A research team at Stanford University in the United States has developed the first synthetic material with a sharp touch and rapid and repeated healing at room temperature. This progress may lead to the emergence of smarter artificial limbs or more flexible self-repairing personal electronic products. The research results were published in the "Nature? Nanotechnology" magazine on November 11.
Researchers have been trying to imitate the excellent properties of human skin, such as the tactile sensation of the skin (the precise information sent to the brain about pressure and temperature) and the efficient self-healing ability. Professor Zhenan Bao and his team from the Department of Chemical Engineering at Stanford University successfully integrated the above two properties into a single synthetic material.
In the past 10 years, artificial skin research has made significant progress, but even the most effective self-healing materials still have major deficiencies. Some are not practical because they must be exposed to high temperatures. Some can heal at room temperature, but repairing the wound will change its mechanical or chemical structure, so it can only be used once. Most importantly, there has not been a self-healing material with good electrical conductivity.
The team of Bao Zhenan successfully achieved the best of both worlds by mixing the two components-the self-healing ability of the plastic polymer and the conductivity of the metal. The plastic they use contains long-chain molecules linked by hydrogen bonds. These molecules are easy to break up. When they are reconnected, the hydrogen bonds can reorganize and restore the structure of the material.
The researchers added tiny metallic nickel particles to this elastic polymer to increase its mechanical strength. The nano-scale surface of nickel particles is rough, which is essential for the material to form conductivity. Each protruding edge accumulates an electric field, making it easier for current to travel from one particle to the next, thereby making the plastic polymer conductive.
The researchers tested the material's ability to recover from mechanical damage and electrical conductivity after damage. They took a thin strip of material and cut it in half. After putting it together and gently pressing it for a few seconds, the material can recover 75% of its original mechanical strength and conductivity; if pressed for 30 minutes, the recovery of the material performance is close to 100%. More importantly, the same sample can be cut repeatedly in the same place. After 50 cuts and repairs, the flexibility and stretch of the sample are still intact.
The team also discussed the pressure-sensitive properties of the material. The process of electrons forming a current in the material is similar to jumping across a stream between stones. Nickel particles play the role of stones, and the distance between them determines how much energy an electron needs to jump from one stone to another. The twisting or pressing on the synthetic skin will change the distance between the nickel particles, which will change the difficulty of electron hopping. These subtle resistance changes can be converted into information that the skin is under pressure and tension. Researchers say the material can detect pressure changes caused by handshake.
Bao Zhenan said that the material is very sensitive to depression and flexion, so future prostheses will have better bending at the joints. Electrical equipment and wires covered with this material can also repair themselves, making electrical maintenance no longer difficult and expensive, especially in hard-to-reach places, such as building walls or vehicles. The research team's next goal is to make the material more transparent and more flexible, suitable for packaging and covering electronic devices or display screens.
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