Nanocrystalline Magnetic Glass-Coated Microwires Using the Effect of Superparamagnetism Are Usable as Temperature Sensors in Biomedical Applications

For the control and study of the post-implantation biomechanical processes of TiAl 6 V 4 implants, the ability of wireless in vivo measurement of various parameters (i.e., temperature in this case) at the tissue–implant interface is required. Compared with other types of sensors, which consist of sensing and transmitting elements, nanocrystalline magnetic glass-coated microwires combine both of these features into unit. Thanks to a Pyrex coating, the microwires are biocompatible, and due to their size, they do not intervene into the surface structures of implants. The studied as-cast microwire has a low Curie temperature due to the high amount of molybdenum, and is not magnetically bistable at room temperature. In order to create its bistability at room temperature and enhance its temperature sensitivity in the range from 37 °C up to 42 °C, the microwire is specially annealed under axial stress above crystallization temperature. Extreme temperature sensitivity in the required temperature range is achieved using the superparamagnetism effect; moreover, due to this effect, the switching field increased in an almost linear way. The temperature dependence of the switching field is employed to sense the temperature in two TiAl 6 V 4 samples produced by additive manufacturing and representing implants with different types of fixations of the microwire onto the surface. Sensitivity up to 0.01 K is achieved.