Extended kinetic theory applied to pressure-controlled shear flows of frictionless spheres between rigid, bumpy planes.

We numerically investigate, through discrete element simulations, the steady flow of identical, frictionless spheres sheared between two parallel, bumpy planes in the absence of gravity and under a fixed normal load. We measure the spatial distributions of solid volume fraction, mean velocity, intensity of agitation and stresses, and confirm previous results on the validity of the equation of state and the viscosity predicted by the kinetic theory of inelastic granular gases. We also directly measure the spatial distributions of the diffusivity and the rate of collisional dissipation of the fluctuation kinetic energy, and successfully test the associated constitutive relations of the extended kinetic theory, , a kinetic theory which includes the role of velocity correlations.

Superlubric Sliding of Graphene Auto-Kirigami with Interfaces Containing Self-Assembled Stripe-Pattern Adsorbates.

Van der Waals heterostructures formed by stacked 2D materials show exceptional electronic, mechanical, and optical properties. Superlubricity, a condition where atomically flat, incommensurate planes of atoms result in ultra-low friction, is a prime example enabling, for example, self-assembly of optically visible graphene nanostructures in air via a sliding auto-kirigami process. Here, it is demonstrated that a subtle but ubiquitous adsorbate stripe structure found on graphene and graphitic surfaces in ambient conditions remains stable within the interface between twisted graphene layers as they slide over each other.

Mechanical Properties of Conducting Printed Nanosheet Network Thin Films Under Uniaxial Compression.

Thin film networks of solution processed nanosheets show remarkable promise for use in a broad range of applications including strain sensors, energy storage, printed devices, textile electronics, and more. While it is known that their electronic properties rely heavily on their morphology, little is known of their mechanical nature, a glaring omission given the effect mechanical deformation has on the morphology of porous systems and the promise of mechanical post processing for tailored properties. Here, this work employs a recent advance in thin film mechanical testing called the Layer Compression Test to perform the first in situ analysis of printed nanosheet network compression.

High-resolution micro-cavity filling sensing by fiber optic interferometry.

In the last decade, new potential applications of micro- and nano-products in telecommunication, medical diagnostics, photovoltaic, and optoelectronic systems have increased the interest to develop micro-engineering technologies. Injection molding of polymeric materials is a recent method being adapted for serial manufacturing of optic components and packaging at the micro- and nano-scale. Quality assurance of replication into small cavities is an important but underdeveloped factor that is needed to ensure high production efficiency in any micro-fabrication industry.

Resilient and agile engineering solutions to address societal challenges such as coronavirus pandemic.

The world is witnessing tumultuous times as major economic powers including the US, UK, Russia, India, and most of Europe continue to be in a state of lockdown. The worst-hit sectors due to this lockdown are sales, production (manufacturing), transport (aerospace and automotive) and tourism. Lockdowns became necessary as a preventive measure to avoid the spread of the contagious and infectious "ronarus isease 20 (COVID-19).

Effect of cross-linking and hydration on microscale flat punch indentation contact to collagen-hyaluronic acid films in the viscoelastic limit.

The properties of the extracellular matrix (ECM) have profound impact upon cell behaviour. As an abundant protein in mammals, collagen is a desirable base material to engineer an ECM tissue scaffold, but its structural weakness generally requires molecular crosslinking or incorporation of additional ECM-based macromolecules such as glycosaminoglycans. We have performed microscopic indentation to test collagen films under dry and aqueous conditions prepared with different levels of physical and chemical crosslinking.

Self-assembly of graphene ribbons by spontaneous self-tearing and peeling from a substrate.

Graphene and related two-dimensional materials have shown unusual and exceptional mechanical properties, with similarities to origami-like paper folding and kirigami-like cutting demonstrated. For paper analogues, a critical difference between macroscopic sheets and a two-dimensional solid is the molecular scale of the thin dimension of the latter, allowing the thermal activation of considerable out-of-plane motion. So far thermal activity has been shown to produce local wrinkles in a free graphene sheet that help in theoretically understanding its stability, for example, and give rise to unexpected long-range bending stiffness.

Data on in vitro and in vivo cell orientation on substrates with different topographies.

