Parallel Microgrooves Research Articles

Low-Cost and Paper-Based Micro-Electromechanical Systems Sensor for the Vibration Monitoring of Shield Cutters.

Vibration sensors are widely used in many fields like industry, agriculture, military, medicine, environment, etc. However, due to the speedy upgrading, most sensors composed of rigid or even toxic materials cause pollution to the environment and give rise to an increased amount of electronic waste. To meet the requirement of green electronics, biodegradable materials are advocated to be used to develop vibration sensors. Herein, a vibration sensor is reported based on a strategy of pencil-drawing graphite on paper. Specifically, a repeated pencil-drawing process is carried out on paper with a zigzag-shaped framework and parallel microgrooves, to form a graphite coating, thus serving as a functional conductive layer for electromechanical signal conversion. To enhance the sensor's sensitivity to vibration, a mass is loaded in the center of the paper, so that higher oscillation amplitude could happen under vibrational excitation. In so doing, the paper-based sensor can respond to vibrations with a wide frequency range from 5 Hz to 1 kHz, and vibrations with a maximum acceleration of 10 g. The results demonstrate that the sensor can not only be utilized for monitoring vibrations generated by the knuckle-knocking of plastic plates or objects falling down but also can be used to detect vibration in areas such as the shield cut head to assess the working conditions of machinery. The paper-based MEMS vibration sensor exhibits merits like easy fabrication, low cost, and being environmentally friendly, which indicates its great application potential in vibration monitoring fields.

Performance characteristics of ultra-thin flat plate oscillating heat pipes with alternate channels and auxiliary micro-grooved structures

Two flat plate oscillating heat pipes (FPOHPs) characterized by the same thickness of 1 mm and alternating channel widths were fabricated using the wet etching technique. HFE-7100 was used as a working fluid at volumetric filling ratios ranging from 30%–60%. The startup and heat transfer characteristics of FPOHPs with and without embedded parallel microgrooves on the bottom wall of wider channels were experimentally compared and evaluated. The dual-diameter FPOHPs could operate at both horizontal and vertical orientations. The introduction of microgrooves reduced the duration of the startup time, lowered the startup temperature, and avoided the temperature overshoot. Furthermore, the microgrooves significantly reduced the temperature of the evaporator. At the combined condition of 30% filling ratio and 24 W power input, the effective thermal conductivities (ETCs) of the FPOHP with microgrooves were 1241 and 1226 W/(m·°C), respectively, at horizontal and vertical orientations, approximately 25.6% and 18.8% higher than those without microgrooves, or approximately 3.1 times higher than pure copper. At the horizontal orientation, the heat transfer enhancement was more pronounced for the micro-grooved FPOHP compared to that without micro-grooves. The micro-grooved structures facilitated the unidirectional fluid circulation and reduced the gravity dependence, showing the application prospects at both terrestrial and microgravity conditions.

Stability of plane Couette flow under anisotropic superhydrophobic effects

We study the linear stability of plane Couette flow subject to an anisotropic slip boundary condition that models the slip effect of parallel microgrooves with a misalignment about the direction of the wall motion. This boundary condition has been reported to be able to destabilize channel flow far below the critical Reynolds number of the no-slip case. Unlike channel flow, the no-slip plane Couette flow is known to be linearly stable at arbitrary Reynolds numbers. Nevertheless, the results show that the slip can cause linear instability at finite Reynolds numbers also. The misalignment angle of the microgrooves that maximizes the destabilizing effect is nearly π/4, and the unstable modes are of small streamwise wavenumbers and relatively large spanwise wavenumbers. The flow is always more destabilized by two slippery walls compared to a single slippery wall. These observations are in qualitative agreement with the slippery channel flow with the same boundary condition, indicating that such an anisotropic superhydrophobic effect has a rather general destabilizing effect in shear flows regardless of the profile of the base flow. The absence of the Tollmien–Schlichting instability allows us to reveal the inverse relationship between the critical Reynolds number and the slip length as well as the misalignment in the small-parameter regime. The results suggest that arbitrary nonvanishing slip length and misalignment, with arbitrarily weak anisotropy, may suffice to destabilize plane Couette flow.

