Master Mold Research Articles

Microvessel-on-Chip Fabrication for the In Vitro Modeling of Nanomedicine Transport.

Tumor-on-chip devices are becoming ideal platforms to recreate in vitro the particular physiological microenvironment of interest for onco-nanomedicine testing and development. This work presents a strategy to produce a round artificial microvessel on-a-chip device for the study of physiologically relevant nanomedicine transport dynamics. The microchannels have a diameter in the range of the tumor capillaries and a semicircular geometry. This geometry is obtained through an intermediate thermal nanoimprint step using a master mold with square-shaped channel structures produced by standard silicon micromachining or by stereolithography three-dimensional (3D) printing. The working microfluidic chip devices are made by casting polydimethylsiloxane on the imprinted intermediate mold. Artificial blood microvessels are created by seeding human endothelial cells into the round-shaped channels acting as the scaffold. The microchip is connected by 3D-printed reservoirs to a pressure controller, allowing for a fine fluidic control. Under physiological flow conditions, the dynamic interaction of nanoparticles (NPs) with the artificial endothelium was assessed by high-magnification fluorescence microscopy. Overtime, internalization of NPs and clustering was observed and the accumulation rate into the endothelial cells could be characterized in real time.

Manufacturing of Polymer-based 1×2 Y-branch Symmetric and Asymmetric Waveguide Coupler through Moulding Technique

Manufacturing of Y-branch coupler depends on high technology production equipment and in-factory accuracy assembly tools. The manufacturing of a 1×2 Y-branch symmetric and asymmetric waveguide coupler based on the mould replication process and Epoxy OG142 as an optical core is presented; an alternative to provide a less complex technique. The polymer optical waveguide adopted two basic designs: the 1×2 Y-branch symmetric coupler as the core structure and the 1×2 asymmetric coupler that allows non-symmetric optical splitting. This paper focused on the main structure fabrication of the 1×2 symmetric and asymmetric waveguide coupler that produces a power output. The fabrication was done by engraving acrylic to produce a master mould using CNC machining tools for optical devices. Both 1×2 devices were made via soft lithography, which duplicated the pattern from the master mould onto a second mould to produce an actual device. Optical polymer epoxy OG142 was injected into the second mould, of which the product was then put on top of acrylic. The device was completed after curing the optical polymer glue, epoxy OG142, by exposing the assembly on the second mould under UV light until both parts bonded. The difference between the simulation and design TOFR value was only ±2%. This showed that the simulation and design are in good agreement, which provides similar performance.

Fabrication of robust and reusable mold with nanostructures and its application to anti-counterfeiting surfaces based on structural colors

In this study, we report a method to fabricate molds and flexible stamps with 2D photonic crystal structures. This includes self-assembly of polystyrene particles into monolayer, oxygen reactive ion etching, thin film (chromium (Cr)) deposition, and polydimethylsiloxane replication. By tuning the thickness of Cr layer, reusable master molds with nano bumps or nano concaves could be prepared selectively. We showed that the replicated flexible stamps out of these molds exhibited structural colors. Characteristics of the colors depended on viewing angle, brightness of background and light source. And the colors even faded out when the background is white or when the stamp was bent. By using this feature, possible strategies for anti-counterfeiting applications have been suggested in this study. Since the molds are reusable and the fabrication method is simple and cost-effective, this study is expected to contribute to nano devices for industries in future.

Organ-on-Chips for Studying Tissue Barriers: Standard Techniques and a Novel Method for Including Porous Membranes Within Microfluidic Devices.

A relevant number of organ-on-chips is aimed at modeling epithelial/endothelial interfaces between tissue compartments. These barriers help tissue function either by protecting (e.g., endothelial blood-brain barrier) or by orchestrating relevant molecular exchanges (e.g., lung alveolar interface) in human organs. Models of these biological systems are aimed at characterizing the transport of molecules, drugs or drug carriers through these specific barriers. Multilayer microdevices are particularly appealing to this goal and techniques for embedding porous membranes within organ-on-chips are therefore at the basis of the development and use of such systems. Here, we discuss and provide procedures for embedding porous membranes within multilayer organ-on-chips. We present standard techniques involving both custom-made polydimethylsiloxane (PDMS) membranes and commercially available plastic membranes. In addition, we present a novel method for fabricating and bonding PDMS porous membranes by using a cost-effective epoxy resin in place of microfabricated silicon wafers as master molds.