This data article contains data related to the research article entitled "Substrate topography: A valuable in vitro tool, but a clinical red herring for in vivo tenogenesis" [1]. We report measurements on tenocyte viability, metabolic activity and proliferation on substrates with different topographies. We also report the effect of substrates with different topographies on host cells in a subcutaneous model.

Characteristics, interactions and coating adherence of heterogeneous polymer/drug coatings for biomedical devices.

With this rise in surgical procedures it is important to focus on the mobility and safety of the patient and reduce the infections that are associated with hip replacements. We examine the mechanical properties of gentamicin sulphate as a model antimicrobial layer for titanium-alloy based prosthetic hips to help prevent methicillin-resistant Staphylococcus aureus infection after surgery. A top layer of poly(lactic-co-glycolic acid) is added to maintain the properties of the gentamicin sulphate as well as providing a drug delivery system.

Controlling droplet-based deposition uniformity of long silver nanowires by micrometer scale substrate patterning.

We report control of droplet-deposit uniformity of long silver nanowires suspended in solutions by microscopic influence of the liquid contact line. Substrates with microfabricated line patterns with a pitch far smaller than mean wire length lead to deposit thickness uniformity compared to unpatterned substrates. For high boiling-point solvents, two significant effects were observed: The substrate patterns suppressed coffee ring staining, and the wire deposits exhibited a common orientation lying perpendicular over top the lines.

Substrate topography: A valuable in vitro tool, but a clinical red herring for in vivo tenogenesis.

Unlabelled: Controlling the cell-substrate interactions at the bio-interface is becoming an inherent element in the design of implantable devices. Modulation of cellular adhesion in vitro, through topographical cues, is a well-documented process that offers control over subsequent cellular functions. However, it is still unclear whether surface topography can be translated into a clinically functional response in vivo at the tissue/device interface.

The influence of anisotropic nano- to micro-topography on in vitro and in vivo osteogenesis.

Aim: Topographically modified substrates are increasingly used in tissue engineering to enhance biomimicry. The overarching hypothesis is that topographical cues will control cellular response at the cell-substrate interface.

Materials & Methods: The influence of anisotropically ordered poly(lactic-co-glycolic acid) substrates (constant groove width of ~1860 nm; constant line width of ~2220 nm; variable groove depth of ~35, 306 and 2046 nm) on in vitro and in vivo osteogenesis were assessed.

Interfacial characteristics and determination of cohesive and adhesive strength of plasma-coated hydroxyapatite via nanoindentation and microscratch techniques.

We investigate the chemical composition and mechanical properties of plasma-deposited hydroxyapatite on grit-blasted Ti-6Al-4V coupons as models of typical prosthetic hip implants. Nanoindentation is used to extract the mechanical properties of the hydroxyapatite (HA) coating and to evaluate the behavior of the material as a function of distance from the interface. A microscratch technique was used to determine parameters of cohesive and adhesive failure of the material that are critical in determining the functionality of these biomedical devices.

Mechanical properties of self-assembled chitin nanofiber networks.

Chitin nanofibers are structural components of the insect cuticle, the exoskeleton of crabs, and mollusk shells. Chitin nanofibers have found broad use in biomedical applications. Here, we study structure-properties-processing relationships of 3 nm chitin nanofiber networks self-assembled from a chitin hexafluoroisopropanol solution.

Fundamental limit to the use of effective medium theories in optics.

The effective medium refractive index of a surface-bound submonolayer of polystyrene nanospheres in water is found to be ill-defined below a rather specific sphere occupied area limit. The submonolayer takes on a recognizable thickness and refractive index only when the average center separation between spheres is at or below the inverse of the wavenumber. An anticipated limit to the Maxwell Garnett theory is therefore confirmed.

Mechanical constraint and release generates long, ordered horizontal pores in anodic alumina templates.

We describe the formation of long, highly ordered arrays of planar oriented anodic aluminum oxide (AAO) pores during plane parallel anodization of thin aluminum 'finger' microstructures fabricated on thermally oxidized silicon substrates and capped with a silicon oxide layer. The pore morphology was found to be strongly influenced by mechanical constraint imposed by the oxide layers surrounding the Al fingers. Tractions induced by the SiO(2) substrate and capping layer led to frustrated volume expansion and restricted oxide flow along the interface, with extrusion of oxide into the primary pore volume, leading to the formation of dendritic pore structures and meandering pore growth.

