The perfect material for connecting electronics to living tissue needs to be soft, flexible, and just as water-friendly as the tissue itself. Essentially, this material should be a hydrogel. In contrast, semiconductors—essential for bioelectronics, like pacemakers, biosensors, and drug delivery systems—are rigid and brittle and do not mix well with water, making them difficult to integrate with hydrogels as they have been traditionally made.
Researchers have tackled this long-standing problem by rethinking how to create hydrogels, enabling the development of a powerful semiconductor that takes the form of a hydrogel. The outcome is a bluish gel that moves gracefully in water, resembling a jellyfish, while also maintaining strong semiconductive properties necessary for relaying information between living tissues and electronic devices.
The ideal material for interfacing electronics with living tissue is soft, stretchable, and just as water-loving as the tissue itself—essentially a hydrogel. Conversely, semiconductors, which are fundamental for bioelectronics like pacemakers, biosensors, and drug delivery systems, are rigid, brittle, and repel water, making it impossible to integrate them within traditional hydrogels.
A recent study published in Science by the UChicago Pritzker School of Molecular Engineering (PME) provides a solution to this issue that has perplexed researchers for years. Under the leadership of Assistant Professor Sihong Wang, the team has developed a gel that, while soft enough to flutter in water like a jellyfish, possesses significant semiconductive capabilities essential for communication between biological tissues and machines.
This innovative material demonstrates tissue-level softness at 81 kPa and can stretch up to 150% strain, with charge-carrier mobility reaching 1.4 cm² V⁻¹ s⁻¹. This means the material works effectively as both a semiconductor and a hydrogel, fulfilling all the requirements needed for an optimal bioelectronic interface.
“Creating implantable bioelectronic devices requires addressing the challenge of achieving tissue-like mechanical properties,” explained Yahao Dai, the lead author of the study. “This ensures that when the device interfaces directly with the tissue, both can deform together, establishing a close bio-interface.”
Although the research primarily addressed challenges in implanted medical devices such as biochemical sensors and pacemakers, Dai noted the material’s potential beyond surgery, including enhancing readings from the skin and improving wound care.
“Its mechanical properties are very soft, and it retains a high degree of hydration similar to living tissue,” said Assistant Professor Sihong Wang. “Moreover, hydrogels are highly porous, facilitating the effective transport of various nutrients and chemicals. These characteristics make hydrogels especially valuable for tissue engineering and drug delivery.”
‘Let’s change our perspective’
Typically, creating a hydrogel involves dissolving a material in water and adding gelling agents to transform the liquid into a gel. While some materials easily dissolve in water, others need chemical adjustments, but fundamentally, the principle is consistent: no water means no hydrogel.
Semiconductors, however, don’t dissolve in water. Rather than attempt tedious methods to adapt them, the UChicago PME researchers reconsidered their approach.
“We thought, ‘Let’s shift our perspective,’ and developed a solvent exchange process,” stated Dai.
Instead of using water to dissolve semiconductors, they utilized an organic solvent that mixes well with water. Following this, they created a gel from the dissolved semiconductors combined with hydrogel precursors. Initially, this resulted in an organogel instead of a hydrogel.
“To eventually convert it into a hydrogel, we immersed the entire material in water to allow the organic solvent to dissipate and water to take its place,” Dai explained.
This solvent-exchange method offers a significant advantage, as it can be applied to various types of polymer semiconductors with different functionalities.
‘One plus one is greater than two’
The hydrogel semiconductor developed by the team, which has been patented and is being commercialized through UChicago’s Polsky Center for Entrepreneurship and Innovation, is a singular material combining both semiconductor and hydrogel properties.
“It’s a unified material that incorporates both semiconducting features and hydrogel characteristics, making it just like any other hydrogel,” Wang explained.
However, unlike standard hydrogels, this new material actually enhances biological functions in two significant ways, outperforming what either hydrogels or semiconductors could achieve independently.
Firstly, the direct bond of this soft material with tissue minimizes the immune responses and inflammation typically caused by implanted medical devices.
Secondly, due to the hydrogels’ porosity, the new material improves biosensing responses and amplifies photo-modulation effects. With biomolecules able to diffuse into the material, the interaction sites for detecting specific biomarkers significantly increase, enhancing sensitivity. In addition to sensing, responses to light for therapeutic applications on tissue surfaces are also heightened, aiding functions like light-driven pacemakers or wound dressings that can be effectively heated with light to accelerate healing.
“It’s a case of ‘one plus one is greater than two,'” Wang humorously concluded.
