Growth and mutual interference of protein seeds under reduced gravity conditions

Abstract

This analysis deals with new models and computational methods as well as with novel results on the relative importance of “controlling forces” in macromolecular crystal growth. The attention is focused in particular on microgravity fluid-dynamic aspects and on the case of the simultaneous growth of different seeds. A “kinetic-coefficient-based” volume of fraction method is specifically and carefully developed according to the complex properties and mechanisms of macromolecular protein crystal growth. It is shown that the size and the shape of the growing crystals play a “critical role” in the relative importance of surface effects and in determining the intensity of convection. Convective effects, in turn, are found to impact growth rates, macroscopic structures of precipitates, particle size and morphology as well as the mechanisms driving growth. The face growth rates in particular depend on the complex multicellular structure of the convective field and on associated “pluming phenomena.” The relative importance of mass transport in liquid phase and surface attachment kinetics is investigated. The simulations show that it does not behave as a “fixed” parameter and that different crystallization conditions may occur in the protein chamber due to mutual interference of the growing seeds, complex convective effects and the “finite size” of the reactor.