Bone growth inspired 'microrobots' that can create their own bone

Date:
January 17, 2022
Source:
Linko"ping University
Summary:
Inspired by the growth of bones in the skeleton, researchers
have developed a combination of materials that can morph into
various shapes before hardening. The material is initially soft,
but later hardens through a bone development process that uses
the same materials found in the skeleton.



FULL STORY ========================================================================== Inspired by the growth of bones in the skeleton, researchers at the universities of Linko"ping in Sweden and Okayama in Japan have developed
a combination of materials that can morph into various shapes before
hardening.

The material is initially soft, but later hardens through a bone
development process that uses the same materials found in the skeleton.


==========================================================================
When we are born, we have gaps in our skulls that are covered by pieces of
soft connective tissue called fontanelles. It is thanks to fontanelles
that our skulls can be deformed during birth and pass successfully
through the birth canal. Post-birth, the fontanelle tissue gradually
changes to hard bone. Now, researchers have combined materials which
together resemble this natural process.

"We want to use this for applications where materials need to have
different properties at different points in time. Firstly, the material is
soft and flexible, and it is then locked into place when it hardens. This material could be used in, for example, complicated bone fractures. It
could also be used in microrobots -- these soft microrobots could be
injected into the body through a thin syringe, and then they would
unfold and develop their own rigid bones," says Edwin Jager, associate professor at the Department of Physics, Chemistry and Biology (IFM)
at Linko"ping University.

The idea was hatched during a research visit in Japan when materials
scientist Edwin Jager met Hiroshi Kamioka and Emilio Hara, who conduct
research into bones. The Japanese researchers had discovered a kind
of biomolecule that could stimulate bone growth under a short period
of time. Would it be possible to combine this biomolecule with Jager's materials research, to develop new materials with variable stiffness?
In the study that followed, published in Advanced Materials, the
researchers constructed a kind of simple "microrobot," one which can
assume different shapes and change stiffness. The researchers began
with a gel material called alginate. On one side of the gel, a polymer
material is grown. This material is electroactive, and it changes its
volume when a low voltage is applied, causing the microrobot to bend
in a specified direction. On the other side of the gel, the researchers attached biomolecules that allow the soft gel material to harden. These biomolecules are extracted from the cell membrane of a kind of cell
that is important for bone development. When the material is immersed
in a cell culture medium -- an environment that resembles the body and
contains calcium and phosphor -- the biomolecules make the gel mineralise
and harden like bone.

One potential application of interest to the researchers is bone
healing. The idea is that the soft material, powered by the electroactive polymer, will be able to manoeuvre itself into spaces in complicated
bone fractures and expand.

When the material has then hardened, it can form the foundation for the construction of new bone. In their study, the researchers demonstrate
that the material can wrap itself around chicken bones, and the artificial
bone that subsequently develops grows together with the chicken bone.

By making patterns in the gel, the researchers can determine how the
simple microrobot will bend when voltage is applied. Perpendicular lines
on the surface of the material make the robot bend in a semicircle,
while diagonal lines make it bend like a corkscrew.

"By controlling how the material turns, we can make the microrobot move
in different ways, and also affect how the material unfurls in broken
bones. We can embed these movements into the material's structure,
making complex programmes for steering these robots unnecessary," says
Edwin Jager.

In order to learn more about the biocompatibility of this combination
of materials, the researchers are now looking further into how its
properties work together with living cells.

The research was carried out with financial support from organisations including the Japanese Society for the Promotion of Science (JSPS)
Bridge Fellowship program and KAKENHI, the Swedish Research Council,
Promobilia and STINT (Swedish Foundation for International Cooperation
in Research and Higher Education).

========================================================================== Story Source: Materials provided by Linko"ping_University. Original
written by Karin So"derlund Leifler. Note: Content may be edited for
style and length.


========================================================================== Journal Reference:
1. Danfeng Cao, Jose G. Martinez, Emilio Satoshi Hara, Edwin
W. H. Jager.

Biohybrid Variable‐Stiffness Soft Actuators that
Self‐Create Bone. Advanced Materials, 2022; 2107345 DOI:
10.1002/adma.202107345 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220117085821.htm

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