First ever 3D-printed biodegradable ‘seed robot’ created to monitor soil conditions

“Our studies started from the observation of nature, 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, in a press release.

Geranium has a seed-carrying structure known as hygromorphic structure, as per the study. This plant seed can change shape in response to environmental factors such as humidity changes. These seeds move independently to explore and penetrate the soil, increasing the likelihood of germination.

The researchers precisely replicated the seed's natural ability to create an artificial robot. To mimic seed design, techniques such as 3D printing combined with electrospinning (electric power fiber production) and fused deposition modeling were used. 

The authors also investigated the best materials for absorbing humidity to create artificial seeds. Finally, a biodegradable thermoplastic polyester was chosen as a material for artificial seed creation. The resulting prototype demonstrated the ability to explore soil samples as well as change shape in relation to its surroundings.

"These biodegradable and energy-autonomous robots will be used as wireless, battery-free tools for surface soil exploration and monitoring. This bioinspired 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," said Luca Cecchini, first author of the study.

The findings were published in the journal Advanced Science.

Study abstract:

Geraniaceae seeds represent a role model in soft robotics thanks to their ability to move autonomously across and into the soil driven by humidity changes. The secret behind their mobility and adaptivity is embodied in the hierarchical structures and anatomical features of the biological hygroscopic tissues, geometrically designed to be selectively responsive to environmental humidity. Following a bioinspired approach, the internal structure and biomechanics of Pelargonium appendiculatum (L.f.) Willd seeds are investigated to develop a model for the design of a soft robot. The authors exploit the re-shaping ability of 4D printed materials to fabricate a seed-like soft robot, according to the natural specifications and model, and using biodegradable and hygroscopic polymers. The robot mimics the movement and performances of the natural seed, reaching a torque value of ≈30 µN m, an extensional force of ≈2.5 mN and it is capable to lift ≈100 times its own weight. Driven by environmental humidity changes, the artificial seed is able to explore a sample soil, adapting its morphology to interact with soil roughness and cracks.