30:70, 10:90. The physical, chemical and mechanical properties of the produced bigels were investigated. The rheological properties of the bigels were determined by examining the strain, frequency and viscosity values at 25℃ and 37℃. Afterwards, cell culture studies were carried out to determine the cytotoxic effect of bigels. In the last step, melatonin, selected as a bioactive agent, was loaded into poly (lactic co-glycolic acid) (PLGA) nanoparticles, bigels in nanoparticles, and bigels in free form, and its in vitro release kinetics were investigated. As a result of the study, it was observed that the bigel with a hydrogel/organogel ratio of 10:90 showed an inhomogeneous distribution in a color close to yellow, while the bigel with a ratio of 90:10 showed a whitish, smooth and homogeneous distribution. In addition, it was observed that the prepared bigels did not show any mechanical difference in all ratios. It was determined that the bigels were viscoelastic at 25°C and 37°C, exhibited solid gel behavior, and their viscosity decreased with increasing shear rate at all bigel ratios. Thus, it was understood that the bigels showed good spreadability. In vitro cytotoxicity experiments with L929 fibroblast cells showed that bigels were not toxic. When the in vitro melatonin release results were evaluated, the fastest melatonin release was observed in the bigels loaded with free melatonin, while the slowest release was seen in the bigels containing melatonin loaded PLGA nanoparticles. In the presented thesis, Aloe vera-based bigels were synthesized for the first time and the transdermal melatonin release potential was investigated in vitro with the contribution of PLGA nanoparticles. It has been evaluated that bigels prepared in the light of the findings can be used as transdermal release systems in the controlled release of various pharmaceutical/cosmetic agents.