Polydimethylsiloxane Channel Research Articles

Fabrication of an Open Microfluidic Device for Immunoblotting.

Given the wide adoption of polydimethylsiloxane (PDMS) for the rapid fabrication of microfluidic networks and the utility of polyacrylamide gel electrophoresis (PAGE), we develop a technique for fabrication of PAGE molecular sieving gels in PDMS microchannel networks. In developing the fabrication protocol, we trade-off constraints on materials properties of these two polymer materials: PDMS is permeable to O2 and the presence of O2 inhibits the polymerization of polyacrylamide. We present a fabrication method compatible with performing PAGE protein separations in a composite PDMS-glass microdevice, that toggles from an "enclosed" microchannel for PAGE and blotting to an "open" PA gel lane for immunoprobing and readout. To overcome the inhibitory effects of O2, we coat the PDMS channel with a 10% benzophenone solution, which quenches the inhibiting effect of O2 when exposed to UV, resulting in a PAGE-in-PDMS device. We then characterize the PAGE separation performance. Using a ladder of small-to-mid mass proteins (Trypsin Inhibitor (TI); Ovalbumin (OVA); Bovine Serum Albumin (BSA)), we observe resolution of the markers in <60 s, with separation resolution exceeding 1.0 and CVs of 8.4% for BSA-OVA and 2.4% for OVA-TI, with comparable reproducibility to glass microdevice PAGE. We show that benzophenone groups incorporated into the gel through methacrylamide can be UV-activated multiple times to photocapture protein. PDMS microchannel network is reversibly bonded to a glass slide allowing direct access to separated proteins and subsequent in situ diffusion-driven immunoprobing and total protein Sypro red staining. We see this PAGE-in-PDMS fabrication technique as expanding the application and use of microfluidic PAGE without the need for a glass microfabrication infrastructure.

(Invited) Cultivation of Rat Nerve Cells on Biodegradable Sheet Made of Poly (lactic-co-glycolic acid) Thin Film with Micropatterns of Polylysine Containing Laminin Layer

Cultivation of Rat Nerve Cells on Biodegradable sheet made of Poly (lactic-co-glycolic acid) thin film with micropatterns of polylysine containing laminin layer Yuki Nakamura, Shunpu Horiuchi, Eiki Koshinuma, Satomitsu Imai, and Yasushiro Nishioka* Department of Precision Machinery Engineering, College of Science and Technology, Nihon University, Funabashi, Chiba 274-8501, Japan Tel & Fax: + 81 – 47 – 469 - 6482 *e-mail: nishioka.yasushiro@nihon-u.ac.jp In regenerative medicine field of nervous system, a technique to fabricate microstructure of neurons on flexible and biodegradable substrates has attracted attention [1]. On the other hand, we have focused on poly lactic-co-glycolic acid (PLGA) as a candidate for the substrate material. The degradation products of PLGA have been reported to be non-cytotoxic and safely removed from host system via normal metabolic activity. Furthermore, it has also been reported that the hydrolysis reaction speed can be modified through controlling the ratio of lactide to glycolide [2]. The characteristics of degradation and removal in vivoare advantageous for regenerative medicine. Neural cell culture on micropatterns of polylysine containing laminin layer has been reported as a technique enabling selective axonal outgrowth of neurons [3]. In this research, biodegradable neuron culture thin films that enable selective axonal outgrowth of neurons were fabricated using PLGA thin films with micro lactic patterns of polylysine with laminin on them. Micro lactic patterns of polylysine with laminin as narrow as 20 μm in width ware defined by using the micromolding in capillaries (MIMIC) technique. Polydimethylsiloxane (PDMS) channel molds used for MIMIC and stencil sheets used for the microstencil method were fabricated by curing a polyether ether ketone mold, which was fabricated by nanoimprinting. The 100µm thick PLGA thin film was fabricated by diluting the PLGA into acetone (5w/w%), packing the solution into a PDMS mold, drawing a vacuum, baking and then cooling it down to cure. The selective growth of neurons on the culture sheet with the micropatterns were confirmed.

