the collective behavior of fibrils in microstructure arrays, [5] and the effects of misorientation between gripping surface and object. [6] Recently, in-line optical observation of the contact area was coupled with machine learning to predict the handling performance of a fibrillar array. [7] These studies established the sufficient adhesive capability of micropatterned polymer surfaces, on par and exceeding current handling technologies.Driven by the miniaturization of electronic and optical components, a growing trend in the industry is the automated handling of micro-objects. [8,9] Such components are typically far below 1 mm in size with a mass of a few milligrams or less. [10] With shrinking size, the competition between surface (adhesion) and volume (inertia) effects shift increasingly to the domination of adhesion: small objects invariably tend to stick. [11] As negligible inertial forces no longer contribute to the release of a micro-object, new release mechanisms need to be designed for accurate placement. External triggers have been used to detach macro-objects, e.g., air pressure, electric fields, temperature changes, or chemical inputs. [12] To avoid external triggers, mechanical switching can be easily integrated into the trajectory of the gripper: the straight and intact fibrils deform compressively or even buckle when subjected to a critical overload; this is associated with a loss of contact under compression-induced buckling and facile detachment from the objects. [13,14] Bucklinginduced drop in adhesion has been investigated in different cases, including in air and vacuum, fibrils with different aspect ratios. [15,16] The figure of merit for such a release mechanism is the switching ratio, i.e., the ratio of the maximum to the minimum adhesive force in the unbuckled and buckled state; for mechanical switching by straight and intact fibril design, it comes to lie typically between 2 and 3. This mechanism has been studied theoretically and experimentally [6,17] but further improvements are required to successfully transfer this mechanism to microhandling: (i) micro-objects tend to stick to the buckled fibrils as the adhesive contact reforms during unloading; (ii) the switching ratio needs to be increased to allow the reliable placement of small and delicate objects; and (iii) elastic buckling is an uncontrolled collapse of the fibril leading to lateral deformation in random directions, which can exert forces on the object and cause imprecise placement.In the present paper, we suggest new microfibril designs that can solve the above-mentioned challenges by enhancing the buckling behavior in controlled directions. In this way, the contact area at maximum compressive force is minimized, Switchable micropatterned adhesives exhibit high potential as novel resourceefficient grippers in future pick-and-place systems. In contrast with the adhesion acting during the "pick" phase, the release during the "place" phase has received little research attention so far. For objects smaller than typically 1 mm, rel...

Migrating cells often encounter a wide variety of topographic features - including the presence of obstacles - when navigating through crowded biological environments. Unravelling the impact of topography and crowding on the dynamics of cells is key to better understand many essential physiological processes such as the immune response. We study how migration and search efficiency of HL-60 cells differentiated into neutrophils in quasi two dimensional environments are influenced by the lateral and vertical confinement and spatial arrangement of obstacles. A microfluidic device is designed to track the cells in confining geometries between two parallel plates with distance h, in which identical micropillars are arranged in regular pillar forests. We find that at each cell pillar contact event, the cell spends a finite time near the pillar surface, which is independent of the height h and the interpillar spacing e. At low pillar density regime, the directional persistence of cells reduces with decreasing h or e, influencing their diffusivity and first-passage properties. The dynamics is strikingly different at high pillar density regime, where the cells are in simultaneous contact with more than one pillar; the cell velocity and persistence are distinctly higher compared to dilute pillar configurations with the same h. Our simulations reveal that the interplay between cell persistence and cell-pillar interactions can dramatically affect cell diffusivity and, thus, its first-passage properties.