Polymers That Mimic Chameleon Skin

Chameleon-like elastomers with molecularly encoded strain-adaptive stiffening and coloration.

Left: molecular structure of a synthesized plastomer; Center: supramolecular structure formed by the assembly of identical plastomers; Right: image showing the iridescent color of the plastomers

August 10, 2018 | Source: CNRS, www2.cnrs.fr, 29 Mar 2018, Dmitri Ivanov

An international team of researchers from the University of North Carolina at Chapel Hill, University of Akron, French National Center for Scientific Research (Centre national de la recherche scientifique), French University of Upper Alsace (Université de Haute-Alsace), and the European Synchrotron Radiation Facility (ESRF) have produced a biocompatible synthetic material that replicates tissue mechanics and alters color when it changes shape, like chameleon skin.  To help mitigate inflammation or necrosis related to medical implants, the team developed a material with similar mechanical properties to those in certain biological tissues that are soft yet stiffen when stretched (e.g., skin, intestinal wall, and heart muscle).  The synthesized physically cross-linked elastomer is composed of a central block onto which side chains are grafted (like a bottle brush) and with linear terminal blocks at each end.  By carefully selecting the polymer's structural parameters, the material followed the same strain curve as a biological tissue.  It is biocompatible as it does not require additives, e.g. solvent, and remains stable in the presence of biological fluids.

Another property of the material is its color change upon deformation.  This is caused by light scattering from the polymer structure.  The terminal blocks of these polymers assemble in nanometer spheres, distributed in a brush-polymer matrix.  Light interferes with this microphase-separated structure to produce color according to the distance between the spheres; so when the material is stretched it changes color.  It is the same mechanism that explains – in large part – how chameleons change color.  By adjusting the length or density of the “brush's” various side chains, these properties can be modulated.  The ability to encode unique mechanical (flexibility and strain profile) and optical properties in a synthetic polymer had never previously been achieved