Surface Topography Of Substrate Research Articles

Understanding the Role of Loss Modulus of Viscoelastic Substrates in the Evaporation Dynamics of Sessile Drops.

Viscoelastic properties of soft substrates play a crucial role in the evaporation dynamics of sessile drops. Recent studies have revealed that the modification of the viscoelastic properties of substrates changes the dynamics of the three-phase contact line, consequently affecting the evaporation behavior of sessile drops. Notably, these modifications occur without any noticeable changes to the substrate's wetting characteristics or surface topography. However, the individual role of storage (G') and loss (G″) moduli of substrates on drop evaporation dynamics remains unexplored. In this study, we investigate the evaporation dynamics of water drops on two groups of poly(dimethylsiloxane)-based viscoelastic substrates possessing either identical G' with varying G″ or identical G″ with varying G'. Our study reveals that on a substrate with constant shear modulus (G'), a reduction of an order of magnitude in loss modulus shifts the evaporation process from the constant contact radius mode to the constant contact angle mode. We hypothesize that this observed shift in behavior stems from the varying viscoelastic dissipation influenced by the plateau modulus and characteristic relaxation time of polymer gels. Our hypothesis is further supported from the observation that the evaporation process persists on the substrate with constant loss modulus (G″). Our study advances the current understanding of drop evaporation on soft substrates that may find potential applications involving soft composites, biological entities, tissue engineering, and wearable electronics.

Effect of laser etching on surface characteristics and porcelain bond to soft milled and direct metal laser sintered cobalt chromium alloys

Statement of problemThe surface topography of metal substrate can affect its bond to porcelain. A neodynium-doped yttrium aluminum garnet (Nd:YAG) laser has been introduced to modify the metal surface topography and improve porcelain bond strength. However, studies on the effect of laser etching on metal to porcelain bond strength are lacking. PurposeThe purpose of this in vitro study was to determine the effect of Nd:YAG laser etching on the surface roughness and wettability of and the porcelain bond strength to cobalt chromium (Co-Cr) substrate fabricated by milling and direct metal laser sintering (DMLS). Material and methodsThirty-two 0.5×3×25-mm Co-Cr specimens were fabricated by milling soft Co-Cr (M group) and DMLS Co-Cr metal powder (DML group). The surface topography of representative specimens from each study group was assessed under a scanning electron microscope (SEM) and an atomic force microscope (AFM). All specimens were assessed for surface roughness using a contact profilometer, and for wettability with a contact angle goniometer. Half of the specimens of each study group (n=8) were subjected to surface laser etching by using a Nd:YAG laser. The specimens subjected to etching were assessed again for surface topography and wettability. All specimens in both study groups were veneered with porcelain. The porcelain bond strength was tested with a 3-point bend test in a universal testing machine. The results were statistically analyzed with 2-way ANOVA test followed by the post hoc Tukey test for pairwise comparisons (α=.05). ResultsAfter etching, the M group had a higher mean ±standard deviation Ra and Rz of 2.9 ±0.6 and 17.7 ±3.2 µm and significantly better wettability and bond strength of 79 ±6 and 52 ±13 MPa. In contrast, after etching, the DMLS group had a significantly lower Ra and Rz of 7.9 ±2.4 and 41.8 ±9.3 µm and significantly lower wettability and bond strength of 87 ±4 and 70 ±10 MPa. The DMLS group had a significantly higher roughness and bond strength than the M group before and after laser etching. The SEM and AFM showed different surface topography in the study groups. ConclusionsThe manufacturing process of Co-Cr substrate had a significant effect on surface characteristics and porcelain bond strength. Laser etching improved the surface topography and bond strength of milled Co-Cr but not of DMLS Co-Cr.

