Soft, transparent robots could soon be doing surgery as engineers at MIT have used advanced hydrogel to make powerful, durable robots

Engineers at MIT have made hydrogel robots capable of swimming, kicking a ball and even catching and releasing live fish.

For years the team led by Xuanhe Zhao and graduate student Hyunwoo Yuk had been mixing up a range of hydrogels, a jelly-like substance made almost entirely of water. Originally they did not intend on using their hydrogels for robotics and instead were focused on developing ways to glue these hydrogels to various surfaces such as glass, metal, ceramic and rubber.

Like many of the greatest scientific inventions, the team had unintentionally developed something revolutionary, a new material for soft robotics.

Like many of the greatest scientific inventions, the team had unintentionally developed something revolutionary, a new material for soft robotics. By using their unique hydrogel creation the MIT team had an advantage over previous soft robotics inventions, which were made using silicone, as silicone is not as safe to use in a clinical setting as hydrogels.

Others have attempted to use hydrogels to make soft robots but the end product was usually brittle and inflexible and therefore prone to bursting. These new hydrogel robots were tested for over a thousand cycles and were found to maintain their robustness.

To construct the robots 3D printing was used to form the simplest part of the structure – a chain of hollow cubes or tubes. To create the more complex designs these components were then cross-linked. Using this technique Yuk and Zhao created a trio of robots with different skills: a simple chain of cubes that would curl up when activated and could kick a rubber ball, a grabber capable of catching fish and a fish-like swimming robot (have a look at the link below).

 

The fish-like hydrogel robot. click link to see it ‘swimming’ http://www.nature.com/article-assets/npg/ncomms/2017/170201/ncomms14230/extref/ncomms14230-s7.mov (Yuk et al, 2017)

What makes these hydrogel robots particularly interesting is the mechanism they are powered by. Traditional hydrogel robots rely on osmosis to cause a shape change. This means that the robot is activated by water gradually entering it but this can take hours and only generates a few millinewtons of force. The robots engineered by Yuk and Zhao instead, used syringe pumps to inject water into the hollow tubes. This enables a rapid and forceful shape change producing a few newtons of force in a second.

Others have attempted to use hydrogels to make soft robots but the end product was usually brittle and inflexible and therefore prone to bursting.

The team were also keen to camouflage their soft robots. Other engineers have used techniques similar to that of octopi and squid to camouflage their hydrogel robots but for this to work they are required to know the background colours that the robot will be used against. Inspired by Leptocephali, transparent eel larvae, Yuk and Zhao realized they could overcome this issue by making their hydrogel robots visually and sonically transparent in water. They achieved this by making hydrogel robots with an exceptionally high water content so that they had visual and sonic properties almost identical to water. The end product was a little robot fish that can swim virtually undetected across a rainbow of colours.

The applications for this new breed of soft robot are far reaching, Yuk says they are now working with medical groups to try and make hydrogel “hands” which could be used in surgery. They could also be used for controlled and sustained delivery of drugs or cells. Marine biologists may be able to take advantage of the technology to produce more realistic robots for interaction with marine animals. Additionally their transparent properties may give these robots a job in the military being used for underwater reconnaissance.

IMAGE: Flickr

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Kate Dearling

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