Blood stem cells can only thrive in the bone marrow, from which they turn into different kinds of blood cells that are needed in the body, including red and white blood cells, which transport oxygen and fight disease. For years, researchers around the world have been trying to find a way to replicate the bone marrow so that they are able to harvest blood stem cells in the laboratory because stem cells cease to be what they are once they are removed from the body.

Now researchers at Karlsruhe Institute of Technology, the Max Planck Institute for Intelligent Systems and the University of Tübingen say that they have designed porous material in which blood stem cells can multiply for as long as four days.

A bath sponge with cells inside

Natural bone marrow is a very complex structure, making it difficult to imitate. Its three-dimensional porous architecture resembles a bath sponge and contains bridging proteins that the stem cells can dock on.

Precisely-sized pores host many cell types that interact with each other and produce chemical messages, allowing the blood stem cells to multiply.

Researchers put a porous polymer into a nutrient solution to cultivate stem cells inside

"We assume that stem cells [do] not only notice the chemical composition of their surroundings. They can probably also feel if their environment is soft or hard, rough or smooth," Cornelia Lee-Thedieck, a researcher at the Karlsruhe Institute of Technology tells DW.

She and her colleagues put everything together that researchers already know about bone marrow and their preferred environment. They replicated the sponge-like structure of bone marrow using a simple polymer. They linked proteins to it and added other cell types.

Treating leukemia

The researchers would like to see the artificial bone marrow help cure leukemia one day. Since new, healthy blood stem cells are needed to treat leukemia, stem cells could be harvested in the lab and transplanted into patients. Currently, the stem cells are isolated from the blood or the bone marrow of a suitable donor.

"Producing artificial bone marrow for culturing and multiplying blood stem cells is a potentially interesting application," says Martin Bornhäuser from the University Hospital Dresden.

"It would make it possible to generate a sufficient number of stem cells from a small amount to transplant into an adult patient," he adds.

Cord blood is a source for blood stem cells

That small amount of stem cells could also come from blood extracted from the placenta and the umbilical cord after childbirth: cord blood. If parents agree, doctors can the cord blood of their child stored and frozen in a blood bank.

Harvesting stem cells

However, the number of stem cells in cord blood is low, according to the bone marrow donor center (DKMS), a non-profit that promotes bone marrow donations and operates a cord blood bank (German). "The circle of possible acceptors is limited to children and adults with a low body weight," it says on its website.

With artificial bone marrow, this would be no longer the case.

"Our long-term objective is to create a structure into which blood stem cells are put," Lee-Thedieck says. "Then they multiply, and we harvest the stem cells and give them to the patient."

But she adds that at the moment the findings are "applied fundamental research."

"We just created a prototype," she notes.

It will be at least another 15 years before this technology is available for patients.

And despite the discovery, the fact remains that scientists are yet to come up with a structure that can imitate the natural bone marrow completely, according to Martin Bornhäuser.

"More applied research projects will be needed to turn this into reality," he says.