Polydimethysiloxane Research Articles

Axisymmetric polydimethysiloxane microchannels for in vitro hemodynamic studies

The current microdevices used for biomedical research are often manufactured using microelectromechanical systems (MEMS) technology. Although it is possible to fabricate precise and reproducible rectangular microchannels using soft lithography techniques, this kind of geometry may not reflect the actual physiology of the microcirculation. Here, we present a simple method to fabricate circular polydimethysiloxane (PDMS) microchannels aiming to mimic an in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal µPIV/PTV. By using a confocal µPTV system individual red blood cells (RBCs) were successfully tracked trough a 75 µm circular PDMS microchannel. The results show that RBC lateral dispersion increases with the volume fraction of RBCs in the solution, i.e. with the hematocrit.

Fluorescence Correlation Spectroscopy Study of Molecular Probe Diffusion in Polymer Melts

Fluorescence correlation spectroscopy (FCS) was employed to study the diffusion of molecular tracers in different polymer melts (polydimethysiloxane (PDMS), 1,4-cis-polyisoprene (PI), poly(vinyleth...

Development of elastomeric lab-on-a-chip devices through Proton Beam Writing (PBW) based fabrication strategies

In recent years, one of the most exciting developments in fluidic device applications is the rapid evolution of miniaturized micro- and nanofluidic systems, the so called “lab-on-a-chip” devices. These devices integrate laboratory functions into a single chip, and are capable of various biochemical analysis and synthesis, such as sample injection and preparation, single cell/molecule observation, bioparticle sequencing and sorting etc. The evolvement of lab-on-a-chip concept implies the use of novel fabrication techniques for the construction of versatile analytical components in a fast and reproducible manner. Endowed with unique three-dimensional fabrication abilities, Proton Beam Writing (PBW) [1], which is capable of producing nanometer scaled fluidic structures with smooth and straight side wall features, has a great potential to develop all sorts of polymer fluidic devices. In this paper, we describe the batch fabrication of Poly-dimethysiloxane (PDMS) elastomeric lab-on-a-chip devices utilizing PBW technique. A series of fabrication processes, involving PBW, nickel electroplating, soft lithography, polymer dynamic coating and hydrophilic treating, were modified and adopted in our work. Subsequent characterization of individual categories of channel devices was carried out for specific fluidic studies. Respective experimental procedures are presented and results are explained. The channel devices demonstrated good fluidic performance and functionality, suggesting their further application in more complex biological investigations, and the versatility of PBW in lab-on-a-chip development.

A soft moulding process for manufacture of net-shape ceramic microcomponents

A soft moulding process for manufacture of ceramic microcomponents, alumina and Al2O3/SiC composite, is introduced in this paper. The process involves fabrication of SU-8 master moulds and production of mirrored polydimethysiloxane (PDMS) soft moulds. Green parts are formed in the PDMS moulds by filling the ceramic slurry into the soft moulds and net-shape green components are obtained after demoulding. The methods for the mould filling using different suspensions were demonstrated: one was aqueous suspension for alumina microcomponent and another was non-aqueous suspension for Al2O3/SiC microcomponent. The measurements showed that the proposed soft lithography process is successful in producing ceramic microcomponents and retaining the fine features in micron scale.

Shear assay measurements of cell adhesion on biomaterials surfaces

The paper examines the adhesion of human osterosarcoma (HOS) cells to selected biomaterials surfaces that are relevant to implantable biomedical systems and bio-micro-electro-mechanical systems (BioMEMS). The four biomaterials that were explored include: silicon, silicon coated with a nanoscale layer of titanium, Ti–6Al–4V, and poly-di-methy-siloxane (PDMS). The interfacial strengths between the HOS cells and the biomaterials surfaces were determined using a shear assay technique. The adhesion forces were determined using a combination of confocal microscopy images of the three-dimensional cell structure, and computational fluid dynamics (CFD) simulations that coupled actual cell morphologies and non-Newtonian fluid properties in the computation of the adhesion forces. After cell detachment by the shear assay, immunofluorescence staining of the biomedical surfaces was used to reveal the proteins associated with cell detachment. These revealed that the nano-scale Ti coating increases the cell/surface adhesion strength. Silicon with Ti coating has the strongest adhesion strength, while the other surfaces had similar adhesion strength. The measured strengths are shown to be largely associated with the detachment of focal adhesion proteins from extra-cellular matrix (ECM) proteins.

