LANZHOU -- Chinese scientists have made progress in the study of flexoelectricity in natural biomass materials, experimentally observing considerable flexoelectricity in wood and expanding understanding of wood's functional properties, according to Lanzhou University.

Conducted by researchers from Lanzhou University, the study has been published in the journal Nature Communications. Its findings provide a new material system and technical support for the development of green, sustainable, flexible electronic devices and self-powered sensors, said the university.

Flexoelectricity refers to the electromechanical coupling phenomenon in which materials generate electricity under strain gradients and is theoretically widely observed in various solid materials.

"To put it simply, it is the phenomenon where materials generate electricity when bent. It differs from the piezoelectric effect, where materials generate electricity when squeezed, and all dielectric materials exhibit such an effect, thus offering broad application prospects," said Liu Shuhai, a professor at the School of Materials and Energy of Lanzhou University.

Flexoelectricity is a widespread electromechanical property of solids, with application prospects in diverse fields, such as sensing, actuating and energy harvesting. It has been widely studied in synthetic materials such as crystals, ceramics and metals, but remains unexplored in natural biomaterials such as wood.

"Due to the complex hierarchical structure of wood and other factors that make accurate identification difficult, directly detecting the flexoelectricity effect in wood and other natural biomass materials is challenging," Liu said.

Researchers amplified the strain gradient in wood through structural reconstitution by combining electrical tests with control experiments to verify the flexoelectric response generated by structural wood during bending deformation.

Compared with other traditional flexoelectric materials, wood-based structural materials demonstrate unique advantages, according to Wang Jizeng, a professor at the School of Civil Engineering and Mechanics of Lanzhou University.

"Wood is widely available, renewable, and biodegradable and features natural hierarchical structures, oriented cell walls, and abundant pore channels, providing a natural structural foundation for strain gradient regulation and electromechanical coupling responses," Wang added.

The study shows that structural wood treated with delignification and compression highlights the green and sustainable features of biomass materials, and also demonstrates the feasibility of achieving high-performance electromechanical functionalization of natural biomass materials through structural engineering.

The researchers further developed a wood-based, self-powered, flexible sensor. It can convert tiny deformations caused by human movement into detectable electrical signals without an external power source, enabling real-time perception of joint movements, such as finger and wrist movements, as well as subtle actions like muscle contractions.

"Our study indicates that structural wood can work as a traditional load-bearing material and also as a core functional unit for green flexible electronics and self-powered sensor components, with potential application prospects in fields such as wearable electronics, health monitoring, human-machine interaction, and intelligent bio-interfaces," said Wang.

"Wood-based flexoelectric materials highlight advantages in environmental friendliness, resource sustainability, mechanical adaptability and functional integration. They will provide new material options for developing next-generation green intelligent devices," Wang added.