Microgroove Patterns Research Articles

Phase Separation Manipulated Gradient Conductivity for A High‐Precision Flexible Pressure Sensor

AbstractPiezoresistive pressure sensors, analyzing and converting external pressure signals to readable electrical signals for monitoring human health, are always subjected to simultaneously possess high signal‐linearity and signal sensitivity. Analogous to the control of sophisticated microstructure for increasing active sensing area, the control of gradient conductivity should enable a linear response via regulating the formed saturation current. Here, inspired by phase separation showing the feasibility of controlling material microstructure and conductivity, a high‐performance flexible pressure sensor via the simultaneous control of microgroove structure and wide‐range gradient conductivity is demonstrated. First, a laser‐etching and dopamine (DA)‐doping synergistic approach is used to induce selective phase separation in poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonic acid) (PEDOT:PSS), achieving broad conductivity modulation (from 297 to 4525 S cm−1) and precise microgroove pattern (15.5 µm). Then, by designing conductivity‐gradient PEDOT: PSS‐based multi‐sublayers and microgroove interlocked structure, the sensor shows extraordinarily comprehensive performance of excellent stress‐sensing sensitivity (4 × 105 kPa−1), high linear responsiveness (99.85%) and wide‐range sensing ability (up to 100 kPa). Consequently, this sensor reveals excellent capability in detecting multi‐mode pressure changes and is expected to branch out into other electronic device designs as a general strategy for the precise manipulation of material physical‐chemical properties.

Advanced micro- & nanostructuring for enhanced biocompatibility of stainless steel by multi-beam and beamshaping technology

Biocompatibility is one of the key issues for implants, especially in the case of stainless steel with medium to low biocompatibility, which may lead to a lack of osseointegration and consequently to implant failure or rejection. To precisely control preferential cell growth sites and, consequently, the biocompatibility of prosthetic devices, two types of surfaces were analyzed, containing periodic nanogrooves laser induced periodic surface structure (LIPSS) and square-shaped micropillars. For the fast and efficient production of these surfaces, the unique combination of high energy ultrashort pulsed laser system with multi-beam and beamshaping technology was applied, resulting in increased productivity by 526% for micropillars and 14 570% for LIPSS compared to single beam methods. In vitro analysis revealed that micro and nanostructured surfaces provide a better environment for cell attachment and proliferation compared to untreated ones, showing an increase of up to 496% in the number of cells compared to the reference. Moreover, the combination of LIPSS and micropillars resulted in a precise cell orientation along the periodic microgroove pattern. The combination of these results demonstrates the possibility of mass production of functionalized implants with control over cell organization and growth. Thus, reducing the risk of implant failure due to low biocompatibility.

Study of the Effect of Cell Prestress on the Cell Membrane Penetration Behavior by Atomic Force Microscopy

In recent years, atomic force microscopes have been used for cell transfection because of their high-precision micro-indentation mode; however, the insertion efficiency of the tip of AFM into cells is extremely low. In this study, NIH3T3 mouse fibroblast cells cultured on a flexible dish with micro-groove patterns were subjected to various substrate strains at 5%, 10%, 15%, and 20%. It was found that the cell stiffness depends on the prestress of the cell membrane, and that the insertion rate of AFM tips into the cell membrane is proportional to the stiffness through the AFM indentation experiment. The finite element analysis proves that prestress increases the bending stiffness of the cytoskeleton, allowing it to better support the cell membrane, which realizes the stress concentration in the contact area between the AFM tip and the cell membrane. The results indicate that the prestress contributes to the mechanical properties of the cell and suggest that the insertion efficiency could be greatly improved with an increase of the prestress of the cell membrane.

Mechanical and morphological responses of osteoblast-like cells to two-photon polymerized microgrooved surfaces.