Determining the optimal PDMS–PDMS bonding technique for microfluidic devices

A number of polydimethysiloxane (PDMS) bonding techniques have been reported in the literature over the last several years as the focus on multilayer PDMS microfluidic devices has increased. Oxygen plasma bonding, despite cost, additional fabrication time and inconsistent bonding results, has remained a widely used method for bonding PDMS layers. A comparative study of four rapid, inexpensive alternative PDMS–PDMS bonding approaches was undertaken to determine relative bond strength. These include corona discharge, partial curing, cross-linker variation and uncured PDMS adhesive. Partial curing and uncured PDMS adhesive demonstrated a considerable improvement in bond strength and consistency by retaining average bond strengths of over 600 kPa, which was more than double the average bond strength of oxygen plasma. A description of each technique and their performance relative to oxygen plasma bonding is included.

Mechanical characterization of a dielectric elastomer microactuator with ion-implanted electrodes

We report on the mechanical characterization and modeling of a non-prestretched dielectric elastomer diaphragm microactuator with ion-implanted electrodes under the influence of a distributed load (pressure). Thin polydimethysiloxane (PDMS) membranes (30 μ m thick, 2–3 mm diameter) were implanted on both side with gold ions by Filtered Cathodic Vacuum Arc (FCVA) and bonded on silicon chips with through-holes. A voltage applied between the implanted electrodes creates a compressive stress in the dielectric and causes the membrane to buckle and form a bump whose height depends on the mechanical properties of the electroactive compound, the voltage and the force applied on the membrane. Maximum unloaded displacements up to 7% of the membrane’s lateral dimensions were achieved, which was reduced to 3% when a distributed force of 1 kPa was applied on the membrane. The maximum mechanical work obtained by the actuators is in the range of 0.3 μ J. An analytical model was developed to calculate the displacement of the Dielectric Elastomer Actuators (DEAs) based on their mechanical and geometrical properties, voltage and applied force. The model shows very good agreement with the measurements and allows accurate performance prediction and dimensioning of such actuators.

Self-formation and release of arbitrary-curvatured structures utilizing droplet deposition and structured surface

This paper proposes a method of micro-fabrication for the formation of complex non-planar shapes by depositing a colloid evaporative droplet onto topographically structured surfaces. The micro-droplet composed of polyurethane (PU) was self-driven by surface tension to adjust their three-dimensional (3D) shapes bound with the surface of the micro-well array. The micro-wells formed from poly-dimethysiloxane (PDMS) consisted of vertical sidewalls to constrain the fluids as boundary conditions in the Young–Laplace equation until drying. Two types of wetting regimes (fully and partially), corresponding to different droplet volume and allocation, were categorized to perform the shaping process in which evolving fluid contours were self-formed utilizing the general principle of minimal surface energy with certain features of the shape set by the wetting of the PDMS. Using the heterogeneous surfaces, slight-concave circular terraces and half-moon shapes with high curvature were fabricated with micrometer dimensions (well diameter of 900 µm). The formed structures were observed to release themselves from the hydrophobic wells by the de-wetting (de-pinned) process in the completion of evaporation. Moreover, the effects of the boundaries were further explored for half-moon shapes by giving three distinct footprints of the partially wetting droplets. In these cases, both experimental results and numerical calculations were performed and compared to illustrate the significant influence of the fluid contact angle (∼90°) and position with a curved boundary line on final formed shape, in particular for the change of curvature ( = 0.62–1.36). Compared to those traditional assays operated on two-dimensional (2D) flat surfaces, this structured-well one could greatly enhance the control of 3D topographic formation in terms of aspect ratio, thickness and curved degree. This novel operation of micro-fabrication is also appropriate for smaller and complex structures by using drop-on-demand inkjet for commercialized mass-production processes.

