Scientists unravel mystery of stripe patterns in nature

Stripe patterns are commonly seen in nature. Birds and fish move in coordinated flocks and schools, fingerprints form unique designs, and zebras can be identified by their distinctive stripes.

What influences such pattern formation has long been a source of mystery, but scientists from the University of Bristol and Saarland University in Germany have shown the answer may lie within, in human red blood cells. The research reveals the stripe patterns that appear when red blood cells are separated in a centrifuge are primarily caused by the cells‘ own attraction and adhesion to neighbouring cells, contrary to previous belief.

Challenging assumptions

Co-lead author Dr. Alexis Darras, Lecturer in Physics at the University of Bristol, said: „It was previously assumed these patterns occurred due to the irregular ageing process and associated water loss of red blood cells during their lifespan of around three months. Our study challenges this and confirms that the real cause is not water loss, it is cell aggregation.“

The role of aggregation

Co-lead author Felix Maurer, a PhD student at Saarland University, explained the mechanics: „Like weather balloons in Earth’s thinning atmosphere, red blood cells distribute so that each cell remains at an equilibrium height, the point where its average density equals that of the surrounding medium.“

Findings showed that stripe formation was driven by the sheer number of cells. „The pattern only emerges through the interaction of very many cells. In our experiment, about one billion cells were in a single tube,“ Felix added. „Without aggregation, that is cells sticking together, the cells distribute evenly and no stripes form.“

These new insights could pave the way for new diagnostic approaches to blood disorders, such as sickle cell anaemia, where cells deform and their flow and clustering behaviour changes.