A stroke happens when blood cannot reach part of the brain, and that area can be badly damaged.
Researchers at Duke University have created an injectable gel called a "scaffold".
A scaffold is a support structure that gives cells a place to grow.
When doctors injected the gel into stroke-damaged brains in mice, something surprising happened.
The brains began to grow new blood vessels, which carry oxygen and nutrients.
The gel also supported the regrowth of damaged nerves.
Best of all, the mice slowly regained their ability to move.
The study was done in animals, so human trials are the next big hope.