P2 hydrogels show stiffer viscoelastic properties in MQ rather than PBS solutions in the absence of Zn(II) (Fig. A and B, respectively). However, with 0.5 equiv. of Zn(II), the P2 hydrogels in MQ have similar mechanical strength with those with absence of Zn(II), but demonstrate a slight increase in mechanical strength only when increasing the temperature from 25 to 37 °C (Fig. , Table ). P2 hydrogels in 10% PBS though become significantly stiffer and show no loss of mechanical strength or stiffness when increasing the temperature from 25 to 37 °C, but rather a slight increase in G′ to 0.304 MPa values (Fig. , Table ). Furthermore, across all conditions, G′ values consistently exceeded G′′ values, indicating the presence of viscoelastic properties characteristic of a gel. When compared to other reported selfassembling peptide hydrogels (2-6 amino acids), our metal crosslinked hydrogels (P1 and P2) display increased viscoelastic properties by at least one order of magnitude, thus clearly demonstrating potential of peptide hydrogels utilizing metals as cross linker. Additionally, the reported G′ values and thixotropy (section 3.3.2) are on the verge of suitable for injection hydrogels, as they exceed the reported limit for injectable biomaterials. Fig 7 Frequency sweep measurements were conducted for P1 (A) and P2 (B) to investigate the impact of Zn 2+ on the mechanical properties of hydrogels prepared in aqueous solution at both room temperature (25 °C) and physiological conditions (37 °C). Similarly, frequency sweep measurements were performed for P2 (C) to assess the influence of Zn 2+ on the mechanical properties of hydrogels prepared in 10% PBS solution at room (25 °C) and physiological conditions (37 °C) (P1 can't form gel under these conditions). To put the observed values into the context of other biopolymer-based hydrogels, collagen was chosen as reference compound. Both peptides outperform their collagen analogues, as illustrated in frequency sweep graphs and the above table (Fig. , Table and 2), while buffer-based hydrogels exhibit enhanced viscoelastic properties compared with their aqueous analogues. The comparison between P1 and P2 with collagen demonstrates sufficient elasticity to endure the applied stress and strain as in bioengineering applications. The thixotropic behavior of P2 hydrogels was systematically evaluated through step-strain rheology experiments. The extent of thixotropy is intricately linked to both the duration of applied shear stress, and the magnitude of the shear rate. Both metallo-hydrogels and non-metallo-hydrogels exhibit remarkable thixotropic properties based on observations of their rapid recovery to the gel-like state. Upon the stopping of the shear force, the storage modulus (G′) of the P2 hydrogel swiftly increased by more than three orders of magnitude within a few seconds. The gel-sol transition, induced by application of shear force, almost instantaneously reverses in a rapid sol-gel transition, once the shear force is discontinued (Fig. ). Interestingly, it can also be seen that the presence of Zn(II) enhances by an order of magnitude both the G′ and G′′ moduli of the P2 hydrogel, without compromising the thixotropic behavior. The remarkable thixotropic behavior and recovery capacity of our peptide hydrogels, underscores their promise as injectable carriers or candidates for 3D printing applications.