Effect of casein on pure lecithin liposome: Mixed biomacromolecular system for providing superior stabilization to hydrophobic molecules.

Formulation of new liposoma-based systems can always be in the spotlight for their unique utilization as carriers. Some changes in the composition of lipids may give rise to new mixed liposomes exhibiting modified size and physico-chemical characteristics. Consequently, these display different encapsulating properties toward various molecules. In this work, we have explored the variations in the model lecithin liposomes with casein additive from their size, shape, microenvironment and dynamics in solution. It is observed that with introduction of casein, the size of the liposome is substantially reduced due to incorporation of the additive in its bilayer. Strong interaction between the hydrophobic side chains of casein and lipid bilayer, and electrostatic repulsion of head groups of lipid are responsible to result small casein-mixed liposomes. Spectral properties of coumarin-153 disclose that the microenvironment of the bi-layer of mixed system is predominantly hydrophobic in nature and much rigid too. Fluorescence-lifetime-imaging-microscopy indicates that casein mixed systems exhibit wider lifetime distribution than pure liposomes with predominance of longer lifetimes, entirely arising from the outer bilayer. This indicates that casein gets incorporated in the bilayer of the vesicle to cater rigid and more hydrophobic microenvironment with an effective decrease in size. It is found that such mixed system is very efficient to stabilize the hydrophobic drugs (curcumin and β-carotene) for prolonged period than the pure liposome or casein-only. The findings are indeed important from the perspective of drug stabilization by liposomes, and is suggestive of possible utilization in oral drug delivery applications involving such size-reduced nano-encapsulates.