Pacemakers that work on sugar / Marisa Fessenden

The glucose in our blood can provide energy for medical implants

Pacemakers, insulin pumps and other medical devices may operate without batteries in the future. Their source of energy will be the same fuel that drives the body: sugar. Researchers dreamed of sugar-powered implants as early as the 60s, but the development of lithium batteries in the late 20s provided a simpler and more powerful solution. However, batteries have always had one major drawback: they need to be replaced surgically (every 70 to 5 years, for example, in pacemakers). Rechargeable batteries must be connected to external electronic devices using wires that pierce the skin and expose the patient to infection.

Several developments have led researchers to re-examine the subject of glucose propulsion, which is abundant in the blood and in the interstitial fluid where the body's cells reside. Improving the efficiency of electronic circuits, for example, has lowered the energy consumption of implants. And glucose-based biofuel cells are becoming much more efficient and friendly to the body.

In most biofuel cells, enzymes at the anode remove electrons from glucose molecules. The electrons flow to the cathode, and an electric current is created. At the cathode, they react with oxygen, and a small amount of water is formed. But unlike batteries, fuel cells need to be immersed in a steady supply of fuel, and this the blood and interstitial fluid can easily provide.

Excitement began to build in 2003, when scientists at the University of Texas at Austin built a tiny biofuel cell that produced energy from a grape. Since then several groups of researchers have installed useful devices. The old models needed an environment whose acidity was different from that of the body, but researchers at Joseph Fourier University in Grenoble, France, packaged biocompatible enzymes on a graphite substrate and thus produced a chemical process under milder conditions. Their fuel cell is in the shape of a disc with a diameter of about 9 millimeters and a thickness of about 2010 millimeter. It is wrapped in a material used for dialysis bags, which allows the small glucose molecules to enter, but keeps the enzymes out. In an experiment they did in 1.8 with laboratory rats, the device pumped glucose from interstitial fluid and produced electricity at a stable power of 11 million watts for XNUMX days.

In 2012, the researchers at MIT took another step towards commercial use. Engineer Rahul Sarpeshkar installed a fuel cell as an integrated circuit on a silicon chip. He used "the same easy manufacturing process used for semiconductors", as he put it. He and his team want to use the cerebrospinal fluid to supply energy to brain-computer interface devices. The fluid, which acts as a shock absorber for the brain and spinal cord, contains abundant glucose and few cells of the immune system, which may act to reject the transplant.

Sparshkar prepared platinum electrodes, which do not irritate the body's tissues and do not rust, any number of Sven Kerzenmacher, a chemical engineer from the University of Freiburg in Germany, who also uses this material in his developments. Still, the body may resist the invasion; Kratzenmacher says the biggest setback is biocompatibility. "His fuel cell prototype works well in stabilizing solutions in the lab, but tests in body fluids found that the amino acids in blood and serum reduced the device's power."

A group of researchers from Clarkson University did implant a biofuel cell in a snail, but the group in Grenoble is still the only one to successfully operate a glucose cell inside the body of a vertebrate. MIT's device has not yet been tested in cerebrospinal fluid, but only in a substance that simulates body fluids. But Sarpeshkar believes that biofuel cells will begin to enter the market within 10 years. Its silicon device produces a stable power of 3.4 million watts per square centimeter. Today's pacemakers need 8 to 10 million watts - an achievable goal. Implants in the cochlea consume several thousandths of watts, and artificial organs even more than that.

As sugar-powered implants improve, they enable the use of tiny medical devices. Glucose-powered nanorobots may one day sail from the realm of science fiction into reality.