Dr. Matthias F. Schneider,
Biological Physics Group, University of Augsburg

Imagine you rinse your dishes and everything keeps sticking harder. What looks like a drama for your kitchen does actually keep you alive as you read these lines.  During blood clotting it was found that an increasing shear rate triggers an increase in adhesion of blood platelets. A phenomenon in clear contradiction to our daily experience, but crucial for life, since mechanical vessel damage by elevated shear rates is taking place at all times and almost everywhere in our body.  

Using acoustic driven microfluidics we mimicked the dynamics of von Willebrand factor under flow and found that this protein acts like a mechanical switch. At high shear rates it goes through a coiled-stretched transition and binds to the surface. Blood platelets which constantly run into the vessel wall stick to the immobilized VWF and initiate haemostasis. Computer simulations including hydrodynamic interactions as well as scaling arguments demonstrated that the stretching transition depends very sensitive on the monomer size, which in turn explains why nature picked a biopolymer with unusually large monomers to do the job. This is an excellent example how the understanding of the physical properties of a soft object solves a whole ballpark of mysterious observations with just one strike. 

Please note:
The lecture starts at 3:30 pm with the opportunity for discussion as from 3:00 pm where coffee, tea and biscuits will be served!