Mimicking biological stress–strain behaviour with synthetic elastomers

• Published in: Nature (London) 2017-09, Vol.549 (7673), p.497-501
• Main Authors: Vatankhah-Varnosfaderani, Mohammad, Daniel, William F. M., Everhart, Matthew H., Pandya, Ashish A., Liang, Heyi, Matyjaszewski, Krzysztof, Dobrynin, Andrey V., Sheiko, Sergei S.
• Format: Article
• Language: English
• Subjects: 119/118; 639/301/923/1028; 639/638/455/303; Biological materials; Biological stress; Biosynthesis; Crosslinking; Elastomers; Humanities and Social Sciences; letter; Lungs; Mechanical properties; Monomers; multidisciplinary; Polydimethylsiloxane; Polymer melts; Polymerization; Polymers; Rheology; Science; Softness; Stiffening; Strain; Stress (physiology); Stress-strain curves; Stress-strain relationships; Surgical implants; Synthetic products; Tissue engineering
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature23673

A polymer code based on a triplet of parameters—network strand length, side-chain length and grafting density—enables materials to be designed with specific combinations of mechanical properties to mimic biological materials. Mimicking biological bounce Controlling mechanical properties, such as stress–strain behaviour, in synthetic polymers often involves screening many samples with different molecular weights, compositions and architectures, and iterating towards the desired properties. However, it is difficult to predict what molecular make-up will yield the desired stress–strain curve, particularly in the case of strain-hardening materials that mimic the mechanical properties of biological tissues such as cartilage, muscle and lungs. Here, Sergei Sheiko and colleagues develop a method to derive grafting density, side-chain length and network strand length for brush- and comb-like polymer networks. This triplet of parameters can be calculated directly from a given stress–strain curve, enabling researchers to predict and synthesize a specific composition and architecture to get the desired mechanical properties, rather than relying on trial-and-error, synthesis-heavy approaches. Despite the versatility of synthetic chemistry, certain combinations of mechanical softness, strength, and toughness can be difficult to achieve in a single material. These combinations are, however, commonplace in biological tissues, and are therefore needed for applications such as medical implants, tissue engineering, soft robotics, and wearable electronics 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Present materials synthesis strategies are predominantly Edisonian, involving the empirical mixing of assorted monomers, crosslinking schemes, and occluded swelling agents, but this approach yields limited property control 2 , 10 , 11 , 12 , 13 , 14 , 15 , 16 . Here we present a general strategy for mimicking the mechanical behaviour of biological materials by precisely encoding their stress–strain curves in solvent-free brush- and comb-like polymer networks (elastomers). The code consists of three independent architectural parameters—network strand length, side-chain length and grafting density. Using prototypical poly(dimethylsiloxane) elastomers, we illustrate how this parametric triplet enables the replication of the strain-stiffening characteristics of jellyfish, lung, and arterial tissues.