pH Sensitive Interpenetrating Network Microgels of Sodium Alginate-Acrylic Acid for the Controlled Release of Ibuprofen V. Ramesh Babu, K. S. V. Krishna Rao, M. Sairam, B. Vijaya Kumar Naidu, Kallappa M. Hosamani, Tejraj M. Aminabhavi Drug Delivery Division, Center of Excellence in Polymer Science, Karnatak University, Dharwad 580003, India Received 15 April 2005; accepted 26 July 2005 DOI 10.1002/app.22760 Published online 19 December 2005 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: pH-Sensitive interpenetrating network (IPN) microgels (MGs) of sodium alginate (NaAlg) and acrylic acid have been prepared by using water-in-oil (W/O) emul- sion technique. The MGs were characterized by Fourier transform infrared spectroscopy (FTIR), differential scan- ning calorimetry (DSC), X-ray diffractometer (X-RD). The release of ibuprofen (IB), an anti-inflammatory drug, from these MGs was studied in pH 1.2 and 7.4 media. MG net- work consists of NaAlg, which disintegrates in the intestinal fluid, while poly(acrylic acid) provides pH-sensitivity to the microgel network. The system developed in this study showed a pH-sensitivity for the release of IB, which was attributed to the diffusion controlled release of the drug through the surfaces of MGs that undergo disintegration after swelling, depending upon the chemical composition of MGs and pH of the medium. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 2671–2678, 2006 Key words: sodium alginate; acrylic acid; IPNs; drug deliv- ery INTRODUCTION Biodegradable polymers have been extensively used to develop controlled release (CR) formulations 1–3 to decrease the release rates of the drugs having short plasma life. Among the various polymers employed, hydrophilic biopolymers are quite suitable in oral ap- plications 4 due to their inherent advantages over the synthetic polymers. Sodium alginate (NaAlg), a natu- ral polysaccharide, composed of d-mannuronic acid and d-guluronic acid is derived from brown sea- weeds. This polysaccharide has been used extensively in food industry as a gelling agent and for encapsula- tion of living cells. 5–7 NaAlg is a biodegradable poly- mer that has been used in drug delivery applica- tions. 8 –10 Earlier literature cites many applications of NaAlg in agriculture 11–13 after when it is crosslinked with glutaraldehyde. From a search of the literature, we find no studies on the use of NaAlg and acrylic acid for the CR of nonsteroidal anti-inflammatory (NASID) drugs. This prompted us to undertake a de- tailed study on the CR of ibuprofen (IB), a water insoluble drug. Pure IB is a nonsteroidal anti-inflam- matory drug used extensively in the treatment of var- ious musculo-skeletal disorders and painful condi- tions. The drug has proven its therapeutic efficacy, tolerability, and safety in the treatment of rheumatoid arthritis, osteoarthritis, and ankylosing spondylitis for the quick relief of pain. 14 However, its short plasma half-life of 1–3 h following oral dosing 15 necessitates frequent administration to maintain the desired con- stant levels. IB can be readily absorbed throughout the gastro-intestinal tract and can be eliminated rapidly after administration. In this research, we have devel- oped the CR, formulations of IB with NaAlg and acrylic acid. Earlier, CR of antihypertensive drugs through the tableted microspheres of cellulose deriv- atives have been reported. 16 –18 In continuation of our ongoing program of research, 19,16 we report here the in vitro CR data for IB through the interpenetrating network (IPN) of microgels (MGs) prepared from NaAlg and acrylic acid in different compositions. Ef- fect of acrylic acid content, crosslinking agent, and drug concentration on the release rates of IB has been investigated. EXPERIMENTAL Materials and methods Acrylic acid, sodium alginate (low viscosity), potas- sium persulfate, light paraffin oil, and glutaraldehyde (25% aqueous solution; GA) were purchased from s.d. Fine Chemicals, Mumbai, India. Tween-80 was pur- chased from Sigma Chemical Co. Ibuprofen (purity Correspondence to: T. M. Aminabhavi (aminabhavi@yahoo. com). Journal of Applied Polymer Science, Vol. 99, 2671–2678 (2006) © 2005 Wiley Periodicals, Inc.