Applying Gradient SMB Processes for the Isolation of Proteins and Antibodies

The simulated moving bed (SMB) technology has been increasingly applied in the last years in order to purify valued added products. Predominantly the classical 4-zone process was used which operates under isocratic conditions keeping the main process parameters constant. Recently more sophisticated operating regimes have been suggested varying certain parameters during the process (e. g. VariCol, PowerFeed and ModiCon). Another significant improvement of the classical SMB process can be achieved based on establishing in the different zones of the unit different elution strengths. The most simple of these gradient SMB processes applies a two 2-step-gradient by introducing the feed in a weaker solvent compared to the desorbent. Using this concept the overall amount of solvent can be reduced and more concentrated product streams can be obtained. Due to the large flexibility regarding an adjustment of retention times the 2-step-gradient-SMB process appears to be in particular attractive to perform bioseparations. In this presentation results of the two case studies will be presented. At first as a model system the separation of bovine IgG from lysozyme and/or BSA will be analyzed. Then the separation of the active dimeric form of the bone morphogenetic protein-2 (BMP-2) from its inactive monomeric form will be investigated. BMP-2 is one of the most interesting of several BMPs which belong to the transforming-growth-factor-β (TGF-β) superfamily. It induces bone formation and thus plays an important role as a pharmaceutical protein. For both separation problems prepacked HiTrapTM Heparin HP columns were applied. The matrix is based on Sepharose HP. The elution behavior can be significantly influenced changing the salt content in the mobile phase. The presentation will present for the two systems studied the dependence of the equilibrium functions of the solutes on the ionic strength. This information provides the platform to identify suitable operating parameters for 2-step-gradient-SMB processes using 3 or 4 zones. Experimental results obtained using a lab-scale SMB unit will be presented