Top Of Pillars Research Articles

InAs heteroepitaxy on nanopillar-patterned GaAs (111)A

Heteroepitaxy on nanopatterned substrates is a means of defect reduction at semiconductor heterointerfaces by exploiting substrate compliance and enhanced elastic lattice relaxation resulting from reduced dimensions. We explore this possibility in the InAs/GaAs(1 1 1)A system using a combination of nanosphere lithography and reactive ion etching of the GaAs(1 1 1)A substrate for nano-patterning of the substrate, yielding pillars with honeycomb and hexagonal arrangements and varied nearest neighbour distances. Substrate patterning is followed by MBE growth of InAs at temperatures of 150–350 °C and growth rates of 0.011 nm/s and 0.11 nm/s. InAs growth in the form of nano-islands on the pillar tops is achieved by lowering the adatom migration length by choosing a low growth temperature of 150 °C at the growth rate 0.011 nm/s. The choice of a higher growth rate of 0.11 nm/s results in higher InAs island nucleation and the formation of hillocks concentrated at the pillar bases due to reduced adatom migration length. A common feature of the growth morphology for all explored conditions is the formation of hillocks or pyramids with sometimes well-defined facets due to the presence of a concave surface curvature at the pillar bases acting as adatom sinks. This InAs growth at the pillar bases and between pillars is investigated in detail in dependence of MBE growth conditions.

A 3D numerical study of a molten solder droplet's wetting and solidifying on a pillar with application to electronic packaging

The 3D problem of spreading and solidification of a molten solder droplet (with a melting temperature of Tm and a radius of Rd) on a circular pillar (with a radius Rpillar and a height Hpillar, having a contact angle θpillar at wall temperature Tpillar) above a substrate has important applications in electronic packaging. In this paper, effects of pillar's contact angle and wall temperature on droplet dynamics and solidification of the solder droplet are studied numerically based on a newly developed 3D multi-component, triple- phase-change LB model. For pillar's wall temperature equal to the melting temperature of the molten droplet (Tpillar = Tm), no solidification takes place in the droplet after its contact with the pillar, and droplet's spreading characteristics depend on the pillar's contact angle. If pillar's contact angle (θpillar) is smaller than a critical contact angle (θpillar)cr, i.e., θpillar < (θpillar)cr, the solder droplet spreads toward the edge of the pillar's top, turning around the corner of the pillar and spreading downward along the pillar's side wall. Based on LB simulated results, a map in terms of (θpillar) versus (Rd/Rpillar) is presented, showing regimes of droplet spreading and not spreading around the corner of the pillar. An analytical expression for predicting the critical contact angle of the pillar is derived, which is shown to divide these two regimes in the map. LB simulations are also carried out for the case when pillar's wall temperature is lower than the melting temperature of the molten droplet (i.e., Tpillar < Tm). Under this situation, it is shown that although no solidification takes place during the initial spreading motion, but solder bumps begin to be formed subsequently due to solidification and droplet's spreading motion is arrested as a result. Since formation of solder bumps on pillar's side wall may lead to short circuit of electric connection between solder bumps with other electric sources in the gap between the pillars, it is important to prevent the formation of solder bumps on pillar's side wall. For this purpose, a map of (θpillar) versus (Rd/Rpillar) at different Stefan numbers (denoting the effect of pillar's wall temperature Tpillar) is obtained to define the regime in which no solder bumps are formed on the pillar's side wall.

Fabrication of sharp silicon hollow microneedles by deep-reactive ion etching towards minimally invasive diagnostics

Microneedle technologies have the potential for expanding the capabilities of wearable health monitoring from physiology to biochemistry. This paper presents the fabrication of silicon hollow microneedles by a deep-reactive ion etching (DRIE) process, with the aim of exploring the feasibility of microneedle-based in-vivo monitoring of biomarkers in skin fluid. Such devices shall have the ability to allow the sensing elements to be integrated either within the needle borehole or on the backside of the device, relying on capillary filling of the borehole with dermal interstitial fluid (ISF) for transporting clinically relevant biomarkers to the sensor sites. The modified DRIE process was utilized for the anisotropic etching of circular holes with diameters as small as 30 μm to a depth of >300 μm by enhancing ion bombardment to efficiently remove the fluorocarbon passivation polymer. Afterward, isotropic wet and/or dry etching was utilized to sharpen the needle due to faster etching at the pillar top, achieving tip radii as small as 5 μm. Such sharp microneedles have been demonstrated to be sufficiently robust to penetrate porcine skin without needing any aids such as an impact-insertion applicator, with the needles remaining mechanically intact after repetitive penetrations. The capillary filling of DRIE-etched through-wafer holes with water has also been demonstrated, showing the feasibility of use to transport the analyte to the target sites.

