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Force-induced activation of covalent bonds in mechanoresponsive polymeric materials


Mechanochemical transduction enables an extraordinary range of physiological processes such as the sense of touch, hearing, balance, muscle contraction, and the growth and remodelling of tissue and bone1,2,3,4,5,6. Although biology is replete with materials systems that actively and functionally respond to mechanical stimuli, the default mechanochemical reaction of bulk polymers to large external stress is the unselective scission of covalent bonds, resulting in damage or failure7. An alternative to this degradation process is the rational molecular design of synthetic materials such that mechanical stress favourably alters material properties. A few mechanosensitive polymers with this property have been developed8,9,10,11,12,13,14; but their active response is mediated through non-covalent processes, which may limit the extent to which properties can be modified and the long-term stability in structural materials. Previously, we have shown with dissolved polymer strands incorporating mechanically sensitive chemical groups—so-called mechanophores—that the directional nature of mechanical forces can selectively break and re-form covalent bonds15,16. We now demonstrate that such force-induced covalent-bond activation can also be realized with mechanophore-linked elastomeric and glassy polymers, by using a mechanophore that changes colour as it undergoes a reversible electrocyclic ring-opening reaction under tensile stress and thus allows us to directly and locally visualize the mechanochemical reaction. We find that pronounced changes in colour and fluorescence emerge with the accumulation of plastic deformation, indicating that in these polymeric materials the transduction of mechanical force into the ring-opening reaction is an activated process. We anticipate that force activation of covalent bonds can serve as a general strategy for the development of new mechanophore building blocks that impart polymeric materials with desirable functionalities ranging from damage sensing to fully regenerative self-healing.

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Figure 1: Chemical structures and bulk polymeric samples.
Figure 2: First-principles dynamics and constrained optimization models of mechanical activation.
Figure 3: Mechanochromic response of mechanophore-linked PMA elastomer under tensile loading.
Figure 4: Mechanochromic response of glassy mechanophore cross-linked PMMA beads under diametral compression.


  1. French, A. S. Mechanotransduction. Annu. Rev. Physiol. 54, 135–152 (1992)

    CAS  Article  Google Scholar 

  2. Orr, A. W., Helmke, B. P., Blackman, B. R. & Schwartz, M. A. Mechanisms of mechanotransduction. Dev. Cell 10, 11–20 (2006)

    CAS  Article  Google Scholar 

  3. Gillespie, P. G. & Walker, R. G. Molecular basis of mechanosensory transduction. Nature 413, 194–202 (2001)

    ADS  CAS  Article  Google Scholar 

  4. Lele, T. P., Thodeti, C. K. & Ingber, D. E. Force meets chemistry: Analysis of mechanochemical conversion in focal adhesions using fluorescence recovery after photobleaching. J. Cell. Biochem. 97, 1175–1183 (2006)

    CAS  Article  Google Scholar 

  5. Mahadevan, L. & Matsudaira, P. Motility powered by supramolecular springs and ratchets. Science 288, 95–99 (2000)

    ADS  CAS  Article  Google Scholar 

  6. Martinac, B. Mechanosensitive ion channels: molecules of mechanotransduction. J. Cell Sci. 117, 2449–2460 (2004)

    CAS  Article  Google Scholar 

  7. Beyer, M. K. & Clausen-Schaumann, H. Mechanochemistry: The mechanical activation of covalent bonds. Chem. Rev. 105, 2921–2948 (2005)

    CAS  Article  Google Scholar 

  8. Löwe, C. & Weder, C. Oligo(p-phenylene vinylene) excimers as molecular probes: deformation-induced color changes in photoluminescent polymer blends. Adv. Mater. 14, 1625–1629 (2002)

    Article  Google Scholar 

  9. Kim, S.-J. & Reneker, D. H. A mechanochromic smart material. Polym. Bull. 31, 367–374 (1993)

    CAS  Article  Google Scholar 

  10. Nallicheri, R. A. & Rubner, M. F. Investigations of the mechanochromic behavior of poly(urethane diacetylene) segmented copolymers. Macromolecules 24, 517–525 (1991)

    ADS  CAS  Article  Google Scholar 

  11. Foulger, S. H. et al. Mechanochromic response of poly(ethylene glycol) methacrylate hydrogel encapsulated crystalline colloidal arrays. Langmuir 17, 6023–6026 (2001)

    CAS  Article  Google Scholar 

  12. Foulger, S. H. et al. Photonic crystal composites with reversible high-frequency stop band shifts. Adv. Mater. 15, 685–689 (2003)

    CAS  Article  Google Scholar 

  13. Comrie, J. E. & Huck, W. T. S. Exploring actuation and mechanotransduction properties of polymer brushes. Macromol. Rapid Commun. 29, 539–546 (2008)

