Effects of swelling on the mechanical properties of a pH-sensitive hydrogel for use in microfluidic devices

Tensile tests were conducted on a 2-hydroxyethyl methacrylate (HEMA)–acrylic acid (AA) comonomer gel sensitive to variations in environmental pH. Mechanical properties (Youngʹs modulus, Poissonʹs ratio, ultimate tensile strength, and percent elongation at break) were determined at different levels of swelling equilibrium. Shifts in ultimate tensile strength (from 300 to 60 kPa) and percent elongation at break (from 150% to 30%) were observed between samples tested in the swollen and unswollen states. Additional tests were conducted to determine the effects of crosslinking and polymerization conditions on mechanical properties. Increasing the crosslinker component from 0.2% to 1% resulted in an increase in Youngʹs modulus (34 to 380 kPa) by an order of magnitude. It is found that adjustment of the crosslinker component of the hydrogel is an effective method of controlling mechanical properties.