PDMS-based Microfluidic Systems Research Articles

Continuous counter-current electrophoretic separation of oleosomes and proteins from oilseeds

Oilseeds, with their high content of oil and protein, will play an important role in the transition to plant based foods. Currently, seed oil extraction involves elevated temperatures and the use of organic solvents, which degrade the quality of both oils and proteins. To take full advantage of the oilseeds, a gentler process is needed. We here propose a mild alkaline extraction followed by a continuous electrophoretic separation process that is based on differences in electrophoretic mobility and recovers intact oleosomes and proteins from the seeds. Rapeseed oleosomes and proteins are both negatively charged at pH ≥ 5, yet exhibit significantly different electrophoretic mobility. Therefore, separation can be achieved by imposing a counter-current hydrodynamic flow rate between their electrophoresis rate. Thus, the compounds with higher mobility, oleosomes, are retained by the electric field, and the compounds with lower mobility, proteins, go along with the flow. The separation was modeled using the Nernst-Planck equation and demonstrated using a PDMS-based microfluidic system. Both the modeling and the experimental studies confirmed that the direction and rate of migration of the compounds can be steered by the electric field strength and the convective flow velocity. The proposed electrophoretic approach is feasible and scaleable, and may be a novel path to separate differently charged components under mild conditions, thereby preserving their original native properties.

Qualified sperm selection based on the rheotaxis and thigmotaxis in a microfluidic system.

In the present study, we used a microfluidic system for studying the combined effects of thigmotaxis and rheotaxis for sperm separation process to achieve the successful Assisted reproductive technology (ART). The designed PDMS-based microfluidic system had four various geometries, including linear, square, zigzag, and sinusoidal. The functionality of separated sperm was evaluated by sperm tracking (ImageJ), motility assay (CASA software), and morphology assay (Papanicolaou ultrafast staining). Probing various geometries revealed 100% motility. In non-linear geometries, sperm's periodic detachment from the walls gave rise to the periodic interaction with the high flow velocity in the center of the channel, resulting in the separation of high-quality sperm with progressive motility. The collected data proved the influence of thigmotaxis on the quality of separated sperm. Morphologically improvement in separated sperm from the sinusoidal geometry was significant than others, which means the sinusoidal structure would be the best candidate for the sperm separation process. The online version contains supplementary material available at 10.1007/s13534-023-00294-8.

A PDMS-based microfluidic system for assessment of the protective role of dexmedetomidine against sepsis-related glycocalyx degradation

A PDMS-based microfluidic system for assessment of the protective role of dexmedetomidine against sepsis-related glycocalyx degradation

Orientation of Liquid Crystalline Molecules on PDMS Surfaces and within PDMS Microfluidic Systems

The unique components of PDMS-based microfluidic systems are those combined with liquid crystalline materials. Their functionality, especially when it comes to optical applications, highly depends on the LC molecular arrangement. This work summarizes experimental investigations on the orientation of molecules within LC:PDMS structures according to the manufacturing technologies. The availability of high-quality molds to pattern PDMS is a significant barrier to the creation of advanced microfluidic systems. The possibility of using inexpensive molds in the rapid and reproducible fabrication process has been particularly examined as an alternative to photolithography. Different geometries, including an innovative approach for the electrical control of the molecular arrangement within PDMS microchannels, are presented. These studies are critical for novel optofluidic systems, introducing further research on LC:PDMS waveguiding structures.

A novel two-layer-integrated microfluidic device for high-throughput yeast proteomic dynamics analysis at the single-cell level.

Current microfluidic methods for studying multicell strains (e.g., m-types) with multienvironments (e.g., n-types) require large numbers of inlets/outlets (m*n), a complicated procedure or expensive machinery. Here, we developed a novel two-layer-integrated method to combine different PDMS microchannel layers with different functions into one chip by a PDMS through-hole array, which improved the design of a PDMS-based microfluidic system. Using this method, we succeeded in converting 2×m×n inlets/outlets into m+n inlets/outlets and reduced the time cost of loading processing (from m×n to m) of the device for studying multicell strains (e.g., m-types) in varied multitemporal environments (i.e., n-types). Using this device, the dynamic behavior of the cell-stress-response proteins was studied when the glucose concentration decreased from 2% to a series of lower concentrations. Our device could also be widely used in high-throughput studies of various stress responses, and the new concept of a multilayer-integrated fabrication method could greatly improve the design of PDMS-based microfluidic systems.

Different in vitro cellular responses to tamoxifen treatment in polydimethylsiloxane-based devices compared to normal cell culture.