Directing ligament-mimetic bi-directional cell organization in scaffolds through zone-specific microarchitecture for ligament tissue engineering

Ligament tissues exhibit zone-specific anisotropic cell organization. The cells in ligament-proper are longitudinally oriented, whereas, the cells in epiligament are circumferentially oriented. Therefore, scaffolds developed to regenerate ligament tissues should possess adequate architectural features to govern ligament-mimetic bi-directional cell organization. The scaffold architectural features along with ligament-mimetic cell organization may ultimately yield neo-tissues with ligament-like extracellular matrix (ECM) structure and biomechanical properties. Towards this goal, we fabricated a silk/gelatin-based core–shell scaffold (csSG) with zone-specific anisotropic architectural features, wherein, the core of the scaffold possessed longitudinally aligned pores while the shell of the scaffold possessed parallel microgrooves that are aligned circumferentially around the surface of the scaffold. The ligament-mimetic architectural features significantly improved the mechanical properties of the scaffold. Moreover, architectural features of the csSG scaffold governed zone-specific anisotropic organization of cells. The cells in the core were longitudinally oriented as observed in the ligament-proper and the cells on the shell were circumferentially oriented as observed in epiligament. This bi-directional cell orientation partially mimicked the complex cellular network in native ligament tissue. Additionally, both the core and the shell individually supported fibrogenic differentiation of stem cells which further improved their potential for ligament tissue engineering. Further, the aligned pores of the core could govern unidirectional organization of ECM deposited by cells which is crucial for regenerating anisotropic tissues like ligaments. Finally, when implanted subcutaneously in mice, the scaffolds retained their anisotropic architecture for at least 2 weeks, were biocompatible, supported cell infiltration and governed anisotropic organization of cells and ECM. Taken together, the fabricated biomimetic csSG scaffold, through its zone-specific architectural features, could govern ligament-mimetic cellular and ECM organization which is ultimately expected to achieve regeneration of ligament tissues with native-like hierarchical structure and biomechanical properties. Consequently, this study introduces bi-directional structural parameters as design criteria for developing scaffolds for ligament tissue engineering.

Enhanced lipophilicity and wear resistance of 20CrMnTi induced by laser surface texturing

Gear transmission is crucial in mechanical engineering, extensively used in automobiles, ships, machine tools, and airplanes. However, as gear systems advance towards higher speeds, heavier loads, and smaller sizes, the tooth surface becomes more prone to pitting, wear, and other failures. The use of laser surface texturing technology has shown great promise in enhancing the hydrophobic and lipophilic properties of material surfaces. Thus, this paper presents a novel approach for machining equally spaced parallel and perpendicular microgrooves on the surface of gear steels (20CrMnTi) to facilitate lubricant storage and enhance the material’s surface lipophilicity. Laser power and scanning speed are optimized as parameters for laser processing to investigate the lipophilic properties, including the contact angle, diffusion velocity, and contact behavior of oil droplets. Comparative analysis of the processed and unprocessed specimens revealed that both static and dynamic contact behaviors are significantly changed. Compared with the unprocessed specimens, the static contact angle of the processed specimens decreases from 47° to 0° and is super lipophilic at different temperatures; the oil droplet diffusion distance increases by a maximum of 1.27 times; the vertical diffusion height increases by a maximum of 2.8 mm; and the wetting hysteresis coefficient increases by a maximum of 2.55 times. Additionally, the friction coefficient decreases during the stable wear phase, and the wear depth is reduced by 33.53 %. The research has demonstrated that the oil-attracting properties of 20CrMnTi can be greatly enhanced using laser micro-nano texture technology. This improves lubrication conditions and wear resistance, providing a novel approach to mitigating failure risks such as pitting and wear in various gear mechanisms. Furthermore, this method effectively extends the service life of gears, making it a valuable tool for gear engineering applications.

Harvesting stem cell exosomes from herringbone microfluidic bioreactor for wound healing

Stem cell exosomes have attracted increasing attention in effective wound treatment, while their mass production are still challenging. In this paper, we proposed a novel herringbone microfluidic bioreactor with cell microcarriers integration for batch-preparation of stem cell exosomes. The microfluidic device was designed with parallel herringbone microgrooves on the top and a microcolumn array at the bottom, which provided a controllable fluidic environment for stem cells culturing on the gelatin methacryloyl (GelMA) microcarriers and for exosomes secretion from these cells. Thus, it was demonstrated that the yield of exosomes by this bioreactor was much higher compared with traditional flask cell culture. Besides, bone mesenchymal stem cells (BMSCs) exosomes harvested from the bioreactor under fluidic stimulation expressed an excellent promoting effect on wound healing. These features indicated that the present microfluidic chip integrated with microcarriers possesses great potential for harvesting exosomes for different biomedical applications.

