OBJECTIVES: Hydrogels are macromolecular networks able to absorb and release water/biological fluids in a reverse-phase manner, in response to specific environmental stimuli. Such stimuli-sensitive behavior makes hydrogels interesting for the design of smart devices applicable to a variety of technological fields. They are able to absorb and retain 10-20% and up to 1000 times the water or biological fluids than their dry weight can. The aim of this study was to extend the work on drug delivery in the stomach at pH 2-2.2. MATERIALS AND METHODS: The authors synthesized sodium alginate (SA)/poly(vinyl alcohol) (PVA) hydrogels. These hydrogels were characterized by fourier transform infrared spectroscopy and scanning electron microscopy, and the swelling properties of the hydrogels were examined at different pH values, in different salts, at different temperatures, and in different acids and bases. RESULTS: The authors studied and reported the swelling effects or variations such as the effects of salts, acids, bases, temperature, and pH. The results for the crosslinking agent glutaraldehyde showed that 8 mL of glutaraldehyde had a higher swelling rate compared to that of 10 mL and 12 mL. CONCLUSION: In this work the authors studied the swelling degree in different acids and bases. It is concluded that the degree of swelling decreases with increases in the concentration of glutaraldehyde and also depending on the concentrations of the acids. The swelling degrees of PVA/SA hydrogels gradually increase with increases in the concentrations of acids (low pH). The swelling of hydrogels decreases with increases in pH (>7) or at high alkaline. Based on the results for salt solutions the swelling behavior was found to be in the order: K>Na>Ca>Mg.