Crystal growth studies in microgravity with the APCF .2. Image analysis studies

Lysozyme crystallization experiments performed in the Advanced Protein Crystallization Facility during SpaceHab-01 mission are analyzed using pictures obtained during the flight. The temporal evolution of experiments performed using free interface diffusion (FID) and dialysis (DIA) techniques was studied to gain a deeper insight into the processes of nucleation and growth. Heterogeneous nucleation on the walls of the reactor predominates over nucleation in the bulk solution. Nucleation takes place simultaneously throughout the protein chamber, which means that the supersaturation inside the reactors has reached homogeneity before nucleation. In terms of precipitation behavior this means that the APCF reactors are working as very slow-mixing batch experiments. Measured growth rates range from 10 to 50 Angstrom/s and decrease asymptotically to zero. L (a linear dimension of the crystals) versus time(1/2) plots are discussed. Large-scale growth rate fluctuations are observed and explained by the interaction between diffusive fields of neighboring crystals. Crystals not attached to the reactor walls are observed to move, with varying velocities and directions of movement, and at a given time, undergo a fast acceleration that projects them towards the walls of the reactor. The amount of information that can be derived from the final data set supplied after the space experiment is limited by the technical features implemented in the APCF. Some recommendations to enhance these features are proposed.