meGrowing cells in the lab is relatively easy, but making them into realistic models of human tissue is more difficult. This requires creating an environment that closely mirrors the conditions of the body’s extracellular matrix (ECM), the molecular scaffold that supports cells. Bioengineers have sought to design materials that mimic the properties of the ECM, including its stiffness, density, and stickiness, and one promising material is hydrogels, thin polymer networks that are mostly filled with water.
Although cells grow happily in hydrogels and the material can be customized to fit the context being modeled, some aspects of the ECM architecture are difficult to reproduce. For example, in some tissues The fibers that make up the ECM are aligned It encourages cells to line up and move in a specific direction.One In hydrogels, fibers do not typically exhibit such coordination, making it more difficult to grow tissues that require such linear structures.
In a recent study, researchers at Rice University explained: new biomaterials Made of peptide nanofibers that self-assemble into aligned hydrogels.2 The research team used salt to control the degree of alignment of the hydrogel fibers and found that this affected the alignment of cells grown on the material. These findings suggest that the new hydrogel could be a promising scaffold for building more realistic tissue models in the laboratory.
“There is a motivation that if we put cells on aligned material, the cells will sense the alignment and align themselves,” he said. Adam Parsid“It’s a kind of useful resource that takes advantage of the cells’ natural way of doing things,” said the bioengineer who led the study. [of sensing] “How to sort.”
For the components of this material, Farsheed selected: A peptide called K2His colleagues Jeffrey Hartgerink‘s lab was designed 15 years ago.three The chemistry of the peptides allows them to self-assemble into nanofibers that form hydrogels when mixed with a salt solution. Hydrogels are made up primarily of water and salt, which together make up 97 percent of the material, mimicking the composition of the human body.
Parsid used a pipette to squeeze K2 into a salt solution to create long “noodles” of hydrogel fibers, but he still needed a strategy to control the alignment of the nanofibers. He realized that he could do this by varying the salt level in the solution. The more salt there was, the more aligned the fibers became.
This provides a simple way to create a better laboratory model of how cells grow in ECM, which has historically been difficult to study. Darin Pochan“To do alignment studies, most people have to come up with completely artificial substrates that are not really applicable to tissue engineering experiments,” he said. “This is much more natural.”
Different amounts of salt can align the nanofibers in the hydrogel to different levels.
Adam Parsid
Next, Farsheed and his colleagues tested how cells would grow in the material. They created hydrogel versions with different levels of alignment, then added pig heart cells, which are known to reorient themselves based on the alignment of the ECM. As Farsheed had expected, the cells aligned only partially in gels with less aligned fibers, which most closely resembled the brain ECM. In gels with moderately organized fibers, which mimicked the ECM found in muscle, the cells aligned more. But he was surprised to see that in the most aligned hydrogels, the cells did not align with the fibers at all.
“It’s a really cool, counterintuitive result,” Pochan said. “This is one of the papers that really sets the standard for this field. We need to understand how aligned the nanostructures are, because that has a huge impact on how cells behave.”
Examining the gels under an electron microscope, Farsheed realized that the fibers in the most aligned hydrogels could be restricting the cells’ mobility as they tried to rearrange themselves. “Our material was so aligned and packed so tightly together that the cells couldn’t physically pull themselves together,” he said.
Pochan is curious to see how the hydrogels will lend themselves to tissue engineering, particularly how robust they are to the addition of other molecules needed for the growth of specific cell types. Pashid’s first test will be to use the gels to create better scaffolds for peripheral nerve models. When using an unaligned scaffold, nerves grown in the lab tend to orient in all directions, which doesn’t resemble the neural circuits found in the body. That makes it harder for researchers to use the models to test the real-world effects of drugs, for example. Pashid hopes that an aligned scaffold will allow for a more realistic model of nerve tissue.
To achieve this, simply creating one-dimensional peptide noodles isn’t enough. Pashid is currently experimenting with using 3D printing to turn these hydrogels into more complex structures, similar to Lincoln Logs or Chex.
“If we can create these more complex structures, we can start to pattern our cells in more complex ways that start to have structures that look and act like the tissues of the body,” Farsheed said.
references
1. Petri RJ et al. Random versus directional persistent cell migration. Nature Rev Mol Cell Biology. 2009;10(8):538-549.
2. Farsheed AC etc. Tunable macroscopic alignment of self-assembled peptide nanofibers. ACS Nano. 2024;18(19):12477-12488.
3. Aulisa L et al. Self-assembly of multidomain peptides: Control of cross-linking and viscoelasticity through sequence modification. Biomacromolecules. 2009;10(9):2694-2698.