Effect of chromium coating thickness on surface adhesion of polyethylene terephthalate optical film

Surface accuracy and shape accuracy are the two key factors that determine the reflective performance of electroforming replication mold. However, the adhesion between the master mold and the replica mold sometimes causes the deformation, fracture and stretching of the microstructure of the mold surface. The reflective performance of the mold surface is reduced. For this reason, this paper proposed a method for reducing the adhesion force by means of a metal Cr transition layer, which was deposited on polyethylene terephthalate (PET) optical film using direct current (DC) magnetron sputtering. The effect of the Cr coating thickness on adhesion force was investigated. The surface of the film was analyzed by the measurement of contact angle, surface energy, surface chemical composition and micro-morphology. The measurements indicate that the surface energy of the PTE films is reduced after being deposited with a thin Cr coating. The reduced surface energy could be due to the fact PET′s polar functional groups were covered by the Cr coating, which must have lower surface energy than the PTE′s surface. In addition, the reduction of surface roughness also helps to reduce the adhesion of PET film surface. The study showed that Cr coating can effectively reduce the surface adhesion of PET optical mold and improve the surface quality of duplicated mold. The work provides a new method to reduce the surface adhesion of PET optical molds for application in electroforming demoulding technology and interfacial adhesion can be adjusted by the thickness of the Cr coating.

Toward Development of a Higher Flow Rate Hemocompatible Biomimetic Microfluidic Blood Oxygenator.

The recent emergence of microfluidic extracorporeal lung support technologies presents an opportunity to achieve high gas transfer efficiency and improved hemocompatibility relative to the current standard of care in extracorporeal membrane oxygenation (ECMO). However, a critical challenge in the field is the ability to scale these devices to clinically relevant blood flow rates, in part because the typically very low blood flow in a single layer of a microfluidic oxygenator device requires stacking of a logistically challenging number of layers. We have developed biomimetic microfluidic oxygenators for the past decade and report here on the development of a high-flow (30 mL/min) single-layer prototype, scalable to larger structures via stacking and assembly with blood distribution manifolds. Microfluidic oxygenators were designed with biomimetic in-layer blood distribution manifolds and arrays of parallel transfer channels, and were fabricated using high precision machined durable metal master molds and microreplication with silicone films, resulting in large area gas transfer devices. Oxygen transfer was evaluated by flowing 100% O2 at 100 mL/min and blood at 0–30 mL/min while monitoring increases in O2 partial pressures in the blood. This design resulted in an oxygen saturation increase from 65% to 95% at 20 mL/min and operation up to 30 mL/min in multiple devices, the highest value yet recorded in a single layer microfluidic device. In addition to evaluation of the device for blood oxygenation, a 6-h in vitro hemocompatibility test was conducted on devices (n = 5) at a 25 mL/min blood flow rate with heparinized swine donor blood against control circuits (n = 3). Initial hemocompatibility results indicate that this technology has the potential to benefit future applications in extracorporeal lung support technologies for acute lung injury.

