Wearable technology is becoming common these days, but the next step is to move technology from being on our bodies to being inside us. The question is, how do you get power to a device that lives under your skin?
Medical implants that are already inside patients today generally use internal batteries. Lithium batteries are common, but not the sort you’d find in your phone. These batteries have a risk of exploding, you don’t want to be anywhere near them when that happens, much less have one inside you! Cardiac pacemakers have been using lithium/iodine-polyvinylpyridine batteries for decades. A technology that was first patented in 1972! This is an early practical example of a solid-state battery since it has a solid rather than liquid electrolyte.
There are various problems with using an internal battery, however. All batteries have a limited lifespan, which means that eventually, you’ll require a procedure to replace or remove them. Battery technology continues to march ahead and there have been advances such as flexible batteries free from toxic chemicals. So don’t discount internal power cells of one sort or another for implants. There have even been some out-there ideas such as using a plutonium battery similar to the devices that power satellites and extraplanetary rovers.
One day we may have safe, long-lasting, high-capacity batteries using materials such as graphene that can recharge quickly. Electrical induction is one way to charge these batteries without invasive wires, but why not just power your implants directly with induction?
Electrical induction happens when electrical energy is used to create a magnetic field, which then, in turn, creates an electrical current in a receiving wire coil. This is how wireless charging works with phones and sealed electric toothbrushes. Induction doesn’t have to be short-range as it is with common wireless charging today.
There have been a few attempts at long-range wireless charging with the ultimate goal being a truly wireless future. So in the context of implantable devices, you might power or charge them through power transmission coils built into the walls of your home and other buildings people commonly occupy, such as office buildings.
Stanford scientists announced major strides in this area back in 2014. They created tiny implants that could receive power wirelessly and charge up devices like pacemakers.
Converting Glucose to Power
Glucose is one of the most important power sources we humans use. It’s not the only way we get energy (for example, ketone bodies are another), but with a body that’s so filled with chemical energy why not use it to power implants?
If we could find some way to convert the glucose in our bloodstream to the electrical power our technology needs, it might be unnecessary to stick batteries inside us or blast ourselves with magnetic fields. It might also help you justify that extra ice cream before bed!
This isn’t a theoretical device, it’s a real technology known as a glucose fuel cell. In 2012 MIT scientists and engineers announced that they had developed a working glucose fuel cell with the potential to power neural prosthetics or any other electronic device in the body that needs juice to work. The idea has been around since at least the 1970s. A glucose fuel cell was even considered as a power source for early pacemakers, but ultimately solid electrolyte batteries won out.
One problem with glucose fuel cells is that they can store up quite a lot of energy, but they can’t release it quickly and at the levels needed for modern implants. In 2016, researchers published the results of using a hybrid device that combines a glucose fuel cell with a supercapacitor, with promising results.
Humans have been using the flow of liquid to generate power for centuries. Water-wheels have provided mechanical power for mills or to lift water for irrigation. Today we use hydroelectric dams for clean energy powered by gravity and the water cycle induced by heat from the sun.
So, why not use the flow of blood through our circulatory system to power nanogenerators? In 2011 Swiss scientists revealed a tiny turbine designed to fit inside a human vein. The idea is to tap a few milliwatts from the 1-1.5 Watts of hydraulic power a human heart generates. Plenty to power medical implants and perhaps other advanced implants one day.
The main worry with nanogenerators is blood clots caused by turbulence. There was a similar concern with artificial hearts or heart assistance devices that use continuous flow designs. These include the Bivacor and Abiomed Impella. Although so far these problems don’t seem to have cropped up, human testing is in early phases so it’s anyone’s guess whether coagulation from spinning pump components in our blood will cause problems.
Artificial Electric Organs
Humans may not come with their own electrical power generator, but eels do! Eels have evolved something very much like a battery but made from biological cells. Inside the eel is an organ that clusters cells that act as an electrolyte into whatever effectively electroplates. So why not engineer an artificial organ for humans that does the same thing, but use that power to run future implantable technology?
In 2017 a team of scientists published a paper in Nature detailing their flexible, biocompatible “organ” inspired by the electric eel. This little powerhouse uses water and salt to work, but the long-term intention is to use bodily fluids instead. Implanted with these biological power stores, the sky might be the limit when it comes to technology integrated with our bodies.
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