Polydimethylsiloxane Curing Research Articles

Flexible and hydrophobic CoFe-LDH @Co MOF @biomass-derived carbon fabrics for effective near-infrared photothermal conversion and electromagnetic attenuation

Near-infrared (NIR) laser countermeasures firing systems and electromagnetic wave shielding are extremely important in military warfare. Herein, a series of biomass-derived carbon flexible textiles with NIR photothermal conversion and microwave absorption capabilities were created by pyrolysis at temperatures ranging from 700 to 1000 °C. A hydrothermal approach was employed to create 2D CoFe-layered double hydroxides (CoFe-LDH), whose positively charged characteristics were securely attached to the hydroxide clusters on the surface of cotton fibers via electrostatic interaction. Subsequently, the adjustable layer spacing of LDH provides ideal in situ growth sites for metal ions and organic ligands of Co MOF. CoFe-LDH@Co MOF@PDMS cotton-derived carbon textiles (CoFe@PCCF) were successfully made using high-temperature pyrolysis, annealed carbonization, and polydimethylsiloxane curing. The intrinsic light absorption of the interwoven and entangled carbon fibers, combined with the plasmonic resonance of its surface metal particles, promotes photothermal conversion of the material, reduces density, and increases absorption during multiple reflections of electromagnetic waves. Furthermore, its qualities can be optimized and modified by modifying parameters like as carbonization temperature and thickness. As a result, CoFe@PCCF-900 shows the minimum reflection loss (RLmin) of −23.03 dB at 1.6 mm thickness and an effective absorption bandwidth (EAB) of 4.53 GHz. The surface temperature of CoFe@PCCF-1000 reaches 74.5 ℃ after 3 seconds of NIR (980 nm, 200 mW) light, indicating quick and stable photothermal conversion. This work provides an opportunity for laser shooting and electromagnetic attenuation low-cost materials.

Digital light processing technique aided 3D printing hierarchical super-wetting mesh coated with hydrophobic SiO2 for highly efficient oil-water separation

Gravity-driven filtration using super-wetting mesh surfaces holds significant promise in addressing oil pollution resulting from human activities. However, conventional techniques need help fabricating efficient separation mesh structures due to their limited stability in oily-water solutions. To overcome this, we employed a Digital Light Processing (DLP) 3D printing technique to fabricate a mesh with a micro-patterned surface using a UV light-curable polyurethane (PU). A post-UV curing step was implemented to transform the soft segments of PU into a solid state. To enhance the super-wetting properties, hydrophobic modified silica (m-SiO2)/UV curable polydimethylsiloxane (PDMS) solution was applied through dip coating, resulting in a hierarchical structure with high surface roughness and superhydrophobic characteristics. In oil–water separation tests, the hierarchical superhydrophobic mesh, featuring a pore size of 300 µm, demonstrated exceptional performance, achieving a remarkable flow flux of 37,410 L/m2 h with a separation efficiency of 97.46 %. Furthermore, the separation efficiency remained consistently above 97.0 % under varying pH conditions and oil mixtures, highlighting the excellent water-repellence capacity of the hierarchical mesh developed in this study.

High-Sensitivity and Wide-Range Flexible Ionic Piezocapacitive Pressure Sensors with Porous Hemisphere Array Electrodes.

The development of high-performance flexible pressure sensors with porous hierarchical microstructures is limited by the complex and time-consuming preparation processes of porous hierarchical microstructures. In this study, a simple modified heat curing process was first proposed to achieve one-step preparation of porous hemispherical microstructures on a polydimethylsiloxane (PDMS) substrate. In this process, a laser-prepared template was used to form surface microstructures on PDMS film. Meanwhile, the thermal decomposition of glucose monohydrate additive during heat curing of PDMS led to the formation of porous structures within PDMS film. Further, based on the obtained PDMS/CNTs electrodes with porous hemisphere array and ionic polymer dielectric layers, high-performance ionic piezocapacitive sensors were realized. Under the synergistic effect of the low-stiffness porous hemisphere microstructure and the electric double layer of the ionic polymer film, the sensor based on an ionic polymer film with a 1:0.75 ratio of P(VDF-HFP):[EMIM][TFSI] not only achieves a sensitivity of up to 106.27 kPa-1 below 3 kPa, but also has a wide measurement range of over 400 kPa, which has obvious advantages in existing flexible piezocapacitive sensors. The rapid response time of 110 s and the good stability of 2300 cycles of the sensor further elucidate its practicality. The application of the sensor in pulse monitoring, speech recognition, and detection of multiple dynamic loads verifies its excellent sensing performance. In short, the proposed heat curing process can simultaneously form porous structures and surface microstructures on PDMS films, greatly simplifying the preparation process of porous hierarchical microstructures and providing a simple and feasible way to obtain high-performance flexible pressure sensors.

