Pillar Spacing Research Articles

Directionality quantification of in vitro grown dorsal root ganglion neurites using Fast Fourier Transform

BackgroundThe directionality analysis of the neurite outgrowths is an important methodology in neuroscience, especially in determining the behavior of neurons grown on silicon substrates. New methodHere we aimed to describe the methodology for quantification of the directionality of neurites based on the Fast Fourier Transform (FFT). We performed an image analysis case study that incorporates several software solutions and provides a rapid and precise technique to determine the directionality of neurites. In order to elicit aligned or unaligned neurite growth patterns, we used adult and newborn dorsal root ganglion (DRG) neurons grown on silicon micro-pillar substrates (MPS) with different pillar widths and spacing. ResultsCompared to the control glass surfaces the neonatal and adult N52 and IB4 DRG neurites exhibited regular growth patterns more pronounced in the MPS regions with s narrow pillar spacing range. The neurites were preferentially oriented along three directional axes at 30°, 90°, and 150°. ConclusionThe proposed methodology showed that FFT analysis is a reliable and easily reproducible method that can be successfully used to test growth patterns of DRG neurites grown on different substrates by considering the direction and angle of the neurites as well as the size of the soma.

Effects of elastic pillars on fluid-flow and heat transfer enhancement in a micro-channel

In this paper, periodic vortices are generated by a fluid passing a cylindrical obstacle, d, near the micro-channel inlet. Two elastic pillars are arranged on the walls, and the effect of the pillar spacing on heat transfer performance is studied using the Arbitrary Lagrangian-Euler method. With the spacing of 10d, the small pillar amplitude of 2 ?m is not conducive to the generation of vortices. The flexible vortex generator has higher heat transfer efficiency and lower pressure loss than the rigid vortex generator. The two pillars with no spacing generate isolated vortices, and the mixing of these vortices is insufficient downstream the pillars. It is found that with the pillar spacing of 5d, the overall performance factor is significantly higher than that with the pillar spacing of 0d and 10d in the Reynolds number range of 800 to 1100. The average Nusselt number with the spacing of 5d increases by 19.2% compared to that with the spacing of 0d at the Reynolds number of 1000. When the Reynolds number is 1100, the overall performance factor is 43% higher than that with a single rigid pillar. The vortices are periodically generated by the two pillars with the 5d spacing, and the disturbance to the boundary layer enhances the heat transfer downstream the region in the micro-channel.

Droplet impact on sparse hydrophobic pillar surface: Impact phenomena, spreading mode, and droplet breakup

Functional surfaces with controllable droplet spreading and breakup dynamics have received widespread attention in self-cleaning, spraying cooling, 3D printing, etc. The arrangement of a microstructure is of great value for the design of functional surfaces. Here, we numerically investigated the droplet impact dynamics on the sparse hydrophobic pillar surface with OpenFOAM. We investigated the effect of Weber number, impact locations, and pillar spacing. Outcomes are most strongly influenced by impact locations, pillar pitch, Weber number, and eight spreading patterns were registered, including circle, square, cross-shaped, Chinese knot, octopus, ellipse, dumbbell, and hexagram. Furthermore, a set of theoretical models were developed for the spreading pattern transition to predict the critical Weber number for different droplet spreading patterns. The breakup dynamics of droplets strongly depend on the spreading patterns and the impact location, which can emit secondary droplets in specific directions. The cross pattern significantly reduces the threshold for secondary droplet generation. The results obtained some essential characteristics for droplet impinging sparse hydrophobic pillar surface, which could provide valuable insights into functional surface design, fluidic-based systems and applications.

Ameboid cell migration through regular arrays of micropillars under confinement

Migrating cells often encounter a wide variety of topographic features—including the presence of obstacles—when navigating through crowded biological environments. Unraveling the impact of topography and crowding on the dynamics of cells is key to better understand many essential physiological processes such as the immune response. We study the impact of geometrical cues on ameboid migration of HL-60 cells differentiated into neutrophils. A microfluidic device is designed to track the cells in confining geometries between two parallel plates with distance h, in which identical micropillars are arranged in regular pillar forests with pillar spacing e. We observe that the cells are temporarily captured near pillars, with a mean contact time that is independent of h and e. By decreasing the vertical confinement h, we find that the cell velocity is not affected, while the persistence reduces; thus, cells are able to preserve their velocity when highly squeezed but lose the ability to control their direction of motion. At a given h, we show that by decreasing the pillar spacing e in the weak lateral confinement regime, the mean escape time of cells from effective local traps between neighboring pillars grows. This effect, together with the increase of cell-pillar contact frequency, leads to the reduction of diffusion constant D. By disentangling the contributions of these two effects on D in numerical simulations, we verify that the impact of cell-pillar contacts on cell diffusivity is more pronounced at smaller pillar spacing.

