11-05-2020 | By Robin Mitchell
Researchers at MIT have developed a specialised conductive gel that allows for conductive polymers to remain on surfaces when exposed to moist environments. Why is this technology promising, and what problems do wearable technologies currently face?
The area of wearable technologies is concerned with creating devices that can be worn or attached to their user. While wearable technologies do exist and are widely available, they are often limited to watches or other wrist bands such as the Apple Smart Watch or the MAX Health Band. Not only are these technologies bulky, but they are almost always ridged and do not move with flexible surfaces such as skin and tissue. The rigidity of these devices often makes them uncomfortable to wear as well as highly noticeable, and devices that are ridged are harder to implant inside the human body as they can damage surrounding soft tissue.
While still in its infancy, there is a growing technology sector that is working to create flexible components and conductors to create almost organic-like designs that could easily be implanted or embedded into human skin while having no impact on the surrounding tissue, the circuit functionality, or visual impact. If such a design could be created, it would open many opportunities to consumers and researchers alike. Firstly, medical monitoring devices could be permanently integrated, allowing for health always to be monitored. Secondly, the ability to always monitor peoples health would prove highly beneficial to the field of medical AI creating systems that could quickly diagnose conditions before they become problematic. Thirdly, implanted designs could also provide medical emergency teams with vital patient information such as allergies, blood type, and pre-existing conditions. But as technology currently stands, this is still very far away, and before we can create such devices, we need to solve the current issues that wearable and flexible technologies face.
Since the human body (both inside and out) is moist, only specific materials can be used when creating sensors and electrode. One popular material, Platinum, is considered ideal as it is moisture-resistant while being highly conductive. Another benefit of Platinum is that it is biologically benign and thus if implanted into the human body will not be rejected (i.e. attacked by the immune system). However, Platinum-based electrodes are ridged, meaning that they can damage surrounding tissue making their use problematic. One potential solution is to use flexible conductive polymers whose can flex and stretch almost as well as tissue while remaining conductive. But these materials often have issues with adhering to moist surfaces, and this problem is amplified when used on the human body, which is not only most but always moving. Therefore, when such polymers are adhered to the skin or implanted will quickly disintegrate and become non-functioning.
A team of researchers from MIT have recently developed a conductive gel that can be applied to flexible polymers and allow them to continue functioning even when submerged in water. The conductive gel developed by the MIT team creates an adhesive layer between the substrate material and conductive polymer that measures just a few nanometers thick but can keep the two materials together regardless of moisture with example substrate materials including glass, polyimide, indium tin oxide, and gold. The strength and capability of the gel come from its ability to penetrate the adhered polymer and create interpenetrating links which are also the reason for its ability to resist moisture.
The new conductive also has the added benefit that it can be applied using a variety of manufacturing processes, including spin coating and dip coating. Since flexible polymer technologies have already been heavily invested in developing a new polymer that works in moist environments would potentially lead to manufacturers having to change entire production lines with new equipment. Since the gel can be applied using standard manufacturing processes, the equipment currently used to produce flexible polymers remains relevant and therefore, more economical to produce. Thus, a manufacturer of a flexible conductive polymer such as PEDOT: PSS is only required to add the production stage to apply the gel.
The conductive gel has been demonstrated to work with polyurethane (a hydrophilic material) being able to turn an LED on while being entirely submerged underwater. However, the researchers have said that other flexible polymers should be able to work as well indicating the practicality of the gel for future commercial use. While more experimentation with the gel is required, the MIT group is looking to license the research to manufacturers as well as getting the gel testing in real-world environments.
The ability to create flexible polymers that can move with the human body opens up massive opportunities for designers and researchers alike. Sensor readings from vital organs can be taken with the use of benign conductors and sensors, circuits can move with the body and not break under flex, and the use of such flexible conductors could even be vital in repairing sensitive tissues such as nerves. While these technologies are still decades away, the research into this conductive gel will open up opportunities into wearable and implantable electronics.