Liquid Metals as Tools for Creating Degradable Devices

Liquid metals – that is, gallium and gallium-based alloys -seem like unlikely candidates for degradable devices, mostly because the term ‘liquid metal’ evokes thoughts of toxic mercury. Although gallium is not found naturally in the human body, gallium is not considered toxic .The body has the ability to get rid of gallium ions and gallium salts have been FDA approved for several therapeutic applications. This opens the possibility of using liquid gallium for a variety of applications that may interact with the body or environment. The unique properties of gallium make it appealing for a variety of applications. For example, it is a conductor yet has liquid properties. In this talk, I will give several examples that show potential applications for liquid metals in the realm of degradable materials. First, liquid metals can be used to initiate and crosslink hydrogel networks that can be used for interfacing with the body. This approach to creating hydrogels avoids the need to use potentially toxic free radical initiators. After forming the network, the liquid metal can be dissolved to form only salts in the hydrogel. Second, liquid metals can be utilized for creating soft and stretchable circuits. The shape of these circuits is stabilized by the thin oxide shell that naturally forms on the metal. Thus, by removing this shell – either chemically or electrochemically – it is possible to get the metal to “bead up”, degrade the circuit, and thereby completely recover the liquid metal. Third, liquid metals can be easily rendered into particle suspensions that have proven useful for drug delivery by loading the drugs on the surface of the particles. The particles get completely degraded once they get inside a cell and release the drug payload. Fourth, the native oxide that forms on the liquid metal can be separated from the metal and deposited on surfaces to create ultrathin (4 nm) thick coatings and circuits that are both transparent and conductive. This environmentally friendly and continuous approach for depositing films avoids the use of slow, vacuum processing and produces films that can, in principle, be dissolved.