Breakage of unstable protein crystals in mechanical solid-liquid separation processes

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As part of the DFG priority program “Disperse, structural and phase changes of proteins and biological agglomerates in biotechnological processes (DiSP Biotech)”, the applicant is investigating the filtration and fracture behavior of mechanically labile protein crystals. The comprehensive analysis of biotechnological processes from cultivation to formulation on the micro to macro scale aims to better understand and optimize the entire process chain. Cornehl et al. showed that crystal size, shape and breakage have a strong influence on the filtration performance of lysozyme crystals. Both, protein expression and crystallization, affect crystal morphology and breakage behavior. Modifications and optimizations of the proteins or crystals have an effect on the subsequent process steps. Ultimately, it must be ensured that the target product passes the complete process chain successfully.The process functions (flux density function and compressive yield stress), which were determined by centrifugal filtration on a small scale in the first project phase, do not take any inhomogeneity of the filter cake into account. In the case of centrifugal filtration the maximum pressure is applied to the bottom of the filter cake, which leads to an inhomogeneous breakage behavior. Pressure stressed filter cakes show a shift in crystal size distribution towards smaller crystals. In addition to the compressive stress, shear stress also occurs in technical filtration processes, which results in crystal breakage and reduces the crystal size. The influence of shear stress on the cake structure and the process functions for protein crystals has to be clarified within the scope of this research project.The μCT analysis allows to investigate structural differences in the filter cake and to determine the crystal size distribution. Models for correcting and transferring process functions from a small-scale to larger filtration units do not exist for mechanically labile protein crystals. However, this is a prerequisite for the application of the process functions to calculate the filtration behavior on larger separation apparatuses. Hence, such a model has to be developed in this project. Supported by CFD simulations, the optimization of separation apparatuses under consideration of breakage mechanisms will be carried out. With 3D printing and rapid prototyping constructive improvements of the filtration apparatus can be realized and compared with regard to the filtration behavior and crystal breakage.