Rationally design of substrate surface topography toward the improvement of Cu-plated coating adhesion

Rationally design of substrate surface topography toward the improvement of Cu-plated coating adhesion

Modeling the evolution of membrane during cell adhesion on the nanostructured substrate

Using nanostructured substrates for enhancing cell adhesion is an important method. However, the physical mechanism of cell adhesion on nanostructured substrate is not well understood yet, particularly the evolution process of membrane during cell adhesion. Here, we propose an analytical model to study quantitatively the evolution of membrane during adhesion process on the nanostructured substrate. The effects of substrate surface topography, receptor-ligand binding, substrate property and membrane property were investigated. We found a small nanopillar radius, low nanopillar density, large binding rate, large receptor density, low non-specific energy, or large stretching modulus can result in a large adhesion rate and a large adhesion depth. Besides, the evolution of membrane on truncated nanocone arrays was also studied by the model. The theoretical results are in good agreement with the experimental observations, which implied that our studies can provide a useful guide to control cell adhesion process and cell motion on nanostructured substrates.

It Takes Two to Tango: Controlling Human Mesenchymal Stromal Cell Response via Substrate Stiffness and Surface Topography

Cells sense extracellular matrix‐induced biophysical signals, which are transduced into intracellular signaling cascades, and trigger a series of cell responses, including adhesion, migration, and lineage commitment. Traditionally, in in vitro context, monofactorial approaches are employed to control cell fate, despite the fact that in vivo cells are exposed simultaneously to a diverse range of signals. Herein, an overview of key mechanotransduction pathways is first provided. Conventional single‐factor and contemporary multifactorial methodologies, based on substrate rigidity and surface topography, are then reviewed to recapitulate in vitro the in vivo niche, in an attempt to elucidate the underlying mechanisms involved in human mesenchymal stromal cell‐material interactions.

Design and fabrication of ordered silicon micro/nano-hybrid hierarchical structures decorated by silica thin layer for superantiwetting surface

The wetting properties of micro/nano-hybrid hierarchical structures offers important applications in many fields. However, the fabrication of hierarchical micro-nanostructures still suffers the limitations of complicated fabrication process, high cost and small area. Here, we develop a novel strategy for the fabrication of uniform micro/nano-hybrid hierarchical silicon structures by combining the photolithography, thermal de-wetting and metal-assisted chemical etching (MACE). The outstanding advantage of this technique is the ability to achieve nano-patterning at the full 4″ or 6″ wafer scale in a very facile and affordable manner, regardless of the substrate surface topography. Moreover, nanostructures generated by this technique can be customized independently at a specific level with very high feature control. By oxidizing the structure and modifying it with specific functional groups or molecules, the wettability of the surface can be transformed from the underwater superoleophobic state with an oil contact angle (OCA) of ∼169° to underwater superoleophilic state (an OCA of ∼8.4°). The transition from superhydrophobic state with a water contact angle (WCA) of ∼175.5° to quasi-superhydrophilic state (a WCA of ∼10.5°) can also be achieved, which is highly desirable for optoelectronics, environment, and biomedicine fields.

Friction surfacing of aluminum to steel: Influence of different substrate surface topographies

In the present study, AA6082 aluminium is deposited onto AISI 4140 steel substrates via friction surfacing (FS). Aiming to understand the influence of substrate surface for the bonding mechanism during the plasticising as well as the deposition phase, three different surface topographies have been manufactured via grinding and machining. Subsequently, FS process parameter dependencies on the deposits have been investigated. The resulting optical appearance, geometry and microstructure of the deposits have been studied. A deeper surface topography was found to facilitate plasticising and therefore FS layer deposition. Defect-free layer-to-substrate (LTS) joints have been generated for all topographies showing a fine-grained recrystallized microstructure as well as flow lines in the AA6082 deposits following closely the substrate surface topography, whereas no metallurgical changes in the AISI4140 substrates have been detected. At the LTS interfaces, a correlation of flow lines to an increased occurrence of high angle grain boundaries is identified. Appearance, geometries and grain size ratios of the AA6082 deposits show a dependency on substrate surface topography. Although complete bonding was achieved in the LTS joints, no distinct diffusion zone or interfacial mixing was observed. Mechanical interlocking on the micro scale was detected only for the samples with ground substrate surfaces.

