New hydrogel semiconductors could lead to better tissue-interfacing bioelectronics

The ideal material for connecting electronics and biological tissue is one that is soft, stretchable, and as water-loving as the tissue itself: a hydrogel. On the other hand, semiconductors, which are key materials in bioelectronics such as pacemakers, biosensors, and drug delivery devices, are hard, brittle, and water-phobic and cannot be dissolved using traditional hydrogel manufacturing methods.

A paper published today in the journal Science from the University of Chicago’s Pritzker School of Molecular Engineering (PME) rethinks the process of creating hydrogels to build strong semiconductors in the form of hydrogels, something that has long puzzled researchers. I solved the problem of octopus. Led by Asst. The result of Professor Sihong Wang’s research group’s work is a bluish gel that splatters like sea jelly in water, but retains enormous semiconductor capabilities needed to transmit information between living tissues and machines.

The material demonstrated a tissue-level elastic modulus with a softness of 81 kPa, a strain stretchability of 150%, and a charge carrier mobility of up to 1.4 cm2 V-1 s-1. This means that the material (containing both semiconductor and hydrogel at the same time) meets all the criteria for an ideal bioelectronic interface.

“One of the challenges we have to address when creating implantable bioelectronic devices is creating devices with tissue-like mechanical properties,” said Yahao, lead author of the new paper. Dai says. “This way, upon direct contact with tissue, they can deform together and form a very intimate biological interface.”

While the paper primarily focused on the challenges faced by implantable medical devices such as biochemical sensors and pacemakers, the material also has potential for non-surgical applications, including improved skin measurements and improved wound care. There are also potential applications, Dai said.

“It has very soft mechanical properties and a high degree of hydration similar to biological tissue,” said University of Chicago PME Asst. Professor Wang Sihong. “Hydrogels are also highly porous, allowing efficient diffusive transport of various types of nutrients and chemicals. All these properties combine to make hydrogels perhaps the most suitable for tissue engineering and drug delivery. It will be a useful material.”

“Let’s change our perspective”

A common method for creating hydrogels is to take the material, dissolve it in water, and add gelling chemicals to swell the new liquid into a gel form. Some materials simply dissolve in water, while others require researchers to tinker with the process and change the chemistry, but the core mechanism is the same. No water or hydrogel required.

However, semiconductors usually do not dissolve in water. Rather than finding time-consuming new means to force the process, the Chicago PME team revisited the problem.

“We started thinking, ‘Okay, let’s change the perspective,’ and came up with the solvent exchange process,” says Dai.

Instead of dissolving the semiconductor in water, they dissolved it in an organic solvent that is miscible with water. Gels were then prepared from dissolved semiconductors and hydrogel precursors. Their gel was initially an organogel rather than a hydrogel.

“To ultimately turn it into a hydrogel, we immersed the entire material system in water and incorporated the water by dissolving the organic solvent,” Dai said.

An important advantage of such solvent exchange-based methods is their wide applicability to different types of polymeric semiconductors with different functionalities.

“One plus one is greater than two.”

The hydrogel semiconductors that the team patented and are commercializing through the Polsky Center for Entrepreneurship and Innovation in Chicago are not a hybrid of a semiconductor and a hydrogel. This is one material that is both a semiconductor and a hydrogel.

“This is just one piece with both semiconducting properties and hydrogel design, meaning this whole piece is just like any other hydrogel,” Wang said.

But unlike other hydrogels, this new material actually improved biological function in two areas, producing better results than either hydrogels or semiconductors could achieve alone.

First, bonding the extremely soft material directly to tissue reduces the immune response and inflammation that typically occurs when implanting medical devices.

Second, because hydrogels are highly porous, new materials enable improved biosensing responses and stronger light modulation effects. Biomolecules can diffuse into the film and undergo volumetric interactions, which significantly increases the number of interaction sites for the biomarkers to be detected, improving sensitivity. In addition to sensing, the response to light for therapeutic functions at tissue surfaces is also increased through more efficient transport of redox-active species. This could benefit features such as light-operated pacemakers and wound dressings that can be heated more efficiently and speed healing when exposed to light.

“It’s a combination of ‘one plus one is greater than two,'” Wang joked.