Jamming transition and normal modes of polydispersed soft particle packing.

The jamming transition of soft particles characterized by narrow size distributions has been well studied by physicists. However, polydispersed systems are more relevant to engineering, and the influence of polydispersity on jamming phenomena is still unexplored. Here, we numerically investigate jamming transitions of polydispersed soft particles in two dimensions.

The contact lens-tear film interface: Investigating the tear envelope.

Purpose: To explore the complex interface between the tear film, a unique mucosal fluid which is fundamental to ocular homeostasis and optimal vision, and an in-situ contact lens. This study exploits the use of a unique tear envelope (TE) extraction technique, which harvests the material-influenced layer of tear film that is in intimate contact with the lens during wear, to specifically investigate the influence of contact lens wear on tear film protein dynamics.

Methods: TEs were collected from freshly removed worn lens using a novel microcentrifuge 'piggyback' technique.

Tailoring Hydrogel Sheet Properties through Co-Monomer Selection in AMPS Copolymer Macromers.

This study investigates hydrogels based on 2-Acrylamido-2-methyl-1-propanesulfonic acid sodium salt (AMPS) copolymers, incorporating N-hydroxyethyl acrylamide (HEA) and 3-sulfopropyl acrylate potassium salt (SPA). The addition of HEA and SPA is designed to fine-tune the hydrogels' water absorption and mechanical properties, ultimately enhancing their characteristics and expanding their potential for biomedical applications. A copolymer of AMPS, 2-carboxyethyl acrylate (CEA) combined with methacrylic acid (MAA) as poly(AMPS-stat-CEA-stat-MAA, PACM), was preliminarily synthesized.

Low cytotoxicity, antibacterial property, and curcumin delivery performance of toughness-enhanced electrospun composite membranes based on poly(lactic acid) and MAX phase (TiAlC).

MXenes, synthesized from their precursor MAX phases, have been extensively researched as additives to enhance the drug delivery performance of polymer matrices, whereas there is a limited number of previous reports on the use of MAX phases themselves for such applications. The use of MAX phases can exclude the complicated synthesis procedure and lessen resultant production and environmental costs required to convert MAX phases to MXenes. Herein, electrospun membranes of poly(lactic acid) (PLA) and a MAX phase (TiAlC) have been fabricated for curcumin delivery.

Encapsulation of propolis extracts in aqueous formulations by using nanovesicles of lipid and poly(styrene--maleic acid).

Bee propolis has been used in alternative medicine to treat various diseases. Due to its limited water solubility, it is often used in combination with alcohol solvents, causing skin irritation and immune response. To solve this, the new drug delivery system, based on the lipid nanodiscs of 1,2-dimyristoyl--glycero-3-phosphochline (DMPC) and poly(styrene--maleic acid) (PSMA), were created in an aqueous media.

In Situ Compatibilized Blends of PLA/PCL/CAB Melt-Blown Films with High Elongation: Investigation of Miscibility, Morphology, Crystallinity and Modelling.

Ternary-blended, melt-blown films of polylactide (PLA), polycaprolactone (PCL) and cellulose acetate butyrate (CAB) were prepared from preliminary miscibility data using a rapid screening method and optical ternary phase diagram (presented as clear, translucent, and opaque regions) as a guide for the composition selection. The compositions that provided optically clear regions were selected for melt blending. The ternary (PLA/PCL/CAB) blends were first melt-extruded and then melt-blown to form films and characterized for their tensile properties, tensile fractured-surface morphology, miscibility, crystallinity, molecular weight and chemical structure.

Moduli and modes in the Mikado model.

We determine how low frequency vibrational modes control the elastic shear modulus of Mikado networks, a minimal mechanical model for semi-flexible fiber networks. From prior work it is known that when the fiber bending modulus is sufficiently small, (i) the shear modulus of 2D Mikado networks scales as a power law in the fiber line density, ∼ , and (ii) the networks also possess an anomalous abundance of soft (low-frequency) vibrational modes with a characteristic frequency ∼ . While it has been suggested that and are identical, the preponderance of evidence indicates that is larger than theoretical predictions for .