Room temperature roll-to-roll additive manufacturing of polydimethylsiloxane-based centrifugal microfluidic device for on-site isolation of ribonucleic acid from whole blood

Polymer-based lab-on-a-disc (LoaD) devices for isolating ribonucleic acid (RNA) from whole blood samples have gained considerable attention for accurate biomedical analysis and point-of-care diagnostics. However, the mass production of these devices remains challenging in manufacturing cost and sustainability, primarily due to the utilization of a laser cutter or router computer numerical control (CNC) machine for engraving and cutting plastics in the conventional prototyping process. Herein, we reported the first energy-efficient room-temperature printing-imprinting integrated roll-to-roll manufacturing platform for mass production of a polydimethylsiloxane (PDMS)-based LoaD to on-site isolate ribonucleic acid (RNA) from undiluted blood samples. We significantly reduced energy consumption and eliminated thermal expansion variations between the mold, substrate, and resists by accelerating the PDMS curing time to less than 10 min at room temperature without using heat or ultraviolet radiation. The additive manufacturing technology was applied to fabricate a multi-depth flexible polymer mold that integrated macro (2 mm) and micro-sized (500 μm) features, which overcomes the economic and environmental challenges of conventional molding techniques. Our integrated R2R platform was enabled to print adhesion-promoting films at the first printing unit and continuously in-line imprint with a high replication accuracy (99%) for high-volume manufacturing of a new centrifugal microfluidic chip with an enhancement of mixing performance by integrating an efficient mixing chamber and serpentine micromixer. This research paved the way for scalable green manufacturing of large-volume polymer-based microfluidic devices, often required in real-world sample-driven analytical systems for clinical bioanalysis.

Rapid Micromolding of Sub-100 µm Microfluidic Channels Using an 8K Stereolithographic Resin 3D Printer.

Engineering microfluidic devices relies on the ability to manufacture sub-100 micrometer fluidic channels. Conventional lithographic methods provide high resolution but require costly exposure tools and outsourcing of masks, which extends the turnaround time to several days. The desire to accelerate design/test cycles has motivated the rapid prototyping of microfluidic channels; however, many of these methods (e.g., laser cutters, craft cutters, fused deposition modeling) have feature sizes of several hundred microns or more. In this paper, we describe a 1-day process for fabricating sub-100 µm channels, leveraging a low-cost (USD 600) 8K digital light projection (DLP) 3D resin printer. The soft lithography process includes mold printing, post-treatment, and casting polydimethylsiloxane (PDMS) elastomer. The process can produce microchannels with 44 µm lateral resolution and 25 µm height, posts as small as 400 µm, aspect ratio up to 7, structures with varying z-height, integrated reservoirs for fluidic connections, and a built-in tray for casting. We discuss strategies to obtain reliable structures, prevent mold warpage, facilitate curing and removal of PDMS during molding, and recycle the solvents used in the process. To our knowledge, this is the first low-cost 3D printer that prints extruded structures that can mold sub-100 µm channels, providing a balance between resolution, turnaround time, and cost (~USD 5 for a 2 × 5 × 0.5 cm3 chip) that will be attractive for many microfluidics labs.

PLA 3D Printing as a Straightforward and Versatile Fabrication Method for PDMS Molds.

