Continuous countercurrent chromatography for the downstream processing of bioproducts: A focus on flow-through technologies

The necessity of ensuring consistent purity for satisfying the high standards required from biopharmaceutical companies led the liquid chromatography to become the gold standard for the downstream purification of biotherapeutics. The possibility of switching between different resins and buffer combinations allows to successfully perform separations of structurally similar molecules by exploiting peculiar properties of the product, including: conformation, charge, hydrophobicity and size. However, underutilization of the resin, low productivity and poor product recovery when aiming at an imposed purity of the product pool have been intrinsic limitations of the single-column batch chromatography. To tackle these drawbacks, multi-column continuous countercurrent operations have been introduced in the field and have become effective solutions to improve the performances of the downstream processing of biopharmaceuticals. Nowadays, most of the new technologies, for both capture and polishing processes, exploit the simulated moving bed (SMB) strategy for the operational configuration. In this chapter, the concepts behind the SMB and the different continuous chromatographic techniques based on the frontal mode, which have been demonstrated successful in the purification of biologics ensuring high yield and productivity, are discussed. In particular, the working principles of each technique are explained in detail, together with some case studies reported to compare their process performances with those obtained with a single-column operation. Finally, a critical presentation of the perspectives of these techniques and the gap still to be covered to reach industrial maturity is introduced.