Autonomous Indication of Mechanical Damage in Polymeric Coatings

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Abstract

High-resolution in situ autonomous visual indication of mechanical damage is achieved through a microcapsule-based polymeric material system. Upon mechanical damage, ruptured microcapsules release a liquid indicator molecule. A sharp color change from light yellow to bright red is triggered when the liberated indicator 2',7'-dichlorofluorescein reacts with the polymeric coating matrix.

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Force-induced activation of covalent bonds in mechanoresponsive polymeric materials.

Douglas Davis, Andrew Hamilton, Jinglei Yang … (2009)

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 bone. 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 failure. 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 developed; 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 bonds. 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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Mechanically-induced chemical changes in polymeric materials.

Mary M. Caruso, Douglas A. Davis, Qilong Shen … (2009)

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Measuring mechanical tension across vinculin reveals regulation of focal adhesion dynamics

Carsten Grashoff, Brenton D Hoffman, Michael Brenner … (2010)

Mechanical forces are central to developmental, physiological and pathological processes1. However, limited understanding of force transmission within sub-cellular structures is a major obstacle to unravelling molecular mechanisms. Here we describe the development of a calibrated biosensor that measures forces across specific proteins in cells with pico-Newton (pN) sensitivity, as demonstrated by single molecule fluorescence force spectroscopy2. The method is applied to vinculin, a protein that connects integrins to actin filaments and whose recruitment to focal adhesions (FAs) is force-dependent3. We show that tension across vinculin in stable FAs is ~2.5 pN and that vinculin recruitment to FAs and force transmission across vinculin are regulated separately. Highest tension across vinculin is associated with adhesion assembly and enlargement. Conversely, vinculin is under low force in disassembling or sliding FAs at the trailing edge of migrating cells. Furthermore, vinculin is required for stabilizing adhesions under force. Together, these data reveal that FA stabilization under force requires both vinculin recruitment and force transmission, and that, surprisingly, these processes can be controlled independently.

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Author and article information

Journal

Title: Advanced Materials

Abbreviated Title: Adv. Mater.

Publisher: Wiley

ISSN: 09359648

Publication date Created: March 2016

Publication date (Print): March 2016

Publication date (Electronic): January 11 2016

Volume: 28

Issue: 11

Pages: 2189-2194

Affiliations

[1 ]Department of Materials Science and Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA

[2 ]Department of Mechanical Science and Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA

[3 ]Department of Aerospace Engineering; Beckman Institute for Advanced Science and Technology; University of Illinois at Urbana-Champaign; Urbana IL 61801 USA