3D printing is gaining traction in research and development as a way to quickly, cheaply, and easily manufacture polydimethylsiloxane (PDMS) molds. The most commonly used method is resin printing, which is relatively expensive and requires specialized printers. This study shows that polylactic acid (PLA) filament printing is a cheaper, more readily available alternative to resin printing, that does not inhibit the curing of PDMS. As a proof of concept, a PLA mold for PDMS-based wells was designed, and 3D printed. We introduce an effective method to smooth the printed PLA mold, based on chloroform vapor treatment. After this chemical post-processing step, the smoothened mold was used to cast a ring of PDMS prepolymer. The PDMS ring was attached to a glass coverslip after oxygen plasma treatment. The PDMS-glass well showed no leakage and was well suited to its intended use. When used for cell culturing, monocyte-derived dendritic cells (moDCs) showed no morphological anomalies, as tested by confocal microscopy, nor did they show an increase in cytokines, as tested using ELISA. This underlines the versatility and strength of PLA filament printing and exemplifies how it can be valuable to a researcher's toolset.

Aging of UV curable PDMS developed for large-scale, high viscosity stereolithography

Polydimethylsiloxane (PDMS) elastomers are silicone rubbers that find widespread application in both academic and industrial settings. This study investigates the use of photosensitive platinum catalysts for UV-activated hydrosilylation of PDMS, which enables the additive manufacturing of PDMS objects through techniques such as stereolithography. Specifically, this study focuses on understanding the aging behavior of Pt-catalyzed, UV-curable PDMS samples, including their mechanical behavior under thermal and UV-accelerated aging conditions. The results show that the Pt-catalyzed, UV-curable PDMS introduced in this research is ‘under-cured’ after being printed and will slowly evolve over time resulting in increased stiffness and decreased elongation, likely due to the formation of additional crosslinks. FTIR spectroscopy indicates that no new chemical bonds or functional groups are generated through the aging process, suggesting that no thermal degradation or polymer chain scissions occur in the polymer matrix. Overall, this PDMS formulation exhibits greater mechanical strength and significantly less reduction in strength with aging, compared with the commonly used, UV-curable thiol-ene PDMS.

Flow Performance and Its Effect on Shape Formation in PDMS Assisted Thermal Reflow Process

A theoretical model is proposed to investigate the mechanism of shape formation in polydimethylsiloxane (PDMS) assisted thermal reflow. The thermal curing of PDMS is characterized by a dual-Arrhenius equation and its effect on the reflow process is discussed. It shows that due to the thermal curing of PDMS, the dynamic wetting and interface evolution are constrained successively. This is quite different from the traditional thermal reflow, and will result in unique flow performance, which will facilitate the abilities of the base constraint and shape retaining for the thermal reflow process. These advantages are critical to obtain well-defined microstructures in a simple and controllable way. Theoretical simulations of shape formation are in good agreement with the experimental results. These results provide a comprehensive understanding on PDMS assisted thermal reflow and offer a theoretical guideline for a facile yet versatile fabrication method for high quality microstructures.

Multifunctional MXene/CNT-based layered film for icing detection, anti-icing, and deicing application

Icing phenomenon usually happens in our daily life, especially in the cold winter or in high altitude areas, which makes us feel inconvenient and greatly threats some fields such as civil aviation or the manufacturing industry. In this study, a multifunctional film with properties of icing detection, anti-icing and deicing was fabricated. One-dimensional material carbon nanotube (CNT) and two-dimensional material Ti3C2Tx MXene were combined by two-step vacuum filtration. Polydimethylsiloxane (PDMS) as the flexible hydrophobic materials was then used to encapsulate layered film. Additionally, PDMS curing process on the sandpaper could make the surface of MXene/CNT layered film possess micro-structures. The low surface energy material PDMS and rough surface structures endow MXene/CNT layered film with good water-repellency. Compared with pure PDMS film (103°), the contact angle of MXene/CNT layered film surface reaches 128°. The result exhibits that a waterdrop(100uL) on the layered film surface takes 1425s to be frozen, which takes longer time than glass and pure PDMS. Additionally, excellent sensibility of the layered film could be used to detect icing phenomenon. The result manifests that gauge factor (GF) of MXene/CNT film reaches 15051 so that different icing stages could be identified by layered film clearly. MXene/CNT layered film possesses good electric heating and photo-thermal properties. The result shows that surface temperature can reach 89 °C with the 2.5 V voltage supply, and temperature reaches 95 °C through the radiation of near-infrared lamp as well. The dual-driven heating of MXene/CNT layered film shows the ability of deicing. 1000 mg ice just takes 223s to be melted entirely by 2.5 V input voltage, and 269s by radiation of 200 mW/cm2, respectively. The multifunctional MXene/CNT based layered film prepared by a simple fabrication method that integrates hydrophobicity, dual-driven heating, and sensibility together, which shows potential application in icing detection, anti-icing, and deicing.

