Emulating Nature's Patch Kit

Inspired by Blood Clotting Process, Researchers Discover Materials Design Method

By Mark Dwortzan

At high fluid flow rates, polymers (blue) and colloids (yellow) self-assemble; at low rates, they dissemble. Synthetic polymer-colloid composites could be used to design new materials and medical devices (Image courtesy of C. Hsieh, MIT)
At high fluid flow rates, polymers (blue) and colloids (yellow) self-assemble; at low rates, they dissemble. Synthetic polymer-colloid composites could be used to design new materials and medical devices (Image courtesy of C. Hsieh, MIT)

When we get a cut and it starts to bleed, an intricate, rapid process takes place to patch things up, a sequence of events that most of us take for granted. First, the breach of the blood vessel wall accelerates blood flow, which triggers the release of a specialized, coiled blood polymer—a chainlike protein composed of multiple, repeating structural units—that unfolds into long strands. Next, these strands adhere to the blood vessel wall at the site of the injury where they form a fibrous mesh. Finally, tiny components in the blood called platelets stick to the mesh, eventually filling all gaps between the strands. The result is a polymer-platelet composite that effectively “plugs the hole” where the skin was wounded. 

To Assistant Professor Matthias Schneider (ME) and MIT Professor of Materials Science & Engineering Alfredo Alexander-Katz, analyzing this process is much more than an academic exercise. Whereas most biological materials, from abalone shells to collar bones, form very slowly, blood clots occur at a fast enough rate to serve as a possible model for the design of novel materials and medical devices.

In a set of experiments conducted in Schneider’s Biological Physics Lab, Schneider demonstrated that the blood clotting process can be generalized to assemble synthetic composites that combine polymers with colloids, or micro-particles dissolved in solution similar to platelets swimming in blood. Based on Schneider’s experiments at BU and computer simulations at MIT, Alexander-Katz developed a theory explaining the composite formation process.

Results of this interdisciplinary collaboration, which appeared in the January 8 online edition of Nature Communications, have important implications for the assembly of polymer-colloid composites. Developed by Schneider, Alexander-Katz and six other researchers in the U.S., Germany (including Schneider’s brother, a physician) and Austria with funding from the National Science Foundation and German Research Foundation, the assembly process could be used to create novel composites with tunable mechanical, chemical or optical properties.

Schneider and Alexander-Katz determined that based on the polymers selected, polymer-colloid composite materials within a fluid could be developed to combine—or fall apart—at a specific fluid flow rate, just as clots form and dissolve at a high and low blood flow rate, respectively. In addition, this process could be paired with light to allow better control. By shining light at a particular frequency the composite could be disassembled. This way the same materials can be used over and over.  

Potential applications include any device in which fluid flows, from kidney dialysis systems to instruments that dispense inks, pigments and coatings, to microfluidic diagnostic devices.

“In any device with fluid flow and valves in narrow tubes, you run the risk of tubes getting jammed,” said Schneider. “Imagine you have to ‘clean’ a tube with a diameter less than that of a hair again and again, to release the blockage. Our research suggests a protocol to design a material that self-assembles when needed and can be dissembled by a flash of light or ultrasound whenever, wherever and how often you want. Devices equipped with such flexibility become more robust and therefore more reliable, which is particularly important for medical devices.”

The research team next aims to understand and model the blood clotting process more precisely, and to explore the potential role of reversible polymer-colloid composites in humans and in smart materials design.

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