3D micro fractal pipettes for capillary based robotic liquid handling.

Miniaturized and mobile liquid handling devices are essential elements to biological or clinical applications. This will innovate the conventional liquid handling methods such as manual or automated pipetting systems. Here, we propose the micro fractal pipette as the candidate device for this objective. It is made of epoxy polymer and printed by innovative 3D nanoprinting technology based on two-photon absorption polymerization with sub-micrometer resolution. We demonstrated the efficient liquid handling performance by using the micro fractal pipette between the source droplet and the target hydrogel substrate. This is due to the high porosity (78%) and the 8.5 times larger cavity surface area compared to the full pyramid. The biomimetic inner cavity microchannel networks contribute to the low pressure drop. The proposed micro fractal pipette could also innovate the versatile and miniaturized liquid handling system, promising to various biological or clinical applications.

Note: On-chip multifunctional fluorescent-magnetic Janus helical microswimmers.

Microswimmers integrated into microfluidic devices that are capable of self-illumination through fluorescence could revolutionize many aspects of technology, especially for biological applications. Few illumination and propulsion techniques of helical microswimmers inside microfluidic channels have been demonstrated. This paper presents the fabrication, detachment, and magnetic propulsions of multifunctional fluorescent-magnetic helical microswimmers integrated inside microfluidics. The fabrication process is based on two-photon laser lithography to pattern 3-D nanostructures from fluorescent photoresist coupled with conventional microfabrication techniques for magnetic thin film deposition by shadowing. After direct integration inside a microfluidic device, injected gas bubble allows gentle detachment of the integrated helical microswimmers whose magnetic propulsion can then be directly applied inside the microfluidic channel using external electromagnetic coil setup. With their small scale, fluorescence, excellent resistance to liquid/gas surface tension, and robust propulsion capability inside the microfluidic channel, the microswimmers can be used as high-resolution and large-range mobile micromanipulators inside microfluidic channels.

Nanoscale Magnetic Domains in Mesoscopic Magnets

The basic magnetic properties of three-dimensional nanostructured materials can be drastically different from those of a continuous film. High-resolution magnetic force microscopy studies of magnetic submicrometer-sized cobalt dots with geometrical dimensions comparable to the width of magnetic domains reveal a variety of intricate domain patterns controlled by the details of the dot geometry. By changing the thickness of the dots, the width of the geometrically constrained magnetic domains can be tuned. Concentric rings and spirals with vortex configurations have been stabilized, with particular incidence in the magnetization reversal process as observed in the ensemble-averaged hysteresis loops.