by Andre on 25 April 2008
It’s a fascinating subject in part because of its relevance to health. As John puts it:
[A]lthough clotting is vital to the preservation of life, blood clots that impede the flow of blood in vivo, called thrombi, are responsible for most heart attacks and strokes and complicate other pathological conditions, including many types of cancer and peripheral vascular disease.
But clots are also interesting purely from the materials perspective. In this context, they are a wonderful programmable material. A single protein monomer—fibrin—encodes the entire hierarchical structure of clots. A solution of fibrin will spontaneously self-assemble into a beautiful branched meshwork that fills a test tube but is still more than 99% water. To accomplish this feat, fibrin is more complex than some of the proteins that make up other networks like those found in the cellular cytoskeleton like actin and tubulin. This complexity makes studying fibrin both a challenge and a thrill. The challenge is to devise experiments that are sufficiently well controlled to interpret, as we tried to do in our single molecule pulling paper from last year (paper [free on Pubmed Central]; post at Biocurious). The thrill comes from the enormous variety of factors that modulate clot structure and function. Fibrin forms a smart material: it responds to external chemical cues found in blood that can cause it to grow or dissolve or to become stiffer and more impervious to mechanical insult. In fact, there are dozens of factors responsible for regulating the formation and degradation of blood clots in humans and these can be leveraged to perform useful experiments or to develop variations on biological clots with new properties.
All of these things are possible, and are indeed already happening, but we still don’t know in detail how the structure and properties of fibrin give rise to its macroscopic properties and that means that we still can’t be as clever as we would like in treating mechanical diseases involving fibrin and in designing new materials inspired by its properties.
But this too is starting to change, so stay tuned…