Polydimethylsiloxane Mold Research Articles

미세 입자 분리를 위한 유체 채널 내 폴리머 벽을 포함한 음파영동 디바이스의 제작

In this paper, we propose acoustophoretic microfluidic devices with an acoustic transparent polymer wall using a simple and low-cost fabrication method followed by MEMS (Micro-Electromechanical Systems) processes. Generally, due to the acoustic standing wave between two opposing walls in microfluidic channel, the particle focusing lines are fixed according to the applied frequency. In the proposed device, however, it is possible to place the particle focusing lines in the arbitrary position within the fluidic domain through the optimized width of polymer wall. The PDMS (Polydimethylsiloxane) mold with thin layer was used as the sealing layer between the Si substrate and cover glass, as well as the decoupling layer between the acoustic boundary and fluidic boundary. The thickness of PDMS mold needed to be minimized to decrease the heating by the acoustic energy absorption of PDMS layer, which was successfully made using the spin-coating of PDMS and the UV tape transfer method. The acoustophoretic device with thin PDMS layer and optimized width of PDMS wall can be applied, for biotechnological applications such as the separation of blood cells and micro-particles.

Semiconducting Polymer Nanowires with Highly Aligned Molecules for Polymer Field Effect Transistors

Conjugated polymers have emerged as promising materials for next-generation electronics. However, in spite of having several advantages, such as a low cost, large area processability and flexibility, polymer-based electronics have their own limitations concerning low electrical performance. To achieve high-performance polymer electronic devices, various strategies have been suggested, including aligning polymer backbones in the desired orientation. In the present paper, we report a simple patterning technique using a polydimethylsiloxane (PDMS) mold that can fabricate highly aligned nanowires of a diketopyrrolopyrrole (DPP)-based donor–acceptor-type copolymer (poly (diketopyrrolopyrrole-alt-thieno [3,2-b] thiophene), DPP-DTT) for high-performance field effect transistors. The morphology of the patterns was controlled by changing the concentration of the DPP-based copolymer solution (1, 3, 5 mg mL−1). The molecular alignment properties of three different patterns were observed with a polarized optical microscope, polarized UV-vis spectroscopy and an X-ray diffractometer. DPP-DTT nanowires made with 1 mg mL−1 solution are highly aligned and the polymer field-effect transistors based on nanowires exhibit more than a five times higher charge carrier mobility as compared to spin-coated film-based devices.

Solution-Driven Imprinting Lithography of Sol-Gel ZnO Thin Films for Liquid Crystal Display.

We present a simple and economically convenient method to fabricate nanopatterned ZnO films by imprinting lithography and use them for the layer alignment of liquid crystal (LC) displays. First, a one-dimensional nanopattern was obtained by laser interference lithography on a silicon wafer, and the silicon mold replica was transferred onto a flexible polydimethylsiloxane (PDMS) sheet for conformal patterning. The so-obtained PDMS mold was then applied on a ZnO film spin-coated on a glass substrate. During the imprinting process, the temperature was controlled from 100 to 250 °C to observe the transferring morphologies of the ZnO film; the nanopattern was successfully transferred at annealing temperatures of 200 and 250 °C because the ZnO film at the sol state filled the cavities of the PDMS nanopattern and solidified, forming a negative replica of the nanopattern. The direction of the nanopatterned ZnO film served as a guide for aligning the LC molecules on the LC surface at the centimeter scale and, due to their elastic characteristics and group behavior, propagating their directional states in the LC bulk. The resulting LC cell exhibited an enhanced electro-optical performance and high thermal endurance above 180 °C. The geometry of the alignment layer increased the electric field on the ZnO film and showed reduced threshold voltage. In addition, since flexible devices are generally based on polyimide, which imidized at around 200 °C, the relatively low annealing temperatures of our fabricated nanopatterned ZnO film allow it to be mounted on such devices without any deterioration of the underlying thermoplastic substrate. Therefore, nanopatterned ZnO has a considerable potential for advanced LC displays.

