Thick Polydimethylsiloxane Research Articles

Rapid in vivo determination of fluoroquinolones in cultured puffer fish (Takifugu obscurus) muscle by solid-phase microextraction coupled with liquid chromatography-tandem mass spectrometry

Fluoroquinolones (FQs) are a group of antimicrobial agents that have been widely used for therapeutic purposes in clinical medicine for human and veterinary diseases, as well as in aquaculture production. Their residues, however, may survive in foods of animal origin, thus causing health risks for human. In this study, a rapid and sensitive method based on in vivo solid-phase microextraction (SPME) coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed to detect the residues of five FQs in cultured puffer fish (Takifugu obscurus). In vitro fiber evaluation experiment demonstrated that, compared with the thicker polydimethylsiloxane (PDMS) coating (165µm), the custom-made biocompatible C18-PAN fibers (45µm) exhibited much higher extraction efficiencies towards FQs (approximately 9–31 times). The custom-made C18-PAN coating also possessed excellent reproducibility in fish muscle with the intra-fiber relative standard deviations (RSDs) ranging from 11.2% to 14.3% (n = 6) and inter-fiber RSDs ranging from 13.1% to 16.1% (n = 6), which was suitable for in vivo sampling. The custom-made SPME fibers were subsequently applied to determine fluoroquinolones in dorsal-epaxial muscle of living puffer fish. The accuracies were verified through the comparison with traditional liquid extraction (LE) method, and the sensitivities were demonstrated to be satisfying with the limits of detection (LODs) ranging from 0.3ngg−1 to 1.5ngg−1. In general, this study presented a convenient and high-efficient method to determine fluoroquinolones in puffer fish by in vivo sampling.

EFFECTS OF SUBSTRATE DEFORMABILITY ON CELL BEHAVIORS: ELASTIC MODULUS VERSUS THICKNESS

The deformability of the substrate stimulating cell mechanotransduction depends not only on elastic modulus but also on the thickness. Polydimethylsiloxane (PDMS) which is widely used in microfluidic chips and platforms can be fabricated in a wide range of elastic modulus and thickness. In this study, we cultured human umbilical vein endothelial cells (HUVECs) on four groups of PDMS substrates of varying thickness and elastic modulus to examine effects of these parameters on morphology, viability and proliferation of cells. Both elastic modulus and thickness affected cell behavior. In general, the thickness of substrates had relatively higher impact on endothelial morphology than elastic modulus. Elongation of HUVECs on thick substrates was more intense compared to those on thin substrates. Both lowering thickness and reducing elastic modulus of PDMS decreased the viability of HUVECs, although thickness was more influential. Decrease in substrate thickness reduced cell proliferation regardless of substrate elastic modulus. In conclusion, our results suggest that endothelial behavior depends on substrate deformability, but cells react differently to the elastic modulus and thickness of PDMS by morphology, viability and growth. Results can improve the comprehension of cell mechanotransduction.

Simple and fast polydimethylsiloxane (PDMS) patterning using a cutting plotter and vinyl adhesives to achieve etching results.

Inhibition of polydimethylsiloxane (PDMS) polymerization could be observed when spin-coated over vinyl substrates. The degree of polymerization, partially curing or fully curing, depended on the PDMS thickness coated over the vinyl substrate. This characteristic was exploited to achieve simple and fast PDMS patterning method using a vinyl adhesive layer patterned through a cutting plotter. The proposed patterning method showed results resembling PDMS etching. Therefore, patterning PDMS over PDMS, glass, silicon, and gold substrates were tested to compare the results with conventional etching methods. Vinyl stencils with widths ranging from 200μm to 1500μm were used for the procedure. To evaluate the accuracy of the cutting plotter, stencil designed on the AutoCAD software and the actual stencil widths were compared. Furthermore, this method's accuracy was also evaluated by comparing the widths of the actual stencils and etched PDMS results.

Flexible microstrip grid array polymer‐conductive rubber antenna for 5G mobile communication applications

AbstractA flexible microstrip grid array antenna (MGAA) fabricated by printing the patch and the ground plane using a 0.25‐mm‐thick conductive rubber layer onto a 1.9 mm thick Polydimethylsiloxane (PDMS) substrate layer is presented in this article. The proposed antenna was designed to operate at 14 GHz frequency band. It is composed of 24 radiating elements to achieve a high gain and compact size characteristics. The measurement results shows that the antenna exhibits wideband characteristics in return loss (S11) covered from 12 to 18 GHz and it can works at bending state without sacrificing the performance. The measured radiation pattern results also present good agreement with the simulated results. All the criteria of this proposed antenna make it as a suitable candidate to be applied for future flexible and conformal‐5G mobile communication applications.

