'Hijacked' balsa wood could make light and tough mechanical sensors

An international team of engineers has “hijacked” balsa wood’s natural structure, transforming the soft but sturdy material into something incredibly lightweight, compressible and resilient.

The researchers from the University of Maryland in the US and Huazhong University of Science and Technology in China said the “carbon sponge” is capable of enduring repeated compression and other extreme mechanical conditions, making it particularly suitable for robust biomedical or health-monitoring devices.

The team used common chemicals to destroy the stiff hemicellulose and lignin fibres that maintain balsa’s cell wall structure. They then heated the wood to 1,000ºC, turning the organic material into carbon alone. 

The process collapsed balsa’s regular rectangular microstructure and replaced it with wavy, interlocking carbon sheets, which co-author Liangbing Hu compared to a cross between a coiled spring and a honeycomb.

The result “opened up a new realm of possibilities” for the material, said the researchers. Unlike normal carbonised wood, which collapses into ash and dust under force, the so-called carbon sponge withstood and rebounded from “substantial” compression up to 10,000 times before it deformed. The team also demonstrated its low weight by resting a chunk on top of a dandelion. 

The engineers incorporated the transformed balsa into a strain sensor prototype suitable for attachment to fingers. It could also be useful in water purification devices and energy storage.

The work appeared in Chem.