California researchers have created a tissue-engineered small-scale small intestine in mice, a breakthrough for regenerative medicine and a step toward growing new intestines for humans. The process re-creates all the layers of cells that make up a functioning intestine.

Tissue engineering, which promises to rebuild or replace injured or failing body parts, has seen some major advancements in recent months, with biological scaffolds used to create new bones in rabbits and regrown muscle in humans. But it’s more difficult to make a complete organ, which has several types of cells that must all function properly.

The small intestine is a good subject for this type of study because it’s a particularly regenerative organ, said Dr. Tracy C. Grikscheit, the lead author of a paper on this research.