Using Conductive Polymer Composites to Build Soft Electronics

Soft electronics are of great interest in the medical sector. The inherent “soft” nature of these electronic systems means that they often withstand various mechanical deformations, making them an interesting prospect for a number of medical applications where flexibility and mechanical strength are key properties of the electronic system, such as health monitoring and medical applications. implants.

Despite the possibility of soft electronics in both monitoring and in vivo applications, many systems still had some reliability issues, some of which caused a system failure. For many commercial and / or industrial applications, device failure is always a concern, but ensuring optimal and safe operation of the electronic device is extremely important in the medical space, especially in applications where the device can be inserted inside. patient.

Thus, ensuring that soft electronic devices can be more reliable for medical applications is one of the key areas in soft electronics, and progress is being made in improving these systems.

The efficient function and reliability of soft electronic systems depend heavily on electrodes and interconnections to connect many components together and combine different components with biological tissues. It is expected that different joints will interact with a number of irregular and non-flat surfaces and conform to them and maintain a high level of stability when these interfaces are subjected to a certain level of mechanical deformation. However, it is in these interfacial areas that there are currently some problems.

Currently, a number of different soft materials and flexible structures have been used to create reliable electrodes that can measure physiological signals from the body in real time. These materials include hydrogels, carbon composites, liquid metal composites, metal composites and conductive polymers. However, despite the ability to produce effective components, the natural biological environment with its soft biological tissues (e.g., skin and muscles) is a challenge for many of these established systems.

The essence of the problems at the interface of the device and the fabric is reduced to low adhesion strength and mechanical mismatch between the components of the device and the biological tissue. This mechanical inconsistency arises because many interfaces are irregular. This discrepancy results in increased noise in the detection signal and an overall decrease in sensitivity when measuring physiological signals. In some cases, in addition to deteriorating measurements, mechanical inconsistencies on the sensing / monitoring interfaces can also lead to complete device failure, so more needs to be done in this area before we start talking about using these types of soft electronics in wide clinical applications. place.

Poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate), widely known and called PEDOT: PSS, is a widely used and versatile polymeric material that has already found application in a variety of medical applications. PEDOT: PSS is a commercially available conductive polymer with a number of beneficial properties that make it suitable for clinical applications such as good solution processing, customizable electronic properties and, most importantly, good biocompatibility.

However, PEDOT: PSS films themselves are generally very rigid and very inflexible, and have low adhesion strength – which is not particularly ideal when it comes to creating soft and flexible electronic systems. Because PEDOT: PSS has a number of other properties that can make it suitable for functioning on the measurement side of these devices, several ways have been tried to make PEDOT: PSS more flexible and stretched.

These routes include doping approaches, polymer blending techniques, hydrogel systems, and polymer composites. While hydrogels are the most flexible, PEDOT: PSS composites are currently exhibiting the most because of their conductivity properties. Although the progress made, the stiffness and mechanical modulus of these composites are still higher than in human tissues, so their suitability is still limited. Another aspect to consider when using some polymer systems is the possibility of plastic deformation, as it is possible that these types of devices will not return to their natural state if they are stretched too much. Researchers continue to study these systems to learn how they can be improved and made more suitable for clinical use.

Recently, a new approach has been implemented to combat the rigidity and rigidity of many PEDOT: PSS composites by alloying the composites with biocompatible supramolecular solvents. This led to the creation of new composites, which became known as composites of self-adhesive conductive polymers (SACP).

The researchers created these new composites based on PEDOT: PSS by taking a mixture of supramolecular solvents (such as citric acid and cyclodextrin) and mixing them with PEDOT: PSS and an elastic polymer network (with PVA and glutaraldehyde). Compared to previous PEDOT: PSS composites, this SACP was much more flexible and less rigid – with low mechanical modulus, low residual strain and high elongation (up to 700%). This flexibility and mechanical properties have also made the composite much higher adhesion strength of the interface compared to its predecessors, while maintaining the high conductivity properties that have made PEDOT: PSS a material of interest to soft electronics.

After understanding the improved potential of SACP over other composites, SACP electrodes have been developed for a number of soft electronic devices, including ACL and Electromyography Monitoring (EMG), as well as an integrated bioelectronic and electromagnetic kit. ACEL) to visualize electromyographic signals during muscle training.

Progress is currently being made in this area to make soft electronic devices more compatible and suitable for medical monitoring, especially over the long term. Several solutions are being sought, and recent research has made a breakthrough in making PEDOT: PSS composites more mechanically suitable and offering a way to deal with the interface problems of many soft electronic systems. Although SACP-based electronics is still in its infancy, it shows some promising capabilities for wearable and convenient bioelectronic devices that can measure the physiological electrical signals of the human body during daily activities.

Help:

Zhou X. et al., Soft, self-adhesive and conductive polymer composites for soft electronics treated in solutions, Nature Communications¸ 13, (2022), 358.

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