Peptide--silica hybrid networks: biomimetic control of network mechanical behavior

Abstract

Self-assembly represents a robust and powerful paradigm for the bottom-up construction of nanostructures. Templated condensation of silica precursors on self-assembled nanoscale peptide fibrils with various surface functionalities can be used to mimic biosilicification. This template-defined approach toward biomineralization was utilized for the controlled fabrication of 3D hybrid nanostructures. The peptides MAX1 and MAX8 used herein form networks consisting of interconnected, self-assembled beta-sheet fibrils. We report a study on the structure--property relationship of self-assembled peptide hydrogels where mineralization of individual fibrils through sol--gel chemistry was achieved. The nanostructure and consequent mechanical characteristics of these hybrid networks can be modulated by changing the stoichiometric parameters of the sol--gel process. The physical characterization of the hybrid networks via electron microscopy and small-angle scattering is detailed and correlated with changes in the network mechanical behavior. The resultant high fidelity templating process suggests that the peptide substrate can be used to template the coating of other functional inorganic materials.

Figure 1

(a) Schematic for self-assembly of MAX8 peptide. (b) Transmission electron microscopy (TEM) image of negatively stained MAX8 fibrils with monodisperse 3 nm diameter.

Figure 2

(a) TEM image of silica-coated MAX8 peptide fibrils showing dark silica shell encasing a light core of the peptide fibrils. (b) Cryo-SEM image silicified MAX8 fibrils. (c) TEM image of silicified MAX1 fibrils. (d) SEM image of silicified MAX1 fibrils showing high porosity and available void space. Samples were prepared for electron microscopy after 1 h of initial addition of the silica precursor to the hydrogel.

Figure 3

(a) Polydisperse core–shell cylinder model fits on SAXS curves of 0.5 wt % MAX1 samples with 0.04 M (○), 0.13 M (□), 0.21 M (△), 0.40 M (◇) TEOS. (b) SAXS data of kinetic series for 0.5 wt % MAX8 samples; scattering curves are grouped by boxes and represent 0.20 M (○) at 2 (red), 15 (green), and 30 (blue) min; 0.32 M(/)TMOS at 2 (red), 15 (green), and 30 (blue) min; and 0.62 M (X) at 2 (red), 15 (green), and 30 (blue) min; the inset plots radial shell thickness values (Å) observed with polydisperse core–shell cylinder fits as a function of time, and the symbols represent evolution of silica shell thicknesses for (●) 0.20 M, (■) 0.32 M, and (▲) 0.62 M TMOS in 0.5 wt % MAX8 hydrogel. (c) Polydisperse core–shell cylinder model fits on SAXS curves of 0.62 M TMOS in 0.5 wt % (△), 0.75 wt % (▽), and 1 wt % (◇) MAX8 samples. (d) Polydisperse core–shell cylinder model fits on SANS curves of 0.5 wt % MAX8 samples with 0.20 M (□) and 0.62 M (▽) TMOS.

Figure 4

Oscillatory rheology time sweep curves for (a) 0.5 wt % and (b) 0.75 wt % preassembled MAX8–TMOS silicified peptide networks: (●) 0 M, (▲) 0.20 M (◆), 0.32 M, (■) 0.62 M in 0.5 wt % MAX8 hydrogel; (c) controls; (△) 0.20 M, (□) 0. 62 M TMOS in solution without peptide.