These Bone Growth-Inspired Microbots Can Create Their Own Bone

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A team of researchers at the universities of Linkoping in Sweden and Okayama in Japan has developed a combination of materials that can morph into different shapes and can be hardened. The team was actually inspired by the growth of bones in the skeleton. The bone development process involves the transformation of soft bones at an initial stage into hardened material that uses the same substances found in the skeleton.

Edwin Jager, associate professor at the Department of Physics, Chemistry, and Biology at Linkoping University said, “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.”

The team came up with the idea during a research visit in Japan where Jager met with Hiroshi Kamioka and Emilio Hara, who conduct research into bones. The researchers had discovered a biomolecule that could strengthen bone growth in a short period of time. They wondered if it could be combined with Jager’s materials research to develop new materials.

In the study, researchers created a simple “microrobot” that can take different shapes and change stiffness. The team started with a gel material called “alginate”. A polymer material is grown on one side of the gel. This material is electroactive, and it changes its volume upon the application of some high voltage. This can cause the microrobot to bend in a specified direction.

Researchers attached biomolecules to the other side of the gel. These biomolecules allow gel material to harden. The material can then be immersed in a cell culture medium, an environment that resembles a body and contains calcium and phosphor. Once it is submerged, the biomolecules make the gel mineralize and harden.

There are many applications for this new material, such as bone healing. When in soft form, it is made to move into spaces in complicated bone fractures before expanding. After hardening, it would form the foundation for the construction of new bone.

The team has deployed the same material in their study, wrapping it around the chicken bones. The artificial bone hat subsequently develops grows together with the chicken bone. By making the patterns in gel, the researchers also determined the criteria for bending microbots upon the application of voltage. 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 programs for steering these robots unnecessary”, says Edwin Jager.

Researchers are now looking into how its features work together with living cells. Actually, they want to learn more about the biocompatibility of this combination of materials.

The study was published in Advanced Materials.

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