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Touch and see: Physical interactions stimulating patterns in artificial cephalopod skin
... These works discovered that eyes and skin have the same structure [64] and can detect light intensity, and change the colour according to light changings [65]. The results of the genome studies enables the creation of artificial skin and skin-cells with all appropriate features [66], [67], [68]. ...
Octopus is an invertebrate belonging to the class of Cephalopoda. The body of an Octopus lacks any morphological joints and rigid parts. Their arms, skin and the complex nervous system are investigated by a several researchers all over the world. Octopuses are the object of inspiration for my scientists in different areas, including AI. Soft- and hardware are developed based on octopus features. Soft-robotics octopus-inspired arms are the most common type of developments. There are a lot of different variants of this solution, each of them is different from the other. In this paper, we describe the most remarkable octopus features, show solutions inspired by octopus and provide new ideas for further work and investigations in combination of AI and bioinspired soft-robotics areas.
... These works discovered that eyes and skin have the same structure [64] and can detect light intensity, and change the colour according to light changings [65]. The results of the genome studies enables the creation of artificial skin and skin-cells with all appropriate features [66], [67], [68]. ...
Octopus is an invertebrate belonging to the class of Cephalopoda. The body of an Octopus lacks any morphological joints and rigid parts. Their arms, skin and the complex nervous system are investigated by a several researchers all over the world. Octopuses are the object of inspiration for my scientists in different areas, including AI. Soft- and hardware are developed based on octopus features. Soft-robotics octopus-inspired arms are the most common type of developments. There are a lot of different variants of this solution, each of them is different from the other. In this paper, we describe the most remarkable octopus features, show solutions inspired by octopus and provide new ideas for further work and investigations in combination of AI and bioinspired soft-robotics areas.
... In practice, this means many researchers working with VHB DEAs are still reliant on applying electrodes by hand [27], [28]. AJP provides contactless technique to overcome this challenge as it can provide consistent, high resolution deposits at stand-off heights approaching 5mm. ...
Soft robotics is a fast growing field of engineering where there are significant opportunities to realize new forms of actuation and sensing. However, there is also a challenge to translate some of the lab-based developments into a robust industrial manufacturing process. Linked to this is also the opportunity to create new forms of functionality in soft robotic devices by employing a flexible, digital manufacturing process for their creation. Overcoming these hurdles, and unlocking the possibilities for greater functionality, is likely to be a key enabler for wider applications and adoption of soft robotics in practical applications. We present a system of computer-controlled Aerosol Jet Printing that will enable complex soft robotic structures to be manufactured. The process is demonstrated through the deposition of a carbon-based conductive ink on to elastomeric substrates for high resolution, conformal and multilayer patterning. Functional demonstrators, in the form of a dielectric elastomer actuator and strain sensor, are produced to showcase the potential of the technique.
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.
Cephalopods are renowned for changing the color and pattern of their skin for both camouflage and communication. Yet, we do not fully understand how cephalopods control the pigmented chromatophore organs in their skin and change their body pattern. Although these changes primarily rely on eyesight, we found that light causes chromatophores to expand in excised pieces of Octopus bimaculoides skin. We call this behavior light-activated chromatophore expansion (or LACE). To uncover how octopus skin senses light, we used antibodies against r-opsin phototransduction proteins to identify sensory neurons that express r-opsin in the skin. We hypothesized that octopus LACE relies on the same r-opsin phototransduction cascade found in octopus eyes. By creating an action spectrum for the latency to LACE, we found that LACE occurred most quickly in response to blue light. We fit our action spectrum data to a standard opsin curve template and estimated the λmax of LACE to be 480 nm. Consistent with our hypothesis, the maximum sensitivity of the light sensors underlying LACE closely matches the known spectral sensitivity of opsin from octopus eyes. LACE in isolated preparations suggests that octopus skin is intrinsically light sensitive and that this dispersed light sense might contribute to their unique and novel patterning abilities. Finally, our data suggest that a common molecular mechanism for light detection in eyes may have been co-opted for light sensing in octopus skin and then used for LACE.
© 2015. Published by The Company of Biologists Ltd.
Young Sepia officinalis (0-5 months) were studied in the laboratory and
in the sea, and their appearance and behaviour compared with that of
adult animals. Cuttlefish lay large eggs and the hatchlings are
miniature replicas of the adults. From the moment of hatching they show
body patterns as complex as those of adults and far more elaborate than
those shown by most juvenile cephalopods. There are 13 body patterns: 6
of these are `chronic' (lasting for minutes or hours) and 7 are `acute'
(lasting for seconds or minutes). The patterns are built up from no
fewer than 34 chromatic, 6 textural, 8 postural and 6 locomotor
components, used in varying combinations and intensities of expression.
