Scientific publications

The cellular cortex is an approximately 200-nm-thick actin network that lies just beneath the cell membrane. It is responsible for the mechanical properties of cells, and as such, it is involved in many cellular processes, including cell migration and cellular interactions with the environment. To develop a clear view of this dense structure, high-resolution imaging is essential. As one such technique, electron microscopy, involves complex sample preparation procedures. The final drying of these samples has significant influence on potential artifacts, like cell shrinkage and the formation of artifactual holes in the actin cortex. In this study, we compared the three most used final sample drying procedures: critical-point drying (CPD), CPD with lens tissue (CPD-LT), and hexamethyldisilazane drying. We show that both hexamethyldisilazane and CPD-LT lead to fewer artifactual mesh holes within the actin cortex than CPD. Moreover, CPD-LT leads to significant reduction in cell height compared to hexamethyldisilazane and CPD. We conclude that the final drying procedure should be chosen according to the reduction in cell height, and so CPD-LT, or according to the spatial separation of the single layers of the actin cortex, and so hexamethyldisilazane.

Abstract Pseudomonas aeruginosa (PA) infections can be notoriously difficult to treat and are often accompanied by the development of antimicrobial resistance (AMR). Quorum sensing inhibitors (QSI) acting on PqsR (MvfR) – a crucial transcriptional regulator serving major functions in PA virulence – can enhance antibiotic efficacy and eventually prevent the AMR. An integrated drug discovery campaign including design, medicinal chemistry-driven hit-to-lead optimization and in-depth biological profiling of a new QSI generation is reported. The QSI possess excellent activity in inhibiting pyocyanin production and PqsR reporter-gene with IC50 values as low as 200 and 11 × 10−9 m, respectively. Drug metabolism and pharmacokinetics (DMPK) as well as safety pharmacology studies especially highlight the promising translational properties of the lead QSI for pulmonary applications. Moreover, target engagement of the lead QSI is shown in a PA mucoid lung infection mouse model. Beyond that, a significant synergistic effect of a QSI-tobramycin (Tob) combination against PA biofilms using a tailor-made squalene-derived nanoparticle (NP) formulation, which enhance the minimum biofilm eradicating concentration (MBEC) of Tob more than 32-fold is demonstrated. The novel lead QSI and the accompanying NP formulation highlight the potential of adjunctive pathoblocker-mediated therapy against PA infections opening up avenues for preclinical development.

Approximately 80% of brain tumours are gliomas. Despite treatment, patient mortality remains high due to local metastasis and relapse. It has been shown that transferrin-functionalised porous silicon nanoparticles (Tf@pSiNPs) can inhibit the migration of U87 glioma cells. However, the underlying mechanisms and the effect of glioma cell heterogeneity, which is a hallmark of the disease, on the efficacy of Tf@pSiNPs remains to be addressed.

The mechanical response of ceramic matrix composites depends critically on the slip along the matrix-fiber interface, which is usually achieved with thin coatings on the fibers. Environmental attack of such coatings (enabled by ingress of reactants through matrix cracks) often leads to significant degradation, through the removal of the coating via volatilization and oxidation of exposed SiC surfaces. The extent of the volatilization region extending from the matrix crack plane (i.e., recession length) is strongly coupled to the formation of oxide, which ultimately fills open gaps and arrests further reactions. This paper presents models to quantify these effects over a broad range of environmental conditions, coating thickness, and matrix crack opening. Analytical solutions are presented for the time to close recession gaps via oxidation, and the associated terminal recession lengths obtained near free surfaces. A broad parameter study illustrates that recession behaviors are controlled by a competition between volatilization and oxidation rates. As such, the extent of recession is highly sensitive to water vapor and temperature, providing an explanation for disparate observations of recession under seemingly similar conditions. The extent of recession in the interior of composites is also illustrated, using a straightforward reaction-transport model. Recession lengths decay rapidly away from the free surface, with the extent of recession penetration scaling with maximum recession at the free surface.

The transport of macromolecular drugs such as oligonucleotides into the lungs has become increasingly relevant in recent years due to their high potency. However, the chemical structure of this group of drugs poses a hurdle to their delivery, caused by the negative charge, membrane impermeability and instability. For example, siRNA to reduce tumour necrosis factor alpha (TNF-α) secretion to reduce inflammatory signals has been successfully delivered by inhalation. In order to increase the effect of the treatment, a co-transport of another anti-inflammatory ingredient was applied. Combining curcumin-loaded mesoporous silica nanoparticles in nanostructured cylindrical microparticles stabilized by the layer-by-layer technique using polyanionic siRNA against TNF-α was used for demonstration. This system showed aerodynamic properties suited for lung deposition (mass median aerodynamic diameter of 2.85 ± 0.44 µm). Furthermore, these inhalable carriers showed no acute in vitro toxicity tested in both alveolar epithelial cells and macrophages up to 48 h incubation. Ultimately, TNF-α release was significantly reduced by the particles, showing an improved activity co-delivering both drugs using such a drug-delivery system for specific inhibition of TNF-α in the lungs

