Abstract
Swellable polymers that respond to pH (including a portion of the physiological pH range) have been prepared from N-isopropylacrylamide (NIPA) copolymerized with acrylic acid, methacrylic acid, ethacrylic acid or propacrylic acid by dispersion polymerization. When the swellable polymer particles are dispersed in a polyvinyl alcohol (PVA) hydrogel membrane, large changes occur in the turbidity of the membrane (which is measured using an absorbance spectrometer) as the pH of the buffer solution in contact with the hydrogel membrane is varied. The swelling of the NIPA copolymer is nonionic, as the ionic strength of the buffer solution in contact with the PVA membrane was increased from 0.1 to 1.0 M without a decrease in the swelling. For many of these NIPA copolymers, swelling was also reversible in both low- and high ionic strength pH-buffered media and at ambient and physiological temperatures. The composition of the formulation used to prepare these copolymers of NIPA can be correlated to the enthalpy and entropy of the pH-induced swelling.
Highlights
PH is routinely measured in the laboratory using a glass electrode [1]
A unique aspect of this study is the use of light crosslinking in the preparation of these NIPA polymers, as many of the formulations used limited the amount of crosslinker, N,N-methylene bisacrylamide (MBA), to 5%
Crosslinked polymers of NIPA copolymerized with an alkyl acrylic acid swell and shrink in response to changes in pH when placed in aqueous media
Summary
PH is routinely measured in the laboratory using a glass electrode [1]. The necessity for continued recalibration and the dependence of the liquid junction potential on solution composition and concentration have limited the application of glass electrodes in clinical, biomedical, and biotechnological analyses. There has been considerable interest in the in-vivo pH sensing of blood during surgery for patients who suffer from tissue ischemia [2], the glass electrode is too bulky for invasive tissue analysis. Conventional glass pH electrodes have been adapted to fermentation reactions and bioreactors, they suffer from several drawbacks, including the necessity for pressurized compensation of the electrolyte and interference by other components (e.g., proteinaceous materials) in the medium
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