Researchers at Linköping University in Sweden and Okayama University in Japan have developed a shape-shifting micro-robot that, under the right conditions, can make a bone-like material on its own. The electroactive material responds to low-voltage electrical current and changes its volume and shape, allowing researchers to pre-program specific movements and control the resulting architecture. The technology could be useful in stimulating bone healing, particularly in problematic fractures. Researchers envision the soft material could maneuver itself into a fracture, expand, and then mineralize and harden to provide a scaffold for bone regeneration.
The search for biomaterials that can stimulate and facilitate bone growth continues, with non-healing fractures being a major cause of patient morbidity. This latest offering is quite sophisticated, although the material still needs further development to realize its full potential. The approach is inspired by the soft connective tissue present in the skull at birth, called fontanelles, which allow a baby’s head to pass through the birth canal and which harden after birth to form full-fledged bones.
“We want to use this for applications where materials need to have different properties at different points in time,” says Edwin Jager, one of the developers of the new technology. “On the one hand, the material is soft and flexible and is fixed when it hardens. This material could be used for complicated bone fractures, for example. It could also be used in micro-robots – these soft micro-robots 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 the one hand, the researchers created an electroactive polymer that changes volume when a low voltage is applied, causing the gel to bend in a certain direction. On the other side of the gel, the researchers attached biomolecules from cells involved in bone formation. When the biomolecules meet the right environment in the body, they begin to mineralize and stiffen, creating a scaffold that allows for additional bone growth.
The researchers have demonstrated a proof-of-concept by immersing their material in a cell culture medium that aims to mimic the environment cells encounter in the body. The calcium and phosphorus in the culture medium stimulated the biomolecules to begin hardening and mineralization.
Researchers hope to develop the material to the point where it can be successfully maneuvered around the body to repair fractures. “By controlling how the material rotates, we can make the microrobot move in different ways and also influence how the material unfolds in broken bones. We can embed these movements into the material structure, eliminating the need for complex programs to control these robots,” says Jager.
Studies in Advanced Materials: Biohybrid Soft Actuators with variable stiffness that create bone themselves
Over: University of Linkoping
