Fig. 2

Schematic of a section of a syringe/needle lumen of radius R. a Shear stress and velocity distribution in delivery device for Newtonian fluid and laminar flow. The velocity profile across the diameter is parabolic. Shear stress (τ) is zero at the centre and increases linearly to its maximum value at the wall. As a cell flows from the syringe to the needle, it will experience increasing velocities along its length, causing it to stretch. b Plug flow behaviour—flow velocities are almost equal across the whole diameter. Shear-thinning materials display this behaviour when their flow in a capillary reaches a steady state