G-jitter-induced motion of a protein crystal under microgravity

Abstract

Direct numerical simulations have been carried out to examine the nature of g-jitter induced convective flows during a typical protein crystal growth experiment in a microgravity environment. The numerical investigations identified six parameters of importance for the motion of a spherical crystal particle in a microgravity environment subjected to single frequency vibrations in one direction: frequency ( f) and amplitude ( A) of the applied vibration, particle radius ( R) and density ( ρ p), fluid density ( ρ f) and fluid viscosity ( ν). In the Stokes regime, the numerical results were found to be in good agreement with the analytical results of Coimbra and Rangel [AIAA J. 39(9)(2001)]. Beyond the Stokes regime (1< Re p<300), the particle motion amplitude was found to approach the cell vibration amplitude to within 1% when the ratio α 2/ S ( α= ρ f / ρ p, S= f R 2/9 ν) becomes greater than about 20. Most importantly, the present results show that the g-jitter-induced convective flows are likely to occur during the microgravity crystal growth on space platforms. In a typical protein crystal growth process involving a crystal of ρ p=1.2 g/cm 3 and 10–1000 μm diameter in an aqueous solution, g-jitter-induced crystal motion and convection have been predicted to occur even at acceleration levels as low as 1.0 μG.