Substrate Topography Research Articles

The Topography of Silica Films Modulates Primary Macrophage Morphology and Function

AbstractMacrophages are major contributors to the rejection of foreign materials introduced to living tissues. Given that cell‐surface interactions can have important effects on phagocytic capacity and cytokine production, changes in macrophage morphology have been reported for different materials and surface patterns. However, the details of how surface topography impacts morphology and function remain unclear. This study investigates whether changes in the surface topography of glassy substrates alter macrophage shape and modulate phagocytic function and the secretion of pro‐inflammatory cytokine IL‐6. The morphology of murine bone marrow–derived macrophages cultured on micro‐ and nanostructured SiO2 films is quantified through fractal analysis. It is observed that membrane protrusions increase on nanostructured surfaces and macrophages adopt unique star‐shaped morphologies on microstructures. Macrophages on both micro‐ and nanostructured surfaces display greater phagocytic capacity, compared to those on flat controls. In contrast, the secretion of pro‐inflammatory cytokine IL‐6 is not increased when cells are cultured on the structured surfaces. The diffusion of a transmembrane receptor is also measured, which reveals no impact of structuring or plasma treatment on receptor diffusion. Altogether, these data indicate that surface topography does not increase IL‐6 production or alter membrane mobility but can significantly impact phagocytosis.

Detection of in Situ Early Corrosion on Polymer-Coated Metal Substrates.

Protective coating systems (PCS) are a common and facile method to protect metal substrates from corrosion. The corrosion control performance of polymer-coated metal substrates is still predominantly evaluated by visual assessment. Unfortunately, for many decades, PCS material development and performance testing has basically been a complicated process of waiting to determine which coating, in relative terms, allows corrosion to occur first from an intentionally created breach through the coating. This type of testing provides only relative ratings between PCS performance. Electrochemical methods, such as electrochemical impedance spectroscopy, each have caveats and pitfalls for qualifying or quantifying polymer-coated metal substrates. When these data are studied carefully, these measurements result in many false positive and false negative results compared with real environmental testing and the paths to failure vary dramatically. The critical issue is that these methods do not result in a scientific basis for understanding either the pathway(s) or progressive milestones toward diminished PCS performance, failure, and the loss of substrate structural integrity for coated substrates. Data supports that ultimately all PCS fail to provide the necessary substrate protection. However, to make substantive gains, scientists and engineers require a rational basis to design, engineer, test, quantify, and/or estimate service life and remaining service life and repair future generations of PCS. Our research goal was to establish a quantifiable characterization protocol (CP) that directly detected, monitored, and ideally quantified the pathway(s) and important milestones of PCS corrosion spatially and temporally, with or without defects which related with testing and assessment variables regardless of environmental severity (real, laboratory, or accelerated). We report herein the CP and the results from an embedded pH-sensitive "turn-on" fluorescent probe blended with a simplified thermoplastic model PCS. The results support that the average-localized macroscopic pH is detected and tracked, and these "molecular titrations" result in values consistent with literature pH citations for premacroscopic corrosion processes, that is, before delamination and a detectable breach. The CPresults are an improvement over visual corrosion detection and yet proportional to the steel substrate corrosion. The CP results deliver extreme early detection (within minutes), spatial and temporal tracking, and potentially quantifiable performance differences for the pathways and milestones toward failure of coated substrates with validated sensitivity to variables such as defect versus defect-free films, blending solvent type(s) influence, differences from varied degrees of annealing relative to Tg (thermoplastic films), substrate topography, and preparation differences. The CP utilizes small sample areas (25 mm spheres) and gathers data in a manner designed to improve statistical relevancy, provide results within short timeframes using real-time testing, diminish materials-testing timelines, and connect results with laboratory, accelerated, and real environmental severity differences. The results support that the CP directly measured the earliest possible in situ corrosion processes using defect and defect-free simplified model PCS.

Controlled Spacing between Nanopatterned Regions in Block Copolymer Films Obtained by Utilizing Substrate Topography for Local Film Thickness Differentiation.