自己整列微粒子の形状転写によるマイクロレンズアレイの製作とモールド変形を利用した非球面化の検討

Aspheric micro-lens arrays have been attracting great attention to improve light distribution control. This study proposes a simple and efficient method for fabricating close-packed aspheric micro-lens array. First, silica particles of ϕ10 μm were self-assembled over ϕ10 mm area using sedimentation method. Then the convex profile of the self-assembled particles was replicated to a spherical micro-lens array mold. The mold material was silicone elastomer or polydimethylsiloxane (PDMS). Then, the mold profile was replicated into ultraviolet (UV) curing resin. By applying uniaxial stretching to the mold during the secondary replication, aspheric micro-lens array was fabricated. Deformation of the PDMS mold under uniaxial stretching was analyzed by using finite element analysis (FEA) for rough estimation. Experimental results showed that intended lens profile was obtained though some defects were observed due to the nonuniformity of the particle diameters. Optical characteristic of elliptic micro-lens array was made clear.

Induction heating ferromagnetic particles embedded PDMS mold for microstructure embossing

Polydimethylsiloxane (PDMS) is an excellent soft mold material with the advantages of precise replication, easy demolding, and low production cost. However, the strength and hardness of PDMS are relatively low, and PDMS cannot be directly inductively heated. In this study, PDMS is embedded with ferromagnetic powders to increase its hardness and make it heatable. Direct induction heating of the PDMS mold can raise its inherent temperature, increase the heating efficiency by 100% compared with pure PDMS, and improve the shortcomings of uneven surface temperature distribution from high thermal resistance. Furthermore, adding the ferromagnetic metal powder to PDMS can improve its conductivity and make the mold a high-low surface temperature gap as low as 1.6 °C. Adding nickel powder to the PDMS mold makes the hardness 2.29 times higher than that of pure PDMS and can withstand a pressure of 7 kg cm−2, which is very conducive to hot embossing. This study used a self-designed five-sided cladding iron block base and a PDMS mold with ferromagnetic metal powder for hot embossing. This heating apparatus can quickly raise the PDMS surface temperature and emboss deep V-groove microstructures on the polycarbonate (PC) film; the replication performance can reach more than 97%.

Liquid Crystal Templated Chiral Plasmonic Films with Dynamic Tunability and Moldability

AbstractThin films sustaining plasmonic circular dichroism (PCD) have acquired high scientific relevance and a great potential for applications. While most efforts in PCD thin film structures focus on lithographically fabricated static metasurfaces, the bottom‐up fabrication of active chiral plasmonic films constitutes an alternative approach. Herein, the preparation of PCD thin films by melting and freezing a mixture of liquid crystal (LC), a chiral dopant, and gold nanoparticles (Au NPs), serving as helical matrix, symmetry breaking inducer, and plasmonic component, respectively is reported. UV–vis and circular dichroism spectroscopies, as well as theoretical modeling are used to disclose the interactions among thin film components, toward maximizing the PCD dissymmetry factor (g‐factor). Variation of substrate temperature affords reversible off/on switching of the chiroptical response. The soft nature of LC matrix enables patterning of the films via a thermal nanoimprinting method, using a polydimethylsiloxane mold for transfer‐printing onto a flexible substrate, leading to stretchable PCD films. The PCD wavelengths can be readily tuned by varying the geometry of the Au NPs. This work provides an efficient technique to produce PCD thin films with active plasmonic properties and mechanical tunability.

A reinforced PDMS mold for hot embossing of cyclic olefin polymer in the fabrication of microfluidic chips.