Comparison of the Elastic-Plastic Transition in Nanocrystalline Nickel Pillars Fabricated by Electron Beam Lithography and Focused Ion Beam Methods

The elastic-plastic transition or yield behaviour was observed during compression of nanocrystalline nickel pillars fabricated by electroplating into electron beam lithography (EBL) forms or by focused ion beam (FIB) milling of the same electroplated structure. The experimental methodology allowed structures with different surface defect source/obstacles and similar bulk defects to be compared. Pillars with 1 to 2 um diameter cross-sections were made with height to diameter aspect ratios from 2:1 to 6:1, grain size of 91 ± 23 nm, and <110>, <111>, <100> textures in the growth direction. The pillars were compressed under a flat punch at constant loading rates from 1.5 to 30 μΝ/s using an instrumented indenter. EBL pillars generally showed a gradual elastic-plastic transition similar to yielding in bulk nickel followed by strain bursts. In contrast, FIB-milled pillars consistently showed stochastic yielding. The Young’s modulus was 55 to 350 GPa for all pillars, agreeing with values in the literature. The yield stress at 0.2% offset strain for EBL pillars ranged from 480 to 1800 MPa, and 320 to 700 MPa for FIB-milled pillars that was narrowed to 550 to 650 MPa after subsequent annealing, with initial deformation localized near the tops of FIB-milled pillars due to geometrical tapering. EBL pillar shear yield strengths exceed the literature reported for Ni and appear to lose their size dependence.

Depinning force of a receding droplet on pillared superhydrophobic surfaces: Analytical models

It was experimentally shown that a depinning force of a receding droplet on a micropillared superhydrophobic surface has an apparently linear correlation with the maximal three-phase contact line attainable along an actual droplet boundary. However, the experimental observation has not yet been supported by any theoretical basis or analysis. This study establishes an analytical model that theoretically supports the experimental observation on the basis of the dynamics of a contact line. The depinning force of a receding droplet was experimentally measured in evaporation on micropillared superhydrophobic surfaces with varying structure pitches but a fixed size. The analytical model was established by considering the energy dissipated by the displacement of a microscopic contact line on pillar tops and the energy consumed for the distortion of a liquid-gas interface between pillar tops. The model shows that the depinning force can theoretically be estimated by the physical dimensions of pillars and the intrinsic hydrophobicity of the surface, showing excellent agreement with the experimental results. Especially, the model indicates that the depinning force is fundamentally determined and practically controllable by the normalized maximal contact line at the droplet boundary, which can effectively be represented as the ratio of the pillar top perimeter to pitch.

Direct application of mechanical stimulation to cell adhesion sites using a novel magnetic-driven micropillar substrate.

Cells change the traction forces generated at their adhesion sites, and these forces play essential roles in regulating various cellular functions. Here, we developed a novel magnetic-driven micropillar array PDMS substrate that can be used for the mechanical stimulation to cellular adhesion sites and for the measurement of associated cellular traction forces. The diameter, length, and center-to-center spacing of the micropillars were 3, 9, and 9μm, respectively. Sufficient quantities of iron particles were successfully embedded into the micropillars, enabling the pillars to bend in response to an external magnetic field. We established two methods to apply magnetic fields to the micropillars (Suresh 2007). Applying a uniform magnetic field of 0.3T bent all of the pillars by ~4μm (Satcher et al. 1997). Creating a magnetic field gradient in the vicinity of the substrate generated a well-defined local force on the pillars. Deflection of the micropillars allowed transfer of external forces to the actin cytoskeleton through adhesion sites formed on the pillar top. Using the magnetic field gradient method, we measured the traction force changes in cultured vascular smooth muscle cells (SMCs) after local cyclic stretch stimulation at one edge of the cells. We found that the responses of SMCs were quite different from cell to cell, and elongated cells with larger pre-tension exhibited significant retraction following stretch stimulation. Our magnetic-driven micropillar substrate should be useful in investigating cellular mechanotransduction mechanisms.

