Researchers at the University of California, Los Angeles (UCLA) have developed a unique design of ultrathin films for producing highly flexible yet mechanically robust bioelectronic membranes. These membranes could pave the way for diagnostic on-skin sensors that fit precisely over the body’s contours and conform to its movements. The researchers report their work in a paper in Science.

Held together by van der Waals forces, which are intermolecular interactions that can only occur at extremely close distances between atoms or molecules, the novel membrane is stretchable and adaptable to dynamically changing biological substrates, while being breathable and permeable to water and air. This durable electronic material could lead to the development of non-invasive electronics for medicine, healthcare, biology, agriculture and horticulture. The researchers term the material a van der Waals thin film (VDWTF), and it could serve as a foundational platform for living organisms to adopt electronic capabilities.

“Conceptually, the membrane is like a much-thinner version of kitchen cling film, with excellent semiconducting electronic functionality and unusual stretchability that naturally adapts to soft biological tissues with highly conformal interfaces,” said Xiangfeng Duan, professor of chemistry and biochemistry at UCLA. “It could open up a diverse range of powerful sensing and signaling applications. For example, wearable health-monitoring devices built with this material can accurately track electrophysiological signals at the organism level or down to the level of individual cells.”

The researchers created several demonstrations with the thin films, including a transistor that sat on top of a succulent plant’s leaf, whose abundant electrolytes were used to create the electronic circuit. They also created a similar transistor for human skin that used electrolytes naturally present on skin cells to complete the circuit. In addition, the team developed an electrocardiogram that uses small circles of the film placed on a person’s right and left forearm, which could detect their blinking during meditation.

“Our proof-of-concept demonstrations using the van der Waals thin film really just hint at the myriad possibilities for this new material,” said Yu Huang, professor and chair of the Materials Science and Engineering Department at the UCLA Samueli School of Engineering. “The membrane could serve as the connection for human-machine interfaces, enhanced robotics and artificial intelligence-enabled technologies that connect directly. This could open a pathway to synthetic electronic-cellular hybrids – cyborg-like living organisms with electronic enhancements.”

The ultrathin, approximately 10nm-thick electronic membranes are made of several atomically thin layers of the inorganic compound molybdenum disulfide, each just 2–3nm thick. The key to maintaining the membrane’s structural integrity while keeping it thin lies in its unique layered patchwork structure. The layers do not form a single continuous sheet but instead are an assemblage of smaller pieces.

Instead of being held in place by rigid covalent bonds, the layers are loosely connected by nonbonding van der Waals forces. This allows them to slide and rotate independently over one another, creating extraordinary pliability while keeping their electronic functionality intact.

This design also allows the membranes to stretch and flex over irregular geometries. The thin films can adhere to soft biological tissues, fitting snugly over their micrometer-scale topologies. They seamlessly merge with, and actively adapt to, dynamically changing biological substrates, such as skin, without tearing or interfering with the membranes’ functionality. The layered patchwork also creates a percolating network of nanochannels, large enough for air and water molecules to pass through, giving the material its permeability and breathability.

With its unusual combination of high electronic performance and malleability, the van der Waals film addresses many of the problems that hamper other candidates for bioelectronic thin films, such as inorganic membranes or organic thin films. Those alternatives have been limited by their thickness, lack of stretchability, incompatibility to merge with irregular geometries of biological surfaces and their poor performance in wet biological environments.

This story is adapted from material from UCLA, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.

Artistic representation of a skin transistor made from van der Waals thin films. Image: Yan et al./UCLA.
Artistic representation of a skin transistor made from van der Waals thin films. Image: Yan et al./UCLA.