In vitro blood flow in a rectangular PDMS microchannel: experimental observations using a confocal micro-PIV system

Progress in microfabricated technologies has attracted the attention of researchers in several areas, including microcirculation. Microfluidic devices are expected to provide powerful tools not only to better understand the biophysical behavior of blood flow in microvessels, but also for disease diagnosis. Such microfluidic devices for biomedical applications must be compatible with state-of-the-art flow measuring techniques, such as confocal microparticle image velocimetry (PIV). This confocal system has the ability to not only quantify flow patterns inside microchannels with high spatial and temporal resolution, but can also be used to obtain velocity measurements for several optically sectioned images along the depth of the microchannel. In this study, we investigated the ability to obtain velocity measurements using physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel (300 microm wide, 45 microm deep) using a confocal micro-PIV system. Applying this combination, measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re = 0.02). Velocity profiles were acquired by successive measurements at different depth positions to obtain three-dimensional (3-D) information on the behavior of both fluid flows. Generally, the velocity profiles were found to be markedly blunt in the central region, mainly due to the low aspect ratio (h/w = 0.15) of the rectangular microchannel. Predictions using a theoretical model for the rectangular microchannel corresponded quite well with the experimental micro-PIV results for the PS fluid. However, for the in vitro blood with 20% hematocrit, small fluctuations were found in the velocity profiles. The present study clearly shows that confocal micro-PIV can be effectively integrated with a PDMS microchannel and used to obtain blood velocity profiles along the full depth of the microchannel because of its unique 3-D optical sectioning ability. Advantages and disadvantages of PDMS microchannels over glass capillaries are also discussed.

Pneumatically actuated elastomeric device for nanoscale surface patterning

The authors present a simple polydimethysiloxane (PDMS) device for nanoscale surface patterning by controllably bringing a hard silicon nitride tip on a PDMS membrane in and out of contact with surfaces using pressurized gas to inflate the membrane. The writing process is analogous to contact printing. By regulating the pressured gas to actuate the silicon nitride tip on the PDMS membrane, the nanometer size features can be easily fabricated on substrates. Moreover, using the dot matrix method, this PDMS device can masklessly fabricate arbitrary patterns. In this letter, a nanometer scale three-line pattern is demonstrated.

STRUCTURAL ANALYSIS OF LIQUID 3D TRANSITION METALS USING CHARGED HARD SPHERE REFERENCE SYSTEM

In this paper, we present a fabrication process to produce the micro-sized magnetic structures based on the hard magnetic powders. Under the magnetic field originated from a micro patterned hard magnetic film, these magnetic powders are magnetically aligned to form arrays of the micro magnets on a polydimethysiloxane (PDMS) substrate. The high magnetic field gradient and stable magnetic flux can be obtained at certain micro-sized area on the surface of the micro magnets. The fabricated structures have been used for trapping iron oxide particles. Generally this fabrication process is simple, low cost and the micro magnets can be used for further applications in biology, medicine and beyond.

Suitability of polydimethylsiloxane rods for the headspace sorptive extraction of polybrominated diphenyl ethers from water samples

The suitability of an inexpensive polydimethysiloxane (PDMS) sorbent, produced on an industrial scale, for the extraction of polybrominated diphenyl ethers (PBDEs), from tetra- to hexabrominated congeners, from water samples was assessed. Experiments were carried out using samples spiked with a pentabromo diphenyl ether (pentaBDE) mixture, PDMS rods with a diameter of 2mm and gas chromatography with micro-electron-capture detection (GC-micro-ECD). Influence of several variables on the efficiency of the enrichment step and the further desorption of the analytes was investigated in detail. The best performance was achieved in the headspace sorptive extraction (HSSE) mode, at 95°C, using 80mL water samples containing a 30% of sodium chloride. Extractions were performed overnight using disposable PDMS rods with a length of 10mm (31μL volume). Analytes were further recovered from the PDMS sorbent using just 1mL of diethyl ether. This solvent was evaporated and extracts reconstituted with 25μL of isooctane. Under final working conditions absolute extraction efficiencies from 69 to 93% and enrichment factors higher than 2200 folds were achieved for all species. The proposed method provided acceptable precisions (relative standard deviations values under 12%), correlation coefficients higher than 0.998 and the yield of the HSSE process remained constant for different water samples.

