Preparation characterization and drug release behavior of thermo-and pH-responsive hydrogels and microspheres

Abstract

In the present work, N-isopropylacrylamide/itaconic acid and N-isopropylacrylamide /maleic acid copolymeric hydrogels were prepared by irradiating the ternary mixtures of Nisopl- opylacrylamide/diprotic acid moieties (itaconic or maleic acid)/water by y-rays at ambient temperature. The influence of external stimuli such as pH and temperature of the swelling media on the equilibrium swelling properties were investigated. The hydrogels showed both temperature and pH responses. The effect of comonomer concentration and irradiation dose on the swelling equilibria and phase transition were studied. For the characterization of network structures of these hydrogels, molecular weight between cross-links and crosslinking densities were also determined. PNIPAAm microspheres (71-500pm) were prepared by using inverse suspension polymerization technique. The selected fraction (1 80- 250pm) was used for preparing NIPAAmIitaconic acid graft copolymer by radiationinduced surface modification technique. Finally, methylene blue, sildenafil citrate and lidocaine were used as model drugs for the investigation of drug adsorption and controlled release behaviour for the hydrogels and micospheres. Specific adsorption capacity of: hydrogels are found to increase with increasing amount of itaconic acid in the gel system. The effect of the initial drug loading amount, temperature and pH of the solution on the controlled release behaviour of the hydrogels were investigated. The release studies show that some of the basic parameters affecting the drug release behaviour of the hydrogels are, pH and temperature of the solution.