Research

In 2008, with Veronique Trappe, I introduced Differential Dynamic Microscopy (DDM). It analyses the differences between frames of an ordinary microscope movie in Fourier space and returns the same kind of information as a light-scattering experiment: how fast things move, at every length scale at once, without tracking individual objects. DDM now runs on microscopes in many laboratories, for samples ranging from proteins and nanoparticles to bacteria and tissues. We keep extending it, for example to samples under oscillatory shear. To see how it works, try DDM, hands on, a page that simulates a DDM experiment in your browser, from the raw movie to the particle size.

Gels, foams and dense suspensions can behave like solids or like liquids depending on how hard and how fast they are pushed. We combine rheology with microscopy to see what happens inside the material while it yields, flows or breaks. For this we built ShearView, a compact open-source shear cell that sits on top of an optical microscope. A current project asks whether gels can be "trained", like muscles, to change their properties after they have formed.

Sheets of cells behave like a soft material that can jam like a solid or flow like a liquid. With biologist colleagues, especially the group of Giorgio Scita in Milan, we measure how epithelial and cancer cells move collectively, how they unjam, and how these physical transitions are tied to development and disease. Our methods also quantify motion inside cells and the mechanics of the cell nucleus.

When a fluid mixture is not in equilibrium, for example while one component diffuses into the other, its concentration fluctuates on unexpectedly large scales. On Earth gravity hides most of this, so we study it in orbit. I took part in the GRADFLEX experiment flown on the FOTON-M3 satellite in 2007, and I now coordinate the science team of the Sedimenting Colloids experiment, planned for the International Space Station, which will look at how particles settle when the effective gravity can be tuned.

Before DDM, my work focused on near-field scattering: measuring scattering information from the speckle pattern recorded close to the sample, first with visible light and later with X-rays at synchrotrons. These ideas still shape how we design experiments today.