Hydrogels, a type of polymeric material with similarities to animal tissues, are revolutionizing biomedical technology through the use of 3D printing in electronics. Their unique properties make them ideal for a wide range of biomedical applications.
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In this article, we discuss methods that are used to 3D print hydrogels, the associated challenges, and promising results from new research that open up new possibilities for the application of 3D hydrogel-printed electronics.
What is a Hydrogel?
Hydrogels are materials that have properties similar to biological tissue, making them ideal for use in medical devices. They are water-swollen and cross-linked polymeric networks that can retain a significant fraction of water within their structure but will also not dissolve in water.
They have a degree of flexibility similar to natural tissue due to their large water content and have been used in a wide range of biomedical applications.
Methods to 3D Print Hydrogels
3D printing technology has been revolutionizing the way we create and manufacture products, from prosthetic limbs to aerospace parts. Some common techniques used to 3D print hydrogels include:
Extrusion-based 3D printing: This method involves extruding a hydrogel solution through a nozzle to create a 3D structure. This technique is commonly used for printing hydrogels with high viscosities, such as alginate and gelatin.
Stereolithography: This method uses a laser to selectively cure a photosensitive hydrogel precursor, creating a 3D structure. It is commonly used for printing hydrogels with high resolution and precision, such as PEGDA hydrogel.
Inkjet printing: This method uses an inkjet printer to deposit droplets of a hydrogel solution onto a substrate, creating a 3D structure. It is also used for high resolution and precision.
Bioprinting: This method uses a 3D printer to deposit cells and hydrogel together to create 3D structures, this technique is commonly used for tissue engineering.
These are just a few examples of the various techniques that have been used to 3D print hydrogels. The specific method used will depend on the properties of the hydrogel and the desired final structure (Puza and Lienkamp, 2022).
Challenges of Creating a 3D Matrix with Hydrogels
Creating complex 3D circuits within a hydrogel matrix has been a challenging task in the past. Hydrogels, which are typically highly absorbent and can swell in response to changes in their environment, can make it difficult to maintain the structural integrity of 3D circuits.
They are also usually soft and weak mechanically, which can make it difficult to create complex 3D structures with high precision. Additionally, most hydrogels are not conductive, which makes it hard to incorporate electrically active materials such as metals or semiconductors into the hydrogel matrix. The lack of techniques that can integrate multiple materials into a hydrogel matrix has also been a challenge in creating 3D circuits.
Approaches to Overcoming the Challenges of 3D Printing Hydrogels on Electronics
Common approaches include developing new hydrogel formulations, using new conductive materials, direct assembly, and hybridization. Most of these are in the early stages of research and development, and more work is needed to optimize these techniques and make them practical for real-world applications.
According to recent research published in the Nature Electronics Journal, The researchers overcame some of these challenges by using a curable hydrogel-based supporting matrix, a stretchable silver-hydrogel ink, and Embedded 3D printing (EM3DP).
The supporting matrix had a yield stress fluid behavior, which means that the shear force generated by the 3D printer's nozzle creates a temporary fluid-like state, allowing the accurate placement of silver-hydrogel ink circuits and electronic components. After printing, the entire matrix and embedded circuitry were cured at 60 degrees Celsius to form soft and stretchable monolithic hydrogel electronics.
The conductive ink used in this process exhibited a high conductivity of around 1.4 x 103 S cm-1. With this 3D printing approach, the researchers were able to create strain sensors, inductors, and biological electrodes.
What is The Significance of These Research Findings?
The methods described in the article are different from other methods previously developed for 3D printing hydrogels in a few key ways. Firstly, the method uses a curable hydrogel-based supporting matrix, which allows for the accurate placement of silver-hydrogel ink circuits and electronic components within the matrix. Also, the EM3DP approach had never been used for hydrogel electronics manufacturing.
This is a significant improvement over existing methods, which have been challenged by the difficulty of creating complex three-dimensional circuits encapsulated within a hydrogel matrix.
Secondly, the method uses stretchable silver-hydrogel ink, which allows for the creation of soft and stretchable monolithic hydrogel electronics. This is a significant improvement over existing methods that have been limited by the materials and manufacturing methods used.
Lastly, the method uses a high-conductivity ink that exhibits a conductivity of around 1.4 x 103 S cm-1, which an improvement over the conductivity of the inks used in previous processes.
Practical Applications of 3D-Printed Hydrogel Electronics
The practical applications of this new research are vast and varied. This method allows for the creation of customizable 3D circuits, which can be used in a variety of biomedical applications. These include creating strain sensors, inductors, biological electrodes, and implantable devices that can monitor and treat a variety of conditions.
They can also be used in the creation of soft robotics, which can be used in a variety of applications such as rehabilitation, prosthetics, and medical devices.
The ability to 3D print hydrogel electronics is a significant breakthrough in the field of electronics. It opens up a whole new world of possibilities for the creation of customized three-dimensional circuits that can be used in a variety of applications, including medical devices and soft robotics.
The potential of this new research is truly exciting, and scientists will continue to work to push the boundaries of what is possible with hydrogel electronics.
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References and Further Reading
Ahmed, E.M. (2015). Hydrogel: Preparation, characterization, and applications: A review. Journal of Advanced Research 6, 105–121. https://doi.org/10.1016/j.jare.2013.07.006
Fadelli, I., Xplore, T. (2023). A new approach for the 3D printing of hydrogel-based electronics [Online]. URL https://techxplore.com/news/2023-01-approach-3d-hydrogel-based-electronics.html (accessed January 17th 2023).
Hui, Y., Yao, Y., Qian, Q., Luo, J., Chen, H., Qiao, Z., Yu, Y., Tao, L., Zhou, N. (2022). Three-dimensional printing of soft hydrogel electronics. Nature Electronics 5, 893–903. https://doi.org/10.1038/s41928-022-00887-8
Jang, T.-S., Jung, H.-D., Pan, H.M., Han, W.T., Chen, S., Song, J. (2018). 3D printing of hydrogel composite systems: Recent advances in technology for tissue engineering. International Journal of Bioprinting 4, 126. https://doi.org/10.18063/IJB.v4i1.126
Puza, F., Lienkamp, K. (2022). 3D Printing of Polymer Hydrogels—From Basic Techniques to Programmable Actuation. Advanced Functional Materials 32, 2205345. https://doi.org/10.1002/adfm.20220534