Microgrooved surfaces are recognized as an important strategy of tissue engineering to promote the alignment of bone cells. In this work, we have investigated the mechanical and morphological aspects of osteoblasts cells after interaction with different micro-structured polymeric surfaces. Femtosecond laser writing technique was used for the construction of circular and parallel microgrooved patterns in biocompatible polymeric surfaces based on pentaerythritol triacrylate. Additionally, we have studied the influence of the biocompatible TiO2 nanocrystals (NCs) related to the cell behavior, when incorporated to the photoresin. The atomic force microscopy technique was used to investigate the biomechanical reaction of the human osteoblast-like MG-63 cells for the different microgroove. It was demonstrated that osteoblasts grown on circular microgrooved surfaces exhibited significantly larger Young's modulus compared to cells sown on flat films. Furthermore, we could observe that TiO2 NCs improved the circular microgrooves effects, resulting in more populated sites, 34% more elongated cells, and increasing the cell stiffness by almost 160%. These results can guide the design and construction of effective scaffold surfaces with circular microgrooves for tissue engineering and bone regeneration.

Micropatterned Hydrogels with Highly Ordered Cellulose Nanocrystals for Visually Monitoring Cardiomyocytes.

Cardiac microphysiological systems are accurate in vitro platforms that reveal the biological mechanisms underlying cardiopathy, accelerating pharmaceutical research in this field. Current cardiac microphysiological devices and organs-on-chips consist of several layers prepared with complex, multi-step processes. Incorporating inorganic photonic crystals may cause long-term biocompatibility issues. Herein, micropatterned hydrogels with anisotropic structural colors are prepared by locking shear-oriented tunicate cellulose nanocrystals (TCNCs) in hydrogel networks through in situ polymerization, allowing the visualization and monitoring of cardiomyocytes. The anisotropic hydrogels are composed of highly ordered TCNCs with bright interference color and micro-grooved methacrylated gelatin with excellent biocompatibility. The microgroove patterns induce cardiomyocyte alignment and the autonomous beating of cardiomyocytes causes the hydrogels to deform, dynamically shifting the interference color. These micropatterned hydrogels could noninvasively monitor real-time changes of cardiomyocytes under pharmaceutical treatment and electrical stimulation through wavelength shifts in the transmittance spectra. This system provides a new way to detect the beat rate of cardiac tissue and it may contribute to high throughput develop.

Electrical and Optoelectronic Properties Enhancement of n-ZnO/p-GaAs Heterojunction Solar Cells via an Optimized Design for Higher Efficiency

In this study, we report the fabrication of high quality AZO/NRs-ZnO/n-ZnO/p-GaAs heterojunction via a novel optimized design. First of all, the electrical proprieties of gallium arsenide (GaAs) substrates were enhanced via an optimized gettering treatment that was based on a variable temperature process (VTP) resulting in an obvious increase of the effective minority carrier lifetime (τeff) from 8.3 ns to 27.6 ns, measured using time-resolved photoluminescence (TRPL). Afterward, the deposition of a zinc oxide (ZnO) emitter was optimized and examined in view of its use both as a light trapping layer (antireflection) and as the n-type partner for the p-type (GaAs) substrate. Nanorod-shaped ZnO was grown successfully on top of the emitter, as an antireflective coating (ARC), to further boost the absorption of light for a large broadband energy harvesting. The interface state of the prepared heterojunction is a key parameter to improve the prepared heterojunction performance, thus, we used laser ablation to create parallel line microgroove patterns in the GaAs front surface. We studied the effect of each step on the performance of the n-ZnO/GaAs heterojunction. The results demonstrate a significant improvement in Voc, Jsc, fill factor (FF), and an obvious enhancement in the I–V characteristics, exhibiting good diode properties, giving rise to the photovoltaic conversion efficiency (η) from 8.31% to 19.7%, more than two times higher than the reference.

Microgroove-patterned Zn metal anode enables ultra-stable and low-overpotential Zn deposition for long-cycling aqueous batteries

The application of zinc (Zn) metal in aqueous Zn metal batteries (ZMBs) has been hindered by the susceptibility of Zn anodes to dendritic electrodeposition due to its inhomogeneous surface structures. Herein, we design uniform microgroove patterns on practically accessible Zn foil anodes using a simple and scalable acid etching strategy. The unique surface structure guides homogeneous Zn deposition, accelerates interfacial reaction kinetics, and inhibits electrolyte corrosion. The resulting Zn anodes afford an excellent plating/stripping stability of 2920 h at an ultralow overpotential of 19.5 mV under 1 mA cm−2/1 mAh cm−2 cycling, with both the cycle life and overpotential ranking among the best records reported thus far. Moreover, the synergetic mechanisms for morphology-induced enhancement were rigorously elucidated. The present strategy contributes a reliable performance baseline for future studies, and can be readily combined with other emerging tactics such as surface coating to accelerate further performance upgrades towards practical ZMBs.

