Soft Robot DraBot Signals Environmental Disruptions

Duke University researchers have revealed an electronics-free, soft robot. It is like a dragonfly that can react to environmental conditions such as temperature, pH, or the presence of oil and fly across the water. The proof-of-principle demonstration could be the antecedent to more autonomous, long-range, superior environmental sentinels for observing a broad range of possible telltale indications of problems. 

On March 25, the Advanced Intelligent Systems publication online described the soft robot.

Due to the flexibility of Soft robots, they are a growing trend in the industry. Soft bodies can handle sensitive things such as living tissues that metal or ceramic elements would damage. Soft bodies can assist robots to fly or squeeze into compact spaces where rigid structures would get stuck. 

The expanding domain was on the mind of Shyni Varghese, professor of materials science and mechanical engineering, biomedical engineering, and orthopedic surgery at Duke when inspiration struck.

“I received an e-mail from Mrs. Varghese, revealing she had a plan for a soft robot that employs a self-healing hydrogel that her partners have developed in the past to respond and move autonomously,” said Vardhman Kumar, a Ph.D. scholar in Varghese’s laboratory and first author of the paper. 

In March 2012, Varghese and her laboratory invented a self-healing hydrogel that immediately responds to variations in pH. Whether two adjacent pieces “painted” with it or a crack in the hydrogel, a shift in acidity prompts the hydrogel to create new bonds, which are entirely reversible when the pH rebounds to its original value.

Varghese’s quickly drafted plan was to discover a technique to apply this hydrogel on a soft robot that could move across water and indicate areas where the pH fluctuations. Along with several other modifications to show variations in its surroundings, she figured her lab could create a soft robot as a sort of self-governing environmental sensor. 

Kumar started designing a soft robot based on the fly with a postdoctoral associate Ung Hyun Ko in Varghese’s laboratory. After many repetitions, the duo settled on the shape of a dragonfly directed with a system of interior microchannels that enable it to be controlled with air pressure.

They built the body — by pouring silicon into an aluminum frame and hardening it –about 2.25 inches long with a 1.4-inch wingspan. The team applied soft lithography to design interior channels and combined them with adjustable silicon tubing. DraBot was born.

Source: Duke University

“The most challenging part is to getting DraBot to respond to air pressure. Also, to control over long ranges using only self-actuators without any electronics was difficult,” said Ko. 

DraBot operates by regulating the air pressure getting inside its wings. Microchannels move the air inside the front wings, where it leaves through a set of holes guided directly inside the back wings. DraBot goes nowhere if both rear wings are down, and therefore the airflow is prevented. And DraBot goes forward when both wings are up.

The group further invented balloon actuators to add an element of control below each of the back wings near to DraBot’s body. When filled, the balloons let the wings to curl upward. By switching which wings are up or down, the engineers explain DraBot where to go.

“We were delighted when we were able to command DraBot. However, it’s based on living things, and living things don’t simply move around on their own, they respond to their surroundings,” said Kumar. 

That’s where self-healing hydrogel comes into play. By applying one set of wings with the hydrogel, the engineers were ready to make DraBot responding to fluctuations in the encompassing water’s pH. If the water is acidic, one side’s front wing combines with the rear wing. Rather than moving in a straight path as instructed, the asymmetry lets the robot spin in a circle. Once the pH reverts to its normal value, the hydrogel “un-heals,” the combined wings separate, and DraBot becomes completely receptive to commands.

To strength its environmental recognition, the engineers also leveraged the sponges beneath the wings and sedated the wings with temperature-responsive components. When DraBot flies across the water with oil hovering on the surface, the sponges will absorb it up and change shade to the corresponding shade of the oil. And when the water becomes overly heated, DraBot’s wings change shade from red to yellow.

The engineers think these sorts of measurements could act as an essential part of an environmental robotic sensor in the future. Responsiveness to pH can recognize freshwater acidification, which is a severe environmental dilemma hitting several geologically-sensitive regions. 

The potentiality to absorb oils makes such long-distance skimming robots a perfect applicant for the immediate detection of oil spills. Varying colors due to temperatures could assist in spotting red tide and the bleaching of coral reefs, which leads to a drop in the population of aquatic life.

Drabot Soft Robot
Source: Duke University

Engineers also discuss various methods that they could enhance on their proof-of-concept. Solid-state sensors or Smart cameras could improve the abilities of DraBot, and designing a kind of onboard propellant would support related bots break free of their tubing.

“Instead of employing air pressure to regulate the wings, I could imagine applying some kind of synthetic biology that generates power,” said Varghese. “That’s a distinct discipline than I operate in, so we’ll have to discuss with some expected partners to see what’s feasible. But that’s section of the joy of operating on an interdisciplinary project like this.”

Journal Reference:

Vardhman Kumar, Ung Hyun Ko, Shyni Varghese, Jiaul Hoque, Gaurav Arya, Yilong Zhou. Micro engineered Materials with Self‐Healing Features for Soft RoboticsAdvanced Intelligent Systems, 2021; 2100005 DOI: 10.1002/aisy.20210000

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