「細胞機能と表面科学」ソフトリソグラフィーを用いた細胞研究・医療用チップの開発

Mechanobiology is indispensable to all living creatures ranging from bacteria to human beings because every living thing continually experiences mechanical stimuli, not only exogenous but also endogenous, and responds appropriately to these stimuli. At the cellular level, there are three major mechanical stresses such as, stretch, shear stress and pressure. We have been intensively investigating systems to apply these mechanical environments to cells. Analysis of these responses is critical to understand the mechanisms and regulation of diverse physiological processes such as arterial and regulation, sensory perception, muscle development, and so on. Therefore, to study mechanobiology, we employed the polydimethysiloxane (PDMS) based technology, which is called soft lithography. In this paper, I am going to focus on biomedical and clinical applications of soft lithography.

A net-shape fabrication process of alumina micro-components using a soft lithography technique

Microceramic components have outstanding properties, such as high temperature resistant, biocompatible, chemically stable and high hardness properties, and could be used in a wide range of applications. However, the fabrication of precision micro-components has long been a barrier and limited their applications. This paper presents a soft lithography technique to fabricate near net-shape alumina micro-components. The process uses elastomer polydimethysiloxane (PDMS) to replace traditional solid moulds and leaves the green patterns intact after demoulding. The whole soft lithography technique involves the following steps: (i) fabricating high aspect ratio SU-8 moulds using UV photolithography, (ii) producing PDMS soft moulds from SU-8 masters, (iii) making aqueous high solids loading alumina suspension, (iv) filling patterned PDMS mould with the aqueous alumina suspension and (v) demoulding and sintering. The rheological properties (zeta potential and viscosity) of aqueous alumina suspensions have been characterized in relation to the varying pH values and concentration of dispersant (D-3005). The optimal parameters of alumina suspension for mould filling have been achieved at a pH value = 11; concentration of dispersant = 0.05 g ml−1; amount of binder = 0.75%; highest solid loading = 70 wt%. After pressurized mould filling, complete, dense and free-standing micro-components have been achieved by using a 70 wt% alumina suspension and an optimum fabrication technique, while the overall linear shrinkage is found to be about 22%.

Low-density neuronal networks cultured using patterned poly-l-lysine on microelectrode arrays

Synaptic activity recorded from low-density networks of cultured rat hippocampal neurons was monitored using microelectrode arrays (MEAs). Neuronal networks were patterned with poly-l-lysine (PLL) using microcontact printing (μCP). Polydimethysiloxane (PDMS) stamps were fabricated with relief structures resulting in patterns of 2μm-wide lines for directing process growth and 20μm-diameter circles for cell soma attachment. These circles were aligned to electrode sites. Different densities of neurons were plated in order to assess the minimal neuron density required for development of an active network. Spontaneous activity was observed at 10–14 days in networks using neuron densities as low as 200cells/mm2. Immunocytochemistry demonstrated the distribution of dendrites along the lines and the location of foci of the presynaptic protein, synaptophysin, on neuron somas and dendrites. Scanning electron microscopy demonstrated that single fluorescent tracks contained multiple processes. Evoked responses of selected portions of the networks were produced by stimulation of specific electrode sites. In addition, the neuronal excitability of the network was increased by the bath application of high K+ (10–12mM). Application of DNQX, an AMPA antagonist, blocked all spontaneous activity, suggesting that the activity is excitatory and mediated through glutamate receptors.