Various types of devices require hierarchically nanopatterned substrates, where the spacing between patterned domains is controlled. Ultraconfined films exhibit extreme morphological sensitivity to slight variations in film thickness when the substrate is highly selective toward one of the blocks. Here, it is shown that using the substrate's topography as a thickness differentiating tool enables the creation of domains with different surface patterns in a fully controlled fashion from a single, unblended block copolymer. This approach is applicable to block copolymers of different compositions and to different topographical patterns and thus opens numerous possibilities for the hierarchical construction of multifunctional devices.

Gallium‐Based Thin Films for Wearable Human Motion Sensors

Wearable electronic circuits based on the films of gallium and its alloys offer promising implementations in health monitoring and gaming sensing applications. However, the complex rheology of liquid metals makes it challenging to manufacture thin gallium‐based devices with reliable, reproducible, and stable properties over time. Herein, the surface coating and topography of silicone substrates are engineered to enable precisely defined, micrometer‐thick liquid metal patterns over large (>10 cm2) surface areas, and high design versatility. Control over the film microstructure meets manufacturing conditions that enable gallium films with a precise, repeatable, and durable electromechanical performance. The robustness and applicability of this technology in a virtual‐reality scenario is demonstrated by implementing thin, soft, and stretchable gallium‐based sensors to accurately monitor human hand kinematics.

Focal adhesion clustering drives endothelial cell morphology on patterned surfaces.

In many cell types, shape and function are intertwined. In vivo, vascular endothelial cells (ECs) are typically elongated and aligned in the direction of blood flow; however, near branches and bifurcations where atherosclerosis develops, ECs are often cuboidal and have no preferred orientation. Thus, understanding the factors that regulate EC shape and alignment is important. In vitro, EC morphology and orientation are exquisitely sensitive to the composition and topography of the substrate on which the cells are cultured; however, the underlying mechanisms remain poorly understood. Different strategies of substrate patterning for regulating EC shape and orientation have been reported including adhesive motifs on planar surfaces and micro- or nano-scale gratings that provide substrate topography. Here, we explore how ECs perceive planar bio-adhesive versus microgrooved topographic surfaces having identical feature dimensions. We show that while the two types of patterned surfaces are equally effective in guiding and directing EC orientation, the cells are considerably more elongated on the planar patterned surfaces than on the microgrooved surfaces. We also demonstrate that the key factor that regulates cellular morphology is focal adhesion clustering which subsequently drives cytoskeletal organization. The present results promise to inform design strategies of novel surfaces for the improved performance of implantable cardiovascular devices.

Control of etch pit formation for epitaxial growth of graphene on germanium

Graphene epitaxy on germanium by chemical vapor deposition is a promising approach to integrate graphene into microelectronics, but the synthesis is still accompanied by several challenges such as the high process temperature, the reproducibility of growth, and the formation of etch pits during the process. We show that the substrate cleaning by preannealing in molecular hydrogen, which is crucial to successful and reproducible graphene growth, requires a high temperature and dose. During both substrate cleaning and graphene growth, etch pits can develop under certain conditions and disrupt the synthesis process. We explain the mechanisms how these etch pits may form by preferential evaporation of substrate, how substrate topography is related to the state of the cleaning process, and how etch pit formation during graphene growth can be controlled by choice of a sufficiently high precursor flow. Our study explains how graphene can be grown reliably on germanium at high temperature and thereby lays the foundation for further optimization of the growth process.

Manipulating the sequences of block copolymer patterns on corrugated substrates

This paper describes manipulating the sequences of cylinder-forming block copolymer patterns on corrugated substrates. Upon thermal annealing, the topographic corrugation of the substrate generates a spontaneous flow-field of the block copolymer and induces thickness-dependent microdomains. The corrugation gradient has some range of surface roughness characterized by its topographic parameters. When the substrate topography matches the dimensions of the intrinsic surface relief structures of the block copolymer, the surface roughening is suppressed by inverted terrace formation, and sequenced patterns of in-plane cylinders and nonbulk lamella phases are generated. As soon as the surface roughening forms on the corrugated substrate with a roughness parameter lower than that of the surface relief structures, the reverse sequences of the alternative microphase separated structures are developed. However, enhanced mobility of the block copolymer induced by solvent annealing suppresses the pattern sequencing and the in-plane cylinders with a relatively high degree of ordering generated over the entire surface of the corrugated substrate. This observation may further enable new approaches for manipulating the sequences of spatially registered hierarchical surface patterns of block copolymers.

