Implanted biomedical devices, such as heart-rate monitors, pacemakers, defibrillators and neural stimulators, rely on some form of battery power to work. And although these batteries have become smaller and much more efficient in recent years, they still only last a few years and need to be regularly replaced – something that requires the patient to undergo surgery. Not exactly an ideal situation.

The best solution to this problem would be to do away with batteries altogether. A team led by John Rogers has now gone some way in addressing this issue with its new device based on lead zirconate titanate (PZT) nanoribbons. PZT has a high piezoelectric voltage and dielectric constant – ideal properties for converting mechanical energy into electrical energy. The material is also highly bendable and mechanically strong.

The device works by harnessing the natural contractile and relaxation motions of the heart, lung and diaphragm, and converting these into electricity. And the good news is that the generator produces more than enough electricity to power implants such as pacemakers, for example. As well as being deployed inside the body, the same technology might even be used to make wearable health monitors if placed directly on the skin, says Rogers.

The Illinois researchers have already confirmed that the device is compatible with the major organs in several animal models. Hearts, lungs and diaphragms from pigs and cows were tested, for instance.

The main element in the device is a capacitor-like structure comprising a layer of PZT 500 nm thick sandwiched between two electrodes – one made of titanium and platinum and the other from chromium and gold. The set-up consists of 12 groups of 10 such structures electrically connected in parallel. The researchers connect each of the 12 groups in series to its neighbouring group to increase the output voltage. They then encapsulate the ensemble in a biocompatible material, such the polymer polyimide, to isolate it from body fluids and tissue. This approach has the added advantage of minimizing the risk of an immune response, explains Rogers.

When the device is bent, strain is generated in the PZT nanoribbons, which produces electrical charge. This results in a voltage being generated between the two electrodes.

Rogers told that his team has just received the go-ahead to perform clinical experiments in live animals to assess how they react in the long-term to the implanted devices. “We are now beginning work in this direction,” he revealed.

The current work is detailed in PNAS doi: 10.1073/pnas.1317233111.

Further reading

Silk helps make bio-integrated electronics (May 2010)
Nanoarray patch takes your temperature to millikelvin precision (Sep 2013)
Hairy solution to making sensitive artificial skin (Aug 2012)
Fingertip mounted silicon nanomembranes provide sensing platform (Aug 2012)