Research Article Development of a Controlled Release of Salicylic Acid Loaded Stearic Acid-Oleic Acid Nanoparticles in Cream for Topical Delivery J. O. Woo, 1 M. Misran, 1 P. F. Lee, 2 and L. P. Tan 3 1 Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia 2 Mechatronics and BioMedical Engineering, Faculty of Engineering & Science, Universiti Tunku Abdul Rahman, Setapak, 53300 Kuala Lumpur, Malaysia 3 Prime Oleochemical Industries Sdn. Bhd., Taman Perindustrian Jaya, 47301 Petaling Jaya, Selangor, Malaysia Correspondence should be addressed to J. O. Woo; juinonn@siswa.um.edu.my Received 30 August 2013; Accepted 28 October 2013; Published 21 January 2014 Academic Editors: K. Lan and N. Micale Copyright © 2014 J. O. Woo et al. Tis is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Lipid nanoparticles are colloidal carrier systems that have extensively been investigated for controlled drug delivery, cosmetic and pharmaceutical applications. In this work, a cost efective stearic acid-oleic acid nanoparticles (SONs) with high loading of salicylic acid, was prepared by melt emulsifcation method combined with ultrasonication technique. Te physicochemical properties, thermal analysis and encapsulation efciency of SONs were studied. TEM micrographs revealed that incorporation of oleic acid induces the formation of elongated spherical particles. Tis observation is in agreement with particle size analysis which also showed that the mean particle size of SONs varied with the amount of OA in the mixture but with no efect on their zeta potential values. Diferential scanning calorimetry analysis showed that the SONs prepared in this method have lower crystallinity as compared to pure stearic acid. Diferent amount of oleic acid incorporated gave diferent degree of perturbation to the crystalline matrix of SONs and hence resulted in lower degrees of crystallinity, thereby improving their encapsulation efciencies. Te optimized SON was further incorporated in cream and its in vitro release study showed a gradual release for 24 hours, denoting the incorporation of salicylic acid in solid matrix of SON and prolonging the in vitro release. 1. Introduction Solid lipid nanoparticles (SLNs) are colloidal particles com- posed of lipids. Tey are colloidal carrier systems that are usually applied in the area of controlled drug delivery and cosmetic and pharmaceutical applications [1–3]. Te rapid development in SLN research is due to their negligible toxicity and biocompatibility with the human body. Besides, the preparation method is more environmentally friendly as less organic solvent is required [4]. Although SLN demonstrated several advantages as excip- ient, it does have limitation especially low encapsulation capacity and expulsion of drug during storage which led to the development of new generation of lipid nanoparticles which is also generally known as nanostructured lipid carri- ers (NLCs) [4]. NLC are SLN incorporated with liquid oil to improve encapsulation efciency and reduce drug expulsion. Incorporation of liquid oil into solid lipid matrix could lead to a massive crystal lattice disturbance and leaves enough space to accommodate drug molecules, and thus, improve active ingredient encapsulation efciency [2, 5]. SLN and NLC can be prepared from diferent types of starting material such as triglycerides, phospholipids, and waxes [6–9]. Among them, fatty acid is one of the most cost efective raw materials and therefore has been widely used in order to reduce the production cost. Terefore, fatty acids were used as raw material in the preparation of SONs in order to develop a cost efective carrier system. Salicylic acid is a common active ingredient used in topi- cal formulation [10] for therapeutic treatment such as acne due to its keratolytic property [11]. However, it may cause a mild to strong skin irritation to certain patients [12]. Hindawi Publishing Corporation e Scientific World Journal Volume 2014, Article ID 205703, 7 pages http://dx.doi.org/10.1155/2014/205703