The perfect material for connecting electronics with living tissue must be soft, stretchable, and as hydrophilic as the tissue itself—essentially, a hydrogel. In contrast, traditional semiconductors, crucial for bioelectronics like pacemakers, biosensors, and drug delivery systems, are rigid, brittle, and repel water, making it impossible to integrate them as hydrogels have been.
A team of researchers at UChicago Pritzker School of Molecular Engineering (PME) has solved this long-standing challenge, innovatively transforming the way hydrogels are created to produce a compelling semiconductor in hydrogel form. Spearheaded by Asst. Prof. Sihong Wang’s research team’s result is a stunning bluish gel that undulates like a jellyfish in the water while maintaining the exceptional semiconductive properties required for effective communication between living tissue and technology.
The material showcases tissue-level moduli as soft as 81 kPa, stretchability of 150% strain, and impressive charge-carrier mobility of up to 1.4 cm² V⁻¹ s⁻¹. This dual functionality—as both semiconductor and hydrogel—makes it an ideal candidate for bioelectronic interfaces, fulfilling all necessary criteria.
“When making implantable bioelectronic devices, one challenge you must address is to make a device with tissue-like mechanical properties,” said Yahao Dai, the first author of the new paper. “That way, when it gets directly interfaced with the tissue, they can deform together and also form a very intimate bio-interface.”
While the paper primarily addressed the challenges of implanted medical devices, including biochemical sensors and pacemakers, Dai emphasized the material’s promising non-surgical applications. These could lead to enhanced skin readings and significantly improved wound care, showcasing its versatile potential beyond just surgical uses.
“It has very soft mechanical properties and a large degree of hydration similar to living tissue,” said UChicago PME Asst. Prof. Sihong Wang. “Hydrogel is also very porous, so it allows the efficient diffusion transport of different kinds of nutrition and chemicals. All these traits combine to make hydrogel probably the most useful material for tissue engineering and drug delivery.”
The conventional method for creating a hydrogel involves dissolving a material in water and introducing gelation chemicals to transform it into a gel. While some materials easily dissolve in water, others necessitate complex modifications to the process. However, the essential principle is unchanged: without water, there can be no hydrogel.
In contrast, semiconductors typically resist dissolution in water. Instead of exploring lengthy and inefficient alternatives, the UChicago PME team chose to rethink the entire process.
Rather than relying on water, they opted for an organic solvent that is soluble in water. They prepared a gel from this organic solution of semiconductors and hydrogel precursors. The result was initially an organogel, paving the way for exciting advancements in material science.
“To eventually turn it into a hydrogel, we then immersed the whole material system into the water to let the organic solvent dissolve out and let the water come in,” Dai said.
One of the key advantages of this solvent-exchange-based method is its versatility across a wide range of polymer semiconductors, each with unique functionalities. The hydrogel semiconductor, which the team has patented and is in the process of commercializing through UChicago’s Polsky Center for Entrepreneurship and Innovation, represents a groundbreaking innovation. It is not merely a blend of a semiconductor and a hydrogel; it is a unified material that embodies the properties of both a semiconductor and a hydrogel simultaneously.
“It’s just one piece that has both semiconducting properties and hydrogel design, meaning that this whole piece is just like any other hydrogel,” Wang said.
The new material stands out from other hydrogels by significantly enhancing biological functions in two crucial aspects, achieving results that neither hydrogels nor semiconductors can deliver independently.
Firstly, its soft composition allows for a direct bond with tissue, minimizing immune responses and inflammation that often accompany medical device implantation.
Secondly, due to its highly porous structure, this innovative material elevates biosensing capabilities and improves photo-modulation effects. With biomolecules freely diffusing into the film, interaction sites for biomarkers increase dramatically, resulting in heightened sensitivity. Moreover, the efficient transport of redox-active species amplifies light-responsive therapeutic functions at tissue surfaces, optimizing technologies such as light-controlled pacemakers and wound dressings that can be heated efficiently by light, thereby accelerating healing.
Journal reference:
- Yahao Dai, Shinya Wai, Pengju Li, Naisong Shan, Zhiqiang Cao, Yang Li, Yunfei Wang, Youdi Liu, Wei Liu, Kan Tang, Yuzi Liu, Muchuan Hua, Songsong Li, Nan Li, Shivani Chatterji, H. Christopher Fry, Sean Lee, Cheng Zhang, Max Weires, Sean Sutyak, Jiuyun Shi, Chenhui Zhu, Jie Xu, Xiaodan Gu, Bozhi Tian, Sihong Wang. Soft hydrogel semiconductors with augmented biointeractive functions. Science, 2024; DOI: 10.1126/science.adp9314