Fabrication of high-transmission microporous membranes by proton beam writing-based molding technique

Porous membranes are widely used as filters in a broad range of micro and nanofluidic applications, e.g. organelle sorters, permeable cell growth substrates, and plasma filtration. Conventional silicon fabrication approaches are not suitable for microporous membranes due to the low mechanical stability of thin film substrates. Other techniques like ion track etching are limited to the production of randomly distributed and randomly orientated pores with non-uniform pore sizes.In this project, we developed a procedure for fabricating high-transmission microporous membranes by proton beam writing (PBW) with a combination of spin-casting and soft lithography. In this approach, focused 2MeV protons were used to lithographically write patterns consisting of hexagonal arrays of high-density pillars of few µm size in a SU-8 layer coated on a silicon wafer. After development, the pillars were conformably coated with a thin film of poly-para-xylylene (Parylene)-C release agent and spin-coated with polydimethylsiloxane (PDMS). To facilitate demolding, a special technique based on the use of a laser-cut sealing tape ring was developed. This method facilitated the successful delamination of 20-μm thick PDMS membrane with high-density micropores from the mold without rupture or damage.

Adhesion of epoxy (pseudobarnacles) to glass that has been treated with hydrophobic carbosilane-based coatings

Derivatives of silacyclobutane were applied as monolayer coatings to provide a release layer for epoxy adhesion. Pull-off tests of epoxy (pseudobarnacles) from both uncoated glass slides and glass slides coated with two silacyclobutane derivatives were performed in order to determine the effects of the silacyclobutane coating on adhesion. It was found that the type of silacyclobutane coatings and the heat treatment used affected the amount of force required to pull-off the epoxy from the glass. More specifically, a removal stress of 1.6 MPa was achieved when using one silacyclobutane derivative. This pull-off stress is close to that of a much thicker polydimethylsiloxane, PDMS (70 μm Sylgard 184™, 1.2 MPa).

Observation Interface of PDMS Membrane in a Microfluidic Chip Based on One-Step Molding

Nowadays, researchers are focusing on sorting, characterizing and detecting micron or submicron particles or bacteria in microfluidic chips. However, some contradictions hinder the applications of conventional microfluidic chips, including the low working distance of high resolving power microscopy and the low light transmittance of conventional microfluidic chips. In this paper, a rapid and readily accessible microfluidic fabrication method is presented to realize observation with high magnification microscopy. With the one-step molding process, the interconnections, the thin observation interface of polydimethylsiloxane (PDMS) membrane and microfluidic channels were integrated into an intact PDMS replica. Three kinds of PDMS replicas with different auxiliary beams were designed and optimized by leakage experiments and analytical software. The observation interfaces of a 170 μm thickness PDMS membrane enlarges the application domain of microfluidic chips. By adopting a solution of high magnification observation, microfluidic devices could be applied widely in medical science, biology and material science.

The evaluation of the refractive indices of bulk and thick polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers by the prism coupling technique

This paper presents the study of the optical properties of bulk and thin-film samples made from polydimethylsiloxane and polydimethyl-diphenylsiloxane elastomers. The chemical structures of the prepared elastomer samples were characterised by infrared spectroscopy. Also their transmission spectra were measured in the visible and infrared regions. The refractive indices of the samples were measured by the prism coupling technique using dark mode spectroscopy for five wavelengths (473, 632.8, 964, 1311 and 1552 nm). Particular focus was placed on the effect of the dependence of refractive index on the conditions of deposition. It has been found that the changes of refractive indices can be achieved by the modification of deposition conditions (hardening temperature and/or A:B mixed agent ratios). In order to obtain more significant changes of the refractive indices, we recommend using polydimethyl-diphenylsiloxane elastomer as a waveguide layer because of it content of phenyl groups, which lead to an increase in the value of the refractive index.

