Synthetic platelets built to treat bleeding

Scientists have created synthetic platelets—the blood components that prevent excessive bleeding and heal wounds. University of California, Santa Barbara researchers, in collaboration with researchers at Scripps Research Institute and Sanford-Burnham Institute in La Jolla, California, report their findings in the journal Advanced Materials. The unique physical and biochemical properties of platelets play an important role in performing complex biological tasks. Smaller than red blood cells, platelets are flexible, disk-shaped cells that are 2-4 micrometers in size. “Upon further optimization and exhaustive testing, the synthetic platelets could be used for various biomedical applications,” says the paper’s first author Nishit Doshi, a researcher from the department of chemical engineering. The challenge Doshi and colleagues faced was to develop a comparably sized particle—roughly 1/50th of the diameter of a strand of hair—that had key structural properties of real platelets. “In order to mimic the size, shape, and surface functionality of natural platelets synthetically, polymeric particles are particularly attractive,” says Doshi. “However, polymeric particles are orders of magnitude more rigid than platelets.” To solve the problem of flexibility, researchers at UC Santa Barbara used a polymeric “template”—a core upon which layers of proteins and polyelectrolytes were deposited, layered, and cross-linked to create a stable synthetic platelet-shaped particle. The rigid polymeric core was then dissolved to give the particle the desired flexibility. The particle was then coated with proteins found on the surface of activated natural platelets or damaged blood vessels, a procedure performed by the researchers at Scripps Research Institute. These synthetic platelets may be used to not only perform the typical functions of human platelets but also may be used to carry imaging agents to identify damaged blood vessels or to deliver drugs that dissolve blood clots. The synthetic platelets represent the latest and one of the most advanced in a line of efforts over the last century to mimic platelet function. While clotting factors and platelets from outside donors are used widely to halt bleeding, immune system responses and thrombosis have been issues. Non-platelet-derived substitutes have also received attention. However, Doshi says, these do not physically resemble the physical features of natural platelets. “This development is a significant milestone in the field of biomimetic materials,” says Samir Mitragotri, professor of chemical engineering and director of UC Santa Barbara’s Center for Bioengineering, and an author of the paper. “By capitalizing on our capabilities in engineering materials, with the expertise in platelet biology that exists in Professor Ruggeri’s laboratory, our synthetic platelets combine unique physical and biological attributes that mimic natural platelets.” In 2009, Doshi and colleagues in the Mitragotri laboratory developed synthetic red blood cells. “This work is a marvelous demonstration of the power of material synthesis applied to medical problems. The synthetic platelets can have profound implications in wound-healing problems for trauma and wounds arising in both battlefield situations and during surgery,” says Frank Doyle, director of UCSB’s Institute of Collaborative Biotechnologies and the Associate Dean of Research in the College of Engineering. Additional authors from Scripps Research Institute and Sanford-Burnham Medical Research Institute contributed to the study, which was funded by the Institute for Collaborative Biotechnologies through a grant from the U.S. Army Research Office and the National Institutes of Health.