Investigation of the effect of substrate morphology on MDCK cell mechanical behavior using atomic force microscopy

Living cells sense and respond to their extracellular environment. Their contact guidance is affected by the underlying substrate morphology. Previous studies of the effect of the substrate pattern on the mechanical behavior of living cells were only limited to the quantification of the cellular elasticity. However, how the length and time scales of the cellular mechanical properties are affected by the patterned substrates are yet to be studied. In this study, the effect of the substrate morphology on the biomechanical behavior of living cells was thoroughly investigated using indentation-based atomic force microscopy. The results showed that the cellular biomechanical behavior was affected by the substrate morphology significantly. The elasticity and viscosity of the cells on the patterned Polydimethylsiloxane (PDMS) substrates were much lower compared to those of the ones cultured on flat PDMS. The poroelastic diffusion coefficient of the cells was higher on the patterned PDMS substrates, specifically on the substrate with 2D pitches. In addition, fluorescence images showed that the substrate topography directly affects the cell cytoskeleton morphology. Together, the results suggested that cell mechanical behavior and morphology can be controlled using substrates with properly designed topography.

Evaporation-induced self-assembly of C60 on SrTiO3(110) reconstructed surfaces

SrTiO3(110) polar surface was treated with repeated cycles of argon ion sputtering and annealing. Three reconstructions, namely (4 × 1), (2 × 8), and (6 × 8), were identified with subsequent scanning tunneling microscopy measurements. Using the evaporation-induced self-assembly method, C60 molecules deposited onto these reconstruction surfaces demonstrated a quasi-close packing growth mode with substantial differences. Influence factors are revealed from the investigation of these differences, such as the substrate structure and topography as well as the intermolecular and molecular-substrate interactions. Our study emphasizes the feasibility of controllable molecular self-assembly through choosing surface reconstructions.

Confinement and substrate topography control cell migration in a 3D computational model

Cell movement in vivo is typically characterized by strong confinement and heterogeneous, three-dimensional environments. Such external constraints on cell motility are known to play important roles in many vital processes e.g. during development, differentiation, and the immune response, as well as in pathologies like cancer metastasis. Here we develop a physics-driven three-dimensional computational modeling framework that describes lamellipodium-based motion of cells in arbitrarily shaped and topographically structured surroundings. We use it to investigate the primary in vitro model scenarios currently studied experimentally: motion in vertical confinement, confinement in microchannels, as well as motion on fibers and on imposed modulations of surface topography. We find that confinement, substrate curvature and topography modulate the cell’s speed, shape and actin organization and can induce changes in the direction of motion along axes defined by the constraints. Our model serves as a benchmark to systematically explore lamellipodium-based motility and its interaction with the environment.

SIMULATION AND EXPERIMENTAL RESEARCH ON ADHESION ENHANCEMENT BETWEEN DIAMOND FILMS AND WC-Co SUBSTRATES BY EMPLOYING AMORPHOUS SiC INTERLAYER

The finite element method (FEM) is employed to analyze the residual stress distribution of bi-layer (a-SiC [Formula: see text] diamond) film system, and the adhesion enhancement mechanism of a-SiC interlayer is further investigated. The influence of a-SiC interlayer on the surface topography of WC-Co substrate is taken into consideration by adopting a 3D surface topography model agreeing with the Atomic Force Microscope (AFM) characterization of a-SiC interlayer. For the sake of comparison, the stress distribution of a diamond film with no interlayer is also simulated. The simulation analysis reveals that the residual stress distribution is much more homogeneous after employing the a-SiC interlayer, which is supposed to be of great importance to the adhesion enhancement of diamond films. Afterwards, the diamond films with and without a-SiC interlayer are fabricated on WC-Co substrates. Raman mapping is carried out to measure the real residual stress distribution of as-fabricated a-SiC diamond films, which is in accordance with the simulation results. Moreover, the a-SiC interlayered diamond film exhibits better adhesion than the diamond film with no interlayer in adhesion evaluation, which can be ascribed to the more homogeneous residual stress distribution and better interfacial bonding after introducing the a-SiC interlayer.

