Advances in high-gradient magnetic fishing for bioprocessing

Claudia Sofia Goncalves Gomes

    Research output: Book/ReportPh.D. thesisResearch

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    High-gradient magnetic fishing (HGMF) is a technique for the downstream processing of biological molecules. HGMF integrates the use of superparamagnetic adsorbents with separation and processing by high-gradient magnetic separation (HGMS) in a high voidage (≥90 %) magnetic filter. The adsorbents are non-porous (low diffusion limitations and less prone to fouling) and very small, ensuring a large specific area available for binding. Since its inception in 2001, the research on HGMF has been focused on proof-of-principle studies and broadening its application for direct product capture with the long term view of developing an industrial biotech tool for quick and efficient (i.e. economic) recovery of valuable macromolecules (Hubbuch et al., 2001; Hubbuch and Thomas, 2002; Heebøll-Nielsen et al., 2003, 2004a, 2004b; Meyer et al., 2005; Ferré, 2005; Ebner, 2005). Despite significant progress, the journey is not over. Although HGMF has been gaining recognition as a bioprocessing tool and has recently been the subject of scale-up studies (Ebner, 2005), it has not yet reached the biotech industry, despite the conventional applications of HGMS that have been established in the mineral and waste water treatment industries since the 1970’s (Svoboda, 1987). Part of the reason that HGMF has not made the transition from laboratory and pilot plant to industry is the lack of fundamental understanding about the generic nature of the technique, in particular the potential scope of its application and knowledge of adsorbent handling using the high-gradient magnetic filter.

    The aim of this thesis is to examine how HGMF can be used for direct capture of high value products present in feedstocks at high concentrations, whether HGMF can be extended to bioprocessing tasks apart from direct product capture, and to answer fundamental questions about how magnetic adsorbents pack in and release from highgradient magnetic filters.

    This thesis begins by introducing HGMS followed by providing an overview of the
    basic concepts related to HGMF and recent developments in the field (Chapter 1). A study is then conducted on the design of a new type of magnetic adsorbent for the purification of immunoglobulin G (IgG) used in diagnostic applications, and which is very similar to the new generation of valuable monoclonal antibody-based pharmaceuticals. These adsorbents employ a well known, although recently developed, ligand called MEP (4-mercaptoethylpyridine) that has been shown to selectively capture IgG from various feedstocks when coupled to packed bed chromatography media (Boschetti, 2002). In the current work, a HGMF process was developed using MEP magnetic adsorbents for the purification of IgG from rabbit anti-serum (Chapter 2).

    Although the work conducted in chapter 2 was successful, it highlighted a number of issues not previously faced by HGMF, in particular how feedstocks with high concentrations of product can be processed to not only give purified products, but concentrated ones. In HGMF, like in other adsorptive techniques, the capacity and selectivity of the adsorbents are critical parameters. However, in HGMF good adsorbent performance is not enough. In order to take advantage of the optimised properties of the adsorbents it is important that the process is not limited by the capacity of the magnetic filter. The magnetic filter capacity determines the amount of adsorbent that can be processed in one cycle and therefore correlates to protein concentration and process productivity. These two important parameters in downstream processing of biological molecules are addressed in chapters 3 and 4. Two strategies are introduced in chapter 3 for predicting filter capacities and the performance of high-gradient magnetic filters are subsequently studied in semicontinuous multicycle processing over a number of cycles (Chapter 4).

    In chapter 5, a systematic study is conducted to examine whether the unique properties of HGMF can be applied for controlling protein hydrolysis processes. For that purpose, an HGMF process employing optimised benzamidine-linked magnetic adsorbents together with a filter selected from the studies in chapter 3 and 4 is used for halting the tryptic hydrolysis of cheese whey proteins at a defined point.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark
    Number of pages200
    Publication statusPublished - Sep 2006

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