Stretching the Imagination with Conformal Displays

FOR THIS “LOOKING BACK” FEATURE, I decided to go back 10 years, close my eyes, and randomly click on the online library. I pulled up the January/February 2014 issue, with arguably one of the most unique covers we ever published (Fig. 1). It features the sepia apama, also called the Australian giant cuttlefish, which is one of many cephalopods that can change the appearance of its skin in an instant, creating one of nature's more intriguing displays. They can mimic the colors, patterns, and even textures of their environment to become essentially invisible to predators or put on luminous displays as a means of communication.

If you are having trouble visualizing this, imagine the well-known invisibility illusion where one side of a truck has a huge flat display on it and the other side has a camera. As the truck drives down the street, the camera looking out the far side of the truck captures an image that is then displayed on the near side, and like magic the vehicle is gone. In our example, it takes a huge display mounted on the side of the truck to achieve this effect. But for a cuttlefish, it only takes the action of millions of chromatophores, which are small, pigmented organs embedded in their skin. Lydia M. Mäthger and Roger T. Hanlon described how this works in their article, “Dynamic Displays in Nature” (Fig. 2).¹ What I found most interesting was how complex the optics, chemistry, and biology are to accomplish this in nature. Various display innovations, such as micro-electromechanical systems (MEMs) devices with diffractive and refractive optics, have tried to mimic these natural systems. Many things still can be learned from the natural world.

In our quest to make displays more ubiquitous and personal, we have been pursuing all manners of properties, such as flexibility and stretchability, to make them more skin-like. Efforts have brought forth contact lenses that contain entire microLED displays, small displays and sensors that can read our biology, and materials we can wrap around our shoes, clothing, and cars to change their appearance (Fig. 3).² Real products, such as rollable displays, are available now, and soon you might be able to adhere an entire flexible phone to your hand or arm. Imagine being able to change your entire appearance with just a tap on your smartwatch, or change from bright colors in the outdoors to conservative tones in the office just by walking in or out of the door?

I have seen more than one science fiction movie where the characters have computing devices on the backs of their hands that light up when needed and then fade to disappear when turned off. When on, they can form holographic images in space and transmit unimaginable amounts of data in an instant, even where no cell service exists. However, I have never seen an explanation for how or when they recharge those devices.

The team at UCLA created a transparent composite electrode comprising a thin percolation network of silver nanowires laid in the surface layer of rubber that could withstand 1,500 cycles of up to 30 percent strain without failure. They used this innovation to create an elastomeric OLED with a polymer light-emitting electrochemical cell (PLEC) architecture (Fig. 4).⁴

Meanwhile, at the University of Tokyo, they reported on several innovations around creating electronic skin.¹ Such a material could be applied directly to the human body and could be used to monitor medical conditions or to provide more sensitive and lifelike prosthetics with sensing “skins.” They developed innovations such as organic flexible transistors, tactile sensors, and touch sensors on ultra-thin polymer sheets (Fig. 5).

The touch sensor was made from a molded pressure-sensitive rubber sandwiched between electrodes. The thin rubber layer used a novel design that uses micrometer-sized pyramid-like structures that expand when compressed, allowing the material to detect the weight of a fly resting on its surface.

These are just a few examples of the great ideas discussed in this issue that chronicled how much already had been tested and studied by then. If you were enthusiastic then, you might be wondering why we do not have all-electronic skin suits, chameleon clothing, and eye implants ready for sale now. Perhaps that is an idea for a future issue.