Synthesis of hydrophobically modified alginate and hydrophobically modified gelatin containing cubic phase for pH- and salt-responsive release of fructose diphosphate

In this study, monoolein cubic phases (MO CP) were prepared for the pH-responsive and salt-responsive release of fructose diphosphate (FDP). The salt-responsive MO CP was synthesized by the Ca2+-mediated ionic gelation of hydrophobically modified alginate (HmAlg) in the water channel of the cubic phase. In addition, the HmAlg were electrostatically interacted with hydrophobically modified gelatin (HmGel) on the surface of MO CP to render pH responsiveness. It was found that both HmAlg and HmGel had surface-active properties that attributed to their immobilization in the MO CP. The loading of HmAlg and HmGel onto the MO CP decreased the phase transition temperature of MO CP due to alterations in the fluidity of the double layer of the MO CP water channel. However, TEM images revealed no alterations in the structure of MO CP after the addition of polymers. It was found that in the presence of salt (NaCl), the loaded FDP was released from the water channel due to the de-gelation and opening of the aqueous channel. Similarly, at pH above the isoelectric point of gelatin, the FDP is released from the aqueous channels because of the breakdown of the HmGel/HmAlg complex. Moreover, the higher skin permeation of FDP-loaded MO CP was also observed, suggesting that the MO CP can assist FDP in permeating the skin.