Publications
456 results found
Poole B, Barzdajn B, Dini D, et al., 2020, The roles of adhesion, internal heat generation and elevated temperatures in normally loaded, sliding rough surfaces, International Journal of Solids and Structures, Vol: 185-186, Pages: 14-28, ISSN: 0020-7683
The thermal effects of plastic and frictional heat generation and elevated temperature were examined along with the role of adhesion in the context of galling wear, using a representative crystal plasticity, normally loaded, sliding surface model. Galling frequency behaviour was predicted for 316L steel. Deformation of the surfaces was dominated by the surface geometry, with no significant effect due to variations in frictional models. Plastic and frictional heating were found to have a minimal effect on the deformation of the surface, with the rapid conduction of heat preventing any highly localised heating. There was no corresponding effect on the predicted galling frequency response.Isothermal, elevated temperature conditions caused a decrease in galling resistance, driven by the temperature sensitivity of the critical resolved shear stress. The extent of deformation, as quantified by the area of plastically deformed material and plastic reach, increased with temperature. Comparisons were made with literature results for several surface amplitude and wavelength conditions. Model results compared favourably with those in the literature. However, the reduction in predicted galling resistance with elevated temperature for a fixed surface was not as severe as observations in the literature, suggesting other mechanisms (e.g. phase transformations, surface coatings and oxides) are likely important.
Feng Z, Yu M, Cheng C, et al., 2020, Uncertainties Investigation and mu-Synthesis Control Design for a Full Car with Series Active Variable Geometry Suspension, International Federation of Automatic Control
Sufian A, Knight C, O'Sullivan C, et al., 2020, Capturing Local Fluid Field Characteristics in Porous Media using Pore Network Models
Pore Network Models (PNMs) provides a computationally efficient approach to model porous media. A PNM employs a network representation of the pore space, where individual pores are taken as nodes of the network and are connected by constrictions which are edges of the network. In assemblies of spheres, this network representation is often achieved using Delaunay-based tessellation methods. Fluid flow is simulated in the network model using a Stokes flow algorithm which solves for continuity at each node in the network using a local conductivity model. The seepage induced drag forces can be obtained from the resulting flow field and geometric properties of the pores and constrictions. While PNMs are computationally efficient, there is a simplification of the pore space geometry and governing fluid equations. To better understand these assumptions, the local flow field and seepage induced drag obtained from a PNM is compared to fully-resolved Immersed Boundary Method (IBM) simulations. The local pressure field was very accurately captured, while the local flow rate exhibited slightly more scatter and sensitivity to the tessellation method. There was a close similarity in the network shortest paths, indicating that PNM captures dominant flow channels. Comparison of streamline profiles demonstrated that local pressure drops coincided with pore constrictions. In addition, the fluid-particle interaction force was determined reasonably accurately using PNMs. This suggests that a PNM is a viable option to investigate the local behaviour in porous media.
Ewen J, Ramos Fernandez E, Smith E, et al., 2020, Nonequilibrium Molecular Dynamics Simulations of Tribological Systems, Modeling and Simulation of Tribological Problems in Technology, Editors: Paggi, Hills, Publisher: Springer Nature, Pages: 95-130, ISBN: 978-3-030-20376-4
Putignano C, Dini D, 2020, Contact Mechanics of Rubber and Soft Matter, Modeling and Simulation of Tribological Problems in Technology, Editors: Paggi, Hills, Publisher: Springer Nature, ISBN: 978-3-030-20376-4
Eder SJ, Ripoll MR, Cihak-Bayr U, et al., 2020, MD simulations of FCC alloys under dry sliding yield a mechanism map for near-surface microstructural development, Tribologie und Schmierungstechnik, Vol: 67, Pages: 38-39, ISSN: 0724-3472
Knight C, O'Sullivan C, Dini D, et al., 2020, Computing drag and interactions between fluid and polydisperse particles in saturated granular materials, Computers and Geotechnics, Vol: 117, Pages: 1-16, ISSN: 0266-352X
Fundamental numerical studies of seepage induced geotechnical instabilities and filtration processes depends on accurate prediction of the forces imparted on the soil grains by the permeating fluid. Hitherto coupled Discrete Element Method (DEM) simulations documented in geomechanics have most often simulated the fluid flow using computational fluid dynamics (CFD) models employing fluid cells that contain a number of particles. Empirical drag models are used to predict the fluid-particle interaction forces using the flow Reynolds number and fluid cell porosity. Experimental verification of the forces predicted by these models at the particle-scale is non-trivial. This contribution uses a high resolution immersed boundary method to model the fluid flow within individual voids in polydisperse samples of spheres to accurately determine the fluid-particle interaction forces. The existing drag models are shown to poorly capture the forces on individual particles in the samples for flow with low Reynolds number values. An alternative approach is proposed in which a radical Voronoi tesselation is applied to estimate a local solids volume fraction for each particle; this local solids fraction can be adopted in combination with existing expressions to estimate the drag force. This tessellation-based approach gives a more accurate prediction of the fluid particle interaction forces.
