Abstract
In this study, we fabricated pH-sensitive polyvinylpyrrolidone/acrylic acid (PVP/AA) hydrogels by a free-radical polymerisation method with variation in the content of monomer, polymer and cross-linking agent. Swelling was performed in USP phosphate buffer solutions of pH 1.2, 5.5, 6.5 and 7.5 with constant ionic strength. Network structure was evaluated by different parameters and FTIR confirmed the formation of cross-linked hydrogels. X-ray crystallography showed molecular dispersion of tramadol HCl. A drug release study was carried out in phosphate buffer solutions of pH 1.2, 5.5 and 7.5 for selected samples. It was observed that swelling and drug release from hydrogels can be modified by changing composition and degree of cross-linking of the hydrogels under investigation. Swelling coefficient was high at higher pH values except for the one containing high PVP content. Drug release increased by increasing the pH of the medium and AA contents in hydrogels while increasing the concentration of cross-linking agent had the opposite effect. Analysis of the drug release mechanism revealed non-Fickian transport of tramadol from the hydrogels.
Highlights
Hydrogels are three-dimensional, water-swollen, cross-linked polymeric networks
Swelling behaviour of hydrogels plays an important role in controlled drug release behaviour
It is obvious that there is a significant variation in the degree of swelling at different pH values
Summary
Hydrogels are three-dimensional, water-swollen, cross-linked polymeric networks. They are able to retain water due to the presence of hydrophilic functional groups attached to their backbone (Satish et al, 2001; Şahiner et al, 2005; Hussain et al, 2011) while their resistance to dissolution arises from the presence of a chemically or physically cross-linked network (Lin, Metters, 2006). Devine (Devine, Higginbotham, 2005), Hafeez (Hafeez et al, 2005), Kadlubowski (Kadłubowski et al, 2007) and Bajpai (Bajpai et al, 2005) have prepared PVP/AA hydrogels and addressed different issues including gel strength, immobilisation of TiO2 nanoparticles, chemical sensor properties and comparison of vitamin B12 release behaviour through traditional dissolution apparatus and flow-through diffusion cells, respectively. These studies never combined detailed analysis of network parameters necessary for the final application, different factors affecting swelling, drug release and nature of drug after encapsulation and analysis of release pattern. The state of the encapsulated drug and release behaviour of a model hydrophilic drug was evaluated in optimum formulations
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