Effect Of Surface Topology Research Articles

Stiffness and surface topology of silicone implants competitively mediate inflammatory responses of macrophages and foreign body response

Adverse inflammatory responses, dominated by macrophages, that are induced by physical cues of silicone implants can heavily damage the life quality of patients via causing fibrosis and device failure. As stiffness and surface topology affect macrophages at the same time, the competition or partnership among physical cues against the regulation of macrophages is still ambiguous. Herein, a series of PDMS implants with different stiffness at ∼ MPa and surface topology at tens of micrometers were fabricated to investigate the relationship, the regulation rule, and the underlying mechanism of the two physical cues against the inflammatory responses of M1 macrophages. There is a competitive rule: surface topology could suppress the inflammatory responses of M1 macrophages in the soft group but did not have the same effect in the stiff group. Without surface topology, lower stiffness unexpectedly evoked stronger inflammatory responses of M1 macrophages. Implanting experiments also proved that the competitive state against mediating in vivo immune responses and the unexpected inflammatory responses. The reason is that stiffness could strongly up-regulate focal adhesion and activate the MAPK/NF-κB signaling axis to evoke inflammatory responses, which could shield the effect of surface topology. Therefore, for patient healthcare, it is crucial to prioritize stiffness while not surface topology at MPa levels to minimize adverse reactions.

Effect of surface topology and wettability on impacting droplet dynamics at moderate Reynolds numbers

Effect of surface topology and wettability on impacting droplet dynamics at moderate Reynolds numbers

Exploring the effects of micro-nano surface topography on MG63 osteoblast-like cell responses: An in vitro study

The osseointegration property of dental and bone implants is a crucial factor for proper healing, and is entirely influenced by the surface characteristics, including surface chemistry and roughness. However, the molecular mechanisms for osteoconductivity remain unclear. This study aimed to investigate the effective cellular interactions and stimulatory effect of surface topology on the differentiation of osteoblast-like cells using in-vitro cell culture. Three different substrates, including micro (MS), nano (NS), and combined micro-nano structures (MNS), were used to evaluate the interaction between cells and surface topography. The fabricated membranes were characterized with FESEM for pore study and XRD analysis to identify the Aluminum oxide. The cell count significantly decreased for electropolished (EP) and microstructure (MS) substrates. The expression level of osteogenesis-related genes during differentiation, including Runt-related transcription factor 2 (Runx2), type I Collagen (Col-I), and Osteocalcin (OC) was determined by real-time PCR. The results showed that MG63 osteoblast-like cells cultured on the MNS and NS substrates had significantly higher expression levels of these genes than those cultured on the MS. Additionally, flow cytometry results showed that F-actin levels were higher in MG63 cells cultured on NS and MNS substrates than those cultured on MS. The desirable biological response of MG63 cells to MNS substrates suggests that electrochemical anodization after acid etch and powder blasting treatments is a possible process for high-grade osseointegration in-vivo.

Scaling of the roughness effects in turbulent flows over systematically-varied irregular rough surfaces

To clarify the effects of surface topology on the scaling of roughness effects, we conduct experiments on turbulent rough-walled channel flows from transitionally to fully rough regimes. We considered three-dimensional irregular rough surfaces with different effective slope ES, skewness factor Sk, and fixed roughness height scales. The ES values are varied from 0.09 to 0.72 for positively and negatively skewed surfaces with Sk=±0.4. It is revealed that the transitional behavior to the fully rough regime is not influenced by Sk, but rather by ES. The transition to the fully rough regime for surfaces with ES≥0.18 is insensitive to the ES values, whereas wavy surfaces with ES=0.09 lead to a moderate transition. The equivalent sand-grain roughness ks steeply increases with increasing ES values from 0.09 to 0.36, whereas a further increase in the ES value does not significantly influence ks. It is also found that positively skewed surfaces with Sk=+0.4 yield larger ks values compared to surfaces with Sk=−0.4; this Sk effect is more pronounced for wavy surfaces with small ES values.

