A pH-sensitive curcumin loaded microemulsion-filled alginate and porous starch composite gels: Characterization, in vitro release kinetics and biological activity

To improve the controlled release and stability of the loaded drug, the alginate–porous starch solution, as the gel matrix (GM), was prepared and added into curcumin-loaded microemulsion (CUR-ME) in a certain proportion, and then mixed with slow-gelling agents (CaCO3 + d-glucono-δ-lactone) to prepared curcumin-loaded microemulsion gel (CUR-ME-G). With increasing the proportion of GM from 25% (CUR-ME3G1) to 83% (CUR-ME1G5), the drug loading efficiency increased from 24% to 98% and the maximum drug loading capacity (14.9 mg/g) was found in CUR-ME1G3 with 75% GM. Moreover, a denser structure that entrapped all microemulsion droplets was formed with increasing the proportion of microemulsion according to the observation of scanning electron microscopy. This was also confirmed by Fourier transform infrared spectroscopy and Raman spectroscopy that no new peaks appeared in CUR-ME-G, while the hydrogen bonding interactions might exist between curcumin and sodium alginate. The in vitro release of the CUR-ME-G followed diffusion-controlled mechanism that was consistent with the first-order kinetic model. The release rate depended on the components of the CUR-ME-G and the pH value of the release medium. CUR-ME-G with curcumin concentration of 0.20% exhibited the best biological activity. CUR-ME-G might provide a potential application in the smart drug delivery systems.