An Emerging Transdermal Drug Delivery System: Fabrication and Characterization of Natural and Biodegradable Polymeric Microneedles Transdermal Patch

Promising drug agents are limited by their inability to reach in systematic circulation system when applied on skin, because of the excellent barrier of biological membranes, such as the stratum corneum (SC) of the skin. It is the outermost layer of the skin, SC, the principal barrier to all the topical application applied on skin. Various strategies were employed by many research group and pharmaceutical companies worldwide, for the formulation of microneedles. Therefore, microneedles (MN’s), used to puncture skin, it created the transient aqueous transport pathway and enhanced the trandermal permeability. Microneedles (MN’s) fabricated with natural and biodegradable polymer, such as carboxymethyl cellulose (CMC), and dextran. Inverse replication of micro milled master mould reproduced, solid out of natural polymeric microneedles, were subsequently assembled into transdermal patch and physiochemical characterized for dissolution index, mechanical strength constructed physical strong and uniform shape and size and inert profile. Although, dissolvable PVP and PVA based microneedle showed physical stability and MN’s, their different analyzed parameter is of promise for the fabrication matrix device of natural biodegradable polymeric microneedle transdermal drug delivery system.

Cheap, versatile, and turnkey fabrication of microfluidic master molds using consumer-grade LCD stereolithography 3D printing

The recent development of 3D printers allowed a lot of limitations in the field of microfabrication to be circumvented. The ever-growing chase for smaller dimensions has come to an end in domains such as microfluidics, and the focus now shifted to a cost-efficiency challenge. In this paper, the use of a high-resolution stereolithography LCD 3D printer is investigated for fast and cheap production of microfluidic master molds. More precisely, the UV LED array and the LCD matrix of the printer act as an illuminator and a programmable photomask for soft lithography. The achieved resolution of around 100 μm is mainly limited by the pixel geometry of the LCD matrix. A tree-shape gradient mixer was fabricated using the presented method. It shows very good performances despite the presence of sidewall ripples due to the uneven pixel geometry of the LCD matrix. Any design can be brought from concept to realization in under 2 h. Given its sub-€1000 cost, this method is a very good entry point for labs wishing to explore the potential of microfluidic devices in their experiments, as well as a teaching tool for introducing students to microfluidics.

Robust, Long-Term, and Exceptionally Sensitive Microneedle-Based Bioimpedance Sensor for Precision Farming.

Precision farming has the potential to increase global food production capacity whilst minimizing traditional inputs. However, the adoption and impact of precision farming are contingent on the availability of sensors that can discern the state of crops, while not interfering with their growth. Electrical impedance spectroscopy offers an avenue for nondestructive monitoring of crops. To that end, it is reported on the deployment of impedimetric sensors utilizing microneedles (MNs) that can be used to pierce the waxy exterior of plants to obtain sensitive impedance spectra in open‐air settings with an average relative noise value of 3.83%. The sensors are fabricated using a novel micromolding and release method that is compatible with UV photocurable and thermosetting polymers. Assessments of the quality of the MNs under scanning electron microscopy show that the replication process is high in fidelity to the original design of the master mold and that it can be used for upward of 20 replication cycles. The sensor's performance is validated against conventional planar sensors for obtaining the impedance values of Arabidopsis thaliana. As a change is detected in impedance due to lighting and hydration, this raises the possibility for their widespread use in precision farming.

Additive Manufacturing Assisted Solvent Casting of 3D Free-Standing Carbonaceous Hydrogels and Aerogels As Electrodes for Supercapacitors

