How healthy is energy harvesting in the medical field, and what’s the prognosis?

Etiology

The only certain thing in electronics is that active devices need power; the rest is optional. There are several ways to provide power. For small devices, the most common currently is batteries, and they require changing or recharging. A not overly onerous task, although some may disagree, if it involves attaching a USB-C cable and plugging the other end into a power supply. But for the growing field of implantable medical devices such as pacemakers, battery replacement involves an invasive surgical procedure risking internal bleeding, inflammation and infection, all of which would be unnecessary if the promise of energy harvesting is realised.

There are a number of options to power medical devices through harvesting ambient energy sources in the human body such as heat, movement, or pressure.  Various research studies that we describe later show that the power that can be gleaned from energy harvesting devices is in the nanowatt to microwatt range, which would be enough to power a device. An increasing number of studies and experiments seem to confirm that energy harvesting can be a solution to provide that needed power.

Treatment plan

One solution is piezoelectric energy harvesting. In simple terms piezoelectric energy harvesting converts mechanical stress – such as a finger pushing on a piezoelectric material – into a current that can then power a device. It has been proposed as a harvesting method for example in road surfaces, shoes, or as we will see in pacemakers. A multi-university group of South Korean researchers demonstrated its potential in a live pig. The team attached a flexible energy harvester to a pig’s heart. The harvester used the contraction and relaxation of the heart’s muscles to power a radio frequency device which transmitted a signal to an external device to turn a light bulb on and off. The team reported a harvested current of 1.75uA (with a voltage of 17.8V). Furthermore, the researchers said that their device showed high biocompatibility. The impressive results of this in vivo demonstration suggest potential applications as implanted heart monitors for those with heart disease.

At the University of Michigan a similar idea was investigated. The researchers simulated a device that harvests energy from the reverberations of heartbeats through the chest. The electricity so generated can then be used to power a pacemaker or defibrillator. In simulations the device was shown to produce 10mW of power, which is eight time more than that required to run a pacemaker.

A rarely considered possibility for energy harvesting in the body is using the flow of blood. The heart pumps five litres of the red stuff every minute. Scientists at Shanghai’s Fudan University in China have developed a novel method to harvest electricity from blood flow using a nano-device. The device, called a fibre-shaped fluidic nanogenerator (FFNG), is a thin carbon nanotube filament that is wound round a fibre core with a half micron diameter. It uses the flow of salt solutions through it to build a harvestable charge. The scientists claim that the power conversion efficiency of the device is high at 20% – which is significantly more than other miniature energy harvesting devices. The device also has characteristics making it suitable in this application: elasticity tunability, light weight, and one dimensionality. The team produced positive results of blood flow energy harvesting from frogs.

If harvesting energy through the methods above doesn’t achieve results it is possible to hook devices up to natural batteries in the body. These biological batteries are located in the ear and usually convert the mechanical activity of the eardrum vibrating into electrochemical signals to send sound information to the brain. To exploit this battery several US institutes – MIT, Massachusetts Eye and Ear Infirmary (MEEI) and Harvard-MIT Division of Health Sciences and Technology – designed a device to harvest its power. The researchers developed a low-power chip that could utilise some of the power from the ‘battery’. The resulting device was then attached by wires to a guinea pig’s ear-battery. The chip itself rested outside the body of the guinea pig, but the team said that it is small enough to nestle in the cavity in the middle of the ear. The team believes that with further miniaturisation of the device it could be used for implanted self-powering hearing aids.

Prognosis

The prognosis is good. There is much research being carried out in the field with some positive results. New devices face a complex process before they can be used in medical practice, but the need is there and once the devices show themselves capable it should not be long before they are approved and implanted into real patients.

 

[Image licensed to Ingram Image]

 

 

Add this: