Replication Of Microstructures Research Articles

Poisson Effect‐Assisted Replication Lithography for Rapid Fabrication of Three‐Dimensional Microstructures

Demands for micro‐ and nano‐fabrication techniques have been increasing over recent decades due to their foundational importance in fields such as electronics, sensors, displays, biotechnologies, and energy technologies. Still, the rapid and efficient fabrication of complex 3D microstructures has long been a challenge due to the inherent limitations of conventional imprint lithography and the slow fabrication speed of maskless lithography systems using femtosecond lasers. This study introduces a novel lithographic replication method for the rapid replication of intricate 3D microstructures with closed‐loops by leveraging the Poisson effect‐driven lateral deformation of soft molds. Specifically, the suggested technique employs an elastomeric soft mold, engraved with negative cavity parts of the target structure separated by intentional gaps. Lateral deformation of the material allows the separated cavities to assemble for replication of target microstructure and defectless release from the soft mold. In addition to the experimental demonstrations of the proposed method using well‐known materials like polydimethysliloxane (PDMS) for the soft mold and UV‐curable polyurethane acrylate (PUA) for replication, essential considerations such as material selection and master mold design are discussed. The presented method not only broadens the capabilities of imprint lithographic techniques but also holds promise for the large scale, continuous fabrication of complex 3D microstructures.

3D-printed bioinspired spicules: Strengthening and toughening via stereolithography

Recently, the replication of biological microstructures has garnered significant attention due to their superior flexural strength and toughness, coupled with lightweight structures. Among the most intriguing biological microstructures renowned for their flexural strength are those found in the Euplectella Aspergillum (EA) marine sponges. The remarkable strength of this sponge is attributed to its complex microstructure, which consists of concentric cylindrical layers known as spicules with organic interlayers. These features effectively impede large crack propagation, imparting extraordinary mechanical properties. However, there have been limited studies aimed at mimicking the spicule microstructure. In this study, structures inspired by spicules were designed and fabricated using the stereolithography (SLA) 3D printing technique. The mechanical properties of concentric cylindrical structures (CCSs) inspired by the spicule microstructure were evaluated, considering factors such as the wall thickness of the cylinders, the number of layers, and core diameter, all of which significantly affect the mechanical response. These results were compared with those obtained from solid rods used as solid samples. The findings indicated that CCSs with five layers or fewer exhibited a flexural strength close to or higher than that of solid rods. Particularly, samples with 4 and 5 cylindrical layers displayed architecture similar to natural spicules. Moreover, in all CCSs, the absorbed energy was at least 3–4 times higher than solid rods. Conversely, CCSs with a cylinder wall thickness of 0.65 mm exhibited a more brittle behavior under the 3-point bending test than those with 0.35 mm and 0.5 mm wall thicknesses. CCSs demonstrated greater resistance to failure, displaying different crack propagation patterns and shear stress distributions under the bending test compared to solid rods. These results underscore that replicating the structure of spicules and producing structures with concentric cylindrical layers can transform a brittle structure into a more flexible one, particularly in load-bearing applications.

Fabrication of biomimetic anisotropic crescent-shaped microstructured surfaces by laser shock imprinting

Abstract The crescent-shaped microstructure bionic to the slip zone of the slippery zone of the carnivorous plant genus Nepenthes was fabricated on the surface of copper foil by laser shock imprinting (LSI). The microstructure of crescent-shaped grooves was initially fabricated on the surface of the micro-mold by etching, and then the microstructure was replicated on the surface of copper foil through plastic deformation under laser shock loading. Increasing the laser shock energy or the number of shocks can increase the degree of replication of the crescent-shaped microstructure, the height of the crescent-shaped microstructure, and the contact angle of water droplets on the surface. The wettability of the surface of the crescent microstructure is anisotropic and increases with an increase in offset distance. The anisotropy of the crescent-shaped microstructure causes the solid–liquid contact line in the direction of the bottom of the arc to become a long and approximately straight line. According to the rule that controlling LSI processing parameters can fabricate surfaces with different heights and wettability, a gradient wetting surface consisting of crescent-shaped microstructures was designed to achieve the directional spreading of droplets. By altering the distribution of crescent-shaped microstructures, a type-I flow channel with the ability to limit the spreading range of water droplets was fabricated.