A study of the permeation and water-structuring behavioural properties of PEG modified hydrated silk fibroin membranes.

The potential of naturally occurring substances as a source of biomedical materials is well-recognised and is being increasingly exploited. Silk fibroin membranes derived fromsilk cocoons exemplify this, for example as substrata for the growth of ocular cells with the aim of generating biomaterial-cell constructs for tissue engineering. This study investigated the transport properties of selected silk fibroin membranes under conditions that allowed equilibrium hydration of the membranes to be maintained.

The influence of structure and morphology on ion permeation in commercial silicone hydrogel contact lenses.

The importance of the microstzructure of silicone hydrogels is widely appreciated but is poorly understood and minimally investigated. To ensure comfort and eye health, these materials must simultaneously exhibit both high oxygen and high water permeability. In contrast with most conventional hydrogels, the water content and water structuring within silicone hydrogels cannot be solely used to predict permeability.

Stress Relaxation above and below the Jamming Transition.

We numerically investigate stress relaxation in soft athermal disks to reveal critical slowing down when the system approaches the jamming point. The exponents describing the divergence of the relaxation time differ dramatically depending on whether the transition is approached from the jammed or unjammed phase. This contrasts sharply with conventional dynamic critical scaling scenarios, where a single exponent characterizes both sides.

A comparison of SMA (styrene maleic acid) and DIBMA (di-isobutylene maleic acid) for membrane protein purification.

The use of styrene maleic acid co-polymer (SMA) for membrane protein extraction and purification has grown in recent years. SMA inserts in the membrane and assembles into small discs of bilayer encircled by polymer, termed SMA lipid particles (SMALPs). This allows purification of membrane proteins whilst maintaining their lipid bilayer environment.

Nonlocal Effects in Inhomogeneous Flows of Soft Athermal Disks.

We numerically investigate nonlocal effects on inhomogeneous flows of soft athermal disks close to but below their jamming transition. We employ molecular dynamics to simulate Kolmogorov flows, in which a sinusoidal flow profile with fixed wave number is externally imposed, resulting in a spatially inhomogeneous shear rate. We find that the resulting rheology is strongly wave-number-dependent, and that particle migration, while present, is not sufficient to describe the resulting stress profiles within a conventional local model.

Clinical and biochemical analysis of the ageing tear film.

Background: Tear film stability is important for healthy visual function, and yet little is known of the ageing mechanisms. The aim of this study was to investigate parallels between biochemical changes and clinical physical parameters, which occur in the tear film of two subject populations differing in age by over 30 years.

Methods: Two distinct age groups were chosen: 11 'younger' (23.

A minimal-length approach unifies rigidity in underconstrained materials.

We present an approach to understand geometric-incompatibility-induced rigidity in underconstrained materials, including subisostatic 2D spring networks and 2D and 3D vertex models for dense biological tissues. We show that in all these models a geometric criterion, represented by a minimal length [Formula: see text], determines the onset of prestresses and rigidity. This allows us to predict not only the correct scalings for the elastic material properties, but also the precise magnitudes for bulk modulus and shear modulus discontinuities at the rigidity transition as well as the magnitude of the Poynting effect.

Investigating the permeation properties of contact lenses and its influence on tear electrolyte composition.

The health of the cornea is paramount; the aim of this study was to assess the permeation of essential tear electrolytes through a range of commercial contact lenses. Donor/receiver conductivity measurements were recorded using a dual-chamber diffusion system which allowed material permeability profiles and coefficients to be calculated. Water structuring properties of the contact lenses were measured by differential scanning calorimetry.

Sticky Matters: Jamming and Rigid Cluster Statistics with Attractive Particle Interactions.

While the large majority of theoretical and numerical studies of the jamming transition consider athermal packings of purely repulsive spheres, real complex fluids and soft solids generically display attraction between particles. By studying the statistics of rigid clusters in simulations of soft particles with an attractive shell, we present evidence for two distinct jamming scenarios. Strongly attractive systems undergo a continuous transition in which rigid clusters grow and ultimately diverge in size at a critical packing fraction.

