3-D Silk Structure Enables Scientists to Grow Blood Cells Outside the Body

A scanning electron micrograph of bone marrow in cancellous bone tissue. Researchers at Tufts University and the University of Pavia have created a silk-based model that mimics bone marrow. Steve Gschmeissner/Science Source

Your blood isn't the uniform river of red it appears to be. It's actually made up of many, varied cells. One class of blood cells is the platelets, which are small, and circulate throughout the blood to activate clotting and stop bleeding. When platelet function is impaired—such as in the case of thrombocytopenia, hemophilia and more than 200 other conditions, according to the Platelet Disorder Support Association—patients run the risk of bleeding in greater, life-threatening amounts. If the blood does not clot, patients may bleed out and die.

Treatments for platelet function disorders have many drawbacks. Platelet transfusions are common, but the process requires donors, and complications due to immune responses are frequent and unpredictable. Sometimes drugs will be prescribed to block antibodies—immune cells—from attacking platelets. A last resort is the removal of a patient's spleen, which eliminates a substantial site of antibody production. But even that doesn't always improve platelet count.

A team of researchers at Tufts University School of Engineering in Massachusetts and the University of Pavia in Italy, however, believe they may have a solution: create functioning human platelets outside of the patient's body. They've created a model that acts exactly like human bone marrow, the environment within the body that stimulates platelet growth.

By building microtubes spun of silk, collagen and fibronectin, and surrounding these tubes with a pervious silk sponge, the scientists were able to mimic the porous environment of bone marrow outside of the body. Once the environment was created, researchers implanted patient-cultured megakaryocytes—the cells that produce platelets—into the system. Reacting as they would if in actual bone marrow, the megakaryocytes went to work, and the researchers had a platelet-making system on their hands.

According to Dr. David Kaplan, one of the lead researchers on the team, silk was key to the process. Because of its structure, silk can be made in varying degrees of stiffness and different forms, which researchers have found affects the formation and release of authentic platelets. Most important, silk does not cause the platelets to clot, meaning that functional platelets can be gathered from the system and used later on—without the quality and storage problems created by donor platelets.

The system doesn't yield as many platelets as healthy human bone marrow, but the researchers are optimistic that they can up that. Of course, it may be a while before the system can be used to treat humans. "The big test is if it can work just as well, or even better in animal trials," says Dr. Mortimer Poncz of the Children's Hospital of Philadelphia. If it's not successful in this context, it's not a viable solution. He notes, however, that "it is a nice step forward."

Megakaryocytes cultured from patients could also allow researchers to design patient-specific treatment courses. The researchers hope future applications will go beyond blood disorders, and include healing ulcers and burns, regenerating bone tissue for dentistry and even certain kinds of plastic surgery.