Large magnetoresistance in few layer graphene stacks with current perpendicular to plane geometry.

A large magnetoresistance (MR) effect of few-layers graphene between two non-magnetic metal electrodes with current perpendicular to graphene plane is studied. A non-saturation and anisotropic MR with the value over 60% at 14 T is observed in a two-layer graphene stack at room temperature. The resistance of the device is only tens of ohms, having the advantage of low power consumption for magnetic device applications.

Memory and threshold resistance switching in Ni/NiO core-shell nanowires.

We report on the first controlled alternation between memory and threshold resistance switching (RS) in single Ni/NiO core-shell nanowires by setting the compliance current (I(CC)) at room temperature. The memory RS is triggered by a high I(CC), while the threshold RS appears by setting a low I(CC), and the Reset process is achieved without setting a I(CC). In combination with first-principles calculations, the physical mechanisms for the memory and threshold RS are fully discussed and attributed to the formation of an oxygen vacancy (Vo) chain conductive filament and the electrical field induced breakdown without forming a conductive filament, respectively.

Surface anchoring structure of a liquid crystal monolayer studied via dual polarization interferometry.

The self-organization of liquid crystal molecules of 4- n -pentyl- 4' -cyanobiphenyl (5CB) forming an oriented monolayer by condensation from the vapor phase onto a silicon oxynitride surface has been observed using the evanescent wave dual slab waveguide dual polarization mode interferometry (DPI) technique. Two distinct stages to the layer formation are observed: After the formation of a layer of molecules lying prone on the surface, further condensation begins to densify the layer and produces a gradual mutual alignment of the molecules until the fully condensed, fully aligned monolayer is reached. At this limit the full coverage 5CB monolayer on this surface and at a temperature of 25 degrees C , is found to be anchored with an average molecular axis polar angle of 56+/-1 degrees and with a measured thickness of 16.

Measuring glassy and viscoelastic polymer flow in molecular-scale gaps using a flat punch mechanical probe.

This paper investigates molecular-scale polymer mechanical deformation during large-strain squeeze flow of polystyrene (PS) films, where the squeeze flow gap is close to the polymer radius of gyration (R(g)). Stress-strain and creep relations were measured during flat punch indentation from an initial film thickness of 170 nm to a residual film thickness of 10 nm in the PS films, varying molecular weight (M(w)) and deformation stress rate by over 2 orders of magnitude while temperatures ranged from 20 to 125 degrees C. In stress-strain curves exhibiting an elastic-to-plastic yield-like knee, the response was independent of M(w), as expected from bulk theory for glassy polymers.

Molecular confinement accelerates deformation of entangled polymers during squeeze flow.

The squeezing of polymers in narrow gaps is important for the dynamics of nanostructure fabrication by nanoimprint embossing and the operation of polymer boundary lubricants. We measured stress versus strain behavior while squeezing entangled polystyrene films to large strains. In confined conditions where films were prepared to a thickness less than the size of the bulk macromolecule, resistance to deformation was markedly reduced for both solid-glass forging and liquid-melt molding.

Variable temperature thin film indentation with a flat punch.

We present modifications to conventional nanoindentation that realize variable temperature, flat punch indentation of ultrathin films. The technique provides generation of large strain, thin film extrusion of precise geometries that idealize the essential flows of nanoimprint lithography, and approximate constant area squeeze flow rheometry performed on thin, macroscopic soft matter samples. Punch radii as small as 185 nm have been realized in ten-to-one confinement ratio testing of 36 nm thick polymer films controllably squeezed in the melt state to a gap width of a few nanometers.

Room temperature mechanical thinning and imprinting of solid films.

The mechanical patterning of thin films has received recent attention due to significant potential for efficient nanostructure fabrication. For solid films, mechanically thinning wide areas remains particularly challenging. In this work, we introduce a new plastic ratchet mechanism involving small amplitude (<10 nm), oscillatory shear motion of the forging die.