Solid Oxide Fuel Cells with 3D Inkjet Printing Modified LSM-YSZ Interface

Solid oxide fuel cells (SOFCs) have drawn attention as an alternative power generation technology due to demonstrated high efficiency and low emissions. The lanthanum strontium manganite (LSM)-yttria-stabilized zirconia (YSZ) cathode is utilized widely for SOFCs due to its high performance and stability. The electrochemical oxygen reduction reaction that occurs in the cathode can be enhanced by the porous LSM-YSZ cathode with good electronic and ionic conductivity. With sufficient electrochemically active reaction sites, the oxygen ion transfer processes in the mixed ionic conductor (YSZ) and at the interface of cathode and electrolyte (LSM-YSZ) become critical for the activity of the cathode. Thus, the pillar shape YSZ microstructure with ~ 150 μm×150 μm×10 μm (L×W×H) size can be fabricated by 3D inkjet printing on the interface of electrolyte and cathode to increase the TPB area and enhance the connection between the dense YSZ electrolyte and mixed YSZ ionic conductor. Scanning Electron Microscopy (SEM) is utilized to assess the morphology and microstructure of the YSZ interface. To investigate the influence of the modified interface on the performance of the SOFC, electrochemical performance testing and characterization are conducted for the SOFCs with/without the modified YSZ layer. The microstructures with different pillar central spacing are also fabricated by 3D inkjet printer to optimize the geometry of the LSM-YSZ interface.

A fracture conductivity model for channel fracturing based on lattice-Boltzmann-method and computational-fluid-dynamics

This paper introduces a new method to predict fracture conductivity for channel fracturing by lattice-Boltzmann-method (LBM) and computational-fluid-dynamics (CFD). Firstly, the deformation of the proppant pillar is tested using uniaxial compression experiments. A non-uniform fracture width model considering the nonlinear deformation of fracture and the embedment of proppant pillars is established. Then, an improved model based on LBM-CFD is proposed to simulate the flow field within the fracture and calculate the fracture conductivity. Finally, parametric analysis is carried out to understand the effects of closure stress, elastic modulus of the reservoir rock, proppant pillar's shape and proppant pillar's spacing on fracture width and conductivity. The results showed that the conductivity decreases gradually with closure stress and increases with elastic modulus. The proppant pillar with the smallest shape ratio can provide the highest conductivity. When the ratio of the proppant pillar's diameter to spacing is about 0.5, the conductivity for channel fracturing is best. The time of proppant-laden fluid (PLF) pulse and proppant-free fluid (PFF) pulse are the keys to the successful implementation of channel fracturing. The simulation results have been applied to the optimization of the pulse time in Shengli Oilfield. The field application proves that channel fracturing design based on our method could result in a large increase in well production. This paper gives critical insights for predicting the conductivity for channel fracturing, which could serve as guidelines for the optimization of proppant pillar's parameters and pulse time in channel fracturing design.

Geometric effects induce anomalous size-dependent active transport in structured environments

A multiscale investigation of swimming bacteria in a micropillar array permits measurement of cell body sizes and long-term diffusivities of individuals in a structured medium. When pillar spacing is on the order of the bacterium size, diffusivity behaves anomalously. While shorter cells are trapped by individual pillars through hydrodynamic attraction, causing them to circulate around the pillars, longer cells escape more easily due to simultaneous interactions with multiple pillars. Such size-dependent trapping and escaping is well characterized by a geometric model, suggesting the essential role of environmental and bacterial geometry in governing long-range transport.