Simulations of saturated boiling heat transfer on bio-inspired two-phase heat sinks by a phase-change lattice Boltzmann method

Pool boiling heat transfer from four types of micro-pillar heat sinks with different wettability patterns is simulated numerically with the latest version of liquid-vapor phase-change lattice Boltzmann model. Effects of pillar geometry and wettability on bubble dynamics are investigated. It is found that bubbles will nucleate either on the hydrophobic pillar top or on the hydrophilic cavity bottom between micro-pillars, depending on wettability and local wall temperature. Among the four types of micro-pillar heat sinks with hybrid wettability patterns, it is found that the bio-inspired heat sink (with hydrophobic pillar tops and hydrophilic base) has the best boiling heat transfer performance with the following desirable features: (i) unique characteristics of orderly separation of vapor and liquid paths at low superheats, (ii) hydrophobic surface characteristics where residual bubbles on hydrophobic pillar tops provide faster bubble departure frequency, (iii) triple phase lines are pinned at corners of micro-pillar, restricting expansion of bubbles into film boiling at high superheats. Simulated results show that geometry of micro-pillars and wettability patterns greatly influence transition boiling regime including the maximum heat flux (CHF) and the Leidenfrost temperature, resulting in pool boiling curves with widely different shapes.

Controlled Growth of Patterned Conducting Polymer Microsuckers on Superhydrophobic Micropillar‐Structured Templates

AbstractMorphology greatly impacts the performance improvement of conducting polymers for signal detection, actuator microfabrication, and droplet manipulation applications. However, most of the previous methods cannot satisfy practical demands due to their intrinsic drawbacks. Here, a general strategy is developed for the fabrication of patterned conducting polymers with precisely controlled microstructures (e.g., polypyrrole microsuckers) by regulating the solid/liquid/gas triphase interface and electrochemical polymerization. By regulating the distance between the Pt plate and micropillar‐structured templates, the growth directions of the microsuckers on the pillar tops change from upward (+26 ± 5°) to downward (−32 ± 7°), and their positions to the pillar tops are changed from proximal to distal due to an adjustment in the solid/liquid/gas triphase interface. The influencing factors on the microsucker growth performance, such as the time and current of electrochemical polymerization, the shape and size of micropillars, the type of conducting polymers, are systematically investigated. Furthermore, the as‐prepared microsuckers can be used for transporting water droplets because of their adjustable adhesion to water, which linearly increased from 33.5 ± 2.3 to 61.1 ± 1.2 µN with an increase in the projected epitaxial length of the microsuckers from 3.38 ± 0.39 to 8.78 ± 0.79 µm.

Optimization of pillar electrodes in subretinal prosthesis for enhanced proximity to target neurons

Objective. High-resolution prosthetic vision requires dense stimulating arrays with small electrodes. However, such miniaturization reduces electrode capacitance and penetration of electric field into tissue. We evaluate potential solutions to these problems with subretinal implants based on utilization of pillar electrodes. Approach. To study integration of three-dimensional (3D) implants with retinal tissue, we fabricated arrays with varying pillar diameter, pitch, and height, and implanted beneath the degenerate retina in rats (Royal College of Surgeons, RCS). Tissue integration was evaluated six weeks post-op using histology and whole-mount confocal fluorescence imaging. The electric field generated by various electrode configurations was calculated in COMSOL, and stimulation thresholds assessed using a model of network-mediated retinal response. Main results. Retinal tissue migrated into the space between pillars with no visible gliosis in 90% of implanted arrays. Pillars with 10 μm height reached the middle of the inner nuclear layer (INL), while 22 μm pillars reached the upper portion of the INL. Electroplated pillars with dome-shaped caps increase the active electrode surface area. Selective deposition of sputtered iridium oxide onto the cap ensures localization of the current injection to the pillar top, obviating the need to insulate the pillar sidewall. According to computational model, pillars having a cathodic return electrode above the INL and active anodic ring electrode at the surface of the implant would enable six times lower stimulation threshold, compared to planar arrays with circumferential return, but suffer from greater cross-talk between the neighboring pixels. Significance. 3D electrodes in subretinal prostheses help reduce electrode-tissue separation and decrease stimulation thresholds to enable smaller pixels, and thereby improve visual acuity of prosthetic vision.