Plasmonic extinction in gold nanoparticle-polymer films as film thickness and nanoparticle separation decrease below resonant wavelength

Plasmonic nanoparticles embedded in polymer films enhance optoelectronic properties of photovoltaics, sensors, and interconnects. This work examined optical extinction of polymer films containing randomly dispersed gold nanoparticles (AuNP) with negligible Rayleigh scattering cross-sections at particle separations and film thicknesses less than (sub-) to greater than (super-) the localized surface plasmon resonant (LSPR) wavelength, λ LSPR . Optical extinction followed opposite trends in sub- and superwavelength films on a per nanoparticle basis. In ∼ 70 - nm -thick polyvinylpyrrolidone films containing 16 nm AuNP, measured resonant extinction per particle decreased as particle separation decreased from ∼ 130 to 76 nm, consistent with trends from Maxwell Garnett effective medium theory and coupled dipole approximation. In ∼ 1 - mm -thick polydimethylsiloxane films containing 16-nm AuNP, resonant extinction per particle plateaued at particle separations ≥ λ LSPR , then increased as particle separation radius decreased from ∼ 514 to 408 nm. Contributions from isolated particles, interparticle interactions and heterogeneities in sub- and super- λ LSPR films containing AuNP at sub- λ LSPR separations were examined. Characterizing optoplasmonics of thin polymer films embedded with plasmonic NP supports rational development of optoelectronic, biomedical, and catalytic activity using these nanocomposites.

Flexible photonic crystal membranes with nanoparticle high refractive index layers.

Flexible photonic crystal slabs with an area of 2 cm2 are fabricated by nanoimprint replication of a 400 nm period linear grating nanostructure into a ≈60 µm thick polydimethylsiloxane membrane and subsequent spin coating of a high refractive index titanium dioxide nanoparticle layer. Samples are prepared with different nanoparticle concentrations. Guided-mode resonances with a quality factor of Q ≈ 40 are observed. The highly flexible nature of the membranes allows for stretching of up to 20% elongation. Resonance peak positions for unstretched samples vary from 555 to 630 nm depending on the particle concentration. Stretching results in a resonance shift for these peaks of up to ≈80 nm, i.e., 3.9 nm per % strain. The color impression of the samples observed with crossed-polarization filters changes from the green to the red regime. The high tunability renders these membranes promising for both tunable optical devices as well as visualization devices.

Unveiling the wet chemical etching characteristics of polydimethylsiloxane film for soft micromachining applications

Micromachining of a polydimethylsiloxane (PDMS) microstructure by wet chemical etching is explored for microelectromechanical systems (MEMS) and microfluidic applications. A 100 µm thick PDMS film was patterned with different microstructure designs by wet chemical etching using a N-methyl-2-pyrrolidone (C16H36FN) and tetra-n-butylammonium fluoride (C5H9NO) mixture solution with 3:1 volume ratio after lithography for studying etching characteristics. The patterning parameters, such as etch rate, surface roughness, pH of etchant solution with time, were thoroughly investigated. A detailed study of surface morphology with etching time revealed nonlinear behaviour of the PDMS surface roughness and etch rate. A maximum rate of 1.45 µm min−1 for 10 min etching with surface roughness of 360 nm was achieved. A new approach of wet chemical etching with pH controlled doped etchant was introduced for lower surface roughness of etched microstructures, and a constant etch rate during etching. Variation of the etching rate and surface roughness by pH controlled etching was performed by doping 5–15 gm l−1 of silicic acid (SiO2xH2O) into the traditional etchant solution. PDMS etching by silicic acid doped etchant solution showed a reduction in surface roughness from 400 nm to 220 nm for the same 15 µm etching. This study is beneficial for micromachining of various MEMS and microfluidic structures such as micropillars, microchannels, and other PDMS microstructures.

SU8 etch mask for patterning PDMS and its application to flexible fluidic microactuators.

Over the past few decades, polydimethylsiloxane (PDMS) has become the material of choice for a variety of microsystem applications, including microfluidics, imprint lithography, and soft microrobotics. For most of these applications, PDMS is processed by replication molding; however, new applications would greatly benefit from the ability to pattern PDMS films using lithography and etching. Metal hardmasks, in conjunction with reactive ion etching (RIE), have been reported as a method for patterning PDMS; however, this approach suffers from a high surface roughness because of metal redeposition and limited etch thickness due to poor etch selectivity. We found that a combination of LOR and SU8 photoresists enables the patterning of thick PDMS layers by RIE without redeposition problems. We demonstrate the ability to etch 1.5-μm pillars in PDMS with a selectivity of 3.4. Furthermore, we use this process to lithographically process flexible fluidic microactuators without any manual transfer or cutting step. The actuator achieves a bidirectional rotation of 50° at a pressure of 200 kPa. This process provides a unique opportunity to scale down these actuators as well as other PDMS-based devices.