    CAS  Article  Google Scholar 

  14. Azzaroni, O. et al. Mechanically induced generation of counterions inside surface-grafted charged macromolecular films: Towards enhanced mechanotransduction in artificial systems. Angew. Chem. Int. Edn Engl. 45, 7440–7443 (2006)

    CAS  Article  Google Scholar 

  15. Hickenboth, C. R. et al. Biasing reaction pathways with mechanical force. Nature 446, 423–427 (2007)

    ADS  CAS  Article  Google Scholar 

  16. Potisek, S. L. et al. Mechanophore-linked addition polymers. J. Am. Chem. Soc. 129, 13808–13809 (2007)

    CAS  Article  Google Scholar 

  17. Tipikin, D. S. Mechanochromism of organic compounds by the example of spiropyran. Russ. J. Phys. Chem. 75, 1720–1722 (2001)

    Google Scholar 

  18. Minkin, V. I. Photo-, thermo-, solvato-, and electrochromic spiroheterocyclic compounds. Chem. Rev. 104, 2751–2776 (2004)

    CAS  Article  Google Scholar 

  19. Percec, V. et al. Ultrafast synthesis of ultrahigh molar mass polymers by metal-catalyzed living radical polymerization of acrylates, methacrylates, and vinyl chloride mediated by SET at 25 degrees C. J. Am. Chem. Soc. 128, 14156–14165 (2006)

    CAS  Article  Google Scholar 

  20. Casale, A. & Porter, R. S. Polymer Stress Reactions Vol. 1, 8–80 and 96–101 (Academic Press, 1978)

    Book  Google Scholar 

  21. Ben-Nun, M. & Martinez, T. J. Ab initio quantum molecular dynamics. Adv. Chem. Phys. 121, 439–512 (2002)

    CAS  Google Scholar 

  22. Sotomayor, M. & Schulten, K. Single-molecule experiments in vitro and in silico. Science 316, 1144–1148 (2007)

    ADS  CAS  Article  Google Scholar 

  23. Saitta, A. M. & Klein, M. L. First-principles molecular dynamics study of the rupture processes of a bulklike polyethylene knot. J. Phys. Chem. B 105, 6495–6499 (2001)

    CAS  Article  Google Scholar 

  24. Beyer, M. K. The mechanical strength of a covalent bond calculated by density functional theory. J. Chem. Phys. 112, 7307–7312 (2000)

    ADS  CAS  Article  Google Scholar 

  25. Hiramatsu, Y. & Oka, Y. Determination of the tensile strength of rock by a compression test of an irregular test piece. Int. J. Rock Mechan. Mining Sci. 3, 89–99 (1966)

    Article  Google Scholar 

  26. Sternberg, E. & Rosenthal, F. The elastic sphere under concentrated loads. J. Appl. Mech. 19, 413–421 (1952)

    MathSciNet  MATH  Google Scholar 

  27. Eyring, E. Viscosity, plasticity, and diffusion as examples of absolute reaction rates. J. Chem. Phys. 4, 283–291 (1936)

    ADS  CAS  Article  Google Scholar 

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We acknowledge the support of the ARO MURI programme (grant number W911NF-07-1-0409) for this research.

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Correspondence to Nancy R. Sottos.

Supplementary information

Supplementary Information

This file contains Supplementary Methods, Supplementary Figures S1-S5 with Legends and Supplementary Tables S1-S2; a Supplementary Discussion, Supplementary Figures S6-S21 with Legends and Supplementary References. (PDF 5761 kb)

Supplementary Video S1

Video S1 shows mechanophore-linked PMA-1-PMA dog bone specimen loaded in uniaxial tension to failure. (MOV 498 kb)

Supplementary Video S2

Video S2 shows SMD simulations of 1t showing C-O spiro bond rupture at a force of 2.0 nN. (MPG 1313 kb)

Supplementary Video S3

Video S3 shows SMD simulations of 3t showing no bond rupture at a force of 2.0 nN. (MPG 1243 kb)

Supplementary Video S4

Video S4 shows SMD simulations of 1e showing spiro C-O bond rupture at a force of 3.0 nN. (MPG 1671 kb)

Supplementary Video S5

Video S5 shows SMD simulations of 1e showing C-O ester bond rupture at a force of 3.0 nN. (MPG 2836 kb)

Supplementary Video S6

Video S6 shows SMD simulations of 3e showing C-C ester bond rupture at a force of 3.0 nN. (MPG 9689 kb)

Supplementary Video S7

Video S7 shows active PMMA-4 beads under compressive loading. (MOV 8587 kb)

Supplementary Video S8

Video S8 shows control PMMA-5 beads under compressive loading. (MOV 5804 kb)

Supplementary Data

This zipped data file shows XYZ coordinate data for all molecules used in molecular modelling. (ZIP 14 kb)

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Davis, D., Hamilton, A., Yang, J. et al. Force-induced activation of covalent bonds in mechanoresponsive polymeric materials. Nature 459, 68–72 (2009).

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