No abstract

A novel approach was developed to prepare a superporous hydrogel with superior mechanical and elastic properties. According to this method, a synthetic monomer was polymerized and crosslinked in the presence of a water-soluble alginate polymer. Later in the process, the alginate part of the synthesized hydrogel was treated with metal cations, which resulted in a hydrogel hybrid with an interpenetrating network structure. In this article, a hydrogel hybrid of acrylamide and alginate is highlighted because of its unique swelling and mechanical properties. This hydrogel hybrid shows resilience and a rubbery property in its fully water-swollen state, which not previously been reported. To help understand the underlying mechanism responsible for such unique properties with hydrogel hybrids, the ionotropic gelation of the alginate polymer was also studied in more detail.

Superporous hydrogels (SPHs) were originally developed as a novel drug delivery system to retain drugs in the gastric medium. These systems should instantly swell in the stomach and maintain their integrity in the harsh stomach environment, while releasing the pharmaceutical active ingredient. For years, the synthetic features and properties of these SPH materials have been modified and improved to meet the requirements for gastric retention applications. Furthermore, an instant swelling hydrogel has also shown potential application for peroral intestinal peptide and protein absorption. This review discusses the formulation, characterization, properties and applications of these polymers.

Superporous hydrogels (SPHs), based on poly(2-hydroxyethyl methacrylate) (PHEMA), were prepared by adding minute amounts of an ioncomplexable hydrophilic acrylic acid. PHEMA SPHs are generally strong, but their swelling is minimal. To improve the swelling, different poly(HEMA-coacrylic 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.

Semi-interpenetrating polymer network (semi-IPN) superporous hydrogels (SPHs) based on poly(3-sulfopropyl acrylate, potassium salt) (PSPA) and linear polymers were synthesized using poly(ethylene glycol) diacrylate (PEGDA) or N,N′-methylenebisacrylamide (BIS) as a crosslinker. The swelling ratio of SPHs was determined by measuring the weight of absorbed water; and the mechanical strength of swollen SPHs was evaluated using texture analyzer. Taguchi orthogonal experimental design [L9(34)] was used to evaluate the influence of four factors, consisting of the ratios of 3-sulfopropyl acrylate (SPA) to PEGDA, to initiator, and to acrylic acid (AAc), and acidification of PSPASPHs, with each containing three levels on the swelling ratio and mechanical strength of semi-IPN PSPA-SPHs. Analysis of variance (ANOVA) of the experimental design results was carried out using a SAS program. The structure of SPHs was examined using a scanning electron microscope (SEM). Among the polymers evaluated, poly(vinyl alcohol) (PVA) was the best linear polymer to improve the mechanical strength of swollen SPHs. ANOVA indicated that the ratio of SPA to PEGDA and to an initiator, as well as acidification had significant effects on the swelling ratios of PSPA-SPHs. The ratio of SPA to AAc and acidification had significant effects on the mechanical strength, which deceased with increased swelling ratio and time. The optimized semi-IPN PSPA-SPH containing 5% w/w PVA had a swelling ratio 20 times greater within minutes and then up to 40 times. The mechanical strength was over 200 g/cm2 for a fully swollen gel in a pH 1.2HCl medium. The optimal PSPA-SPH has swelling and mechanical properties suitable for development of gastro retentive drug delivery systems.