Embedded electronics on soft contact lenses
Soft contact lenses could display information to the wearer and provide continuous medical monitoring.
Currently transparent electrodes are usually made from a material known as indium tin oxide (ITO). Although it works, it is brittle, cracks and loses functionality if flexed. It also degrades over time, and is somewhat expensive due to the limited quantities of indium metal.
UNIST (Ulsan National Institute of Science and Technology) scientists have combined graphene with silver nanowires to form a thin, transparent and stretchable electrode.
Graphene is well known as good a candidate for transparent electrode because of their unique electrical properties and high mechanical flexibility. However, scalable graphene synthesis methods for commercialisation produces lower quality graphene with individual segments called grains that increase the electrical resistance at boundaries between these grains.
Silver nanowires, on the other hand, have high resistance because they are randomly oriented like a jumble of toothpicks facing in different directions. In this random orientation, there are many contact between nanowires, resulting in high resistance due to large junction resistance of nanowires.
Due to these drawbacks, neither is good for conducting electricity, but a hybrid structure, combined from two materials overcomes their weaknesses. It presents a high electrical and optical performance with mechanical flexibility and stretchability for flexible electronics.
There’s almost no change in its resistance when bent and folded. The structure developed by the research team, may soon find use in a variety of other applications.
The research team demonstrated Inorganic light-emitting diode (ILDED) devices fitted on a soft eye contact lens using the transparent, stretchable interconnects of the hybrid electrodes as an application example.
“We believe the hybridisation between twodimensional and one-dimensional nanomaterials presents a promising strategy toward flexible, wearable electronics and implantable biosensor devices, and indicate the substantial promise of future electronics,” said Jang-Ung Park, professor at UNIST, who led the effort.
As an in study, the LED embedded contact lens was worn by a live rabbit eye for five hours and none of abnormal behaviour, such as bloodshot eye or the rubbing of eye areas had been observed.