Deformation and flow of neutrophils in micropipets
The undeformed human neutrophil in the resting, passive state is shaped like a sphere with a diamter of about 8 μm. Thus, it must deform significantly in order to flow through the small capillaries (approximately 4 μm) of the body. To model and understand this process we study the deformation and flow of neutrophils into uniform and tapered glass pipers with pipet openings on the order of 4 μm. We find, as others have, that the passive neutrophil does not behave as a 'standard solid' but instead deforms and flows smoothly like a liquid drop. This liquid drop has a persistent 'surface' tension that is very small - about 0.02-0.04 dyn/cm. In some instances the tension appears to increase as the surface area of the cell is expanded. The apparent viscosity of this liquid drop is very large - about 103 poise - and appears to decrease somewhat at higher rates of flow. For slow flows over long periods of time the cell can 'activate' without sticking to the pipet wall and without forming pseudopods. In these instances the cell behaves as a viscoelastic gel with a much larger resistance to deformation and flow than that exhibited by a resting cell.