Discrete layers of interacting growing protein seeds: convective and morphological stages of evolution

The growth of several macromolecular seeds uniformly distributed on the bottom of a protein reactor (i.e. a discrete layer of N crystals embedded within a horizontal layer of liquid with no-slip boundaries) under microgravity conditions is investigated for different values of N and for two values of the geometrical aspect ratio of the container. The fluid-dynamics of the growth reactor and the morphological (shape-change) evolution of the crystals are analyzed by means of a recently developed moving boundary method based on differential equations coming from the protein "surface incorporation kinetics". The face growth rates are found to depend on the complex multi-cellular structure of the convective field and on associated ‘pluming phenomena’. This correspondence is an indirect evidence of the fact that mass transport in the bulk and surface attachment kinetics are competitive as rate-limiting steps for growth. Significant adjustments in the roll pattern take place as time passes. The convective field undergoes an interesting sequence of transitions to different values of the mode and to different numbers of rising solutal jets. The structure of the velocity field and the solutal effects, in turn, exhibit sensitivity to the number of interacting crystals if this number is small. In the opposite case, a certain degree of periodicity can be highlighted for a core zone not affected by edge effects. The results with no-slip lateral walls are compared with those for periodic boundary conditions to assess the role played by geometrical constraints in determining edge effects and the wavelength selection process. The numerical method provides "microscopic" and "morphological" details as well as general rules and trends about the macroscopic evolution (i.e. "ensemble behaviors") of the system.