The Impact of Biological Bedforms on Near‐Bed and Subsurface Flow: A Laboratory‐Evaluated Numerical Study of Flow in the Vicinity of Pits and Mounds

AbstractThe complex surface topography of river substrates controls near‐bed hydraulics and drives the exchange of subsurface and surface flow. In rivers, the topographic structures that are studied are usually formed by the flow, but it is known that many animals also create biogenic bedforms, such as pits and mounds. Here, a large‐eddy simulation model of flow over a pit and a mound is evaluated with flume experiments. The model includes actual bedform topography, and the topographic complexity of the surrounding bed surface. Subsurface grains are organized in a body‐centered cubic packing arrangement. Model evaluation showed strong agreement between experimental and modeling results for velocity (R2 > 0.8) and good agreement for Reynolds stresses (R2 > 0.7), which is comparable to other similar studies. Simulation of the pit shows that the length of the downwelling region is smaller than the upwelling region and that the velocity magnitude is higher in the downwelling region. Simulation of the mound reveals that the flow is forced into the bed upstream of the mound and reemerges near the top of the mound. The recirculation zone is limited at the leeside of the mound. With increasing Reynolds number, the depth of the upwelling region at the leeside of the mound increases. The analysis of shear stress indicates that sediments on the upstream edge of the pit and on the downstream face of the mound are relatively unstable. These results demonstrate the effect of biogenic structures on the near‐bed flow field, hyporheic exchange, and sediment stability.

Effect of ion peening and pulsed plasma nitriding on the structural properties of TiN coatings sputtered onto 100Cr6 steel

Ion peening with noble gas is typically used to generate lattice imperfections and a nanostructure within the bombarded metal surfaces. This might have therefore an impact on subsequent plasma nitriding, thus allowing for enhancing the adhesion and wear resistance of hard ceramic coatings deposited onto steel surfaces. In this work, the influence of pre-treating a 100Cr6 steel surface by Xe+ ion bombardment and pulsed plasma nitriding was investigated with respect to surface roughness, wear resistance and residual stresses of thin TiN coatings deposited by reactive ion beam assisted deposition.Xe+ ion bombardment was carried out using a 400 eV acceleration energy produced by a broad Kaufman cell and subsequent thermo-chemical nitrogen diffusion was accomplished at 520 °C. The results show that Xe+ ion bombardment intensifies nitrogen diffusion without inducing significant changes in the substrate topography. The combined pre-treatment with Xe+ ion bombardment and subsequent pulsed plasma nitriding leads to a reduction of compressive stresses in the TiN coatings. The presence of porosity in the white layer diminished the wear resistance.

Myoblast maturity on aligned microfiber bundles at the onset of strain application impacts myogenic outcomes

Engineered skeletal muscle grafts may be employed in various applications including the treatment of volumetric muscle loss (VML) and pharmacological drug screening. To recapitulate the well-defined structure of native muscle, tensile strains have been applied to the grafts. In this study, we cultured C2C12 murine myoblasts on electrospun fibrin microfiber bundles for 7 days in custom-built bioreactor units and investigated the impact of strain regimen and delayed onset of tensile straining on myogenic outcomes. The substrate topography induced uniaxial alignment of cells in all (strained and unstrained) groups. The engineered grafts in strained groups were subjected to 10% strain amplitude for 6 h per day. We found that both static and cyclic uniaxial strains resulted in similar morphological and gene expression outcomes. However, relative to 0% strain groups, there were stark increases in myotube diameter, myosin heavy chain (MHC) coverage, and expression of key myogenic genes (Pax 7, Troponin, MHC I, MHC IIb, MHC IIx) only if strain was applied at Days 5–7 rather than Days 3–7. This finding suggests that a critical indicator of myogenic improvement under strain in our system is the phenotype of the cells at the onset of strain and suggests that this is a key parameter that should be considered in studies where myoblasts are subjected to biophysical stimulation to promote tissue formation. Statement of SignificanceThis is the first report on the impact of the timing of the initial application of mechanical strain for improving the myogenic outcomes of 3D engineered skeletal muscle grafts. In this work, immature skeletal myoblasts were grown on topographically aligned, electrospun fibrin microfiber bundles and we applied 10% uniaxial static or cyclic strain. We concluded that the maturity of myoblasts prior to strain application, rather than strain waveform, was the primary predictor of improved myogenic outcomes, including myogenic gene expression and myotube morphology. Elucidating the optimal conditions for strain application is a vital step in recapitulating physiological myogenic properties in tissue engineered skeletal muscle constructs, with applications for treating volumetric muscle loss, disease modeling, and drug testing.