A biomimetic compound eye lens for photocurrent enhancement at low temperatures

In this study, an artificial compound eye lens (ACEL) was fabricated using a laser cutting machine and polyvinyl alcohol (PVA) solution. A laser cutter was used to punch micro-sized holes (500 μm diameter—the smallest possible diameter) into an acrylic plate; this punched plate was then placed on the aqueous PVA solution, and the water was evaporated. The plate was used as the mold to obtain a polydimethylsiloxane (PDMS) micro lens array film, which was fixed to a dome-shaped three-dimensional-printed mold for further PDMS curing, and a hemispherical compound eye lens was obtained. Using a gallium nitride (GaN) photodetector, a light detection experiment was performed with the ACEL, bare lens, and no lens by irradiating light at various angles under low temperatures. The photodetector with the ACEL generated a high photocurrent under several conditions. In particular, when the light was irradiated at 0° and below −20 °C, the photocurrent of the GaN sensor with the ACEL increased by 61% and 81% compared with the photocurrent of the GaN sensor with the bare lens and without a lens, respectively. In this study, a sensor for detecting light with ACEL was demonstrated in low-temperature environments, such as indoor refrigerated storages and external conditions in Antarctica and Arctic.

A simple, low cost and reusable microfluidic gradient strategy and its application in modeling cancer invasion

Microfluidic chemical gradient generators enable precise spatiotemporal control of chemotactic signals to study cellular behavior with high resolution and reliability. However, time and cost consuming preparation steps for cell adhesion in microchannels as well as requirement of pumping facilities usually complicate the application of the microfluidic assays. Here, we introduce a simple strategy for preparation of a reusable and stand-alone microfluidic gradient generator to study cellular behavior. Polydimethylsiloxane (PDMS) is directly mounted on the commercial polystyrene-based cell culture surfaces by manipulating the PDMS curing time to optimize bonding strength. The stand-alone strategy not only offers pumpless application of this microfluidic device but also ensures minimal fluidic pressure and consequently a leakage-free system. Elimination of any surface treatment or coating significantly facilitates the preparation of the microfluidic assay and offers a detachable PDMS microchip which can be reused following to a simple cleaning and sterilization step. The chemotactic signal in our microchip is further characterized using numerical and experimental evaluations and it is demonstrated that the device can generate both linear and polynomial signals. Finally, the feasibility of the strategy in deciphering cellular behavior is demonstrated by exploring cancer cell migration and invasion in response to chemical stimuli. The introduced strategy can significantly decrease the complexity of the microfluidic chemotaxis assays and increase their throughput for various cellular and molecular studies.

Controlled Methodology for Development of a Polydimethylsiloxane-Polytetrafluoroethylene-Based Composite for Enhanced Chemical Resistance: A Structure-Property Relationship Study.

