Imagine a material that can be 3D printed into complex electronic structures, conducts electricity efficiently, works safely with the body, and does not need lengthy chemical treatment after printing. Scientists have now taken an important step toward making this possible.
A research team led by Oh has developed a new type of conductive ink called PEDOT:PSS-ionic liquid colloidal (PILC) ink. The material is designed for 3D printing of bioelectronic devices and could help researchers build flexible sensors, medical implants and other electronic systems that interact directly with the human body.
The development addresses several major problems that have limited the use of conductive polymers in 3D printing.
Why PEDOT:PSS Is Important
Three-dimensional printing has become an important manufacturing technology because it can quickly create customized objects with complicated shapes. In healthcare and biomedical research, 3D printing is especially useful because devices can be designed for specific body parts and applications.
One promising material for these applications is PEDOT:PSS, a conductive polymer. It has several properties that make it attractive for bioelectronics. It can conduct electrical signals, has mechanical properties closer to soft biological tissues than many traditional electronic materials, and can be used to interface electronics with the body.
However, conventional PEDOT:PSS is difficult to 3D print.
The material does not naturally have enough mechanical strength to maintain complicated printed structures. Researchers have therefore added chemicals such as dimethylsulfoxide (DMSO) or ionic liquids to improve its printing performance.
The problem is that some of these additives can be unsuitable for direct biological applications. They may need to be removed through repeated washing, heating or other post-processing steps.
This creates a major limitation: the material may be printable, but the printed device cannot always be used immediately.
A One-Shot Solution
The team developed PILC ink using a different approach.
The researchers used an ionic-liquid-assisted process combined with centrifugation. This changes how the PEDOT:PSS material is organized at the microscopic level.
During the process, PEDOT forms densely packed colloidal structures connected through a hydrogen-bonded network. At the same time, excess ionic liquid and unwanted PSS components can be removed during centrifugation.
The result is a material that combines several important properties in a single ink.
According to the researchers, PILC ink reaches a conductivity of approximately 286 S/cm, compared with roughly 1 S/cm for pristine PEDOT:PSS under the reported comparison.
That high conductivity is important because bioelectronic devices need to efficiently transmit electrical signals between the device and biological tissue.
Tall and Complex Structures Become Possible
Another major advantage is the material's mechanical behavior.
For successful 3D printing, an ink must be fluid enough to pass through a printing nozzle but strong enough to hold its shape after being deposited.
PILC ink demonstrates this balance.
The researchers report a storage modulus of about 10⁵ Pa and a yield stress of about 10³ Pa. These properties allow the printed material to support itself instead of spreading or collapsing immediately.
This means the ink can be used to create structures with a high vertical aspect ratio.
The researchers demonstrated structures with printing resolution of approximately 50 micrometres and suspended structures with overhangs of around 2 millimetres.
This is significant because conventional conductive polymer inks can struggle when researchers attempt to print tall, narrow or suspended structures.
Instead of being limited to relatively flat patterns, the new ink can create more complicated three-dimensional architectures.
No Long Post-Treatment
Perhaps one of the most important features of PILC ink is its potential for immediate use after printing.
Traditional conductive polymer printing can involve additional processing to remove chemicals or improve conductivity. Such procedures can take considerable time and may involve repeated washing or heating.
The centrifugation-based preparation of PILC ink removes excess components before the material is used for printing.
As a result, the researchers report that the printed material does not require additional post-treatment for biocompatibility.
This could make the process much faster and more practical for rapid prototyping of biomedical electronics.
From Circuit Boards to Wearable Sensors
The researchers demonstrated the versatility of PILC ink through several different applications.
One example was the fabrication of three-dimensional circuit boards. Because the ink can conduct electricity and maintain complex printed shapes, it can potentially be used to create customized electronic structures.
The team also used the material to create on-skin electronic tattoos, or e-tattoos, capable of monitoring physiological signals.
These flexible devices can record signals such as electromyography (EMG), which is associated with muscle activity, and electrocardiography (ECG), which records the electrical activity of the heart.
Such technology could eventually contribute to wearable healthcare systems that continuously monitor physiological activity while remaining lightweight and flexible.
Potential for Implantable Bioelectronics
The research becomes even more interesting when the material is used inside the body.
The scientists demonstrated PILC-based implantable bioelectronics for applications including opto-electrocorticography (ECoG) recording and stimulation of the sciatic nerve.
In one demonstration, the system achieved low-voltage sciatic nerve stimulation at approximately 60 millivolts.
The team also demonstrated recording from deeper brain layers using 3D vertical spike arrays.
These examples show why three-dimensional printing could be valuable for future neural interfaces. Instead of relying only on flat electrodes, researchers could potentially design electronic structures that better match the three-dimensional geometry of biological tissues.
Why This Could Matter for Future Medicine
Modern medical electronics increasingly need to be smaller, softer, more flexible and more closely integrated with the human body.
Traditional rigid electronic components can create mechanical mismatches with soft tissues. Conductive polymers such as PEDOT:PSS offer a possible alternative because their properties can be more compatible with biological environments.
PILC ink adds another important advantage: customizable three-dimensional manufacturing.
Researchers could potentially design a device around a particular nerve, tissue surface or anatomical structure and then rapidly manufacture it using 3D printing.
This could be particularly valuable in personalized medicine, where medical devices may need to be customized for individual patients.
Challenges Still Remain
Although the results are promising, the technology is still at the research stage.
Future studies will need to examine the long-term stability, durability and safety of printed devices, particularly for implants that must operate inside the body for extended periods.
Researchers will also need to determine how the material performs when devices are repeatedly bent, stretched or exposed to biological fluids.
Scaling the technology from laboratory demonstrations to reliable commercial manufacturing will be another important challenge.
A New Direction for 3D-Printed Bioelectronics
The development of PILC ink demonstrates how material engineering can overcome several limitations at the same time.
The new ink combines high electrical conductivity, approximately 50-micrometre printing resolution, strong structural integrity, three-dimensional printability and reported biocompatibility without post-print treatment.
Most importantly, it provides researchers with a way to rapidly create complex conductive structures rather than spending long periods on post-processing.
From wearable health sensors and customized circuit boards to neural implants and nerve stimulation devices, the potential applications are broad.
The technology does not mean that fully personalized 3D-printed medical electronics are ready for everyday clinical use. However, it provides an important platform for researchers working toward that goal.
If these properties can be maintained over long periods and translated into reliable medical devices, 3D printing could move bioelectronics from simple flat sensors toward highly customized three-dimensional systems designed to work more naturally with the human body.
Reference: Oh, B., Baek, S., Nam, K.S. et al. 3D printable and biocompatible PEDOT:PSS-ionic liquid colloids with high conductivity for rapid on-demand fabrication of 3D bioelectronics. Nat Commun 15, 5839 (2024). https://doi.org/10.1038/s41467-024-50264-6
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