Self-assembled Hydrogel Fiber Bundles from Oppositely Charged Polyelectrolytes Mimic Micro-/nanoscale Hierarchy of Collagen.

Fiber bundles are present in many tissues throughout the body. In most cases, collagen subunits spontaneously self-assemble into a fibrilar structure that provides ductility to bone and constitutes the basis of muscle contraction. Translating these natural architectural features into a biomimetic scaffold still remains a great challenge. Here, we propose a simple strategy to engineer biomimetic fiber bundles that replicate the self-assembly and hierarchy of natural collagen fibers. The electrostatic interaction of methacrylated gellan gum (MeGG) with a countercharged chitosan (CHT) polymer led to the complexation of the polyelectrolytes. When directed through a polydimethylsiloxane (PDMS) channel, the polyelectrolytes formed a hierarchical fibrous hydrogel demonstrating nano-scale periodic light/dark bands similar to D-periodic bands in native collagen and aligned parallel fibrils at micro-scale. Importantly, collagen-mimicking hydrogel fibers exhibited robust mechanical properties (MPa scale) at a single fiber bundle level and enabled encapsulation of cells inside the fibers under cell-friendly mild conditions. Presence of carboxyl- (in gellan gum) or amino- (in chitosan) functionalities further enabled controlled peptide functionalization such as RGD for biochemical mimicry (cell adhesion sites) of native collagen. This biomimetic aligned fibrous hydrogel system can potentially be used as a scaffold for tissue engineering as well as a drug/gene delivery vehicle.

Design and Validation of a Microfluidic Chip with Micropillar Arrays for Three-dimensional Cell Culture

Abstract A microfluidic chip with micropillar arrays for three-dimensional (3D) cell culture was designed and validated. The chip consisted of a polydimethylsiloxane (PDMS) channel plate and a glass cover plate. One cell culture chamber composed of two rows of micropillar arrays and two lateral channels for transporting the culture medium were integrated on the PDMS channel plate. The spacing between micropillars greatly affected the chip performances, which was critical for the design of the chip. In this work, the spacing between micropillars was optimized by numerical simulation and experimental validation. With the optimized microfluidic chip, the mixture of cells and extracellular matrix mimics could be steadily injected into the chamber, the nutrients in the medium from lateral channels could quickly diffuse into the chamber, and the cell metabolites could also timely diffuse out of the chamber. To test the stability of the microenvironment constructed in the optimized chip, neural stem cells were three-dimensionally cultured.

A Metamaterial-Inspired Wideband Microwave Interferometry Sensor for Dielectric Spectroscopy of Liquid Chemicals

A miniaturized wideband interferometry-based sensor for complex dielectric spectroscopy of liquid chemicals is presented in this paper. Two composite right-/left-hand (CRLH) transmission lines (TLs) are employed in a direct downconversion architecture. The material under test (MUT) is placed in direct contact with the printed interdigital capacitor of the artificial TL as the sensing component. Since the employed CRLH TL provides nonlinear dispersion characteristics, improved sensitivity with wideband (4.2–8 GHz) operation is achieved compared with resonator- or TL-based interferometers. The sensor circuit board is realized based on common printed circuit board technology, and the fluidic polydimethylsiloxane channels are fabricated and bonded to the circuit board using 3-D printing and soft lithography techniques. The measured results of pure liquid chemical characterization suggest the mean squared errors of ~1.1% and ~1.6% for $\epsilon ^{\prime }_{r}$ and $\epsilon ^{\prime \prime }_{r}$ , respectively, compared with the MUT’s theoretical model. Moreover, binary mixture characterization is carried out based on $\epsilon ^{\prime }_{r}$ measurements with an accuracy of 1%.