Activity-assisted barrier crossing of self-propelled colloids over parallel microgrooves.

We report a systematic study of the dynamics of self-propelled particles (SPPs) over a one-dimensional periodic potential landscape U_{0}(x), which is fabricated on a microgroove-patterned polydimethylsiloxane (PDMS) substrate. From the measured nonequilibrium probability density function P(x;F_{0}) of the SPPs, we find that the escape dynamics of the slow rotating SPPs across the potential landscape can be described by an effective potential U_{eff}(x;F_{0}), once the self-propulsion force F_{0} is included into the potential under the fixed angle approximation. This work demonstrates that the parallel microgrooves provide a versatile platform for a quantitative understanding of the interplay among the self-propulsion force F_{0}, spatial confinement by U_{0}(x), and thermal noise, as well as its effects on activity-assisted escape dynamics and transport of the SPPs.

Direct formation of periodic parallel microgrooves on glass using CO 2 laser irradiation

Direct laser structuring is an interesting candidate for a rapid, large area and maskless method for formation of various microstructures pattern on glass substrates without the use of mold. Before the desired pattern shape and scale could be obtained, the relationship between the type of laser used, substrate material and laser irradiation parameters must be understood. In this work, direct formation of periodic parallel microgrooves on optical glass substrate using CO2 laser irradiation is proposed. The effect of the laser scanning speed and initial glass temperature to the formation of periodic micro-grooves with various width and height was investigated. As a result, smooth and crack-free parallel microgrooves were successfully fabricated on KPSFN214-P optical glass with dimension ranging from 287μm to 456μm in width dimension and 4.2μm to 11.9μm in height.

Promoting and Orienting Axon Extension Using Scaffold-Free Dental Pulp Stem Cell Sheets.

Current treatments of facial nerve injury result in poor functional outcomes due to slow and inefficient axon regeneration and aberrant reinnervation. To address these clinical challenges, bioactive scaffold-free cell sheets were engineered using neurotrophic dental pulp stem/progenitor cells (DPCs) and their aligned extracellular matrix (ECM). DPCs endogenously supply high levels of neurotrophic factors (NTFs), growth factors capable of stimulating axonal regeneration, and an aligned ECM provides guidance cues to direct axon extension. Human DPCs were grown on a substrate comprising parallel microgrooves, inducing the cells to align and deposit a linearly aligned, collagenous ECM. The resulting cell sheets were robust and could be easily removed from the underlying substrate. DPC sheets produced NTFs at levels previously shown capable of promoting axon regeneration, and, moreover, inducing DPC alignment increased the expression of select NTFs relative to unaligned controls. Furthermore, the aligned DPC sheets were able to stimulate functional neuritogenic effects in neuron-like cells in vitro. Neuronally differentiated neuroblastoma SH-SY5Y cells produced neurites that were significantly more oriented and less branched when cultured on aligned cell sheets relative to unaligned sheets. These data demonstrate that the linearly aligned DPC sheets can biomechanically support axon regeneration and improve axonal guidance which, when applied to a facial nerve injury, will result in more accurate reinnervation. The aligned DPC sheets generated here could be used in combination with commercially available nerve conduits to enhance their bioactivity or be formed into stand-alone scaffold-free nerve conduits capable of facilitating improved facial nerve recovery.

Functional Acrylic Surfaces Obtained by Scratching

By using sandpaper of different grit, we have scratched up smooth sheets of acrylic to cover their surfaces with disordered but near parallel micro-grooves. This procedure allowed us to transform the acrylic surface into a functional surface; measuring the capillary rise of silicone oil up to an average height h¯, we found that h¯ evolves as a power law of the form h¯∼tn, where t is the elapsed time from the start of the flow and n takes the values 0.40 or 0.50, depending on the different inclinations of the sheets. Such behavior can be understood alluding to the theoretical predictions for the capillary rise in very tight, open capillary wedges. We also explore other functionalities of such surfaces, as the loss of mass of water sessile droplets on them and the generic role of worn surfaces, in the short survival time of SARS-CoV-2, the virus that causes COVID-19.