Nearly all these components occur in young animals: 26 of the chromatic,
all the textural and locomotor, and 6 of the postural components.
Nevertheless, patterning does change with age and we have recorded this
and correlated the changes with behaviour. The components are built up
from units, which themselves comprise four elements organized in precise
relation to one another: chromatophores, iridophores, leucophores and
skin muscles. The chromatophores are always especially important: they
are muscular organs innervated directly from the brain and controlled
ultimately by the highest centres (optic lobes). The areas in the Sepia
brain that control patterning are already well developed at hatching,
for the appearance of the skin is as much part of the brain's motor
program as is the attitude of the arms or fins, or the posture of the
entire animal. The iridophores and leucophores develop later and are
especially important constituents of many adult patterns, notably the
Intense Zebra of the mature male. Experiments confirm that patterning is
neurally controlled and apparently mediated exclusively by the visual
system. Young cuttlefish use patterning primarily for concealment,
utilizing such strategies as general colour resemblance, disruptive
coloration, obliterative shading, shadow elimination, disguise and
adaptive behaviour. Older animals also conceal themselves but
increasingly use patterns for signalling, both interspecifically
(warning or `deimatic' displays) and intraspecifically (sexual
signalling). Laboratory-reared cuttlefish were released in the sea and
observed underwater. They quickly and effectively concealed themselves
on the substrate; it was easy for the human observer to lose them and
many passing fish behaved as if they were not there. One local predator,
Serranus cabrilla, was observed to attack them and no fewer than 35
attacks were recorded, only six of which were successful.
Laboratory-reared cuttlefish apparently distinguished between these
predators and other, non-predatory, fish the first time they encountered
them in nature.
Dielectric elastomer generators are high-energy-density electromechanical transducers. Their performance is affected by dissipative losses. This paper presents a theoretical analysis of a dielectric elastomer generator with two dissipative processes: viscoelasticity and current leakage. Conversion cycles are shown to attain steady-state after several cycles. Performance parameters such as electrical energy generated per cycle, average power, and mechanical to electrical energy conversion efficiency are introduced. Trade-offs between large electrical energy and power output and poor conversion efficiency are discussed. Excessive current leakage results in negative efficiency-the dielectric elastomer generator wastes energy instead of generating it. The general framework developed in this paper helps in the design and assessment of conversion cycles for dissipative dielectric elastomer generators. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4714557]
It has previously been shown that providing dielectric elastomer actuators with a level of pre-stretch can improve properties such as breakdown strength, actuation strain and efficiency. The actuation in such actuators depends on an interplay between the highly nonlinear hyperelastic stress–strain behaviour with the electrostatic Maxwell's stress; however, the direct effects of pre-stretch on the electromechanical coupling have still not been investigated in detail. We compare several experimental results found in the literature on the hyperelastic parameters of the Ogden model for the commonly used material VHB 4910, and introduce a more detailed and thus more accurate fit to a previous uniaxial stress–strain experiment. Electrostatic actuation models for a pure shear cuboid dielectric elastomer actuator with pre-stretch are introduced, for both intensive and extensive variables. For both intensive and extensive variables the constant strain (blocked stress or force) as well as the actuation strain is presented. It is shown how in the particular case of isotropic amorphous elastomers the pre-stretch does not affect the electromechanical coupling directly, and that the enhancement in actuation strain due to pre-stretch occurs through the alteration of the geometrical dimensions of the actuator. Also, the presence of the optimum load is explained as being due to the plateau region in the force–stretch curve, and it is shown that pre-stretch is not able to affect its position. Finally, it is shown how the simplified Ogden fit leads to entirely different conclusions for actuation strain in terms of extensive variables as does the detailed fit, emphasizing the importance of employing accurate hyperelastic models for the stress–stretch behaviour of the elastomer.
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.
Cephalopods have arguably the largest and most complex nervous systems amongst the invertebrates; but despite the squid giant axon being one of the best studied nerve cells in neuroscience, and the availability of superb information on the morphology of some cephalopod brains, there is surprisingly little known about the operation of the neural networks that underlie the sophisticated range of behaviour these animals display. This review focuses on a few of the best studied neural networks: the giant fiber system, the chromatophore system, the statocyst system, the visual system and the learning and memory system, with a view to summarizing our current knowledge and stimulating new studies, particularly on the activities of identified central neurons, to provide a more complete understanding of networks within the cephalopod nervous system.
