Shape-Shifting Microbot to Repair Bones

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Researchers at Linköping University in Sweden and Okayama University in Japan developed a shape-shifting microrobot that can self-create a bone-like material under the right conditions. The electroactive material responds to low voltage electric current and changes its volume and shape, allowing the researchers to pre-program specific movements and guiding the resulting architecture. The technology could be useful in stimulating bone healing, particularly in problematic fractures. The researchers envisage that the soft material could maneuver itself into a fracture, expand and then mineralize and harden, providing a scaffold for bone regeneration.   

The quest to develop biomaterials that can stimulate and facilitate bone growth continues, with non-healing fractures representing a major source of patient morbidity. This latest offering is quite sophisticated, although the material will require further development to unlock its full potential. The approach is inspired by the soft connective tissue present in the skull at birth, called fontanelles, that allow a baby’s head to pass through the birth canal, and which harden after birth to form fully fledged bone.

“We want to use this for applications where materials need to have different properties at different points in time,” said Edwin Jager, one of the developers of the new technology. “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 technology consists of a base alginate hydrogel. On one side, the researchers created an electroactive polymer that changes its volume when a low voltage is applied, causing the gel to bend in a specific direction. On the other side of the gel, the researchers affixed biomolecules from cells that are involved in bone development. When the biomolecules encounter the correct environment inside the body they will begin to mineralize and stiffen, creating a scaffold that will allow additional bone to grow.

The researchers have shown a proof-of-concept by immersing their material into cell culture medium, which aims to mimic the environment that cells encounter in the body. The calcium and phosphor within the culture medium stimulated the biomolecules to begin hardening and mineralizing.

The researchers hope that they can develop the material to the point where it could be successfully maneuvered within the body to repair fractures. “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,” said Jager.

Study in Advanced Materials: Biohybrid Variable-Stiffness Soft Actuators that Self-Create Bone

Via: Linköping University

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