Robotic research and development has grown by leaps and bounds in recent years especially for industrial applications. Home robotics so far is limited to small robotic appliances such a vacuums. The age of the home android robot is still a long way off, but closer than you might think. Any android robot would need a skin of some kind and a skin color. Imagine if this skin could change colors when every the owner ( is that the right word?) desires. New research into e-skin suggests that this is possible.
Some animals, such as the chameleon and cephalopod, have the remarkable capability to change their skin colour. This unique characteristic has long inspired scientists to develop materials and devices to mimic such a function. However, it requires the complex integration of stretchability, colour-changing and tactile sensing. Here we show an all-solution processed chameleon-inspired stretchable electronic skin (e-skin), in which the e-skin colour can easily be controlled through varying the applied pressure along with the applied pressure duration. As such, the e-skin’s colour change can also be in turn utilized to distinguish the pressure applied. The integration of the stretchable, highly tunable resistive pressure sensor and the fully stretchable organic electrochromic device enables the demonstration of a stretchable electrochromically active e-skin with tactile-sensing control.
This system will have wide range applications such as interactive wearable devices, artificial prosthetics and smart robots.
Human skin provides a remarkable network of sensors with highly sensitive pressure, temperature and vibration sensing. Skin can transduce environmental stimuli into physiological signals, which are then interpreted by brain. Electronic skin (e-skin) is an artificial skin that mimics the properties of skin using electronic devices. Inspired by human skin, e-skin has been found many potential applications such as wearable devices, artificial prosthetics, health monitoring and smart robots.
Unlike human skin, both animal and insect skin exhibit additional functions, for example, the chameleon’s skin has colour-changing abilities. A chameleon shifts its skin colour through controlling the skin pigment cell for purposes in camouflage, temperature maintenance and communication. Since chameleons cannot generate any body heat, the colour of their skin can in turn be used to regulate their body temperature. Mimicking the colour-changing ability of chameleons can also be achieved using approaches such as mechanical or electrical control. Whitesides and colleagues reported a soft machine equipped with microfluidic channels that can be colour-filled or colour-flushed by pumping a coloured liquid through the channels. Rogers and colleagues reported an adaptive optoelectronic camouflage system using a leucodye composite, which can produce black and white patterns to match its surroundings. Zhao and colleagues reported a soft material system for generating voltage-controlled on-demand fluorescent patterns that can be modulated to exhibit manifold geometries. Despite these achievements, the above devices nonetheless only demonstrated colour-changing abilities, it lacks the crucial function of skin, namely, tactile sensing. Javey and colleagues recently furthered these advancements by describing a user-interactive e-skin for instantaneous pressure visualization on a polyimide substrate. This e-skin is capable of correlating the applied pressure to the brightness of the devices as well as spatially mapping the applied pressure. However, the e-skin needs a constant bias to maintain its light/colour, which is not ideal for low power consumption system. In addition, since the device is fabricated on a plastic substrate, it is not stretchable.
Human skin is generally considered as an ‘ideal’ low power consumption sensor. To mimic this property, creating a low power consumption system is highly relevant for e-skin applications. In addition, presence of both parameters in tactile sensing and stretchability are also important because tactile sensing of skin allows the body to communicate with the outside environment, whereas the stretchability of skin enables us free movement.
In the following, we describe a bio-inspired stretchable e-skin with interactive colour-changing and tactile-sensing properties (Fig. 1). This concept is realized through the development and integration of a stretchable highly tunable resistive pressure sensor (PS) and stretchable organic electrochromic devices (ECDs). This e-skin, besides detecting applied pressure, is also able to distinguish varying applied pressures through real-time visible colour change. This work demonstrates low power consumption, interactive and colour-changeable e-skin, which is readily prepared by a cost-efficient all-solution processing approach.
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