Hu S, Cao X, Reddyhoff T, et al., 2019, Self-compensating liquid repellent surfaces with stratified morphology, ACS Applied Materials and Interfaces, Vol: 12, Pages: 4174-4182, ISSN: 1944-8244
Artificial liquid repellent surfaces have recently attracted vast scientific attention; however, achieving mechanical robustness remains a formidable challenge before industrialization can be realized. To this end, inspired by plateaus in geological landscapes, a self-compensating strategy is developed to pave the way for the synthesis of durable repellent surfaces. This self-compensating surface comprises tall hydrophobic structural elements, which can repel liquid droplets. When these elements are damaged, they expose shorter structural elements that also suspend the droplets and thus preserve interfacial repellency. An example of this plateau-inspired stratified surface was created by 3D direct laser lithography micro-nano fabrication. Even after being subjected to serious frictional damage, it maintained static repellency to water with a contact angle above 147 and was simultaneously able to endure high pressures arising from droplet impacts. Extending the scope of nature-inspired functional surfaces from conventional biomimetics to geological landscapes, this works demonstrates that the plateau-inspired self-compensating strategy can provide an unprecedented level of robustness in terms of sustained liquid repellency.
Ciniero A, Fatti G, Righi MC, et al., 2019, A combined experimental and theoretical study on the mechanisms behind tribocharging phenomenon and the influence of triboemission, Tribology Online, Vol: 14, Pages: 367-374, ISSN: 1881-218X
This work describes recent research into the mechanisms behind tribocharging and the influence of triboemission. The term tribocharging is a type of contact-induced electrification and refers to the transfer of charge between rubbing components. The term triboemission, on the other hand, refers to emission of electrons, ions and photons generated when surfaces are rubbed together. The understanding of tribocharging is of wide interest for several industrial applications and in particular the combination of tribocharging and triboemission may be important in lubricated contacts in the formation of boundary lubricant films. We report the use of a unique vacuum measurement system that enables to measure surface charge variations while simultaneously recording triboemission events during the sliding of a diamond tip on silica specimens. Results show for the first time that tribocharging and triboemission behavior are linked and depend on the surface wear. The contribution of contact-induced electrification to the charging of the surface is then described by means of density functional theory (DFT). Results give insight into the transfer of charge from the SiO2 amorphous surface (silica) to the C(111) surface (diamond ) and into the variation of charging during simulated sliding contact.
Vidotto M, Botnariuc D, De Momi E, et al., 2019, Correction to: a computational fluid dynamics approach to determine white matter permeability, Biomechanics and Modeling in Mechanobiology, Vol: 18, Pages: 2003-2003, ISSN: 1617-7940
The article "A computational fluid dynamics approach to determine white matter permeability" written by Marco Vidotto, Daniela Botnariuc, Elena De Momi and Daniele Dini was originally published electronically on the publisher's Internet portal (currently SpringerLink) on 20 February 2019 without open access.