Kinematical behaviour of capillary-driven nematic flow in polydimethylsiloxane microchannels: The effects of the dimensions of the channels

In this work we investigate the kinematical behaviour of capillary-driven nematic flows confined in polydimethylsiloxane (PDMS) microchannels. We show that the highly hydrophobic PDMS surfaces have affinity for the cyano-based nematogen 5CB, and are fairly lyophilic with the nematogen. The liquid crystal can flow into the PDMS microchannels without applying any external force. The kinematic behaviour of the nematic flow is sensitive to the geometry of the microchannels. The geometrical effects can be described using an analytic function, also known as the geometrical term. In theory, a scaling-down of the size of the channels will cause a drastic increase in the velocity of the nematic flow. We measured the velocities of the nematic flows in PDMS channels of different sizes. Our preliminary results show that the experimental measurement is highly consistent with the theoretical predictions.

Enzymatic determination of urinary citrate based on flow injection system using NUV spectroscopy and PLS regression

In this study, a flow injection analysis (FIA) system with enzymatic detection was proposed for determination of citrate in urine using a lab-made microfluidic chip. A microfluidic device based on polydimethylsiloxane (PDMS) channels was designed and fabricated. And the analytical variables of this method, such as accuracy, precision and interference factors, have been discussed. Furthermore, in order to determinate the citrate concentration in real samples, three univariate calibration models with different standard solutions of citrate and one partial least squares regression (PLSR) model using near ultraviolet (NUV) spectroscopy were established, and the predictive performance of the proposed models was evaluated externally by making the correlation analysis between prediction values and reference values from capillary electrophoresis (CE) of citrate level in real urine samples. The correlation coefficients of three univariate models were 0.9989, 0.9955 and 0.9976 within the range from 0.1mM to 6mM and the root-mean-square error of prediction (RMSEP) for univariate models and PLSR model were 0.65mM and 0.40mM, respectively. The models were validated and the values of correlation coefficients of prediction found for univariate and multivariate models were 0.85 and 0.88, respectively. Results indicate that multivariate calibration based on NUV/PLS method has improved the practicability greatly comparing with the univariate regression in urinary citrate analysis because of its high sensitivity and validity of prediction. What’s more, combining with the advantages of enzymatic detection and microfluidic chip, this method looks more promising in the complex biomedical analysis without tedious pretreatments.

Rapid fabrication of rounded microchannels via extrusion printing of molds using a thixotropic ink

This paper reports a direct-write strategy that rapidly produces rounded cross-sectional molds for casting of microfluidic channels in polydimethylsiloxane (PDMS). Robotically controlled microextrusion of a thixotropic ink through a micronozzle onto a substrate surface generates user-defined positive relief structures that serve as molds. Printed lateral resolutions of less than 10μm can be achieved by using a micronozzle with dimensions of a few micrometers and microscopic visual feedback. The cross-sectional geometries of the microchannels can be easily adjusted by regulating parameters such as the printing speed, applied pressure, micronozzle-substrate distance, and number of stacks. As a result of the “liquid rope coiling” effect, this technique provides a straightforward way of producing a serpentine microchannel. To demonstrate the feasibility of extrusion printing, several complex microfluidic structures were cast in PDMS from their printed molds. This strategy provides a simple but flexible approach to on-demand prototyping of microfluidic molds with controllable, rounded cross-sections for microfluidic structures.

