Abstract
Hierarchical assembly of self-healing adhesive proteins creates strong and robust structural and interfacial materials, but understanding of the molecular design and structure–property relationships of structural proteins remains unclear. Elucidating this relationship would allow rational design of next generation genetically engineered self-healing structural proteins. Here we report a general self-healing and -assembly strategy based on a multiphase recombinant protein based material. Segmented structure of the protein shows soft glycine- and tyrosine-rich segments with self-healing capability and hard beta-sheet segments. The soft segments are strongly plasticized by water, lowering the self-healing temperature close to body temperature. The hard segments self-assemble into nanoconfined domains to reinforce the material. The healing strength scales sublinearly with contact time, which associates with diffusion and wetting of autohesion. The finding suggests that recombinant structural proteins from heterologous expression have potential as strong and repairable engineering materials.
Highlights
5 mm Recently, evidence of supramolecular self-assembly was found in the protein complex of squid ring teeth (SRT)[14,15]
We used differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) to show that a recombinant 18 kDa SRT protein from Loligo vulgaris (LvSRT-18kDA) has a glass transition temperature of Tg ≈ 34 °C when plasticized by water
We report self-healing of this recombinant protein, which is achieved in mild conditions, by pressing in rubbery state in aquatic media
Summary
Quantitative characterization of the self-healing was done by measuring the forces and energies needed to separate two protein surfaces after they have been joined together. To this end, we used spherical probe adhesion tests[21], where a protein-coated glass sphere (radius of curvature R = 2 0.67 mm) was pressed against a protein-coated flat glass surface under water (Figs 2A and S2). The first few experiments in water shows a large dispersion in the measurements, indicating plastic deformations in the films when repeatedly probing the same point, but in general, the adhesion was not sensitive to mild changes in the pH. We previously reported that the steady state adhesion (t ≈ days) of native SRT to glass slides is reduced when the ion concentration is increased; this does not contradict our current results, but rather shows that the steady state adhesion strength of SRT to glass is limited by
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