Water droplet bouncing on a hierarchical superhydrophobic surface fabricated by hydrothermal synthesis and ultraprecision machining

The ability of a water droplet to bounce on a superhydrophobic surface is an important indication of the surface wetting properties. In this study, a method integrating hydrothermal synthesis with ultraprecision machining (UPM) is reported for fabricating a hierarchical NiO-FAS-17 coated copper microgroove surface. Contact angles and water droplet bouncing behaviors were tested to evaluate the hydrophobicity of sample surfaces. Large contact angles over 160° and small contact angle hysteresis not exceeding 5° were recorded, showing good water repellency for the NiO-FAS-17 coating. The droplet bouncing results presented a larger first rebound height and stronger tendency of droplet break-up on the hierarchical NiO-FAS-17 coated microgroove surface in comparison with the NiO-FAS-17 coated flat surface, indicating a better hydrophobicity of the hierarchical surface. This reveals that the hydrophobicity of a surface can be enhanced by introducing UPM fabricated microgroove patterns into nanostructured surfaces that already possess good hydrophobicity.

Tribological Performance of Crosshatch Pattern Textured and Heat Treated Dual Engineered Ti6Al4V Surface under Bio-Lubricated Line Contact Configuration

This study combines the laser surface texturing technology and heat treatment process to fabricate a dual surface engineered Ti6Al4V consisting of micro-groove crosshatch pattern texture covered with hard TiO2 oxide coating to reduced friction and improve the wear resistance at the bio-lubricated interface. Crosshatch texture with 25 μm width, 5 μm depth at 25% area density were fabricated using nanosecond Nd:YAG laser over Ti6Al4V surface and then heat treated at 600 °C for 48 hours. XRD result showed rutile TiO2 phase formation along with the presence of anatase TiO2, Al2O3 and Ti3O minor phases whereas, the surface hardness was increased to 1538±41 HV. Bio-tribology experiments were carried out for 45 and 90 o oriented micro-groove crosshatch textures, with and without heat treatment, under partially replicating hip implant articulation. Results demonstrated 60% friction reduction corresponding to the 45 o oriented crosshatch texture with heat treatment. Further, the worn-out surface morphology showed reduced wear damage and good wear debris entrapment inside the micro-grooves.

Construction of micro-grooved PCL/nanohydroxyapatite membranes by non-solvent induced phase separation method and its evaluation for use as a substrate for human periodontal ligament fibroblasts

Micro-patterned membrane constructs based on neat, and nanohydroxyapatite (HA)-blended poly(ε-caprolactone) were developed using the phase separation micro-molding (PSµM) technique. Physical, chemical, thermal, mechanical and in vitro biological properties of the constructs were evaluated. Human periodontal ligament fibroblasts (hPDLFs) were cultured on the surface of the patterned membranes. The effect of micro-patterning on the morphology and osteogenic differentiation capacity of cells was evaluated by SEM and AR-S staining. SEM findings revealed that hPDLFs were able to adhere to ridges, but generally tended to settle along microgroove pattern channels with multiple filopodia. Micro-groove structure led to a narrower elongation of the cytoplasm, orientation and directionality for migration along the groove. After 30 days of culture, the cells had grown to form multiple layers covering the entire patterned surface, while maintaining the alignment of the cells. Extracellular mineralization and osteogenic differentiation of hPDLFs was demonstrated by high AR-S staining, particularly on HA-blended constructs.

Spatial Controls of Ligamentous Tissue Orientations Using the Additively Manufactured Platforms in an In Vivo Model: A Pilot Study

The periodontal ligaments (PDLs) with specific orientations to tooth-root surfaces play a key role in generating biomechanical responses between the alveolar bone and cementum as a tooth-supporting tissue. However, control of angulations and regeneration of the ligamentous tissues within micron-scaled interfaces remains challenging. To overcome this limitation, this study investigated surface fabrications with microgroove patterns to control orientations of rat PDL cells in vitro and fibrous tissues in vivo. After being harvested, rat PDL cells were cultured and three different microgroove patterns (∠PDL groove = 0°, ∠PDL groove = 45°, and ∠PDL groove = 90°) were created by the digital slicing step in 3D printing. Cell-seeded scaffolds were subcutaneously transplanted at 3 and 6 weeks. In histology images, rat PDL cells were spatially controlled to angularly organize following the microgroove patterns and fibrous tissues were formed in scaffolds with specific angulations, which were reflected by additively manufactured microgroove topographies. Based on the results, specifically characterized surface topographies were significant to directly/indirectly organizing rat PDL cell alignments and fibrous tissue orientations. Therefore, interactions between surface topographies and tissue organizations could be one of the key moderators for the multiple tissue complex (bone-ligament-cementum) neogenesis in periodontal tissue engineering.