Hot embossing is a cost-effective and flexible fabrication technology with high replication accuracy for feature sizes as small as 50 nm. Here we develop a reinforced polydimethylsiloxane (PDMS) mold for hot embossing of cyclic olefin polymer (COP) sheets in the fabrication of microfluidic chips and demonstrate the method by fabricating chips for automated sample digitization in digital nucleic acid assays. The PDMS is hardened by adding an investment powder as a dopant and is constrained with an aluminum frame to prevent lateral expansion during hot pressing. The reinforced PDMS mold demonstrated excellent performance in hot embossing (180 °C, 103 kPa, 5 min) for micropatterning COP sheets, with highly reproducible features as small as 10 μm (width of draining channel). In contrast, the microscale features were inconsistent and distorted when omitting either the investment powder or frame from the PDMS mold. COP chips were assembled by thermally bonding patterned and unpatterned COP sheets. We tested the performance of the COP chip for automated sample digitization in a digital LAMP assay used to quantify human papillomavirus-18 (HPV-18) DNA. A mixture of nucleic acid amplification reagents was loaded into the main channel of the chip using a syringe pump, then the solution was spontaneously partitioned into chambers (∼0.6 nL), which were then isolated by flowing oil through the chip. The digital LAMP assay produced accurately absolute quantitation of DNA at concentrations ranging from 10 to 1000 copies per μL. The strategy presented here provides a simple, low-cost method to prepare molds for hot embossing, which facilitates rapid validation of microfluidic designs.

Superior nanopatterns via adjustable nanoimprint lithography on aluminum oxide in high-K thin films with ultraviolet curable polymer.

The present study substantiate that ultraviolet-nanoimprint lithography (UV-NIL) can be used to transfer a one-dimensional nano-pattern onto a high-k thin film of aluminum oxide mixed with a UV photocuring agent. Polydimethylsiloxane (PDMS) molds fabricated on silicon wafers were made using deep ultraviolet laser interference lithography in order to investigate one-dimension nanopatterns. These imprinted nano-patterns induce geometric deformations in the liquid crystal (LC), creating collective and elastic properties, which act as a guide for homogeneous alignment. The nanoimprint method can process a large area, so it can be processed much easier, faster, and more accurately than the conventional rubbing method. Moreover, the optical properties of the nano-imprinted aluminum oxide (AlO) thin-film are about 1.5p% superior to that of conventional commercialized cells, so it has a high effect on the luminance and color gamut of the display. After pattern imprinting, atomic force microscope (AFM) was performed to confirm the result. We can compared the cycle of AlO mixed with UV photocuring agent PDMS pattern cycle, the period is 776 and 750 nm, the width is 468 and 450 nm, the spacing is 292 and 300 nm, and the height is 40 and 30 nm. The nano-imprinted film appears to replicate the width, amplitude, and spacing of the PDMS template. In addition, X-ray photoelectron spectroscopy was performed to determine the chemical properties of the thin film and it was confirmed that UV irradiation induces oxidation, thus increases the intensity significantly. The binding energies of Al 2p and C–O spectra were situated at 74.27 ± 0.5 eV and 531.78 ± 0.5 eV, respectively.

Design Rule for Constructing Buckling-Free Polymeric Stencil with Microdot Apertures.

A polymeric stencil with microdot apertures made by using polydimethylsiloxane (PDMS) molds with pillar patterns has many advantages, including conformal contact, easy processability, flexibility, and low cost compared to conventional silicon-based membranes. However, due to the inherent deformability of PDMS materials in response to external pressure, it is challenging to construct structurally stable stencils with high structural fidelity. Here, we propose a design rule on the buckling pressure for constructing polymeric stencils without process failure. To investigate the critical buckling pressure (Pcr), stencils are fabricated by using different PDMS molds with aspect ratio variations (AR: 1.6, 2.0, 4.0, and 5.3). By observing the buckled morphology of apertures, the structures can be classified into two groups: low (AR 1.6 and 2.0) and high (AR 4.0 and 5.3) AR groups, and Pcr decreases as AR increases in each group. To investigate the results theoretically, the analysis based on Euler’s buckling theory and slenderness ratio is conducted, indicating that the theory is only valid for the high-AR group herein. Besides, considering the correction factor, Pcr agrees well with the experimental results.

Polycarbonate Masters for Soft Lithography.

