Goodbye, implants rejection!

A group of Russian physicists, with the contribution from their Swiss colleagues, developed a way to use the therapeutic effect of heating or cooling the tissues due to the magnetocaloric effect. The article with the results of the work was published in the latest issue of the International Journal of Refrigeration.

A team of the Lomonosov Moscow State University scientists proposed a new way to use the magnetocaloric effect for the targeted delivery of drugs to the implants. Vladimir Zverev, one of the authors (Lomonosov Moscow State University, Faculty of Physics) claims that this is a unique method that uses a negative magnetocaloric effect.

The gist of the magnetocaloric effect (MCE) is reduced to the fact that when exposed to an external magnetic field, the magnetic material changes its temperature, sometimes rising and sometimes, on the contrary, falling (depending on the material). This significant physical phenomenon was discovered in the nineteenth century, although the effect has been described only in 1917. Over the past century, the MCE has been minutely studied, but the interest of researchers increased dramatically in recent decades. This is due to, first, a significant contribution to the physics of magnetic materials, and, second, a fairly extensive area of its possible applications. It can be very successfully used in low-temperature physics, for the production of heat engines, refrigeration and so on.  

 However, the majority of these applications is not ready for commercial use yet, mainly due to the unavailability of the technology. Speaking, for example, about domestic magnetic refrigerators, although they are being developed today by many scientific and industrial laboratories around the world, according to Vladimir Zverev, a member of the Physics Department of MSU, such refrigerators, if they were made today, would be very expensive.

'For such a refrigerator magnetic field of around one Tesla is required, which at today's possibilities makes the prices very high and therefore commercially unacceptable – the very device to generate such a field will cost at least fifteen hundred dollars. It remains to wait for them to fall in price', Vladimir Zverev says.  

However, this did not prevent the authors from suggesting a new application of the magnetocaloric effect, almost ready for massive use – this time in medicine.  

One of the developed methods is called “magnetic fluid hypothermia” and consists in heating cancer tumors with special magnetic nanoparticles, delivered directly to the tumor site. To do this, the researchers developed and created a unique tool to create an alternating high-frequency magnetic field with no analogues in the world, as Vladimir Zverev says. Today, with the help of this facility in the Blokhin Scientific Cancer Centre, the primary research of various cancerous cell cultures was conducted.

The studies on mice were also carried out, which proved biocompatibility and non-toxicity of the microparticles. The experiments on the microparticles' pharmacokinetics are conducted as well, which demonstrate its ability of retention in the tumor, spreading in the body with the blood flow etc.  

 If the possibility of using such magnetocaloric effect in the scientific literature is at least mentioned – in fact that the heating of the tumor may lead to its degradation has long been known, – the second method, proposed by the scientists, is quite unique.

 It is known that one of the problems when implanted of foreign parts in human- artificial joints, abdominal nets, stents esophagus, urinary and biliary ducts, etc. – is the likelihood of rejection. The authors offer to apply a special coating to implants (yet at the stage of the preparation for installing), consisting of several layers. The first layer is a magnetic material, which is cooled in an external magnetic field (a material with a negative magnetocaloric effect).

This layer may be a thin film or a suspension of magnetic microparticles. The second layer is the polymer matrix, in which, as a sponge, absorbs the drug. The polymer matrix is in direct thermal contact with the magnetocaloric material. This entire structure is placed in the body during the operation.

The fact that the polymer used in the technology at the normal body temperature, i.e. at a temperature above 37 degrees, behaves like a jelly, which holds the drug inside. When the magnetic field lowers the temperature, the polymer transits in a liquid state and releases drug at the site of theimplantation. For example, when, after insertion of the implant an inflammation occurs, the non-invasive application of an external magnetic field (for example, in MRI) allows to release the desired dose of drug over the desired time and place.

This method of the 'targeted' drug delivery is good, in particular, by the fact that it only affects the source of inflammation and remains the rest of the body uninfluenced, that is, by definition, completely harmless. There is a problem though – it is unclear what to do if the coated drug is over.

Zverev says that this problem is solvable: 'First, in some cases just a single drug input is need, for example, to paste the abdominal mesh. A release dosage portions of the drug can be controlled by regulating the magnitude of the external magnetic field. It is also possible to replenish a the coat, using the fact that a drug may be chemically linked to the magnetic particles which can be 'dragded' to the desired location in the body by an external magnetic field. This method we haven't developed however, and it is only ideas yet'.