In Situ Visualization of Particle Motions during Wipe Sampling of Explosives and Other Trace Particulate Materials.

Surface texture tailoring has the potential to increase the effectiveness of dry particle collection wipes, as a wipe's topographical features control the intimate surface contact made with particles on the substrate (critical for van der Waals-governed adhesion). However, texture-tailoring approaches have not yet been widely explored, in part because of a lack of understanding of the specific wipe topographies and wipe/particle interactions that maximize particle collection. Here we describe an in situ optical microscopy technique that enables direct observation of micrometer-scale particle-wipe interactions occurring at the wipe-substrate interface during contact sampling. The technique is demonstrated for nonwoven meta-aramid (Nomex) collection wipes with particles ranging from 1 to 90 μm in diameter and substrates of different topographies (glass andnylon coil zipper). Experiments with hemispherically coated Janus particles allow rolling motions to be distinguished from sliding motions, providing detailed information about how particles move prior to capture or release by the wipe. Particle-fiber and particle-particle interactions are seen to play important roles in particle capture, suggesting that conventional sphere-on-plane models are inadequate to describe adhesion behavior in these systems. Micrographs show how loose, flexible fibers in roughened textile wipes interrogate the valleys of uneven substrate topographies, allowing capture of particles that might otherwise be trapped within the substrate's grooves and depressions. The materials used in this work are specifically relevant to explosives detection, but the in situ visualization technique is transferable for the study of any application involving dry particle collection, such as toxic substance sampling and dust removal.

Assessment of synergistic effects of LP-MOCVD TiO2 and Ti surface finish for dental implant purposes

Three differently treated titanium substrates to be used in dental implant applications and with different surficial morphology were coated with titanium dioxide (TiO 2 ) films by using Low-Pressure Metal Organic Chemical Vapor Deposition (MOCVD). No literature references were found on the performance evaluation of the TiO 2 MOCVD coatings on substrates with different pristine morphology; in this work the influence of the pristine Ti surface characteristics on TiO 2 crystalline structure, morphology, wettability as well as on ion release, electrochemical behavior, tribocorrosion performance, and nano-mechanical properties were studied and discussed. It was shown that the pristine substrate influenced both the crystalline phases' formation and crystallite size. Scanning electron microscopy analyses and roughness evaluation showed the optimal conformal coverage of all the MOCVD coatings for all substrates, with grain size depending on the substrate morphology and topography. The wettability of the TiO 2 coated Ti substrates highlighted a superhydrophilic behavior and, if stored in air, decreased as a function of the time aging. Ions release tests, nanoindentation measurements, tribocorrosion, and potentiodynamic polarization experiments suggest the enhancement of functional properties of the coated samples. Titania sandblasted/acid etched coated Ti substrates generally showed the best performance of the functional properties for their use in dental implant fabrications. • TiO 2 coated samples allow better wettability in aqueous media. • Titania surface functionalization is a good strategy to reduce ion release. • Tribocorrosion studies indicate better behavior for TiO 2 coated samples. • TiO 2 surface functionalization improves the mechanical properties of bulk titanium.

