We describe herein, a general, efficient, and scalable process to design magneto-responsive thermoplastic elastomer-based (nano)­composites that can be repeatedly healed in a few tens of seconds by triggering polymer melting upon exposure to a high-frequency magnetic field. Three series of composites loaded with 1–15 vol % of Fe3O4 nanoparticles, Fe nanoparticles, or Fe microparticles were produced and characterized in depth with the aim to identify the physical properties required for two applications: (1) material healing, which we evaluate through the rewelding of precut samples and subsequent tensile tests, and (2) surface smoothening of 3D-printed objects, serving to remove superficial defects and improve their appearance. The optimal formulation consisting of a composite reinforced with 5 vol % of Fe nanoparticles ensures a high ability to heat while keeping a low viscosity in the molten state being ideal for polymer processing.

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This study aims to enhance the low-frequency induction heating (LFIH) effect in a thermoplastic polymer doped with iron oxide magnetic particles, which are promising candidates for several medical applications thanks to their confirmed biocompatibility. Two main approaches were proposed to successfully boost the heating ability; i.e., improving the magnetic concentration of the composite with higher filler content of 30 wt %, and doubling the frequency excitation after optimization of the inductor design. To test the magnetic properties of the ferromagnetic composite, a measurement of permeability as a function of temperature, frequency, and particle content was carried out. Thermal transfer based COMSOL simulations together with experimental tests have been performed, demonstrating feasibility of the proposed approach to significantly enhance the target temperature in a magnetic composite. These results are encouraging and confirmed that IH can be exploited in medical applications, especially for the treatment of varicose veins where local heating remains a true challenge.Polymers 2020, 12, 386 2 of 16 because of the electric currents induced by the fluctuating magnetic field. Both effects result in heating of the treated object, but the second is the main heat source in IH processes.Compared to other classical heating techniques, such as flame heating, resistance heating, and traditional ovens or furnaces, IH offers fast, clean, and precise temperature control in a contactless and efficient way. It is one of the most preferred heating technologies in industrial [2], domestic [3], and medical applications [4]. Although the process parameters in many industrial and domestic applications are already well-known, there are still some issues that need further optimization: heating of low-resistivity materials, accurate heating of biological tissues, faster design for complex IH load geometries, and accurate 3D FEA simulation of the whole IH system [5]. The third major area of IH is medicine, and this field is not as mature as industrial or domestic applications. It has lately attracted a great deal of research interest. IH was initially applied only in manufacturing and sterilization of many surgical instruments because it is a clean, fast, and portable heat source.IH has recently started to be introduced in minimally-invasive hyperthermia as a cancer treatment therapy by inducing a temperatures of about 41-45 • C to the cancerous cells [6,7]. In order to precisely deliver the power to the tumor, a ferromagnetic material is usually placed in the area to be treated. This technique efficiently destroys cancer tissue while minimizing the damage to the surrounding healthy cells. Moreover, this local treatment can markedly reduce pain compared to chemotherapy. The frequencies used for hyperthermia are usually inside the margins of radiofrequency (i.e., hundreds of kHz to few MHz) [8,9] or microwaves (hundreds of MHz to 10 GHz); i.e., non-ionizing radiation frequencies. However, frequencies over 100 kHz can produce signifi...