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to its simplicity and low cost. The approach relies on casting of elastomers, such as polydimethylsiloxane (PDMS), on masters fabricated from photoresists on silicon substrates. These masters, however, can be expensive, complicated to fabricate, and fragile. Here we describe an optimized replica molding approach to preserve the original masters by heat molding of polycarbonate (PC) sheets on PDMS molds. The process is faster and simpler than previously reported methods and does not result in a loss of resolution or aspect ratio for the features. The generated PC masters were used to successfully replicate a wide range of microfluidic devices, including rectangular channels with aspect ratios from 0.025 to 7.3, large area spiral channels, and micropost arrays with 5 µm spacing. Moreover, fabrication of rounded features, such as semi-spherical microwells, was possible and easy. Quantitative analysis of the replicated features showed variability of <2%. The approach is low cost, does not require cleanroom setting or hazardous chemicals, and is rapid and simple. The fabricated masters are rigid and survive numerous replication cycles. Moreover, damaged or missing masters can be easily replaced by reproduction from previously cast PDMS replicas. All of these advantages make the PC masters highly desirable for long-term preservation of soft lithography masters for microfluidic devices.

Silk Fibroin/Poly(vinyl Alcohol) Microneedles as Carriers for the Delivery of Singlet Oxygen Photosensitizers.

Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitizing drug and visible light produces highly cytotoxic reactive oxygen species (ROS) that leads to cell death. One of the main drawbacks of PDT for topical treatments is the limited skin penetration of some photosensitizers commonly used in this therapy. In this study, we propose the use of polymeric microneedles (MNs) prepared from silk fibroin and poly(vinyl alcohol) (PVA) to increase the penetration efficiency of porphyrin as possible applications in photodynamic therapy. The microneedle arrays were fabricated from mixtures in different proportions (1:0, 7:3, 1:1, 3:7, and 0:1) of silk fibroin and PVA solutions (7%); the polymer solutions were cast in polydimethylsiloxane (PDMS) molds and dried overnight. Patches containing grids of 10 × 10 microneedles with a square-based pyramidal shape were successfully produced through this approach. The polymer microneedle arrays showed good mechanical strength under compression force and sufficient insertion depth in both Parafilm M and excised porcine skin at different application forces (5, 20, 30, and 40 N) using a commercial applicator. We observe an increase in the cumulative permeation of 5-[4-(2-carboxyethanoyl) aminophenyl]-10,15,20-tris-(4-sulphonatophenyl) porphyrin trisodium through porcine skin treated with the polymer microneedles after 24 h. MNs may be a promising carrier for the transdermal delivery of photosensitizers for PDT, improving the permeation of photosensitizer molecules through the skin, thus improving the efficiency of this therapy for topical applications.

Nanopattern transfer on bismuth gallium oxide surface via sol-gel stamp process applied for uniform liquid crystal alignment

A convenient aligning method using nanoimprint lithography is introduced. Sol-gel-processed bismuth gallium oxide (BGO) thin films that are one-dimensionally nanopatterned by polydimethylsiloxane molds are used for the liquid crystal (LC) alignment layer. The one-dimensional nanopatterns are transferred to the films at a curing temperature of 250 °C. Atomic force microscopy data present clear line grooves on the surfaces, which allow the LCs to align parallel to this pattern in one direction. Polarized optical microscopy and pre-tilt angle data support uniformity of the LC alignment, indicating that the surface nanopatterns act as alignment guides for LC molecules. X-ray photoelectron spectroscopy data shows active thermal oxidation at a curing temperature of 250 °C, which contributes to nanopattern transfer on BGO film. Thermal endurance tests of the BGO films show good thermal stability until 180 °C. The twisted nematic cells in the BGO layer also show superior electro-optical performances compared with the conventional rubbed polyimide layer. From these characteristics of the nanopatterned BGO alignment layer and owing to its simple fabrication, we expect that this new alignment technique can be used for producing next-generation LC devices to replace the conventional rubbing process.

A Microfabrication Method of PCL Scaffolds for Tissue Engineering by Simultaneous Two PDMS Molds Replication.

