IONOTROPIC GELATION IN A BICONTINUOUS CUBIC PHASE

Lipid-water systems are known to display cubic phases which are bicont inuous, a property where the entire space of the sample is divided int o two disconnected regions which are simultaneously continuous. 1-Mono oleoyl-rac-glycerol (C 1 8: 1, [cis] -9), or monoolein, is a polar lip id which exhibits bicontinuous cubic phases over a wide range of lipid /water ratios. We have studied the gelation of the aqueous region in t he cubic phase of monoolein using sodium alginate, a water-soluble pol ysaccharide. Phase diagram studies conducted using optical microscopy and differential scanning calorimetry indicate that the addition of al ginate and subsequent gelation, induced ionotropically by the addition of calcium chloride, does not significantly modify the phase behavior of the lipid. However, X-ray diffraction studies show that the additi on of alginate induces a structural transformation from a Pn3m to an I a3d cubic structure, with a concomitant increase in the unit-cell dime nsion. A small amount of protein, bovine serum albumin, could also be incorporated into both gelled and ungelled samples without disturbing the cubic structure. The release of protein from the gelled cubic phas e is considerably slower than from the ungelled sample, making them id eal systems for controlled release applications.