Bio-inspired Polymer Composite Actuator

Technology #15637

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A PEE-PPy composite film (black) is composed of PPy polymer chains (gray lines) and a PEE-borate network (red lines). The structure changes (involving H bonds and borate ester bonds) in response to water (blue dots) sorption and desorption.
Professor Robert Langer
Department of Chemical Engineering, MIT
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Professor Daniel Anderson
Chemical Engineering and Institute for Medical Engineering and Science, MIT
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Professor Omid Farokhzad
Harvard Medical School
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Professor Liang Guo
Department of Electrical and Computer Engineering, OSU
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Mingming Ma
Koch Institute Integrative Cancer Research, MIT
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Lauren Foster
MIT Technology Licensing Officer
Patent Protection

Polymer composite actuator and generator driven by water gradients

US Patent 9,236,556
Bio-inspired Polymer Composite Actuator and Generator Driven by Water Gradients
Science, January 11, 2013, pg. 186-189


This polymer composite actuator is useful for ambient energy harvest and conversion. Additionally, the responsive polymer material may be used to fabricate polymeric actuators and ambient energy scavengers for electronic, mechanical and biomedical applications. This material might, for example, be used to develop a smart artificial skin or a smart sensor that can sense small amounts of water or other chemicals and change its shape, size or mechanical properties upon contact.

Problem Addressed

Responsive polymer materials that reversibly change shape, size or mechanical properties in response to external stimuli have attracted considerable interest, due to their potential applications as artificial actuators for biomedical and mechanical purposes. Polymer gels (e.g. hydrogels) responsive to water have been developed for the fabrication of actuators, but exhibit slower response, lower stress generation and marginal stability in comparison with animal muscle fibers. Polypyurrole (PPy) is an electroactive polymer with many desirable properties as artificial muscles, such as fast response, high stress generation, low operational voltage, low weight, environmental stability and biocompatibility.

The inventors have created unique water-responsive composite material made of PPy and poly-ol borate that combines the responsive properties of polymer gels with the superior function of PPy. This general strategy of combining one stiff matrix for mechanical integrity with one dynamic network for responsive properties could be useful for designing other responsive composite materials for broad applications in the biomedical, materials and sensing fields.


Inspired by the cross-linked network structure of animal dermis, in which rigid collagen fibers reinforce an elastic network of elastin microfibrils to form a sturdy, flexible and responsive materials, the inventors created a dynamic polymer composite of rigid PPy imbedded with flexible, inter-penetrating polyol-borate network that is responsive to ambient stimuli, such as water absorption and release. The polyol-borate network is sensitive to water and facilitates changes in the mechanical rigidity of the polymer composite. The composite exhibits fast, reversible and dramatic mechanical deformation and recovery reminiscent of “fast twitch” muscle activity in response to environmental moisture. This muscle-like composite material is used to make a mechanical actuator driven by an environmental water gradient, by absorbing water from moist substrates and then ejecting the bound water into low humidity air. This absorption and desorption of water is accompanied by film expansion and contraction that results in rapid locomotion. The contractile stress reaches 27 MPa upon water release, which is 80 times more powerful than the strongest mammalian skeletal muscle. Upon water absorption, a free film can lift objects 380 times heavier or transport cargo 10 times heavier than itself. Incorporated with superparamagnetic nanoparticles, the film can be actively directed by a magnet.


  • Water-driven actuator combines most of the superior properties of PPy-based electro-actuators with the stimuli-responsive properties of polymer gels
  • Collects ambient energy and converts it into mechanical energy, rather than consuming electrical energy for actuation
  • No need of electrochemical oxidation or reduction for its actuation
  • Sensitive polymer composite may be used for designing a wide range of sensors