rare earth magnetsSince first discovery of magnetism and magnets in ancient Greece and China, this phenomena has found its place in a wide variety of applications. Uses range from early use as a compass helping navigate uncharted and unknown waters, to modern medicine in early cancer detection. This blog will describe a novel medical application and then provide an overview of magnetism and rare earth magnets.

Using Rare-Earth Magnetism to prepare tissue sample cultures

In conventional culture preparation, a tissue piece is disrupted by blending, mixing, emulsifying, dispersing, or stirring the tissue sample to achieve a consistent composition and structure throughout designated area.

The current processes or methods of homogenizing can be broken down into three (3) major categories, ultrasonic, pressure, and mechanical. Mechanical mostly uses high speed rotating blades

We developed and built a prototype for homogenizing tissue samples (IE liver or brain) using rare earth magnets. Our prototype was achieved homogenization of tissue samples with coated rare earth magnetic beads, set to chaotic motion by fluctuated the magnetic field created by permanent magnets attached to a rotating disc.


Schematics of rotating rare earth magnet and magnetic beads


With this application we eliminated any possibility of crosscontamination, while significantly increasing the sample amount that could be homogenized at a same time (up to 20X).

Experimental prototype

rare earth magnetsHomogenization – sequential presentation


What is magnetism?

Wikipedia defines Magnetism as “a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments.”

Charges in motion (as in a current) produce magnetic fields. This is one source of magnetism.

Another source is the electron itself. Electrons behave as if they were tiny magnets. Every electron in an atom behaves as a magnet in two ways, each having two magnetic dipole moments:

  • Spin magnetic dipole moment – due to the “rotation” of an electron.
  • Orbital magnetic dipole moment – due to the “revolution” of an electron about the nucleus.


Orbital magnetic moment                                  Spin magnetic moment

Materials may be classified by their response to externally applied magnetic fields as diamagnetic, paramagnetic, or ferromagnetic.

Diamagnetism is the tendency of a material to oppose an applied magnetic field, and therefore, to be repelled by a magnetic field (silver, lead, copper, water, diamond…).

Paramagnetism is a form of magnetism where paramagnetic material is only attracted when in the presence of an externally applied  magnetic field (Aluminum, Platinum, Magnesium, Tungsten…).

Ferromagnetism is characterized by a possible permanent magnetization, removed from external magnetic field they stay magnetized (iron, nickel, cobalt…).

Rare-Earth Magnets

The rare earth elements (REE) are a group of 17 (metallic) elements which appear in the periodic table.

Rare earth elements have a partially occupied f electron shell (which can accommodate up to 14 electrons). The spin of these electrons can be aligned, resulting in very strong magnetic fields, and therefore, these elements are used in compact high-strength magnets.

The rare earth elements are metals that are ferromagnetic, meaning that like iron they can be magnetized, but their Curie temperatures  (Tc), the temperature at which the material loses its magnetism, are below room temperature. However, they form compounds with metals such as iron, nickel, and cobalt, and some of these have a Tc well above room temperature.

The grade, or “N rating”, of the magnet refers to the Maximum Energy Product of the material that the magnet is made from. It refers to the maximum strength to which the material can be magnetized. The grade of neodymium magnets is generally measured in units millions of Gauss Oersted (MGOe). Generally speaking, the higher the grade, the stronger the magnet. The highest “N rating” is N52.

Rade Gadzic is a senior mechanical engineer at StarFish Medical.  This is his first blog. His patents include a Magnetic Homogenizer Apparatus.

Device Images: Certo Labs Inc.


3 responses to “Using rare earth magnets in medical devices”

  1. Jim Kasper says:

    Very interesting! What do you coat your beads with?
    What method of sterilization?

    I love Magnets. Still wondering why they are the best for this task.

  2. Rade Gadzic says:

    Hi Jim,
    First, let me thank you for contacting me, it’s much appreciated.
    To answer your question “Why magnets “ actually the answer is simple it is a throughput, originally we started homogenizing samples in 4 vials, but then when we made the second prototype, we jumped to 16 vials without changing set up, which was one motor, disc with magnets, and tray for holding vials. We could easily increase this number to 32, or 48 etc.
    The second advantage was an easy extraction of the magnets from vials.
    Regarding plating, first we started with bare (not plated) magnets, but they were too brittle and would break, so we used nickel plated ones, which provided to be stronger. Nd-Fe-B magnets have improved dramatically over the last 10 years. But they still contain iron and other reactive phases and will rust.
    Furthermore, for the final product, we planned to overmold /encase magnets using hard plastic.

    Regarding sterilization, magnets would first be washed and then autoclaved. As I remember, with autoclaving of magnets you should be very cautious with conditions because it could lower retentive force a bit.

    I hope I answered your questions, as you I was always impressed with magnets and magnetism.
    I’m curious are you working on a similar project? Maybe we could help.

  3. Alex Kong says:

    Very impressive.Good to see that magnet is widely applied in medical device.We are a micro magnet manufacturer.In recent years we produced some really small neodymium magnet parts for medical devices,some of them samll to 0.2mm diameter.We don’t how the device work but it is inside human body.
    If you need any help about micro magnet,especially for medical purpose,we can help.Our website is http://www.ckmagnet.com

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