Mechanism of zirconia microgroove surface structure for osseointegration

Zirconia implants have a promising perspective because of their antibacterial, corrosion resistance, wear resistance, and excellent esthetic effects. Improving the surface morphology of materials to promote osseointegration has always been the focus of implant research and development. Here, we fabricated microgroove (MG) patterns on the surface of zirconia materials using femtosecond laser etching technology. The surface structure of the MGs reduces metal impurities and increases the roughness and hydrophilicity of the material. The MGs on the surface of zirconia can promote the adhesion, proliferation, and osteogenic differentiation of MC3T3-E1 cells. In simulated clinical applications, the micro-groove structure on the surface of zirconia can reduce the stress of the surrounding bone tissue and lead to good osseointegration. Differential gene expression analysis provides a molecular basis for the mechanism research that regulates osteoblast differentiation. In short, this MG structure on the surface of zirconia has great potential for clinical transformation in the field of dental implants.

Chitosan Micro-Grooved Membranes with Increased Asymmetry for the Improvement of the Schwann Cell Response in Nerve Regeneration

Peripheral nerve injuries are a common condition in which a nerve is damaged, affecting more than one million people every year. There are still no efficient therapeutic treatments for these injuries. Artificial scaffolds can offer new opportunities for nerve regeneration applications; in this framework, chitosan is emerging as a promising biomaterial. Here, we set up a simple and effective method for the production of micro-structured chitosan films by solvent casting, with high fidelity in the micro-pattern reproducibility. Three types of chitosan directional micro-grooved patterns, presenting different levels of symmetricity, were developed for application in nerve regenerative medicine: gratings (GR), isosceles triangles (ISO) and scalene triangles (SCA). The directional patterns were tested with a Schwann cell line. The most asymmetric topography (SCA), although it polarized the cell shaping less efficiently, promoted higher cell proliferation and a faster cell migration, both individually and collectively, with a higher directional persistence of motion. Overall, the use of micro-structured asymmetrical directional topographies may be exploited to enhance the nerve regeneration process mediated by chitosan scaffolds.

Nanosecond laser surface texturing of type 316L stainless steel for contact guidance of bone cells and superior corrosion resistance

Osseointegration and corrosion resistance of artificial implants are two major factors that decide their acceptance or rejection by human bodies. This paper provides a robust method for improving the biological performance and corrosion resistance of type 316 L stainless steel (SS) through laser surface texturing (LST). Usage of the second harmonic of a nanosecond Nd:YAG laser, line focusing and optimized range of laser fluence enabled processing of a larger surface area making the method compatible for practical applications as artificial implants. Four different micro-groove patterns were generated on type 316 L SS sample at various laser powers such as 10 mW, 50 mW, 100 mW and 200 mW. Investigation pertaining to adhesion, orientation, and spreading of U2OS osteosarcoma bone cells on sample surface was carried out. Qualitative and quantitative analysis employing confocal and Field Emission-Scanning Electron Microscope imaging, revealed better alignment, larger density and contact guidance of the cells on LST samples. Corrosion studies were done by potentiodynamic polarization and electrochemical impedance spectroscopy coupled with Mott-Schottky (M-S) analysis in simulated body fluid at 37o C. Detailed electrochemical analysis showed significant improvement in corrosion resistance and reduced pitting corrosion for the sample laser treated at 200 mW. The superior anticorrosive behaviour of the sample was due to formation of a dense oxide layer of Fe, Cr and Ni with lower defect density on its surface. Present studies clearly indicated the advantages of nanosecond laser surface texturing to improve the biocompatibility of type 316 L SS in terms of contact guidance of cells with higher viability and superior corrosion resistance.