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].
Improving on Our ExplanationIntellectual Impact and LegacyFurther ReadingReferences
We present a cellular automaton (CA) to simulate the reaction-diffusion processes which determine the pigmentation of natural mollusc shells. We obtained self-organization into stationary (Turing) structures, travelling waves and the four classes formed in Wolfram's automata. In particular, very complex “undecidable” structures (Wolfram's class IV) obtained at the transition between periodicity (class II) and chaos (class III). Agreement between the calculations and natural shells suggests evidence for class IV behaviour in the natural process.
The electrostriction of elastomeric polymer dielectrics with compliant electrodes is potentially useful as a small-scale, solid-state actuator technology. Electrostrictive polymer (EP) materials are capable of efficient and fast response with high strains (> 30%)) good actuation pressures (up to 1.9 MPa), and high specific energy densities (up to 0.1 J g-'). In this article, the mechanism of electrostriction is shown to be due to the electrostatic attraction of free charges on the electrodes. Although EP actuators are electrostatics based, they are shown to produce 5-20 times the effective actuation pressure of conventional air-gap electrostatics at the same electric field strength. The thin uniform dielectric films necessary for fabrication of EP actuators have been fabricated by techniques such as spin coating, casting, and dipping. A variety of materials and techniques have been used to produce the compliant electrodes, including lift-off stenciling techniques for powdered graphite, selective wetting of ionically conductive polymers, and spray coating of carbon blacks and fibrils in polymeric binders. Prototype actuators have been demonstrated in a variety of configurations such as stretched films, stacks, rolls, tubes, and unimorphs. Potential applications of the technology in areas such as microrobots, sound generators, and displays are discussed in this article. 0 1998 Published by Elsevier Science S.A.
The mechanical behavior of elastomeric materials is known to be rate-dependent and to exhibit hysteresis upon cyclic loading. Although these features of the rubbery constitutive response are well-recognized and important to its function, few models attempt to quantify these aspects of response perhaps due to the complex nature of the behavior and its apparent inconsistency with regard to current reasonably successful models of rubber elasticity.In this paper a detailed experimental investigation probing the material response of carbon black filled Chloroprene rubber subjected to different time-dependent strain histories is presented. Some of the key observations from the experiments are: (1) both filled and unfilled elastomers show significant amounts of hysteresis during cyclic loading; (2) the amount of carbon black particles does not strongly influence the normalized amount of hysteresis; (3) both filled and unfilled elastomers are strain-rate dependent and the rate dependence is higher during the uploading than during the unloading; (4) at fixed strain, the stress is observed to approach the same equilibrium level with relaxation time whether loading or unloading.Based on the experimental data a new constitutive model has been developed. The foundation of the model is that the mechanical behavior can be decomposed into two parts: an equilibrium network corresponding to the state that is approached in long time stress relaxation tests; and a second network capturing the non-linear rate-dependent deviation from the equilibrium state. The time-dependence of the second network is further assumed to be governed by the reptational motion of molecules having the ability to significantly change conformation and thereby relaxing the overall stress state.By comparing the predictions from the proposed three-dimensional constitutive model with experimental data for uniaxial compression and plane strain compression we conclude that the constitutive model predicts rate-dependence and relaxation behavior well.
We review a number of biologically motivated cellular automata (CA) that arise in models of excitable and oscillatory media, in developmental biology, in neurobiology, and in population biology. We suggest technical and theoretical arguments that permit greater speed and enhanced realism, and apply these to several classical examples of pattern formation. We also describe CA that arise in models for fibroblast aggregation, branching networks, trail following, and neuronal maps.
For goal-directed arm movements, the nervous system generates a sequence of motor commands that bring the arm toward the target. Control of the octopus arm is especially complex because the arm can be moved in any direction, with a virtually infinite number of degrees of freedom. Here we show that arm extensions can be evoked mechanically or electrically in arms whose connection with the brain has been severed. These extensions show kinematic features that are almost identical to normal behavior, suggesting that the basic motor program for voluntary movement is embedded within the neural circuitry of the arm itself. Such peripheral motor programs represent considerable simplification in the motor control of this highly redundant appendage.
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’.
The static actuation of dielectric elastomer actuators: how does pre-stretch improve actuation?
- G Kofod
G. Kofod, "The static actuation of dielectric elastomer actuators: how does pre-stretch improve actuation?" Journal
of Physics D: Applied Physics, vol. 41, no. 21, p. 215405,
2008.