Wettability of soft PLGA surfaces predicted by experimentally augmented atomistic models

A challenging topic in surface engineering is predicting the wetting properties of soft interfaces with different liquids. However, a robust computational protocol suitable for predicting wettability with molecular precision is still lacking. In this article, we propose a workflow based on molecular dynamics simulations to predict the wettability of polymer surfaces and test it against the experimental contact angle of several polar and nonpolar liquids, namely water, formamide, toluene, and hexane. The specific case study addressed here focuses on a poly(lactic-co-glycolic acid) (PLGA) flat surface, but the proposed experimental-modeling protocol may have broader fields of application. The structural properties of PLGA slabs have been modeled on the surface roughness determined with microscopy measurements, while the computed surface tensions and contact angles were validated against standardized characterization tests, reaching a discrepancy of less than 3% in the case of water. Overall, this work represents the initial step toward an integrated multiscale framework for predicting the wettability of more complex soft interfaces, which will eventually take into account the effect of surface topology at higher scales and synergically be employed with experimental characterization techniques.Impact statementControlling the wettability of surfaces has important implications for energy (e.g., self-cleaning solar panels), mechanical (e.g., enhanced heat transfer), chemical (e.g., fluids separation), and biomedical (e.g., implants biocompatibility) industries. Wetting properties arise from a combination of chemical and physical features of surfaces, which are inherently intertwined and multiscale. Therefore, tailoring wettability to target functionalities is a time-intensive process, especially if relying on a trial-and-error approach only. This becomes even more challenging with soft materials, since their surface configuration depends on the solid-liquid interactions at the molecular level and could not be defined a priori. The improved accuracy of atomistic models allows detailing how the effective properties of materials arise from their nanoscale features. In this article, we propose and validate a new molecular dynamics protocol for assessing the wettability of soft interfaces with polar and nonpolar liquids. The prediction capabilities of simulations are augmented by a close comparison with microscopy and contact angle experiments. Since smooth copolymer surfaces are considered, here the effort mainly focuses on the effect of chemical features on wettability. In perspective, the proposed atomistic in silico approach could be coupled with computational models at higher scales to include the effect of surface microstructures, eventually easing the development of multi-scale surfaces with tunable wettability.Graphical abstract

Effect of Surface Topology on the Apparent Thermal Diffusivity of Thin Samples at LFA Measurements.

This paper deals with the problem of the influence of surface topography on the results of thermal diffusivity measurements when determined using the instantaneous surface heat source method, also called the pulse method. The analysis was based on numerical tests carried out using Comsol Multiphysics software. The results of experimental investigations on the actual material structure using an electron microscope, an optical microscope and a profilometer were used to develop a numerical model. The influence of the non-uniformity of the surface of the tested sample on the determined values of half-time of the thermal response of the sample’s rough surface to the impulse forcing on the opposing flat surface was determined by developing the data for simulated measurements. The effect of the position of the response data reading area on the obtained simulation results was also analyzed. The obtained results can be used to improve the accuracy of experimental heat transfer studies performed on thin-film engineering structures depending on the uniformity and parallelism of the material applied to engineering structures. The difference in half-life determination error results for various analyzed models can be as high as 16.7%, depending on the surface from which the responses of the heating impulse are read. With an equivalent model in which 10% of the material volume corresponds to the rough part as a single inclusion, hemisphere, the error in determining thermal diffusivity was equal to 3.8%. An increase in the number of inclusions with smaller weight reduces an error in the determination of thermal diffusivity, as presented in the paper.

External Validity of Calibrated Measurements from a Laser-Projection Transnasal Fiberoptic High-Speed Videoendoscopy System

