MSGID: 1:317/3 640ab266   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Knots smaller than human hair make materials unusually tough    
      
     Date:   
         March 9, 2023   
     Source:   
         California Institute of Technology   
     Summary:   
         A micro-architected material made from tiny knots proves tougher   
         and more durable than unknotted counterparts.   
      
      
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   FULL STORY   
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   In the latest advance in nano- and micro-architected materials, engineers   
   at Caltech have developed a new material made from numerous interconnected   
   microscale knots.   
      
      
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   The knots make the material far tougher than identically structured but   
   unknotted materials: they absorb more energy and are able to deform more   
   while still being able to return to their original shape undamaged. These   
   new knotted materials may find applications in biomedicine as well as in   
   aerospace applications due to their durability, possible biocompatibility,   
   and extreme deformability.   
      
   "The capability to overcome the general trade-off between material   
   deformability and tensile toughness [the ability to be stretched without   
   breaking] offers new ways to design devices that are extremely flexible,   
   durable, and can operate in extreme conditions," says former Caltech   
   graduate student Widianto P. Moestopo (MS ' 19, PhD '22), now at Lawrence   
   Livermore National Laboratory. Moestopo is the lead author of a paper   
   on the nanoscale knots that was published on March 8 in Science Advances.   
      
   Moestopo helped develop the material in the lab of Julia R. Greer,   
   the Ruben F.   
      
   and Donna Mettler Professor of Materials Science, Mechanics and Medical   
   Engineering; Fletcher Jones Foundation director of the Kavli Nanoscience   
   Institute; and senior author of the Science Advancespaper. Greer is   
   at the forefront of the creation of such nano-architected materials,   
   or materials whose structure is designed and organized at a nanometer   
   scale and that consequently exhibit unusual, often surprising properties.   
      
   "Embarking on understanding how the knots would affect the mechanical   
   response of micro-architected materials was a new out-of-the-box idea,"   
   Greer says. "We had done extensive research on studying the mechanical   
   deformation of many other types of micro-textiles, for example, lattices   
   and woven materials.   
      
   Venturing into the world of knots allowed us to gain deeper insights into   
   the role of friction and energy dissipation, and proved to be meaningful."   
   Each knot is around 70 micrometers in height and width, and each fiber   
   has a radius of around 1.7 micrometers (around one-hundredth the radius   
   of a human hair). While these are not the smallest knots ever made --   
   in 2017 chemists tied a knot made from an individual strand of atoms --   
   this does represent the first time that a materialcomposed of numerous   
   knots at this scale has ever been created. Further, it demonstrates   
   the potential value of including these nanoscale knots in a material --   
   for example, for suturing or tethering in biomedicine.   
      
   The knotted materials, which were created out of polymers, exhibit a   
   tensile toughness that far surpasses materials that are unknotted but   
   otherwise structurally identical, including ones where individual strands   
   are interwoven instead of knotted. When compared to their unknotted   
   counterparts, the knotted materials absorb 92 percent more energy and   
   require more than twice the amount of strain to snap when pulled.   
      
   The knots were not tied but rather manufactured in a knotted state by   
   using advanced high-resolution 3D lithography capable of producing   
   structures in the nanoscale. The samples detailed in the Science   
   Advancespaper contain simple knots -- an overhand knot with an extra twist   
   that provides additional friction to absorb additional energy while the   
   material is stretched. In the future, the team plans to explore materials   
   constructed from more complex knots.   
      
   Moestopo's interest in knots grew out of research he was conducting   
   in 2020 during the COVID-19 lockdowns. "I came across some works from   
   researchers who are studying the mechanics of physical knots as opposed to   
   knots in a purely mathematical sense. I do not consider myself a climber,   
   a sailor, or a mathematician, but I have tied knots throughout my life, so   
   I thought it was worth trying to insert knots into my designs," he says.   
      
       * RELATED_TOPICS   
             o Matter_&_Energy   
                   # Materials_Science # Nanotechnology # Civil_Engineering   
                   # Engineering_and_Construction # Physics # Chemistry #   
                   Weapons_Technology # Engineering   
       * RELATED_TERMS   
             o Knot_theory o Parachute o Triboelectric_effect o Concrete   
             o Density o Tensile_strength o Glass o Chelation   
      
   ==========================================================================   
   Story Source: Materials provided by   
   California_Institute_of_Technology. Original written by Robert   
   Perkins. Note: Content may be edited for style and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Widianto P. Moestopo, Sammy Shaker, Weiting Deng, Julia   
      R. Greer. Knots   
         are not for naught: Design, properties, and topology of hierarchical   
         intertwined microarchitected materials. Science Advances, 2023;   
         9 (10) DOI: 10.1126/sciadv.ade6725   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230309164732.htm   
      
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