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How Bionic Skin Could Solve Real World Problems

by Rachel Crowell
June 5, 2017 | Our Future

From our favorite bionic pet, Chris P. Bacon, to the development of softer, more human robots, the days of bionic body parts are no longer limited to comic book characters. And thanks to a new 3-D printing process developed by researchers at the University of Minnesota, new bionic skin could lead to innovations ranging from touch-enhanced surgical robots to chemical and explosive detection devices that could be used to keep soldiers safer in war zones and (in case you need any more of a reason to believe robots could take over the world) to giving robots a sense of touch.

Welcome to the future.

Professor of mechanical engineering and lead researcher on the study Michael McAlpine and his lab build "3-D printers that can print a variety of functional products including electronic materials and devices," he explained. In 2013, McAlpine was part of a team that was internationally recognized for developing a bionic ear that could listen to music. With this project, his team demonstrated that you can 3-D print and integrate human cells and electronics, McAlpine said.

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The team’s latest development? 3-D printed touch sensors that could act as “bionic skin” on robots, human skin, and more. This bionic skin is “far more sophisticated” than the 2013 bionic ear, said McAlpine.

The researchers are able to test each sensor by touching it, according to McAlpine.

“When you touch it, the coil [in the sensor] compresses and you get an electrical signal.”

Printing the bionic skin

The 3-D printers in McAlpine’s lab can print materials that commercially available printers can’t. The 3-D printers that are currently on the market can only print hard plastics, said McAlpine. In this study, McAlpine’s team printed sensors with several layers, which are printed in the following order:

  1. A pure silicon base layer
  2. A bottom electrode that’s made from a mixture of 75 percent silver and 25 percent silicon conductive ink
  3. A sensor layer composed of 68 percent silver and 32 percent silicon
  4. An additional layer of pure silicon
  5. A supporting layer of “sacrificial ink.” This layer stays in place while the sensor sets. After that, this layer is washed away.
  6. A top electrode, which is composed of the same 75 percent silver and 25 percent silicon conductive ink as the bottom electrode

Watch the bionic skin being printed onto a model hand in the video below:

3-D scanning and printing on the model hand

The model hand was “just something we had laying around [the lab],” according to McAlpine.

Before printing on the fake hand, the team scanned it using a 3-D scanner. In the future, the team plans to streamline this process. They are currently building scanners that can scan in real time.

After this improved technology is available, the team hopes it will be possible to conduct the scanning and printing as one integrated step, according to McAlpine.

“We’re not there yet but that’s exactly where we’re going.”

Creating this combined scanning and printing step will make it a bit more simple to print on real human hands, but the team still has many challenges to overcome before this vision may become a reality.

Gearing up for what’s next: Printing bionic skin on top of real human skin

The potential applications for the bionic skin are almost endless. In addition to its surgical and military applications, the bionic skin could also be used to “give robots a sense of touch.” These tactile sensors could even be integrated with McAlpine’s previously-developed bionic ear. This combination of technologies might lead to a device that could be used to restore hearing in certain people.

However, all of these possible applications hinge on McAlpine’s team demonstrating one next step: printing their sensors onto human skin.

Bionic Skin pbs rewire
Illustration of the sensors as they're printed onto a model hand using a specialized 3-D printer developed at the University of Minnesota. Image credit: Michael McAlpine and Shuang-Zhuang Guo.

With the recent study, McAlpine’s team demonstrated 3-D printing onto complex surfaces, an advancement that’s “a very useful tool,” according to James Pikul, a professor in the University of Pennsylvania’s Department of Mechanical Engineering and Applied Mechanics. Pikul is familiar with the bionic skin study, but wasn’t involved with conducting it.

“I didn’t see any major flaws [with the study],” said Pikul. “I think the whole idea is super interesting.”

Pikul’s own research focuses on using new materials to create new engineering technologies which he applies to the field of soft robotics. Unlike regular robotics, soft robotics is used to create robots with a stiffness that’s more comparable to skin, Pikul said. One area he researches is energy storage for robotics.

“One of the biggest advantages [of soft robots] is that you can integrate them with humans better,” said Pikul. Regular robots can be dangerous to interact with because they are made of strong, hard materials, and they often move at high speeds. Soft robotics materials are more easily able to bend and “dynamically flex with the body,” Pikul added.

The transition from printing on model hands to human hands is a significant jump, but Pikul believes it’s not insurmountable. There are two types of challenges McAlpine’s team will have to overcome: chemical ones and technological ones, he added.

Since it’s made of materials ranging from soft skin to hard bones, “the human is very complex,” said Pikul. “The shapes [in the human body] are very nonlinear. They are mostly curved surfaces.”

This poses a printing challenge, as it’s easier to print on a flat surface than a curved one.

While the recent study showed that it’s possible to 3-D print the sensors onto a model hand that has a similar curve as a human hand, movement is one major challenge that’s present when researchers attempt to 3-D print on real human hands.

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If you’re trying to get a sensor printed on your hand, no matter how still you try to stay, “Your hand will not be perfectly still,” notes Pikul. As your hand moves, the printer that’s printing the bionic skin onto your hand will need to detect this movement, track it and follow the position of your hand in order for the device to print out correctly.

Printing on human subjects also requires materials that are biocompatible, Pikul added. The bionic skin needs to be able to adjust to human movements (such as the bending of body parts) once it’s printed. Also, it needs to be made of chemicals that can be directly applied to human skin without causing harmful reactions.

Before the team attempts printing on human skin, the researchers are considering switching from conductive to semiconductive inks, according to McAlpine. When you touch a semiconductive device, its conductivity changes, McAlpine said. Silicon computer chips are one type of semiconductive device.

In the past, the team already showed that they can 3-D print semiconductors. (Conductive inks are easier to 3-D print with than semiconductive inks. It’s also easier to measure the electrical signals generated in sensors made using conductive inks, according to McAlpine. That’s why his team used conductive inks in this initial study.)

“The chemical challenge is a serious challenge,” said Pikul. The process of overcoming that challenge is “where new and exciting work could be.”

The work is at a very early stage, McAlpine said. His team is currently working on further developing their ink and other materials in preparation for printing the bionic skin on a human hand.

Bionic Skin pbs rewire
These images show the 3-D scanning and printing processes, from the starting point (a) to the finished product (i). Images courtesy of Michael McAlpine.

Once this key step has been achieved, the team will either collaborate with other researchers or let other researchers handle using the bionic skin to solve real world problems, such as detecting dangerous chemicals and explosives, McAlpine said.

Since the 3-D printers that his team created aren’t commercially available, McAlpine said his team has a bit of a “monopoly” on this type of 3-D printing, creating a situation where researchers from other institutions are approaching them with collaboration offers.

“Really, we are one of the few groups in the country that can do this sort of thing…Right now, we are having a lot of fun collaborating with [other] people,” said McAlpine.

If you like this, you might also like:

Soft Robotics Engineer Kari Love Started as a Broadway Costume Designer

How the Ultra-Realistic Robot Creatures in ‘Spy in the Wild’ Were Created


Rachel Crowell
Rachel Crowell is a Midwest-based writer exploring science and math. Rachel lives in Iowa with Delilah, a golden retriever a stranger once called “the cutest thing in America.” Outside of STEM topics, Rachel welcomes writing opportunities on everything from art to finance. Follow Rachel on Twitter at @writesRCrowell. Reach Rachel at [email protected]
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