Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 119, Issue 31, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2120021119
Keywords
2D-layered materials; tandem repeat proteins; mechanical properties; biomimetics
Categories
Funding
- DARPA [D19AC00016]
- Airforce Office of Sponsored Research [FA9550-18-1-0235]
- Army Research Office [W911NF-16-1-0019]
- Huck Endowment of Pennsylvania State University
- Nanyang Technological University [002479-00001]
- Agency for Science, Technology and Research (A*STAR)
- A*STAR Computational Resource Centre, Singapore (ACRC)
- National Supercomputing Centre, Singapore (NSCC)
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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.
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.
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