Bond behavior of CFRP sheets-to-steel shear joints with different steel surface treatments

The current study focuses on the bond behavior of CFRP sheets-to-steel double-lap shear (DLS) joints with different steel surface treatments. A total of 18 DLS joints are tested in tension. The effects of six different steel surface treatments on the mechanical response of the DLS joints are investigated. The steel surface treatments include power tool polishing with four different sandpapers in grit sizes, grit blasting and pre-coating silane coupling agent. The surface topography and roughness of the steel substrates with different treatments are evaluated from test results, and their relationship with mechanical behavior and failure modes is established qualitatively. The geometric characteristics of the surface are strongly correlated with the average ultimate loads of the DLS joints. Based on the measured load-slip curves, the bond-slip (B-S) relationship is predicted, which removes the effect of the actual deformation of the steel substrates on the slip. Regression analyses of quantifying the B-S relationship are conducted to establish the simplified B-S model applied to the CFRP sheets-to-steel bonded interface, and the effects of different steel surface treatments are considered in this model. The accuracy of the simplified B-S model is verified through comparison with the experimental results.

Effect of Substrate Roughness and Contact Scale on the Tribological Performance of MoS2 Coatings

This present study aimed to clarify the effect of contact scale and surface topography of substrates with different roughnesses on the actual contact area, tangential stiffness, and tangential deformation of the substrate at micro- and macro-scales via finite element method (FEM) simulations, as well as the final tribological performances of MoS2 coatings by experiments. The MoS2 coatings were deposited on stainless steel (SS) substrates with different roughnesses, and the settings in the simulation models were based on the roughness of the SS substrates. The predicted tribological behavior of the simulation results was confirmed by the morphological and compositional analysis of the wear track using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), 3D profilometer, and Raman spectroscopy. The results showed that the substrate with a surface roughness of Ra 600 nm (R600), coated by MoS2 nanosheets, exhibited excellent tribological properties at both micro- and macro-scales. At the micro-scale, the lubrication lifetime of R600 was as long as 930 cycles, while the substrates with surface roughnesses of Ra 60 nm (R60) and Ra 6 nm (R6) had a lubrication lifetime of 290 cycles and 47 cycles, respectively. At the macro-scale, the lifetime of the substrate R600 was 9509 cycles, which was nearly six times longer than the 1616 cycles of substrate R60. For the rough surface of substrate, the surface grooves could not only effectively preserve the lubricant but also continuously release them, ensuring that the lubricants with low shear strength were always present in the contact interface. It was further verified that the high surface roughness of the substrate reduced friction and wear by reducing the actual contact area and enhancing the tangential stiffness of asperities, thereby prolonging the lubrication lifetime. The wear mechanisms were discussed in terms of the morphology and chemical composition of the wear tracks.

Stability of supported hybrid lipid bilayers on chemically and topographically-modified surfaces

Hybrid lipid bilayers are a particular case of supported lipid bilayers with the two monolayer leaflets composed by different types of molecules. These nanostructures can be produced in a well-controlled array fashion and are suitable for the study of biomembrane-related phenomena via electrochemical or plasmonic sensing. Understanding how the underlying solid surface affects the supported membrane formation and organization is necessary for the potential use of these hybrid platforms in applications for which surfaces are not flat and topographically complex. Here we assess the role of lipid phase, substrate surface energy and topography on the formation and stability of hybrid supported membranes from vesicle precursors using complementary surface-sensitive techniques, namely quartz crystal microbalance with dissipation and atomic force microscopy. The stability of hybrid bilayers against thermal and osmotic changes is evaluated and compared to standard supported lipid bilayers formed onto hydrophilic SiO2. Force spectroscopy measurements reveal an overall weaker lateral organization of hybrid membranes as a result of the underlying self-assembled monolayer being not optimally organized. Hybrid bilayers display a decoupled behavior between the two leaflets when vertically compressed at constant speed. On microcontact printed Au surfaces, hybrid bilayers were formed over printed patches, while surprisingly, supported lipid bilayers were observed on non-patterned Au regions suggesting a non-trivial self-assembled monolayer reorganization when in aqueous environment.

Self-assembled polylactic acid (PLA): Synthesis, properties and biomedical applications.