Hypoxic behavior in cells under controlled microfluidic environment

BackgroundDepleted oxygen levels, known as hypoxia, causes considerable changes in the cellular metabolism. Hypoxia-inducible factors (HIF) act as the major protagonist in orchestrating manifold hypoxic responses by escaping cellular degradation mechanisms. These complex and dynamic intracellular responses are significantly dependent on the extracellular environment. In this study, we present a detailed model of a hypoxic cellular microenvironment in a microfluidic setting involving HIF hydroxylation. MethodsWe have modeled the induction of hypoxia in a microfluidic chip by an unsteady permeation of oxygen from the microchannel through a porous polydimethylsiloxane channel wall. Extracellular and intracellular interactions were modeled with two different mathematical descriptions. Intracellular space is directly coupled to the extracellular environment through uptake and consumption of oxygen and ascorbate similar to cells in vivo. ResultsOur results indicate a sharp switch in HIF hydroxylation behavior with changing prolyl hydroxylase levels from 0.1 to 4.0μM. Furthermore, we studied the effects of extracellular ascorbate concentration, using a new model, to predict its accumulation inside the cell over a relevant physiological range. In different hypoxic conditions, the cellular environment showed a significant dependence on oxygen levels in resulting intracellular response. ConclusionsChange in hydroxylation behavior and nutrient supplementation can have significant potential in designing novel therapeutic interventions in cancer and ischemia/reperfusion injuries. General significanceThe hybrid mathematical model can effectively predict intracellular behavior due to external influences providing valuable directions in designing future experiments.

A Hydrophobic Ionic Liquid Compartmentalized Sampling/Labelling and Its Separation Techniques in Polydimethylsiloxane Microchip Capillary Electrophoresis

This paper demonstrated a novel compartmentalized sampling/labelling method and its separation techniques using a hydrophobic ionic liquid (IL) – 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imidate (BmimNTf2) as immiscible phase, which is capable of minimizing signal losses during microchip capillary electrophoresis (MCE). The MCE device consists of a silica tube connecting to a straight polydimethylsiloxane (PDMS) separation channel. Poly(diallyldimethylammonium chloride) (PDDAC) was coated on the inner surface of channel for easing the introduction of IL plugs, and enhancing the IL wetting on the PDMS surface for realizing sample releasing. Electroosmotic flow (EOF)-based sample compartmentalization was carried out in a sequenced injection manner by order of leading IL plug/sample segment/terminal IL plug into sampling tube. The moving of the sample segment was easily controlled by applying electrical voltage across both end of the chip without sample volume change. This approach effectively prevented analytes diffusion before the injection into MCE channel. When the sample segment was manipulated to the PDDAC modified PDMS channel, the sample plug then was released from isolation under EOF while IL plugs adsorbed onto channel surface owing to strong adhesion. A mixture of flavin adenine nucleotide (FAD) and flavin mononucleotide (FMN) was successfully separated on a 2.5-cm-long separation channel, for which the theoretical number of plates was 15,000 and 17,000, respectively. The obtained peak intensity was increased by 6.3-folds compared to the corresponding value from conventional electrokinetic injection with same sampling time. Furthermore, based on the compartmented sample segment served as an interim reactor, an on-chip fluorescence labelling is demonstrated.

Microfluidic biochips for simple impedimetric detection of thrombin based on label-free DNA aptamers

This paper presents a proof-of-concept microfluidic aptamer-based sensor for thrombin point-of-care testing using electrochemical impedance spectroscopy. The disposable biosensor is composed of a polydimethylsiloxane (PDMS) channel layer over a glass substrate. The substrate surface has an Au working electrode and a Pt reference/counter electrode. In this study, human thrombin was used as a biomarker for disease diagnosis. An unlabeled aptamer specific to thrombin was immobilized on a working electrode and electrochemical impedance was measured as thrombin was injected into the biosensor. Thrombin was detected by measuring change in impedance. The proposed biochip had a detection range of 0.1–100,000 ng mL−1 for thrombin concentration and a limit of detection of 0.1 ng mL−1. The results indicated that our biochip could be an effective tool for other molecular diagnostic systems.

A hydrophobic ionic liquid compartmentalized sampling/labeling and its separation techniques in polydimethylsiloxane microchip capillary electrophoresis.