Evidence-based practice and precision medicine can significantly benefit from the ability to perform calibrated spatial measurements (eg, mm) from endoscopic images. However, calibrated measurements are not readily available from laryngeal images. Laser-projection endoscopes can provide the required information for performing calibrated spatial measurements, but their applications require a process known as calibration. During calibration, a set of benchtop recordings are used to determine the effect of confounding factors of spatial measurements, and also to learn their proper compensation strategies. Calibration benchtop recordings are acquired from flat surfaces and at a perpendicular imaging angle which is significantly different from in-vivo situations, where a three-dimensional (3D) surface gets recorded at a semi-unknown imaging angle. The aim of this study was to quantify changes in calibrated vertical and horizontal measurement accuracies as we move from the controlled condition of calibration to more realistic and uncontrolled settings. A flat surface was positioned in front of a calibrated laser-projection transnasal fiberoptic endoscope at different working distances and imaging angles. Calibrated vertical and horizontal measurement errors were computed from each condition. Multiple linear regression analyses were used to quantify the dependence of vertical and horizontal measurement errors on the imaging angle and working distance. Next, a 3D-printed surface was positioned in front of the laser-projection endoscope at different working distances. Calibrated vertical and horizontal measurement errors were computed from each condition and then they were compared to measurement errors from a flat surface positioned at comparable working distances. The outcome of analyses supported a significant effect of imaging angle on calibrated vertical measurement accuracy, while no significant effect of imaging angle on calibrated horizontal measurement accuracy was established. Additionally, the result of multiple linear regression analyses showed that the coefficient of imaging angle was two times larger than the working distance, which further highlights the significant effect of imaging angle on vertical measurement accuracy. Comparing the magnitude of calibrated vertical and horizontal measurement errors between the 3D surface and a flat surface suggested a significant effect of surface topology on calibrated measurement accuracies. The mean percent magnitude of error of vertical and horizontal measurement errors from the 3D surface were respectively around 6% and 11%, at most working distances, which are acceptable for many applications. However, the significant effect of imaging angle and surface topology on measurement errors highlights the need for further research on these confounding factors. It also suggests that significant improvements in measurement accuracies may be achieved if these factors are properly accounted for during the calibration process. Last but not least, this study highlights the need for the evaluation of laser-projection endoscopes in uncontrolled and more realistic settings. Specifically, evaluations of laser-projection endoscopes in very controlled settings could significantly overestimate their accuracies and hence it will not represent their actual performances during in-vivo data acquisitions.

Improved in-situ calibration applied to infrared thermography under high angles of view

Infrared Thermography is a capable tool for resolving surface temperatures with high resolution and accuracy, even on complex surfaces. With current calibration techniques, the surface emissivity needs to be constant and close to unity to ensure a low calibration error. This is commonly achieved with special surface coatings. These coatings however, show a reduction of emissivity with increasing angle of view. Performing a state of the art in situ calibration with temperature calibration points (e.g. thermocouples) thus can lead to a measurement error on curved surfaces when assuming constant emissivity. In this paper, an adapted calibration procedure is presented considering the effects of surface topology. The process is closely linked to the basic in situ calibration with only few additional steps needed. If the angle of view θ(e. g. the camera position) is known in the experiment, this new procedure allows a correction of the induced effects and thus a reduction of measurement uncertainty. This can be achieved by only using a single additional in situ calibration pair. Data from a validation experiment is presented for two different camera systems (MWIR, LWIR), showing that the error can be reduced from ΔTS,rel>5% to ΔTS,rel<1.5% at θ≈65°, allowing the acquisition of temperature data on complex surfaces. With exact emissivity functions and camera positions, temperature acquisition can even be performed up to angles of view of θ≈80° with tolerable error.

Effect of surface topology on the galloping instability of rectangular cylinders

The effect of geometry on the transverse galloping instability of rectangular cylinders was studied experimentally for Reynolds numbers between 1,000 and 10,000. In particular, a comparison was made between a rectangular cylinder with rounded corners and a smooth surface, and the same baseline geometry with added surface topology synthesized from two-dimensional Fourier-modes. The effects of the topology amplitude and wavelength were investigated. From measurements of the normal (galloping direction) force coefficient variation with angle-of-attack, it was found that the added surface topology generally had a destabilizing effect relative to the smooth cylinder. At the lowest Reynolds number, the smooth cylinder was stable, while the cylinders with added topology were unstable with respect to galloping. For Reynolds numbers from 5,000 to 10,000, the added topology did not cause a similar instability. However, there was a monotonic increase in the slope of the normal force coefficient at zero angle-of-attack with increasing surface height amplitude, thus moving the geometry closer to the instability threshold. This effect diminished as Reynolds number increased. Overall, for the range of parameters investigated herein, whenever the cylinders with topology were unstable to soft or hard galloping, the larger topology exhibited more favorable galloping resistance characteristics than the one with smaller topology. Topology wavelength was found to have no effect on the galloping behavior of the cylinder for Reynolds numbers below 7500, and a moderate increase in the normal force slope at zero angle of attack with decreasing wavelength for larger Reynolds numbers. The latter effect was associated with an increase in the angle of attack at which the cylinder could become unstable to hard galloping.