Study on warpage and filling behavior of glass in non-isothermal hot embossing

Non-isothermal hot embossing has great potential in the mass production of glass micro optical components due to the relatively short heating-cooling cycle time. However, warpage was induced by the temperature gradient inside the glass replica during hot embossing, resulting in a deteriorated optical performance. Therefore, it is non-trivial to investigate the effects of process parameters on warping and filling behaviors of glass in non-isothermal hot embossing. Firstly, a high-quality microhole was fabricated on monocrystalline silicon carbide (SiC) mold by focused ion beam (FIB) lithography. By using a novel home-made gravity-assisted hot embossing machine, the geometric information (i.e., warpage and microstructures) on SiC mold was transferred into the surface of N-BK7 glass replica. The experimental results indicate that high embossing temperature enables not only the minimization of warpage but also the enhancement of microstructure replication accuracy. Furthermore, increasing embossing force enhances filling capacity but increases warpage amplitude. Interestingly, fast heating/cooling rates and short embossing time enable a small warpage as well as a high embossing efficiency. By optimizing the process parameters, especially the embossing temperature, a small warpage amplitude of 3 μm and a high transfer ratio of 99.11% were achieved, which can meet the high requirement of precision optical components.

Effects of Cavity Thickness and Mold Surface Roughness on the Polymer Flow during Micro Injection Molding.

In micro injection molding, the cavity thickness and surface roughness are the main effects factors of polymer flow in the die designing and affect the quality of molded products significantly. In this study, the effects of cavity thickness and roughness of cavity surface were investigated mainly on polymer flow during molding and on the roughness of molded products. The parts were molded in the cavities with the thickness from 0.05 mm to 0.25 mm and surface roughness from Ra = 46.55 nm to Ra = 462.57 nm, respectively. The filling integrities and roughness replication ratio of molded parts were used to evaluate the statements of polymer flow and microstructure replication during micro injection molding, respectively. The results showed that the filling integrity changing trends in the thinner cavities were obviously different or even opposite to those in the thicker cavities with the changing of cavity surface roughness instead of single trend in the conventional studies. For each cavity surface roughness, the filling integrity showed an upward trend with the increasing cavity thickness. In different cavity thickness, the maximum gap of filling integrity was 23.76 mm, reaching 544.94% from 0.05 mm to 0.25 mm. Additionally, the surface roughness ratio was slightly smaller than one before, reaching the polymer surface roughness limit around Ra = 71.27 nm, which was decided by the nature of the polymer itself. This study proposed the references for the design and fabrication of mold cavities and parts, and saved time and cost in the actual product manufacturing.

Modelling and Validation of Microstructure Replication on Aluminum Foils from Laser-Patterned Stamps

Modelling and Validation of Microstructure Replication on Aluminum Foils from Laser-Patterned Stamps

Impact of Die Coatings on Forming Conditions in Electromagnetic Embossing of Thin Sheet Metal

In electromagnetic embossing, the interaction of the magnetic field and the induced current density results in body forces that enable the replication of optical microstructures into thin sheet metals. However, as the sheet metal is completely penetrated by the magnetic field, electromagnetic properties of the dies need to be considered in process design, as they influence the forming conditions by changing the field distribution, force vectors and eddy current densities. With die coatings like electroless nickel–phosphorus (NiP), the electromagnetic properties of the die change. Therefore, the effect of both - die substrate and coating material - was studied to find advantageous conditions for electromagnetic embossing. Within two-dimensional electromagnetic field simulation, the electromagnetic properties of coating and substrate material were varied in addition to the coating thickness. To validate the results, electromagnetic embossing experiments were carried out. Here, different dies were fabricated from aluminum (uncoated) and cold work steel with 200 µm and 400 µm thick electroless nickel–phosphorus coatings that were subsequently micro-structured in optical surface quality. It was demonstrated by numerical and experimental results that the coating and the substrate influence the electromagnetic embossing significantly in correspondence to their shielding behavior and field interaction due to electromagnetic properties and coating thickness.