This paper demonstrates a novel compartmentalized sampling/labeling method and its separation techniques using a hydrophobic ionic liquid (IL)-1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imidate (BmimNTf2 )-as the immiscible phase, which is capable of minimizing signal losses during microchip capillary electrophoresis (MCE). The MCE device consists of a silica tube connected to a straight polydimethylsiloxane (PDMS) separation channel. Poly(diallyldimethylammonium chloride) (PDDAC) was coated on the inner surface of channel to ease the introduction of IL plugs and enhance the IL wetting on the PDMS surface for sample releasing. Electroosmotic flow (EOF)-based sample compartmentalization was carried out through a sequenced injection into sampling tubes with the following order: leading IL plug/sample segment/terminal IL plug. The movement of the sample segment was easily controlled by applying an electrical voltage across both ends of the chip without a sample volume change. This approach effectively prevented analyte diffusion before injection into MCE channels. When the sample segment was manipulated to the PDDAC-modified PDMS channel, the sample plug then was released from isolation under EOF while IL plugs adsorbed onto channel surfaces owing to strong adhesion. A mixture of flavin adenine nucleotides (FAD) and flavin mononucleotides (FMN) was successfully separated on a 2.5cm long separation channel, for which the theoretical numbers of plates were 15000 and 17000, respectively. The obtained peak intensity was increased 6.3-fold over the corresponding value from conventional electrokinetic injection with the same sampling time. Furthermore, based on the compartmented sample segment serving as an interim reactor, an on-chip fluorescence labeling is demonstrated.

Design and microfabrication of a miniature fiber optic probe with integrated lenses and mirrors for Raman and fluorescence measurements.

Fiber optics coupled to components such as lenses and mirrors have seen extensive use as probes for Raman and fluorescence measurements. Probes can be placed directly on or into a sample to allow for simplified and remote application of these optical techniques. The size and complexity of such probes however limits their application. We have used microfabrication in polydimethylsiloxane (PDMS) to create compact probes that are 0.5mm thick by 1mm wide. The miniature probes incorporate pre-aligned mirrors, lenses, and two fiber optic guides to allow separate input and output optical paths suitable for Raman and fluorescence spectroscopy measurements. The fabricated probe has 70% unidirectional optical throughput and generates no spectral artifacts in the wavelength range of 200 to 800nm. The probe is demonstrated for measurement of fluorescence within microfluidic devices and collection of Raman spectra from a pharmaceutical tablet. The fluorescence limit of detection was 6nM when using the probe to measure resorufin inside a 150-μm inner diameter glass capillary, 100nM for resorufin in a 60-μm-deep × 100-μm-wide PDMS channel, and 11nM for fluorescein in a 25-μm-deep × 80-μm-wide glass channel. It is demonstrated that the same probe can be used on different sample types, e.g., microfluidic chips and tablets. Compared to existing Raman and fluorescence probes, the microfabricated probes enable measurement in smaller spaces and have lower fabrication cost. Graphical abstract A microfabricated spectroscopic probe with integrated optics was developed for chemical detection in small spaces and in remote applications.

Development of a Multi-Stage Electroosmotic Flow Pump Using Liquid Metal Electrodes.

Injection of liquid metal into a polydimethylsiloxane (PDMS) channel can provide a simple, cheap, and fast method to fabricate a noncontact electrode for micro electroosmotic flow (EOF) pumps. In this study, a multi-stage EOF pump using liquid metal noncontact electrodes was proposed and demonstrated for high-flow-velocity applications. To test the pumping performance of this EOF pump and measure the flow velocity, fluorescent particles were added into deionized (DI) water to trace the flow. According to the experimental results, the pump with a five-stage design can drive a water flow of 5.57 μm/s at 10 V, while the PDMS gap between the electrode and the pumping channel is 20 μm. To provide the guidance for the pump design, parametric studies were performed and fully discussed, such as the PDMS gap, pumping channel dimension, and stage number. This multi-stage EOF pump shows potential for many high-flow-velocity microfluidic applications.

