Nov 2022
The increasing interest in vaccines and gene therapy, together with the need to decrease the cost per dose, has led to the development of new downstream processing tools or their conversion from other application areas. Chromatography is one of the most expensive steps in the downstream processing platform for purifying a biopharmaceutical, one reason being that many chromatographic processes are still operated in batch mode. Single-column batch chromatography (SCBC) is simple to implement and can achieve high purity, but at the cost of decreased yield as well as increased solvent consumption. In SCBC the product and waste cuts are collected at the downstream end of the column but at different times. Therefore, time (or elution volume) is the only manipulated variable with which to define the fractional cuts. Furthermore, a solvent gradient can only be introduced at the upstream end of the system. This does not allow much flexibility to dynamically adjust the solvent composition profile along the length of the chromatographic medium. Although packing the stationary phase into a single column works well for many binary separations, this seems to be overly restrictive for center-cut separation—one in which the target product is contained in the intermediate of three main fractions or cuts.
One process-based way to reduce the overall cost of the downstream chromatographic steps is by changing to a continuous processing mode, which, in principle, yields higher throughput, lower buffer consumption, higher capacity utilization and reduced column volume, hence increased productivity. This is due to the addition of extra degrees of freedom arising from the division of the stationary phase into a circular train of columns, which makes the manipulation of the cuts and generation of the solvent gradient much more flexible; moreover, with such a column arrangement some of the cuts can be recirculated from the downstream end of the system to its upstream end in an open-loop configuration.
Several continuous multicolumn processes have been developed over the past two decades to overcome the disadvantages of traditional SCBC, including VARICOL, Sequential Multicolumn Chromatography (SMCC), Multicolumn Countercurrent Solvent Gradient Process (MCSGP), Gradient With Steady State Recycle (GSSR), CaptureSMB, and Multicolumn Periodic Counter-Current (3C- & 4C-PCC) chromatography, among others. All these processes have been proven to achieve high purity while maintaining high yield and reducing solvent consumption by significant margins.
Despite the clear advantages of continuous chromatography, the biopharmaceutical industry is somewhat skeptical about switching to continuous or quasi-continuous, multi-column chromatography. This is, in part, due to the fact that innovation in this industry has traditionally been more product- than process-oriented, but also due to the increased complexity in terms of process design and validation. However, the implementation of single-use and ready-to-process technologies are mitigating these issues.
Here, we give an historical overview of the developments in continuous multicolumn chromatography for downstream processing of biomolecules. This is one example in the field of chemical & biological engineering where large-scale, multicolumn adsorption processes, initially developed for the continuous purification of small molecules, have been downscaled and operated with a small number of columns for purification of large, complex biomolecules.
José P. B. Mota is full professor of Chemical Engineering at the Chemistry Department of NOVA School of Science and Technology (FCT-NOVA) of NOVA University Lisbon (Portugal), where he is the director of its PhD program in Chemical and Biological Engineering. He is also head of the Thematic Line Energy – Clean & Renewable at LAQV, the Laboratory for Green Chemistry and Clean Processes of REQUIMTE, the Portuguese Network for Chemistry and Technology. He has authored over one hundred and fifty papers in the areas of separation science and transport phenomena. He has received several international awards and has served as member of the Scientific Council of Sciences and Engineering (CCCE) of the Portuguese National Science Foundation (FCT/MCTES) and is on the Board of Directors of the International Adsorption Society (IAS). He is a member of the scientific committees of the Fundamentals of Adsorption series of conferences and international Symposiums on Preparative and Industrial Chromatography and Allied Techniques. He is the chairman of the 18th Symposium on Preparative and Industrial Chromatography and Allied Techniques, held in Lisbon in 2022, and the chairman of the upcoming 15th International Conference on Fundamentals of Adsorption, which will be held in May 2025 in Oporto, Portugal.