A revolution in soft electronics is underway, with conductive gels enabling seamless integration between technology and living tissue
While our bodies are soft, wet, and flexible, modern electronics are typically rigid, dry, and brittle. This mismatch becomes painfully obvious when you try to attach a conventional rigid sensor to your skin for a few days, or when implanted medical devices cause inflammation because the body recognizes them as foreign objects due to their unnatural stiffness 1 .
PEDOT:PSS-based organogels are as soft as biological tissue but can carry electrical signals like metals, enabling seamless integration between technology and the human body 3 .
These are water-based polymer networks that have been used for decades in applications from contact lenses to wound dressings. Their high water content makes them biologically compatible, but this same feature becomes a limitation as they can dehydrate in air and freeze at low temperatures, losing their functionality 1 .
By replacing water with organic solvents like ethylene glycol (EG), researchers created organogels that resist both freezing and dehydration. This makes them stable across a much wider range of environmental conditions while maintaining the soft, flexible nature of gels 1 .
The real breakthrough came when scientists found ways to make these soft materials electrically conductive. This is typically achieved by incorporating conductive polymers like PEDOT:PSS, which stands for poly(3,4-ethylenedioxythiophene):polystyrene sulfonate 5 .
PEDOT:PSS has emerged as the superstar in conductive gel research due to its unique combination of properties:
The material consists of two components: the conductive PEDOT and the water-soluble PSS, which helps disperse the PEDOT in solution while providing structural stability 9 .
Early conductive hydrogels faced a significant problem: they dried out or froze, limiting their practical use. Additionally, when used as electrodes, conventional hydrogels could undergo electrochemical reactions when voltage was applied, degrading their performance over time 3 .
In 2015, researchers from Seoul National University demonstrated a clever approach to creating stable PEDOT:PSS/acrylamide organogels 3 . Their method addressed both the environmental stability and electrical stability issues that had plagued previous materials.
The researchers first created a conventional PEDOT:PSS and acrylamide hydrogel using standard polymerization techniques.
The hydrogel was placed in a dialysis system, which allowed small ions and molecules to pass through a membrane while retaining the larger polymer structures. This step removed residual ions that could interfere with electrical performance.
The dialyzed hydrogel was then immersed in ethylene glycol (EG), gradually replacing the water molecules in the gel with EG. This transformed the material from a hydrogel to an organogel.
The resulting PEDOT:PSS/acrylamide organogel maintained the soft, flexible properties of the original hydrogel but with dramatically improved environmental stability 3 .
| Property | Conventional Hydrogels | Organogels | Hybrid Systems |
|---|---|---|---|
| Solvent | Water-based | Organic solvents (e.g., ethylene glycol) | Combination of aqueous & organic phases |
| Environmental Stability | Prone to dehydration and freezing | Resists dehydration and freezing | Enhanced stability under extreme conditions |
| Adhesion to Tissues | Generally good | Relatively low | Can be engineered for strong adhesion |
| Electrical Stability | Can undergo electrochemical reactions | Prevents electrochemically driven current | Stable performance |
| Typical Applications | Short-term biomedical devices | Long-term implants, soft robotics | Multifunctional devices |
The PEDOT:PSS/acrylamide organogels displayed an impressive set of properties that make them suitable for practical applications.
Unlike conventional hydrogels where electrical conduction occurs primarily through ions (which can lead to electrochemical reactions), the organogels demonstrated pure electronic conduction without electrochemical side effects 3 .
By replacing water with ethylene glycol, the organogels gained remarkable stability. Ethylene glycol has a much lower freezing point than water (-12°C vs 0°C) and evaporates more slowly .
The combination of PEDOT:PSS with acrylamide created materials with a unique combination of softness and durability. The acrylamide provided a flexible, stretchable network 7 .
| Property | Performance Value | Significance |
|---|---|---|
| Stretchability | Up to 300% strain | Can withstand extreme deformation without failure |
| Environmental Stability | Resists dehydration and freezing | Suitable for long-term use in varying conditions |
| Conduction Type | Electronic (not ionic) | Prevents electrochemical reactions during use |
| Circuit Function | Maintains operation while stretched | Enables truly stretchable electronics |
The development of stable conductive organogels opens up numerous exciting applications across multiple fields.
Imagine a skin-like sensor that continuously monitors your vital signs without causing discomfort or skin irritation. Conductive organogels can form comfortable, long-term wearable sensors that track muscle activity, heart rate, and other physiological signals 4 7 .
Traditional robots are rigid and struggle with delicate tasks. Organogel-based electronics could enable softer, more adaptable robots that can handle fragile objects or navigate complex environments. Their stability across temperature ranges makes them particularly suitable for robots working in extreme conditions 1 .
Electroencephalography (EEG) measures brain activity but typically requires messy gels and uncomfortable electrodes. Organogel-based electrodes could provide comfortable, long-term monitoring of brain signals for both medical diagnosis and brain-computer interfaces 8 .
While PEDOT:PSS/acrylamide organogels represent a significant advance, researchers continue to refine these materials for even better performance.
Some studies have explored adding surfactants like Triton X-100 to reorganize the PEDOT:PSS structure into more conductive nanofibrillar networks, potentially boosting performance further 8 .
Scientists are developing organohydrogels that combine aqueous and organic phases to create materials with the advantages of both systems—potentially achieving even better performance for specific applications 1 .
While generally biocompatible, ensuring long-term safety of these materials—particularly the organic solvent components—remains an area of active investigation, especially for implantable applications .
As research progresses, we may eventually see these squishy circuits used in applications we can scarcely imagine today—perhaps even forming the basis for direct neural interfaces that connect our biological wetware with digital technologies in a seamless, comfortable union. The era of rigid, bulky electronics may gradually give way to a future where our devices are as soft, flexible, and adaptable as we are.