Researchers at the University of Chicago’s Pritzker School of Molecular Engineering have created a groundbreaking hydrogel that doubles as a semiconductor. The material combines the soft, flexible properties of biological tissues with the electronic capabilities of semiconductors, making it ideal for advanced medical devices.
In a study published in Science, the research team, led by Sihong Wang, developed a stretchy, jelly-like material that provides the robust semiconducting properties necessary for use in devices such as pacemakers, biosensors and drug delivery systems.
Rethinking hydrogel design
Hydrogels are ideal for many biomedical applications because they are soft, flexible and water-absorbent – just like human tissues. Material scientists, long recognizing the vast potential of hydrogels, have pushed the boundaries of this class of material. One way is to create hydrogels with semiconducting abilities that can be useful for transmitting information between living tissues and bioelectronic device interfaces – in other words, a hydrogel semiconductor.
Imparting semiconducting properties to hydrogels is no easy task, however. Semiconductors, while known for their remarkable electronic properties, are typically rigid, brittle and water-repellent, making them inherently incompatible with hydrogels. By overcoming this fundamental mismatch, Wang and his team have created a material that could revolutionize the way medical devices interface with the human body.
Traditional hydrogels are made by dissolving hydrogel precursors (monomers or polymers) in water and adding chemicals to crosslink the polymers and form a water-swelled state. Since most polymers are inherently insulating, creating a hydrogel with semiconducting properties requires a special class of semiconducting polymers. The challenges do not stop there, however. These polymers typically only dissolve in organic solvents, not in water.
“The question becomes how to achieve a well-dispersed distribution of these semiconducting materials within a hydrogel matrix,” says first author Yahao Dai, a PhD student in the Wang lab. “This isn’t just about randomly dispersing particles into the matrix. To achieve strong electrical performance, a 3D interconnected network is essential for effective charge transport. So, the fundamental question is: how do you build a hydrophobic, 3D interconnected network within the hydrogel matrix?”
To address this challenge, the researchers first dissolved the polymer in an organic solvent that is miscible with water, forming an organogel – a gel-like material composed of an organic liquid phase in a 3D gel network. They then immersed the organogel in water and allowed the water to gradually replace the organic solvent, transforming it into a hydrogel.
The researchers point out that this versatile solvent exchange process can be adapted to a variety of semiconducting polymers, opening up new possibilities for hydrogel semiconductors with diverse applications.
A two-in-one material
The result is a hydrogel semiconductor material that’s soft enough to match the feel of human tissue. With a Young’s modulus as low as 81 kPa – comparable to that of jelly – and the ability to stretch up to 150% of its original length, this material mimics the flexibility and softness of living tissue. These tissue-like characteristics allow the material to seamlessly interface with the human body, reducing the inflammation and immune responses that are often triggered by rigid medical implants.
The material also has a high charge carrier mobility, a measure of its ability to efficiently transmit electrical signals, of up to 1.4 cm2/V/s. This makes it suitable for biomedical devices that require effective semiconducting performance.
The potential applications extend beyond implanted devices. The material’s high hydration and porosity enable efficient volumetric biosensing and mass transport throughout the entire thickness of the semiconducting layer, which is useful for biosensing, tissue engineering and drug delivery applications. The hydrogel also responds to light effectively, opening up possibilities for light-controlled therapies, such as light-activated wireless pacemakers or wound dressings that use heat to accelerate healing.
A vision for transforming healthcare
The research team’s hydrogel material is now patented and being commercialized through UChicago’s Polsky Center for Entrepreneurship and Innovation. “Our goal is to further develop this material system and enhance its performance and application space,” says Dai. While the immediate focus is on enhancing the electrical and light modulation properties of the hydrogel, the team envisions future work in biochemical sensing.
Living bioelectronics capture physiological signals and deliver targeted therapy
“An important consideration is how to functionalize various bioreceptors within the hydrogel semiconductor,” explains Dai. “As each biomarker requires a specific bioreceptor, the goal is to target as many biomarkers as possible.”
The team is already exploring new methods to incorporate bioreceptors, such as antibodies and aptamers, within the hydrogels. With these advances, this class of semiconductor hydrogels could act as next-generation interfaces between human tissues and bioelectronic devices, from sensors to tailored drug-delivery systems. This breakthrough material may soon bridge the gap between living systems and electronics in ways once thought impossible.
