Synthesis and evaluation of pH dependent polyethylene glycol-co-acrylic acid hydrogels for controlled release of venlafaxine HCl

pH dependent polyethylene glycol/acrylic acid(AA/PEG) hydrogels of an anti-depressant, venlafaxine hydrochloride were prepared by free-radical co-polymerization method, using benzyl peroxide (BPO) as initiator and methylene bisacrylamide (MBA) as cross-linker. Different formulations were prepared with varying concentration of polymer, monomer and cross-linker to study their effect on gel swelling, diffusion characteristics and subsequent drug release. Structural parameters of AA/PEG hydrogels were investigated by measuring diffusion co-efficient, volume fraction of polymer in the swollen state, effective molecular weight of polymer chain between cross-linking points, the number of links between two crosslink and solvent interaction parameters. Swelling coefficients were found to be increased with increase in pH i.e. minimum at pH 1.2 and maximum at pH 7.5. Increase in acrylic acid concentration increases swelling while increase in cross-linker concentration has an opposite effect due to denser structure. AA/PEG hydrogels were characterized by fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-Ray diffraction (XRD), thermo gravimetric analysis (TGA) to determine the polymer structure, its morphology and strength. Drug release studies performed at pH 1.2, 5.5 and 7.5 shows higher release at higher pH. Drug release was increased by increasing acrylic acid concentration and decreasing cross-linker concentration.