Swelling behavior of poly (N-hydroxymethylacrylamide-co-acrylic acid) hydrogels and release of potassium nitrate as fertilizer

Poly (N-hydroxymethylacrylamide-co-acrylic acid) [P(NHMA-AAx)] hydrogels were prepared by free-radical polymerization in aqueous solution at 56°C, using N,N′-methylenebisacrylamide as the cross-linking agent. The synthesized hydrogels were subsequently investigated by a series of characterization techniques including Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis and differential scanning calorimetry analysis. The effects of comonomer composition in the feed, pH, temperature and ionic strength on the swelling behavior were studied. Results indicated that the swelling capabilities of P(NHMA-AAx) hydrogels decreased with the increase in N-hydroxymethylacrylamide (NHMA) content in the polymeric matrix and ionic strength of the medium. Additionally, the hydrogels showed both temperature and pH responses. The dynamic swelling behaviors of hydrogels at different pH values followed a non-Fickian type. The P(NHMA-AAx) hydrogels were also loaded with potassium nitrate (KNO3) as a model agrochemical, and the release kinetics of fertilizer from the hydrogels was studied as a function of KNO3 and NHMA concentrations. Moreover, various kinetic parameters, such as release exponents and diffusion coefficients, were calculated.

Swelling and Mechanical Properties of Modified HEMA-based Superporous Hydrogels

Superporous hydrogels (SPHs), based on poly(2-hydroxyethyl methacrylate) (PHEMA), were prepared by adding minute amounts of an ion-complexable hydrophilic acrylic acid. PHEMA SPHs are generally strong, but their swelling is minimal. To improve the swelling, different poly(HEMA-co-acrylic acid) hydrogels were polymerized and crosslinked, then physically treated with divalent calcium and trivalent aluminum cations. The incorporation of acrylic acid copolymer into the SPH, followed by crosslinking of the copolymer with calcium or aluminum ions produced SPHs with improved swelling and strength. Cells in the presence of hydrogel showed high viability indicating the absence of cytotoxicity and stimulatory effect.

Electroresponsive Polyacrylamide-grafted-xanthan Hydrogels for Drug Delivery

An electroresponsive drug delivery system was developed using poly(acrylamide-grafted-xanthan gum) (PAAm-g-XG) hydrogel for transdermal delivery of ketoprofen. The electrically sensitive PAAm-g-XG copolymer was synthesized by free radical polymerization under nitrogen atmosphere followed by alkaline hydrolysis. When a swollen PAAm-g-XG hydrogel was placed in between a pair of electrodes, deswelling of the hydrogel was observed in the vicinity of electrodes carrying the electric stimulus. The membrane-controlled drug delivery systems were prepared using drug-loaded PAAm-g-XG hydrogel as the reservoir and crosslinked with poly(vinyl alcohol) to form films as rate controlling membranes (RCM). The in vitro drug permeation study from the formulations was performed through excised rat abdominal skin. Drug permeation across the skin was greatly enhanced in the presence of electric stimulus as compared to passive diffusion and was found to be dependent upon the applied electric current strength and crosslink density of RCM. A pulsated pattern of drug release was observed as the electric stimulus was switched `on' and `off.' The skin histopathology study demonstrated that, after the application of an electrical stimulus, there were changes in the structure of stratum corneum and cell structure. These PAAm-g-XG hydrogel could be useful as transdermal drug delivery systems actuated by an electric signal to provide on-demand release of drugs.