Menga N, Carbone G, Dini D, 2019, Corrigendum to “Do uniform tangential interfacial stresses enhance adhesion?” [Journal of the Mechanics and Physics of Solids 112 (2018) 145–156], Journal of the Mechanics and Physics of Solids, Vol: 133, Pages: 103744-103744, ISSN: 0022-5096
Profito FJ, Zachariadis DC, Dini D, 2019, Partitioned fluid-structure interaction techniques applied to the mixed-elastohydrodynamic solution of dynamically loaded connecting-rod big-end bearings, Tribology International, Vol: 140, ISSN: 0301-679X
The present contribution proposes different partitioned techniques, which are commonly used in fluid-structure interaction (FSI) applications, in the context of tribological simulations of the transient mixed-elastohydrodynamic problem of dynamically loaded connecting-rod bearings. With the premise that the FSI framework developed is general, in the current work the fluid flow effects have been considered through the averaged Reynolds equation by Patir & Cheng and the mass-conserving Elrod-Adams cavitation model. The multiphysics simulation framework developed has been used to simulate the connecting-rod big-end bearings of both heavy-duty diesel and high-speed motorcycle engines. In the latter case, the influence of polymer concentration in VM-containing oils with similar HTHS150 values on the bearing power loss is investigated and discussed in details.
Heyes DM, Dini D, Costigliola L, et al., 2019, Transport coefficients of the Lennard-Jones fluid close to the freezing line., J Chem Phys, Vol: 151, Pages: 204502-204502
Molecular dynamics simulations have been carried out along four Lennard-Jones (LJ) fluid isomorphs close to the freezing line, covering a temperature, T, in the range of 0.8-350 and a number density, ρ, in the range of 1.1-3.0 in LJ units. Analysis of the transport coefficients is via the Green-Kubo time correlation function method. The radial distribution function, percolation threshold connectivity distance, self-diffusion coefficient, and shear viscosity are shown to be invariant along an isomorph to a very good approximation when scaled with Rosenfeld's macroscopic units, although there are some small departures for T ≃ 1 and lower temperatures. The thermal conductivity is shown for the first time also to be isomorph invariant. In contrast, the Einstein and moment-based frequencies, and especially the bulk viscosity, ηb, show poor isomorphic collapse at low T but not surprisingly tend to an "inverse power" potential limiting value in the high T limit. In the case of the bulk viscosity, the significant departures from invariance arise from oscillations in the pressure autocorrelation function at intermediate times, which scale for inverse power potential systems but not for the LJ case, at least in part, as the pressure and bulk elastic moduli are not isomorph invariant.
Xu Y, Balint D, Dini D, 2019, A new hardness formula incorporating the effect of source density on indentation response: a discrete dislocation plasticity analysis, Surface and Coatings Technology, Vol: 374, Pages: 763-773, ISSN: 0257-8972
Planar discrete dislocation plasticity (DDP) calculations that simulate thin single crystal films bonded to a rigid substrate indented by a rigid wedge are performed for different values of film thickness and dislocation source density. As in prior studies, an indentation size effect (ISE) is observed when indentation depth is sufficiently small relative to the film thickness. Thedependence of the ISE on dislocation source density is quantified in this study, and a modified form of the scaling law for the dependence of hardness on indentation depth, first derived by Nix and Gao, is proposed, which is valid over the entire range of indentation depths and correlates the length scale parameter with the average dislocation source spacing. Nanoindentation experimental data from the literature are fitted using this formula, which further verifies the proposed scaling of indentation pressure on dislocation source density.
Biancofiore L, Giacopini M, Dini D, 2019, Interplay between wall slip and cavitation: A complementary variable approach, Tribology International, Vol: 137, Pages: 324-339, ISSN: 0301-679X
In this work a stable and reliable numerical model based on complementary variables is developed to study lubricated contacts characterised by slip at one or both surfaces and in the presence of cavitation. This model can be used to predict surface behaviour when cavitation induced by e.g. the presence of surface texture, slip, or a combination of the two is encountered, with varying surface parameters. For this purpose, two different algorithms are coupled to predict the formation of cavitation, through a mass-conserving formulation, and the presence of slip at the wall. The possible slippage is described by a limiting shear criterion formulated using a Tresca model. To show the flexibility of our model, several bearing geometries have been analysed, such as a twin parabolic slider, a cosine profile used to mimic a bearing, and a pocketed slider bearing employed to study the effect of surface texture. We observe that the lubrication performance (i.e. low friction coefficient) can be improved by using materials that promote slippage at the moving wall. The location of the slippage region can be optimised to find the lowest value of friction coefficient. Our theoretical developments and numerical implementation are shown to produce useful guidelines to improve and optimise the design of textured superoleophobic surfaces in the presence of lubricated contacts.
