Next-Generation Self-adaptable and Growing Robots

The long term vision of this research line is to open the way for a disruptively new paradigm of movement in robotics inspired by the moving-by-growing abilities of plants for high-tech applications. Growth is a very interesting feature of living beings that can inspire a generation of robots endowed with new and unprecedented abilities of movement. Growth involves the cellular activity of both animals and plants, although the evolution of organisms in these two kingdoms is completely different. Specifically, plant growth is “indeterminate”, since it extends throughout life. To move from one point to another, plants must grow and continuously adapt their body to the external environmental conditions. They move greatly, on a different time scale, purposively, effectively and efficiently. Thus, plants can provide new paradigms of movement for robots that will be able to move by growing and adapt their morphology to the external environments[1]

The potential impact of plant-like, self-creating robots could be huge and wide. From a scientific and technological viewpoint, the impact of these researches can be measured in the pushing of the boundaries of bioinspired soft robotics forward and improvement of plant science knowledge. Moreover, the plant-like robots, during the growing process, create compliant, semi-permanent hollow structures by material deposition, which can represent useful solutions to act in unstructured environments, for example after a disaster, moving among debris to look for survivors. The hollow structure can also be used to eventually supply water or drugs, or simply to insert cameras. This approach could represent another way to create pipes or to colonize areas searching specific targets. As some natural (climbing) plants, these growing artefacts could be used to support existing buildings or structures.

The “evolution” of Plantoids

 History

In our laboratories, we pioneered the work in plant-inspired robotics since 2007, when the European Space Agency (ESA) funded a feasibility study aiming at evaluating the effectiveness of artificial systems inspired by plant roots in space applications for the exploration of the subsoil and the anchorage of the system (report of the 8th of February, 2008 available)[2].

In the first years of study, the focus of the research was in the biological/behavioural analysis of real plants and in the artificial implementation of an innovative actuator based on electro-osmotic principle for the realization of the elongation and bending regions [3],[4].

On the 1st of May 2012, the European PLANTOID project (FP7-ICT-2011-C - Innovative Robotic Artefacts Inspired by Plant Roots for Soil Monitoring) started, coordinated by Dr Barbara Mazzolai. The PLANTOID was the first project in the world where a robot inspired by plants was proposed and developed. Also, during the project and thanks to plant inspiration, for the first time, the concept of "moving by growing" in robotics was introduced, giving rise to the next generation of robots able to grow, or otherwise, robots able to build and change their shape by the addition of new material.

In 2013, inspired by root-sloughing-cells process and elongation from the tip concept, a new root design was presented[5]. The proposed device translates at the same time the cells elongation and outward flow at the apical level of the root and the low frictional interaction with the soil provided by the sloughing cells to an engineering prototype able to penetrate more efficiently into the soil with respect to a push from the top. The main drawback of the proposed solution was the tissue flexibility, used as an interface between internal probe and soil, which does not create a solid structure permitting the soil pressure to act on the inner shaft during penetration.
To overcome this limit, a new artificial solution based on the root-growing strategy was realized[6]. Similar to natural roots, the proposed device was able to penetrate the medium imitating the growth of new cells by adding layers of artificial material at its tip. The device that performs the material deposition process (e.g. the growing mechanism) creates a straight tubular structure while moving down pushed by the newly added layer. The developed structure, which forms the body of the robot, does not move with respect to the soil and only the tip performs the penetration. 
In parallel, another approach was proposed to study the bending in an artificial root[7]. A soft bending mechanism based on three springs assembled at 120° was realized. Here the springs could simulate the cells elongation by generating and transmitting linear motions to a sensorized tip. Thanks to the flexibility of the springs and their arrangement and differential elongation, it was possible to obtain the bending of the root and emulate the real root behaviour. This prototype allowed to deepen in the study of root adaptive behaviours[7],[8].
A solution to combine growing and bending capabilities was proposed[9]. This plant root-like robot creates its body structure through additive manufacturing techniques. Specifically, the robotic root is composed of a growing body, a growing mechanism, and a tip with sensors for
environmental perception and an embedded control to imitate plant-like behaviours. The growing mechanism is a customized 3D printer-like system able to build tubular hollow structures by depositing circular layers of fused thermoplastic material at the tip level. By applying a differential deposition of the material it is possible to create an asymmetry in the structure that results in a bending of the body. With this implementation, it is possible to achieve both straight and curvilinear penetration. The developed structure is stiff and anchors to the soil acting as support for the further penetration of the tip.

The successful results of the PLANTOID project open up new perspectives of movements, actuation, manufacturing and behaviour inspired by plants in robotics, that build the foundations of the 4-years funded project GROWBOT (“GrowBot: Towards a new generation of plant-inspired growing artefacts” submitted in the call H2020-FETPROACT-2018-01, topic Living technologies).

 

[1] Del Dottore, E., Sadeghi, A., Mondini, A., Mattoli, V., & Mazzolai, B. (2018). Toward Growing Robots: A Historical Evolution from Cellular to Plant-Inspired Robotics. Frontiers in Robotics and AI, 5, 16

[2] Seidl, T., Mugnai, S., Corradi, P., Mondini, A., Mattoli, V., Azzarello, E., ... & Dario, P. (2008). Biomimetic transfer of plant roots for planetary anchoring. In Proc 59th Int Astronautics Conf.

[3] Mazzolai, B., Corradi, P., Mondini, A., Mattoli, V., Laschi, C., Mancuso, S., ... & Dario, P. (2008). Inspiration from plant roots: a robotic root apex for soil exploration. Proceedings of Biological Approaches for Engineering, University of Southampton, 50-3.

[4] Mazzolai, B., Mondini, A., Corradi, P., Laschi, C., Mattoli, V., Sinibaldi, E., & Dario, P. (2011). A miniaturized mechatronic system inspired by plant roots for soil exploration. IEEE/ASME Transactions on Mechatronics16(2), 201-212.

[5] Sadeghi, A., Tonazzini, A., Popova, L., & Mazzolai, B. (2013, May). Robotic mechanism for soil penetration inspired by plant root. In 2013 IEEE International Conference on Robotics and Automation (pp. 3457-3462). IEEE.

[6] Sadeghi, A., Tonazzini, A., Popova, L., & Mazzolai, B. (2014). A novel growing device inspired by plant root soil penetration behaviors. PloS one9(2), e90139.

[7] Sadeghi, A., Mondini, A., Del Dottore, E., Mattoli, V., Beccai, L., Taccola, S., ... & Mazzolai, B. (2016). A plant-inspired robot with soft differential bending capabilities. Bioinspiration & biomimetics12(1), 015001.

[8] Del Dottore, E., Mondini, A., Sadeghi, A., & Mazzolai, B. (2018). Swarming Behavior Emerging from the Uptake–Kinetics Feedback Control in a Plant-Root-Inspired Robot. Applied Sciences8(1), 47.

[9] Sadeghi, A., Mondini, A., e Mazzolai, B. (2017) Toward Self-Growing Soft Robots Inspired by Plant Roots and Based on Additive Manufacturing Technologies. Soft Robotics, 4 (3), 211–223.