Swimmers Heal on the Move Following Catastrophic Damage.

Herein, we describe the development of 2D self-healing small-scale swimmers capable of autonomous propulsion and "on-the-fly" structural recovery in large containers. Incorporation of magnetic Nd2Fe14B microparticles in specialized printed strips results in rapid reorientation and reattachment of the moving tail to its complementary broken static piece to restore the original swimmer structure and propulsion behavior. The swimmers display functional recovery independent of user input. Measurements of the magnetic hysteresis and fields were used to assess the behavior of the healing mechanism in real swimming situations. Damage position and multiple magnetic strip patterns have been examined and their influence upon the recovery efficiency has been compared. Owing to its versatility, fast response, and simplicity the new self-healing strategy represents an important step toward the development of new "on-the-fly" repairing strategies for small-scale swimmers and robots.

Small-Scale Propellers Deliver Miniature Versions of Themselves.

Small-scale actuators and propellers have benefited from advances in materials and manufacturing to become more lifelike. Inspired by animal species, multi-generational chemically powered artificial propellers that carry small versions of themselves and deliver them "on-the-fly" are described. The released replicas are capable of autonomous propulsion and propelling immediately after detachment. Release occurs without human involvement and relies solely on sacrificial layers separating the carriers and replicas. These layers are composed of transient natural polymers, which dissolve under the swimming conditions to release the confined replicas. Judicious selection of the responsive transient materials, layer thickness, and solution conditions (e.g., pH), leads to programmable delivery of the replicas. Finally, the ability of the same carrier propellers to carry and transport multiple generations of propellers and deliver them at predetermined times is demonstrated.

Biomimetic Platelet-Camouflaged Nanorobots for Binding and Isolation of Biological Threats.

One emerging and exciting topic in robotics research is the design of micro-/nanoscale robots for biomedical operations. Unlike industrial robots that are developed primarily to automate routine and dangerous tasks, biomedical nanorobots are designed for complex, physiologically relevant environments, and tasks that involve unanticipated biological events. Here, a biologically interfaced nanorobot is reported, made of magnetic helical nanomotors cloaked with the plasma membrane of human platelets. The resulting biomimetic nanorobots possess a biological membrane coating consisting of diverse functional proteins associated with human platelets. Compared to uncoated nanomotors which experience severe biofouling effects and hence hindered propulsion in whole blood, the platelet-membrane-cloaked nanomotors disguise as human platelets and display efficient propulsion in blood over long time periods. The biointerfaced nanorobots display platelet-mimicking properties, including adhesion and binding to toxins and platelet-adhering pathogens, such as Shiga toxin and Staphylococcus aureus bacteria. The locomotion capacity and platelet-mimicking biological function of the biomimetic nanomotors offer efficient binding and isolation of these biological threats. The dynamic biointerfacing platform enabled by platelet-membrane cloaked nanorobots thus holds considerable promise for diverse biomedical and biodefense applications.

Micromotors Spontaneously Neutralize Gastric Acid for pH-Responsive Payload Release.

The highly acidic gastric environment creates a physiological barrier for using therapeutic drugs in the stomach. While proton pump inhibitors have been widely used for blocking acid-producing enzymes, this approach can cause various adverse effects. Reported herein is a new microdevice, consisting of magnesium-based micromotors which can autonomously and temporally neutralize gastric acid through efficient chemical propulsion in the gastric fluid by rapidly depleting the localized protons. Coating these micromotors with a cargo-containing pH-responsive polymer layer leads to autonomous release of the encapsulated payload upon gastric-acid neutralization by the motors. Testing in a mouse model demonstrate that these motors can safely and rapidly neutralize gastric acid and simultaneously release payload without causing noticeable acute toxicity or affecting the stomach function, and the normal stomach pH is restored within 24 h post motor administration.

Metal-Organic Frameworks as Micromotors with Tunable Engines and Brakes.

Herein, we report that UiO-type (UiO = University of Oslo) metal-organic frameworks (MOFs) can be transformed into self-propelled micromotors by employing several different metal-based propulsion systems. Incorporation of a bipyridine ligand into the UiO-67 lattice transforms the crystallites, upon metalation, into single-site, metal-based catalytic "engines" to power the micromotors with chemical fuel. The "engine performance" (i.e., propulsion) of the single-site powered micromotors has been tuned by the choice of the metal ion utilized. In addition, a chemical "braking" system was achieved by adding chelating agents capable of sequestering the metal ion engines and thereby suppressing the catalytic activity, with different chelators displaying different deceleration capacities. These results demonstrate that MOFs can be powered by various engines and halted by different brakes, resulting in a high degree of motion design and control at the nanoscale.

Enteric Micromotor Can Selectively Position and Spontaneously Propel in the Gastrointestinal Tract.

The gastrointestinal (GI) tract, which hosts hundreds of bacteria species, becomes the most exciting organ for the emerging microbiome research. Some of these GI microbes are hostile and cause a variety of diseases. These bacteria colonize in different segments of the GI tract dependent on the local physicochemical and biological factors. Therefore, selectively locating therapeutic or imaging agents to specific GI segments is of significant importance for studying gut microbiome and treating various GI-related diseases. Herein, we demonstrate an enteric micromotor system capable of precise positioning and controllable retention in desired segments of the GI tract. These motors, consisting of magnesium-based tubular micromotors coated with an enteric polymer layer, act as a robust nanobiotechnology tool for site-specific GI delivery. The micromotors can deliver payload to a particular location via dissolution of their enteric coating to activate their propulsion at the target site toward localized tissue penetration and retention.

Magnetically Propelled Fish-Like Nanoswimmers.

The swimming locomotion of fish involves a complex interplay between a deformable body and induced flow in the surrounding fluid. While innovative robotic devices, inspired by physicomechanical designs evolved in fish, have been created for underwater propulsion of large swimmers, scaling such powerful locomotion into micro-/nanoscale propulsion remains challenging. Here, a magnetically propelled fish-like artificial nanoswimmer is demonstrated that emulates the body and caudal fin propulsion swimming mechanism displayed by fish. To mimic the deformable fish body for periodic shape changes, template-electrosynthesized multisegment nanowire swimmers are used to construct the artificial nanofishes (diameter 200 nm; length 4.8 µm). The resulting nanofish consists a gold segment as the head, two nickel segments as the body, and one gold segment as the caudal fin, with three flexible porous silver hinges linking each segment. Under an oscillating magnetic field, the propulsive nickel elements bend the body and caudal fin periodically to generate travelling-wave motions with speeds exceeding 30 µm s-1 . The propulsion dynamics is studied theoretically using the immersed boundary method. Such body-deformable nanofishes exhibit a high swimming efficiency and can serve as promising biomimetic nanorobotic devices for nanoscale biomedical applications.