In a quest for renewable and highly efficient energy storage devices, carbonaceous hydrogels obtained from biopolymers have received much attention owing to their multifunctional properties [1]. The ability to fine-tune the structures of these hydrogels and the prospects of fabricating 3D hydrogels-based carbon electrodes with highly porous and interconnected nanostructure is believed to provide efficient migration of electrolyte ions and electrons. Even though additive manufacturing (AM) of hydrogels with 3D structures could simplify the fabrication, the printability of each material varies greatly. Furthermore, the mechanical properties of hydrogels are often too weak to withstand the printing of structures with a certain height [2].Herein, we demonstrate a facile and versatile method for the fabrication of novel and highly porous 3D carbon aerogel electrodes from bio-hydrogels based on additive manufacturing assisted solvent casting process followed by freeze drying and pyrolysis. Firstly, the negative templates with the required resolution and geometry were 3D printed using high-resolution stereolithography (SLA) based AM technology to be used as master molds and the pattern were transferred to the biopolymeric hydrogels during ionic crosslinking induced self-assembly, leading to gelation. After completion of the gelling process, the casted hydrogel was removed from the master mold, washed with deionized water, frozen using solid carbon dioxide (dry ice) and lyophilized (freeze-dried) to preserve the structure. The lyophilized free-standing aerogels were then converted to free-standing 3D pyrolytic carbon aerogels in a high-temperature tubular furnace at 900°C under a nitrogen environment. Different characterization techniques such as FTIR, BET, SEM, Raman, XRD and XPS were employed to access the influence of the process parameters on the final microstructure of the 3D carbon aerogels. The as-prepared 3D free-standing carbon aerogel when used as a binder-free electrode showed outstanding charge storage capability and kinetics arising from interconnected 3D porous channels. The versatility of this approach was further verified by the successful preparation of novel multifunctional 3D free-standing carbon aerogel hybrids using GO, CNT and/or metal oxides and its application as a structured binder-free supercapacitor electrode with improved electrochemical performance.With the advantageous features of synergistically regulating the structure and composition, the proposed method combining AM and casting could be used as a versatile tool to develop structured bio-hydrogels, to be used as precursor material for constructing novel architectured free-standing carbon electrode materials with well-defined geometry and controlled pore size distribution. The final shape of carbon electrode depends on the 3D geometry of the additive manufactured negative template used for the replication during solvent casting. This technique would broaden the library of hydrogels materials that could be constructed freely in three-dimensions for the fabrication of structured and free-standing porous bio-carbon based electrodes for high-performance supercapacitor application.

A well plate-based multiplexed platform for incorporation of organoids into an organ-on-a-chip system with a perfusable vasculature.

Owing to their high spatiotemporal precision and adaptability to different host cells, organ-on-a-chip systems are showing great promise in drug discovery, developmental biology studies and disease modeling. However, many current micro-engineered biomimetic systems are limited in technological application because of culture media mixing that does not allow direct incorporation of techniques from stem cell biology, such as organoids. Here, we describe a detailed alternative method to cultivate millimeter-scale functional vascularized tissues on a biofabricated platform, termed 'integrated vasculature for assessing dynamic events', that enables facile incorporation of organoid technology. Utilizing the 3D stamping technique with a synthetic polymeric elastomer, a scaffold termed 'AngioTube' is generated with a central microchannel that has the mechanical stability to support a perfusable vascular system and the self-assembly of various parenchymal tissues. We demonstrate an increase in user familiarity and content analysis by situating the scaffold on a footprint of a 96-well plate. Uniquely, the platform can be used for facile connection of two or more tissue compartments in series through a common vasculature. Built-in micropores enable the studies of cell invasion involved in both angiogenesis and metastasis. We describe how this protocol can be applied to create both vascularized cardiac and hepatic tissues, metastatic breast cancer tissue and personalized pancreatic cancer tissue through incorporation of patient-derived organoids. Platform assembly to populating the scaffold with cells of interest into perfusable functional vascularized tissue will require 12-14 d and an additional 4 d if pre-polymer and master molds are needed.

A highly robust approach to fabricate the mass-customizable mold of sharp-tipped biodegradable polymer microneedles for drug delivery

A skin-perforable dissolving microneedle is a promising mediator for painlessly delivering active pharmaceutical compounds across the skin. All the microneedle manufacturing processes so far, however, are much sensitive to input variation and unfavorable for make-to-order approach. Here, a robust method for fabricating mass-customizable master molds is developed to prepare sharp-tipped biodegradable polymer microneedles. Our approach combines the predrying and chip casting (PCC) of an ultrathick photoresist layer with a substrateless, inclined, and rotational exposure (SIR exposure). The PCC achieves the uniform reduction of solvent across the photoresist thickness which is critically required for the formation of a sharp tip; the SIR exposure creates master molds whose geometry is easily customizable and virtually insensitive to a variation in ultraviolet (UV) exposure dose. A theoretical model for the spatiotemporal distribution of UV dose under SIR exposure is established to show the technological superiority of our method. Next, our method’s applicability is proven by fabricating a set of poly(lactic-co-glycolic) acid (PLGA) microneedles and performing both porcine skin penetration test and their in vitro degradation test. Our approach is verified to be robust in manufacturing mass-customizable molds for skin-perforable dissolving microneedles and to have high compatibility with almost all existing biodegradable polymers. The findings of this study lead to both a significant growth of dissolving microneedle-mediated drug delivery and better understanding of drug release kinetics.

