MIT engineers developed a metal-free, Jell-O-like material that is as soft and tough as biological tissue and can conduct electricity similarly to conventional metals. The new material, which is a type of high-performance conducting polymer hydrogel, may one day replace metals in the electrodes of medical devices.
Do an image search for “electronic implants,” and you’ll draw up a wide assortment of devices, from traditional pacemakers and cochlear implants to more futuristic brain and retinal microchips aimed at augmenting vision, treating depression, and restoring mobility.
Some implants are hard and bulky, while others are flexible and thin. But no matter their form and function, nearly all implants incorporate electrodes — small conductive elements that attach directly to target tissues to electrically stimulate muscles and nerves.
Implantable electrodes are predominantly made from rigid metals that are electrically conductive by nature. But over time, metals can aggravate tissues, causing scarring and inflammation that in turn can degrade an implant’s performance.
Now, MIT engineers have developed a metal-free, Jell-O-like material that is as soft and tough as biological tissue and can conduct electricity similarly to conventional metals. The material can be made into a printable ink, which the researchers patterned into flexible, rubbery electrodes. The new material, which is a type of high-performance conducting polymer hydrogel, may one day replace metals as functional, gel-based electrodes, with the look and feel of biological tissue.
This material operates like metal electrodes but is made from gels that are similar to our bodies, and with similar water content.
The vast majority of polymers are insulating by nature, meaning that electricity does not pass easily through them. But there exists a small and special class of polymers that can in fact pass electrons through their bulk. Some conductive polymers were first shown to exhibit high electrical conductivity in the 1970s — work that was later awarded a Nobel Prize in Chemistry.
Recently, researchers have tried using conductive polymers to fabricate soft, metal-free electrodes for use in bioelectronic implants and other medical devices. These efforts have aimed to make soft yet tough, electrically conductive films and patches, primarily by mixing particles of conductive polymers, with hydrogel — a type of soft and spongy water-rich polymer.
Researchers hoped the combination of conductive polymer and hydrogel would yield a flexible, biocompatible, and electrically conductive gel. But the materials made to date were either too weak and brittle, or they exhibited poor electrical performance.
In their new study, the researchers found they needed a new recipe to mix conductive polymers with hydrogels in a way that enhanced both the electrical and mechanical properties of the respective ingredients.
People previously relied on homogenous, random mixing of the two materials.
Such mixtures produced gels made of randomly dispersed polymer particles. The group realized that to preserve the electrical and mechanical strengths of the conductive polymer and the hydrogel respectively, both ingredients should be mixed in a way that they slightly repel — a state known as phase separation. In this slightly separated state, each ingredient could then link its respective polymers to form long, microscopic strands, while also mixing as a whole.
The researchers then tweaked the recipe to cook the spaghettified gel into an ink, which they fed through a 3D printer, and printed onto films of pure hydrogel, in patterns similar to conventional metal electrodes.
The researchers then implanted the printed, Jell-O-like electrodes onto the heart, sciatic nerve, and spinal cord of rats. The team tested the electrodes’ electrical and mechanical performance in the animals for up to two months and found the devices remained stable throughout, with little inflammation or scarring to the surrounding tissues. The electrodes also were able to relay electrical pulses from the heart to an external monitor, as well as deliver small pulses to the sciatic nerve and spinal cord, which in turn stimulated motor activity in the associated muscles and limbs.
Going forward, the researcher envisions that an immediate application for the new material may be for people recovering from heart surgery.
These patients need a few weeks of electrical support to avoid heart attack as a side effect of surgery. So, doctors stitch a metallic electrode on the surface of the heart and stimulate it over weeks. The researcher says that they may replace those metal electrodes with their gel to minimize complications and side effects that people currently just accept.
The team is working to extend the material’s lifetime and performance. Then, the gel could be used as a soft electrical interface between organs and longer-term implants, including pacemakers and deep-brain stimulators.
News Source: MIT
