Directional and self-propelled flow in open channels has a variety of applications, including microfluidic and medical devices, industrial filtration processes, fog-harvesting, and condensing apparatuses. Here, we present versatile three-dimensional-printed liquid diodes that enable spontaneous unidirectional flow over long distances for a wide range of liquid contact angles (CAs). Typically, we can achieve average flow velocities of several millimeters per second over a distance of tens to hundreds millimeters. The diodes have two key design principles. First, a sudden widening in the channels' width, in combination with a small bump, the pitch, ensure pinning of the liquid in the backward direction. Second, an adjustable reservoir with differing expansion angles, the bulga, is introduced to manipulate the liquid velocity. Using a combination of experiments and lattice Boltzmann simulations, we provide a comprehensive analysis of the flow behavior and speed within the channels depending on CAs, pitch heights, and bulga angles. This provides guidelines for the fabrication of bespoke liquid diodes with optimal design for their potential applications. As a feasibility investigation, we test our design for condensation of water from fog and subsequent transport uphill.

Additive manufacturing of high‐resolution conductive metallic patterns is the current focus of interest for several different applications. The print of sensors, antennas, and screens on transparent materials enables the manufacture of smart structural electronics. Laser‐induced forward transfer (LIFT) is a direct write technique capable of depositing microdroplets of metals from the solid phase by means of laser irradiation. Patterns are achieved by printing drops in a sequential fashion. Due to high heat conductivity of metals, droplets solidify before smearing; therefore, LIFT‐printed structures exhibit high surface roughness, which harms their functioning and limits their applications. Herein, a new procedure is developed for the fabrication of continuous metallic lines at the micrometer resolution on smooth transparent substrates, using a combination of subnanosecond LIFT and a laser melting post‐treatment. The melting process is conducted using laser pulses with the timescale of a microsecond. It is shown how one can find an optimized melting process to achieve smooth lines, without introducing oxidation or balling effect. In addition, choosing the proper alloy ensures strong adhesion of the printed structure.

Various insects can entrap and stabilize air plastrons and bubbles underwater. When these bubbles interact with surfaces underwater, they create air capillary bridges that de-wet surfaces and even allow underwater reversible adhesion. In this study, a robotic arm with interchangeable three-dimensional (3D)-printed bubble-stabilizing units is used to create air capillary bridges underwater for manipulation of small objects. Particles of various sizes and shapes, thin sheets and substrates of diverse surface tensions, from hydrophilic to superhydrophobic, can be lifted, transported, placed, and oriented using one- or two-dimensional arrays of bubbles. Underwater adhesion, derived from the air capillary bridges, is quantified depending on the number, arrangement, and size of bubbles and the contact angle of the counter surface. This includes a variety of commercially available materials and chemically modified surfaces. Overall, it is possible to manipulate millimeter- to sub-millimeter-scale objects underwater. This includes cleaning submerged surfaces from colloids and arbitrary contaminations, folding thin sheets to create three-dimensional structures, and precisely placing and aligning objects of various geometries. The robotic underwater manipulator can be used for automation and control in cell culture experiments, lab-on-chip devices, and manipulation of objects underwater. It offers the ability to control the transport and release of small objects without the need for chemical adhesives, suction-based adhesion, anchoring devices, or grabbers.