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Cell Separation Using Magnetic Beads: How Do Cell Separation Beads Work and How to Remove Magnetic Beads from Cells

April 2021

Cell Separation Using Magnetic Beads

Due to a constant demand for enriched cell samples, there are a variety of methods used to isolate and extract target cells from a mixture. One of the more common techniques is magnetic-activated cell sorting (MACS). MACS uses magnetic beads and a magnetic separation column to perform cell enrichment.

MACS

The goal of MACS, also called immunomagnetic cell separation, is to isolate a single cell type from a heterogeneous population. MACS uses antibody interactions to bind magnetic particles to the surface markers of targeted cells, followed by a magnetic field activation to draw the target cells away from the rest of the sample. When performing positive selection MACS, the magnets attach to the desired cells and isolate them for extraction. When performing negative selection MACS, the magnets attach to unwanted cells, leaving only the desired sample behind for collection.

How Magnetic Beads Work

When performing immunomagnetic cell sorting, magnetic beads are coated with specific antibodies, lectins, or enzymes that match surface markers of the target cell group. Whether the researcher uses positive or negative selection will determine which cell population is being targeted. The magnetic beads are then released into the heterogeneous solution to bind with the target cells.

The behavior displayed by magnetic beads in a magnetic field depends on their size. For example, very small beads are paramagnetic, meaning they have no inherent magnetism when not in a magnetic field. However, when an external magnetic field is applied, the beads will rapidly become magnetized. When the magnetic field is removed, they will demagnetize once again. This property is integral to MACS because it allows the experimenter to manipulate the cells which are bound to beads.

Magnetic Separation Columns

Once the cells are properly labeled, they are passed between separation columns that suspend target particles in a magnetic field. All unmarked substances pass through the columns without being stopped, separating them from the marked cells. Once the sample is properly isolated, the magnetic field can be turned off, releasing the target cells bound to magnetic beads from suspension.

How to Remove Magnetic Beads from Cells

The ability to remove magnetic beads from target cells depends both on the beads used in the experiment and the bond created between bead and cell. The most common method of removing beads is to purchase an additional kit that will break down the link. Those products typically harness the following strategies:

  • Positive isolation, which outcompetes the existing bond, resulting in cells free of not only beads but antibodies as well.
  • Releasing a DNase enzyme that severs the link between the bead and the antibody, leaving the researcher with bead-free cells.
  • Releasing biotin to outcompete the antibody-bead link and result in bead-free cells.

Unfortunately, these methods can cause irreversible damage to fragile cell populations. There are a variety of tips to increase the likelihood of removing magnetic beads:

  • Wait 2-3 days before removing so the bonds are weaker
  • Switch to a different removal reagent
  • Switch to a different brand of magnetic beads

If these strategies do not sufficiently reduce the number of lost cells throughout separation, it may be in your best interest to switch cell isolation methods altogether.

Preparing Magnetic Beads for Second Use

Buying isolation kits for every experiment can become expensive very quickly. One way to save money with MACS is to try and use magnetic beads more than once. After magnetic beads have been successfully removed from target cells, they can be carefully cleaned and sometimes rebound and reused. If a scientist hopes to rebind the beads with a new antibody, enzyme, or lectin, they must be thoroughly washed with a stringent washing buffer and non-ionic detergent. This will help remove any residual substances that may have been left on the surface of the beads.

BACS

While there are ways to make MACS more cost-effective, it may be more beneficial to change your cell separation technique. Akadeum Life Sciences in Ann Arbor, MI, has developed an innovative new technology that harnesses the buoyant force of tiny bubbles to separate cells without magnetic beads. BACS, or buoyancy-activated cell sorting, uses a similar mechanism to MACS to bind microbubbles to target cells with antigen-specific antibodies.

After all the target cells have bound to bubbles, they will float to the top of the solution as it settles. BACS can take place directly in the sample container and requires no extra equipment beyond an isolation kit. The microbubble workflow is fast, easy, and exceptionally gentle on delicate cells.

Microbubbles vs. Magnetic Beads

When comparing the efficacy of microbubbles and magnetic beads, there are a few key differences to note:

  • Cell Loss — The harsh magnetic field used in MACS can rupture cell membranes, reducing throughput and increasing extracellular debris in a solution. When using magnetic columns in the separation process, it’s also possible for blockage to occur from the magnetic field. If a high concentration of target cells is suspended, then other particles may not be able to properly pass through. BACS works gently to maintain cell health and physiology without damaging cell population.
  • Cost — Microbubble kits are affordable and easy to use, and require no additional equipment like magnets, columns, or other expensive consumables.
  • Procedure Time — In total, a standard MACS workflow takes approximately 2-3 hours to complete, including setup, run time, and cleanup. On the other hand, Akadeum’s immunology enrichment kits take 30-45 minutes, and depletion products like the Human Red Blood Cell Depletion Kit, take 10-15 minutes.
  • Complexity — MACS requires knowledge and practice to carry out, and mistakes can be costly. MACS is also limited by its specialized equipment. BACS only requires an isolation kit and a gentle mix in the sample container. The microbubble platform is inherently flexible and scalable, enabling interrogation of larger volumes or multiple small volumes processed simultaneously to greatly increase throughput without having to increase equipment footprint. 

Akadeum Life Sciences

If you’re planning to perform cell separation for a wide range of downstream applications, you can greatly increase cell throughput by switching to BACS. The speed, ease, and gentle nature of microbubbles set them ahead of other isolation methods. Reduce cell loss and increase procedural efficacy by checking out our products or contacting us today.

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