Bioinspired stretchable molecular composites of 2D-layered materials and tandem repeat proteins

Protein based composites, such as nacre and bone, show astounding evolutionary capa-bilities, including tunable physical properties. Inspired by natural composites, we studied assembly of atomistically thin inorganic sheets with genetically engineered poly-meric proteins to achieve mechanically compliant and ultra-tough materials. Although bare inorganic nanosheets are brittle, we designed flexible composites with proteins, which are insensitive to flaws due to critical structural length scale (similar to 2 nm). These pro-teins, inspired by squid ring teeth, adhere to inorganic sheets via secondary structures (i.e., beta-sheets and alpha-helices), which is essential for producing high stretchability (59 +/- 1% fracture strain) and toughness (54.8 +/- 2 MJ/m3). We find that the mechanical proper-ties can be optimized by adjusting the protein molecular weight and tandem repetition. These exceptional mechanical responses greatly exceed the current state-of-the-art stretch-ability for layered composites by over a factor of three, demonstrating the promise of engineering materials with reconfigurable physical properties.SignificanceMolecular composites are ubiquitous in nature (e.g., bone and nacre) that have important functions from self-defense to carbon sequestering. Various life forms on Earth sequester carbon (e.g., shell-building marine animals) by combining proteins and inorganic layered composites. These composites become insensitive to flaws as soon as the structural size reaches a critical length. We studied mechanical properties of atomistically thin inorganic layers with tandem repeat proteins through fine control of their molecular weight. Mechanical properties are tunable and exceed state state-of-the-art composites, which cannot be explained by an existing theoretical model. This finding opens a perspective on failure mechanism for composites, which depends on interfacial rather than bulk properties. Controlling interfacial strength ultimately engender new design rules for nature-inspired composites.

Automated summary

Inspired by natural composites, researchers have successfully assembled genetically engineered polymeric proteins with inorganic sheets to create materials with mechanical compliance and ultra-toughness. The mechanical properties of these composites can be optimized by adjusting protein molecular weight and repetition. These exceptional materials exceed the current state-of-the-art stretchability for layered composites by over three times, demonstrating the promise of engineering materials with reconfigurable physical properties.