Lipolysis and structure controlled drug release from reversed hexagonal mesophase

The present work investigates a system composed of a ternary reversed hexagonal mesophase (H _II) loaded with a lipase for modulating drug delivery capabilities of the system. Thermomyces lanuginosa lipase was solubilized into H _II mesophase for the benefits of continuing lipolysis of the lipids, consequently disordering and decomposing the hexagonal mesophase and thereby enhancing the diffusion of the encapsulated drug. A single transition from the H _II structure to a random micellar phase was detected during the lipolysis. In the first lipolysis stage the hexagonal system (glycerol monooleate, tricaprylin, and water) preserved its symmetry within ca. 200min. During this step about 40-60% molar of the lipids were hydrolyzed, and a gradual shrinking of the H _II cylinders (decrease of 8Å in lattice parameter) was detected. In the second lipolysis stage, the H _II mesophase gradually disintegrated (faster rate) and the release of a model drug (sodium diclofenac) was significantly enhanced, which was assumed to be lipolysis rate-controlled. After about 15h the H _II mesophase was disintegrated into two dispersed immiscible phases. The release obeyed two-step Higuchi kinetics with two consecutive linear correlations of the drug release.