Stability Evaluation and Structural Parameters Optimization of Stope Based on Area Bearing Theory

A reasonable and stable stope structure is the premise of realizing safe mining of underground metal ore. To safely mine the gently inclined medium-thick ore body, stope stability in Bainiuchang Mine was analyzed based on the pillar area bearing theory, and stope stability with regard to nine groups of structural parameters was numerically simulated. The results show that the existing stope structural parameters failed to maintain stability requirements and tended to be exposed to the risk of stope collapse. The middle section of the pillar as well as stope roofs and floors are vulnerable due to tensile stress when mining by open stoping, and the compressive stress concentration is prone to occur at the junction of the pillars, stope side walls, roofs and floors. Shear stress contributes little to pillar failure. The reasonable stope structural parameters of open stoping for the gently inclined medium-thick ore body in Bainiuchang mine are optimized using ANSYS numerical simulation: stope height 4.5 m, pillar diameter 4 m, pillar spacing 7 m and pillar row spacing 8 m. The onsite trial shows that the ore recovery rate reaches 82% under these parameters, which also realizes the equilibrium of safety and economy.

Progress towards wafer-scale fabrication based on gel casting technique for 1–3 randomised piezocomposite μUS linear array

Microultrasound (μUS) linear arrays operating at frequencies over 25 MHz have applications in high resolution biomedical imaging. 1–3 connectively piezoceramic – polymer composite (“piezocomposite”) material is attractive for fabrication of these devices due to its high effective electromechanical coupling coefficient and low acoustic impedance for better acoustic matching between transducer and tissue. However, a major concern with this type of material comes from interference between the fundamental thickness-mode resonance and spurious modes, which is usually generated by wave propagation and reflection within the repetitive and symmetrical structure of classical piezocomposite. In general, a fine spatial scale is required of the material structure to suppress the spurious modes; however, the fabrication process is challenging using standard dice-and-fill methods at the fine scales required for high frequencies. A promising way to overcome this challenge is to manipulate the lateral geometry and spacing of the piezoceramic pillars with a random distribution. In this work, gel casting in association with a micromoulding technique has been developed for manufacturing 1–3 randomised piezocomposite active material for μUS linear arrays. 48 vol% solid loading of piezoceramic powder with 30 wt% Hydantoin resin content was employed to prepare a low viscosity aqueous suspension. Through varying powder size, it was found that the suspension with 1.22 µm powder had the highest viscosity, ~ 0.47 Pa.s, and a short gelation time, ~ 10 mins. However, all suspensions had viscosities less than 1 Pa.s at a shear rate of 100 s−1, indicating that they had good flowability. The green body samples showed mean flexural strength 49.7 ± 2.49 MPa. After piezocomposite fabrication with randomised pillars, surface planarisation was used to obtain reliable edge definition of photolithographically-defined electrodes. 20-element arrays with 50-μm element pitch were configured using a bilayer lift-off process. The 1–3 randomised piezocomposite demonstrated its capability to minimise the effects of spurious modes in the thickness mode frequency range, while the thickness resonances provided k33 = 0.67. Without a matching layer, the array produced a − 6 dB bandwidth of 38.4%- and − 20-dB pulse length of 0.26 μs. These results show that 1–3 randomised piezocomposite fabricated from gel-casting associated with a micromoulding technique is feasible for fabrication of μUS linear arrays and may offer a route to small wafer-scale production.

The integrated contribution of surface topology to anti-icing effectiveness

The effects of topology parameters at micro-scale on anti-icing performance have not been investigated theoretically and clearly. In this work, we figured out the affection of structure parameters and derived quantities to anti-icing performance in terms of adhesive strength. Well-textured silicon microstructure with different topologies and surface energies was generated via the lithography process. The parameters including pillar height, top diameter, and spacing were simultaneously investigated through the transition energy barrier approach. The results demonstrated the integrated contribution of all parameters in anti-icing performance, instead of independent effects. Furthermore, our results disclosed the correlation contribution of edge and top effects in adhesion strength. This insight should lead to an understanding of icing phenomena and the design of icephobic surfaces.

Study on Dominant Frequency Attenuation of Blasting Vibration for Ultra-Small-Spacing Tunnel

