Fig. 3. Mechanical characterization of BSA-hydrogels immersed in cations of various concentrations.

(A) Picture of a gel casted using a bone-shaped silicone mold (left and middle) and attached in the force-clamp rheometer (right). (B) Stress versus strain of BSA hydrogels immersed in Zn²⁺ (left) and Cu²⁺ (right) and pulled until breaking. (C) Toughness (left), failure stress (middle), and maximum elongation (right) of BSA hydrogels incubated with increasing concentrations of Zn²⁺ (magenta) and Cu²⁺(blue). Toughness increased from 1.0 ± 0.1 to 2.8 ± 0.7 kJ/mol in the presence of 1.5 M Zn²⁺ and to 2.9 ± 0.7 kJ/mol in the presence of 1.5 M Cu²⁺. The breaking stress increases from 15 ± 2 to 33 ± 5 kPa when BSA hydrogels were treated with 1.5 M Zn²⁺ and to 36 ± 5 kPa when treated with 1.5 M Cu²⁺. The failing strain shows little variation (106 ± 18% versus 107 ± 15% in 1.5 M Zn²⁺ and 146 ± 21% in 1.5 M Cu²⁺). Error bars are SD (n = 3). (Photo credit: Luai R. Khoury, UWM; Marina Slawinski, UWM).