Despite weaker hydrogen bonding attraction between peptides, the serine-based peptides still form selfsupporting hydrogels at concentrations above c*. This implies that an overall charge of magnitude 2 is the more dominant factor in determining whether a self-supporting, percolating gel network is formed . These observations and conclusions reinforce predictions from a previously reported theoretical model that attempted to determine the self-assembly energetics of this system. This model predicted that the overall charge of the system had a greater influence over the degree and strength of self-assembly rather than the precise amino acid choice . Even though the change in polar amino acid does not affect hydrogel formation, these chemical changes in peptide structure can be used to tune the physical properties of the hydrogel. In particular, the mechanical properties of the hydrogel are dependent on the cohesive energy between peptide molecules. The rheological properties of these P11 peptide hydrogels are measured and compared in Figure . The elastic moduli (G') for the glutamine-based peptides (P11-4 (Q,-2) and P11-8 (Q,+2)) are higher than those of the comparative serine-based peptides (P11-9 (S,-2) and P11-12 (S, +2)) by two or three orders of magnitude respectively. From simple tube inversion experiments, it can also be seen that the serine-based hydrogels are weak enough to break and flow under gravity (also demonstrated by the high phase angle of P11-12 (S,+2) gels). This compares with glutamine-based peptide gels that do not flow under gravity. Taken together, this demonstrates that the increased intermolecular hydrogen bonding in a glutamine-based peptide generates a stiffer gel than a corresponding serine-based peptide gel under the same conditions. While highly charged peptides were not observed to self-assemble under physiological conditions, our finding that the overall magnitude of the charge is the dominant factor for gelation suggested that these peptides might gel in a combination where the overall net charge of the peptide assemblies was reduced to within the range required for gel formation (~ +/-2). To test this hypothesis, we combined the peptides P11-13 (Q,-6) and P11-14 (Q,+4) in an equimolar ratio to see if this could induce self-assembly. Neither peptide underwent self-assembly in isolation under physiological conditions at any concentration.