The middle rock pillar in ultra-small-spacing tunnels is significantly narrow, and the stability of the primary support and lining are easily influenced by the blasting vibration wave from an adjacent tunnel. Therefore, understanding the vibration frequency characteristics is essential for the blasting vibration control. Based on the blasting works on a double-track roadway tunnel (Jiuwuji tunnel in Guizhou, China), this study investigates the dominant frequency attenuation in the preceding tunnel with the middle rock pillar spacing ranging from 4.0 m to 9.4 m. The results show that the ranges of the dominant frequency distributions on the primary support and lining are widely within 200 Hz, but there are varieties in their propagation laws. The distribution of the dominant frequencies on the primary support is broader than that on the lining; and the dominant frequencies are concentrated on a specific range when the lining is far from the blast face beside a particular value, which is not present on the primary support. As the presence of cavity and changing medium between the lining and the primary support, it made a significant contribution to the filtering the vibration waves. Furthermore, on the primary support, the high-frequency part of the vibration waves attenuates rapidly with distance, and then, the practical prediction equations describing dominant frequency attenuation were proposed. The comparison on frequency characteristics per delay for the millisecond delay blasting shows that multiple delay sequences blast contributes to a multi-structured amplitude spectrum of blast vibration waves; and the varies of the equivalent explosion sources dimensions and numbers of free surfaces in each blast delay resulting in diverse vibration waveforms. Finally, the dominant frequencies determined by different methods were compared, and the results show a nonlinear relationship between the ZCFs and DFs. The above research conclusion expands the understanding of blasting vibration in tunnel engineering, particularly in the frequency distribution.

Performance analysis of inclined microjet impingement heat sink with porous medium

The purpose of this research is to find out how well inclined microjet array heat sinks with porous pillars in microchannels perform in electronic cooling applications. The investigation is carried out through CFD analysis for laminar flow with water as heat transfer fluid. Outlet temperature and pressure drop variations are analysed by varying the number of nozzles, jet spacing and porosity of the porous pillars for determining the thermal and hydraulic performance of the inclined micro jet heat sink. The performance of the microjet heat sink was evaluated for a jet array consisting of 2, 6, 10, 14. 18 jets with porous pillars of different porosity values. The idea behind adding porous medium in microchannels was to increase the heat transfer rate between the solid–liquid interface. A constant heat flux of 200 kW/m2 was provided at the bottom surface of the copper substrate to simulate the actual heat generation in electronic devices. The results showed there was a significant improvement in thermal effectiveness in the inclined microjet heat sink with the addition of porous medium. The outlet temperature of water increased by 4.5 °C with the addition of porous medium. Although some rise in pressure drop was also observed, the penalty of it was not as significant when compared with the improvement in heat transfer performance.

Femtosecond Laser Regulated Ultrafast Growth of Mushroom-Like Architecture for Oil Repellency and Manipulation.

Natural organisms can create various microstructures via a spontaneous growth mode. In contrast, artificial protruding microstructures are constructed by subtractive methods that waste materials and time or by additive methods that require additional materials. Here, we report a facile and straightforward strategy for a laser-induced self-growing mushroom-like microstructure on a flat surface. By simply controlling the localized femtosecond laser heating and ablation on the poly(ethylene terephthalate) tape/heat-shrinkable polystyrene bilayer surface, it is discovered that a mushroom-like architecture can spontaneously and rapidly grow out from the original surface within 0.36 s. The dimension of the re-entrant micropillar array (cap diameter, pillar spacing, and height) can be accurately controlled through the intentional control of laser scanning. Followed by a fluorination and spray coating, the obtained surface can realize the repellency and manipulation of oil droplets. This work provides new opportunities in the fields of microfabrication, microfluidics, microreactor engineering, and wearable antifouling electronics.

Survival of polymeric microstructures subjected to interrogatory touch.

Polymeric arrays of microrelief structures have a range of potential applications. For example, to influence wettability, to act as biologically inspired adhesives, to resist biofouling, and to play a role in the "feel" of an object during tactile interaction. Here, we investigate the damage to micropillar arrays comprising pillars of different modulus, spacing, diameter, and aspect ratio due to the sliding of a silicone cast of a human finger. The goal is to determine the effect of these parameters on the types of damage observed, including adhesive failure and ploughing of material from the finger onto the array. Our experiments point to four principal conclusions [1]. Aspect ratio is the dominant parameter in determining survivability through its effect on the bending stiffness of micropillars [2]. All else equal, micropillars with larger diameter are less susceptible to breakage and collapse [3]. The spacing of pillars in the array largely determines which type of adhesive failure occurs in non-surviving arrays [4]. Elastic modulus plays an important role in survivability. Clear evidence of elastic recovery was seen in the more flexible polymer and this recovery led to more instances of pristine survivability where the stiffer polymer tended to ablate PDMS. We developed a simple model to describe the observed bending of micropillars, based on the quasi-static mechanics of beam-columns, that indicated they experience forces ranging from 10-4-10-7 N to deflect into adhesive contact. Taken together, results obtained using our framework should inform design considerations for microstructures intended to be handled by human users.