Electroplating through Fluidic Channels as Production Technology for 3D Interconnect Devices and Sensing Structures

Three dimensional moulded interconnect devices (3D-MID) have been a growing market in the last decades [1]. They combine mechanical and electrical functionality. Besides the established production technologies of 3D-MIDs, as Laser Direct Structuring (LDS), one and two component injection moulding and hot stamping [2], innovative new processes are developed. All of the them are printing technologies for example Flamecon [3] technology, the Plasmadust process [4] or the Aerosol Jet Printing [5]. We present a production technology which employs 3D printing, vacuum casting, physical vapour deposition, electroplating through fluidic channels and ion beam etching to create interconnects and sensitive structures. The technology can be applied to create in plane and three dimensional structures. The deposition of high current electric conductors is possible, as well as deposition of functional sensor elements on different substrate materials. The employed process chain contains additive manufacturing techniques. We used a milled substrate made of Acrylnitril-Butadien-Styrol (ABS) Polymer instead of an injection moulded one as the studying object for the three dimensional deposition, and a Kapton® foil as a planar substrate. Preparation of the substrate is done by depositing a nickel iron (81/19) seed layer of several hundred nanometres thickness by physical vapour deposition. Using conductive sprays as seed layers will be explored in future. The fluidic channels for the electrolyte are made by vacuum casting a master profile with Polydimethylsiloxane (PDMS). We employed milled and three dimensional printed masters in the casting process. The fluid is guided into the PDMS channels by attaching hose connector to the master shape before the PDMS casting. The anode wire is embedded into the PDMS form after casting. Electroplating is done by clamping the PDMS shape onto the substrate. The exchange of the electrolyte is realised using a peristaltic pump, which leads the electrolyte through the fluidic channels by creating a vacuum. The anode to cathode spacing is about 1mm. The applied currents vary from 2 mA to 20 mA. The low current is applied to create functional sensor structures of nickel-iron layers of only a few microns thickness. Higher currents are applied to create thick conducting structures out of copper of about 100 µm. The seed layer is removed by ion beam etching. Future work will prove the use of wet chemical etching. The deposited structures are analysed regarding the thickness homogeneity in reference to the flow direction, the edge angle and the geometric reproduction compared to the master profile. An analysis of thin structures concerning their sensing ability is also done. [1] J. Franke, Three-Dimensional Molded Interconnect Devices (3D-MID). 2014. [2] A. Islam, H. N. Hansen, P. T. Tang, and J. Sun, “Process chains for the manufacturing of molded interconnect devices,” Int. J. Adv. Manuf. Technol., vol. 42, no. 9–10, pp. 831–841, 2009. [3] R. Süss-Wolf and M. Paolis, “Leoni Flamecon® ein neues Metallisirungsverfahren stellt sich vor.,” Met. 61, no. 11, pp. 739–741, 2007. [4] D. Fertigungs-magazin, “Alles im Blick mit nur einem Klick Via Tablet die komplette Fertigungslinie Hohe Effi zienz durch einen optimal gestalteten Druckprozess,” no. April, 2014. [5] J. Hoerber, J. Glasschroeder, M. Pfeffer, J. Schilp, M. Zaeh, and J. Franke, “Approaches for additive manufacturing of 3D electronic applications,” Procedia CIRP, vol. 17, pp. 806–811, 2014.

Study of Different Sol-Gel Coatings to Enhance the Lifetime of PDMS Devices: Evaluation of Their Biocompatibility.

A study of PDMS (polydimethylsiloxane) sol-gel–coated channels fabricated using soft lithography and a laser direct writing technique is presented. PDMS is a biocompatible material that presents a high versatility to reproduce several structures. It is widely employed in the fabrication of preclinical devices due to its advantages but it presents a rapid chemical deterioration to organic solvents. The use of sol-gel layers to cover the PDMS overcomes this problem since it provides the robustness of glass for the structures made with PDMS, decreasing its deterioration and changing the biocompatibility of the surface. In this work, PDMS channels are coated with three different kinds of sol-gel compositions (60MTES/40TEOS, 70MTES/30TISP and 80MTES/20TISP). The endothelial cell adhesion to the different coated devices is evaluated in order to determine the most suitable sol-gel preparation conditions to enhance cellular adhesion.

