Magnetic separation has been an emerging technology in the recent decades in biomedical science and industry in which magnetic property and behavior – known as “magnetism” – of micro/nano-sized particles are employed for the separation of macromolecules of interest (e.g. nucleic acids, proteins, peptides etc) from biological samples or chemical suspensions.
Sometimes during biomagnetic separation in a magnetic separation rack, different steps in the process require using different volumes. For example, if you have produced a ‘mother batch’ of magnetic beads and this large batch needs to be aliquoted so that each aliquot of beads can be uniquely coated, you will need the ability to move easily between volumes.
Although separation time may be one of the most obvious parameters to validate in your magnetic separation rack production, it is certainly not the most critical. Classical magnetic separation rack use non-homogeneous magnetic separation. When scaling up production on these devices, larger volumes can lead to longer and longer separation times.
Any small magnetic separation rack (i.e. the types used to develop a prototype product before scaling up) generates magnetic fields that decay rapidly with distance. However, scaling up the process can be problematic because the size of the classical magnetic separation rack itself grows rapidly with desired batch volume. Because the magnetic field profile and the magnetic force are not the same in a larger device, the safety of users and the safety of ancillary equipment can become a serious issue.
Electromagnets are the classical way to generate intense magnetic fields. If you apply the electrical current across a coil, the magnetic field is quite small. But if you wrap the coils around an iron yoke, you can generate much stronger magnetic fields. Unfortunately, if you need to scale up a magnetic separation process, you also need to increase the electrical power to the magnetic separation rack and the amount of iron and copper used for the coil.
A very common problem that occurs when scaling up non-homogeneous magnetic separation processes in a magnetic separation rack is irreversible aggregation of the magnetic beads. When the process is scaled up, the magnetic force experienced by the beads closest to the magnet is very high.
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When using a standard magnetic separation rack, often you will experience a decrease in bead and biomolecule yield when scaling up your production process. This causes the scaled up process to be less economically efficient than it could be with yields commensurate to your original production.
Classic magnetic separation rack devices are designed such that both the magnetic field gradient and the magnetic state of the beads vary with the position of the beads. This means that once a process has been validated at a specific volume (i.e. your process has low material losses and no irreversible aggregation), it is difficult to change batch size without needing to re-validate the process.
Any small volume classic magnetic separation rack is relatively cheap and does a fairly good job at separating magnetic beads. However, if the process involves multiple instances of capture and elution steps, irreversible aggregation becomes a real problem. In small volume separations (i.e. on the order of milliliters), using the appropriate techniques can give you excellent re-suspension results.