Elastic wave propagation in structures with triply periodic minimal surfaces

We study the elastic wave propagation behavior of triply periodic minimal surface structures. Triply periodic minimal surfaces (TPMS) are surfaces with periodicity in three independent directions and a mean surface curvature of zero. Here, we apply the finite element method to obtain the dispersion curves of six different TPMS structures: Schwarz' P, Schwarz' D, Gyroid, Fischer-Koch's S, Schoen's I-WP, and Schoen's F-RD. The dispersion curves are obtained by modeling their respective unit cells, appropriately applying the Floquet-Bloch periodic boundary condition, and then performing an eigenfrequency analysis while sweeping over the boundaries of their respective irreducible Brillouin zones. We then classify each band according to their respective propagation modes (P- or S-waves) and study the effect of surface topology on each mode. Finally, we discuss the generation of directional and polarized bandgaps in these structures.

PLGA Microspheres Coated with Cancer Cell-Derived Vesicles for Improved Internalization into Antigen-Presenting Cells and Immune Stimulation.

Microspheres (MS; 1-3 μm) with different degrees of surface roughness were prepared to assess the effects of surface topology on internalization into antigen-presenting cells (APCs; macrophages and dendritic cells). In this study, we demonstrated that the intracellular uptake of MS is readily enhanced by surface modification with nanoparticles or cancer cell-derived vesicles (VE) to modulate their surface topology. MS coated with nanovesicles (MS-VE) with high surface roughness was more successfully and efficiently engulfed by APCs, compared with bare MS and those with low surface roughness. Incorporated MPLA within MS-VEs (M/MS-VE) triggered greatly elevated release of immune stimulating cytokines, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α), from macrophages and dendritic cells, compared to free MPLA. Taken together, this MS-VE could serve as a platform system for the delivery of immune stimulators and antigens to APCs with negligible toxicity.

Icephobic performance of superhydrophobic coatings: A numerical analysis

Understanding the mechanism of cloud-sized particles impact and freezing is crucial to find viable solutions to prevent ice accumulation on critical aerodynamic surfaces such as aircraft wing or nacelle. It has been reported that superhydrophobic surfaces (SHS) have promising anti-icing properties due to their excellent water-repellent characteristics. However, due to the complexity of the freezing phenomenon on superhydrophobic surfaces, the anti-icing performance of such surfaces has not been fully understood. A multi-region multiphase flow solver including phase change has been developed to model the icing of a micro-droplet as it impinges on a superhydrophobic substrate with a given thickness, texture, and solid material thermal properties. The Navier-Stokes equation expressing the flow distribution of the liquid and the gas, coupled with the volume of fluid (VOF) method for tracking the liquid-gas and liquid-solid interfaces, was solved numerically using the finite volume methodology. The superhydrophobic morphology is modeled through a series of micro-structured arrays with squared cross-sectional pillars. As such, the thermal contact resistance is inherently accounted by the inclusion of air pockets underneath the micro-droplet. Consequently, the direct effect of surface topology and thermal properties on droplet maximum spreading diameter, penetration to the surface asperities, contact time, and the freezing onset have been investigated. Finally, icephobicity of two similar SHSs with various thermal properties were compared.

Significantly enhanced convective heat transfer through surface modification in nanochannels

The subject of convective heat transfer in micro-/nano-scale channels is of utmost importance for the effective cooling of small-scale electronic devices with high power density. The overall heat convection in these channels largely depends on interfacial (wall-fluid) thermal transport. In this work, we demonstrate that a carefully designed surface topology can enhance heat dissipation in nanochannels. Specifically, we found that both uniformly and randomly distributed surface roughness can substantially increase the overall heat transfer between the wall and fluid in the nanochannels. Moreover, we reveal that depositing a coating layer, of which the vibrational density of states bridge those of the walls and the flowing fluid, can significantly enhance wall-fluid interfacial heat transfer. This work reveals the critical effect of surface topology and material choice of the channel wall on heat dissipation in nanochannels, which is important for the cooling of small-scale devices.