A polydimethylsiloxane coating to minimize weathering effects on granite

The impact of common weathering mechanisms on granite has been elucidated. A sprayable polydimethylsiloxane (PDMS) solution and a commercial reference coating formulation (Faceal Oleo HD) have been applied on granite to produce durable surface coatings that minimize weathering effects. Sufficiently thick PDMS coatings display superior stability in all the studied weathering tests when compared to the reference coating, as the impact of weathering on the hydrophobic functionality of the PDMS-coated samples is minimal. Furthermore, due to the excellent water and salt blocking behavior of PDMS, the PDMS-coated stones display an overall better stability against weathering compared to untreated stones.

Microfluidic Neurons, a New Way in Neuromorphic Engineering?

This article describes a new way to explore neuromorphic engineering, the biomimetic artificial neuron using microfluidic techniques. This new device could replace silicon neurons and solve the issues of biocompatibility and power consumption. The biological neuron transmits electrical signals based on ion flow through their plasma membrane. Action potentials are propagated along axons and represent the fundamental electrical signals by which information are transmitted from one place to another in the nervous system. Based on this physiological behavior, we propose a microfluidic structure composed of chambers representing the intra and extracellular environments, connected by channels actuated by Quake valves. These channels are equipped with selective ion permeable membranes to mimic the exchange of chemical species found in the biological neuron. A thick polydimethylsiloxane (PDMS) membrane is used to create the Quake valve membrane. Integrated electrodes are used to measure the potential difference between the intracellular and extracellular environments: the membrane potential.

A microfabricated strain gauge array on polymer substrate for tactile neuroprostheses in rats

In this study, we present the design, microfabrication and characterization of a tactile sensor system which can be used for sensory neuroprostheses in rats. The sensor system consists of an array of 2 × 7 cells, each of which has a series combination of four strain gauges. Each group of four strain gauges is placed around a square membrane with a size of 2.5 × 2.5 mm2. Unlike most common tactile sensors based on silicon substrates, we used 3D-printed polylactic acid as a substrate, because it is not brittle, and under local extremes, it would prevent the catastrophic failure of all cells. The strain gauges were fabricated by depositing and patterning a 50 nm thick aluminum (Al) film on a polyimide sheet with a thickness of 0.125 mm. Polydimethylsiloxane (PDMS) elastomer was bonded on the top surface of the PI membrane. The PDMS layer was prepared in two different thicknesses, 1.2 and 1.7 mm, to investigate its effect on the static response of the sensor. The sensitivity and the maximum allowable force, corresponding to the maximum deformation of 0.9 mm at the center of each cell, changed based on the thickness of the PDMS layer. Sensor cells operated linearly up to 3 N with an average sensitivity of 200 mΩ N−1 (0.7 Ω mm−1) for 1.2 mm thick PDMS. These values changed to 4 N and 70 mΩ N−1 (0.3 Ω mm−1), respectively, for 1.7 mm thick PDMS. The nonlinearity was less than 3%. The cells had low cross-talk (~5 mΩ N−1 and 0.02 Ω mm−1) relative to the average sensitivity. Additionally, the dynamic response of the sensor was characterized at several frequencies by using a vibrotactile stimulation system previously designed for psychophysics experiments. The sensor was also tested inside the rat conditioning chamber to demonstrate the relevant signals in a tactile neuroprosthesis.

Effects of peel angle on peel force of adhesive tape from soft adherend

In the case of the peeling of adhesive tapes from soft adherends, the contributions of the compressive force at the adhered portion as well as the larger deformation of adherend have essential roles in determining the peeling properties. In this paper, the peel force of an adhesive tape from a soft adherend has been measured to understand the peeling mechanism, which is greatly affected by the peel angle. A commercially available pressure-sensitive adhesive was used as the tape, and a cross-linked polydimethylsiloxane (PDMS) was used as the soft adherend. The purpose of this study is to clarify the effects of the peel angle on the peel behavior of this system at room temperature under different material specifications and different experimental conditions. The factors that affect the peel force of the PDMS adherend included the degree of cross-linking in PDMS, the thickness of PDMS, peel angle, and peel velocity. Two characteristic peel patterns were observed, which depended on the material specifications and different experimental conditions. The peel mechanism was discussed in terms of the deformation of the adherend.

