The cells die before they can talk to each other. That’s been the stubborn problem with growing brain tissue in labs: stem cells stressed by their artificial environment stop sending the molecular signals needed to build neural networks. Instead of forming functional connections, they spread damage to their neighbors and the whole culture degrades.
Researchers at the University of Illinois Urbana-Champaign have engineered a solution using tiny microgels packed with antioxidant crystals. Published in Advanced Functional Materials, their work demonstrates how a single dose of these protective capsules, called CROSS (Cellular RedOx Spreading Shield), can keep stem cell cultures healthy for up to seven days. That’s long enough for the cells to produce the high-quality communication molecules that actually build working brain tissue.
The breakthrough addresses a cascade problem. When cells experience oxidative stress, they age prematurely and release defective extracellular vesicles, the tiny packages cells use to send instructions to their neighbors. Those corrupted messages spread through the culture like biological rust, preventing the formation of neural networks that can fire electrical signals. Conventional antioxidants break down too quickly to stop this spread, requiring constant replenishment that disrupts the delicate growing conditions.
Slow-release crystals stop damage at the source
The team, led by chemical engineering professor Hyunjoon Kong and chemistry professor Hee Sun Han, used droplet microfluidics to trap crystalline N-acetylcysteine inside polymer shells. The crystals dissolve slowly, creating a diffusion barrier that releases antioxidant protection gradually rather than all at once. This steady supply prevented stressed or aging cells from contaminating their neighbors.
When researchers compared stem cells protected by CROSS to unprotected controls, the difference was stark. Protected cells produced extracellular vesicles packed with neurogenic microRNA, the molecular instructions that tell neighboring cells to develop into functional neurons with dense synaptic connections. Vesicles from stressed cells did the opposite, actively impairing network development. The team confirmed this using calcium transient imaging and graph theory analysis, which showed that tissues built with CROSS-protected vesicles were electrophysiologically active, firing signals like real brain tissue.
“Our new microfluidic process provides a simple and versatile method for creating improved drug delivery carriers that can be tailored for various biological products,” Kong explains. “The small CROSS materials developed in this study could also help make the production of cell-based therapies more efficient, support the building of lab-grown tissues, and ultimately contribute to new treatment options for a range of diseases.”
From disease models to therapeutic manufacturing
The technology has immediate applications in studying neurological diseases like Alzheimer’s and Parkinson’s, where researchers need reliable tissue models that behave like actual human brains. But the implications extend further. By producing consistent, high-quality extracellular vesicles at scale, CROSS could support manufacturing of therapeutic particles for regenerative medicine, potentially helping repair damaged nerves in patients.
The scalability matters for another emerging field: biohybrid computing, where biological neural networks interface with electronic hardware. Those systems require stable, reliable neural tissue that can maintain electrical activity over extended periods. CROSS addresses one of the field’s quiet bottlenecks by ensuring that lab-grown brain tissue doesn’t just survive but actively develops the connectivity needed for complex information processing.
The work was performed by Ryan Miller, now a postdoctoral fellow at Georgia Tech, and represents a shift from simply keeping cells alive to ensuring they remain productive enough to build functional systems. By solving oxidative stress at its source rather than treating symptoms, the researchers have made lab-grown brain tissue both more practical and more powerful as a research tool.
Advanced Functional Materials: 10.1002/adfm.202522252
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