Vidotto M, Botnariuc D, De Momi E, et al., 2019, A computational fluid dynamics approach to determine white matter permeability, Biomechanics and Modeling in Mechanobiology, Vol: 4, Pages: 1111-1122, ISSN: 1617-7940
Glioblastomas represent a challenging problem with an extremely poor survival rate. Since these tumour cells have a highly invasive character, an effective surgical resection as well as chemotherapy and radiotherapy is very difficult. Convection-enhanced delivery (CED), a technique that consists in the injection of a therapeutic agent directly into the parenchyma, has shown encouraging results. Its efficacy depends on the ability to predict, in the pre-operative phase, the distribution of the drug inside the tumour. This paper proposes a method to compute a fundamental parameter for CED modelling outcomes, the hydraulic permeability, in three brain structures. Therefore, a bidimensional brain-like structure was built out of the main geometrical features of the white matter: axon diameter distribution extrapolated from electron microscopy images, extracellular space (ECS) volume fraction and ECS width. The axons were randomly allocated inside a defined border, and the ECS volume fraction as well as the ECS width maintained in a physiological range. To achieve this result, an outward packing method coupled with a disc shrinking technique was implemented. The fluid flow through the axons was computed by solving Navier–Stokes equations within the computational fluid dynamics solver ANSYS. From the fluid and pressure fields, an homogenisation technique allowed establishing the optimal representative volume element (RVE) size. The hydraulic permeability computed on the RVE was found in good agreement with experimental data from the literature.
Yu M, Evangelou S, Dini D, 2019, Position control of parallel active link suspension with backlash, IEEE Transactions on Industrial Electronics, Vol: 67, Pages: 4741-4751, ISSN: 0278-0046
In this paper, a position control scheme for the novel Parallel Active Link Suspension (PALS) with backlash is developed to enhance the vehicle ride comfort and road holding. A PALS-retrofitted quarter car test rig is adopted, with the torque flow and backlash effect on the suspension performance analyzed. An elastic linear equivalent model of the PALS-retrofitted quarter car, which bridges the actuator position and the equivalent force between the sprung and unsprung masses, is proposed and mathematically derived, with both the geometry and backlash nonlinearities compensated. A position control scheme is then synthesized, with an outer-loop H∞ control for ride comfort and road holding enhancement and an inner-loop cascaded proportional-integral control for the reference position tracking. Experiments with the PALS-retrofitted quarter car test rig are performed over road cases of a harmonic road, a smoothed bump and frequency swept road excitation. As compared to a conventional torque control scheme, the newly proposed position control maintains the performance enhancement by the PALS, while it notably attenuates the overshoot in the actuator’s speed variation, and thereby it benefits the PALS with less power demand and less suspension deflection increment.
Zhan W, Rodriguez y Baena F, Dini D, 2019, Effect of tissue permeability and drug diffusion anisotropy on convection-enhanced delivery, Drug Delivery, Vol: 26, Pages: 773-781, ISSN: 1071-7544
Although convection-enhanced delivery (CED) can successfully facilitate a bypass of the blood brain barrier, its treatment efficacy remains highly limited in clinic. This can be partially attributed to the brain anisotropic characteristics that lead to the difficulties in controlling the drug spatial distribution. Here, the responses of six different drugs to the tissue anisotropy are examined through a parametric study performed using a multiphysics model, which considers interstitial fluid flow, tissue deformation and interlinked drug transport processes in CED. The delivery outcomes are evaluated in terms of the penetration depth and delivery volume for effective therapy. Simulation results demonstrate that the effective penetration depth in a given direction can be improved with the increase of the corresponding component of anisotropic characteristics. The anisotropic tissue permeability could only reshape the drug distribution in space but has limited contribution to the total effective delivery volume. On the other hand, drugs respond in different ways to the anisotropic diffusivity. The large delivery volumes of fluorouracil, carmustine, cisplatin and doxorubicin could be achieved in relatively isotropic tissue, while paclitaxel and methotrexate are able to cover enlarged regions into anisotropic tissues. Results obtained from this study serve as a guide for the design of CED treatments.
