Physicochemical studies on local anaesthetic loaded second generation nanolipid carriers

This study aimed to investigate the effect of hydrocarbon chain length of nonionic surfactants, Tween 40 and Tween 60, on the physicochemical properties of nanostructured lipid carriers (NLCs). Two local anaesthetics, lidocaine (LIDO) and procaine hydrochloride (PRO·HCl), were incorporated in the NLCs. NLC formulations were prepared using sorbitantristearate (Span 65), soy lecithin (SLC) and stearic acid (SA) in a 2:2:1 mole ratio employing the hot homogenization technique. The systems were characterized by combined dynamic light scattering (DLS), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and spectroscopic studies. The formulations were found to be stable up to 60 days when kept at 4°C. NLCs stabilized by Tween 60 were superior to the corresponding Tween 40 based formulations. A spherical morphology with smooth surfaces was evidenced by TEM measurements. DSC and polarity studies indicated that LIDO altered the crystallinity of the lipid matrices as it could insert into the core of the NLC. Entrapment efficiency (EE) and loading content (LC) studies revealed that Tween 60 stabilized NLCs have better drug loading capability than the Tween 40 based formulation. Controlled and prolonged drug release was experienced by Tween 60 stabilized drug loaded NLCs as studied by in vitro release kinetics. The developed NLCs could thus be considered to have prospects as novel drug carriers for controlled/sustained release to improve the time duration of anaesthesia, especially for topical application.