Inspired by plants: Develop new processes for the growth of synthetic materials that can grow like plants

An interdisciplinary team of scientists and engineers at the University of Minnesona Twin Cities has developed a new process
that has never been seen before to enable synthetic materials to grow.
This new approach will allow researchers to build better soft robots that can navigate
hard-to-reach places, complex terrain and potential areas inside the human body.
The paper, published in the journal Proceedings of the National Academy of Sciences (PNAS), provides an inspiration
for the combined application of biology and materials science.

Many natural organisms such as fungal hyphae and plant roots grow at their tips, and Tip Growth demonstrates exemplary processes of material synthesis and drive coupling, providing a blueprint
for how to achieve growth in synthetic systems.
Inspired by plant and fungal growth, the researchers developed a new process
based on the growth of self-lubricating photopolymerization and extrusion of synthetic materials.
This strategy enables a new, continuous, light-based method of manufacturing special-shaped parts that was previously impossible with state-of-the-art three-dimensional (3D) printing or other methods
.
The researchers used this material growth pattern to produce a soft robot that could grow quickly and continuously, thus solving the main limitations of the growth process of soft robots due to limited scalability, lack of permanent structure, and inability to pass through tortuous paths, demonstrating the potential
of soft robot growth to provide new capabilities in the field of manufacturing and soft robots.

Soft robots are an emerging field where robots are made of soft, pliable materials rather than rigid materials
.
Soft-growth robots can "make new materials," "grow" on the move, and can be used for operations in tortuous, complex parts that humans can't reach, such as inspecting or installing underground pipes, or navigating
biomedical applications inside the human body.
Previous soft-grown robots would drag solid materials behind them and transform them into longer-lasting structures through heating and/or pressure, just as
3D printers are injected with solid fibers to produce products in their shape.
However, the trajectory of solid materials becomes more difficult at bends and turns, which makes it difficult for robots to navigate
through obstructed terrain or winding paths.

As plants grow outwards, plants use water to transport building materials, transforming into solid roots at the tip of the root
.
The University of Minnesota team identified three basic principles for the tip growth of biological organisms: fluid pressure creates driving forces, local polymerization produces structures, and fluid-mediated transport
of constituent substances.
Based on these properties, the researchers developed a synthetic material growth process called self-lubricating interface photopolymerization extrusion (E-SLIP), which continuously pushes the material from one opening with liquid raw materials, using photopolymerization technology to create solid contour polymer parts
with adjustable mechanical properties.
With this technique, soft robots can more easily pass through obstacles and curved paths without having to drag any solid material behind
it.
To demonstrate the utility of E-SLIP, the researchers created a tip-growing soft robot, introducing its basic control principles and highlighting its ability to grow at speeds of up to 12 cm/min and lengths up to
1.
5 meters.
This constantly "growing" soft robot is capable of performing a range of tasks, including exploring, digging and traversing winding paths, highlighting the potential of synthetic growth as a platform for infrastructure, exploration and on-demand manufacturing
of sensing in a variety of environments.

"This is the first time these concepts have been fundamentally demonstrated," said Chris Ellison, the paper's first author and professor in the Department of Chemical Engineering and Materials Science at the University of Minnesota's Twin Cities, "and developing new manufacturing methods is critical
to our nation's competitiveness and bringing new products to people.
" On the robotic side, robots are increasingly being used in dangerous, remote environments, and these are the areas where
this work can have an impact.
Matthew Hausladen, Ph.
D.
, of the Department of Chemical Engineering and Materials Science at the University of Minnesota's Twin Cities and another author of the paper, said, "We were really inspired
by the way plants and fungi grow.
" "We adopted the idea that plants and fungi add matter to the ends of their bodies, either on the tip of the root or on the new shoots, and we translate it into an engineered system
.
"

This new process is also used
in manufacturing.
Since the researchers' technique uses only liquids and light, operations that use heat, press, and expensive machines to create and shape materials may not be necessary
.