SLNs can Serve as the New Brachytherapy Seed: Determining Influence of Surfactants on Particle Size of Solid Lipid Microparticles and Development of Hydrophobised Copper Nanoparticles for Potential Insertion

Abstract

Solid lipid nanoparticles (SLNs) or technically speaking, larger solid lipid microparticles are emerging as a noninvasive technique for drug-delivery, carrying forward advantages of conventional nanostructured systems and eliminating their drawbacks. This study involves the analysis of solid lipid microparticles generated via hot high-shear homogenization technique with tristearin as the main lipid component and phosphate buffer (pH 7.00) as the aqueous phase (phase volume 0.2). This study aims to identify the effects of the chosen lipid, and four non-ionic surfactants (Tween®20, Tween®80, Lutrol F68 and Lutrol F127) on particle size of solid lipid microparticles. Samples generating particle sizes of less than 200 nm were further analysed via SEM to determine morphological characteristics of SLNs. SLN composition is crucial as it determines various chemical and physical properties of the particle itself. Firstly, selection of lipids is key, as it the major component of the particle. Lipids display different polymorphic transitions upon crystallization affecting loading efficiency, drug distribution, drug loading, particle size, particle shape and overall stability. Secondly, selection of surfactants is vital as they overcome stability problems with reducing surface tension, particle aggregation and steric interactions. The aim of this study was to determine the optimal functioning surfactant concentration that would produce particle sizes less than 200 nm. SLNs generated in this study displayed a reduced particle size (90-150 nm) when using 2% w/v Tween®80 plus 5:1 F68; higher molecular weight surfactant, with a low molecular weight poloxamer. Based on previous research, these results can be explained via the surfactant characteristics in solution. The length of the fatty acid chains associated with Tween®20 and 80 provide a potential behavioural pattern on the SLN; longer chains surrounding the SLN structure increase stability of the particle but also increase particle size. Poloxamer use is that of a co-surfactant, fulfilling what Tween® fails to complete. In which higher molecular weight poloxamers can potentially explain the large particle size as the longer PEO terminal chains protrude from the particle after its insertion.