Not very far away, "tissue engineering" will become one of the most important branches of medical science for curing many types of diseases. This branch needs the cooperation of a wide range of sciences like medicine, chemistry, cellular biology, and genetic and mechanical engineering. Different parameters affect the final produced tissue, but the most important one is the quality and biocompatibility of the scaffold with the desired tissue which can provide the functionality of "native ECM" as well. The quality of the scaffold is directly dependent on its materials, design, and method of fabrication. As to the design and fabrication, there are two main categories: (a) random microporosity such as phase separation, electrospinning, and fused deposition modeling (3D printing) and (b) designed microporosity mostly achievable by stereo lithography and soft lithography. The method of fabrication implemented in this research is a novel method in soft lithography employing a type of "replica molding" with one pair of polydimethylsiloxane (PDMS) molds in contrast to traditional replica molding with just one single mold. In this operation, the solution of polycaprolactone in chloroform is initially prepared, and one droplet of the solution is placed between the molds while a preset pressure is applied to maintain the molds tightly together during the solidification of the polymer layer and vaporization of the solvent. Thus, a perfect warp and woof pattern is created. In this research, it has been approved that this is a feasible method for creating complex patterns and simple straight fiber patterns with different spacings and pore sizes. Cell attachment and migration was studied to find the optimum pore size. It was shown that the small pore size improves the cells' adhesion while reducing cell migration capability within the scaffold.

Silicon Based Coplanar Capacitive Device for Liquid Sensor Applications.

The development of silicon-based sensor devices has enabled the possibility to pursue novel integrated smart sensor technologies. Under this scenario, capacitive sensor devices are one viable option for implementing different kinds of applications. In this paper, an interdigitated coplanar capacitive device fabricated over a silicon substrate is presented and its potential use as liquid sensor is demonstrated. Additionally, a detailed capacitance model, which includes the parasitic capacitances introduced by the silicon substrate, was developed. The capacitance model has been theoretically validated through finite-element simulations as well as experimentally by comparison with fabricated devices. A polydimethylsiloxane mold has been fabricated and bonded to the sensor device with the aim of defining a cavity to collect the liquid sample into the device’s active region. The active capacitance component correlates to the electric field coupling between adjacent metal lines. Therefore, any change to the dielectric constant of the medium above the coplanar metal lines will produce a change to the device capacitance. Finally, the main guidelines for device performance improvement are depicted.

Fabrication of large-scale infrared diffractive lens arrays on chalcogenide glass by means of step-and-repeat hot imprinting and non-isothermal glass molding

In this study, a new cost-effective and high-precision process chain for the fabrication of large-scale infrared (IR) diffractive lens arrays on chalcogenide glass is proposed. First, a positive diffractive lens array is fabricated on a polymethylmethacrylate (PMMA) master substrate by employing a step-and-repeat hot imprinting process. The direct hot imprinting can transfer microstructures from a heated mold to the polymer substrate accurately. Repeating the hot imprinting process along a predetermined path, the desired diffractive lens array is obtained. Unlike photolithography and electron-beam writing, which are expensive technologies with sophisticated process steps, the hot imprinting is an easier, cheaper, and more eco-friendly method for fabricating diffractive features with continuous profile. Afterwards a casting process is applied to create a polydimethylsiloxane (PDMS) mold with negative features. The diffractive lens array is successfully transferred from the master substrate to the PDMS elastomer, which is used as a mold in subsequent precision glass molding. Finally, microstructures on the PDMS mold are replicated to the chalcogenide glass by non-isothermal glass molding. In this process, the PDMS mold and workpiece are set at different temperatures. Specifically the PDMS mold at low temperature maintains enough rigidity to press the features onto the softened chalcogenide glass, which is kept at a relatively higher temperature, resulting in a replica of high-fidelity diffractive lens array on the chalcogenide glass. Surface profiles and optical performance of the fabricated components are characterized quantitatively. Results showed that large-scale diffractive lens array can be successfully fabricated on chalcogenide glass by this proposed process chain with high quality and integrity.

