Fig 1.
Model system for self-healing composite hydrogel.
A: Thermogelation is caused by triple helix formation leading to trifunctional crosslinks. B: A schematic of the composite gel; all elements are roughly to scale.
Fig 2.
Dynamic light scattering of dilute solution of SiO2 nanopartices, to which increasing amounts of protein polymers CR4 and T9-CR4-T9 have been added.
Hydrodynamic radius RH(nm) versus protein polymer concentration Cprot(g/L). Orange squares: T 9- C R4- T 9, blue circles: C R4. Error bars indicate the range observed for three repeats.
Fig 3.
Composite gel formation and final moduli for 1mM T9-CR4-T9.
A: Linear oscillatory rheology at fixed frequency and amplitude (ω = 6.28rad/s, γ = 1%) versus gelation time for different volume fractions of SiO2 nanoparticles. Dark blue: 0%, light blue: 2%, green: 3.5%, yellow: 5%, dark red: 7%. For 3.5% (green) and 7% (dark red) filler fraction, duplicates of the experiments are also given to illustrate the degree of reproducibility. B: The modulus after 10h (open symbols) and 20h (filled symbols) of gel formation; the color/symbol combination indicates the volume fraction of filler and is used for all figures, colors are as in A. The dash-dotted line indicates the linear Guth-Smallwood-Eshelby prediction (see text); the dashed line indicates a ϕ3/2 fit to indicate the nonlinear nature of the trend. The vertical dashed line indicates the boundary between the one phase (1ϕ) and two phase (2ϕ) regions.
Fig 4.
Limited compatibility of SiO2 nanoparticles with 1mM T9-CR4-T9.
Pure protein sample is transparent. Composite samples (from 2% to 7%) are slightly turbid; no obvious phase separation occurs even after 50 hours. A composite sample with 10% particles phase separates a high temperature (50°C, right).
Fig 5.
Transmittance of samples with various fractions of particles.
The vertical dashed line indicates the boundary between the one phase (1ϕ) and two phase (2ϕ) regions.
Fig 6.
A and B are from a pure protein sample pictures, small dots are proteins. C and D are from a 7% composite sample. Large dots are SiO2 nanoparticles. Intermediate concentrations and full images are available in S1 Figs.
Fig 7.
Frequency dependent storage and loss moduli G’(ω) and G”(ω) of 1mM T9-CR4-T9 composite hydrogels, at different particle concentrations.
A: Storage modulus G’(ω) versus frequency ω. B: Storage modulus G’(ω) versus particle volume fraction [%], for a number of frequencies ω, as indicated. Also indicated is the phase boundary at 7.5%. C: Loss modulus G”(ω). Color coding is the same as in Fig 3. D: The average adsorption timescale τads of the silica-protein binding is relevant for the frequency dependence of the rheology.
Fig 8.
Fracture of 1mM T9-CR4-T9 composite hydrogels for a range of volume fractions of SiO2 nanoparticles.
A: Storage modulus G’(ω) at ω = 6.28rad/s, as a function of strain γ for different fraction of SiO2 nanoparticles. Colors as in Fig 3A. B: The derivative ΔG′/Δγ measuring the change in modulus in the strain amplitude sweep. Note the logarthmic scale on the vertical axis. The peak position represents the strain at break, the full width at half the maximum (FWHM) the error bar on the peak location. Inset: strain-at-break as a function of volume fraction of SiO2 nanoparticles taken from the strain sweep of A. Colors and symbols as in Fig 3B. C: Stress τ versus strain γ at a constant shear rate of . D: strain-at-break as obtained from the flow curves in C, which we take as the fracture point (solid symbols). Open symbols are the fracture points obtained from the strain sweeps and as reproduced from B. The vertical dashed line indicates the boundary between the one phase (1ϕ) and two phase (2ϕ) regions. E: the different bond rupture mechanisms for protein-protein (pp) bond rupturing, protein-silica (ps) rupture and phase-separation induced boundary-boundary (bb) rupture as referred to in panel A.
Fig 9.
Recovery after strain sweep fracture as shown in Fig 8.
For t<0, A: Show the last part of the formation dynamics as well (see Fig 3A), which ended about 4.5 hours before the recovery process started. The intervening time was used for frequency-dependent measurements and the strain sweep. B: The modulus reduction due to fracture (ΔG’/G’max, solid symbol) and eventual recovery ratio (G’recov/G’max, open symbol) as a function of filler fraction. For ϕ = 7% the recovery ratio is larger than one as the network had not reached equilibrium yet at the end of the formation period and throughout the experiment slowly continues its strengthening. The vertical dashed line indicates the boundary between the one phase (1ϕ) and two phase (2ϕ) regions.