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Soft Matter and Biological Physics

Dr Pietro Cicuta

Lecturer in Physics
Fellow, Corpus Christi College

Telephone: 01223 337462
E-mail: pc245 [at]

We are interested in understanding soft materials and some problems that remain unresolved in biology. There is a strong synergy between these two themes, due to the fact that many experimental techniques and theoretical concepts can be applied in both. We work across most of the spectrum of BSS activity. For example, we use optical tweezers, microrheology, advanced confocal microscopy and image analysis methods to address dynamics both in colloidal and cellular systems. Another example are liquid interfaces and membranes, which play an important role in both complex fluids and biological systems. Below is a very short summary of current research lines.

Liquid interfaces, surface monolayers, particle rafts

granular layer

Diagram of customised Langmuir trough setup, used to study stress propagation in two dimensional layers. Images show rafts of large and rough-shaped rubber particles. Recent work has shown that stress is transmitted through these layers in a similar way as in piles of grains.

This is the longest running research line, we have addressed in particular the problem of how polymers form monolayered films on interfaces, and the physics properties of these structures. We are also working on protein films of industrial interest, and on the behavior of colloidal particles and grains (rafts) confined to two dimensions. Various new methods have been developed to characterise surface viscoelasicity, including modifications of the Langmuir trough and Surface Dynamic Light Scattering.

Model Membranes


Ternary mixtures of phospholipids and cholesterol phase separate below a critical temperature. Phase separation is imaged in fluorescence, thanks to the preferential partitioning of a fluorescent dye into one phase. This process may have a role in regulating biological activity at membranes.

Membrane mechanics is characterised by bending, shear and compression moduli. Furthermore, multicomponent membranes can phase separate, and in this case each phase has different moduli, and there is a line tension between the coexisting phases. Working with giant vesicles that mimic the composition of biological cell membranes, we are trying to understand the coupling between the phase behavior and the membrane properties.

Cell Membranes


An erythrocyte (red blood cell) is "grabbed" at opposite ends by a pair of colloidal particles held in optical traps. The cell is dynamically stretched, measuring its mechanical properties.

We have been studying the Red Blood Cell, which has a relatively simple membrane structure made of a phospholipid bilayer tethered to a thin cortical network of semiflexible filaments. We have observed very complex dynamics upon stretching the cell, which we have interpreted as a stress induced remodeling of the cytoskeletal network.

Biological applications of Optical Traps


This animated gif shows a colloidal bead being dragged to the membrane of a macrophage cell. The interaction with beads of different coatings are being studied, as well as with bacteria.

Optical Traps allow to move objects in solution (typically cells or colloidal particles), and to exert forces of the order of a few tens of pico-Newtons. We have a very advanced optical trap system which is easily programmed to perform sets of measurements, or to automatically perform certain "actions" based on video feedback from the experiment. This powerful instrument is being used also in collaboration with a few biologists, to study interesting problems such as cell infection by bacteria and other parasites.

Hydrodynamic interaction

We have recently started studying the hydrodynamic coupling between colloidal particles in solution, with a view to understand better the mechanisms of propulsion and synchronisation that take place in many biological systems (e.g. motility of bacteria, metachronal waves).

Microrheology and Image analysis

A theme that spans across all our activities is the extraction of maximum information from image and video data. Microrheology is an example of this: the motion of tracer particles is tracked, and this information characterises the material in which the particles are embedded. Applications of this in our group are to study the mechanics of the cell cytoskeleton and the process of gelation in polymer and particulate systems. We are also actively developing new image analysis, for example for detection of cell edges and cell tracking.