Flexible M-Tooth Hybrid Micro-Structure-Based Capacitive Pressure Sensor With High Sensitivity and Wide Sensing Range

A novel flexible capacitive pressure sensor based on hybrid micro-structured (HM) polydimethylsiloxane (PDMS) dielectric layer was developed. The HM-PDMS with M-tooth structured patterns was fabricated using a laser engraved acrylic master mold. The top and bottom electrodes were fabricated by depositing silver (Ag) on flexible polyethylene terephthalate (PET) substrate using additive screen-printing process. The pressure sensor was assembled by sandwiching two HM-PDMS based dielectric layers between the top and bottom electrodes. The capability of the developed pressure sensor to detect a wide range of pressure was investigated by applying varying pressure from 0 to 1 kPa, 1 to 10 kPa, and 10 kPa to 40 kPa. A sensitivity of 51.36% kPa-1, 8.37% kPa-1, and 2.46% kPa-1 was obtained for the pressure ranges of 0 to 1 kPa, 1 to 10 kPa, and 10 to 40 kPa, respectively. The capacitive pressure sensor response, hysteresis, and repeatability of the fabricated pressure sensor is investigated and presented in this paper. To demonstrate the wide sensing range of the pressure sensor, the sensor was attached to face mask for breath monitoring applications that require low pressure sensing of ~20 Pa, and to the hand glove for fingertip pressure monitoring applications that require relatively high pressure sensing of ~3 kPa.

Gecko-Inspired Biomimetic Surfaces with Annular Wedge Structures Fabricated by Ultraprecision Machining and Replica Molding.

The current research on gecko-inspired dry adhesives is focused on micropillar arrays with different terminal shapes, such as flat, spherical, mushroom, and spatula tips. The corresponding processing methods are mostly chemical methods, including lithography, etching, and deposition, which not only are complex, expensive, and environmentally unfriendly, but also cannot completely ensure microstructural integrity or performance stability. The present study demonstrates a high-precision, high-efficiency, and green method for the fabrication of a gecko-inspired surface, which can promote its application in dexterous robot hands and mechanical grippers. Based on the bendable lamellar structures of the gecko, annular wedge adhesive surfaces that stick to the finger surfaces of dexterous robot hands to improve their load capacity are proposed and fabricated via a suitable combined processing method of ultraprecision machining and replica molding. The greater the width, the higher the replication integrity, and when the minimum width is 20 μm, the replication error is less than 5.5% due to the superior processing performance of the nickel–phosphorus (Ni–P) plating of the master mold. The fabricated annular wedge structures with an optimized width of 20 μm not only exhibit a strong friction force of up to 35.48 mN under a preload of 20 mN in the GCr15/poly(dimethylsiloxane) (PDMS) friction pair but also demonstrate an obviously improved anisotropic friction characteristic of up to λ = 1.36, as the molecular force exhibits a stronger increase as compared to the decrease of the mechanical force of the structure with a small width.

