Wood is widely recognised as a natural insulator, meaning it’s not an effective conductor of electricity. However, researchers have discovered that modifying specific types of wood can enable them to conduct electricity and even be transformed into organic transistors. In a paper published in the Proceedings of the National Academy of Sciences, engineers from Linköping University in Sweden successfully changed balsa wood’s properties.
How it works
The process involved removing lignin, a natural binding substance present in wood and plants. After the lignin extraction, a network of tubes called lumina, responsible for water transportation in the balsa wood, remains. The hollowed-out balsa wood is then immersed in a liquid solution containing a conductive polymer, resulting in a material that can carry electrolyte-rich water through its lumina, creating a novel, natural transistor.
Prior to using balsa wood, researchers experimented with other types of wood, such as birch and ash, to create conductive materials. However, these alternatives lacked structural stability after being immersed in the polymer solution and did not absorb the polymer sufficiently. Moreover, balsa wood, unlike the other tested woods, maintains a consistent composition across the summer and winter seasons.
A building block for electronic devices embedded into trees and plants
According to Isak Engquist, the lead researcher involved in the project, “there is an emerging research field called electronic plants, where scientists look at different ways to send signals inside plants or to incorporate functionality such as sensors in plants, even in living plants.”
Engquist and his team created the wood equivalent of a standard transistor – an electronic component that can boost electric curre,nts or act as a switch for electric signals up to 1 Hz. A single computer chip, the size of a fingernail holds billions of minuscule transistors made from semiconductor materials such as silicon. Each semiconductor transistor can switch on and off billions of times per second.
Compared with silicon transistors, the wood transistors are significantly larger, each 3 centimetres long. They also have much slower switching speeds that only allow them to switch off in about 1 second, and to switch on in about 5 seconds.
Transformational for agricultural and forestry applications
As reported in New Scientist, the researchers confirmed that the wood transistors may be most sustainable and biocompatible for specific agriculture or forestry applications, like monitoring plants’ resilience to environmental stress and climate change.
The researchers demonstrated and assessed the wood transistor’s performance during multiple switching test runs. This signifies an “exciting engineering possibility for utilising wood” as a scaffold “that can incorporate electrical materials into devices,” says Tian Li at Purdue University in Indiana, who was not involved in the study.
Researchers may cultivate conductive wood with the polymer already inside, says Engquist. This could involve using different conductive polymers to permeate the wood without first removing the lignin.
“Most likely, each piece of wood, or each plant, would incorporate only a few wood electrochemical transistors, and these would be on the millimetre-size scale,” says Engquist.
Future developments in this field may also allow for the creation of more advanced electronic devices integrated into plants and trees. This could lead to innovations like self-powered sensors and energy-harvesting systems, which would further contribute to sustainable and eco-friendly technology solutions.