Melt Electrowriting of Isomalt for High‐Resolution Templating of Embedded Microchannels

AbstractFabrication of microchannels using 3D printing of sugars as fugitive material is explored in different fields, including microfluidics. However, establishing reproducible methods for the controlled production of sugar structures with sub‐100 μm dimensions remains a challenge. This study pioneers the processing of sugars by melt electrowriting (MEW) enabling the fabrication of structures with so far unprecedented resolution from Isomalt. Based on a systematic variation of process parameters, fibers with diameters down to 20 μm can be fabricated. The flexibility in the adjustment of fiber diameter by on‐demand alteration of MEW parameters enables generating constructs with perfusable channels within polydimethylsiloxane molds. These channels have a diameter that can be adjusted from 30 to 200 μm in a single design. Taken together, the experiments show that MEW strongly benefits from the thermal and physical stability of Isomalt, providing a robust platform for the fabrication of small‐diameter embedded microchannel systems.

Heat and pressure-assisted soft lithography for size-tunable nanoscale structures

Polydimethylsiloxane (PDMS) has been widely used as a mold material to fabricate multiscale patterns, owing to its cost-effectiveness, flexibility, and optical transparency. However, it is important to analyze and understand the deformation of nanoscale patterns due to mechanical and thermal inputs during the replication step. Here, we present an analysis of nanoscale deformation of PDMS molds in response to heat and pressure during the repetitive molding process of thermoplastic polymers. The width and height of the nano-sized ridges of PDMS molds decreased as the number of replications of thermoplastic polymers increased. The decoupling experiments showed that the heat and pressure induced considerable deformation of the width and height of nano-sized ridges of PDMS molds. Using the precisely controlled deformation of nanostructures in PDMS molds, we demonstrated that nanostructures of different sizes can be fabricated on representative thermoplastic and UV-curable polymers consistently.

The Combined Thermoresponsive Cell-Imprinted Substrate, Induced Differentiation, and "KLC Sheet" Formation

Purpose: Stem cells can exhibit restorative effects with the commitment to functional cells.Cell-imprinted topographies provide adaptable templates and certain dimensions for thedifferentiation and bioactivity of stem cells. Cell sheet technology using the thermo-responsivepolymers detaches the "cell sheets" easier with less destructive effects on the extracellularmatrix (ECM). Here, we aim to dictate keratinocyte-like differentiation of mesenchymal stemcells (MSCs) by using combined cell imprinting and sheet technology. Methods: We developed the poly dimethyl siloxane (PDMS) substrate having keratinocytecell-imprinted topography grafted with the PNIPAAm polymer. Adipose tissue-derived MSCs(AT-MSCs) were cultured on PDMS substrate for 14 days and keratinocyte-like differentiationmonitored via the expression of involucrin, P63, and cytokeratin 14. Results: Data showed the efficiency of the current protocol in the fabrication of PDMSmolds. The culture of AT-MSCs induced typical keratinocyte morphology and up-regulatedthe expression of cytokeratin-14, Involucrin, and P63 compared to AT-MSCs cultured on theplastic surface (P < 0.05). Besides, KLC sheets were generated once slight changes occur in theenvironment temperature. Conclusion: These data showed the hypothesis that keratinocyte cell imprinted substrate canorient AT-MSCs toward KLCs by providing a specific niche and topography.

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Manufacture of Binary Nanofeatured Polymeric Films Using Nanosphere Lithography and Ultraviolet Roller Imprinting.

This paper describes the manufacture of binary nanostructured films utilizing nanosphere lithography and ultraviolet (UV) roller imprinting. To manufacture the binary nanofeatured template, polystyrene nanocolloids of two distinct dimensions (900 and 300 nm) were primarily self-assembly spun coated on a silicon substrate. A roller imprinting facility equipped with polydimethylsiloxane molds and ultraviolet radiation was employed. During the imprinting procedure, the roller was steered by a motor and compressed the ultraviolet-curable polymeric layer against the glass substrate, where the nanofeatured layer was cured by the UV light source. Binary nanofeatured films were thus obtained. The influence of distinct processing variables on the imprinting of nanofeatured films was investigated. The empirical data suggested that with appropriate processing conditions, binary nanofeatured plastic films can be satisfactorily manufactured. It also demonstrated that roller imprinting combined with ultraviolet radiation can offer an easy yet effective method to prepare binary nanofeatured films, with a miniatured processing time and enhanced part quality.