Mechanical force induces mitochondrial fission.

Eukaryotic cells are densely packed with macromolecular complexes and intertwining organelles, continually transported and reshaped. Intriguingly, organelles avoid clashing and entangling with each other in such limited space. Mitochondria form extensive networks constantly remodeled by fission and fusion. Here, we show that mitochondrial fission is triggered by mechanical forces. Mechano-stimulation of mitochondria - via encounter with motile intracellular pathogens, via external pressure applied by an atomic force microscope, or via cell migration across uneven microsurfaces - results in the recruitment of the mitochondrial fission machinery, and subsequent division. We propose that MFF, owing to affinity for narrow mitochondria, acts as a membrane-bound force sensor to recruit the fission machinery to mechanically strained sites. Thus, mitochondria adapt to the environment by sensing and responding to biomechanical cues. Our findings that mechanical triggers can be coupled to biochemical responses in membrane dynamics may explain how organelles orderly cohabit in the crowded cytoplasm.

Additive Manufacturing of Metal Structures at the Micrometer Scale.

Currently, the focus of additive manufacturing (AM) is shifting from simple prototyping to actual production. One driving factor of this process is the ability of AM to build geometries that are not accessible by subtractive fabrication techniques. While these techniques often call for a geometry that is easiest to manufacture, AM enables the geometry required for best performance to be built by freeing the design process from restrictions imposed by traditional machining. At the micrometer scale, the design limitations of standard fabrication techniques are even more severe. Microscale AM thus holds great potential, as confirmed by the rapid success of commercial micro-stereolithography tools as an enabling technology for a broad range of scientific applications. For metals, however, there is still no established AM solution at small scales. To tackle the limited resolution of standard metal AM methods (a few tens of micrometers at best), various new techniques aimed at the micrometer scale and below are presently under development. Here, we review these recent efforts. Specifically, we feature the techniques of direct ink writing, electrohydrodynamic printing, laser-assisted electrophoretic deposition, laser-induced forward transfer, local electroplating methods, laser-induced photoreduction and focused electron or ion beam induced deposition. Although these methods have proven to facilitate the AM of metals with feature sizes in the range of 0.1-10 µm, they are still in a prototype stage and their potential is not fully explored yet. For instance, comprehensive studies of material availability and material properties are often lacking, yet compulsory for actual applications. We address these items while critically discussing and comparing the potential of current microscale metal AM techniques.

Template-Free 3D Microprinting of Metals Using a Force-Controlled Nanopipette for Layer-by-Layer Electrodeposition.

A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries.

Patterning gold nanoparticles in liquid environment with high ionic strength for local fabrication of up to 100 µm long metallic interconnections.

Metallic interconnections were fabricated in situ using the FluidFM as scanning probe lithography tool. In contrast to other SPL tools, the closed fluidic circuit of the FluidFM enables a pressure-controlled deposition of metallic nanoparticles in liquid environment. Taking advantage of the salt concentration of the liquid environment (i.e. the ionic strength) to tailor the resulting particle density in the deposited layer, a protocol was established for direct patterning of conductive interconnecting structures. The FluidFM microchannel was filled with an aqueous solution of negatively charged gold nanoparticles (AuNPs) to be delivered onto a glass surface coated with a polycation favoring electrostatic adhesion. The deposited structures were analyzed both topographically and electrically to optimize the external parameters such as contact time, salt concentration of the liquid environment and size of the AuNPs. Using this optimized protocol we succeeded in the local fabrication of conductive metallic wires between two prefabricated macroelectrodes in liquid environment. In a subsequent step, the conductivity of the deposited structure was improved by gold annealing.