Indium Tin Oxide Microsystem for Electrochemical Detection of Exocytosis of Migratory Dendritic Cells

AbstractThe design, fabrication and test of an indium tin oxide (ITO) microdevice to investigate exocytotic behaviors of migratory dendritic cells (DCs) in confined three‐dimensional environment were reported in this work. Indeed, immature DCs were able to migrate into micro‐fabricated biocompatible polydimethylsiloxane (PDMS) channels that mimic their natural constrained environment of tissues for patrolling in search of danger associated antigens through an endocytotic process called macropinocytosis. In order to coordinate membrane trafficking and prevent cell volume increment, DCs will release part of their contents back to the extracellular medium while migrating. Through electrochemical measurements, we demonstrated that exocytotic events of migratory DCs could be monitored by our ITO microdevice. In addition, the transparency of ITO electrode should facilitate future combining assays of exocytosis with other fluorescence‐based measurements of cell physiology.

A PDMS-Based Microfluidic Hanging Drop Chip for Embryoid Body Formation.

The conventional hanging drop technique is the most widely used method for embryoid body (EB) formation. However, this method is labor intensive and limited by the difficulty in exchanging the medium. Here, we report a microfluidic chip-based approach for high-throughput formation of EBs. The device consists of microfluidic channels with 6 × 12 opening wells in PDMS supported by a glass substrate. The PDMS channels were fabricated by replicating polydimethyl-siloxane (PDMS) from SU-8 mold. The droplet formation in the chip was tested with different hydrostatic pressures to obtain optimal operation pressures for the wells with 1000 μm diameter openings. The droplets formed at the opening wells were used to culture mouse embryonic stem cells which could subsequently developed into EBs in the hanging droplets. This device also allows for medium exchange of the hanging droplets making it possible to perform immunochemistry staining and characterize EBs on chip.

Alignment of columnar phase confined in polydimethylsiloxane microchannels

ABSTRACTThe alignment of a discotic liquid crystal confined in polydimethylsiloxane (PDMS) channels with a rectangular cross-section is studied. The microchannels were produced in PDMS using the mold-replica technique. In the PDMS channels, the disc-like molecules of the disogen were found to adopt an edge-on anchoring at the PDMS surface, and macroscopically, the discogen layer is planarly aligned. Using Newton colour scale technique it was revealed that discotic columns were aligned parallel to the channels.

Self-regenerating and hybrid irreversible/reversible PDMS microfluidic devices.

This paper outlines a straightforward, fast, and low-cost method to fabricate polydimethylsiloxane (PDMS) chips. Termed sandwich bonding (SWB), this method requires only a laboratory oven. Initially, SWB relies on the reversible bonding of a coverslip over PDMS channels. The coverslip is smaller than the substrate, leaving a border around the substrate exposed. Subsequently, a liquid composed of PDMS monomers and a curing agent is poured onto the structure. Finally, the cover is cured. We focused on PDMS/glass chips because of their key advantages in microfluidics. Despite its simplicity, this method created high-performance microfluidic channels. Such structures featured self-regeneration after leakages and hybrid irreversible/reversible behavior. The reversible nature was achieved by removing the cover of PDMS with acetone. Thus, the PDMS substrate and glass coverslip could be detached for reuse. These abilities are essential in the stages of research and development. Additionally, SWB avoids the use of surface oxidation, half-cured PDMS as an adhesive, and surface chemical modification. As a consequence, SWB allows surface modifications before the bonding, a long time for alignment, the enclosure of sub-micron channels, and the prototyping of hybrid devices. Here, the technique was successfully applied to bond PDMS to Au and Al.