Synthesis and characterization of novel ..
Poly(ε-caprolactone)/Depolymerized Chitosan ..
Chitosan a biopolymer derived from chitin, the most abundant natural biopolymer next to the cellulose, is inherently biocompatible (), biodegradable () and antimicrobial (). Hence, it is a widely opted candidate for investigating its medical applications such as drug delivery, wound dressing, etc., after suitable modifications (). But its poor physical properties such as high brittleness and poor solubility require improvement to widen its medical applications particularly in drug delivery, as a carrier matrix. Many chemical and biochemical routes have been reported to modify chitosan to improve the aforesaid properties (). Among these grafting of chitosan by graft copolymerization using biocompatible and other synthetic vinyl monomers is one of the most effective methods widely employed to incorporate desirable properties into chitosan without sacrificing its biodegradable nature. Chitosan grafting using single vinyl monomers for drug delivery and other applications has been well studied (). But only limited studies have been made on chitosan grafting with two monomers for drug delivery applications. The hydrophobicity and hydrophilicity of the carrier contribute a lot in controlling the drug release characteristics apart from its flexibility. Hence, the present investigation is focused on the chitosan grafting using the hydrophilic itaconic acid (IA) and the comparatively more hydrophobic 2-hydroxyethyl methacrylate (HEMA) as comonomers and evaluation of the resulted chitosan grafts as a tunable drug carrier with tramadol hydrochloride (TRM), an opioid analgesic as a model drug. HEMA and IA were the preferred comonomers for grafting on the ground that they do not display any cell toxicity and hemolytic activity and possess good resistance toward penetration of microbes (). In addition to this introduction of itaconic acid through grafting on the surface of chitosan may impart pH sensitive swelling behavior because when the acid groups are ionized, the coiled chains extend dramatically responding to the electrostatic repulsions of the generated charges with increased uptake of solvent in the network. Moreover, the polymer–polymer and the polymer–solvent interactions show an abrupt re-adjustment in small ranges of pH and this is translated to a chain transition between extended and compacted coil states (). By introducing hydrophilic IA and comparatively more hydrophobic HEMA as comonomers in the graft, the hydrophobic–hydrophilic balance in the graft copolymer structure and their interactions between the polymeric chains and the aqueous media can be altered to control and achieve the desirable drug release characteristics.
Preparation and characterization of chitosan-graft-poly …
The proposed mechanism for the radical graft copolymerization of HEMA and IA at the reported grafting site () on CTS is shown in . Since for the increased concentration of HEMA at fixed concentrations of CTS and IA in the monomer feed, the copolymer formed are brittle and the tablet fabrication was difficult as it breaks, in the present study graft copolymers were synthesized with fixed CTS and HEMA concentrations with varying concentrations of IA. The percentages of grafting obtained for varying IA content in the feed depicted in indicates that graft copolymer yield increases only marginally with increasing IA concentration due to lower reactivity ratio of IA compared to HEMA (). The disproportionate yield of the graft copolymer with increasing concentration IA may also be attributed to the decreased adsorption of IA monomer on the copolymer with increasing IA concentration as reported in the copolymerization of HEMA and IA (). The % graft yields were calculated by taking the average of three grafting yields obtained under identical conditions for each composition and were in the range 60–80% depending on the % composition of monomers and chitosan. Since the graft copolymer is insoluble in most of the common organic solvents, its molecular weight or inherent viscosity and its NMR spectra could not be studied in the present study. But the graft copolymer swells in aqueous acetic acid.