Scientists have already successfully coaxed stem cells into becoming red blood cells, which could be used to create "man-made" blood for transfusion. Red blood cells, however, aren't the only component of human blood. Now, researchers at Harvard-affiliated Brigham and Women’s Hospital have also created functional human platelets, using a bioreactor that simulates the medium in which blood cells are naturally produced – bone marrow.

The main role of platelets (also known as thrombocytes) is to stop wounds from bleeding, by essentially "plugging the hole" in the skin with a clot. Without sufficient numbers of them in the blood, spontaneous and excessive bleeding can occur. Such shortages can be caused by diseases, as a result of undergoing chemotherapy, or by other factors. In these situations, transfusions of platelets harvested from donated blood are often necessary.

In previous studies, scientists have successfully gotten induced pluripotent stem cells to change into megakaryocytes – these are the cells that ordinarily sit in the bone marrow and release platelets into the bloodstream. Unfortunately, it's proven difficult to get those lab-grown megakaryocytes to produce platelets outside of the body.

That's where Brigham and Women’s new "bioreactor-on-a-chip" comes into the picture. By mimicking bone marrow's extracellular matrix composition, stiffness, micro-channel size and shear forces, it persuades the megakaryocytes to produce anywhere from 10 to 90 percent more platelets than was previously possible.

It is hoped that once the technology is scaled up, platelets made with it could be used to address shortages of donated natural platelets, and to minimize the risk of diseases being transmitted between donors and recipients. Human clinical trials are planned to begin in 2017.

The research was led by Dr. Jonathan Thon, and is described in a paper recently published in the journal Blood.