On altering the wetting behaviour and corrosion resistance of a large metallic surface area by wire electrochemical texturing

This paper presents a novel and practically applicable method for a quick fabrication of uniform surface patterns (periodic micro-pillars with rectangular and square cross-section) on a large surface area of any conducting or semi-conducting material using Wire Electrochemical Micromachining (Wire-ECMM). Micro pillars with a rectangular cross-section are generated by machining mutually perpendicular micro channels. The depth, spacing, and cross-sectional area of pillars are controlled by varying the process parameters and tool travel distance. Primary pillars (level-1 texture) are machined with a constant Direct Current (DC) voltage and secondary pillars (level-2 texture) are machined with a pulsed DC voltage using a tungsten wire of diameter 100 μm. An aqueous solution of sodium nitrate (NaNO 3 ) is selected as an electrolyte having a pH of about 7.01. A good repeatability in the geometrical parameters of a pillar profile is observed on analysing 3D profilometer micrographs of the textured surfaces. Wetting behaviour of textured surfaces with different geometrical parameters is observed using drop shape analyser. A surface with two levels of textures offers highest contact angle of 147.3° with deionized water. Corrosion current and resistance of the textured surfaces are obtained using Linear Sweep Voltammetry (LSV) and Electrochemical Impedance Spectroscopy (EIS), respectively. Results suggest that corrosion resistance depends upon the area of texture and is highest for the sample with the largest textured area. Also, a sample with the smallest value of area factor (ratio of total area of the top surface of all the pillars in a region to the total projected area of a region) offers highest resistance to corrosion. • A novel approach for large area texturing on any conducting and semi-conducting surface using Wire Electrochemical Micromachining (Wire-ECMM). • A study of the influence of different process parameters on various geometrical features of a textured surface. • A detailed characterization of different textured surfaces using SEM imaging and surface topography. • In depth analysis of the wetting and corrosion behaviour of the textured surfaces using drop shape analyser and Electrochemical Impedance Spectroscopy (EIS).

Bubble dynamics and dry spot formation during boiling on a hierarchical structured surface: A lattice Boltzmann study

In this paper, the bubble dynamics and the mechanism of dry spot formation during boiling on a two-level hierarchical structured surface are numerically investigated using a three-dimensional thermal multiphase lattice Boltzmann model with liquid–vapor phase change. The hierarchical structured surface consists of three parts: a smooth surface basement, primary pillars on the basement, and secondary pillars overlaid on the primary pillars. It is found that the boiling heat transfer on the hierarchical structured surface is significantly dependent on the bubble departure frequency and the dry area fraction, which are in turn affected by the structural parameters of secondary pillars. Increasing the height or width of the secondary pillars is found to effectively increase the bubble departure frequency, but it may also enlarge the size of dry spots on the hierarchical structured surface. The numerical investigation shows that, in order to prevent the formation of dry spots on the hierarchical structured surface, an effective approach is to reduce the proportion of the contact line on the lateral walls of secondary pillars to the whole contact line, which can be realized by reducing the area of the lateral walls of secondary pillars or appropriately increasing the secondary pillar spacing. The optimum boiling performance on the hierarchical structured surface is found to be achieved under the situation that the bubble departure frequency is sufficiently high, but the dry spot area is as small as possible.

Wettability of complex Long-Chain alkanes droplets on Pillar-type surfaces

To reveal the difference in wettability of long-chain alkane and simple molecular materials on the structural surfaces, we employ long-time molecular dynamics simulation to study the wettability of complex alkane droplets on flat and pillar-type surfaces by comparing the contact angle and the transition of the wetting state. The results showed that the transition of the wetting state depended on the joint action of potential coefficient, pillar spacing, and pillar height, and the wetting state of droplets could transform into each other among Wenzel state, Cross state, and Cassie state. The accurate ranges of the predicted values of the Cassie formula were the weaker fluid–solid attraction and smaller pillar spacing. In contrast, the accurate ranges of the predicted values of the Wenzel formula were the stronger fluid–solid attraction and smaller roughness. When the fluid–solid attraction was strong and the pillar spacing was small, both the Wenzel and Cassie formula could accurately predict the corresponding contact angle. By giving the corresponding conditions of the Cross state and revealing the differences in alkane droplets with variable chain lengths in the transition of the wetting state, it could serve as a reliable reference for subsequent simulations of complex materials on nanostructure surfaces.

