Capillary micromechanics: Measuring the elasticity of microscopic soft objects

f microscopic deformable particles. ion of soft particles as they are forced both the compressive and the shear rements on a model system of poly-rements on bulk gels of identical anical properties and should thus be iological materials. techniques such as atomic force microscopy (AFM) or 15 approach directly characterizes the elastic properties of entire soft objects. We use a microfluidic setup where particles are deformed in tapered microcapillaries; direct imaging of their deformation with an optical microscope enables us to charac-terize both the compressive and the shear modulus of a soft Fig. 1 Experimental setup: A dilute suspensions of soft particles flows PAPER www.rsc.org/softmatter | Soft MatterLecce, Via Arnesano, I-73100 Lecce, Italytowards the tapered tip of a microcapillary as a result of an applied pressure difference. For low pressure values < 103 Pa we exploit gravity and use the height difference of the sample reservoir and outlet of the microcapillary tip to apply a hydrostatic pressure. Higher pressures can be achieved by connecting the sample reservoir to a pressure regulator. As a single particle blocks the flow of fluid, the particle deforms until the pressure-induced external stresses are balanced by its internal elastic stress. The pressure-dependence of the shape and size of the particle is thus a direct measure of its elastic properties