Google
Yelp
Facebook
Twitter
ChEnected
344984 Consistent Freezing of Bulk Protein Solutions - the Importance of Heat Flow Direction
Purpose
Cryoconcentration during freezing is a major concern for safe storage and transport of bulk protein solutions. As water crystallizes, solutes concentrate at the interface forming a dense layer. This leads to natural convection, causing a generalized heterogeneous distribution of solutes i.e. proteins, sugars, buffer salts. The relative proportions of the solution constituents throughout the ice matrix are dependent of the freezing process and high levels of heterogeneity can compromise protein stability during storage and thaw. These phenomena are greatly dependent of the kinetics and geometry of the freezing process. In this work, we address the influence of the geometry of freezing direction (axial or radial) in the frozen solution’s heterogeneity in terms of local concentration of solutes and thermal history.
Solutions of bovine hemoglobin were frozen radially and axially (from bottom to top) using in small-scale and pilot-scale freezing systems. Concentration of hemoglobin, sucrose and pH were measured trough ice sampling and temperature profiles were measured at several locations. Computational fluid dynamics (CFD), based on the enthalpy-porosity model, was used to predict the ice front velocity, maximum freezable height and concentration of solutes.
The results showed that natural convection is the major cause for the solutes cryoconcentration. A significant improvement in cryoconcentration was observed when the freezing geometry was non-convective, i.e. the freezing front progression was unidirectional from bottom to top. Using this geometry, it was possible to obtain less than 10% variation in solutes concentration throughout the frozen solutions. This result was reproducible, even when the volume was increased by 2 orders of magnitude (from 30 ml to 3 L).The temperature profiles obtained for the non-convective freezing geometry were predicted using a relatively simple CFD model.
The reproducible solutes distribution, predictable temperature profiles and scalability, demonstrates that the bottom to top freezing geometry enables an extended control over the freezing process. This geometry has therefore the potential to contribute to a better understanding and control of the risks inherent to frozen storage, thus providing approaches more consistent with Quality by Design directives.