Condensation Behavior of Hierarchical Nano/Microstructured Surfaces Inspired by Euphorbia myrsinites.

In nature, many extant species exhibit functionalized surface structures during evolution. In particular, wettability affects the functionalization of the surface, and nano/microstructures have been found to enable functions, such as droplet jumping, thereby making self-cleaning, antifog, antibacterial, and antireflection surfaces. Important efforts are underway to understand the surface structure of plant leaves and establish rational design tools for the development of new engineering materials. In this study, we focused on the hierarchical nano/microstructure of the leaves of Euphorbia myrsinites (hereinafter, E. myrsinites), which has a hierarchical shape with microsized papillae, covered with nanosized protruding wax, and observed the condensation behavior on the leaf surface. Si is vertically etched via reactive ion etching (RIE) to artificially mimic the hierarchical nano/microstructures on the leaves of E. myrsinites. We made four types of artificial hierarchical structures, with micropillars having pillar diameters of 5.6 and 16 μm (pillar spacing of 20 and 40 μm, respectively) and heights of 6.5 and 19.5 μm, and nanopillars formed on the surface. The optical observation with a microscope revealed a very high density of condensed droplets on the artificial surface and a stable jumping behavior of droplets of 10 μm or more. Furthermore, in the samples with a micropillar diameter of 5.6 μm and a micropillar height of 19.5 μm, the droplets that had jumped and fallen thereupon bounced off, thereby preventing reattachment. As a result, no droplets of 35 μm or more could exist even after 10 min. In addition, it was clear that a small underlying droplet of less than 10 μm was generated at the bottom of the relatively large secondary droplet existing on the large micropillar of 16 μm, and a frequent coalescence of the droplets occurred. This study revealed the phenomenon of condensation on the surface of plants as well as made it possible to improve the heat exchange process by significantly promoting the heat transfer of condensation using artificial surfaces.

Experimental investigation of the effect of cylindrical array structure on heat transfer performance during nucleate boiling

Using deionized water as the working fluid, a visualized pool boiling study was carried out on the surface of cylindrical pillar arrays of different sizes and the ordinary smooth surface under atmospheric pressure, and the boiling heat transfer curve and the change of heat transfer coefficient were studied. A high-speed camera is used to quantitatively measure the bubble dynamics, including bubble departure diameter and nucleation sites density. The results show that the onset of nucleate boiling temperature of all cylindrical pillar arrays has been significantly reduced, while the heat transfer coefficient is increased by 23.4%-163.4% compared to that of the smooth surface. The decrease of the pillar spacing helps to improve the performance of boiling heat transfer. The smaller gap optimizes the capillary flow of the liquid to a certain extent, thus facilitating the departure of bubbles, thereby inducing the working fluid to quickly replenish the dry area. The reduction of the diameter of the pillars is beneficial to improve the boiling heat transfer performance. More nucleation sites on the wall promote the bubbles to merge more quickly and reach the bubble departure diameter more easily, thus enhancing the evaporation of the micro-liquid layer and promoting the heat transfer. The correlation expressions as well as the upper and lower limits are obtained by fitting the change of heat transfer coefficient curve. Compared with the data in the literature, the S6 surface with the best performance shows obvious heat transfer advantages.

Novel hole-pillar spacer design for improved hydrodynamics and biofouling mitigation in membrane filtration

Feed spacers are the critical components of any spiral-wound filtration module, dictating the filtration performance. Three spacer designs, namely a non-woven commercial spacer (varying filament cross-section), a symmetric pillar spacer, and a novel hole-pillar spacer (constant filament diameter) were studied using Direct Numerical Simulations (DNS), 3-D printed and subsequently experimentally tested in a lab-scale ultrafiltration set-up with high biofouling potential feed water at various feed pressures. Independent of the applied pressure, the novel hole-pillar spacer showed initially the lowest feed channel pressure drop, the lowest shear stress, and the highest permeate flux compared to the commercial and pillar spacers. Furthermore, less biofilm thickness development on membrane surface was visualized by Optical Coherent Tomography (OCT) imaging for the proposed hole-pillar spacer. At higher feed pressure, a thicker biofilm developed on membrane surface for all spacer designs explaining the stronger decrease in permeate flux at high pressure. The findings systematically demonstrated the role of various spacer designs and applied pressure on the performance of pre-treatment process, while identifying specific shear stress distribution guidelines for engineering a new spacer design in different filtration techniques.