The physical properties of cytoskeletal networks are contributors in a number of mechanical responses of cells, including cellular deformation and locomotion, and are crucial for the proper action of living cells. Local chemical gradients modulate cytoskeletal functionality including the interactions of the cytoskeleton with other cellular components. Actin is a major constituent of the cytoskeleton. Introducing a microfluidic-based platform, we explored the impact of concentration gradients on the formation and structural properties of actin networks. Microfluidic-controlled flow-free and steady-state experimental conditions allow for the generation of chemical gradients of different profiles, such as linear or step-like. We discovered specific features of actin networks emerging in defined gradients. In particular, we analyzed the effects of spatial conditions on network properties, bending rigidities of network links, and the network elasticity.

Existing approaches to red blood cell (RBC) experiments on the single-cell level usually rely on chemical or physical manipulations that often cause difficulties with preserving the RBC's integrity in a controlled microenvironment. Here, we introduce a straightforward, self-filling microfluidic device that autonomously separates and isolates single RBCs directly from unprocessed human blood samples and confines them in diffusion-controlled microchambers by solely exploiting their unique intrinsic properties. We were able to study the photo-induced oxygenation cycle of single functional RBCs by Raman microscopy without the limitations typically observed in optical tweezers based methods. Using bright-field microscopy, our noninvasive approach further enabled the time-resolved analysis of RBC flickering during the reversible shape evolution from the discocyte to the echinocyte morphology. Due to its specialized geometry, our device is particularly suited for studying the temporal behavior of single RBCs under precise control of their environment that will provide important insights into the RBC's biomedical and biophysical properties. Published by AIP Publishing. [http://dx

Nanocarriers encapsulating gold nanoparticles (AuNPs) hold tremendous promise for numerous biomedical applications. So far only a few fabrication strategies have been investigated and efficient processes for the manufacturing of gold nanohybrids (AuNHybs) are still missing. We encapsulated a tetrachloroaurate/citrate mixture within nanocarriers and initiated the AuNP formation after self-assembly of the nanomaterial by a temperature shift. This nanoreactor approach was successfully combined with the film-rehydration, nanoprecipitation, or microfluidics method. Different nanomaterials were validated including phospholipids and copolymers and the process was optimized towards encapsulation efficiency and physico-chemical homogeneity of AuNHybs. Our nanoreactor technology is versatile, efficient, and highly reproducible. Dynamic light scattering and electron microscopy techniques confirmed that generated lipid and polymer based AuNHybs were of uniform size below 130 nm and contained a single AuNP. The AuNHyb solutions had a deep-red color and exhibited the specific surface plasmon absorption of AuNPs. The unique optical properties of AuNHybs were used to visualize cellular uptake of nanocarriers in vitro demonstrating the promising applicability of AuNHybs as bioimaging tool.

Analyzing the behavior of semiflexible polymers experiencing hydrodynamic forces is an important step toward a better understanding of polymer dynamics in microfluidic applications as well as in living cells. In particular, studying conformational changes of fluorescently labeled, semiflexible actin filaments in flow fields of spatially varying flow strength will significantly contribute to this goal. The experimental situation is realized in flows through structured microchannels with alternating high‐ and low‐velocity segments. While entering the wider channel segments, the semiflexible filaments undergo a buckling transition under compression whereas they are stretched with a suppression of thermal fluctuations in the extensional regime when reentering the narrow segments. The nature of these nonequilibrium and nonstationary conformational transitions is characterized by analyzing the evolution of the end‐to‐end distances, center‐of‐mass velocities, and bending energies along the passage of the filaments through the channels.

Seeing physiological processes at the nanoscale in living organisms without labeling is an ultimate goal in life sciences. Using X-ray ptychography, we explored in situ the dynamics of unstained, living fission yeast Schizosaccharomyces pombe cells in natural, aqueous environment at the nanoscale. In contrast to previous X-ray imaging studies on biological matter, in this work the eukaryotic cells were alive even after several ptychographic X-ray scans, which allowed us to visualize the chromatin motion as well as the autophagic cell death induced by the ionizing radiation. The accumulated radiation of the sequential scans allowed for the determination of a characteristic dose of autophagic vacuole formation and the lethal dose for fission yeast. The presented results demonstrate a practical method that opens another way of looking at living biological specimens and processes in a time-resolved label-free setting.