Microstructured collagen films for 3D corneal stroma modelling

ABSTRACT Purpose/aim Corneal injury is a major cause of impaired vision around the globe. The fine structure of the corneal stroma plays a pivotal role in the phenotype and behavior of the embedded cells during homeostasis and healing after trauma or infection. In order to study healing processes in the cornea, it is important to create culture systems that functionally mimic the natural environment. Materials and methods Collagen solution was vitrified on top of a grated film to achieve thin collagen films with parallel microgrooves. Keratocytes (corneal stromal cells) were cultured on the films either as a single layer or as stacked layers of films and cells. SEM and F-actin staining were used to analyze the pattern transference onto the collagen and the cell orientation on the films. Cell viability was analyzed with MTS and live/dead staining. Keratocytes, fibroblasts, and myofibroblasts were cultured to study the pattern’s effect on phenotype. Results A microstructured collagen film-based culture system that guides keratocytes (stromal cells) to their native, layerwise perpendicular orientation in 3D and that can support fibroblasts and myofibroblasts was created. The films are thin and transparent enough to observe cells at least three layers deep. The cells maintain viability in 2D and 3D cultures and the films can support fibroblast and myofibroblast phenotypes. Conclusions The films provide an easily reproducible stroma model that maintains high cell viability and improves the preservation of the keratocyte phenotype in keratocytes that are differentiated to fibroblasts.

Experimental investigation of a capillary-assisted high performance evaporator

A particular architecture for a miniaturized evaporator is proposed in which liquid is spread on the heat source using a thin capillary structure connected to two manifolds. The vapor produced by the heat source is extracted from the device using a separate outlet. A prototype has been designed, manufactured and integrated in a mechanically pumped loop in order to evaluate the evaporator efficiency in terms of heat transfer coefficient and induced pressure drop. In this paper, a capillary structure consisting in parallel rectangular micro-grooves is investigated with HFE7000 used as the working fluid. Results show that the evaporator is able to extract heat flux of the order of 10 W.cm-2 with heat transfer coefficients close to 104 W.m-2.K-1 while inducing pressure losses below a few hundred Pascal. Direct visualizations of the flow in the capillary structure allowed a precise characterization of the evaporator functioning mode, in particular the existence of two distinct two-phase flow regimes depending on the flooding of the capillary structure: nucleate boiling and liquid films evaporation. In order to predict the occurrence of these operating modes, a hydraulic model of the evaporator assembly has been developed and validated thanks to dedicated experimental campaigns. In particular, this model is able to predict the separation between the nucleate boiling and evaporation mode and highlights the fact that the capillary limit is not the main restricting factor in terms of the device maximum manageable heat flux.

A Novel Stereocomplex Poly(lactic acid) with Shish-Kebab Crystals and Bionic Surface Structures as Bioimplant Materials for Tissue Engineering Applications.

The development of green material possessing with great mechanical properties and biocompatibility has become a primary goal for high-performance biological material applications. Herein, the oriented shish-kebab crystals of stereocomplex poly(lactic acid) (SC-PLA) are first reported to be successfully fabricated through a feasible solid-state drawing (SSD) process to simultaneously enhance the mechanical performance and biocompatibility. The resultant biomaterial exhibits a tensile strength of 373 MPa and elongation about 9%, with elastic modulus about 8.1 GPa. Such an outstanding toughening effect is due to an amalgamation of enhanced crystallinity of epitaxial secondary growth lamellae and orientation degree of the fibrous backbone of the SC-PLA samples, both gradually increasing with the draw ratio of SSD increasing. Uniquely distinguished from the typical biomedical polymer with the smooth surface structure, the as-obtained SC-PLA samples possess a surface morphology of parallel microgrooves within ridge structures, attributing to the highly oriented fibrous backbone structure complemented with regularly arranged epitaxial lamellas. This unique trait well represents the human vascular endothelial microstructure that is desirable for cell adhesion-growth to extend its proliferation, differentiation, and activity on the surface of SC-PLA.

