Calculations of the magnitude of responsivities in pH-, temperature- and ion- responsive hydrogels

Abstract

Stimuli-responsive hydrogels (SRHs) were prepared by thermal free radical redox polymerization in the aqueous solution of N-isopropyl acrylamide (NIPAAm), acrylamide (AAm) with any weak organic acid (such as propenoic acid, cis-butenedioic acid, crotonic acid, methacrylic acid, methylfumaric acid, itaconic acid, aconitic acid in the presence of N,N′ -methylene bisacrylamide. DSC thermograms were taken to find the transition zone parameters of SRHs. Swelling studies were carried out to determine the effects of stimuli such as temperature, pH, and ionic strength on the swelling-shrinkage behavior of SRHs and to calculate the magnitude of the stimuli. A sigmoidal equation was used to calculate the parameters such as transition point, the magnitude of the stimulus, minimum and maximum swelling, the amplitude of the transition zone, etc. of the temperature or pH transition zones of SRHs, while the exponential decay equation was used to calculate the parameters of the swelling-ionic strength relationship of the same gels. With the idea that SRHs can be used as a biomaterial, swelling values of SRHs at the pH values of the body fluids at 37 ◦C were calculated with the help of these sigmoidal equation parameters. Similarly, swelling values of SRHs in hypertonic, isotonic, and hypotonic saline solutions were determined with the help of these exponential decay equation parameters. In conclusion, calculating the responsivity magnitude with the sigmoidal equation or exponential decay equation approach can be a useful tool for chemists, chemical engineers, bioengineers, biomedicine, bio materials, polymer, and plastic scientists to find the transition zone parameters of stimuli-responsive hydrogels.