Figure 2.

Crosslinking alginate gels covalently or ionically leads to substrates that are either purely elastic or exhibit stress relaxation, respectively. (a) Stress relaxation of covalently and ionically crosslinked alginate gels. Covalent crosslinking led to elastic gels that show little stress relaxation. Ionically crosslinked gels were viscoelastic and exhibited stress relaxation over time under a constant strain. (b) Shear storage and shear loss modulus as a function of frequency for ionically and covalently crosslinked gels. All values are normalized by the shear storage modulus at 1 Hz for that gel. Data are shown as mean +/− s.d., n = 3 for each data point. (c) Initial Young’s modulus of covalently (elastic) or ionically (stress relaxing) crosslinked alginate gels as measured by atomic force microscopy for different concentrations of crosslinker (see Supplementary Table 1). Data are shown as mean +/− s.d., n = 3 independent gels tested for each measurement.