The surface morphology and topography of cell culture substrates play an important role in cell proliferation and growth. Regulation of the surface microstructure allows the development of tissue culture media suitable for different cells. Polylactic acid (PLA) is a biobased and biodegradable (under defined conditions) polymer with low immunogenicity, non-toxicity, and good mechanical properties, which have facilitated their pharmaceutical and biomedical applications. This review summarizes recent advances in the synthesis and self-assembly of surface microstructure based on PLA materials and discusses their biomedical applications such as cell culturing and tissue engineering.

How changes to the substrate’s physical characteristics can influence the deposition of touch and salivary deposits

An in-depth study into the physical substrate characteristics such as substrate surface roughness, topography, and physicochemical characteristics like wettability and surface free energy (SFE) was conducted to investigate the impact on the deposition and adherence of touch and salivary deposits on aluminium and polypropylene. A robust protocol was established to generate a set of substrates with a controlled linear surface roughness range (0.5–3.5 µm) in order to identify the impact of surface roughness on DNA transfer, persistence, prevalence, and recovery (DNA-TPPR). The polypropylene substrate was shown to produce fibres when artificially roughened, becoming more prominent at a higher surface roughness range, and has shown to have a direct impact on the distribution of salivary and touch deposits. At the low to moderate surface roughness range 0.5–2.0 µm, salivary and touch deposits have generally shown to follow the topographical features of the substrate they were deposited on, before a plateau of the surface roughness measure on the deposit was observed, indicating that a saturation point was reached and the grooves in the substrate were beginning to fill. Touch deposits have shown to maintain a consistent deposition height pre-surface roughness threshold, irrespective of substrate surface roughness while the deposition height of salivary deposits was heavily influenced by substrate surface roughness and topography. The substrate SFE, wettability, hydrophobicity, and the surface tension of the deposit was shown to drive the adhesion properties of the saliva and touch deposits on the respective substrates, and it was observed that this may be of importance for the improvement of the current DNA-TPPR understanding, DNA sampling protocols, and DNA transfer considerations within casework.

Regulation of Mesenchymal Stem Cell Morphology Using Hydrogel Substrates with Tunable Topography and Photoswitchable Stiffness.

Cell function can be directly influenced by the mechanical and structural properties of the extracellular environment. In particular, cell morphology and phenotype can be regulated via the modulation of both the stiffness and surface topography of cell culture substrates. Previous studies have highlighted the ability to design cell culture substrates to optimise cell function. Many such examples, however, employ photo-crosslinkable polymers with a terminal stiffness or surface profile. This study presents a system of polyacrylamide hydrogels, where the surface topography can be tailored and the matrix stiffness can be altered in situ with photoirradiation. The process allows for the temporal regulation of the extracellular environment. Specifically, the surface topography can be tailored via reticulation parameters to include creased features with control over the periodicity, length and branching. The matrix stiffness can also be dynamically tuned via exposure to an appropriate dosage and wavelength of light, thus, allowing for the temporal regulation of the extracellular environment. When cultured on the surface of the hydrogels, the morphology and alignment of immortalised human mesenchymal stem cells can be directly influenced through the tailoring of surface creases, while cell size can be altered via changes in matrix stiffness. This system offers a new platform to study cellular mechanosensing and the influence of extracellular cues on cell phenotype and function.

Powder spreading over realistic laser melted surfaces in metal additive manufacturing

Powder recoating is a key step in metal Additive Manufacturing (AM) processes where powder is spread across laser processed surfaces to add material for the next layer. Achieving the desired thin powder layers that are both sufficiently dense and uniform is essential for maintaining the requisite geometric tolerances and final part quality. In this study, we focus on the influence of the substrate surface topography by comparing spreading performance over a set of realistic surfaces. We simulate powder spreading over these surfaces using a calibrated non-spherical particle Discrete Element Model for Ti-6Al-4V that incorporates cohesion and Coulomb friction interactions between particles and surfaces. We identify the four key length scales of the recoating process determined by frictional contacts, powder size distribution, the layer thickness and the melted surface topography. We find that realistic AM surfaces show markedly different powder coverage compared to an idealised flat-plane. Rougher surfaces are found to be recoated with larger amounts of powder than smoother surfaces, as smaller particles get trapped by the grooves and valleys across the surface. Counterintuitively, we find that a finer more cohesive powder can achieve the best layer coverage over realistic surfaces - indicating that powder flowability is an incomplete measure of powder spreading performance on realistic AM surfaces. We also demonstrate how the recoating process can significantly size segregate the feedstock powder, favouring deposition of smaller sized particles on the melted surfaces.