Yu M, Cheng C, Evangelou S, et al., 2019, Robust Control for a Full-Car Prototype of Series Active Variable Geometry Suspension, 2019 IEEE Conference on Decision and Control (CDC)
Ayestarán Latorre C, Ewen JP, Gattinoni C, et al., 2019, Simulating surfactant-iron oxide interfaces: from density functional theory to molecular dynamics, The Journal of Physical Chemistry B, Vol: 123, Pages: 6870-6881, ISSN: 1520-6106
Understanding the behaviour of surfactant molecules on iron oxide surfaces is important for many industrial applications. Molecular dynamics (MD) simulations of such systems have been limited by the absence of a force-field (FF) which accurately describes the molecule-surface interactions. In this study, interaction energies from density functional theory (DFT) + U calculations with a van der Waals functional are used to parameterize a classical FF for MD simulations of amide surfactants on iron oxide surfaces. The Original FF, which was derived using mixing rules and surface Lennard-Jones (LJ) parameters developed for nonpolar molecules, were shown to significantly underestimate the adsorption energy and overestimate the equilibrium adsorption distance compared to DFT. Conversely, the Optimized FF showed excellent agreement with the interaction energies obtained from DFT calculations for a wide range of surface coverages and molecular conformations near to and adsorbed on α-Fe2O3(0001). This was facilitated through the use of a Morse potential for strong chemisorption interactions, modified LJ parameters for weaker physisorption interactions, and adjusted partial charges for the electrostatic interactions. The Original FF and Optimized FF were compared in classical nonequilibrium molecular dynamics (NEMD) simulations of amide molecules confined between iron oxide surfaces. When the Optimized FF was employed, the amide molecules were pulled closer to the surface and the orientation of the headgroups was more similar to that observed in the DFT calculations compared to the Original FF. The Optimized FF proposed here facilitates classical MD simulations of anhydrous amide-iron oxide interfaces in which the interactions are representative of accurate DFT calculations.
Ferretti A, Giacopini M, Dini D, et al., 2019, Experimental measurement of roughness data and evaluation of Greenwood/Tripp parameters for the elastohydrodynamic analysis of a conrod small-end/piston pin coupling, SAE Technical Papers, Pages: 2019-24-0081-2019-24-0081, ISSN: 0148-7191
Hu S, Cao X, Reddyhoff T, et al., 2019, Three-dimensional printed surfaces inspired by bi-Gaussian stratified plateaus, ACS Applied Materials and Interfaces, Vol: 11, Pages: 20528-20534, ISSN: 1944-8244
Wettability of artificial surfaces is attracting increasing attention for its relevant technological applications. Functional performance is often achieved by mimicking the topographical structures found in natural flora and fauna; however, surface attributes inspired by geological landscapes have so far escaped attention. We reproduced a stratified morphology of plateaus with a bi-Gaussian height distribution using a three-dimensional direct laser lithography. The plateau-inspired artificial surface exhibits a hydrophobic behavior even if fabricated from a hydrophilic material, giving rise to a new wetting mechanism that divides the well-known macroscopic Wenzel and Cassie states into four substates. We have also successfully applied the plateau-inspired structure to droplet manipulation.
Ebrahimi M, Balint D, Sutton A, et al., 2019, A discrete crack dynamics model of toughening in brittle polycrystalline material by crack deflection, Engineering Fracture Mechanics, Vol: 214, Pages: 95-111, ISSN: 0013-7944
This paper focuses on the study of the effect of the interfacial strength of grain boundaries and elliptical inclusions on crack path deflection. The method is developed to channel a crack into a toughening configuration (arrays of elliptical holes and inclusions are considered) in order to obtain the optimised microstructure required to enhance fracture toughness through different mechanisms. The proposed technique is shown to reproduce experimental crack propagation paths in various configurations and is capable of capturing the effect of that variation of the GB and the inclusion interfacial strength; it provides a powerful tool to understand the interplay between microstructural features and improve materials performance.
