Compressive and shear properties of alginate gel: Effects of sodium ions and alginate concentration

The equilibrium and viscoelastic properties of alginate gel crosslinked wit h Ca2+ were determined as a function of alginate concentration and duration of exposure to physiologic concentrations of NaCl. Compressive and shear s tress relaxation tests and oscillatory shear tests were performed to measur e the material properties at two time periods after storage in NaCl compare d to no NaCl exposure. The effect of concentration was determined by testin g 1-3% alginate gel in a bath of physiological NaCl and CaCl2. After 15 h o f exposure to NaCl, the compressive, equilibrium shear, and dynamic shear m oduli decreased by 63, 84, and 90% of control values, respectively. The mat erial properties exhibited no further changes after 7 days of exposure to N aCl. The loss angle and amplitude of the relaxation function in the shear a lso decreased, indicating less viscous behaviors in both dynamic and transi ent configurations. All moduli, but not the loss angle, significantly incre ased with increasing alginate concentration. The observed decrease in compr essive and shear stiffness for alginate gel after exposure to Na+ was signi ficant and indicated that physiological conditions will soften the gel over a time period of up to 7 days after gelation. The alginate gel retains sig nificant solidlike behaviors, however, as measured by a loss angle of appro ximately 3 degrees. This study provides the first available data for materi al properties of alginate gel tested in physiological saline. (C) 1999 John Wiley & Sons, Inc.