Cell culture systems based on polydimethylsiloxane (PDMS) microfluidic devices offer great flexibility because of their simple fabrication and adaptability. PDMS devices also make it straightforward to set up parallel experiments and can facilitate process automation, potentially speeding up the drug discovery process. However, cells grown in PDMS-based systems can develop in different ways to those grown with conventional culturing systems because of the differences in the containers' surfaces. Despite the growing number of studies on microfluidic cell culture devices, the differences in cellular behavior in PDMS-based devices and normal cell culture systems are poorly characterized. In this work, we investigated the proliferation and autophagy of MCF7 cells cultured in uncoated and Parylene-C coated PDMS wells. Using a quantitative method combining solid phase extraction and liquid chromatography mass spectrometry we developed, we showed that Tamoxifen uptake into the surfaces of uncoated PDMS wells can change the drug's effective concentration in the culture medium, affecting the results of Tamoxifen-induced autophagy and cytotoxicity assays. Such changes must be carefully analyzed before transferring in vitro experiments from a traditional culture environment to a PDMS-based microfluidic system. We also found that cells cultured in Parylene-C coated PDMS wells showed similar proliferation and drug response characteristics to cells cultured in standard polystyrene (PS) plates, indicating that Parylene-C deposition offers an easy way of limiting the uptake of small molecules into porous PDMS materials and significantly improves the performance of PDMS-based device for cell related research.

Reactivity of poly(dimethylsiloxane) toward acidic permanganate

Poly(dimethylsiloxane) (PDMS) has been widely used in various microfluidic devices because it is considered to be one of the most inert materials available. A PDMS-based microfluidic system for the synthesis of manganese oxide (MO) nanoparticles is developed and tested. However, synthesis of MO nanoparticles in the PDMS-based microfluidic system is unsuccessful due to an unexpected reaction between acidic permanganate and PDMS. PDMS is pitted and coated with MnO2 and opalized silica, which are confirmed by SEM and EDX. The products of the reaction between PDMS and acidic permanganate are mainly MnO2, Cl2, SiO2 and CO2, respectively. Here we report for the first time the reactivity of PDMS toward acidic permangante resulting in a new process to coat the channel walls with MnO2.

Biofunctionalization and self-interaction chromatography in PDMS microchannels

In this paper we present an experimental protocol for protein immobilization on polydimethylsiloxane (PDMS) polymer surfaces and the subsequent application of a chromatographic PDMS microfluidic chip to measure protein–protein interactions. The PDMS surface modification steps are quantitatively and qualitatively experimentally analyzed using an array of techniques (water contact angle measurement, fluorescence spectroscopy and X-ray photoelectron spectroscopy). The protocol involves PDMS acidic surface activation using a potassium disulfite/potassium peroxidisulfate/acrylic acid mixture, followed by amination with 3-aminopropyl diethoxymethylsilane, followed by glutaraldehyde grafting and subsequent covalent protein binding. The applicability of such a miniaturized PDMS-based microfluidic system has been exemplified by measuring protein–protein interactions in a fast and accurate fashion for three model proteins, namely: hen egg white lysozyme, bovine ribonuclease-A and α-chymotrypsinogen. The protein interaction results align well with existing literature data using different materials and techniques. As the fabrication process for PDMS-based microstructures is relatively cheap, quick and requires limited lab expertise/access to specialized equipments, we consider that the implementation of such a flexible, easy to fabricate, PDMS-based microfluidic system for estimating protein interactions an important step toward quickly mapping protein phase behavior and measuring protein (self/cross) interactions in complex biological systems.

Biofunctionalization of PDMS-based microfluidic systems

Biofunctionalization of PDMS-based microfluidic systems

An Electromagnetically-Actuated All-PDMS Valveless Micropump for Drug Delivery

This paper presents the fabrication process of a single-chamber planar valveless micropump driven by an external electromagnetic actuator. This micropump features a pair of micro diffuser and nozzle elements used to rectify the fluid flow, and an elastic magnetic membrane used to regulate the pressure in the enclosed fluid chamber. Polydimethylsiloxane (PDMS) is used as the main construction material of this proposed micropump, including the structural substrate and the planar actuation membrane embedded with a thin micro magnet. Both the Finite Element Method and experimental analysis are used to assess the PDMS-membrane actuation under the applied electromagnetic forces and characterize the pump performance at variable working conditions. The resonant frequency of this micropump is identified experimentally and de-ionized (DI) water is loaded to account for the coupling effects of the working fluid. The experimental data was used to demonstrate the reliability of flow rates and how it can be controlled by consistently adjusting the driving frequencies and currents. The proposed micropump is capable of delivering a maximum flow rate of 319.6 μL/min and a maximum hydrostatic backpressure of 950 Pa (9.5 cm H2O). The planar design feature of the pump allows for potential integration of the pump with other PDMS-based microfluidic systems for biomedical applications.

