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Smart squid skin: patterns in networks of artificial chromatophores
... Fisherman et al. developed an artificial chromatophore cell array using a dielectric elastomer (DE). Dynamic color-changing mode could be achieved by relative feedback control mechanism of regional strain [30]. Wang et al. manufactured a bionic machine chameleon utilizing bimetallic nano-point array and electrochemical bias method basing on plasma modulation techniques [31]. ...
To adapt to a complex and variable environment, self-adaptive camouflage technology is becoming more and more important in all kinds of military applications by overcoming the weakness of the static camouflage. In nature, the chameleon can achieve self-adaptive camouflage by changing its skin color in real time with the change of the background color. To imitate the chameleon skin, a camouflaged film controlled by a color-changing microfluidic system is proposed in this paper. The film with microfluidic channels fabricated by soft materials can achieve dynamic cloaking and camouflage by circulating color liquids through channels inside the film. By sensing and collecting environmental color change information, the control signal of the microfluidic system can be adjusted in real time to imitate chameleon skin. The microstructure of the film and the working principle of the microfluidic color-changing system are introduced. The mechanism to generate the control signal by information processing of background colors is illustrated. “Canny” double-threshold edge detection algorithm and color similarity are used to analyze and evaluate the camouflage. The tested results show that camouflaged images have a relatively high compatibility with environmental backgrounds and the dynamic cloaking effect can be achieved.
Cephalopods are unrivaled in the natural world in their ability to alter their visual appearance. These mollusks have evolved a complex system of dermal units under neural, hormonal, and muscular control to produce an astonishing variety of body patterns. With parallels to the pixels on a television screen, cephalopod chromatophores can be coordinated to produce dramatic, dynamic, and rhythmic displays, defined collectively here as “dynamic patterns.” This study examines the nature, context, and potential functions of dynamic patterns across diverse cephalopod taxa. Examples are presented for 21 species, including 11 previously unreported in the scientific literature. These range from simple flashing or flickering patterns, to highly complex passing wave patterns involving multiple skin fields.
For dielectric elastomers (DEs), the inherent viscoelasticity leads to a time-dependent deformation during actuation. To describe such a viscoelastic behavior, a constitutive model is developed by utilizing a combined Kelvin-Voigt-Maxwell (KVM) model. The established model captures both the initial jumping deformation and the following slow creeping. Subsequently, with an employment of VHB 4910 elastomer, experiments are performed to validate the viscoelastic KVM model. The results indicate a good agreement between the simulation and experimental data. Effect of the parameters in KVM model on the viscoelastic deformation of DEs is also investigated.
Cephalopods employ their chromomorphic skins for rapid and versatile active camouflage and signalling effects. This is achieved using dense networks of pigmented, muscle-driven chromatophore cells which are neurally stimulated to actuate and affect local skin colouring. This allows cephalopods to adopt numerous dynamic and complex skin patterns, most commonly used to blend into the environment or to communicate with other animals. Our ultimate goal is to create an artificial skin that can mimic such pattern generation techniques, and that could produce a host of novel and compliant devices such as cloaking suits and dynamic illuminated clothing. This paper presents the design, mathematical modelling and analysis of a dynamic biomimetic pattern generation system using bioinspired artificial chromatophores. The artificial skin is made from electroactive dielectric elastomer: a soft, planar-actuating smart material that we show can be effective at mimicking the actuation of biological chromatophores. The proposed system achieves dynamic pattern generation by imposing simple local rules into the artificial chromatophore cells so that they can sense their surroundings in order to manipulate their actuation. By modelling sets of artificial chromatophores in linear arrays of cells, we explore the capability of the system to generate a variety of dynamic pattern types. We show that it is possible to mimic patterning seen in cephalopods, such as the passing cloud display, and other complex dynamic patterning.
© 2015 The Author(s) Published by the Royal Society. All rights reserved.
Some of the most exciting possibilities for dielectric elastomer artificial muscles consist of biologically inspired networks
of smart actuators working towards common goals. However, the creation of these networks will only be realised once intelligence
and feedback can be fully distributed throughout an artificial muscle device. Here we show that dielectric elastomer artificial
muscles can be built with intrinsic sensor, control, and driver circuitry, bringing them closer in capability to their natural
analogues. This was achieved by exploiting the piezoresistive behaviour of the actuator’s highly compliant electrodes using
what we have called the dielectric elastomer switch. We developed suitable switching material using carbon loaded silicone
grease and experimentally demonstrated the primitives required for self-sensing actuators and digital computation, namely
compliant electromechanical NAND gates and oscillator circuits. We anticipate that dielectric elastomer switches will reduce
the need for bulky and rigid external circuitry as well as provide the simple distributed intelligence required for soft,
biologically inspired networks of actuators. Examples include many-degree-of-freedom robotic hearts, intestines, and manipulators;
wearable assistive devices; smart sensor skins and fabrics; and ultimately new types of artificial muscle embedded, electromechanical
computers.
Chromatophores are the pigment-containing cells in the skins of animals such as fish and cephalopods which have chromomorphic (colour-changing) and controllable goniochromic (iridescent-changing) properties. These animals control the optical properties of their skins for camouflage and, it is speculated, for communication. The ability to replicate these properties in soft artificial skin structures opens up new possibilities for active camouflage, thermal regulation and active photovoltaics. This paper presents the design and implementation of soft and compliant artificial chromatophores based on the cutaneous chromatophores in fish and cephalopods. We demonstrate artificial chromatophores that are actuated by electroactive polymer artificial muscles, mimicking the radially orientated muscles found in natural chromatophores. It is shown how bio-inspired chromomorphism may be achieved using both areal expansion of dielectric elastomer structures and by the hydrostatic translocation of pigmented fluid into an artificial dermal melanophore.