Effect of surface topology on the wettability of superhydrophobic surfaces

In this paper, we develop a numerical model capable of predicting the apparent contact angle and the wetting state of liquid droplets on superhydrophobic surfaces using Surface Evolver. Specifically, our work investigates the effect of microscopic surface topology on contact angle and the state of wettability. Accordingly, surfaces with four different pillar geometries were investigated: square, cylindrical, parabolic, and conical. The performance of superhydrophobic surfaces was also tested for different solid-liquid material combinations. Our results reveal that cylindrical pillars prevent the transition from Cassie-Baxter to Wenzel wetting state at lower Young contact angles. Furthermore, superhydrophobic surfaces lose their repellency against organic liquids. Nonetheless, a surface with inverted conical pillars is both superhydrophobic and superoleophobic.

A Novel Approach to Increase Dynamic Fracture Toughness of Additively Manufactured Polymer

An experimental study is performed to investigate the dynamic fracture of additive manufactured Acrylonitrile Butadiene Styrene (ABS). A single edge notched bending (SENB) specimen with three orientations, namely horizontal builds with 45°/−45° (H45), 0°/90° (H90) raster orientations, and vertical builds with layers perpendicular to the pre-crack (V0) are considered for this study. In addition, a novel toughening mechanism is explored by changing the surface topology to deflect the crack paths. A modified split Hopkinson pressure bar with a copper pulse shaper (to increase the raising time of incident loading pulse) is used to conduct a three-point bend impact experiment to characterize the dynamic fracture initiation toughness and crack dynamics of 3D printed specimens. Real-time crack initiation and propagation is captured by using a high-speed video camera. Using the load history diagram, accurate fracture initiation load is found to determine dynamic fracture initiation toughness. Fracture initiation toughness is increased by 138% for a V0 specimen configuration compared to H90. Three different sized circular patterns (with diameters of 1, 1.75 and 2.5 mm) and a square pattern (with a length of 1.53 mm) are considered to observe the effect of surface topology on the dynamic fracture initiation toughness. Introducing surface pattern to the specimen increases the fracture toughness by 58% as compared to specimens without surface pattern. Surface pattern also exhibits two steps of crack growth and decreases the initial crack propagation velocity significantly for all three orientations. Additionally, higher fracture initiation toughness is achieved with the increase in the size of the pattern and the change of the pattern shape.

Understanding the Effect of Surface Terrain on Pollution Transport around Gebeng Industrial Area

Objectives:Air pollution dispersion is greatly affected by the wind speed and direction. Most often the pollution dispersion from industrial area is not fully understood. In the present work, the effect of surface topology on the wind speed and atmospheric turbulent around the Gebeng industrial area in Pahang was studied using a Computational Fluid Dynamics (CFD) method. Methods/Statistical Analysis: The typical southeastern wind with a speed of about 1.3003 m/s corresponding to the actual speed of approximately 5 km/h was considered for validation. The turbulent flow was modelled using k-e model. The model was compared with the Laser Doppler Velocimetry (LDV) measurement onthe scale-down rig. Findings:The CFD prediction showed good agreementwithin 10% deviation with the experimental measurement via LDV. It was found that the plume of noxious gas driven by the eastern wind can affect the nearby residential area R2, whereas the western wind is affecting the residential area R1. In the presence of hill obstacle, the gas plume moves southward into the flat terrain. Application/ Improvements: Results from this work may be useful to understand the risk of air pollutant dispersion around Gebeng industrial area.

An accelerated buoyancy adhesion assay combined with 3-D morphometric analysis for assessing osteoblast adhesion on microgrooved substrata

An accelerated negative buoyancy method has been developed to assess cell adhesion strength. This method has been used in conjunction with 3-D morphometric analysis to understand the effects of surface topology on cell response. Aligned micro-grooved surface topographies (with a range of groove depths) were produced on stainless steel 316L substrates by laser ablation. An investigation was carried out on the effect of the micro-grooved surface topography on cell adhesion strength, cell and nucleus volumes, cell phenotypic expression and attachment patterns. Increased hydrophobicity and anisotropic wettability was observed on surfaces with deeper grooves. A reduction was noted in cell volume, projected areas and adhesion sites for deeper grooves, linked to lower cell proliferation and differentiation rates and also to reduced adhesion strength. The results suggest that the centrifugation assay combined with three-dimensional cell morphometric analysis has considerable potential for obtaining improved understanding of the cell/substrate interface.

