The concept of IPN goes back at least as far as 1914 when the first interpenetrating polymer network was invented by Aylsworth [10]. This was a mixture of natural rubber, sulphur, and partly reacted phenol-formaldehyde resins. The term IPN was introduced for the first time by Miller in 1960s in a scientific study

about polystyrene networks [11]. Since that time the field of IPN has expended dramatically. Figure 1 (a) A polymer blend; (b) a graft copolymer; (c) a block copolymer; (d) semi-IPN; (e) full IPN; F- cross-linked copolymer. Advances in polymer science have led to the development of several novel drug delivery systems. IPNs have shown superior performances over Inhibitors,research,lifescience,medical the conventional individual polymers Inhibitors,research,lifescience,medical and, consequently, the ranges of applications have grown rapidly for such class of materials. The advanced properties of IPNs have attracted considerable attention in pharmaceutical field especially in the area of drug delivery. These biocompatible, nontoxic,

and biodegradable polymer networks are now acquiring unique place in delivering bioactive molecules, particularly in fda approved controlled and targeted drug delivery applications. Various research investigations have shown that a variety of drugs can be delivered effectively via IPN based delivery systems (Table 1). Table 1 Delivery of variety of drugs via different IPN based novel carriers. Inhibitors,research,lifescience,medical 2. Classification of IPN 2.1. Based on Chemical Bonding [12] 2.1.1. Covalent Semi-IPN When two separate polymer systems that are cross-linked form a single polymer network, it Inhibitors,research,lifescience,medical is called covalent semi-IPN. 2.1.2. Noncovalent Semi-IPN In noncovalent semi-IPNs only one of the polymer systems is cross-linked. 2.1.3. Noncovalent Full IPN A noncovalent full IPN is one in which the two separate polymers are cross-linked independently. 2.2. Based on Method of Synthesis IPNs are of different types: sequential IPN, subsequent IPN, latex IPN, gradient IPN, and thermoplastic Inhibitors,research,lifescience,medical IPN. 2.2.1. Sequential IPN In sequential IPN, the first cross-linked polymer network is swollen by the monomer of the

second polymer that is Entinostat polymerized and/or cross-linked afterwards. In this class an IPN is formed by polymerizing the first mixture of monomer (I), cross-linker, and initiator to form a network. The network is swollen with the second combination of monomer (II) and cross-linker which is polymerized to form an IPN [6]. Sequential IPNs are easy to synthesize. The primary requirement is that monomer (II) and coreactants swell properly into polymer network I. Usually elastomers are used for network I because they swell easily compared to glassy network (Figure 2). Figure 2 Sequential IPN formation. 2.2.2. Simultaneous IPN An IPN is formed by polymerization of two different monomer and cross-linking agent pairs together in one step [6, 7].

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