Active colloids are an emergent class of out-of-equilibrium materials demonstrating complex collective phases and tunable functionalities. Microscopic particles energized by external fields exhibit a plethora of fascinating collective phenomena, yet mechanisms of control and manipulation of active phases often remains lacking. Here we report the emergence of unconfined macroscopic vortices in a system of ferromagnetic rollers energized by a vertical alternating magnetic field and elucidate the complex nature of a magnetic roller-vortex interactions with inert scatterers. We demonstrate that active self-organized vortices have an ability to spontaneously switch the direction of rotation and move across the surface. We reveal the capability of certain non-active particles to pin the vortex and manipulate its dynamics. Building on our findings, we demonstrate the potential of magnetic roller vortices to effectively capture and transport inert particles at the microscale.

Synchronized active spinners spontaneously form dynamic lattices with reconfigurable order and tunable transport characteristics.

We demonstrate experimentally and in computer simulations that magnetic microfloaters can self-organize into various functional structures while energized by an external alternating (ac) magnetic field. The structures exhibit self-propelled motion and an ability to carry a cargo along a pre-defined path. The morphology of the self-assembled swimmers is controlled by the frequency and amplitude of the magnetic field.

We present measurements of the net electrical surface charge of silicon dioxide (SiO₂) in contact with solvents of dielectric constants between 5 and 80. Our experimental approach relies on observing the thermal motion of single silica particles confined in an electrostatic fluidic trap created by SiO₂ surfaces. We compare the experimentally measured functional form of the trapping potential with that from free energy calculations and thereby determine the net surface charge in the system. Our findings clearly demonstrate that contrary to popular perception, even in the absence of surfactants, the net electrical charge of ionizable surfaces in contact with apolar solvents can be large enough to lead to significant repulsive forces. A charge regulation model for SiO₂ surfaces with a single tunable parameter explains our measurements. This model may find general applicability in estimating the net charge of ionizable surfaces, given system parameters such as the dissociation or association constants of the ionizable groups and the pH, ionic strength, and dielectric constant of the solvent phase.

Diffractive optical elements such as periodic gratings are fundamental devices in X‐ray imaging – a technique that medical, material science, and security scans rely upon. Fabrication of such structures with high aspect ratios at the nanoscale creates opportunities to further advance such applications, especially in terms of relaxing X‐ray source coherence requirements. This is because typical grating‐based X‐ray phase imaging techniques (e.g., Talbot self‐imaging) require a coherence length of at least one grating period and ideally longer. In this paper, the fabrication challenges in achieving high‐aspect ratio nanogratings filled with gold are addressed by a combination of laser interference and nanoimprint lithography, physical vapor deposition, metal assisted chemical etching (MACE), and electroplating. This relatively simple and cost‐efficient approach is unlocked by an innovative post‐MACE drying step with hexamethyldisilazane, which effectively minimizes the stiction of the nanostructures. The theoretical limits of the approach are discussed and, experimentally, X‐ray nanogratings with aspect ratios >40 are demonstrated. Finally, their excellent diffractive abilities are shown when exposed to a hard (12.2 keV) monochromatic X‐ray beam at a synchrotron facility, and thus potential applicability in phase‐based X‐ray imaging.

Metastatic cancer cells can overcome detachment-induced cell death and can proliferate in anchorage-independent conditions. A recent study revealed that a co-treatment with two drugs that interfere with cell metabolism, metformin and 2-deoxy-D-glucose, promotes detachment of viable MDA-MB-231 breast cancer cells. In the present study, we analyzed if these detached viable MDA-MB-231 cells also exhibit other features related to cancer metastatic potential, i.e., if they are softer and more prone to adhere to epithelial cells. The cell mechanics of attached cells and floating cells were analyzed by optical tweezers and cell deformability cytometry, respectively. The adhesion was assessed on a confluent monolayer of HUVEC cells, with MDA-MB-231 cells either in static conditions or in a microfluidic flow. Additionally, to test if adhesion was affected by the state of the epithelial glycocalyx, HUVEC cells were treated with neuraminidase and tunicamycin. It was found that the treated MDA-MB-231 cells were more prone to adhere to HUVEC cells and that they were softer than the control, both in the floating state and after re-seeding to a substrate. The changes in the HUVEC glycocalyx, however, did not increase the adhesion potential of MDA-MB-231.