Crumpled Carbon Nanotube Forests to Power Medical Devices

Most implantable and wearable medical devices benefit from having on-board batteries powering them, but because conventional batteries have specific internal geometries, they end up being blocky and not flexible. This limits development of the electronic devices, especially pliable ones, since the human body itself is mostly soft and flexible.
While flexible electronics is already a well established field, most flexible devices have still relied on inflexible batteries. Researchers at Researchers at Michigan State University have just developed stretchable supercapacitors, devices that can hold onto electrical charge and release it as necessary, that can be pulled to 800% of their original size and continue working.

The capability is made possible thanks to so-called crumpled carbon nanotube forests (CNT forests). These forests are able to conduct electricity because of the individual carbon nanotube “trees” swing ad-hoc and come in contact with other nanotubes. The material is no more than 30 micrometers in height, and it can be shaped into different forms to comply with whatever requirements a given device has.

“It’s more robust; it’s truly a design breakthrough,” said Changyong Cao, director of Michigan State’s Soft Machines and Electronics Laboratory. “Even when it’s stretched up to 300% along each direction, it still conducts efficiently. Other designs lose efficiency, can usually be stretched in only one direction or malfunction completely when they are stretched at much lower levels.”

From the study abstract in journal A dvanced Energy Materials :

In this work, a new type of highly stretchable and reliable supercapacitor is developed based on crumpled vertically aligned carbon nanotube (CNT) forests transferred onto an elastomer substrate with the assistance of a thermal annealing process in atmosphere environment. The crumpled CNT‐forest electrodes demonstrated good electrochemical performance and stability under either uniaxial (300%) or biaxial strains (300% × 300%) for thousands of stretching–relaxing cycles. The resulting supercapacitors can sustain a stretchability of 800% and possess a specific capacitance of 5 mF cm−2at the scan rate of 50 mV s−1. Furthermore, the crumpled CNT‐forest electrodes can be easily decorated with impregnated metal oxide nanoparticles to improve the specific capacitance and energy density of the supercapacitors.