Emerging Technologies Inspired by Plants - Bioinspired Approaches for Human-Centric Technologies - page 114

This pressure is dissipated into the expansion of a soil cavity and into the frictional
resistance of the soil to advance the root.
As the root cap moves through the soil, cells are sloughed off, and the structure
constantly needs to be replaced. The root cap is covered with a thick layer of
mucilage, which is secreted by the root tip and helps lubricate the root as it pushes
through the soil. Mature cells (located behind the apex) are anchored to the soil to
allow the apex to move forward. This anchoring is achieved by using root hairs,
secondary roots, and root waving. While the mature root is anchored to the soil, root
growth from the tip represents both the development and movement of this organ
(Fig. 4.1 ). This process enables roots to adapt their morphology and organ devel-
opment to environmental conditions, even in hard soil, because the cell division and
morphology are directly influenced by the surrounding environment. Additionally,
EFT results in the reduction of dynamic frictional resistance during penetration due
to the movement of only a limited part of the root body, the apex.
An estimation of the EFT strategy to increase the efficiency of the root during
soil penetration is difficult to calculate. Additionally, these biological strategies are
not immediately applicable to new engineering solutions. The development of
dedicated bioengineering tools to quantify mechanical and physical biological
properties can offer some support in studies related to penetration capabilities and
in biomimetic approaches. To quantify the relevance of EFT in penetration with
respect to the entire body insertion, two sets of penetration tests were performed in
granular substrates by using a probe (Tonazzini et al. 2013 ). These tests demon-
strated that the amount of penetration energy required for EFT was less than the
energy required for NoEFT for all of the initial depths that were considered. There
was a significant difference between the results achieved for different initial depths.
The reduction increased from approximately 20 % at an initial depth of 100 mm to
50 % at an initial depth of 250 mm. These results indicate that increasing the
penetration depth could reduce the energy consumption by more than 50 % by using
penetration with EFT. Therefore, EFT in plant roots represents an efficient solution
for penetrating deep soils and is a source of inspiration for designing a robotic
system to explore soil.

4.3 Plant Root-Like Robotic Artifacts: The PLANTOIDS

The plant root features that were previously mentioned can be considered in the
design and development of a new generation of hardware and software technolo-
gies. These technological solutions are called “PLANTOIDS,” which are robotic
systems equipped with distributed sensing, actuation, and intelligence to perform
environmental exploration and monitoring tasks.
PLANTOIDS were inspired by an attempt to reproduce the penetration, explo-
ration, and adaptation capabilities of plant roots. Using a biomimetic approach, this
technology has two major goals: (1) to detail and synthesize principles that enable
plant roots to effectively and efficiently explore and adapt

to underground