Fabrication of Anti-Reflective Surface with Superhydrophobicity/High Oleophobicity and Enhanced Mechanical Durability via Nanosecond Laser Surface Texturing.

In this work, anti-reflective surface with superhydrophobicity/oleophobicity and enhanced abrasion resistance was fabricated on steel alloy surface. Two different surface patterns (i.e., parallel microgrooves and spot arrays) were created by nanosecond laser ablation and chemical immersion. The surface micro/nanostructure, spectral reflectance, wettability, and abrasion resistance of all the samples were determined. The experimental results showed that the laser-chemical treated surfaces exhibited much lower spectral reflectance and significantly enhanced surface integrities compared with the untreated surface. Firstly, the contact angles of water, glycerol, and engine oil on the laser-chemical treated surfaces were increased up to 158.9°, 157.2°, and 130.0° respectively, meaning the laser-chemical treated surfaces achieved both superhydrophobicity and high oleophobicity. Secondly, the laser-chemical treated surface showed enhanced abrasion resistance. The experimental results indicated that the spectral reflectance of the laser-chemical treated surfaces remained almost unchanged, while the laser-chemical treated surface patterned with parallel microgrooves sustained superhydrophobicity with a water contact angle of 150.2° even after more than one hundred abrasion cycles, demonstrating the superior mechanical durability. Overall, this fabrication method has shown its effectiveness for fabrication of multifunctional metal surface integrating the surface functionalities of anti-reflectivity, superhydrophobicity/high oleophobicity, and enhanced abrasion resistance.

Flow boiling in microchannels enhanced by parallel microgrooves fabricated on the bottom surfaces

Flow boiling in microchannels is one of the most desirable cooling solutions for high power electronics. However, it is challenging to promote the flow boiling performance, particularly critical heat flux (CHF), due to their unfavorable liquid rewetting. Inlet restrictors (IRs) have been successfully used to manage two-phase instabilities in flow boiling in microchannels. However, IRs would result in extremely high pressure drop. In this study, without using IRs, parallel microgrooves (W=50 µm, H=250 µm, L=10 mm) are fabricated on the bottom surface of five parallel microchannels (W=200 µm, H=250 µm, L=10 mm) to effectively manage two-phase flow instabilities without sacrificing pressure drop. Our visualization study shows that these microgrooves can enable rewetting at highhigh frequencies up to 151 Hz and enhance thin film evaporation with the highest thin film ratio of 0.65. A highly desirable periodic rewetting mechanism can substantially delay CHF conditions and enhance heat transfer rates. Flow boiling in the present microchannel configuration has been systematically characterized with mass flux ranging from 100 kg/m2s to 600 kg/m2s. Compared to plain-wall microchannels, flow boiling heat transfer coefficient (HTC) is enhanced up to ~72% at a mass flux of 210 kg/m2s due to the sustainable thin film evaporation. Moreover, CHF is substantially enhanced by ~155% at a mass flux of 389 kg/m2s due to the rapid and periodic rewetting enabled by these decorated microgrooves. We also observed that the enhancement of HTC fades when mass flux exceeds 346 kg/m2s due to flooding.

The effect of femtosecond laser fluence and pitches between V-shaped microgrooves on the dynamics of capillary flow

Open microgroove is one kind of capillary-driven superwicking surface structure. In this study, arrays of parallel V-shaped microgrooves were fabricated on an aluminum surface by using a femtosecond laser to obtain a superwicking surface which can quickly transport the water uphill against gravity. The relationships between the flowing time and flowing distance were investigated and compared with theoretical results. We demonstrated both laser fluence and scanning step size can affect the superwicking performance. The aluminum surfaces fabricated at a laser fluence of 18.49 J/cm2 and 52.67 J/cm2 showed the best superwicking performances with the average water flow velocities approximately 16.2 mm/s and 16.4 mm/s, respectively, in the distance of 30 mm. On the other hand, the superwicking surfaces show an anisotropic flow characteristic due to the parallel microgrooves structure. However, when the scanning step size drops to 25 µm, the surface will form irregular rough structures that result in the isotropic flow characteristics. Moreover, by using a thermal camera, we found that after a 10 µL water droplet was dropped into the heated surface, the superwicking surface temperature quickly dropped from 92.4 °C to 82.5 °C which indicated that laser processing of the superwicking surface has potential application in heat dissipation.

