DLS determination of the total micelle volume (TMV) in polymer micelle systems

Purpose: Amphiphilic polymers form polymer micelles in aqueous solution and entrap lipophilic drugs in the inner core. In this work we want to evaluate the potential capacity of substituted PVA to solubilize lipophilic drugs, by determining the available total micelle volume, using light scattering technique. Methods: PVA reacts with oleoyl and linoleoyl chloride to introduce a hydrophobic chain (PVA-OL, PVA-LINOL). DLS measurements were carried out on the polymers and the drug-polymer solutions, to define the characteristics of polymer aggregates. Results: The product between the mean diameter of each aggregate and the counts per second indicate TMV and can predict the complexing ability of the amphiphilic micelles towards hydrophobic drugs. TMV was found higher for PVA-LINOL than PVA-OL and increased increasing the polymer concentration in solution. Differences can be attributed to the larger hydrophobic domains created by the presence of the linoleoyl moiety. The increase in temperature increased TMV of both polymers, due to the increased micelle size, as counts decreased. In the presence of the drug, the micelle size was always higher than that of the polymers alone, while the counts were found constant, indicating that the complexation of the drug in the micelles do not require a reorganization of the aggregation status of the polymer in solution. Conclusion: PVA-OL and PVA-LINOL form micelles able to encapsulate lipophilic drugs. The parameters increasing TMV, such as acyl chain steric hindrance, increased polymer concentration, increased temperature, improve the complexing ability of the polymer micelles towards the drugs. Their stability towards the drug release and the possibility to reduce their diameter by filtration make these systems particularly interesting for passive drug targeting in tumour tissues.