Investigating the effects of size, charge, viscosity and bilayer flexibility on liposomal delivery under convective...

Convective flow is one of the main mechanisms of mass transfer employed in drug delivery (e.g. osmotic pumps) and working in material transport in the body (e.g. blood circulation). Although convective flow has been investigated extensively, not much data is available on convective behavior of nanoparticles, the subject of the present investigation. Here, liposomes with different sizes, charges, bilayer flexibilities and medium viscosities were encountered convective flow and changes in their properties were monitored over 48h. For large particles (>350nm), neutral liposomes (NL) showed significant phase separation and decreased lipid content over time, while positively or negatively charged liposomes remained homogenous. Reduction of size in NLs to about 100nm resolved phase separation problem, but their lipid content still showed reduction; no such a problem was observed in charged small liposomes. When bilayer flexibility of large NLs was increased, neither phase separation nor decreased lipid content was observed. Increasing medium viscosity for large NLs from 3.4cP to 45.2cP again solved the problem and a uniform liposomal delivery was observed. These results indicate that size, charge, bilayer flexibility and viscosity affect convective liposomal delivery and that uniform delivery is possible even in large liposomes by optimizing such factors.