Enhancement of boiling heat transfer using hydrophilic-hydrophobic mixed surfaces: A lattice Boltzmann study

In this paper, the boiling heat transfer performance on a type of hydrophilic-hydrophobic mixed surfaces and the underlying enhancement mechanism are numerically investigated using a thermal multiphase lattice Boltzmann model with liquid–vapor phase change. The mixed surface is textured with pillars consisting of hydrophilic side walls and hydrophobic tops, in which the combination of mixed wettability and microstructures is applied. It is found that the hydrophobicity of the tops of pillars promotes bubble nucleation and reduces the required wall superheat for the onset of nucleate boiling; however, it also makes the boiling process enter into the film boiling regime at a lower wall superheat. The interaction between the bubbles nucleated at the corners and the bubbles on the tops of pillars is observed during the boiling process on the mixed surface, which speeds up the departure of the bubbles nucleated at the corners. Moreover, comparisons of the heat flux and the heat transfer coefficient are made between textured surfaces with different wettability: homogeneous wettability, heterogeneous wettability, and hydrophilic-hydrophobic mixed wettability, which reveal that increasing the contact angle of the tops of pillars leads to a leftward shift of the boiling curve and a leftward and upward shift of the heat transfer coefficient curve. Furthermore, the effects of the pillar height and width are also studied.

High-performance flexible surface-enhanced Raman scattering substrates fabricated by depositing Ag nanoislands on the dragonfly wing

Natural dragonfly wing (DW), as a template, was deposited on noble metal sliver (Ag) nanoislands by magnetron sputtering to fabricate a flexible, low-cost, large-scale and environment-friendly surface-enhanced Raman scattering (SERS) substrate (Ag/DW substrate). Generally, materials with regular surface nanostructures are chosen for the templates, the selection of our new material with irregular surface nanostructures for substrates provides a new idea for the preparation of high-performance SERS-active substrates and many biomimetic materials. The optimum sputtering time of metal Ag was also investigated at which the prepared SERS-active substrates revealed remarkable SERS activities to 4-aminothiophenol (4-ATP) and crystal violet (CV). Even more surprisingly, the Ag/DW substrate with such an irregular template had reached the enhancement factor (EF) of ∼1.05×105 and the detection limit of 10−10M to 4-ATP. The 3D finite-different time-domain (3D-FDTD) simulation illustrated that the “hot spots” between neighbouring Ag nanoislands at the top of pillars played a most important role in generating electromagnetic (EM) enhancement and strengthening Raman signals.

A novel patterned magnetic micropillar array substrate for analysis of cellular mechanical responses

Traction forces generated at cellular focal adhesions (FAs) play an essential role in regulating various cellular functions. These forces (1–100 nN) can be measured by observing the local displacement of a flexible substrate upon which cells have been plated. Approaches employing this method include using microfabricated arrays of poly(dimethylsiloxane) (PDMS) micropillars that bend by cellular traction forces. A tool capable of applying a force to FAs independently, by actively moving the micropillars, should become a powerful tool to delineate the cellular mechanotransduction mechanisms. Here, we developed a patterned magnetic micropillar array PDMS substrate that can be used for the mechanical stimulation of cellular FAs and the measurement of associated traction forces. The diameter, length, and center-to-center spacing of the micropillars were 3, 9, and 9 µm, respectively. Iron particles were embedded into the micropillars, enabling the pillars to bend in response to an external magnetic field, which also controlled their location on the substrate. Applying a magnetic field of 0.3 T bent the pillars by ∼4 µm and allowed transfer of external forces to the actin cytoskeleton through FAs formed on the pillar top. Using this approach, we investigated the traction force changes in cultured aortic smooth muscle cells (SMCs) after local compressive stimuli to release cell pretension. The mechanical responses of SMCs were roughly classified into two types: almost a half of the cells showed a little decrease of traction force at each pillar following compressive stimulation, although cell area increased significantly; and the rest showed the opposite, with increased forces and a simultaneous decrease in area. The traction forces of SMCs fluctuated markedly during the local compression. The root mean square of traction forces significantly increased during the compression, and returned to the baseline level after its release. These results suggest that the fluctuation of forces may be caused by active reorganization of the actin cytoskeleton and/or its dynamic interaction with myosin molecules. Thus, our magnetic micropillar substrate would be useful in investigating the mechanotransduction mechanisms of cells.

Coexistence of Pinning and Moving on a Contact Line.