Droplet motion on contrasting striated surfaces

Liquid droplets move readily under the influence of surface tension gradients on their substrates. Substrates decorated with parallel microgrooves, or striations, presenting the advantage of homogeneous chemical properties yet varying the topological characteristics on either side of a straight-line boundary, are considered in this study. The basic type of geometry consists of hydrophobic micro-striations/rails perpendicular to the boundary, with the systematic variation of the width to spacing ratio, thus changing the solid–liquid contact fraction and inducing a well-defined wettability contrast across the boundary. Droplets in the Cassie–Baxter state, straddling the boundary, move along the wettability contrast in order to reduce the overall surface free energy. The results show the importance of the average solid fraction and contrasting fraction in a wide range of given geometries across the boundary on droplet motion. A unified criterion for contrasting striated surfaces, which describes the displacement and the velocity of the droplets, is suggested, providing guidelines for droplet manipulation on micro-striated/railed surfaces.

Directional liquid spreading on laser textured aluminum surface

The wettability property of a material surface is highly dependent on the topography of the surface micro/nanostructure. Femtosecond (fs) laser can be used to fabricate various kinds of surface micro/nanostructures. We present parallel microgroove arrays with unique cross-sectional profiles on the surface of an aluminum foil induced by varying the laser fluence and the scanning spacing. The laser textured aluminum surface shows directional spreading of water and inherently hydrophilic aluminum surface becomes superhydrophilic. A water droplet spreads highly anisotropically on the processed area and flows preferentially along the microgrooves. The maximum average spreading velocity of water droplet along the laser textured microgrooves is ~ 200 mm/s, while it is much slower in the direction perpendicular to the microgrooves, which is 41 mm/s. Moreover, the spreading distance of water and time t in both directions have a linear relation with t1/2. The fast-self-spreading motion of water along the microgroove is due to its capillary pressure and a local energy barrier at the boundary between two parallel microgrooves. In addition, laser-modified surface roughness and laser-altered chemical composition on the aluminum surface play a role in enhancing the superhydrophilicity and the directional water spreading behavior. Our research can be applied in the fields of microfluidics, lab-on-chip technology, chemical and biological sensors and heat transfer devices.

Quantitative Study of Morphological Features of Stem Cells onto Photopatterned Azopolymer Films.

In the last decade, the use of photolithography for the fabrication of structured substrates with controlled morphological patterns that are able to interact with cells at micrometric and nanometric size scales is strongly growing. A promising simple and versatile microfabrication method is based on the physical mass transport induced by visible light in photosensitive azobenzene-containing polymers (or azopolymers). Such light-driven material transport produces a modulation of the surface of the azopolymer film, whose geometry is controlled by the intensity and the polarization distributions of the irradiated light. Herein, two anisotropic structured azopolymer films have been used as substrates to evaluate the effects of topological signals on the in vitro response of human mesenchymal stem cells (hMSCs). The light-induced substrate patterns consist of parallel microgrooves, which are produced in a spatially confined or over large-scale areas of the samples, respectively. The analysis of confocal optical images of the in vitro hMSC cells grown on the patterned films offered relevant information about cell morphology—i.e., nuclei deformation and actin filaments elongation—in relation to the geometry and the spatial extent of the structured area of substrates. The results, together with the possibility of simple, versatile, and cost-effective light-induced structuration of azopolymers, promise the successful use of these materials as anisotropic platforms to study the cell guidance mechanisms governing in vitro tissue formation.

Capillary Nylon 6 polymer material produced by femtosecond laser processing.

A wicking Nylon 6 polymer material was produced through surface structuring by a direct femtosecond laser nano/microstructuring approach. The produced wicking structure is an array of parallel microgrooves, the surface of which is textured with irregular nanostructures and fine microstructures. High-speed imaging of water spreading vertically uphill against the gravity discloses a series of capillary flow regimes with h ∝ t, h ∝ t1/2, and h ∝ t1/3 scaling laws, where h is the height of capillary rise and t is the time. In the initial stage, the capillary flow occurs with a single front, from which at a certain time a precursor front forms and advances ahead of the main one. Our study shows that the onset of the precursor front occurs in h ∝ t flow regime. The created material exhibits excellent wicking properties and may find applications in various technologically important areas.