Escape route: The laser‐initiated release of fluorescently labeled polymers from polyelectrolyte‐multilayer microcapsules is demonstrated inside living cancer cells. A polymer is incorporated in capsules with metal nanoparticles in their walls, which serve as light‐absorbing centers. The capsules are internalized by cells and near‐infrared light ruptures the walls of the capsules, thus releasing the content into the cells.

Fluchtweg: Die Laser‐initiierte Freisetzung von fluoreszenzmarkierten Polymeren aus Polyelektrolytmultischicht‐Mikrokapseln in lebenden Krebszellen wird vorgestellt. Ein Polymer wird in Kapseln eingeschlossen, die als Lichtabsorptionszentren fungierende Metallnanopartikel in den Wänden enthalten. Die Kapseln werden von Zellen aufgenommen, und Nah‐Infrarotlicht bricht die Kapselwände auf, sodass der Inhalt in die Zellen gelangt.

The spontaneous formation of vortices is a hallmark of collective cellular activity. Here, we study the onset and persistence of coherent angular motion as a function of the number of cells N confined in circular micropatterns. We find that the persistence of coherent angular motion increases with N but exhibits a pronounced discontinuity accompanied by a geometric rearrangement of cells to a configuration containing a central cell. Computer simulations based on a generalized Potts model reproduce the emergence of vortex states and show in agreement with experiment that their stability depends on the interplay of the spatial arrangement and internal polarization of neighboring cells. Hence, the distinct migrational states in finite size ensembles reveal significant insight into the local interaction rules guiding collective migration.

We propose a combination of atomic force microscopy (AFM) and optical microscopy for the investigation of particle uptake by cells. Positively and negatively charged polymer microcapsules were chosen as model particles, because their interaction with cells had already been investigated in detail. AFM measurements allowed the recording of adhesion forces on a single-molecule level. Due to the micrometer size of the capsules, the number of ingested capsules could be counted by optical microscopy. The combination of both methods allowed combined measurement of the adhesion forces and the uptake rate for the same model particle. As a demonstration of this system, the correlation between the adhesion of positively or negatively charged polymer microcapsules onto cell surfaces and the uptake of these microcapsules by cells has been investigated for several cell lines. As is to be expected, we find a correlation between both processes, which is in agreement with adsorption-dependent uptake of the polymer microcapsules by cells.

No abstract

Micro-patterned surfaces are frequently used in high-throughput single-cell studies, as they allow one to image isolated cells in defined geometries. Commonly, cells are seeded in excess onto the entire chip, and non-adherent cells are removed from the unpatterned sectors by rinsing. Here, we report on the phenomenon of cellular self-organization, which allows for autonomous positioning of cells on micropatterned surfaces over time. We prepared substrates with a regular lattice of protein-coated adhesion sites surrounded by PLL-g-PEG passivated areas, and studied the time course of cell ordering. After seeding, cells randomly migrate over the passivated surface until they find and permanently attach to adhesion sites. Efficient cellular self-organization was observed for three commonly used cell lines (HuH7, A549, and MDA-MB-436), with occupancy levels typically reaching 40-60% after 3-5 h. The time required for sorting was found to increase with increasing distance between adhesion sites, and is well described by the time-to-capture in a random-search model. Our approach thus paves the way for automated filling of cell arrays, enabling high-throughput single-cell analysis of cell samples without losses.

Semiconductor nanocrystals (NCs) are increasingly being used as photoluminescen markers in biological imaging. Their brightness, large Stokes shift, and high photostability compared to organic fluorophores permit the exploration of biological phenomena at the single-molecule scale with superior temporal resolution and spatial precision. NCs have predominantly been used as extracellular markers for tagging and tracking membrane proteins. Successful internalization and intracellular labelling with NCs have been demonstrated for both fixed immunolabelled and live cells. However, the precise localization and subcellular compartment labelled are less clear. Generally, live cell studies are limited by the requirement of fairly invasive protocols for loading NCs and the relatively large size of NCs compared to the cellular machinery, along with the subsequent sequestration of NCs in endosomal/lysosomal compartments. For long-period observation the potential cytotoxicity of cytoplasmically loaded NCs must be evaluated. This review focuses on the challenges of intracellular uses of NCs.

Micropatterning techniques have become an important tool for the study of cell behavior in controlled microenvironments. As a consequence, several approaches for the creation of micropatterns have been developed in recent years. However, the diversity of substrates, coatings and complex patterns used in cell science is so great that no single existing technique is capable of fabricating designs suitable for all experimental conditions. Hence, there is a need for patterning protocols that are flexible with regard to the materials used and compatible with different patterning strategies to create more elaborate setups. In this work, we present a versatile approach to micropatterning. The protocol is based on plasma treatment, protein coating, and a PLL-PEG backfill step, and produces homogeneous patterns on a variety of substrates. Protein density within the patterns can be controlled, and density gradients of surface-bound protein can be formed. Moreover, by combining the method with microcontact printing, it is possible to generate patterns composed of three different components within one iteration of the protocol. The technique is simple to implement and should enable cell science labs to create a broad range of complex and highly specialized microenvironments.