Self‐sealing thermoplastic fluoroelastomer enables rapid fabrication of modular microreactors

AbstractA novel fluorinated soft thermoplastic elastomer (sTPE) for microfluidics is presented. It allows the rapid fabrication of microfluidic devices through a 30‐second hot embossing cycle at 220°C followed by self‐sealing through simple conformal contact at room temperature, or with baking. The material shows high chemical resistance, particularly in comparison to polydimethylsiloxane (PDMS), to many common organic solvents and can be rapidly micropatterned with high fidelity using a variety of microfluidic master molds thanks to its low mechanical stiffness. Self‐sealing of the material is reversible and withstands pressures of up to 2.8 bar with room temperature sealing and four bar with baking at 185°C for 2 hours. The elastomeric, transparent sTPE exhibits material characteristics that make it suited for use as a microreactor, such as low absorption, surface roughness and oxygen permeability, while also allowing a facile and scalable fabrication process. Modular microfluidic devices, leveraging the fast and reversible room temperature self‐sealing, are demonstrated for the generation of water droplets in a toluene continuous phase using T‐junctions of variable size. The sTPE offers an alternative to common microfluidic materials, overcoming some of their key drawbacks, and giving scope for low‐cost and high‐throughput devices for flow chemistry applications.

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography.

Bio-inspired surfaces with superamphiphobic properties are well known as effective candidates for antifouling technology. However, the limitation of large-area mastering, patterning and pattern collapsing upon physical contact are the bottleneck for practical utilization in marine and medical applications. In this study, a roll-to-plate nanoimprint lithography (R2P NIL) process using Morphotonics’ automated Portis NIL600 tool was used to replicate high aspect ratio (5.0) micro-structures via reusable intermediate flexible stamps that were fabricated from silicon master molds. Two types of Morphotonics’ in-house UV-curable resins were used to replicate a micro-pillar (PIL) and circular rings with eight stripe supporters (C-RESS) micro-structure onto polycarbonate (PC) and polyethylene terephthalate (PET) foil substrates. The pattern quality and surface wettability was compared to a conventional polydimethylsiloxane (PDMS) soft lithography process. It was found that the heights of the R2P NIL replicated PIL and C-RESS patterns deviated less than 6% and 5% from the pattern design, respectively. Moreover, the surface wettability of the imprinted PIL and C-RESS patterns was found to be superhydro- and oleophobic and hydro- and oleophobic, respectively, with good robustness for the C-RESS micro-structure. Therefore, the R2P NIL process is expected to be a promising method to fabricate robust C-RESS micro-structures for large-scale anti-biofouling application.

Design and Development of a Three-Dimensionally Printed Microscope Mask Alignment Adapter for the Fabrication of Multilayer Microfluidic Devices.

This project aims to develop an easy-to-use and cost-effective platform for the fabrication of precise, multilayer microfluidic devices, which typically can only be achieved using costly equipment in a clean room setting. The key part of the platform is a three dimensionally (3D) printed microscope mask alignment adapter (MMAA) compatible with regular optical microscopes and ultraviolet (UV) light exposure systems. The overall process of creating the device has been vastly simplified because of the work done to optimize the device design. The process entails finding the proper dimensions for the equipment available in the laboratory and 3D-printing the MMAA with the optimized specifications. Experimental results show that the optimized MMAA designed and manufactured by 3D printing performs well with a common microscope and light exposure system. Using a master mold prepared by the 3D-printed MMAA, the resulting microfluidic devices with multilayered structures contain alignment errors of <10 µm, which is sufficient for common microchips. Although human error through transportation of the device to the UV light exposure system can cause larger fabrication errors, the minimal errors achieved in this study are attainable with practice and care. Furthermore, the MMAA can be customized to fit any microscope and UV exposure system by making changes to the modeling file in the 3D printing system. This project provides smaller laboratories with a useful research tool as it only requires the use of equipment that is typically already available to laboratories that produce and use microfluidic devices. The following detailed protocol outlines the design and 3D printing process for the MMAA. In addition, the steps for procuring a multilayer master mold using the MMAA and producing poly(dimethylsiloxane) (PDMS) microfluidic chips is also described herein.