Textured surfaces are instrumental in water repellency or fluid wicking applications, where the pinning and depinning of the liquid-gas interface plays an important role. Previous work showed that a contact line can exhibit nonuniform behavior due to heterogeneities in surface chemistry or roughness. We demonstrate that such nonuniformities can be achieved even without varying the local energy barrier. Around a cylindrical pillar, an interface can reside in an intermediate state where segments of the contact line are pinned to the pillar top while the rest of the contact line moves along the sidewall. This partially pinned mode is due to the global nonaxisymmetric pattern of the surface features and exists for all textured surfaces, especially when superhydrophobic surfaces are about to be flooded or when capillary wicks are close to dryout.

Friction and Wetting Transitions of Magnetic Droplets on Micropillared Superhydrophobic Surfaces.

Reliable characterization of wetting properties is essential for the development and optimization of superhydrophobic surfaces. Here, the dynamics of superhydrophobicity is studied including droplet friction and wetting transitions by using droplet oscillations on micropillared surfaces. Analyzing droplet oscillations by high-speed camera makes it possible to obtain energy dissipation parameters such as contact angle hysteresis force and viscous damping coefficients, which indicate pinning and viscous losses, respectively. It is shown that the dissipative forces increase with increasing solid fraction and magnetic force. For 10 µm diameter pillars, the solid fraction range within which droplet oscillations are possible is between 0.97% and 2.18%. Beyond the upper limit, the oscillations become heavily damped due to high friction force. Below the lower limit, the droplet is no longer supported by the pillar tops and undergoes a Cassie-Wenzel transition. This transition is found to occur at lower pressure for a moving droplet than for a static droplet. The findings can help to optimize micropillared surfaces for low-friction droplet transport.

Photoresponsive wettability switching of TiO 2 ‐coated micropillar arrays with different geometries of overhang roofs

In this work, micropillar array structures with overhang roofs which increase the switching range of the TiO2 photoresponsive wettability, have been fabricated. The liquid droplet placed on the micropillar array exhibits the Cassie–Baxter superhydrophobic state because of the receding of the liquid–air interface to the pillar top, when its contact angle (θ TiO2) on the TiO2 surface exceeds than the geometrical angle (ψ) between the overhang roof and the vertical micropillar shaft. The Cassie–Baxter state can be transformed into the Wenzel state at a relatively large surface area of the micropillar array when the magnitude of θ TiO2 becomes smaller than ψ after ultraviolet irradiation due to the photoinduced superhydrophilicity of TiO2. The rutile TiO2-coated micropillar array with a small ψ exhibits faster reverse wettability transformation from the Wenzel state to the Cassie–Baxter state despite the relatively small θ TiO2 increase in the dark. In addition, the wettability reversal time was shortened from 180 to 6 min after decreasing ψ from 51° to 9°.

Numerical study on splashing of high-speed microdroplet impact on dry microstructured surfaces

The high-speed impact of µm-sized droplets on solid surfaces is a key phenomenon in many industrial applications. In this work, we aim to investigate splashing of high-speed microdroplet impact on micropatterned surfaces through full three-dimensional numerical simulations. An adaptive mesh refinement method is employed to address the challenging issues facing simulations of high-speed impact of microdroplets on the rough surface, such as thin spreading lamella, secondary droplet breakup, and small features of rough surfaces. Validation examples are first presented to evaluate the accuracy of the simulation code for modeling high-speed droplet impact on the textured rough surface. Then, we carried out 3D simulations of a 10 µm diameter water droplet impact on textured surfaces with different impact velocities. We find that during spreading a large portion of the thin lamella actually surfs over the top of pillars with only center area of impact saturated with liquid. When splashing does not occur, the maximum spreading factor for µm-sized droplet impact on smooth surface can be correctly predicted with existing simplified models, whereas these models need to be adjusted for predictions for textured surfaces. Both impact velocity and surface morphology play an important role in the splashing phenomenon. Increasing pillar spacing or reducing pillar height makes droplet impact more prone to splashing. Splashing on surfaces of larger pillar spacing is characterized by the breakup of high-speed jets. Larger impact velocity results in more intensified splashing. For a given impact velocity, densely packed pillars (i.e., smaller pillar spacing) or higher pillars can reduce or even suppress the splashing due to viscous drag effect from pillars in wetted region. The existing splashing threshold models that depend only on surface roughness fail in the prediction of the critical speed for splashing on textured surfaces.