The analysis of volatiles from thermally oxidized virgin olive oil using dynamic sorption–thermal desorption and solid phase micro‐extraction techniques

SummaryVirgin olive oil was thermally oxidized by heating in a conventional oven. Volatiles produced during this process were isolated either by dynamic headspace‐thermal desorption (DHS‐TD) with Tenax‐TA trapping material, or solid phase micro‐extraction (SPME) with nonpolar polydimethysiloxane (PDMS) and polydimethysiloxane‐divinylbenzene (PDMS/DVB) fibres. Volatiles collected in the former case were isolated by using gas chromatography (GC) and characterized by an ion trap mass spectrometer, while those extracted by SPME were isolated by GC and characterized by the use of a time‐of‐flight‐mass spectrometer (TOFMS). More compounds were isolated by DHS‐TD compared to SPME which is, however, a quick process that can be even faster when combined with the high speed chromatography equipment of TOFMS. Fifty‐eight compounds were isolated from olive oil samples using the PDMS/DVB bi‐polar fibres and 39 using the nonpolar PDMS. A quick descriptive analysis of oxidized olive oil is best obtained by using the SPME technique with a PDMS/DVB bi‐polar fibre.

A method of printing carbon nanotube thin films

This paper describes a fabrication method for carbon nanotube thin films on various substrates including PET (polyethylene terephthalate), glass, polymethyl-methacrylate (PMMA), and silicon. The method combines a polydimethysiloxane (PDMS) based transfer-printing technique with vacuum filtration, and allows controlled deposition—and patterning if needed—of large area highly conducting carbon nanotube films with high homogeneity. In the visible and infrared range, the performance characteristics of fabricated films are comparable to that of indium tin oxide (ITO) on flexible substrates.

Indirect removal of SU-8 photoresist using PDMS technique

SU-8 photoresist shows superior images for thick film lithography and has been utilized as an electroplating mold. However, crosslinked SU-8 is difficult to remove reliably from high-aspect-ratio microstructures (HARMs) without damage or alteration to the electroplated metal. In this paper, an indirect SU-8 removal method is proposed. Instead of directly using SU-8 microstructure as the electroplating mold, a polydimethysiloxane (PDMS) replica is employed. The metallic micromold insert obtained through this method can be easily peeled off from the PDMS replica, meanwhile with high resolution and smooth surfaces.

Mechanical Properties and Filler Distribution as a Function of Filler Content in Silica Filled PDMS Samples

ABSTRACTAtomic force microscopy (AFM) phase imaging and tensile stress-strain measurements are used to study a series of model compression molded fumed silica filled polydimethysiloxane (PDMS) samples with filler content of zero, 20, 35, and 50 parts per hundred (phr) to determine the relationship between filler content and stress-strain properties. AFM phase imaging was used to determine filler size, degree of aggregation, and distribution within the soft PDMS matrix. A small tensile stage was used to measure mechanical properties. Samples were not pulled to break in order to study Mullins and aging effects. Several identical 35 phr samples were subjected to an initial stress, and then one each was reevaluated over intervals up to 26 weeks to determine the degree to which these samples recovered their initial stress-strain behavior as a function of time. One sample was tested before and after heat treatment to determine if heating accelerated recovery of the stress-strain behavior. The effect of filler surface treatment on mechanical properties was examined for two samples containing 35 phr filler treated or untreated with hexamethyldisilazane (HMDZ), respectively. Fiduciary marks were used on several samples to determine permanent set. 35 phr filler samples were found to give the optimum mechanical properties. A clear Mullins effect was seen. Within experimental error, no change was seen in mechanical behavior as a function of time or heat-treatment. The mechanical properties of the sample containing the HDMZ treated silica were adversely affected. AFM phase images revealed aggregation and nonuniform distribution of the filler for all samples. Finally, a permanent set of about 3 to 6 percent was observed for the 35 phr samples.

Segmental Relaxation in End-Linked Poly(dimethylsiloxane) Networks

End-linked polydimethysiloxane (PDMS) networks were prepared by end-linking vinyl-terminated PDMS chains with tetrafunctional silanes. Dielectric α-relaxation spectra, thermal expansivities, and the (rubbery) elastic modulus were measured for these materials. From the cross-link density at which marked changes occur in the segmental relaxation times and the Tα-scaled temperature dependence (fragility), a characteristic length for the α-relaxation was determined. The result, 14 Å at Tα, is quite close to the length scale associated with constraint of crystallization in similar PDMS networks. Cross-linking also affects the thermal expansion and elastic modulus, although these properties exhibit a smoother variation with cross-link density.