Differential scanning calorimetry studies on sunscreen loaded solid lipid nanoparticles prepared by the phase inversion temperature method

Solid lipid nanoparticles (SLN) are regarded as interesting carriers to improve sunscreens' safety and effectiveness. In this work, surfactant effects on the physico-chemical properties of SLN loading two of the most widely used UV-filters, octylmethoxycinnamate (OMC) and butylmethoxydibenzoylmethane (BMBM), were evaluated and the interactions between SLN components and loaded UV-filters were investigated by differential scanning calorimetry (DSC). All the SLN showed a mean size ranging from 30 to 95 nm, and a single peak in size distribution. The use of isoceth-20 or oleth-20 as primary surfactants did not provide SLN with suitable physico-chemical properties since: (a) OMC loaded SLN proved unstable; (b) BMBM could not be loaded. OMC or BMBM loaded SLN prepared using ceteth-20 as primary surfactant were stable but their loading capacity lowered when both sunscreens were loaded simultaneously. DSC analyses showed that OMC distributed inside the SLN and caused a decrease of the lipid matrix molecules cooperativity while BMBM did not affect SLN calorimetric behaviour. When OMC and BMBM were loaded together into these SLN, an interaction between BMBM and OMC occurred. These results suggest that the interactions between sunscreens and between sunscreens and SLN components deserve further investigation to evaluate their effect on UV-filter-loaded SLN effectiveness. (C) 2011 Elsevier B.V. All rights reserved.