A general strategy towards controllable replication of butterfly wings for robust light photocatalysis

• A general strategy towards controllable replication of butterfly wings was proposed. • Controlled anatase and rutile phase of TiO 2 can be realized simply via the tuning of the treatment parameters. • TiO 2 replicas exhibit significantly enhanced photocatalytic activity to decompose methylene blue under solar light illumination. • The enhancement can be attributed to a synergy effect of the presence of Ti 3+ doping, the air-TO 2 interaction, and hierarchical microstructure. • This work offers a scalable and precise approach to replicate various bio-templates based on transition metal oxides. Large-scale replication of the hierarchical microstructure of bio-template is a long-standing challenge due to the large shrinkage when the bio-templates are burned off. In this work, TiO 2 based biomimetic metamaterials have been successfully synthesized by sputtering technique, followed by tape assisted transferring and thermal oxidation process. Tile-like arrays of the scale replicas with ridge-lamellae hierarchical microstructures have been obtained and exhibit bright blue-purple structure color. More interestingly, they exhibit significantly enhanced photocatalytic activity to decompose methylene blue under solar light illumination, with the degradation rate of methylene blue almost five times that of TiO 2 thin films with the same sample area. The enhancement on the visible light photocatalytic activity in TiO 2 replicas can be attributed to a synergy effect of the presence of Ti 3+ doping, the air-TO 2 interaction, and hierarchical microstructure. The controlling factors that affect the microstructure, structural color and photocatalytic activity of the TiO 2 replicas have been discussed in detail. This work offers a scalable and precise approach to replicate various bio-templates based on transition metal oxides, such as ZnO, Fe 3 O 4 , CoO, and VO 2 , thereby providing the new opportunity for infrared sensing, photocatalytic and photonic applications.

Self-Cleaning Biomimetic Surfaces—The Effect of Microstructure and Hydrophobicity on Conidia Repellence

Modification of surface structure for the promotion of food safety and health protection is a technology of interest among many industries. With this study, we aimed specifically to develop a tenable solution for the fabrication of self-cleaning biomimetic surface structures for agricultural applications such as post-harvest packing materials and greenhouse cover screens. Phytopathogenic fungi such as Botrytis cinerea are a major concern for agricultural systems. These molds are spread by airborne conidia that contaminate surfaces and infect plants and fresh produce, causing significant losses. The research examined the adhesive role of microstructures of natural and synthetic surfaces and assessed the feasibility of structured biomimetic surfaces to easily wash off fungal conidia. Soft lithography was used to create polydimethylsiloxane (PDMS) replications of Solanum lycopersicum (tomato) and Colocasia esculenta (elephant ear) leaves. Conidia of B. cinerea were applied to natural surfaces for a washing procedure and the ratios between applied and remaining conidia were compared using microscopy imaging. The obtained results confirmed the hypothesis that the dust-repellent C. esculenta leaves have a higher conidia-repellency compared to tomato leaves which are known for their high sensitivities to phytopathogenic molds. This study found that microstructure replication does not mimic conidia repellency found in nature and that conidia repellency is affected by a mix of parameters, including microstructure and hydrophobicity. To examine the effect of hydrophobicity, the study included measurements and analyses of apparent contact angles of natural and synthetic surfaces including activated (hydrophilic) surfaces. No correlation was found between the surface apparent contact angle and conidia repellency ability, demonstrating variation in washing capability correlated to microstructure and hydrophobicity. It was also found that a microscale sub-surface (tomato trichromes) had a high conidia-repelling capability, demonstrating an important role of non-superhydrophobic microstructures.