Sufian A, Knight C, O'Sullivan C, et al., 2019, Ability of a pore network model to predict fluid flow and drag in saturated granular materials, Computers and Geotechnics, Vol: 110, Pages: 344-366, ISSN: 0266-352X
The local flow field and seepage induced drag obtained from Pore Network Models (PNM) is compared to Immersed Boundary Method (IBM) simulations, for a range of linear graded and bimodal samples. PNM were generated using a weighted Delaunay Tessellation (DT), along with the Modified Delaunay Tessellation (MDT) which considers the merging of tetrahedral Delaunay cells. Two local conductivity models are compared in simulating fluid flow in the PNM. The local pressure field was very accurately captured, while the local flux (flow rate) exhibited more scatter and sensitivity to the choice of the local conductance model. PNM based on the MDT clearly provided a better correlation with the IBM. There was close similarity in the network shortest paths, indicating that the PNM captures dominant flow channels. Comparison of streamline profiles demonstrated that local pressure drops coincided with the pore constrictions. A rigorous validation was undertaken for the drag force calculated from the PNM by comparing with analytical solutions for ordered array of spheres. This method was subsequently applied to all samples, and the calculated force was compared with the IBM data. Linear graded samples were able to calculate the force with reasonable accuracy, while the bimodal samples exhibited slightly more scatter.
Rosenkranz A, Costa HL, Profito F, et al., 2019, Influence of surface texturing on hydrodynamic friction in plane converging bearings - An experimental and numerical approach, Tribology International, Vol: 134, Pages: 190-204, ISSN: 0301-679X
The frictional behaviour of plane converging bearings was experimentally and numerically studied for four texture geometries fabricated by ultra-short pulse laser texturing (single pocket, line-, cross- and dot-like texture) and convergence ratios under full-film lubrication in the presence of thick oil films (up to 100 μm). Regarding the experiments, small variations in the spread of results between different textures and a general improvement over the untextured reference can be observed. Numerical simulations help to clarify the expected variations and conditions under which these occur. For high convergences, the simulations demonstrated that textures are beneficial for friction reduction, regardless of load and relative texture's position. For low convergences, a significant friction reduction occurs for textures being located at the bearing's inlet.
Shen L, Denner F, Morgan N, et al., 2019, Transient structures in rupturing thin-films: Marangoni-induced symmetry-breaking pattern formation in viscous fluids
In the minutes immediately preceeding the rupture of a soap bubble,distinctive and repeatable patterns can be observed. These quasi-stabletransient structures are associated with the instabilities of the complexMarangoni flows on the curved thin film in the presence of a surfactantsolution. Here, we report a generalised Cahn-Hilliard-Swift-Hohenberg modelderived using asymptotic theory which describes the quasi-elastic wrinklingpattern formation and the consequent coarsening dynamics in a curvedsurfactant-laden thin film. By testing the theory against experiments on soapbubbles, we find quantitative agreement with the analytical predictions of thenucleation and the early coarsening phases associated with the patterns. Ourfindings provide fundamental physical understanding that can be used to(de-)stabilise thin films in the presence of surfactants and have importantimplications for both natural and industrial contexts, such as the productionof thin coating films, foams, emulsions and sprays.
Heyes D, Smith ER, Dini D, 2019, Shear stress relaxation and diffusion in simple liquids by molecular dynamics simulations: Analytic expressions and paths to viscosity, The Journal of Chemical Physics, Vol: 150, ISSN: 0021-9606
The results are reported of an equilibrium molecular dynamics simulation study of the shear viscosity, η, and self-diffusion coefficient, D, of the Lennard-Jones liquid using the Green-Kubo (GK) method. Semiempirical analytic expressions for both GK time correlation functions were fitted to the simulation data and used to derive analytic expressions for the time dependent diffusion coefficient and shear viscosity, and also the correlation function frequency transforms. In the case of the shear viscosity for a state point near the triple point, a sech function was found to fit the correlation function significantly better than a gaussian in the ballistic short time regime. A reformulation of the shear GK formula in terms of a time series of time integrals (“viscuits”) and contributions to the viscosity from components based on the initial stress (“visclets”) enable the GK expressions to be recast in terms of probability distributions which could be used in coarse grained stochastic models of nanoscale flow. The visclet treatment shows that stress relaxation is statistically independent of the initial stress for equilibrium and metastable liquids, suggesting that shear stress relaxation in liquids is diffusion controlled. By contrast, the velocity autocorrelation function is sensitive to the initial velocity. Weak oscillations and a plateau at intermediate times originate to a greater extent from the high velocity tail of the Maxwell-Boltzmann velocity distribution. Simple approximate analytic expressions for the mean square displacement and the self Van Hove correlation function are also derived.