Tuning thermal transport across monolayer MoS2/Si heterostructure via substrate nanogrooving

Substrate-supported two-dimensional (2D) material heterostructures have been widely applied in electronic and photonic devices. However, the substrate reduces the original high thermal conductivity of 2D materials and limits the heat dissipation due to the interface thermal resistance. Here, the effects of the substrate surface topography on the thermal transport properties of the MoS2-Si heterostructure are investigated via molecular dynamics simulations. The decreased in-plane thermal conductivity of the monolayer MoS2 and surprisingly enhanced interface thermal transport of the MoS2-Si heterostructure are found by introducing the shallow nanogroove on the substrate surface. The results are ascribed to the morphology change of the supported MoS2, which bends to fit the substrate surface topography due to the van der Waals force at the small groove depth. In addition, the force weakens and the supported MoS2 restores to flat with the increase of groove depth, resulting in higher in-plane thermal conductivity and thermal resistance compared to those without grooves, which is due to the disappearance of the substrate effect in the nanogroove area. This work elucidates the fundamental understanding of heat transfer in heterostructures. It provides new insights to enhance the heat dissipation in electronic devices by introducing nanoscale roughness.

A Biocompatibility Study of Plasma Nanocoatings onto Cobalt Chromium L605 Alloy for Cardiovascular Stent Applications.

The objective of this study was to evaluate the biocompatibility of trimethylsilane (TMS) plasma nanocoatings modified with NH3/O2 (2:1 molar ratio) plasma post-treatment onto cobalt chromium (CoCr) L605 alloy coupons and stents for cardiovascular stent applications. Biocompatibility of plasma nanocoatings was evaluated by coating adhesion, corrosion behavior, ion releasing, cytotoxicity, and cell proliferation. Surface chemistry and wettability were studied to understand effects of surface properties on biocompatibility. Results show that NH3/O2 post-treated TMS plasma nanocoatings are hydrophilic with water contact angle of 48.5° and have a typical surface composition of O (39.39 at.%), Si (31.92 at.%), C (24.12 at.%), and N (2.77 at.%). The plasma nanocoatings were conformal to substrate surface topography and had excellent adhesion to the alloy substrates, as assessed by tape test (ASTM D3359), and showed no cracking or peeling off L605 stent surfaces after dilation. The plasma nanocoatings also improve the corrosion resistance of CoCr L605 alloy by increasing corrosion potential and decreasing corrosion rates with no pitting corrosion and no mineral adsorption layer. Ion releasing test revealed that Co, Cr, and Ni ion concentrations were reduced by 64–79%, 67–69%, and 57–72%, respectively, in the plasma-nanocoated L605 samples as compared to uncoated L605 control samples. The plasma nanocoatings showed no sign of cytotoxicity from the test results according to ISO 10993-05 and 10993-12. Seven-day cell culture demonstrated that, in comparison with the uncoated L605 control surfaces, the plasma nanocoating surfaces showed 62 ± 7.3% decrease in porcine coronary artery smooth muscle cells (PCASMCs) density and had comparable density of porcine coronary artery endothelial cells (PCAECs). These results suggest that TMS plasma nanocoatings with NH3/O2 plasma post-treatment possess the desired biocompatibility for stent applications and support the hypothesis that nanocoated stents could be very effective for in-stent restenosis prevention.