Wetting kinetics and interfacial structure of AgCu alloy spreading on TB8 substrates

AgCu filler metal spreading over TB8 substrate under a high-purity argon atmosphere was conducted at 920 °C. Effects of surface roughness and topography of the substrate on the wetting kinetics were investigated. The interfacial microstructures of AgCu eutectic alloy/TB8 substrate solidified couples was analyzed by optical microscope, scanning electron microscope, energy dispersive spectrometer and transmission electron microscope. Results revealed that the substrate surface roughness and topography had significant influences on the wetting kinetics and spreading process. The spreading was preferential when AgCu molten metal over an anisotropically microstructured surface. When the surface of the substrate was not anisotropic, the spreading morphology was almost a perfect circle. An additional capillary driving force exists when the molten metal flows on the rough surface, which leads to a better wettability. The interfacial microstructure of the resolidified AgCu on the TB8 substrate was Ag(ss)/ Ti3Cu4/Ti2Cu/ /Ti(ss) + Ti2Cu/TB8, and the spreading edge domain near the triple-line is rich in Ag.

Topography guiding the accelerated and persistently directional cell migration induced by vaccinia virus

The rapid transmission of vaccinia virus (VACV) in vivo is thought to be closely related to the cell migration induced by it. Cell migration involved in dynamic changes of cell-substrate adhesion and actin cytoskeleton organization, which can influence by the micro/nano-scale topographic structures that cells are naturally exposed to via contact guidance. However, migration behaviors of VACV-infected cells exposed to topographic cues are still unknown. Herein, we designed an open chip with microgrooved poly(dimethyl siloxane) (PDMS) substrate to explore the topography roles in VACV-induced cell migration. Differed from the random cell migration observed in traditional scratch assay on planar substrate, VACV-infected cells had a tendency to persistently migrate along the axis parallel to microgroove with increased velocity. Moreover, infected cells exhibited a dominant elongated protrusion aligned to the micro-grating axis compare to the shorter lamella extended in any direction on smooth substrate. Interestingly, the Golgi complex preferred to relocate behind the nucleus confined within the micro-grating axis in majority of infected migratory cells. The directional polarization of cells embodied in protrusion formation and Golgi reorientation was responsible for the directionally persistent migration behaviors induced by VACV on microgrooved substrate. Infected cells response to substrate topography, causing the actin-filled stretched protrusion containing numerous virions and accelerated movement is likely to facilitate direct and rapid spread of VACV. This work opens a window for us to understand the migration behaviors of infected cells in vivo, and also provides a cue for revealing the relationship between virus-induced cell migration and virus rapid spread.

Hydrogel-Templated Transfer-Printing of Conductive Nanonetworks for Wearable Sensors on Topographic Flexible Substrates.

Transfer-printing enables the assembly of functional nanomaterials on unconventional substrates with a desired layout in a controllable manner. However, transfer-printing to substrates with complex surfaces remains a challenge. Herein, we show that hydrogels serve as effective template material platforms for the assembly and transfer-printing of conductive nanonetwork patterns for flexible sensors on various topographic surfaces in a very simple yet versatile manner. The non-adherence, nanoporous structure, and molding capability of the hydrophilic hydrogel enable the assembly of conductive nanonetwork patterns on the hydrogel surface and transfer of the nanonetworks onto various flexible and topographic substrates. Flexible strain sensors and pressure sensors that monitor finger motions and arterial pulses are successfully demonstrated using the hydrogel-templated approach. The rich chemistry of polymeric networks, facile molding capability, and biocompatibility of hydrogels could be further combined with additive technology for hydrogels and electronic materials for emerging four-dimensional functional materials and soft bioelectronics.

Effect of substrate topography for graphene-based humidity sensors

Chemical vapor deposition graphene (CVDG) and electrochemical exfoliated graphene (ECG) were transferred and spin-coated on the nanoporous alumina substrate (NS) and flat alumina substrate (FS) to investigate the effect of substrate topography for graphene-based humidity sensors. The electrical resistance change of two graphene types on different substrate topography could be measured to estimate the environmental relative humidity. The relationship between graphene types, substrate topography, wettability, and humidity sensing performance was studied and discussed. The results of the water contact angle of CVDG on NS/FS and ECG on NS/FS were 77.0 ± 5.0°, 88.8 ± 4.9°, 55.9 ± 7.0°, and 59.8 ± 3.2°, respectively. The response, linearity and hysteresis characteristics of four graphene-based humidity sensors were measured and estimated. The ECG on NS humidity sensor shows the best performance in regards to the response, linearity and hysteresis.