Cuttlefish and other cephalopods achieve dynamic background matching with two general classes of body patterns: uniform (or uniformly stippled) patterns and mottle patterns. Both pattern types have been described chiefly by the size scale and contrast of their skin components. Mottle body patterns in cephalopods have been characterized previously as small-to-moderate-scale light and dark skin patches (i.e. mottles) distributed somewhat evenly across the body surface. Here we move beyond this commonly accepted qualitative description by quantitatively measuring the scale and contrast of mottled skin components and relating these statistics to specific visual background stimuli (psychophysics approach) that evoke this type of background-matching pattern. Cuttlefish were tested on artificial and natural substrates to experimentally determine some primary visual background cues that evoke mottle patterns. Randomly distributed small-scale light and dark objects (or with some repetition of small-scale shapes/sizes) on a lighter substrate with moderate contrast are essential visual cues to elicit mottle camouflage patterns in cuttlefish. Lowering the mean luminance of the substrate without changing its spatial properties can modulate the mottle pattern toward disruptive patterns, which are of larger scale, different shape and higher contrast. Backgrounds throughout nature consist of a continuous range of spatial scales; backgrounds with medium-sized light/dark patches of moderate contrast are those in which cuttlefish Mottle patterns appear to be the most frequently observed.
This paper experimentally studied the large nonlinear deformation of VHB 4910 elastomer by uniaxial tests. The study reveals that the monotonic tensile stress-strain, hysteresis, cyclic stress softening and multistep stress relaxation of this elastomer exhibit rate-sensitivity. Toughness, failure stress, failure strain are shown to vary with strain rate. Maximum cyclic stress, hysteresis loss, residual strains in cyclic loading-unloading, stress relaxation in multistep relaxation tests are also shown to be rate-sensitive. The analytical models are also proposed to predict certain important parameters such as dissipative work, cyclic stress softening, cyclic residual strain and relaxation stress in different states of deformation.
Traveling waves (from action potential propagation to swimming body motions or intestinal peristalsis) are ubiquitous phenomena in biological systems and yet are diverse in form, function, and mechanism. An interesting such phenomenon occurs in cephalopod skin, in the form of moving pigmentation patterns called “passing clouds” [1]. These dynamic pigmentation patterns result from the coordinated activation of large chromatophore arrays [2]. Here, we introduce a new model system for the study of passing clouds, Metasepia tullbergi, in which wave displays are very frequent and thus amenable to laboratory investigations. The mantle of Metasepia contains four main regions of wave travel, each supporting a different propagation direction. The four regions are not always active simultaneously, but those that are show synchronized activity and maintain a constant wavelength and a period-independent duty cycle, despite a large range of possible periods (from 1.5 s to 10 s). The wave patterns can be superposed on a variety of other ongoing textural and chromatic patterns of the skin. Finally, a traveling wave can even disappear transiently and reappear in a different position (“blink”), revealing ongoing but invisible propagation. Our findings provide useful clues about classes of likely mechanisms for the generation and propagation of these traveling waves. They rule out wave propagation mechanisms based on delayed excitation from a pacemaker [ 3] but are consistent with two other alternatives, such as coupled arrays of central pattern generators [ 3] and dynamic attractors on a network with circular topology [ 4].
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Dielectric Elastomer Actuators (DEA) have been studied extensively under laboratory conditions where they have shown promising performance. However, in practical applications, they have not achieved their full potential. Here the results of detailed analytical and experimental studies of the failure modes and performance boundaries of DEAs are codified into design principles for these actuators. Analysis shows that the performance of DEAs made with highly viscoelastic is governed by four key mechanisms: pull-in failure, dielectric strength failure, viscoelasticity and current leakage. A design map showing the effect of these four mechanisms on performance under varying working conditions is proposed. This study shows that the viscous nature of DEA is very important in their performance/reliability trade-offs. A proper balance of performance and reliability is key to successful design of DEAs.
The chromatophores of cephalopods differ fundamentally from those of other animals: they are neuromuscular organs rather than cells and are not controlled hormonally. They constitute a unique motor system that operates upon the environment without applying any force to it. Each chromatophore organ comprises an elastic sacculus containing pigment, to which is attached a set of obliquely striated radial muscles, each with its nerves and glia. When excited the muscles contract, expanding the chromatophore; when they relax, energy stored in the elastic sacculus retracts it. The physiology and pharmacology of the chromatophore nerves and muscles of loliginid squids are discussed in detail. Attention is drawn to the multiple innervation of dorsal mantle chromatophores, of crucial importance in pattern generation. The size and density of the chromatophores varies according to habit and lifestyle. Differently coloured chromatophores are distributed precisely with respect to each other, and to reflecting structures beneath them. Some of the rules for establishing this exact arrangement have been elucidated by ontogenetic studies. The chromatophores are not innervated uniformly: specific nerve fibres innervate groups of chromatophores within the fixed, morphological array, producing ‘physiological units’ expressed as visible ‘chromatomotor fields’.
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