For this change to happen, the stem cells need a steady supply of a growth factor such as transforming growth factor-beta 1 (TGF-b-1), a protein that boosts cell growth and helps immature cells morph into chondrocytes. While dumping the growth factor into the petri dish in the beginning and then waiting to see what happens will work, it’s not an optimal way to grow a sheet of cartilage. That’s because once the cartilage tissue begins to expand, the cells would devour all of the growth factor and thus the neocartilage may not be big enough or strong enough to use as replacement tissue.

Alsberg’s group wanted to figure out an effective way to provide the cultures with a steady amount of growth factor. The team turned to tiny gelatin beads called, microspheres. They laced the beads with TGF-b-1 — think Jell-O spiked with nutrients — and added them to the cell cultures.

The spiked beads tricked the cultures of immature cells into thinking they were still inside the body. Chemicals released by the cells slowly degraded the beads, keeping a steady diet of growth factor. The beads also provided a handy structure that stem cells could latch onto on their way to becoming chondrocytes. The space between the microspheres allowed room for the chondrocytes to make the matrix that gives cartilage its bounce and strength. In three weeks, the cartilage was strong enough to handle but not quite as strong as natural cartilage.

One day, Alsberg hopes to use this technique to grow neocartilage for humans, by taking immature cells from each patient, and using those cells in the laboratory to make sheets of cartilage that mimic the strength and bounce of cartilage produced in the body. Then, neocartilage will be transplanted back into the patient, filling any defects, and perhaps halting the cycle of damage that leads to osteoarthritis.