Partially hydrolyzed crosslinked alginate-graft-polymethacrylamide as a novel biopolymer-based superabsorbent hydrogel having pH-responsive Properties

Abstract

In this study, a series of highly swelling hydrogels based on sodium alginate (NaAlg) and polymethacrylamide (PMAM) was prepared through free radical polymerization. The graft copolymerization reaction was performed in a homogeneous medium and in the presence of ammonium persulfate (APS) as an initiator and N,N'-methylenebisacrylamide (MBA) as a crosslinker. The crosslinked graft copolymer, alginate-graft-polymethacrylamide (Alg-g-PMAM), was then partially hydrolyzed by NaOH solution to yield a hydrogel, hydrolyzed alginate-graft-polymethacrylamide (H-Alg-g-PMAM). During alkaline hydrolysis, the carboxamide groups of Alg-g-PMAM were converted into hydrophilic carboxylate anions. Either the Alg-g-PMAM or the H-Alg-g-PMAM was characterized by FTIR spectroscopy. The effects of the grafting variables (i.e., concentration of MBA, MAM, and APS) and the alkaline hydrolysis conditions (i.e., NaOH concentration, hydrolysis time, and temperature) were optimized systematically to achieve a hydrogel having the maximum swelling capacity. Measurements of the absorbency in various aqueous salt solutions indicated that the swelling capacity decreased upon increasing the ionic strength of the swelling medium. This behavior could be attributed to a charge screening effect for monovalent cations, as well as ionic crosslinking for multivalent cations. Because of the high swelling capacity in salt solutions, however, the hydrogels might be considered as anti-salt superabsorbents. The swelling behavior of the superabsorbing hydrogels was also measured in solutions having values of pH ranging from 1 to 13. Furthermore, the pH reversibility and on/off switching behavior, measured at pH 2.0 and 8.0, suggested that the synthesized hydrogels were excellent candidates for the controlled delivery of bioactive agents. Finally, we performed preliminary investigations of the swelling kinetics of the synthesized hydrogels at various particle sizes.

Synthesis and absorbency of gelatin-graft-poly(sodium acrylate-co-acrylamide) superabsorbent hydrogel with saltand pH-responsiveness properties

“…The reason of the swelling loss for the highly basic solutions is the charge screening effect of excess Na + in the swelling media, which shield the carboxylate anions and prevent effective anion-anion repulsion. Similar swelling-pH dependencies have been reported in the case of other hydrogel systems [35][36][37]. …”

pH-responsive carboxymethylcellulose-g-poly(sodium acrylate)/polyvinylpyrrolidone semi-IPN hydrogels with enhanced responsive and swelling properties

“…Also, the introduction of carboxyl groups endows the superabsorbent hydrogel with enhanced pH-responsive characteristics. 29 Based on above background, the pH-responsive semi-IPN superabsorbent hydrogels were synthesized by the solution polymerization reaction. The structure and morphologies of the semi-IPN hydrogels were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscope (SEM).…”

Preparation and properties of alginate/polyaspartate composite hydrogels

“…9,10 Alginate (Alg) hydrogels are proving to have a wide range of uses as biomaterials, such as a scaffold for tissue engineering, delivery vehicles for drugs, and model extracellular matrices for basic biological studies. [11][12][13] Alginate, an anionic polysaccharide composed of (1-4)-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G), has found a wide range of applications in the bioencapsulation of drugs, proteins and cells. The gelling properties of its guluronic residues with divalent ions, such as calcium, permit the formation of alginate matrices for gels, films, beads, and pellets.…”