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Invited speakers

Kerstin Blank (Max Planck Institute of Colloids and Interfaces) (10.30-11.15)
Molecular control of mechanoresponsive coiled coil-crosslinked hydrogels
Coiled coils are highly abundant motifs in structural proteins. Consisting of two (or more) α-helices wound around each other in a superhelical fashion, they represent essential structural elements of the cytoskeleton and the extracellular matrix (ECM). Synthetic coiled coil sequences are further used as dynamo-mechanical supramolecular crosslinks in biomimetic hydrogels. Considering their function as mechanical building blocks, surprisingly little is known about the structural determinants that define the molecular mechanical properties of coiled coils and how these affect the viscoelastic properties of coiled coil-based self-assembled materials. Using atomic force microscope (AFM)-based single-molecule force spectroscopy, we have established the sequence-structure-MECHANICS relationships of a series of synthetic coiled coils. Based on this knowledge, we have developed a library of coiled coil sequences with tuneable mechanical properties and synthesized a series of poly(ethylene glycol)-based hydrogels using these coiled coils as dynamic crosslinks. The resulting hydrogels consist entirely of mechanically characterized molecular building blocks and allow for establishing a direct relationship between molecular and bulk mechanics. Using theoretical models, we obtain a direct correlation between the single-molecule parameters and the bulk mechanical response of the hydrogel, as determined with rheology. Serving as a new platform of ECM mimic, this series of hydrogels will allow for dissecting local and global mechanical processes that determine cellular mechanosensing.
Christian Sproncken (TU Eindhoven) (11.15-11.45)
Hanneke Gelderblom (TU Eindhoven) (13.30-14.15)
Droplet dynamics: from laser impact to living liquids
The impact of a laser pulse onto a liquid drop induces a violent response: the drop gets propelled to high speeds, strongly deforms and breaks up into tiny pieces. When drops impact onto a surface, similar deformation and fragmentation occurs. I will discuss the fundamental physics behind these phenomena and their -unexpected- application in nanolithography. In addition, I will outline my future research plans focusing on capillary flows in biofluids, such as drops of living liquids.
Clara Abaurrea Velasco (Utrecht University) (14.15-14.45)
Active vesicles: a minimal model for cell motility
Self-assembly is a key mechanism for structure formation in passive soft matter. In systems with intrinsic driving forces, in addition activity crucially determines structure and dynamics. An important active system is the cytoskeleton of biological cells, a highly dynamic three-dimensional network of polar filaments and molecular motors. It provides stability and generates and transmits mechanical forces. Here, we present a generic two-dimensional model of active vesicles, where self-propelled filaments attached to rings form mechanosensitive active agents. Using deformable, semiflexible polymer rings we find universal correlations between shape and motility. To probe the internal dynamics of the vesicles in response to stimuli, we study the effect of substrate patterning on shape and motility. The active vesicles show experimentally observed shapes and motion patterns reminiscent of circular-fluctuating cells, keratocytes, and neutrophils.
Lucile Michels (Wageningen University) (16.00-16.30)
A microviscosimetry toolbox for plant cells and tissues based on molecular rotors
In cells microviscosity determines the diffusion rate of organelles and biomolecules. As a result it has a direct influence on fundamental cellular processes requiring signaling and transport, such as division and differentiation. So far little is known about the physical regulation of such processes, and measuring the spatio-temporal microviscosity variations could provide insight on the cellular dynamics involved. In recent years, fluorescent molecular rotors in combination with fluorescence lifetime imaging microscopy (FLIM) have emerged as convenient tools to measure microviscosity non-invasively. For now due to the highly heterogeneous nature of cells, getting a microviscosity map throughout all cellular compartments has remained a challenge, and the dye internalization has been limited to membranes. Here we established a toolbox of four water-soluble BODIPY-based molecular rotors for mapping viscosity patterns within plant cells. Those rotors are able to target different cell compartments with a high selectivity.
Corrado Rainone (University of Amsterdam) (16.30-17.00)
Wave attenuation in glasses: Rayleigh and generalized-Rayleigh scattering scaling
The attenuation of long-wavelength phonons (waves) by glassy disorder plays a central role in various glass anomalies (such as the behavior of their thermal conductivity at low temperatures) yet it is neither fully characterized, nor fully understood. Here we use a combination of theory and extensive computer simulations to reveal the macroscopic low-frequency behavior. Below a recently identified crossover wavenumber, finite-size effects dominate the wave attenuation, which are quantitatively described by a theory of disordered phonon bands. Above that frequency, we reveal it to be affected by quasilocalized nonphononic excitations, which live in the same frequency ranges as long-wavelenght phonons and are a generic signature of glasses. In particular, we show that in a frequency range in which their number is small, the attenuation rate follows a Rayleigh scattering scaling, and that in a frequency range in which this number is sufficiently large, a recently observed logarithmic correction to Rayleigh scattering emerges. Our results suggest that macroscopic glasses, in particular glasses generated by conventional laboratory quenches that are known to strongly suppress quasilocalized nonphononic excitations, exhibit Rayleigh scaling at the lowest wavenumbers and a crossover to generalized-Rayleigh scaling at higher ones. Some supporting experimental evidence from recent literature is presented.