When donated blood is scarce, platelets are even scarcer. These cell fragments, which are essential for blood clotting, have a short lifespan. While whole blood can be refrigerated for up to a month, platelets only last a week at most.
“Even if you have a lot of donations, you can’t keep them for long,” says Ashley Brown, an associate professor in the joint biomedical engineering program at North Carolina State University and the University of North Carolina at Chapel Hill.
To address this problem, Brown and his team created an artificial substitute that could be stored for long periods of time. in a recent article in Scientific translational medicinedescribe the use of their synthetic platelets to stop bleeding and promote healing in rodents and pigs.
Natural platelets circulate in the blood and prevent or stop bleeding by forming clots. Sometimes the body needs more. People with traumatic injuries, cancer, and certain chronic conditions that remove platelets from the blood often require transfusions. Platelets are usually collected through a process called apheresis, in which a donor’s blood is passed through a tube to a machine that separates the platelets. These are funneled into a bag and the rest of the blood is returned to the donor.
Their limited shelf life also means they are not typically stored in rural hospitals and cannot be easily transported. Brown’s goal is to create an alternative that is easy to store and ship and can be administered to patients sooner, such as in an ambulance or on the battlefield, and regardless of blood type.
To make their synthetic platelets, Brown and his team used a soft, water-based gel called a hydrogel to form nanoparticles that mimic the size, mechanics and shape of natural platelets. They then designed an antibody fragment that binds to fibrin, a protein that helps platelets form clots, and decorated the surface of the nanoparticles with this fibrin antibody. When an injury occurs, platelets rush to the site of damage to form a temporary plug. Fibrin is also activated in this process and accumulates at the wound site, eventually producing a clot.
To find the optimal dose of artificial platelets needed to stop bleeding, the researchers tested a variety of doses in mice. They then gave infusions of the artificial version to mice, rats and pigs and compared them with animals that received natural platelets and those that were not treated with either. All animals in the study suffered severe internal bleeding. They discovered that synthetic platelets could travel through the bloodstream to the wound site to promote clotting and speed healing.
Cure rates were similar in animals receiving synthetic platelets and those receiving natural platelets. Overall, both groups did better than the untreated group. Interestingly, the researchers only had to use about a tenth of the artificial particles to obtain the same healing effects as with natural platelets. “Our mechanism of action is to bind to fibrin, so it could be that our particles are more efficient at that binding,” says Brown. There is also variability in the way laboratories prepare natural platelets that can affect their quality, which could have accentuated this difference.