Material Characterization and Transfer of Large-Area Ultra-Thin Polydimethylsiloxane Membranes

Fabrication of ultra-thin (1-20-μm thickness) polydimethylsiloxane (PDMS) films is enabled with a hexane dilution process and an underlying gelatin release layer. The release and transfer of these films over large areas (>5 cm) allows measurement of the thickness-dependent and process-dependent mechanical properties of ultra-thin PDMS membranes, reported for the first time. The effective Young's modulus of 1-μm-thick PDMS, measured by bulge testing, is approximately ten times larger than that of 0.5-mm-thick material, following a continuous power-law relationship over the entire thickness range. Mesh-patterned metal electrodes of 2-μm minimum feature size are embedded in selected membranes. Metal evaporation and subsequent reactive ion etch patterning on PDMS increases its Young's modulus due to the increase in cross-link formation and hardening of the surface. The results are meaningful in design and fabrication of soft electronics, microsensors, microvalves, and micropumps.

Surface 3D Micro Free Forms: Multifunctional Microstructured Mesoporous α-Alumina by in Situ Slip Casting Using Excimer Laser Ablated Polycarbonate Molds.

Ceramic surface microstructuring is a rapidly growing field with a variety of applications in tribology, wetting, biology, and so on. However, there are limitations to large-area microstructuring and fabrication of three-dimensional (3D) micro free forms. Here, we present a route to obtain intricate surface structures through in situ slip casting using polydimethylsiloxane (PDMS) negative molds which are replicated from excimer laser ablated polycarbonate (PC) master molds. PC sheets are ablated with a nanosecond KrF (λ = 248 nm) excimer laser mask projection system to obtain micron-scale 3D surface features over a large area of up to 3 m(2). Complex surface structures that include 3D free forms such as 3D topography of Switzerland, shallow structures such as diffractive optical elements (60 nm step) and conical micropillars have been obtained. The samples are defect-free produced with thicknesses of up to 10 mm and 120 mm diameter. The drying process of the slip cast alumina slurry takes place as a one-dimensional process, through surface evaporation and water permeation through the PDMS membrane. This allows homogeneous one-dimensional shrinkage during the drying process, independent of the sample's lateral dimensions. A linear mass diffusion model has been proposed to predict and explain the drying process of these ceramic colloidal suspensions. The calculated drying time is linearly proportional to the height of the slurry and the thickness of the negatively structured PDMS and is validated by the experimental results. An experimentally observed optimum Sylgard PDMS thickness range of ∼400 μm to 1 mm has achieved the best quality microstructured green compacts. Further, the model predicts that the drying time is independent of the microstructured areas and was validated using experimental observations carried out with microstructured areas of 300 mm(2), 1200 mm(2), and 120 cm(2). Therefore, in principle, the structures can be further replicated in areas up to 3 m(2) with the same drying time for the same slurry height. The surface-structured ceramics display interesting wetting properties, for example, eicosane-coated mesoporous microstructured alumina shows superhydrophobic behavior. Additionally, ceramic bulk samples could be further used as second-generation very hard and low-wear molds for further microfabrication.

Modeling Compound Loss from Polydimethylsiloxane Passive Samplers

Volatile losses were measured from polydimethylsiloxane (PDMS) passive samplers during determination of contaminant porewater concentrations in sediments. Volatile losses could occur between the time of retrieval and processing of the passive sampler or in intertidal environments where the passive sampler could potentially be exposed above the water surface at low tide. A model was developed to predict losses of absorbed compounds as a function of sorbent geometry and the Henry’s Law Coefficient and PDMS-water partition coefficient of the compound of interest. The model suggests that thin layers of PDMS typically used to minimize equilibration times in passive sampling (≤30 µm) may not provide quantitative measurement of naphthalenes or other lighter volatile compounds without special efforts to reduce losses. The results suggest that the samplers should be processed rapidly onsite or kept at low temperatures after retrieval to maximize retention of more volatile compounds or designed with thick PDMS layers. The results also suggest that less volatile compounds, including phenanthrene, and higher molecular weight polynuclear aromatic hydrocarbons (PAHs) exhibit minimal evaporative losses with typical sample processing times.

Cultivation of Rat Nerve Cells on Nanoimprinted Microstructures on Polydimethylsiloxane Sheets

Regenerative medical research has attracted much attention in recent years. Here, we fabricated micro trench structures with varying widths of 15 and 150 μm and depths of 30 and 60 μm using the nanoimprint technique on a 100 μm thick polydimethylsiloxane culture sheet used as a biocompatible polymer culture sheet. Rat neurons were observed to grow after 3 days selectively within those micro trenches with widths larger than 15 μm, and they were coated with polylysine.