A team of engineers at Duke University has developed a new electronics-free, soft robot that could play a big role in monitoring environmental conditions in the future. The robot is shaped like a dragonfly, and it can skim across water while reacting to environmental conditions like pH, temperature, and the presence of oil.
The new proof-of-principle demonstration was detailed in the journal Advanced Intelligent Systems on March 25.
Soft robots continue to advance and improve, and they are growing in importance thanks to their versatility. They are capable of handling delicate objects like biological tissues, and they can fit into tighter spaces compared to other rigid robots.
Shyni Varghee, the one responsible for the idea, is professor of biomedical engineering, mechanical engineering and materials science, and orthopaedic surgery at Duke.
Vardham Kumas is a PhD student in Varghese’s lab and first author of the paper.
“I got an email from Shyni from the airport saying she had an idea for a soft robot that uses a self-healing hydrogel that her group has invented in the past to react and move autonomously,” Kumar said. “But that was the extent of the email, and I didn’t hear from her again for days. So the idea sort of sat in limbo for a little while until I had enough free time to pursue it, and Shyni said to go for it.”
Back in 2012, Varghese’s lab developed a self-healing hydrogel capable of reacting to changes in pH in just seconds. A change in acidity causes new bonds to be formed on the hydrogel, and this can be reversed when the pH returns to original level.
Part of Varghese’s new idea was to use the hydrogel on a soft robot to enable it to travel across water while detecting pH changes in different places. She sought out a way for the lab to come up with this type of robot that acts like an autonomous environmental sensor.
Joined by Ung Hyun Ko, a postdoctoral fellow in Varghese’s lab, Kumar designed a soft robot based on a fly. After various attempts, the team decided on the shape of a dragonfly, and it was engineered with a network of interior microchannels enabling it to be controlled by air pressure.
The body of the soft robot is about 2.25 inches long, and its wingspan is 1.4 inches. It was created by pouring silicone into an aluminum mold before baking it. Soft lithography was relied on to create interior channels that were connected with silicone tubing.
The resulting soft robot was termed DraBot.
“Getting DraBot to respond to air pressure controls over long distances using only self-actuators without any electronics was difficult,” said Ko. “That was definitely the most challenging part.”
DraBot controls the air pressure that comes into its wings, and microchannels then carry the air into the front wings. It then escapes through holes that are pointed directly into the back wings. DraBot will not move if the airflow is blocked by both back wings being down. However, if both wings are up, it moves forward.
The team also developed balloon actuators to give more control, and they are located under each of the back wings near the robot’s body. When these are inflated, the wing curls upward, and the researchers can control where the robot goes by changing which wings are up or down.
“We were happy when we were able to control DraBot, but it’s based on living things,” said Kumar. “And living things don’t just move around on their own, they react to their environment.”
The team utilized the self-healing hydrogel by painting one set of winds with it, which made DraBot responsive to any changes in the water’s pH. If it is too acidic, one side’s front wing fuses with the back, causing the robot to spin in a circle rather than straight. After the pH returns to a normal level, the hydrogen reverses and the wings separate once again, allowing DraBot to become fully responsive to commands.
The researchers also added temperature-responsive materials, which enables DraBot to skim over water and soak up oil with sponges. The color of the sponges change depending on the color of the oil, and when the water is too warm, the robot’s wings change color as well.
The new developments could help combat environmental problems in the future. For example, such a robot could detect freshwater acidification, which affects various geologically-sensitive regions. It could also help detect oil spills early or detect early signs of red tide and coral bleaching.
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