Wu P-J, Masouleh MI, Paterson C, et al., 2019, Detection of proteoglycan loss from articular cartilage using Brillouin microscopy, with applications to osteoarthritis, Biomedical Optics Express, Vol: 10, Pages: 2457-2466, ISSN: 2156-7085
The degeneration of articular cartilage (AC) occurs in osteoarthritis (OA), which is a leading cause of pain and disability in middle-aged and older people. The early disease-related changes in cartilage extra-cellular matrix (ECM) start with depletion of proteoglycan (PG), leading to an increase in tissue hydration and permeability. These early compositional changes are small (<10%) and hence difficult to register with conventional non-invasive imaging technologies (magnetic resonance and ultrasound imaging). Here we apply Brillouin microscopy for detecting changes in the mechanical properties and composition of porcine AC. OA-like degradation is mimicked by enzymatic tissue digestion, and we compare Brillouin microscopy measurements against histological staining of PG depletion over varying digestion times and enzyme concentrations. The non-destructive nature of Brillouin imaging technology opens new avenues for creating minimally invasive arthroscopic devices for OA diagnostics and therapeutic monitoring.
Hu S, Reddyhoff T, Puhan D, et al., 2019, Bi-Gaussian stratified wetting model on rough surfaces, Langmuir, Vol: 35, Pages: 5967-5974, ISSN: 0743-7463
Wetting mechanisms on rough surfaces were understood from either a monolayer or a multiscale perspective. However, it has recently been shown that the bi-Gaussian stratified nature of real surfaces should be accounted for when modeling mechanisms of lubrication, sealing, contact, friction, acoustic emission, and manufacture. In this work, a model combining Wenzel and Cassie theories was put forward to predict the static contact angle of a droplet on a bi-Gaussian stratified surface. The model was initially applied to numerically simulated surfaces and subsequently demonstrated on hydrophilic steel and hydrophobic self-assembled monolayer specimens with preset bi-Gaussian stratified topographies. In the Wenzel state, both the upper and the lower surface components are fully wetted. In the Cassie state, the upper component is still completely wetted, while the lower component serves as gas traps and reservoirs. By this model, wetting evolution was assessed, and the existence of different wetting states and potential state transitions was predicted.
Fatti G, Righi MC, Dini D, et al., 2019, First-principles insights into the structural and electronic properties of polytetrafluoroethylene in its high-pressure phase (form III), Journal of Physical Chemistry C, Vol: 123, Pages: 6250-6255, ISSN: 1932-7447
Polytetrafluoroethylene (PTFE), commercially known as Teflon, is one the most effective insulating polymers for a wide range of applications because of its peculiar electronic, mechanical, and thermal properties. Several studies have attempted to elucidate the structural and electronic properties of PTFE; however, some important aspects of its structural and electronic characteristics are still under debate. To shed light on these fundamental features, we have employed a first-principles approach to optimize the two coexisting PTFE structures (monoclinic and orthorhombic) at high pressure by using the characteristic zigzag planar chain configuration. Our electronic analysis of the optimized structures shows charge transfer from carbons to fluorines, supporting the PTFE electronegative character. In addition, band structure calculations show that the band gap is estimated to be around 5 eV, which correlates with previous studies. Moreover, the analysis of the valence and conduction states reveals an intrachain and an interchain character of the charge distribution, suggesting additional insights into the PTFE electronic properties.
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