Laser Beam Helps Protect Signal Proteins Used for Tissue Engineering

A University of Washington research group has used laser light to tether and untether signal proteins to the scaffolds used in tissue engineering. The signals that these proteins send to control cell migration, division, and differentiation are critical to growing tissues in the lab but the proteins are fragile. Traditional methods used to keep proteins on scaffolds can kill more than 90% of the proteins’ functionality.

The new technique allows the researchers to load a hydrogel (scaffold) with many different types of protein signals and then expose the hydrogel to laser light to untether proteins from specific sections of the material. By exposing only portions of the hydrogel to the laser light, the team can control where protein signals remain tethered to the hydrogel. Tethering and untethering the proteins makes it possible to create patterns of signal proteins throughout a biomaterial scaffold to grow tissues composed of different types of cells.

Photorelease of proteins from a hydrogel. Top: The mCherry red fluorescent proteins are tethered to the hydrogel. Researchers can cleave the tether with directed light (blue arrows), releasing the mCherry from the hydrogel (blue arrows). Bottom: An image of the hydrogel after mCherry release patterned in the shape of the University of Washington mascot (black). Scale bar is 100 μm. Courtesy of Shadish, Benuska, and DeForest, 2019, Nature Materials.

The proteins are modified so they can be chemically tethered to the scaffold using light. By exposing the tethers to laser light, the proteins can be photoreleased.

The team tested the photorelease process using a hydrogel loaded with a protein signal. The researchers introduced a human cell line into the hydrogel and observed the growth factors binding to the cell membranes. They used a laser beam to untether the protein signals on one side only of an individual cell. On the tethered side, the proteins stayed on the outside of the cell since they were still stuck to the hydrogel. On the untethered side, the protein signals were internalized by the cell.

Photorelease of epidermal growth factor (EGF) proteins on one side of a human cell. Left: EGF (green) is tethered to a hydrogel of a single human cell (center). The cell membrane binds EGF, making its membrane green. Middle: The hydrogel after using a laser to untether and release EGF proteins on the top portion of the cell. Right: An image showing the difference in green fluorescent color between post- and prerelease images. Note the increase in color in the top portion of the cell, which indicates that the cell has started to internalize the untethered EGF proteins but only on one side. Scale bar is 10 μm. Courtesy of Shadish, Benuska, and DeForest, 2019, Nature Materials.

“Based on how we target the laser light, we can ensure that different cells — or even different parts of single cells — are receiving different environmental signals,” said professor Cole DeForest.

(l) to (r): Cole DeForest, Gabrielle Benuska, Jared Shadish. Courtesy of Dennis Wise/University of Washington.

Such precise control at the single-cell level could help not only with tissue engineering, but with basic research in cell biology, DeForest said. Researchers could use the novel platform to better understand how protein signals work together to control cell differentiation, heal diseased tissue, and promote human development.

“This platform allows us to precisely control when and where bioactive protein signals are presented to cells within materials,” DeForest said. “That opens the door to many exciting applications in tissue engineering and therapeutics research.”

The research was published in Nature Materials (https://doi.org/10.1038/s41563-019-0367-7).