The Synergy of Topographical Micropatterning and Ta|TaCu Bilayered Thin Film on Titanium Implants Enables Dual-Functions of Enhanced Osteogenesis and Anti-Infection.

Poor osteogenesis and implant-associated infection are the two leading causes of failure for dental and orthopedic implants. Surface design with enhanced osteogenesis often fails in antibacterial activity, or vice versa. Herein, a surface design strategy, which overcomes this trade-off via the synergistic effects of topographical micropatterning and a bilayered nanostructured metallic thin film is presented. A specific microgrooved pattern is fabricated on the titanium surface, followed by sequential deposition of a nanostructured copper (Cu)-containing tantalum (Ta) (TaCu) layer and a pure Ta cap layer. The microgrooved patterns coupled with the nanorough Ta cap layer shows strong contact guidance to preosteoblasts and significantly enhances the osteogenic differentiation in vitro, while the controlled local sustained release of Cu ions is responsible for high antibacterial activity. Importantly, rat calvarial defect models in vivo further confirm that the synergy of microgrooved patterns and the Ta|TaCu bilayered thin film on titanium surface could effectively promote bone regeneration. The present effective and versatile surface design strategy provides significant insight into intelligent surface engineering that can control biological response at the site of healing in dental and orthopedic implants.

The Topographical Optimization of 3D Microgroove Pattern Intervals for Ligamentous Cell Orientations: In Vitro.

Specific orientations of periodontal ligaments (PDLs) to tooth-root surface play an important role in offering positional stabilities of teeth, transmitting and absorbing various stresses under masticatory/occlusal loading conditions, or promoting tissue remodeling by mechanical stimulations to periodontal cells. However, it is still challenging to spatially control PDL orientations and collective PDL cell alignments using 3D scaffold architectures. Here, we investigated the optimization of scaffold topographies in order to control orientations of human PDL cells with predictability in in vitro. The 3D PDL-guiding architectures were designed by computer-aided design (CAD) and microgroove patterns on the scaffold surfaces were created with four different slice intervals such as 25.40 µm (μG-25), 19.05 µm (μG-19), 12.70 µm (μG-12), and 6.35 µm (μG-6) by the digital slicing step. After scaffold design and 3D wax printing, poly-ε-caprolactone (PCL) was casted into 3D printed molds and human PDL cells were cultured for 7 days. In the results, μG-25 with low vertical resolution can angularly organize seeded cells predictably rather than μG-6 created by the highest resolution for high surface quality (or smooth surface). Moreover, nuclear orientations and deformability were quantitatively analyzed and a significant correlation between microgroove pattern intervals and cell alignments was calculated for the topographic optimization. In conclusion, controllable microgroove intervals can specifically organize human PDL cells by 3D printing, which can create various surface topographies with structural consistence. The optimal surface topography (μG-25) can angularly guide human PDL cells, but 6.35 µm-thick patterns (μG-6) showed random organization of cell collectivity.

Promote anti- /de- frosting by suppressing directional ice bridging

Condensation frost is one of the most common types of icing encountered in nature and industrial applications, while its accretion induces multiple non-negligible negative impacts. Many passive anti-/de- frosting approaches by tailoring surface topology and chemistry have been reported recently. To date, however, reliable engineered surfaced that can be compatible with heat exchangers from both mechanical and economic perspectives are limited. In this paper, we present a hierarchically structured surface that can profoundly reduce the frost coverage, and meanwhile promote the rapid removal of frost melts. This surface consists of microgroove pattern and nanoblade structure, where the former provides preferential sites for the growth of condensed droplets, and the latter promises a robust water repellent nature. During frosting, the ice phase spreads only among droplets on groove edges while condensed droplets in valleys are completely evaporated off, yielding a typical pattern that ice stripes distribute discretely in the dry background. During defrosting, frost melts coalesce into large droplets that spontaneously depart the substrate surface. Our results open up a new avenue for surface engineering, particularly on the design of economic and scalable anti-/de- frosting surfaces.

