Material designers and entrepreneurs have long hoped for wearable electronics to come on the market, but as yet, technology has not been able to make electrical devices small enough, flexible enough, and strong enough to be practical.

While high demand for rubber-like electronic materials have produced a wide range of options for integrated electronics, such as single-crystal inorganics or amorphous ceramics [using a range of materials, including silicon, rubrene, indium gallium zinc oxide, and even poly(3-hexylthiophene-2,5-diyl) (P3HT)], none of these materials are mechanically stretchable.

But now, nanotechnology specialists have found a way to make wearable electronics a reality by using carbon nanotubes as a raw material.

The breakthrough was made by a team from the University of Houston (UH) who state that they have developed stretchable semiconductors with high carrier mobility (the speed at which electrons can move through a material).

Semi-conductors like this are highly-sought after, as they can conduct an electrical current with minimal resistance while maintaining strength and flexibility, paving the way for truly wearable electronics. Furthermore, the team, led by Cunjiang Yu, an assistant professor of mechanical engineering at UH, have also added logic circuits to their wearable devices, as well as ‘sensory skins’ and ‘rubbery integrated electronics’.

The key to the discovery was employing the strength, flexibility, and conductivity of carbon nanotubes. As the online journal Design Newsreports the researchers, “… achieved their breakthrough to remedy these issues by discovering that adding tiny amounts of metallic carbon nanotubes to the rubbery semiconductor of P3HT, or polydimethylsiloxane composite, can lead to improved carrier mobility.”

The team have now published their results in the journal Science Advances, where they announce the introduction of, “… a stretchable rubbery semiconductor with a high effective mobility and report on fully rubbery transistors and integrated electronics and circuits. The stretchable rubbery semiconductor exploits π-π stacking P3HT–nanofibrils (NFs) percolated in a silicone matrix. We use metallic carbon nanotubes (m-CNTs) as surface dopants, which substantially enhance the effective carrier mobility by offering superior carrier transportation paths to shorten the transport distance within the channel.”

(A) An optical microscopic image of a rubbery transistor. (B) Schematic exploded view of the rubbery transistor structure and schematic illustration of charge carrier transport routes. 

Adding that, “The strategy of using metallic carbon nanotube (m-CNT) doping to substantially enhance the effective mobility of the intrinsically stretchable semiconductor proves to be feasible. Our rubbery semiconductor of m-CNT–doped P3HT-NFs/PDMS compared with previously reported intrinsically stretchable polymer semiconductors has clear merits, including much higher μFE [Field-effect mobility, proving its ability to transport a charge], fabrication from commercially available materials, scalability, and repeatability in material and device manufacturing.”

The team also describe how their product of, “… integrated electronics, logic gates, and sensory skins from high effective mobility rubbery semiconductors suggests that integrated electronics in a fully rubbery format, in contrast to traditional rigid and brittle counterparts, can be developed.”

Looking ahead, the researchers hope to further develop their ideas for wearable electronics. This includes higher-level integrated circuitry, bioelectronics and other electronic biomedical applications, as well as stretchable integrated circuits.

Given the widespread use of electronic devices in everyday lives, investors are now speculating on which products would wearable tech be best suited. A wearable smartphone? A wearable GPS device for hikers and bikers? Wearable medical sensors? A wearable child-locating device?

What would you do with a wearable electronic device?  


Photo credit: ScienceAdvances, & VulcanPost