Development of a PDMS‐based microchip electrophoresis device for continuous online in vivo monitoring of microdialysis samples

A PDMS-based microfluidic system for online coupling of microdialysis sampling to microchip electrophoresis with fluorescence detection for in vivo analysis of amino acid neurotransmitters using naphthalene-2,3-dicarboxaldehyde and sodium cyanide as the derivatization reagents is described. Fabricating chips from PDMS rather than glass was found to be simpler and more reproducible, especially for chips with complex designs. The microchip incorporated a 20-cm serpentine channel in which sample plugs were introduced using a "simple" injection scheme; this made fluid handling and injection on-chip easier for the online system compared with gated or valve-based injection. The microchip was evaluated offline for the analysis of amino acid standards and rat brain microdialysis samples. Next, precolumn derivatization was incorporated into the chip and in vivo online microdialysis-microchip electrophoresis studies were performed. The system was employed for the continuous monitoring of amino acid neurotransmitters in the extracellular fluid of the brain of an anesthetized rat. Fluorescein was dosed intravenously and monitored simultaneously online as a marker of in vivo blood-brain barrier permeability. The microdialysis-microchip electrophoresis system described here will be employed in the future for simultaneous monitoring of changes in blood-brain barrier permeability and levels of amino acid neurotransmitters in the rat stroke model.

An overlapping crisscross micromixer using chaotic mixing principles

A novel PDMS-based microfluidic system incorporating an overlapping crisscross entrance with patterned groove microchannels in sequence serves as a high-performance micromixer. Such a design is characterized as involving two chaotic mixing mechanisms: the split entrance streams through the first overlapping crisscross junction are stretched and folded about the parabolic point within the patterned channel, and the reoriented streams are merged and restretched about the hyperbolic point at the next junction. The multiplicative mixing quality is thus revealed to increase 21% as installed with the staggered bas-relief structures on the walls and 29% through the second intersection of the overlapping crisscross micromixer. This microfluidic device has a fairly constant mixing index for the Reynolds number through a wide range between 0.01 and 10; it is potentially capable of being extended to achieve a key element of a lab-on-a-chip. Use of both numerical analysis and a confocal microscope elucidates the detailed mixing pattern; the results of these approaches agree convincingly.

Long-term stability of PDMS-based microfluidic systems used for biocatalytic reactions

This paper reports on the changes of PDMS interface characteristics due to the long-term influence of aqueous alkaline solutions, which are frequently used fluids in biocatalytic reactions. Soft lithographic techniques were used to produce polymeric microfluidic systems containing a fluidic layer with multiple cavities for biocatalytic reactions and a pneumatic control layer. The surface energy, the surface roughness and the absorption of liquids on PDMS are analysed as they are important factors affecting the microfluidic current. The results obtained can be used to provide design guidelines for adapting PDMS-based microfluidic devices in long-term bio catalysis reactions.

Planar micro-check valves exploiting large polymer compliance

This paper presents three types of microfabricated planar check valves that exploit the large compliance of elastomeric polymers such as polydimethylsiloxane (PDMS). The micro-check valves consist of a thin compliant flap and a rigid stopper embedded in close proximity in a microchannel. The flap is perpendicular to the flow and lies near the stopper, forming a restricted fluid path inside the channel. The shape and size of the gap between the flap and stopper vary with the applied pressure, resulting in large flow resistance for forward flow and small resistance for reverse flow. The microfabricated valves have either two- or three-dimensional arrangement of valving elements. In particular, a interesting normally closed check valve was designed and fabricated using a special technique, in which the flap and stopper are, as fabricated, in intimate contact and form a zero-gap between them. Testing results show that the check valves can achieve a diodicity up to 10 5. The check valves can be fabricated using the standard replica molding technique from PDMS, and thus are highly amenable to integration with other PDMS-based microfluidic systems. The planar check valves can potentially used in lab-on-a-chip systems due to its high diodicity, planar configuration and use of inexpensive polymeric materials.

A high performance microfluidic system integrated with the micropump and microvalve on the same substrate

We present a microfluidic system with microvalves and a micropump that are easily integrated on the same substrate using the same fabrication process. The fabricated microfluidic system is suitable for use as a disposable device and its characteristics are optimized for use as a micro chemical analysis system. The system is realized by means of a polydimethylsiloxane(PDMS)-glass chip and an indium tin oxide heater. We demonstrate the integration of the micropump and microvalves using a new thermopneumatic-actuated PDMS-based microfluidic system. A maximum pumping rate of about 730 nl/min is observed at a duty-ratio of 1% and a frequency of 2 Hz with a fixed power of 500 mW. The measured power at flow cut-off is 500 mW for the microvalve whose channel width, depth and membrane thickness were 400, 110 and 320 μm, respectively.