Polydimethylsiloxane (PDMS) polymers are highly appreciated materials that are broadly applied in several industries, from baby bottle nipples to rockets. Momentive researchers are continuously working to understand and expand the scope of PDMS-based materials. Fluorofunctional PDMS has helped the world to apply in specialty applications. Efforts are taken to develop such siloxane–fluoropolymer composite materials with good thermal, solvent, and chemical resistance performances. We leveraged inherently flexible PDMS as the model matrix, whereas polytetrafluoroethylene (PTFE) was used as the additive to impart the functional benefits, offering great value in comparison to the individual polymers. The composites were made at three different mixing temperatures, that is, 0–35 °C, and different loadings of PTFE, that is, 0.5–8% (w/w), were selected as the model condition. A strong dependency of the mixing temperature against the performance attributes of the developed composites was noted. Mechanical and thermal stability of the composites were evaluated along with optical properties. X-ray diffraction demonstrated the change in the crystallite size of the PTFE particles as a function of processing temperature. Compared to the phase II crystallite structure of the PTFE, the fibrils formed in phase IV imparted a better reinforcing capability toward the PDMS matrix. A synergistic balance between higher filler loading and mechanical properties of the composite can be achieved by doping the formulation with short-chain curable PDMS, with 238% increment of tensile strength at 8 wt % PTFE loading when compared to the control sample. The learning was extended to check the applicability of doping such PTFE powder in commercial liquid silicone rubber (LSR). In the window of study, the formulated LSR demonstrated improved mechanical properties with additional functional benefits like resistance toward engine oil and other chemical solvents.

Hydrophobic interpenetrating polyamide-PDMS membranes for desalination, pesticides removal and enhanced chlorine tolerance

Hydrophobic membranes for desalination and toxic organic pollutant removal have been fabricated using polyamide - PDMS (polydimethylsiloxane) chemistries in a one-step protocol. The curing of polyamide and PDMS are orthogonal and co-curing both networks imparts hydrophobicity to the thin film composite membranes. The membranes exhibit increased adsorption of pesticides from the feed water along with maintaining excellent salt rejection capability (97% NaCl rejection), thus giving the membranes a multifunctional character. Three toxic pesticides have been used in this study to demonstrate the viability of combining osmosis desalination technology with organic matter adsorption. The membranes also show excellent resistance to fouling by toxic pesticides (85% salt rejection vs 67% for commercial membranes in the presence of pesticides) and significantly improved chlorine tolerance (93.8% salt rejection vs 86.5% for commercial membranes after 20h of exposure to sodium hypochlorite solution).

Microwave irradiation-based rapid curing of PDMS for microfluidic applications

Microfluidic devices are routinely fabricated using replica moulding. The master relief structure is generally constructed on a silicon substrate and the stamps are made using polydimethylsiloxane (PDMS), cured via the slow process of hot-air convective heating. An alternative method that greatly reduces this cure time is presented here. It employs a low-cost, consumer-grade microwave oven and speeds up the curing process by permitting a much higher heat flux to be applied to the prepolymer. A specific pulsed irradiation protocol has been devised which achieves precisely controlled energy delivery for this purpose. This is necessary because silicon’s relatively much stronger microwave absorption causes uncontrollable temperature overshoots that could degrade PDMS if continuously irradiated. The protocol has been arrived at after due optimization of operational parameters, achieved via simulation of a finite element model. It has been implemented by modifying the control circuitry of the consumer grade oven. Cure times as low as two minutes have been demonstrated. Optical and mechanical characterization results show no adverse effect on the performance of PDMS cured using the proposed method. Thus, it can be used for the rapid fabrication of PDMS-based microfluidic devices and would be especially beneficial for research labs looking to speed up microfluidic device development iterations.

PDMS leaching and its implications for on-chip studies focusing on bone regeneration applications