High modulus hydrogels for ophthalmic and related biomedical applications.

This paper presents three families of semi-interpenetrating polymer network (SIPN) hydrogels based on an ester-based polyurethane (EBPU) and hydrophilic monomers: N,N-dimethylacrylamide (NNDMA), N-vinyl pyrrolidone (NVP) and acryloylmorpholine (AMO) as potential materials for keratoprosthesis, orthokeratology and mini-scleral lens application. Hydrogels sheets were synthesized via free-radical polymerization with methods developed in-house. SIPN hydrogels were characterized for their equilibrium water content, mechanical and surface properties.

Coarsening and mechanics in the bubble model for wet foams.

Aqueous foams are an important model system that displays coarsening dynamics. Coarsening in dispersions and foams is well understood in the dilute and dry limits, where the gas fraction tends to zero and one, respectively. However, foams are known to undergo a jamming transition from a fluidlike to a solidlike state at an intermediate gas fraction ϕ_{c}.

Normal Stresses, Contraction, and Stiffening in Sheared Elastic Networks.

When elastic solids are sheared, a nonlinear effect named after Poynting gives rise to normal stresses or changes in volume. We provide a novel relation between the Poynting effect and the microscopic Grüneisen parameter, which quantifies how stretching shifts vibrational modes. By applying this relation to random spring networks, a minimal model for, e.

Hydrophobic and hydrophilic effects on water structuring and adhesion in denture adhesives.

Denture adhesives are designed to be moisture-sensitive through the inclusion of a blend of polymer salts with varying degrees of water-sensitivity. This enables the adhesive to mix with saliva in vivo and activate its high tack, through the formation of a mucilaginous layer. We report for the first time, the use of differential scanning calorimetry to study a series of hydrophobic and hydrophilic polymeric systems in order to correlate water-structuring behavior with adhesion strength.

Softening and yielding of soft glassy materials.

Solids deform and fluids flow, but soft glassy materials, such as emulsions, foams, suspensions, and pastes, exhibit an intricate mix of solid- and liquid-like behavior. While much progress has been made to understand their elastic (small strain) and flow (infinite strain) properties, such understanding is lacking for the softening and yielding phenomena that connect these asymptotic regimes. Here we present a comprehensive framework for softening and yielding of soft glassy materials, based on extensive numerical simulations of oscillatory rheological tests, and show that two distinct scenarios unfold depending on the material's packing density.

Viscous forces and bulk viscoelasticity near jamming.

When weakly jammed packings of soft, viscous, non-Brownian spheres are probed mechanically, they respond with a complex admixture of elastic and viscous effects. While many of these effects are understood for specific, approximate models of the particles' interactions, there are a number of proposed force laws in the literature, especially for viscous interactions. We numerically measure the complex shear modulus G* of jammed packings for various viscous force laws that damp relative velocities between pairs of contacting particles or between a particle and the continuous fluid phase.

Stress relaxation in viscous soft spheres.

We report the results of molecular dynamics simulations of stress relaxation tests in athermal viscous soft sphere packings close to their unjamming transition. By systematically and simultaneously varying both the amplitude of the applied strain step and the pressure of the initial condition, we access both linear and nonlinear response regimes and control the distance to jamming. Stress relaxation in viscoelastic solids is characterized by a relaxation time τ* that separates short time scales, where viscous loss is substantial, from long time scales, where elastic storage dominates and the response is essentially quasistatic.

The potential influence of Schirmer strip variables on dry eye disease characterisation, and on tear collection and analysis.

Purpose: The use of the Schirmer strips (SS) as a tool in the characterisation of dry eye disease, depends upon the quantitative assessment of tear production and constituents. The aim of this study was to ascertain the extent to which the properties of commercially available SS can vary and the way in which this baseline information may relate to their comparability in clinical use.

Methods: Five SS were analysed: Clement Clarke®, TearFlo®, Bio Schirmer®, Omni Schirmer® and JingMing®.