Electrochemical Formation of Free-Standing 3D Structures Using Injection of Additives

A new method of electrochemical formation of free-standing 3D structures based on the injection of additives that controls the deposition rate was demonstrated using copper-chloride-polyethylene glycol as an example. A densely-packed defect-free pillar was formed upon the injection of chloride-free electrolyte into a chloride-containing electrolyte, where copper deposition was fully suppressed. The effects of diffusion coefficient, injection rate and the distance between injection nozzle and pillar top were evaluated with numerical simulation. A fast diffusion species, a moderate injection rate and a small gap between injection and pillar were found beneficial to obtaining the best contrast in the growth rates between pillar and background. The demonstration of free-standing copper structure in this paper provides an alternative path for electrochemical 3D printing of various metallic materials.

Visualization of the Evaporating Liquid-Vapor Interface in Micropillar Arrays

We captured interesting static and dynamic behavior of the liquid-vapor interface in well-defined silicon micropillar arrays during thermally driven evaporation of water from the microstructured surface. The 3-D shape of the meniscus was characterized via laser interferometry where bright and dark fringes result from the interference of incident and reflected monochromatic light due to a variable thickness thin liquid film (FIG. 1). During steady state evaporation experiments, water was supplied to the sample with a syringe pump at 10 μL/min. FIG. 2a and 2b show a SEM image of a typical fabricated micropillar array and a schematic of the experimental setup, respectively. When water wicks through the micropillar array, the meniscus in a unit cell (four pillars in FIG. 1) assumes an equilibrium shape depending on the location from the liquid source/reservoir and the ambient conditions (ambient evaporation at Qin = 0 W). At this point, the meniscus is pinned at the top of the pillars. As the evaporation rate increases due the applied heat flux, the meniscus increases in curvature, thus increasing the capillary pressure to sustain the higher evaporation rate. This is evidenced by the increasing number of fringes in the unit cell when Qin is increased (0 W, 0.11 W, 0.44 W, and 0.99 W, FIG. 1a-1d respectively). Beyond a maximum curvature, the meniscus de-pins from the pillar top surface and recedes within the unit cell. This occurs when the capillary pressure generated at this curvature, cannot balance the viscous loss resulting from flow through the micropillar array. We observed that this receding shape was independent of the applied heat, and only depended on the micropillar array geometry and the intrinsic wettability of the material. Representative meniscus profiles along the diagonal direction of the unit cell obtained from image analysis of FIG. 1 at various Qin are shown in FIG. 2c.

Cell motility regulation on a stepped micro pillar array device (SMPAD) with a discrete stiffness gradient.

Our tissues consist of individual cells that respond to the elasticity of their environment, which varies between and within tissues. To better understand mechanically driven cell migration, it is necessary to manipulate the stiffness gradient across a substrate. Here, we have demonstrated a new variant of the microfabricated polymeric pillar array platform that can decouple the stiffness gradient from the ECM protein area. This goal is achieved via a "stepped" micro pillar array device (SMPAD) in which the contact area with the cell was kept constant while the diameter of the pillar bodies was altered to attain the proper mechanical stiffness. Using double-step SU-8 mold fabrication, the diameter of the top of every pillar was kept uniform, whereas that of the bottom was changed, to achieve the desired substrate rigidity. Fibronectin was immobilized on the pillar tops, providing a focal adhesion site for cells. C2C12, HeLa and NIH3T3 cells were cultured on the SMPAD, and the motion of the cells was observed by time-lapse microscopy. Using this simple platform, which produces a purely physical stimulus, we observed that various types of cell behavior are affected by the mechanical stimulus of the environment. We also demonstrated directed cell migration guided by a discrete rigidity gradient by varying stiffness. Interestingly, cell velocity was highest at the highest stiffness. Our approach enables the regulation of the mechanical properties of the polymeric pillar array device and eliminates the effects of the size of the contact area. This technique is a unique tool for studying cellular motion and behavior relative to various stiffness gradients in the environment.

Adhesion characteristics of Staphylococcus aureus bacterial cells on funnel-shaped palladium–cobalt alloy nanostructures

ABSTRACTThe adhesion properties of Staphylococcus aureus on palladium–cobalt (Pd–Co) alloy nanostructures with various cross-sectional geometries have been characterised. They include solid core, hollow, c-shaped, and x-shaped pillars. These pillars have unique funnel-shaped geometric features on the top surfaces with average included angles between ∼142o and ∼149o. The success rates of cell attachment on these pillar tops were quantified by using field emission scanning electron microscopy techniques. Results show the Staphylococcus aureus attachment rates of Pd–Co solid core, hollow, and x-shaped pillars are statistically indistinguishable with success rate up to 82%. X-shaped pillars have the lowest attachment rate among the four geometries of 46 ± 5%.