Soft and Mushy: Meet the New Generation of Biocompatible Memory Devices

In a move that opens the door to a new generation of biocompatible electronic devices, researchers from North Carolina State University (NC State; Raleigh) have developed a memory device that is soft and functions well in wet environments. "We've created a memory device with the physical properties of Jell-O," remarks Michael Dickey, an assistant professor of chemical and biomolecular engineering at NC State and coauthor of a paper describing the research.

Typically made of rigid, brittle materials, conventional electronics do not function well in wet environments. In contrast, the NC State device is made using a liquid alloy of gallium and indium metals set into water-based gels--similar to gels used in biological research. "Our memory device is soft and pliable, and functions extremely well in wet environments--similar to the human brain," Dickey says.

The device functions much like so-called "memristors." Its individual components have two states: one that conducts electricity and one that does not. These two states can be used to represent the 1s and 0s used in binary language. While most conventional electronics use electrons to create these 1s and 0s in computer chips, this mushy memory device uses ions to do the same thing.

In each of the device's circuits, the metal alloy--resting on either side of a conductive piece of gel--functions as the circuit's electrode. When the alloy electrode is exposed to a positive charge, it creates an oxidized skin that makes it resistant to electricity--designated as 0. When the electrode is exposed to a negative charge, the oxidized skin disappears and the alloy becomes electrically conducive--designated as 1.

Normally, whenever a negative charge is applied to one side of the electrode, the positive charge would move to the other side and create another oxidized skin, meaning that the electrode would always be resistive. To solve this problem, the researchers doped one side of the gel slab with a polymer to prevent the formation of a stable oxidized skin. Thus, one electrode is always conducive, giving the device the 1s and 0s it needs for electronic memory.

While prototypes of the device have not yet been optimized to hold significant amounts of memory, they work well in environments that would be hostile to traditional electronics. Because the device can function in wet environments and is made from biocompatible materials, it could eventually be used for interfacing electronics with such biological systems as cells, enzymes, or tissue. "These properties may be used for biological sensors or for medical monitoring," Dickey comments.

To see how the device works, check out this video: