Mesoporous synthetic hectorites: A versatile layered host with drug delivery application Ghanshyam V. Joshi, Radheshyam R. Pawar, Bhavesh D. Kevadiya, Hari C. Bajaj ⇑ Discipline of Inorganic Materials and Catalysis, Central Salt and Marine Chemicals Research Institute (CSMCRI), Council of Scientific and Industrial Research (CSIR), G.B.marg, Bhavnagar-364 021, Gujarat, India article info Article history: Received 25 October 2010 Received in revised form 29 November 2010 Accepted 30 December 2010 Available online 4 January 2011 Keywords: Mesoporous synthetic hectorites Quinine Adsorption Drug delivery abstract The efficacy of mesoporous synthetic hectorites (MSH) as drug delivery carrier was examined. Mesopor- ous synthetic hectorites have been synthesized (both with and without organic template) by hydrother- mal crystallization of gels containing silica, magnesium hydroxide, lithium fluoride, and an organic template. 1,3-didecyl-2-methylimidazolium chloride (DDMI) was used as pore directing agent. The nano- composites involving quinine (QUI), an antimalarial drug adsorbed onto mesoporous synthetic hectorites were assembled. The nanocomposites were characterized by X-ray diffraction (XRD), surface area, Fourier transform infrared spectroscopy (FT-IR), and thermal analysis techniques. The decrease in the surface area and pore volume after drug adsorption suggested the adsorption of drug in the mesopores. The syn- thesized MSH–QUI nanocomposites were coated with sodium alginate (AL) via gelation technique. The in vitro drug release rate of the nanocomposites was monitored in the sequential buffer environments at 37 ± 0.5 °C. The drug release profile was dependent upon the pore size of the MSH. The drug release rate in the gastric environments was controlled by alginate coating. Different dissolution–diffusion kinetic models were applied to study the release kinetics of QUI from the carriers, and it was found that this process can be described by the Elovich equation. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Smectite clays, synthetic or natural, are an important, widely abundant, and low-cost materials with unique swelling, intercala- tion, and ion-exchange properties [1–5]. In comparison with natu- ral smectites, synthetic hectorites acquires some advantages such as (i) the pore size distribution can be controlled through synthetic methods, (ii) the purity and composition of synthetic clay is much higher compared to natural minerals, (iii) reproducibility can be controlled by synthetic routes [6,7]. As synthetic hectorites find applications in the field of catalysts, catalyst supports, and clay–polymer nanocomposites, efforts have been made to tailor both pore size and structure of the hectorites [8,9]. In a typical syn- thesis of MSH, the sol–gel is hydrothermally treated to crystallize an organic–clay composite. The structure directing agent is then removed by calcinations, generating an inorganic network with a narrow distribution of pores in the mesoporous range [7–10]. Controlled drug delivery systems may offer a range of advanta- ges to biomedicine, such as controlled drug release rate, protection from drug hydrolysis and other types of chemical degradation, pro- tection from enzymatic degradation, reduction of toxicity, and improvement of drug availability [11]. A great deal of attention has been paid in utilizing nanoporous clay minerals as drug deliv- ery carrier in pharmaceutical fields. The safety proof data of clay minerals clearly suggest them to be non-toxic for transdermal application and oral administration [12]. The advantageous surface reactivity of minerals likes adsorption, cation exchange, and swell- ing makes them key material for pharmaceutical industries [13]. Among the clay minerals, montmorillonite (MMT) [14] and layered double hydroxide (LDH) [15] are the most popular for the drug delivery application. However, there are few reports suggesting laponite, a commercially available hectorite as drug hosting mate- rial [12,16,17]. Quinine an antiprotozoal and an antimyotonic, is known for the treatment of malaria caused by Plasmodium species. Controlled re- lease form of quinine provides reduction in the adverse side effects often associated with immediate release dosage [18,19]. In the present study, we have focused on the applicability of synthetic hectorites for the drug delivery purpose. Our group has for the first time synthesized organo hectorites by using imidazolium cations as template [20]. However, to the best of our knowledge, no sys- tematic study has yet been reported on the drug delivery carrier for the synthetic hectorite/drug nanocomposites. Quinine was ad- sorbed on the hectorite clays. The clay–drug nanocomposites were systematic characterized by PXRD, surface area, FT-IR, and TGA. The clay–drug nanocomposites were further coated with alginate 1387-1811/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2010.12.040 ⇑ Corresponding author. Tel.: +91 278 2471793; fax: +91 278 2567562. E-mail address: hcbajaj@csmcri.org (H.C. Bajaj). Microporous and Mesoporous Materials 142 (2011) 542–548 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso