Flexible, implantable LEDs could revolutionise drug and laser therapy

Bendy, stretchy and biocompatible arrays of light-emitting diodes (LEDs) and photodetectors would soon be used to activate drugs or monitor medical conditions inside the human body.

John Rogers at the University of Illinois and colleagues used the established semiconductor gallium arsenide (GaA) and conventional metals for diodes and detectors.

Rogers's team has shown that by depositing coiled interconnecting metal wires onto the plastic, they could create a mesh-like array of LEDs and photodetectors that could withstand extreme mechanical deformation.

The mesh is then bonded to a pre-stretched sheet of rubber, which is encapsulated in a bio-compatible transparent piece of rubber.

The resulting circuit can be bent, twisted and stretched in any direction.

Tests have shown that the behaviour of the LEDs and photodetectors remains unchanged even after the circuit is repeatedly stretched by 75%.

Yet, the flexibility has little to do with the devices themselves: it is mainly down to the interconnecting wires, whose coiled-up state accommodates a huge amount of expansion.

Rogers said he and colleagues are developing medical devices for use in vivo through their company in Cambridge, Massachusetts.

They believe versions of their rubber circuits could be used to administer light-activated drugs, and possibly also in the nascent field of phototherapy, which attempts to hasten the healing of wounds with lasers.

Brian Derby, a materials scientist at the University of Manchester, agreed that the development is less a scientific breakthrough than a feat of engineering.

But he has spotted a drawback with the use of interconnecting wires which takes the mechanical strain and keeps the device density low.

"The large spacing of the LEDs or photodetectors will lead to a limited range of applications — no flexible displays, for example," Derby said.

The findings were reported in Nature Materials.