Swelling/deswelling of anionic copolymer gels

Area of Science:

• Polymer Science
• Materials Science
• Biomedical Engineering

Background:

• Ionic gels are vital for controlled drug delivery systems.
• Understanding fluid diffusion in gels is key for site-specific applications.
• Polymeric networks of poly(2-hydroxyethyl methacrylate) with methacrylic or acrylic acid were investigated.

Purpose of the Study:

• To investigate the dynamic and equilibrium swelling properties of ionic gels.
• To determine the influence of pH, ionic strength, counterion, and buffer composition on gel swelling.
• To elucidate the water diffusion mechanisms within these polymeric networks.

Main Methods:

• Studied swelling properties of poly(2-hydroxyethyl methacrylate-co-methacrylic acid) and poly(2-hydroxyethyl methacrylate-co-acrylic acid) gels.
• Varied pH, ionic strength, counterion type, and buffer composition of the swelling medium.
• Analyzed water diffusion mechanisms, classifying them as Fickian or anomalous.

Main Results:

• Water diffusion became more anomalous with increasing pH and decreasing ionic strength (at pH ≥ pKa,gel).
• Fickian diffusion was observed in unbuffered media at pH 4.0 (below pKa,gel).
• Diffusion mechanism at pH 4.0 was independent of ionic strength; pKa,gel was between 5.5 and 6.

Conclusions:

• Gel swelling behavior is governed by ion osmotic swelling pressure and ion exchange kinetics.
• Diffusion mechanisms are sensitive to environmental factors like pH and ionic strength.
• Findings provide insights into designing ionic gels for effective controlled drug delivery.