Last week a video with a Lego type doll of a liquid metal Terminator T-1000 went viral; recreate the scene from the movie Terminator 2: Judgment Day (1991) in which he escapes from a cell through the bars. A liquid metal (gallium) encrusted with ferromagnetic microparticles of neodymium-iron-boron (NdFeB) has been used; Since it is not a material with shape memory, a mold has been used so that the doll recovers its shape. It is published in the magazine Matter (Cell Press) as a magnetoactive material with solid-liquid phase transition. The Lego doll moves using a magnet (static magnetic field); to melt it, it is heated using a variable magnetic field; the liquid passes through the bars guided by a magnet that takes it until it falls into the mould; there it regains its shape when cooled to room temperature; The whole process takes about 8 minutes (500 seconds). Beyond this curiosity, this type of material promises multiple applications in welding and intelligent assembly, drug delivery, drug extraction, and object manipulation in robotics, among many others.
This magnetoactive liquid metal, called MPTM for Magnetoactive Phase Transitional Matter, has good mechanical properties in the solid state; it has a mechanical stress of 21.2 MPa (megapascals) and a Young’s modulus of 1.98 GPa (gigapascals), with which it can support a weight of up to 30 kg. In addition, in the liquid state it shows great morphological adaptability (ability to elongate, divide and fuse). Various applications of this new material are shown in the article. As gallium appears to be biocompatible, the new material could also be biocompatible, which is why it is proposed to be used to capture foreign bodies in the stomach and to dose drugs. Its use is also proposed as a substitute for screws (in the article they are called universal screws) and for welding electronic circuits. In these applications gallium is not a good liquid metal, since its melting point is 30 °C; the authors of the article propose to use other liquid metals in such applications (but do not use them in their study), such as Bi32.5Sn16.5In51 (62 °C) of Bi58Sn42 (138°C). Undoubtedly, magneoactive liquid metals hold promise, but it is a long time before we see them in practical applications.
This article would have gone unnoticed if the authors had not had the happy idea of recreating a Lego T-1000 and the famous movie scene. The article is very easy to read, so I recommend you enjoy Qingyuan Wang, Chengfeng Pan, …, Lelun Jiang, “Magnetoactive liquid-solid phase transitional matter,” Matter (25 Jan 2023), doi: https://doi.org /10.1016/j.matt.2022.12.003. For those interested in biomedical applications, I recommend consulting Sen Chen, Ruiqi Zhao, …, Jing Liu, “Toxicity and Biocompatibility of Liquid Metals,” Advanced Healthcare Materials 12: 2201924 (24 Jan 2023), doi: https://doi.org /10.1002/adhm.202201924.
This video combines all the videos of the supplementary information of the article. The movement of a small cube of the new material can be controlled by a magnet so that it follows a path; with two independently controlled you can manipulate an object; He can even jump over obstacles (if the person controlling the magnet is skilled at it). Of course, the most striking is the famous viral video of the T-1000 (watch how the liquid falls into the mold). In the end you have some applications in the soldering of circuits, universal screws, removal of foreign bodies in a model of a stomach and the dosage of drugs.
As usual in this type of article, the authors suggest that their material is bio-inspired; in this case in the sea cucumber or sea cucumber and thus they take the opportunity to include a photo of a Holothuria arguinensis and a funny cartoon. Still, the idea of embedding tiny magnets in liquid metal doesn’t seem to require biological inspiration. The small magnets allow control of the movement (by applying an external static magnetic field) and make it easy to heat the liquid metal so that it melts (by applying a variable magnetic field).
The biomedical applications of new materials always have two major limitations: biocompatibility (which has not been demonstrated for the new material) and the enormous complexity of real biologics (compared to the models usually used in trials). A liquid metal that could leave droplets inside the body seems unpromising to me.
The application that seems most reasonable to me is universal screws and welding in complicated places, where it is easier for a liquid to enter. But the need to use magnets is a big limitation, because the magnetic field drops off very quickly with distance. In addition, it is required to use liquid metals that can withstand much higher temperatures than the gallium used in these experiments. There really isn’t much more to tell about the article in Matter, which presents very little technical information about the new material, limiting itself to talking about its potential applications (with toy experiments). It will be necessary to be aware of these materials. But in the meantime, maybe it’s a good time to enjoy the viralized video again.