Hygromorphs: from pine cones to biomimetic bilayers

Reyssat, Étienne; Mahadevan, L.

doi:10.1098/rsif.2009.0184

Cited by 416 publications

(391 citation statements)

References 14 publications

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“…This relatively fast response has important consequences for power output and it can be explained by the small thickness of the spore monolayer, where wetting and drying can both occur very fast. Quantitatively, both the classical Washburn law for wetting and diffusive evaporation for drying follow similar dynamical laws with the time for both scaling as with thickness of the sheet, and the diffusivity 15 . Because power depends on these time constants, thinner films have a considerable advantage.…”

Section: Spores Of Bacillus As Building Blocks Of High Energy Densitymentioning

confidence: 76%

“…A more general treatment of curvature can be found in ref. [15]. The AFM allows measurement of the slope of the cantilever at the location of the laser spot, rather than measurement of the radius of curvature.…”

Section: Methodsmentioning

confidence: 99%

“…Strain at the surface of the rubber sheet near the spores is estimated from 2t/3R x (the neutral plane is 2t/3 below the surface, see also Eqs. 2.3--2.6 of ref [15]. We determined E from the stress strain curves for a rectangular strip of the same latex rubber sample (1.3 MPa).…”

Section: Methodsmentioning

confidence: 99%

“…we used a simple estimate for the maximum strain in a bilayer plate 15,23 . For a given ratio of the elastic modulus of the passive sheet to the spore layer, there is an optimum ratio of thicknesses that maximizes energy transfer (see supplementary online text).…”

Section: Spores Of Bacillus As Building Blocks Of High Energy Densitymentioning

confidence: 99%

“…We also identified a mutant spore form that nearly doubles the energy density relative to its wild type, highlighting the possibility for further improvements with genetic engineering of spores. We found that spores can self--assemble into dense, submicron--thick monolayers on substrates like silicon microcantilevers and elastomer sheets, creating bio--hybrid hygromorph actuators 15 . The spore monolayers forming these hygromorphs exhibited high--energy density and rapid response to changing water potentials.…”

mentioning

confidence: 94%

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Bacillus spores as building blocks for stimuli-responsive materials and nanogenerators

et al. 2014

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Materials that respond mechanically to external chemical stimuli have wide--ranging applications in biomedical devices, adaptive architectural systems, robotics, and energy harvesting 1 . Synthesis and design principles inspired by biological systems have led to materials with capabilities for highly controlled and complex shape change 2 , oscillations 3 , fluid transport 4 , and homeostasis 5 . Despite the enhanced control over material behavior, the effectiveness of synthetic stimuli--responsive materials in generating work has been limited when compared to mechanical actuators 6 . Biological organisms with structures responsive to water gradients could potentially offer a solution for the limited work density of stimuli--responsive materials. Because water--responsive biological structures accomplish vital tasks like ascent of sap 7,8 , dispersal and self--burial of seeds 9,10 , they could possibly exhibit high energy densities and serve as building blocks of stimuli--responsive materials effective in generating work. Furthermore, biological nature of these materials offers the possibility of improving their characteristics through genetic mutations 11,12 . Here we report the discovery that the response of the spores of Bacillus to water potential gradients exhibit energy densities more than 10 MJ/m 3 , exceeding best synthetic water--responsive materials by 1000--fold 13,14 . We also identified a mutant spore form that nearly doubles the energy density relative to its wild type, highlighting the possibility for further improvements with genetic engineering of spores. We found that spores can self--assemble into dense, submicron--thick monolayers on substrates like silicon microcantilevers and elastomer sheets, creating bio--hybrid hygromorph actuators 15 . The spore monolayers forming these hygromorphs exhibited high--energy density and rapid response to changing water potentials. As an application of the strong mechanical response of spores, we have built an energy harvesting device that can remotely generate electrical power from an evaporating body of water. These results demonstrate that spores have a significant potential as building blocks of stimuli--responsive materials with dramatically enhanced capabilities for energy harvesting, storage, and actuation of robotic devices.Bacillus spores are dormant cells that can withstand harsh environmental conditions for long periods of time and still maintain biological functionality 16 (Fig. 1a,b). Despite their dormancy, spores are dynamic structures. For example, Bacillus spores respond to changes in relative humidity (RH) by expanding and shrinking and changing their diameter by as much as 12% 17--19 . We have used an atomic force microscope (AFM) based experiment (Fig. 2c) to determine the energy density of individual spores as they respond to changes in RH. By adjusting force and RH, we have created a thermodynamic cycle, in which individual spores go through four stages illustrated in Fig. 1d. In stage I, the spores rest at low RH (~20%). In stage II,...

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Section: Spores Of Bacillus As Building Blocks Of High Energy Densitymentioning

confidence: 76%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Spores Of Bacillus As Building Blocks Of High Energy Densitymentioning

confidence: 99%

mentioning

confidence: 94%

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