3-DOF ultrasonic elliptical vibration tool holder based on coupled resonance modes for manufacturing micro-groove

This paper reports the innovative design of three degrees of freedom ultrasonic elliptical vibration tool holder (3-DOF UEVTH) based on coupled resonance modes. The purpose of the 3-DOF UEVTH was to fabricate a unique microgroove (μ-groove) pattern compared to traditional cutting (TC). The 3-DOF UEVTH consisted of three key components: a prismatic horn, a backed mass, and a full set of three sandwiched piezo actuators. Modal analysis was applied to determine the 3-DOF UEVTH final dimension. The 3-DOF UEVTH operated in a natural frequency of approximately 24 kHz, which was verified by both simulations and experimental assessments. The 3-DOF UEVTH produced an amplitude on the micro-scale at a resonance frequency of approximately 0.42, 0.5, and 0.6 μm for x-, y- and z-axis directions, respectively. The transient analysis was performed to estimate the 3D-elliptical trajectory, and the device feasibility was examined during microgrooving (μ-grooving) on AISI 1045 material. An excellent topography was obtained using this innovative design.

Laser-chemical treated superhydrophobic surface as a barrier to marine atmospheric corrosion

A time efficient and cost-effective laser-based surface texturing technique combining nanosecond laser ablation and chemical immersion treatment was developed for steel alloy to achieve enhanced corrosion resistance in marine atmospheric environment. Three different surface patterns were created by nanosecond laser ablation and the laser patterned samples were subsequently immersed in 1H,1H,2H,2H-perfluorooctyl silane (FOTS) solution to tune surface chemistry. Dual-scale surface structure was formulated on the laser-chemical treated surface, as confirmed by the scanning electron microscopy (SEM) and confocal laser scanning microscope analyses. X-ray photoelectron spectroscopy (XPS) analysis was conducted to validate that desired surface chemistry was achieved on the laser-chemical treated surface. The effect of surface pattern on several key surface functionalities, including surface wettability, corrosion resistance and chemical stability was systematically presented in this work. Firstly, it was demonstrated via wettability measurements that the laser-chemical treated surface achieved superhydrophobicity with a water contact angle of 158.9°. Secondly, electrochemical and NaCl deliquescence tests were conducted to determine the corrosion resistance of the laser-chemical treated surfaces in marine atmospheric environments. It was confirmed that the laser-chemical treated surface can prevent marine atmospheric corrosion induced by salt deliquescence. Furthermore, it was revealed by electrochemical test that the laser-chemical treated superhydrophobic surface exhibited distinctly better anti-corrosion performance. The experimental results showed that the corrosion rate for the laser-chemical treated surface with microgroove pattern is approximately 5.4% of the corrosion rate for the untreated surface, indicating significant improvement of corrosion resistance for the laser-chemical treated surface. Thirdly, the high water contact angle of 151.0° sustained on the laser-chemical treated surface after electrochemical tests helped confirm the improvement of its chemical stability in corrosion medium. These experimental findings clearly demonstrate the developed nanosecond laser-chemical treatment method can be very effective for fabrication of stable superhydrophobic metal surface as a barrier to marine atmospheric corrosion with enhanced corrosion resistance.

Culture of neural stem cells on conductive and microgrooved polymeric scaffolds fabricated via electrospun fiber-template lithography

We developed polymeric scaffolds that can provide both topographical and electrical stimuli on mouse neural stem cells (mNSCs) for potential use in nerve tissue engineering. In contrast to conventional patterning techniques such as imprinting, soft/photolithography, and three-dimensional printing, microgroove patterns were generated by using aligned electrospun fibers as templates, via a process denoted as electrospun fiber-template lithography. The preparation of polyvinylpyrrolidone fibers, followed by the deposition of poly(lactic-co-glycolic acid) (PLGA) and the removal of the fiber template, produced freestanding PLGA scaffolds with microgrooves having widths of 1.72 ± 0.24 μm. The subsequent deposition of polypyrrole (PPy) via chemical oxidative polymerization added conductivity to the microgrooved PLGA scaffolds. The resultant scaffolds were cytocompatible with mNSCs. The microgroove patterns enhanced the alignment and elongation of mNSCs, and the PPy layer promoted the interaction of cells with the surface by forming more and longer filopodia compared with the nonconductive surface. Finally, the neuron differentiation of mNSCs was evaluated by monitoring the Tuj-1 neuronal gene expression. The presence of both microgrooves and the conductive PPy layer enhanced the neuronal differentiation of mNSCs even without electrical stimulation, and the neuronal differentiation was further enhanced by stimulation with a sufficient electrical pulse (1.0 V).