Scientists around the world are trying to grow miniature organs in laboratories to better understand diseases and develop new medical treatments. These tiny lab-grown organs, known as organoids, are made from stem cells and can mimic the structure and function of real human organs such as the brain, intestine, or glands.
However, one major challenge has slowed progress. Even when scientists grow organoids under similar conditions, they rarely develop in exactly the same way. Each organoid can take a slightly different shape or structure, which makes experiments difficult to repeat and compare.
Now, researchers at the University of California, San Francisco (UCSF) have developed a new material that helps organoids grow in a more controlled and predictable way. Their findings, published in Nature Materials on March 10, could improve how scientists study diseases and may eventually help in the creation of replacement tissues for patients.
Understanding Organoids
Organoids are tiny three-dimensional structures grown from stem cells in a laboratory dish. Stem cells have the unique ability to transform into many different types of cells in the body. When placed in the right environment, they can organize themselves into miniature versions of organs.
For example, scientists can grow organoids that resemble parts of the intestine, brain, liver, or salivary glands. These structures allow researchers to observe how tissues grow, how diseases develop, and how drugs affect human cells—without needing to test directly on patients.
Despite their promise, organoids have one major weakness: they do not always grow in the same shape or pattern. This unpredictability makes it difficult to perform reliable experiments.
Researchers have long suspected that the environment surrounding the cells plays an important role in how organoids develop.
The Role of Matrigel
Most organoids are grown inside a material called Matrigel, a gel that provides structural support to cells. It acts like a scaffold, allowing cells to attach and grow in three dimensions instead of spreading flat across a surface.
Matrigel has been widely used because it contains proteins and molecules that resemble those found in the human body. However, it has a problem when scientists try to use 3D bioprinting techniques.
When Matrigel is in liquid form, it is too thin and runny to hold printed cells in place. But once it solidifies, it becomes too stiff and pushes back against growing tissues. This makes it difficult to precisely arrange cells into shapes such as tubes, lines, or clusters.
Scientists needed a material that could both hold cells in place during printing and allow them to grow naturally afterward.
Creating a Better Environment for Cells
To solve this problem, the UCSF research team developed a new mixture by adding tiny particles of alginate into liquid Matrigel.
Alginate is a natural carbohydrate extracted from algae. It is commonly used in food, medicine, and biotechnology because it forms soft gels that are safe and stable.
By mixing microscopic alginate particles with Matrigel, the researchers created a new material that behaves somewhat like wet sand. This mixture can hold its shape well enough for 3D printing but still allows cells to move and grow.
The key idea was to make the material behave more like the soft but supportive environment inside the human body, where tissues naturally develop.
Why Stress Relaxation Is Important
The most important property of the new material is something scientists call stress relaxation.
Stress relaxation describes how a material gradually releases pressure when something pushes or pulls on it. In living tissues, cells constantly move, divide, and change shape. As they grow, they push against their surroundings.
If the surrounding material is too rigid, the cells cannot move properly and development slows or stops. If the environment is too soft or fluid, the cells lose structure and grow unpredictably.
Professor Zev Gartner, a pharmaceutical chemistry researcher at UCSF and senior author of the study, explained that the timing of this relaxation is critical.
According to Gartner, the material must give way at the same speed that tissues naturally reshape themselves. When the environment relaxes at the right pace, cells can organize into stable structures.
The new alginate-Matrigel mixture achieves this balance.
Printing Living Structures
With this improved material, the researchers were able to 3D print stem cells directly into precise shapes before they began developing.
For example, they printed cells in:
Small clusters
Long lines
Organized groups with specific spacing
Because the new gel holds its form, these printed patterns stayed intact long enough for cells to begin growing together.
As the cells multiplied and pushed outward, the gel slowly relaxed, allowing the developing organoids to expand naturally.
This approach combines the precision of 3D printing with the self-organizing ability of living cells.
From Printed Cells to Living Organoids
The team tested their method on several types of organoid-forming cells, including:
Mouse intestinal cells
Mouse salivary gland cells
Human vascular cells
Human stem-cell-derived brain cells
In each case, the printed cells successfully developed into organoids with consistent shapes and sizes.
Some organoids even formed developmental buds, which are small growing structures similar to those seen during natural organ development in embryos.
One of the most impressive results came from the intestinal cells. When these cells were printed in long lines, they eventually formed tube-like structures capable of carrying fluid, similar to real human intestinal tissue.
This level of organization is difficult to achieve using traditional organoid methods.
Letting Cells Build Themselves
One of the most interesting aspects of this research is that scientists are not manually constructing organs piece by piece.
Instead, they are simply placing cells in the right starting positions and allowing biology to do the rest.
Professor Gartner described this idea in a simple way: scientists are not building tissues like Lego blocks. Instead, they create the right conditions so that cells follow their natural developmental instructions.
Cells already contain the genetic programs needed to build complex tissues. By providing the correct environment, scientists can guide those programs to produce more predictable results.
Future Possibilities
This breakthrough could have major implications for biomedical research and medicine.
More reliable organoids could help scientists:
Study diseases more accurately
Researchers could model conditions such as cancer, neurological disorders, or digestive diseases using consistent organoid structures.
Test new drugs safely
Pharmaceutical companies could test treatments on organoids before moving to human trials.
Understand human development
Scientists could observe how organs form during early development.
Create replacement tissues
In the future, bioprinting technologies may allow researchers to grow tissues that could replace damaged organs.
Although fully functional printed organs are still a long way off, the new stress-relaxing material represents an important step toward that goal.
A Step Toward Self-Building Organs
The ultimate vision of this research is a future where scientists can guide cells to build complex organs on their own.
By printing cells into specific patterns and providing the right environment, tissues may eventually grow into structures that closely resemble real organs.
This approach could transform regenerative medicine.
Instead of constructing organs artificially, scientists may one day simply start the process and let biology complete the design.
With innovations like the alginate-Matrigel material developed at UCSF, that future is becoming more realistic.
Reference: Austin J. Graham et al, Stress-relaxing granular bioprinting materials enable complex and uniform organoid self-organization, Nature Materials (2026). DOI: 10.1038/s41563-026-02519-4
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