Bioinspired Granular Media Friction Pad: A Universal System for Friction Enhancement on Variety of Substrates

The granular media friction pad (GMFP) inspired by the biological smooth attachment pads of cockroaches and grasshoppers employs passive jamming, to create high friction forces on a large variety of substrates. The granular medium inside the pad is encased by a flexible membrane which at contact formation greatly adapts to the substrate profile. Upon applying load, the granular medium undergoes the jamming transition and changes from fluid-like to solid-like properties. The jammed granular medium, in combination with the deformation of the encasing elastic membrane, results in high friction forces on a multitude of substrate topographies. Here we explore the effect of elasticity variation on the generation of friction by varying granular media filling quantity as well as membrane modulus and thickness. We systematically investigate contact area and robustness against substrate contamination, and we also determine friction coefficients for various loading forces and substrates. Depending on the substrate topography and loading forces, a low filling quantity and a thin, elastic membrane can be favorable, in order to generate the highest friction forces.

The Role of Substrate Topography and Stiffness on MSC Cells Functions: Key Material Properties for Biomimetic Bone Tissue Engineering

The hypothesis of the present research is that by altering the substrate topography and/or stiffness to make it biomimetic, we can modulate cells behavior. Substrates with similar surface chemistry and varying stiffnesses and topographies were prepared. Bulk PCL and CNTs-reinforced PCL composites were manufactured by solvent casting method and electrospinning and further processed to obtain tunable moduli of elasticity in the range of few MPa. To ensure the same chemical profile for the substrates, a protein coating was added. Substrate topography and properties were investigated. Further on, the feedback of Wharton’s Jelly Umbilical Cord Mesenchymal Stem Cells to substrates characteristics was investigated. Solvent casting scaffolds displayed superior mechanical properties compared to the corresponding electrospun films. However, the biomimetic fibrous texture of the electrospun substrates induced improved feedback of the cells with respect to their viability and proliferation. Cells’ adhesion and differentiation was remarkably pronounced on solvent casting substrates compared to the electrospun substrates. Soft substates improved cells multiplication and migration, while stiff substrates induced differentiation into bone cells. Aspects related to the key factors and the ideal properties of substrates and microenvironments were clarified, aiming towards the deep understanding of the required optimum biomimetic features of biomaterials.

Decoding natural astrocyte rhythms: dynamic actin waves result from environmental sensing by primary rodent astrocytes

Astrocytes are key regulators of brain homeostasis, which is essential for proper cognitive function. The role of cytoskeletal dynamics in this critical regulatory process is unknown. Here we find that actin is dynamic in certain subcellular regions, especially near the cell boundary. Our results further indicate that actin dynamics concentrates into “hotspot” regions that selectively respond to certain chemophysical stimuli, specifically the homeostatic challenges of ion or water concentration increases. Substrate topography makes actin dynamics more frequent yet weaker, and it also alters actin network structure. Superresolution images analyzed with a filament extraction algorithm demonstrate that surface topography is associated with a predominant perpendicular alignment of actin filaments near the cell boundary whereas flat substrates result in an actin cortex mainly parallel to the cell boundary. Thus, actin structure and dynamics together integrate information from different aspects of the environment that might steer the operation of neural cell networks.TeaserAstrocytes display dynamic actin that is modulated by combinations of chemophysical stimuli and environmental topographies.

Morphological types in the Deccan Volcanic Province, India: implications on emplacement dynamics of continental flood basalts

We review and compare morphologies from continental basaltic lavas, using examples from the Deccan Volcanic Province to compile their internal configurations, mutual associations and compare them. The mechanism of endogenous transfer of lava within an insulating (rapidly developed) crust provides an efficient mode of dispersal of the molten lava in flood basalts. The growth of the lava flow can be achieved by a single extrusion or by multiple pulses of endogenous emplacement that enable the lava to efficiently spread over large areas and thicken.We show that the morphology of a lobe manifests the response of the molten lava to several parameters (including volumetric rate of emplacement, substrate topography, viscosity, vapour loss, etc) that govern the dynamics and cooling history of basaltic lava after it starts to spread on the surface. The lateral transition from one morphology to another within lobes of a lava flow is a testimony to the interactive response of the lava dynamics and rheology to variation in the local systems in which they were emplaced. The morphologies do not evolve as rigid partitioned categories from ‘áā and pāhoehoe lava types’ but as parametric progression of interactive variations in the spreading and cooling lava.A hierarchical recognition of lobes, flows and flow fields and mapping of the morphology (and their lateral transition or continuity) combined with the stacking patterns provides the volcanological framework for a sound stratigraphic mapping of flood basalts. Such an architectural documentation of flood basalt provinces will lead to robust models of their eruptive histories.

Impact of the process conditions on polymer pattern morphology during spin coating over topological surfaces

Polymer phase separation of a binary system over prepatterned substrate topography during spin casting.

Structure and Tribological Properties of AlCrN + CrCN Coating

The paper presents results of the investigation of the AlCrN and AlCrN + CrCN coatings, deposited by arc evaporation method on the austenitic steel substrate. Topography studies performed with the use of AFM showed that the roughness value was 24 nm for AlCrN and 14 nm for CrCN. Chemical analysis carried out with energy dispersive X-rays spectroscopy confirmed the chemical composition of the coatings. Transmission electron microscopy (TEM) investigations showed a column structure of AlCrN and CrCN layers with a width in the range of 10–200 nm. Tribological properties analyzed using a scratch test and ball-on-disc method showed a good adhesion of the coatings to the substrate (LC2 is 40 and 46 N for AlCrN and AlCrN + CrCN, respectively) and its high wear resistance; the use of an additional CrCN layers caused a decrease in the friction coefficient by 19%. Structure modification of the AlCrN + CrCN coating system and the related improvement in its mechanical and tribological properties allowed increasing the lifetime of the coated elements. The original approach was to produce a dual-layer coating, consisting of an internal, hard AlCrN layer and an external layer of CrCN, providing good tribological properties, as well as an appropriate forming of the transition zone between the layers.