Cell Adhesion Behaviors on Spider Silk Fibers, Films, and Nanofibers

Silk-based materials have garnered attention for use as medical supplies due to their mechanical toughness and low cytotoxicity. Silkworm silk has been applied as surgical sutures for decades. In contrast, the utilization of spider silk is limited mainly because of its scarcity. Although the biomimicry of spider silk has been developed using recombinant protein expression systems with the use of genetic engineering, the product often results in lower molecular weight and a lack of the N- or C-terminal regions. The incomplete sequence of the spider silk-like protein prevents the objective evaluation of the native spider silk as a medical application and retards the development of spider silk-inspired materials. Here, we reeled the native spider silk directly from live spiders and investigated the cell adhesion behavior based on three kinds of surface topography of spider silk-based substrates, namely, fibers, films, and non-woven fabrics. The cell adhesion behavior was largely influenced by the surface micro/nanostructure rather than the wettability of the surface. This study will contribute to promote the utilization of spider silk in the medical field as a candidate for promising bio-based fibers in the context of sustainable development goals.

Anti-cancer Drug Susceptibility of Breast Cancer Cells Incubated on Electrospun Polymeric Fiber Substrates

In this study, we examined the effect of a combination of surface topographies (fiber alignments) and different stiffness of poly(L-lactic acid) (PLLA) substrates on the direct relationship between anti-cancer drug (CDDP) sensitivity for MDA-MB-231 cells and mesenchymal properties under both normal and hypoxic conditions. In addition, we studied the induction of epithelial–mesenchymal transition (EMT). The CDDP treatment under hypoxia indicated poor adhesion of MDA-MB-231 cells as well as significant repression of E-cadherin (CDH1). The robust connection between drug sensitivity and repression of epithelial cell marker of E-cadherin (CDH1) mediated by substrate surface topography contributed to the anti-cancer drug resistance of MDA-MB-231 cells. PLLA substrates did not cause a significant change in the induction and acquisition of EMT, indicating that EMT exerted no effect on drug susceptibility.

An experimental evaluation of the thermal interface resistance between cold sprayed copper/ laser-textured alumina bi-layered composites

The removal of heat across composite structures comprising a metal-ceramic interface is a common engineering challenge. To maximise heat removal, it is essential that the thermal interface resistance is minimised. This paper describes an experimental study of the thermal interface resistance between copper-alumina bi-layered composites. Samples are prepared using a novel cold spray copper particle deposition process on alumina substrates. To facilitate particle adhesion and enhance heat transfer contact area, substrates were textured with an ordered crosshatch pattern, using a micro-machining ablation laser, at different powers. Thermal resistance measurements were made using the transient light-flash method for bi-layered materials, using a NETZSCH LFA 467 hyper-flash analyser. The results show that the developed process produces a copper-alumina interface with a very low thermal resistance. In addition, the results suggest some correlation between substrate surface topography and the resistance, and an inverse relationship with the interface adhesion shear strength. The lowest measured resistance range was 1.56×10−6−1.49×10−9m2·K/W, for a temperature range of 20−500∘C, and a corresponding adhesion strength of 16.79MPa.

Enhancing the Up-conversion luminescence using All dielectric Three-Dimensional multiscale anodized aluminum oxide nanowire structure

Light management at nanometric dimension for boosting the enhancement of photo luminescence from Lanthanide doped up-conversion nanoparticles (UCNPs) has evidenced epochal advancement attributed to their conspicuous emission properties and plethora of potential applications. In this work, a multiscale funnel shape three dimensional (3D) anodized aluminum oxide (AAO) nanowire topography is explored to improve up-conversion luminescence (UCL) of synthesized core shell (C/S) NaYF4:Yb3+,Tm3+/NaYF4 UCNPs dispersed in chloroform. The different hexagonally arranged AAO topographies, based on cost-effective and modified self-aggregation fabrication method, are presented. These unique topographies of nanowire structures provide archetypal for enhanced UCL and have been investigated to study the effect of light management in detail. The systematic studies indicate that UCL enhancement is substantiated by the prolonged light path due to multiple scattering, and guided modes in the length of nanowire structures with the modified surface topography hoisted by capillary force inside the nanowires. The length of the nanowire and structure’s topographies are endorsed as structural parameters to tune the reflection as well as resonance mode for tuning the enhancement. The overall UCL enhancement for an optimized wire length and surface topography of AAO substrate is found to be ∼ 115 fold in ultra-violate regime at low excitation power density.