Polydimethylsiloxane (PDMS) is among the most widely used materials for organ-on-chip systems. Despite its multiple beneficial characteristics from an engineering point of view, there is a concern about the effect of PDMS on the cells cultured in such devices. The aim of this study was to enhance the understanding of the effect of PDMS on cellular behavior in a context relevant for on-chip studies. The focus was put on an indirect effect of PDMS, namely leaching of uncrosslinked oligomers, particularly for bone regeneration applications. PDMS-based chips were prepared and analyzed for the potential release of PDMS oligomers within the microfluidic channel when kept at different flow rates. Leaching of uncrosslinked oligomers from PDMS was quantified as silicon concentration by inductively coupled plasma - optical emission spectrometry and further confirmed by mass spectrometry. Subsequently, PDMS-leached media, with a silicon concentration matching the on-chip experiment, were prepared to study cell proliferation and osteogenic differentiation of MC3T3-E1 pre-osteoblasts and human mesenchymal stem cells. The silicon concentration initially detected in the media was inversely proportional to the tested flow rates and decreased to control levels within 52 h. In addition, by curing the material overnight instead of 2 h, regardless of the curing temperature (65 and 80 °C), a large reduction in silicon concentration was found, indicating the importance of the PDMS curing parameters. Furthermore, it was shown that PDMS oligomers enhanced the differentiation of MC3T3-E1 pre-osteoblasts, this being a cell type dependent effect as no changes in cell differentiation were observed for human mesenchymal stem cells. Overall, this study illustrates the importance of optimization steps when using PDMS devices for biological studies, in particular PDMS curing conditions and extensive washing steps prior to an experiment. • PDMS oligomers leach out from PDMS-based microfluidic chips. • The amount of PDMS oligomers is reduced by longer curing times or washing. • MC3T3-E1 pre-osteoblasts show enhanced differentiation after indirect PDMS exposure. • The effect of PDMS oligomers on cellular behavior is cell type specific.

Enhanced Surface-Enhanced Raman Scattering (SERS) Sensitivity by the Self-Assembly of Silver Nanoparticles (Ag NPs) Laminated on Polydimethylsiloxane (PDMS)

Herein, a transparent and reproducible substrate, fabricated using polydimethylsiloxane (PDMS) laminated with self-assembled Ag nanoparticles (Ag NPs), was employed as a universal surface-enhanced Raman scattering (SERS) substrate for the detection of targets with various matrices. The Ag NPs were assembled in a two-dimensional manner via a self-assembly technique. Due to the electrostatic interaction between the Ag NPs, the reproducibility of the assembly was ensured by the fixed density of the assembled Ag NPs at saturated assembly states. The assembled pattern and plasmon resonance of the Ag NPs were well preserved during the molding and curing of PDMS. As a result, the Ag NP laminated PDMS film exhibited a SERS effect to the adsorbed p-aminothiophenol comparable to that of the assembled Ag NPs on a glass slide. Extra SERS enhancement was achieved by construction of a Ag (PDMS)/molecule/Ag (glass) configuration due to the electromagnetic coupling between the Ag NPs. The Raman scattering of 4-mercaptobenzoic acid and benzotriazole modified on the surfaces of a smooth Au electrode and copper foil, respectively, was detected with the aid of the Ag NP-laminated PDMS film. Furthermore, malachite green dispersed in a KBr solid matrix was quantitatively determined with a detection limit of 0.5 μg/g. It is suggested that the SERS enhancement and consequential SERS detection sensitivity of the target molecules may be further maximized by adjusting the distance between the target molecules and the Ag NPs laminated on the PDMS film.

Inertial Microfluidics with Integrated Vortex Generators Using Liquid Metal Droplets as Fugitive Ink

AbstractThis work demonstrates a simple method for fabricating nearly spherical dome structures on top of lithographically defined microfluidic channels using gallium‐based liquid metal droplets as fugitive ink. The droplets remain stable during the pouring and curing of polydimethylsiloxane and can be easily removed by applying a basic solution. This facilitates the formation of domes with diameters of a few hundred micrometers patterned on the desired locations of the channel. The expansion of the channel at the interface of the dome leads to formation of a large vortex inside the dome. Experiments using high‐speed imaging along with numerical simulations show the utility of the vortex‐induced flow rotation for orbiting of human monocytes and polystyrene microbeads inside the dome. The lateral displacement of liquids caused by the vortex is further utilized for creating controllable multiband flow/color profiles within a T‐mixer. The method enables the fabrication of customized, complex, and 3D microfluidic systems utilizing planar microfabricated structures.