Effect of Topology of Hydrophobic Surfaces on Their Wetting States by Coarse-grained Simulations

Researches have showed that there are two factors that can affect the wettability of solid surface: the chemical composition and the surface roughness. In this communication, coarse-grained molecular dynamics simulations based on BMW-Martini force field were used to study the effect of surface topology of hydrophobic surfaces on their wetting states. Simulation results show that the increase of surface roughness has little effect on the hydrophobicity of a hydrophobic surface, but does have effect on its wetting state. For the studied pillar spacing ranges (d≤4.7 nm), the wetting behavior of water droplets on hydrophobic surfaces with pillared structure is affected by two factors, i.e., pillar spacing and pillar height. For each pillar spacing, there exists a critical pillar height; a wetting transition from the Wenzel state to the Cassie-Baxter state on pillared hydrophobic surface can be observed, and the critical pillar height increases with the pillar spacing. Through a further analysis for the studied surfaces, we find that the wetting transition is related to the ratio of pillar spacing to pillar height, when the ratio is no more than 2, the Wenzel wetting state can be observed; while when the ratio exceeds 2, the Cassie-Baxter state can be observed. Through energy analysis, we find that the wetting transition is mainly dependent on the Van der Waals interaction. When the roughness of a surface is below the critical value, the interaction between the water droplet and surface is very strong, so that water droplet can easily enter into the space between pillars on the surface to form Wenzel state; however, when exceeding the critical value, the interaction between water droplets and surface is weakened, and water droplet is difficult to enter into the gaps, so a Cassie-Baxter state can be observed. This work could provide some guidance for the development of hydrophobic materials.

Investigating surface topology and cyclic‐RGD peptide functionalization on vascular endothelialization

The advantages of endothelialization of a stent surface in comparison with the bare metal and drug-eluting stents used today include reduced late-stent restenosis and in-stent thrombosis. In this article, we study the effect of surface topology and functionalization of tantalum (Ta) with cyclic-(arginine-glycine-aspartic acid-d-phenylalanine-lysine) (cRGDfK) on the attachment, spreading, and growth of vascular endothelial cells. Self-assembled nanodimpling on Ta surfaces was performed using a one-step electropolishing technique. Next, cRGDfK was covalently bonded onto the surface using silane chemistry. Our results suggest that nanotexturing alone was sufficient to enhance cell spreading, but the combination of a nanodimpled surfaces along with the cRGDfK peptide may produce a better endothelialization coating on the surface in terms of higher cell density, better cell spreading, and more cell-cell interactions, when compared to using cRGDfK peptide functionalization alone or nanotexturing alone. We believe that future research should look into how to implement both modifications (topographic and chemical modifications) to optimize the stent surface for endothelialization.

Fabrication and analysis of PMMA, ABS, PS, and PC superhydrophobic surfaces using the spray method

In this study, superhydrophobic surfaces were fabricated using a facile spraying technique with poly(methyl methacrylate) (PMMA), acrylonitrile butadiene styrene (ABS), polystyrene (PS) and polycarbonate (PC). Also, the surface energy was qualitatively analyzed via the water contact angle with respect to the spraying time and the sprayed position. Firstly, PMMA, ABS, PS and PC were dissolved by using solvents such as methyl chloride, methanol, THF (tetrahydrofuran), and methanol, respectively. After that, the dissolved polymer was sprayed onto a thin film of the same polymer for various spraying times. Nozzle size, pressure and spraying distance were fixed as 0.2 mm, 0.1 bar, and 100 mm, respectively, after several feasibility experiments. For the sprayed surfaces, the topology was analyzed with scanning electron microscopy (SEM) and confocal microscopy, and the surface energy was qualitatively analyzed using the water-contactangle measurement. According to a quantitative analysis using the roughness factor and he Wenzel equation, all specimens could be assumed to be in a Wenzel state. To convert the Wenzel state into a Cassie-Baxster state by decreasing the surface energy of polymer-sprayed specimen, we treated the polymer-sprayed surfaces by using trichloro (1H, 1H, 2H, 2H-perfluorooctyl) silane. Consequently, non-sticky superhydrophobic surfaces having water contact angles greater than 155° and water sliding angles lower than 8° were fabricated. The water contact angle and the water sliding angle were measured by using a contact-angle-measuring device. In addition, a brief qualitative analysis of the effect of surface topology on the water sliding angle was conducted for the polymer-sprayed specimens.