Researchers at the Istituto Italiano di Tecnologia in Genova have created what they say is the first 4D-printed, biomimetic, biodegradable, soft robot that changes shape in response to humidity and can navigate through soil. The researchers say the device has great potential as a new means of monitoring the environment. Photo: Istituto Italiano di Tecnología.
4D printing is the process of using 3D printing to create objects that can change their shape or properties in response to environmental factors such as light and temperature. The technology has been used previously to create self-assembling, programmable material technologies. Now, 4D technology has been used to create a soft robot capable of analyzing soil. The researchers drew inspiration from the seed structure of the South African geranium, which changes shape in response to environmental humidity.
“Our studies started from the observation of nature, with the aim to imitate the strategies of living beings or their structures and replicate them in robotic technologies with low environmental impact in terms of energy and pollution,” said Barbara Mazzolai, corresponding author of the study.
The seeds of the family of flowering plants, which includes geraniums, exploit their hygroscopic (humidity-activated) properties by detaching themselves under the right environmental conditions. After detaching, they change shape and independently penetrate the soil, increasing the chances of germination. After investigating the structure and biomechanics of the natural seed, researchers replicated it using a combination of 3D printing and electrospinning techniques. Electrospinning is a method of fiber production that uses electric force to draw charged polymers up to fiber diameters.
The researchers used fused deposition modeling (FDM) to print a substrate layer comprised of polycaprolactone (PCL), a biodegradable thermoplastic polyester, that was activated using oxygen plasma to make it hydrophilic. Then they added to the substrate electrospun hygroscopic fibers composed of a polyethylene oxide shell and a cellulose nanocrystal core.
In tests, the soft robot explored a soil sample, adapting its shape to interact with its roughness and cracks. They found it to be quite energy efficient and capable of lifting around 100 times its own weight.
“With this latest research, we have further proved that it is possible to create innovative solutions that not only have the objective of monitoring the well-being of our planet, but that do so without altering it,” Mazzolai said.
The researchers are hopeful that the device’s low cost, simple design and data-collecting capabilities will be particularly useful in remote areas. “These biodegradable and energy-autonomous robots will be used as wireless, battery-free tools for surface soil exploration and monitoring,” said Luca Cecchini, first author of the study. “This bio-inspired approach has allowed us to create low-cost instruments that can be used to collect in-situ data with high spatial and temporal resolution, especially in remote areas where no monitoring data are available.”
The study was published in the journal Advanced Science.