Nature Commun. 4, 1333 (2013)

Assembling polymer–colloid composites demands careful, often tedious, fine-tuning. But there are several examples in nature that make the task look all too easy. Take blood clots: the human body is capable of forming a polymer–platelet composite within seconds of injury — outperforming comparable industrial-assembly processes. Now, Hsieh Chen and colleagues have drawn inspiration from clotting to show that polymer–colloid composites assemble via a universal process that can be engineered to obtain aggregates of variable density and microstructure.

The formation of a haemostatic plug during clotting is known to be regulated by fluid flow, and rendered more effective with increasing shear rate. Chen et al. studied a dilute polymer–colloid mixture, using both simulation and experiment, and found that the reversible aggregation exhibited by their system was also mediated by shear forces. Through a simple scaling argument they were able to demonstrate the universality of the phenomenon.

The authors' finding that aggregation occurs only above a critical shear rate will likely prove important in understanding how plugs are generated exclusively at injury sites — and may even inform the design of novel composites with tunable mechanical, chemical and optical properties.