Fabrication of permanent self-lubricating 2D material-reinforced nickel mould tools using electroforming

In the replication of polymeric micro/nano structures, adhesion and friction between mould tool and polymer cause significant feature failure. For the first time, this work developed a novel strategy for the fabrication of high-hardness and self-lubricating 2D material-reinforced nickel mould tools using electroforming to achieve high precision replication of polymeric micro structures. In this study, layered 2D material, including graphene oxide (GO), molybdenum disulfate (MoS2), and tungsten disulfide (WS2), for the fabrication of self-lubricating mould tools, were systematically studied. Our results demonstrated that nickel/WS2 mould tools, followed by nickel/GO and nickel/MoS2 mould tools, presented the most significant microhardness improvement. A maximum microhardness of ∼660 HV together with a minimum crystallite size of 12 nm was achieved from 0.5 g/L WS2, indicating a 3.67 times microhardness increase and 3 times crystallite size reduction relative to the pure nickel mould tool. The enhanced microhardness can be attributed to the 2D material-induced crystal refinement, and inherent hardness and incorporation content of 2D material. Additionally, friction and wear tests revealed that a low concentration of WS2 at 0.14 g/L achieved the lowest coefficient of friction (COF) and superior wear resistance. The COFs in the initial stage and steady state stage were 0.08 and 0.18, respectively, implying decreases of 42.8% and 72.3%, respectively, and a 27-fold increase in lifetime compared with those of the pure nickel mould tool. Such a significant improvement in tribological properties was due to the formation of self-lubricating transfer film by the interlayer shear effect of few-layered 2D material nanosheets. Finally, defect-free polymeric microfluidic chips were micro hot embossed using an optimal self-lubricating nickel/WS2 mould tool for validation. This work provides significant insight into the fabrication of potential self-lubricating micro/nano mould tools for microfluidics applications.

Design of Precision Hot Embossing Machine for Micropatterning on PMMA

Abstract A microfluidic chip requires microchannels to be created on a substrate. This paper focuses on the design and development of a precision hot embossing machine for replication of microstructures on a polymethyl methacrylate (PMMA) substrate. Kinematic coupling using three spherical balls in radial v-grooves is used to achieve precise positioning of the mold insert with the base. Flexure-based parallel guidance mechanism is used for one degree-of-freedom (DOF) motion required for the embossing process. The mechanism allows the motion of the mold normal to the substrate surface. Flexure-based kinematic coupling with the thermal center is designed to mitigate thermal stress build-up during heating and cooling of the mold insert. An Arduino-based microcontroller is developed to control the temperature profile during the process. A prototype is fabricated and experiments are performed with an aluminum mold insert on a PMMA substrate. The result shows the feasibility of the concept and the setup can be used to develop a cost-effective precision hot embossing machine for creating micropatterns for microfluidic applications.

Study on Preparation of Microstructured Optical Membrane

Micro-structured optical film is one of the micro-optical elements and has a great market demand. This article studies the microstructured optical film formed by UV imprinting: The influence of embossing pressure on microstructure replication accuracy was explored. The larger the pressure, the better the material filling. When the pressure is 5N, the microstructure replication is complete; The relationship between the radiation intensity and warpage deformation was explored, and the decrease in the intensity of the UV light source can effectively reduce the warpage deformation; The influence of the material formula on the optical properties of the product was explored. When the oligomer content was 55%, the film had a high light transmittance. At the same time, the prepared film was subjected to an apparent inspection with good microstructure replication accuracy.Microstructured optical elements are widely used in optical fields such as semiconductors, lasers, beam shaping [1-2] and solar energy [3-5] due to their unique advantages such as small size and high performance. As a key component in many industries, it has a high market demand rate. However, the microstructure forming process is complicated, the manufacturing cost is high, and the accuracy is difficult to guarantee, which has restricted its development. With the advancement of science and technology and the increase in market demand, more and more researchers and enterprises have put their eyes on the research of preparing micro-structured optical elements.At present, the commonly used microstructures are mainly icrolens array [6-8], and the processing methods include micro-imprinting [9-10], etching [11], electron beam direct writing, and micro-injection [12], etc. This article studies the UV-curing embossing process in micro-embossing. This processing method has the advantages of fast molding, high efficiency, and environmental protection. And this process is conducive to mass production and has a broad market application prospect.In this paper, the forming process and material formulation of microstructured optical film prepared by light-cured micro-imprinting were investigated, and the microstructure morphology of the preparation was analyzed apparently.