Extrusion-based printing of sacrificial Carbopol ink for fabrication of microfluidic devices

Current technologies for manufacturing of microfluidic devices include soft-lithography, wet and dry etching, thermoforming, micro-machining and three-dimensional (3D) printing. Among them, soft-lithography has been the mostly preferred one in medical and pharmaceutical fields due to its ability to generate polydimethylsiloxane (PDMS) devices with resin biocompatibility, throughput and transparency for imaging. It is a multi-step process requiring the preparation of a silicon wafer pattern, which is fabricated using photolithography according to a defined mask. Photolithography is a costly, complicated and time-consuming process requiring a clean-room environment, and the technology is not readily accessible in most of the developing countries. In addition, generated patterns on photolithography-made silicon wafers do not allow building 3D intricate shapes and silicon direct bonding is thus utilized for closed fluid channels and complex 3D structures. 3D Printing of PDMS has recently gained significant interest due to its ability to define complex 3D shapes directly from user-defined designs. In this work, we investigated Carbopol as a sacrificial gel in order to create microfluidic channels in PDMS devices. Our study demonstrated that Carbopol ink possessed a shear-thinning behavior and enabled the extrusion-based printing of channel templates, which were overlaid with PDMS to create microfluidic devices upon curing of PDMS and removal of the sacrificial Carbopol ink. To demonstrate the effectiveness of the fabricated devices, channels were lined up with human umbilical vein endothelial cells (HUVECs) and human bone marrow endothelial cells (BMECs) in separate devices, where both HUVECs and BMECs demonstrated the formation of endothelium with highly aligned cells in the direction of fluid flow. Overall, we here present a highly affordable and practical approach in fabrication of PDMS devices with closed fluid channels, which have great potential in a myriad of applications from cancer treatments to infectious disease diagnostics to artificial organs.

Flexible graphene-coated carbon fiber veil/polydimethylsiloxane mats as electrothermal materials with rapid responsiveness

Flexible electrothermal mats with rapid responsiveness were prepared by spray-coating of graphene nanoplates (GNP) acetone dispersion on carbon fiber veil and following curing of polydimethylsiloxane (PDMS) on the mats. Morphological feature, electrical property, and electrothermal behavior of the mats with different area density from 55 to 20 g m−2 were investigated. Scanning electronic microscope (SEM) confirmed that pristine graphene nanoplates were uniformly deposited on the surface of carbon fiber resulting in volume resistance decreased substantially. Compared with the carbon fiber veil without coated GNP, the electric heating behavior of graphene-coated carbon fiber/PDMS mats were improved largely, such as the stead-state maximum temperature reached 297 °C, the maximum heating rate reached 5°Cs−1 tested by an infrared camera, the maximum power density reached 11.11 kW m−2. The respond time from room temperature 25 °C–200 °C was only 40 s tested by infrared thermal image. Even under high twisting/bending state or continuous stepwise voltage changes, the graphene-coated carbon fiber/PDMS mats retained stable electrical heating performance in aspects of temperature responsiveness and steady-state maximum temperature.

Cutting edge microfluidics: Xurography and a microwave

Microfluidic technologies enable precise fluidic manipulation at the microscale, with applications ranging from inexpensive medical diagnostics to automaton devices for extraterrestrial in situ analysis. However, development of microfluidic tools typically requires high-maintenance infrastructure and resource-intensive development processes, limiting their broad adoption. Furthermore, the development of effective microfluidic tools requires iterative design processes, multiplicatively increasing development time and cost. Rapid prototyping techniques minimize these expenses, accelerating development time and reducing manufacturing cost of microfluidic devices. Here, we use the print-and-peel (PAP) technique of xurography to fabricate master molds in conjunction with microwave thermal processing of polydimethylsiloxane (PDMS) to rapidly fabricate PDMS-based microfluidics. Three types of tape (3M Blue Platinum, PVC and Kapton Tape) and three types of backing substrates (Soda lime glass, Silicon, Ceramic glass) were employed, enabling fabrication of microfluidic devices from design to device in as little as five minutes. Minimum feature widths of ˜200 μm and feature heights of ˜60 μm were determined. Proof-of-concept devices made using these methods were employed for electrophoretic flow focusing applications. To the best of our knowledge, this process represents the most rapid method for fabrication of PDMS microfluidics to date due to microwave thermal processing, enabling curing of PDMS in as little as 90 s. This work can significantly minimize device fabrication time and the start-up cost of fabrication infrastructure, enhancing efficiency and making microfluidics accessible to a broader user base.