INTRODUCTION The term hydrogels was originally introduced by Wichterle and Lim in 1960s and its biological application was put forward. 1 Since then, hydrogel technology has evolved at a huge scale in pharmaceutical industry. The term hydrogel is self explanatory for their existence, since the evolution of life on earth. The structure of plants, the components of extracellular matrix, the bio-films of microorganisms are everywhere, all the swollen moieties in nature are the proofs of their occurrence. The first paper sighted was by DuPont scientist in 1936 for medical applications, which introduced the spark that was enlightened in 1960 by Wichlerte and Lim who worked on poly (2- hydroxyethylmethacrylate) poly(HEMA). 1 It highlighted the properties of this brittle polymer as ORIENTAL JOURNAL OF CHEMISTRY www.orientjchem.org Est. 1984 An International Open Free Access, Peer Reviewed Research Journal ISSN: 0970-020 X CODEN: OJCHEG 2013, Vol. 29, No. (3): Pg. 861-870 Hydrogels: Smart Materials for Drug Delivery ARTI VASHIST and SHARIF AHMAD* Department of Chemistry, Jamia Millia Islamia, New Delhi - 110 025 India. *Corresponding author E-mail: sharifahmad_jmi@yahoo.co.in DOI: http://dx.doi.org/10.13005/ojc/290303 (Received: July 12, 2013; Accepted: August 04, 2013) ABSTRACT The limitations associated with the conventional therapeutics have intended the use of controlled drug delivery systems. In recent years, the hydrogel technology has been an integral part of human health care. The pharmaceutical industry has been developing hydrogel based drug delivery system in an advanced manner by tuning the structure, shape and surface modifications of the biopolymers. The present review highlights the role of hydrogels in drug delivery. It also highlights the use of important polymers and their applications in drug delivery. In addition, the use of nanocomposite hydrogels with reference to the inorganic and magnetic nanoparticles is also discussed. Key words: Hydrogels, Drug delivery, Biomaterials, Starch, Nanocomposite. a highly water swollen, soft and elastic gel. This led to the keen interest in hydrogels as a class of biomaterials and their application as drug delivery systems. The natural and synthetic polymer in demand for the synthesis of DDS is tabulated below. The emphasis in this review is to highlight the few special biopolymers like hydroxyethylcellulose (HEC), Poly (lactic –glycolic acid) (PLGA), starch, NIPAAm (N-isopropylacrylamide). Hydrogels are defined as a three dimensional biopolymeric networks, which have the tendency to absorb large quantity of water and they themselves are not soluble in water. A three dimensional network formation occurs by the cross linking of the polymeric chains. This cross linking can occur via physical interactions, covalent bonding, hydrogen bonding and by van der walls interactions. 2 The chemistry behind the interpenetrating hydrogel