Researchers at Washington University in St. Louis have engineered injectable bioelectric hydrogels designed to monitor various biological activities, including heart rate. This innovative approach could potentially replace conventional devices that are typically constructed from metals, silicon, plastic, and glass, which require surgical implantation.
A team from the McKelvey School of Engineering, led by Alexandra Rutz, an assistant professor of biomedical engineering, along with Anna Goestenkors, a fifth-year doctoral student, has developed granular hydrogels made from microparticles. These hydrogels can be injected into the body, allowing them to spread over tissues or encapsulate cells and tissues to monitor and stimulate biological activity. Their findings were published on October 8 in the journal Small.
The microparticles consist of spherical hydrogels made from the conducting polymer known as PEDOT:PSS. When tightly packed, they resemble wet sand or paste, capable of holding their form due to micropores. These hydrogels can also be 3D printed or shaped while preserving their structure, and can revert to individual microparticles when placed in a liquid medium.
“Granular hydrogels have not been extensively explored for these applications, but we believe that this material can be injected with a needle directly at the site,” Rutz explained. “We are attempting to utilize techniques from tissue engineering to enable these electronically conducting materials to mimic bodily properties while leveraging their functions for more advanced applications.”
Goestenkors added, “The connections between the particles are not permanent, allowing them to move relative to one another. The material behaves like a liquid under force, enabling it to be injected or extruded. Upon removing the force, the material regains its connections and returns to a paste-like solid state, making it highly adaptable.”
The researchers demonstrated that these individual particles could be extruded through a 3D printing nozzle to create strands. The process involved creating a water-and-oil emulsion, akin to mixing an oil-and-vinegar salad dressing. After heating the oil, they introduced the polymer, which, when stirred, formed tiny droplets in the oil. The heat then crosslinked the polymer, resulting in stable hydrogels.
As part of their research, an experiment was conducted in the lab of Barani Raman, the Dennis & Barbara Kessler Professor at McKelvey Engineering and co-director of WashU”s Center for Cyborg and BioRobotic Research. Goestenkors placed small clumps of the microparticles on locust antennae tips, which are equipped with olfactory receptor neurons. The particles enabled the measurement of local field potentials correlating with odors detected by the locusts.
“With further advancements, we envision these conducting granular hydrogels being utilized as 3D printed customized electrodes that can adapt to diverse topographical surfaces or fully encapsulate biological components, tissue engineering scaffolds, or injectable therapies,” Rutz stated.
Rutz and Goestenkors have filed for a U.S. patent covering the fabrication and applications of conducting polymer microparticles and conducting granular hydrogels. They are collaborating with WashU”s Office of Technology Management to protect their intellectual property and advance commercialization efforts.
This research received support from various initiatives at Washington University in St. Louis, including the Women”s Health Technologies Collaboration Initiation Grant, Center for Regenerative Medicine Seed Grant, and the Ovarian Cancer Research Innovation Fund Award.
