Fig. 3. In situ mineralization increases gel stiffness with minimal use of minerals.

The change in the stiffness (ΔG_p, left axis, blue bars, the difference between the moduli of mineral-containing gels and their corresponding mineral-free metal-ion crosslinked gels), maximum magnetization (M_max, middle axis, green bars, from Supplementary Fig. 7) and the mineral volume fraction (Φ_maximum, right axis, orange bars) of conventional Fe₃O₄ nanoparticle gels (from ref. ¹⁵) and In Situ gels (this work). The gel stiffness increases by ~35,000 Pa upon in situ incorporation of only ~0.2 vol% minerals but decreases by ~5000 Pa upon traditional incorporation of ~2 vol% pre-synthesized nanoparticles. The M_max increases linearly with each in situ mineralization cycle without compromising stiffness. The asterisk indicates that the gel magnetic properties were not quantified in this past work¹⁵. The error bars indicate standard deviations from three independent samples.