Engineering news
Researchers at Stanford University have developed a self-healing artificial muscle that can expand and contract when exposed to an electrical pulse.
To create the rubber-like material, short polymer strands were cross-linked in a fishnet pattern and these were attached to molecules to create a chemical coordination complex called ligand. Several ligands are then connected to make longer stretchable chains and finally, metal ions are introduced to the structure to form combined compounds.
When the material is strained, the knots loosen and allow the ligands to separate and when relaxed, the affinity between the metal ions and the ligands pulls the fishnet taut, resulting in a strong, stretchable and self-repairing elastomer. The metallic component in the compound causes the material to twitch when exposed to an electric field.
In one experiment the team was able to stretch a 1in polymer film beyond 100ins, which exceeded the 45in stretch limit on their measuring machine. They found that changing the amount or type of metal ion included in the compound could vary the stretch and healing properties of the substance. The sample film was created by decreasing the ratio of ion atoms to the polymers and organic molecules in the material.
Professor Zhenan Bao, chemical engineer at Stanford, said: “The polymers become linked together like a big net through the metal ions and the ligands. Each metal ion binds to at least two ligands, so if one ligand breaks away on one side, the metal ion may still be connected to a ligand on the other side. And when the stress is released, the ion can readily reconnect with another ligand if it is close enough.”
Further tests showed that the elastomer could self-repair at room temperature and at temperatures as low as -20°C, whereas damaged polymers typically require a solvent or heat treatment to restore their properties.
With its attributes the researchers propose that the material could be used as artificial muscle or form part of a complex physical structure for artificial skin, which can be used to restore some sensory capabilities to people with prosthetic limbs. The research also has implications for developments in wearable technology and for medical treatments.