January 14, 2009

Artificial Bone Marrow

Researchers have succeeded in creating bone marrow that can produce white and red blood cells, a discovery that has many potential health applications
Researchers at the University of Michigan have created artificial bone marrow. It can produce both red and white blood cells, including B cells, a specialized type of immune cell. The most immediate practical application is likely to be the production of large quantities of blood for transfusions. There are also many other potential applications.

The artificial marrow or the cells it produces could form the basis for a simplified drug testing system...

It's hard to overstate the importance of this creation, if the artificial marrow continues to function. Blood for transfusions is always needed by hospitals and supply can be erratic. A laboratory process that can constantly produce blood or blood fractions would go a long way towards eliminating this problem. The artificial marrow or the cells it produces could form the basis for a simplified drug testing system, an alternative to conducting tests on laboratory animals. There are a number of potential therapeutic applications involving specific types of immune cells. And the marrow could serve as an invaluable source of biological material for researchers, material that previously could only be obtained in small amounts from living creatures.

Bone marrow is the flexible material present in the hollow interior of bones. A major function of bone marrow is the production of new blood and immune cells; hundreds of billions of new cells are produced daily, for eventual release into the blood system.

Bone marrow is not merely a collection of cells. It is a highly structured and compartmentalized organ, containing a vast number of blood vessels and nerves. The marrow in the over 200 adult human bones forms a connected organ system, which replenishes many types of the body's cells, in response to a complex signaling system.

Designing an artificial system that possesses even some of the organization of human bone marrow is a tremendous task. It starts with a scaffold, a structure that supports and allows for formation of the bone marrow, as bones do in humans. The scaffold used in the work at Michigan was made of a transparent polymer which nutrients can pass through. This polymer was molded into a network that contained tiny spheres with pores or spaces between them, akin to the way a rack of billiard balls are arranged. The exact size and geometry of the spheres and pores is critical to the functioning of the artificial marrow: it must mimic biological conditions closely enough to allow many different cell types to, grow, divide and differentiate inside of the pores.

The scaffolds were seeded with stromal (stem) cells and osteoblasts (cells from which bone develop) from human bone marrow. The resulting material exhibits several characteristics of human bone marrow. It can continuously produce both red and white blood cells and it also gives a human-like immune response to added flu virus. Though not designed for transplantation, when the artificial marrow was transplanted into immune-deficient mice, the mice began producing immune cells, and blood vessels grew into the transplanted marrow, as they would in biological bone marrow.

Nicholas Kotov, a professor in the University of Michigan departments of Chemical Engineering, Materials and Science Engineering, and Biomedical Engineering, was the principal investigator on the project. An article detailing the research will appear in the February 2009 issue of Biomaterials.
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