Harvesting Energy from the Body

Cardiac pacemakers, one of the products of modern biomedical engineering research, are implantable devices which run off batteries and are installed inside the body. Just like any other battery operated device, the power runs out after a certain time. Once the battery dies, the chest has to be opened up to replace the pacemaker. Michael McAlpine, a professor of mechanical engineering at Princeton University, says that if there is a way to harvest energy from the movement of the internal organs, the battery life can be prolonged or can even totally replace the battery on the devices.

This has become the focus of the biomedical science research of John Rogers and his colleagues. Rogers is a professor of materials science and engineering at the University of Illinois at Urbana-Champaign. His research team has developed flexible, energy-storing devices which are able to convert the continuous movements of body parts such as the heart and the diaphragm into reusable energy. The power captured by the device is said to be sufficient to provide power to certain implantable devices such as pacemakers.

In a paper published in PNAS, the device was described to be composed of thin ribbons of lead zirconate titanate (PZT) which are surrounded by flexible, biocompatible plastic, integrated with a rechargeable battery and rectifier. Rat muscle was grown on the devices to ensure that the device would not be toxic to the body. Flexibility was measured through 20 million cycles of testing. The devices were then sutured into place on different organs of cows, sheep and pigs, including their hearts, diaphragms, and lungs. It was determined that the implantation showed no disruption on the organ’s movements. Furthermore, it was found out that the devices produced sufficient energy to charge a human pacemaker.

The potential of this new technology is not limited to providing energy to pacemakers. Amin Karami, an assistant professor of mechanical and aerospace engineering at SUNY Buffalo, pointed out that an energy-harvesting device such as this one could provide power not only to pacemakers but also other implantable devices as well such as cardiac defibrillators and brain stimulators.

This innovative technology shows great promise. However, it is yet to be tested for clinical use. Several concerns have been raised regarding the device including its invasiveness as it needs to be stitched on the organ. The PZT component of the energy-harvester, which contains lead, can also raise potential problems. A small leak on the device can poison the heart and the surrounding tissues. This however may be addressed by the more recent piezoelectrics which can replace PZT, and does not contain lead, Alpine said.

Rogers explained that although the device has been proven to work in animal models, it is yet to be evaluated in long term researches. He pointed out that there is a probability that the endurance of the device and their integration with the heart may show deficiencies. “I don’t think we’ll see problems, but you have to go through that process to find out”, Rogers added.

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