In Vitro release of Propolis phenolic compounds from Poloxamer 407-Based Hydrogels

Hydrogels are three-dimensional hydrophilic polymeric networks that are able to absorb large amounts of water. Poloxamer-based hydrogels have advantages such as reverse thermal gelation, prolonged release of the active substances, biocompatibility, low toxicity [1]. The natural material propolis is provided antioxidant, anti-inflammatory and antibacterial activities by biologically active compounds [2]. The objective of this study was to investigate the release of propolis phenolic acids (vanilic acid, caffeic acid, p-coumaric acid, ferulic acid) and vanillin from poloxamer 407-based hydrogels in vitro. The formulations containing 20–30% (w/w) of poloxamer 407 and an equal amount of aqueous propolis extract. Semisolid formulations were characterized by pH, viscosity and its dependence on temperature. In vitro release experiments were performed at 32 ± 0,5˚C temperature using the modified Franz type diffusion cells. The samples were analysed by HPLC. The pH of the hydrogels was within the range of 4,86–5,20, which are suitable to be applied on the skin. The viscosity of these formulations increased from 0,22 ± 0,02 to 492,35 ± 28,33 Pa·s increasing the poloxamer 407 concentration. Hydrogel containing 20% of poloxamer showed to be the most sensitive system for the changes of temperature. The release kinetics of propolis phenolic compounds conformed to zero order model (r2=0.988). The release of investigated phenolic compounds decreased increasing the concentration of poloxamer 407 from 20% to 30%. During 4 hours the largest amount (129,1 ± 8,1 μg/cm2) of these compounds was released from hydrogel, containing 20% of poloxamer. The released amount was 1,8–2,3 times higher as compared with the released amounts of phenolic compounds from 25% and 30% of hydrogels.The results of physico-chemical and biopharmaceutical studies revealed that hydrogel containing 25% of poloxamer 407 is the most suitable to be appli