Energy-absorbing wood composite for improved damage tolerance inspired by mollusc shells

The crossed lamellar structure (CLS) found in mollusc shells is an excellent example for nature’s ability to form complex hierarchical microstructures with a remarkable balance between strength and toughness. The CLS has become the subject of numerous studies focusing on the replication of the unique microstructure using synthetic composites. The present study proposes a wood composite replicating the CLS’ middle layer microstructure and investigates the mechanical properties using three-point bending tests. The morphology of the failure mechanisms is recorded using digital microscopy and the experimental data are compared to those from ply- and solid woods. The results show a successful replication of the dominating failure mechanisms of crack deflection and crack bridging. While strength decreased significantly by ∼60%, toughness increased remarkable by ∼70% compared to plywood and was in the range of solid wood. The small data scattering from the wooden CLS samples compared to solid wood further hints on a stable failure mechanism and uniform energy-absorption. The results document that wood can be used to design an energy-absorbing composite based on the CLS-inspired ductile microstructure.

A 3D Biohybrid Real-Scale Model of the Brain Cancer Microenvironment for Advanced In Vitro Testing.

The modeling of the pathological microenvironment of the central nervous system (CNS) represents a disrupting approach for drug screening for advanced therapies against tumors and neuronal disorders. The in vitro investigations of the crossing and diffusion of drugs through the blood–brain barrier (BBB) are still not completely reliable, due to technological limits in the replication of 3D microstructures that can faithfully mimic the in vivo scenario. Here, an innovative 1:1 scale 3D-printed realistic biohybrid model of the brain tumor microenvironment, with both luminal and parenchyma compartments, is presented. The dynamically controllable microfluidic device, fabricated through two-photon lithography, enables the triple co-culture of hCMEC/D3 cells, forming the internal biohybrid endothelium of the capillaries, of astrocytes, and of magnetically-driven spheroids of U87 glioblastoma cells. Tumor spheroids are obtained from culturing glioblas-toma cells inside 3D microcages loaded with superparamagnetic iron oxide nanoparticles (SPIONs). The system proves to be capable in hindering dextran diffusion through the bioinspired BBB, while allowing chemotherapy-loaded nanocarriers to cross it. The proper formation of the selective barrier and the good performance of the anti-tumor treatment demonstrate that the proposed device can be successfully exploited as a realistic in vitro model for high-throughput drug screening in CNS diseases.

Biomimetic Replication of Root Surface Microstructure using Alteration of Soft Lithography

Biomimetic Replication of Root Surface Microstructure using Alteration of Soft Lithography

Biomimetic Replication of Root Surface Microstructure using Alteration of Soft Lithography.

Biomimetics is the use of chemistry and material sciences to mimic biological systems, specifically biological structures, to better humankind. Recently, biomimetic surfaces mimicking the microstructure of leaf surface, were used to study the effects of leaf microstructure on leaf-environment interactions. However, no such tool exists for roots. We developed a tool allowing the synthetic mimicry of the root surface microstructure into an artificial surface. We relied on the soft lithography method, known for leaf surface microstructure replication, using a two-step process. The first step is the more challenging one as it involves the biological tissue. Here, we used a different polymer and curing strategy, relying on the strong, rigid, polyurethane, cured by UV for the root molding. This allowed us to achieve a reliable negative image of the root surface microstructure including the delicate, challenging features such as root hairs. We then used this negative image as a template to achieve the root surface microstructure replication using both the well-established polydimethyl siloxane (PDMS) as well as a cellulose derivative, ethyl cellulose, which represents a closer mimic of the root and which can also be degraded by cellulase enzymes secreted by microorganisms. This newly formed platform can be used to study the microstructural effects of the surface in root-microorganism interactions in a similar manner to what has previously been shown in leaves. Additionally, the system enables us to track the microorganism's locations, relative to surface features, and in the future its activity, in the form of cellulase secretion.

