Optical micrograph of the liquid metal pattern deposited using an automated system and the corresponding two-dimensional surface morphology used to evaluate pattern quality.
The next generation of flexible, high-performance sensors and circuits (e.g., flexible heaters, strain gauges, and thermocouples) must be mechanically compliant while maintaining reliable electrical conductivity. Achieving these capabilities motivates the development of new materials and fabrication techniques. Eutectic gallium–indium (EGaIn) liquid metal was selected as the conductive medium for enabling such devices. As a room-temperature liquid, it remains highly deformable and self-adaptive under mechanical loading while providing excellent thermal and electrical conductivity with minimal performance degradation. To advance the development of this sensors and circuits, stencil lithography and spray printing are combined and incorporated into an automated deposition system to minimize human error and improve pattern accuracy and consistency.
The combined liquid metal patterning technique is intended to enable the fabrication of high-strain sensors for solid-state actuators made from shape memory polymers (SMPs), shape memory alloys (SMAs), or similar smart materials. Integrating liquid metal–based conductive patterns onto these substrates will support the investigation of coupled electromechanical and thermo-electro-mechanical behavior during actuation. When SMAs are used as the substrate, an electrically insulating layer is required to prevent short-circuiting between the liquid metal and the underlying alloy. This layer must exhibit high electrical resistivity, low thermal conductivity, adequate strain tolerance, and minimal processing time. Electrochemical anodization was selected to produce a thin, protective oxide film on NiTi surfaces that meets these requirements. This anodization layer provides effective electrical insulation while remaining compatible with the actuator’s deformation. Multiple surface characterization techniques were used to evaluate the morphology, chemical composition, elemental distribution, and thickness of the resulting oxide film.
Together, the integration of liquid metal deposition, smart material actuation, and electrochemical anodization for shape memory alloys establishes a cohesive framework for developing next-generation flexible sensors and circuits. By patterning liquid metal onto active substrates such as SMPs and SMAs, and insulating SMA surfaces with a mechanically compatible anodization film, these systems enable direct analysis of coupled electromechanical and thermomechanical behavior. The resulting sensors will undergo extensive mechanical testing to assess durability, reusability, and long-term electrical stability under cyclic actuation. This combined approach provides a pathway for evaluating the operational limits of liquid metal–based sensors and determining their viability for high-strain and performance-critical applications, ultimately offering insight into their practical implementation in real-world systems.
Graduate Student: Jessica Zamarripa