Portable devices that can be worn by patients have come a long way in the last few years thanks, in part, to important advances in flexible electronics and devices that can mould themselves to the soft structure of skin and tissue. Indeed, a host of novel biocompatible applications, such as patch-like thermometers that stick to the skin like temporary tattoos and electronic circuits that interface with internal organs such as the heart and brain, have already seen the light of day. Sophisticated though such structures are, most of them are unable to independently store recorded data in memory modules during long-term patient monitoring. Also missing is the fact that they cannot deliver drugs in response to diagnoses made by analysing the data patterns collected.

A team led by Dae-Hyeong Kim of Seoul National University has now developed a new system that addresses these shortcomings. The device, which measures around 4 × 2 cm and is 0.3 mm thick, contains movement sensors made from single-crystal silicon nanomembranes that detect strain – generated, for example, when muscles expand and contract. The data obtained by these sensors is stored in ultrathin oxide nanomembranes in which uniformly sized gold nanoparticles are embedded. This part of the device also analyses the data collected and triggers the release of therapeutic drugs if needed, which are contained inside porous silica nanoparticles.

Transdermal drug delivery

"All these multifunctional arrays of sensors and memory, which are fabricated using conventional semiconductor-industry techniques, are then transfer-printed onto a commercially available plastic hydrocolloid patch that can be placed directly onto the patient's skin – for example, on their wrist," explained Kim.

And that is not all: thanks to a thermal actuator made of resistive heaters, the drugs can be made to diffuse into the skin at optimal rates. Finally, a sensor made of thin patterned metal films monitors skin temperature during drug delivery to make sure that the skin does not overheat.

"We have shown that our wearable device can monitor and record body movements from muscle contractions, such as tremors, and if a patient twists his arms or legs," Kim told our sister site nanotechweb.org. These types of movement disorders occur in patients with diseases like Parkinson's or epilepsy. "The device is also robust and continues to function just as well even if repeatedly bent, twisted or stretched on the skin."

The team, which includes researchers from the University of Texas at Austin and MC10 Inc. in Massachusetts (co-founded by John Rogers of the University of Illinois), says that it is now looking to improve its device by making it completely wireless.

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