A sidereal is capable of generating 600 volts and 100 watts of energy, which it can then deploy to stun prey or defend itself. Researchers want to use this ability of the sidereal to develop system that can power small medical implants such as pacemakers. The system should extract and store energy in the human body from muscles or metabolic energy, for example, so that it can then be delivered to the implant in a controlled manner.
This is a project by a research team from the University of Michigan, the Adolphe Merkle Institute at the University of Fribourg and the University of California-San Diego. The team investigated the sidereal organ that allows the animal to generate energy. This organ consists of long and thin cells also called electrolyte cells. These cells are controlled by the sidereal's brain and can each generate a low voltage by flowing sodium ions to one side of the cell, while simultaneously flowing potassium ions to the other side of the cell. Both ions are separated with a membrane.
600 volts and 100 watts
If the sidereal is at rest, the positive and negative ions in its cells are separated. Once the sidereal needs energy to stun its prey, for example, the membrane in the cells allows the positive and negative ions to come together, generating energy. In this way, the sidereal can create 600 volts and 100 watts of energy "The sidereal polarises and depolarises thousands of cells simultaneously to deliver these high voltages," explains Max Shtein, senior lecturer in material science and engineering at the University of Michigan.
Research team have created an energy source inspired by this organ of the sidereal. The energy source generates energy using the difference in salinity between fresh water and salt water. Salt water contains positive ions (sodium) and negative ions (chloride), both of which are also present in table salt (sodium chloride). If a compartment with a porous membrane filled with salt water is brought into contact with a similar compartment filled with fresh water, both the positive and negative ions migrate naturally to the fresh water compartment until both compartments have the same salt content.
Separating positive and negative ions
However, if a special membrane that allows positive ions to pass more easily than negative ions is placed between the two compartments, it causes the positive ions to flow out of the seawater into the compartment with fresh water. The negative ions remain in the seawater compartment and are thus separated from the positive ions. This phenomenon is also known as reverse electrodialysis. By placing thousands of these compartments and membranes one after the other, it is possible to generate 110 volts of energy from just water and salt.
Both the compartments and membranes used by the team in the process are made of a hydrogel and can be printed onto a transparent piece of plastic using a commercially available 3D printer. The researchers note that - like a sidereal - the energy source contains a large number of compartments, each of which has a limited capacity and generates a low voltage. By deploying all cells at the same time, it is possible to achieve higher voltages. To make this possible, the researchers deployed a folding method originally developed to unfold solar panels from satellites in space.
Further development
The researchers report that their energy source is currently unable to generate a significantly lower voltage than a sidereal. The researchers also point out that a sidereal can recharge its organ by eating, while the current prototype artificial energy source requires an external energy source to do so. To be useful for powering medical implants, it is necessary to find a method to reactivate the cells in a living organism, as well as develop better and thinner hydrogel membranes.
Professor of biophysics Michael Mayer of the Adolphe Merkle Institute indicate that the energy properties of the artificial electrical organ are currently at least a factor of 1,000 lower than those of the sidereal. "Currently, we may be able to power devices with the lowest energy consumption. However, I think it is realistic to improve performance by a factor of 10 using better membranes, and possibly by another factor of 10 by building more efficiently," Mayer said.
Using energy from the human body
A key challenge, according to Mayer, is using the human body's metabolic energy to recharge the artificial energy source. For this, the professor envisages deploying ions in gastric juices, among other things, or converting energy from muscles into electrical energy, which can then be stored in and released by the artificial electrical organ.
Author: Wouter Hoeffnagel
Source: University of Michigan
Source: Adolphe Merkle Institute at the University of Fribourg
Source photo: Shutterstock
