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aggregation of magnetic beads, sonication method

Mixing and Homogenizing Magnetic Bead Suspensions in Bioreactors

sonication method bioreactorBioreactors are an advanced phase of any production process, as small scale production has been left behind and scale up is being developed. Increasing the working and production volume brings many benefits to the process, but it is also more difficult to work with larger volumes, including when we work with magnetic beads.

When the volume of homogenized magnetic beads is so large that the manipulation of any type of vessel would be cumbersome and impractical, researchers and technicians favor bioreactors instead of roller bottles to process the beads. In a bioreactor the vessel is fixed and therefore a roller mixer cannot be used. The option used for mixing and homogenizing the beads in a bioreactor is to use an overhead mixer.



This post is about overhead mixers to homogenize magnetic bead suspensions. Just like the sonication method, these mixers can solve magnetic bead aggregation in some way. If you are interested in this topic, download our free ebook The basic guide for resuspending magnetic beads:

Download our Free Guide on magnetic bead resuspension HERE.

Overhead mixers

Unless the sonication method, overhead mixers are used to mix large volumes

Overhead mixers are in large demand in biotechnology mainly because of the need to grow large populations of cells in bioreactors. When cell cultures are grown in this manner, they need to be homogenized for optimal growth conditions and so overhead mixers have been developed over the years to deal with these processes with minimal contamination. The advances in overhead mixer and bioreactor technology can also be applied to magnetic bead suspension processes.

An overhead mixer is comprised of an electrical or air-driven motor attached to a shaft with an agitator blade on the end. The rotation speed of the shaft and blade can be varied depending on the volume and suspension characteristics (i.e. bead density, viscosity of the buffer and concentration).


The problems with overhead mixers

Overhead mixers are not the most desired choice of technicians for the homogenization of magnetic beads for three main reasons:

1.   The risk of contamination from outside particles and from mechanical wear is great even if the apparatus uses sealed rings. There is also fear that as the suspension is mixed by the rotating blades, particles from outside the vessel or from the wearing of mechanical parts can drop into the vessel.

2.   Depending on the shape of the blades, if they are not well-designed, some researchers are concerned that the blades may damage the magnetic beads or even the attached ligands.

3.   You must avoid using magnetic materials in the blades and shaft. Typically the materials that are commonly used for the shaft and blade such as stainless steel can have residual magnetism if the parts are not carefully machined and so this is a concern.

Similar concerns with this method are experienced in other areas of biotechnology and in upstream processes. These potential problems can dramatically affect production results. The good news is that these problems and concerns have been successfully addressed in other biotechnological processes. The fact is even with these concerns, overhead mixing in a bioreactor is the best option if the vessel is fixed and if large volumes need to be homogenized.

Don’t forget to check these posts from our blog in order to get a deeper insight into magnetic bead resuspension:

Dr. Lluís Martínez

The basic guide for re-suspending magnetic beads

Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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