A D V A N C E D M A T E R I A L S & P R O C E S S E S | S E P T E M B E R 2 0 2 2 5 6 3D PRINTSHOP META-BOTS PRINTED IN ONE-STEP PROCESS Tiny robots that move, jump, and walk have been 3D printed in one single step by a team of UCLA engineers. The breakthrough enabled the entire mechanical and electronic systems needed to operate a robot to be manufactured all at once by a new type of 3D printing process for engineered active materials with multiple functions (also known as metamaterials). Once 3D printed, a “meta-bot” will be capable of propulsion, movement, sensing, and decision-making. The printed metamaterials consist of an internal network of sensory, moving, and structural elements and can move by themselves following programmed commands. With the internal network of moving and sensing already in place, the only external component needed is a small battery to power the robot. The key in the UCLA-led, all-inone method is the design and printing of piezoelectric metamaterials, a class of intricate lattice materials that can change shape and move in response to an electric field or create electrical charge as a result of physical forces. The use of active materials that can translate electricity to motions is not new. However, these materials generally have limits in their range of motion and distance of travel. They also need to be connected to gearbox-like transmission systems to achieve desired motions. By contrast, the UCLA- developed robotic materials—each the size of a penny—are composed of intricate piezoelectric and structural elements that are designed to bend, flex, twist, rotate, expand, or contract at high speeds. The methodology could lead to new designs for biomedical robots, such as self-steering endoscopes or tiny swimming robots, that can emit ultrasounds and navigate themselves near blood vessels to deliver drug doses at specific target sites inside the body. These “meta-bots” can also explore hazardous environments. In a collapsed building, for example, a swarm of such tiny robots armed with integrated sensing parts could quickly access confined spaces, assess threat levels, and help rescue efforts by finding people trapped in the rubble. samueli. ucla.edu. LPBF PRINTED SHAPE MEMORY ALLOYS WITH SUPERELASTICITY Researchers from Texas A&M University recently optimized a framework that allows them to print shape memory alloys with superior tensile superelasticity. Nickel-titanium shape memory alloys have various applications due to their ability to return to their original shape upon heating or upon removal of the applied stress. Laser powder bed fusion is an additive manufacturing technique that presents a way to produce nickel-titanium shape memory alloys effectively and efficiently, offering a pathway to quick manufacturing or prototyping. This technique, similar to polymer 3D printing, uses a laser to fuse metal or alloy powders layer by layer. The layer-by-layer process is beneficial because it can create parts with complex geometries that would be impossible in traditional manufacturing. Unfortunately, most nickel-titanium materials cannot withstand the current laser powder bed fusion process, often resulting in printing defects such as porosity, warping, or delamination caused by large thermal gradient and brittleness from oxidation. In addition, the laser can change the composition of the material due to evaporation during printing. To combat this issue, researchers used an optimization framework they created in a previous study, which can determine optimal process parameters to achieve defect-free structure and specific material properties. With this framework, as well as the change in composition and refined process parameters, the researchers fabricated nickel-titanium parts that consistently exhibited a room temperature tensile superelasticity of 6% in the as-printed condition (without post-fabrication heat treatment). This level of superelasticity is nearly double the amount previously seen in literature for 3D printing. tamu.edu. Electron micrograph of nickel-titanium powder (left) and 3D-printed nickel-titanium lattices (right). Courtesy of Texas A&M Engineering. A 3D-printed “meta-bot” developed by UCLA engineers is capable of propulsion, movement, sensing and decisionmaking. Courtesy of Rayne Research Group/UCLA.
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