Roll-to-roll nanoimprint lithography using a seamless cylindrical mold nanopatterned with a high-speed mastering process

The advanced optical and wetting properties of metamaterials, plasmonic structures, and nanostructured surfaces have been repeatedly demonstrated in lab-scale experiments. Extending these exciting discoveries to large-area surfaces can transform technologies ranging from solar energy and virtual reality to biosensors and anti-microbial surfaces. Although photolithography is ideal for nanopatterning of small, expensive items such as computer chips, nanopatterning of large-area surfaces is virtually impossible with traditional lithographic techniques due to their exceptionally slow patterning rates and high costs. This article presents a high-throughput process that achieves large-area nanopatterning by combining roll-to-roll (R2R) nanoimprint lithography (NIL) and nanocoining, a process that can seamlessly nanopattern around a cylinder hundreds of times faster than electron-beam lithography. Here, nanocoining is used to fabricate a cylindrical mold with nanofeatures spaced by 600 nm and microfeatures spaced by 2 μm. This cylindrical drum mold is then used on a R2R NIL setup to pattern over 60 feet of polymer film. Microscopy is used to compare the feature shapes throughout the process. This scalable process offers the potential to transfer exciting lab-scale demonstrations to industrial-scale manufacturing without the prohibitively high cost usually associated with the fabrication of a master mold.

Fabrication Protocol for Thermoplastic Microfluidic Devices: Nanoliter Volume Bioreactors for Cell Culturing.

Microfluidic devices consist of microchannels etched or embossed into substrates made of polymer, glass or silicon. Intricate connections of the microchannels to reactors with some smart mechanical structures such as traps or curvatures fulfil the desired functionalities such as mixing, separation, flow control or setting the environment for biochemical reactions. Here, we describe the fabrication methods of a thermoplastic microbioreactor step by step. First, material selection is made, then, production methods are determined with the equipment that can be easily procured in a laboratory. COP with its outstanding characteristics among many polymers was chosen. Two types of microbioreactors, with and without electrodes, are designed with AutoCAD and L-edit softwares. Photolithography and electrochemical wet etching are used for master mold preparation. Thermal evaporator is employed for pure chromium and gold deposition on COP substrate and etchants are used to form the interdigitated electrodes. Once the master mold produced, hot embossing is used to obtain the designed shape on drilled and planarized COP. Cover COP, with or without electrodes, is bonded to the hot embossed COP via thermo-compression and thermoplastic microfluidic device is realized. Tubings are connected to the device and a bridge between the macro and micro world is established. Yeast or mammalian cells labeled or tagged with GFP/RFP on specific gene products are loaded into the microfluidic device, and real time data on cell dimensions and fluorescence intensity are collected using inverted fluorescence microscope, and finally image processing is used to analyze the acquired data.

Nanoimprinting for High-Throughput Fabrication of Geometrically Precise Pillars to Regulate Cell Behavior

Developing high-throughput nanopatterning techniques that also allow for precise control over the dimensions of the fabricated features is essential for the study of cell-nanopattern interactions. Here, we developed a process that fulfills both of these criteria. Firstly, we used electron-beam lithography (EBL) to fabricate precisely controlled arrays of high aspect ratio submicron pillars with varying values of interspacing on a large area (3 × 5 mm2) of fused silica substrates. Two types of etching procedures with two different systems were developed to etch the fused silica and create the final desired height. We then studied the interactions of preosteoblasts (MC3T3-E1) with these pillars. Varying interspacing was observed to significantly affect the morphological characteristics of the cell, the organization of actin fibers, and the formation of focal adhesions. The expression of osteopontin (OPN) significantly increased on the patterns, indicating the potential of the pillars for inducing osteogenic differentiation. The EBL arrays of pillars were thereafter used as master molds in two subsequent processing steps, namely soft lithography (using hybrid PDMS) and thermal nanoimprint lithography for high-fidelity replication of the pillars on the substrates of interest. The molding parameters were optimized to maximize the fidelity of the generated patterns and minimize the wear and tear of the master mold. Comparing the replicated feature with those present on the original mold confirmed that the geometry and dimensions of the replicated pillars closely resemble those of the original ones (i.e., 1% deviation in pillar interspacing, < 20% deviation in pillar diameter). The method proposed in this study, therefore, enables the precise fabrication of submicron- and nanopatterns on a wide variety of substrate materials that are relevant for systematic cell studies.