Ultraviolet Beam Lithography System for Digital Fabrication of Roller Molds

This article presents a digital ultraviolet (UV) beam lithography system for fabricating microstructures of arbitrary patterns on a roller mold. This roller mold can then be used in roller imprinting for fast and large-area replication of microstructures on substrates. This digital optomechanical system consists of a UV light source, a digital micromirror device (DMD) and its electronic controller, a high-precision image lens, a fiber array integrated with microlenses on both ends, and a two-axis ( x – θ ) servo-controlled motion stage. It exposes a photoresist (PR) layer coated on the cylindrical surface of a roller with a linear array of 192 small UV spots focused by a microlens/fiber array. On the other end of the fibers, UV light is fed by DMD's micromirrors so that the UV light can be dynamically modulated. Finally, by synchronizing the electronics of DMD chip and the mechanical movement (rotation and translation) of the roller, one can achieve arbitrary UV patterning on the roller's PR layer in a digital and maskless manner. This system can successfully achieve UV patterning with a smallest linewidth of 8 μ m, a pattern resolution of 2.5 μ m, and a total patterning width of 192 mm on a roller with a diameter of 100 mm.

Algorithm for Micro‐Profiling from Image of the Injection Molds Complex Surfaces

AbstractNature is an excellent source of inspiration. Understanding nature can lead to new discoveries of new materials, applications, products. Scientists have found out technologies that seek to mimic some of life's unique innovations. In Germany researchers have developed a synthetic shark skin made of elastic silicone that reduces bio‐fouling. Engineers from the Massachusetts Institute of Technology have developed some “biomimicry” material out of glass and plastic that collects minute amounts of water, just like the Namib Desert beetle's back. Polymer composites are used for a very good replication of the mold cavities surface microstructures. Transformation of image to surface could be an economical solution for machining the injection mold cavities for mimic the inspiration source. In this paper an algorithm for combining the tool paths obtained on an image‐to‐surface technique with the tool paths on a complex shaped cavity is presented. The algorithm is tested by micro‐milling an injection mold surface of a cavity for a scale model stone wall and the injection molding experiments have proven the high quality of detail replication.

A quick response and tribologically durable graphene heater for rapid heat cycle molding and its applications in injection molding

A novel one-step approach was employed to achieve direct, high-strength graphene coating on a silicon wafer through chemical vapor deposition (CVD). The coated graphene on the silicon wafer was then assembled into a thin-film heater to realize rapid heat cycle molding (RHCM) with significantly enhanced thermal management and response. As soon as the applied power was turned on, the temperature rose immediately. The surface temperature of the graphene heater increased with the applied power and time, and the highest temperature exceeded 300 °C. The average heating rate reached 11.6 °C/s at an applied power of 360 W. Four-point temperature testing and temperature response during cyclic heating and cooling showed great temperature uniformity and stability. A tribology test was carried out to characterize the wear resistance of the graphene coating as a function of different coating times. As the coating time (graphene thickness) increased, the coefficient of friction (COF) for the coating decreased, and the wear resistance increased. The graphene heater with a 48 Ω surface resistance made by a 60 min coating time proved to be the best choice for RHCM with regard to the heating efficiency. The graphene heater was used in the RHCM of long-glass-fiber-reinforced (LGFR) PP composites to reduce the width and depth of the weld lines, decrease the floating fiber phenomenon, and improve the surface quality. The graphene heater also has great potential in other high-precision molding applications that require smooth surface, low molded-in residual stresses and birefringence, and superior replication of surface microstructures.

A biomimetic platform for studying root-environment interaction

AimsMicrostructure plays an important role in biological systems. Microstructural features are critical in the interaction between two biological organisms, for example, a microorganism and the surface of a plant. However, isolating the structural effect of the interaction from all other parameters is challenging when working directly with the natural system. Replicating microstructure of leaves was recently shown to be a powerful research tool for studying leaf-environment interaction. However, no such tool exists for roots. Roots present a special challenge because of their delicacy (specifically of root hairs) and their 3D structure. We aim at developing such a tool for roots.MethodsBiomimetics use synthetic systems to mimic the structure of biological systems, enabling the isolation of structural function. Here we present a method which adapts tools from leaf microstructure replication to roots. We introduce new polymers for this replication.ResultsWe find that Polyurethane methacrylate (PUMA) with fast UV curing gives a reliable replication of the tomato root surface microstructure. We show that our system is compatible with the pathogenic soilborne bacterium Ralstonia solanacearum.ConclusionsThis newly developed tool may be used to study the effect of microstructure, isolated from all other effects, on the interaction of roots with their environment.