Smart materials are becoming smarter

January 20, 2020

A researcher from Baltic Federal University together with his colleagues developed a composite material that can change its temperature and parameters under the influence of magnetic and electrical fields. Smart materials are safe for human health, and with these properties can be used to manufacture implants (or surface coating for them) that would work as sensors. The article was published in the Scientific Reports journal.

Composites are a new type of materials that consist of heterogeneous components (metals, ceramics, glass, plastic, carbon, etc) and combine their properties. To create such a material, a filler with certain stability and rigidity is placed into a flexible matrix. Various compositions and matrix-filler ratios create a wide range of materials with given sets of characteristics. Composites may be used in different fields, from construction to energy, medicine, and space research. Polymer composites are currently considered one of the most promising smart materials for biomedical applications.

A researcher from Immanuel Kant Baltic Federal University together with his team used this approach to develop smart materials for biological implants. The authors of the study wanted the implant to act as a sensor, e.g. to measure a patient's body temperature and other health indicators in real time, and also to release drugs into a patient's body in given amounts and at given intervals. To create such an implant, the scientists had to find a combination of materials with the required properties. In its recent study the team described a composite material constructed from Gd5(Si,Ge)4 magnetic nanoparticles incorporated into a polyvinylidenfluoride (PVDF) matrix.

PVDF is a flexible and biocompatible (i.e. harmless for the body) polymer that is used as a surgical suture material. It also possesses piezoelectric properties: when PVDF is stretched or compressed, electric voltage occurs in it (this is called direct piezoeffect), and when voltage is applied to it, the material changes in size (reverse piezoeffect). Due to these properties, PVDF is effectively used in sensors. Moreover, it has also been used to create new magnetoelectric materials, such as composite multiferroics. The magnetic and ferroelectric characteristics of such materials are mutually manageable, i.e. their electrical properties can be controlled with a magnetic field, and magnetic characteristics - with an electric one. Thanks to its properties, PVDF may be used as a basis for implant coating or even the implants themselves.

"The novelty of our approach lies in the use of specific magnetic particles as a filler of a piezopolymer matrix. Along with magnetic properties they also possess the magnetocaloric effect, i.e. change their temperature under the influence of a magnetic field. Magnetocaloric materials are a promising basis for the development of alternative cooling systems, the so-called 'magnetic freezers'. It's also recently been suggested that they could be used in biomedical applications," said Karim Amirov, a Candidate of Physics and Mathematics, a senior researcher at the Laboratory for New Magnetic Materials, Kant Baltic Federal University. According to him, to create magnetoelectric smart composites, magnetocaloric substances are added to PVDF (dissolved in the dimethylformamide solvent) and evenly spread. After that the polymer is dried down in line with a specific temperature and time protocol. The result is a flexible piezopolymer plate of a given shape with incorporated magnetic particles. Such a plate can be easily cut with scissors.

Thus, the use of the new magnetocaloric particles led to the development of a smart composite material combining magnetoelectric and magnetocaloric properties. The first ones make the material a sensor detecting both magnetic and electric fields, and the second turn it into a heating or cooling element depending on magnetic field changes.
The participants of the study also represented the Institute of Physics for Advanced Materials, Nanotechnology and Photonics (IFIMUP) at the University of Porto (Portugal), Institute of Physics Gleb Wataghin at the University of Campinas (Brazil), Amirkhanov Institute of Physics at the Dagestan Federal Research Center of the Russian Academy of Sciences, Institute of Physics at the Fluminense Federal University (Brazil), and the University of Aveiro (Portugal).

Picture. PVDF chains nucleates around the magnetic grains. Andrade et al. / Scientific Reports, 2019

Immanuel Kant Baltic Federal University

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