The mechanical properties of cells are important for many biological processes, including wound healing, cancers, and embryogenesis. Currently, our understanding of cell mechanical properties remains incomplete. Different techniques have been used to probe different aspects of the mechanical properties of cells, among them microplate rheology, optical tweezers, micropipette aspiration, and magnetic twisting cytometry. These techniques have given rise to different theoretical descriptions, reaching from simple Kelvin-Voigt or Maxwell models to fractional such as power law models, and their combinations. Atomic force microscopy (AFM) is a flexible technique that enables global and local probing of adherent cells. Here, using an AFM, we indented single retinal pigmented epithelium cells adhering to the bottom of a culture dish. The indentation was performed at two locations: above the nucleus, and towards the periphery of the cell. We applied creep compliance, stress relaxation, and oscillatory rheological tests to wild type and drug modified cells. Considering known fractional and semi-fractional descriptions, we found the extracted parameters to correlate. Moreover, the Young’s modulus as obtained from the initial indentation strongly correlated with all of the parameters from the applied power-law descriptions. Our study shows that the results from different rheological tests are directly comparable. This can be used in the future, for example, to reduce the number of measurements in planned experiments. Apparently, under these experimental conditions, the cells possess a limited number of degrees of freedom as their rheological properties change.

We carry out computational simulations of the Valsalva compression of an inferior vena cava (IVC) with a filter implanted in it. We find that when we treat the IVC wall as simply a boundary between 2 fluids and apply an external pressure on the IVC, the deformation magnitudes and patterns do not agree with data in the literature. We conclude that IVC compression is mainly caused by solid bodies (i.e. tissue and organs) compressing the IVC, and develop a model to simulate this phenomenon. We calibrate our model to data in the literature for Valsalva compression with and without an implanted filter. We then use our approach to predict the area reduction of the IVC during breathing when 2 different types of filters are implanted. Not surprisingly, we find that a compliant filter is less able to resist the compression of the IVC during respiration than a stiffer one, and we quantify the difference. We anticipate that, with further development, our model can be used to make assessments of design and testing parameters that can help to avoid fatigue failure of a filter that is subjected to millions of compressions due to breathing.

The bending of a superelastic Nitinol cantilever is analyzed, where the deformation is caused by a non-parallel, rigid, friction free constraining surface that approaches the cantilever at an angle, making contact first with its tip. The analysis accounts for geometric nonlinearity and the materially nonlinear behavior of the Nitinol. The constraining surface first causes a severe bending of the cantilever, then reverses its direction of motion and allows the cantilever to partially unbend. The severe bending causes an austenite to martensite phase transformation while the unbending allows partial or full reversal of the phase change, with these transformations being associated with the materially nonlinear response of the Nitinol. In the analysis, a single-cycle of bending and unbending is considered on the one hand, and, on the other, a partial cycle of bending and unbending is followed by fatigue straining of the cantilever. To impose the fatigue straining, the constraining surface is moved up and down cyclically. The results provide the state of mean strain and strain amplitude that the cantilever will experience during fatigue straining. It is noted that recent investigations of the fatigue properties of Nitinol show that, contrary to assumptions that previously prevailed, its fatigue life is influenced by the mean strain during strain cycling.

The theory of anisotropic generalised plane strain of line forces and dislocation lines is embedded in the three-dimensional elasticity of point forces and dislocation densities. Embedding in real space is achieved by slicing in reciprocal space using the projection-slice theorem.

Shear-driven strain localization has been observed in a wide variety of materials and may take the form of shear bands or kink bands. Based on observations of kink bands in plastically anisotropic metallic nanolaminates and single crystal metals, we posit that, for the specific case of isochoric deformation, the kinematics of kink band formation are indistinguishable from those of plane strain shear band formation. The only distinction between shear bands and kink bands in these systems would then be that kink bands ‘lock up’ at a particular value of material rotation while shear bands may progress to arbitrarily high strains. In order to investigate whether strong material anisotropy is sufficient to arrest shear localization at a geometry that matches the classic kink band geometry, we model the development of a band of simple shear within an anisotropic perfectly plastic material. The resulting analytical model provides the stress state needed to maintain the kinematics of simple shear as a function of material anisotropy, deformation band orientation, and shear strain (or equivalently, material rotation). It is found that plastic anisotropy can promote either kink band or shear band formation depending on the loading orientation. When the deviatoric stress is positive parallel to the plane of anisotropy, shear localization may progress without bound and a shear band is produced. When the deviatoric stress is negative parallel to the plane of anisotropy, shear localization is arrested after a certain material rotation, resulting in a kink band. Examination of the requisite applied stress state during kink band formation provides an explanation for the experimentally-observed ‘lock up’ geometry. Solutions for the band boundary inclination angle are obtained and used to provide bounds on permissible band angles for both shear bands and kink bands.