Multilayer Polydimethylsiloxane Research Articles

Preparation of stable multilayer PDMS composite pervaporation membrane incorporated with in-situ transformed metal organic frameworks for enhanced butanol recovery

In this study, stable and non-defective multilayer polydimethylsiloxane (PDMS) composite pervaporation mixed matrix membranes incorporated with in-situ transformed metal organic frameworks was successfully synthesized via ligand vapor phase infiltration and spin-coating. Metal zinc sources were uniformly distributed in PDMS which were in-situ transformed into homogeneous zeolitic imidazolate framework-8 (ZIF-8) nanoparticles, effectively alleviating the aggregation of ZIF-8. Thermal cross-linking of PDMS and the formation of MOFs occurred simultaneously, omitting the complicated preparation and re-dispersion steps of MOF nanoparticles. MOF nanoparticles and PDMS formed a more stabilized composite structure by in-situ transformation, in which PDMS and metal of MOFs can interact with the -Si-O- of silane coupling groups on membrane surface to construct solid multilayer composite membrane, ensuring long-term stability. Moreover, with the aid of hydrophobic interlayer, polymer infiltration into channels of substrate was restricted and casting solution spread out smoothly, facilitating the formation of defect-free PDMS selective layer. Various techniques including Attenuated Total Reflection-Fourier Transform Infrared Spectrometer, Field Emission Scanning Electron Microscopy, Atomic Force Microscope and X-ray Diffraction were applied to explore the morphology, composition and structure of nanoparticles and membranes, and pervaporation tests were taken to investigate the behavior of hydrophobic polymer-based multilayer membranes. For the recovery of low concentration n-butanol, the prepared non-defective multilayer TAO/ZIF-8/K-PDMS composite membrane displayed excellently total permeate flux of 2890 g m−2 h−1 with competitive separation factor of 40.3.

Abstract 6791: Investigation of sex hormone effects in an organ chip model of endothelial barrier dysfunction in the triple negative breast cancer microenvironment

Abstract Inflammation and pathological vasculature are common features of the tumor microenvironment (TME). Sex hormones potently modulate vascular physiology and immune cell functions, and there are established correlations with the outcomes of triple negative (TNBC) despite the defining feature of receptor negativity. Circulating estrogens and androgens have been hypothesized as drivers of TNBC through the actions exerted by receptor-positive cells in the TME. Here, we present an organ chip model of the TNBC microenvironment for quantifying the impact of configurable TME variables such as the ECM composition and the relative densities and phenotypes of tumor cells, cancer associated fibroblasts, and myeloid cells on endothelial barrier function. After establishing baselines of vascular permeability in the presence and absence of TNBC cells, we tested the effect of estradiol, estrone, and dihydrotestosterone on barrier permeability. Multilayer polydimethylsiloxane (PDMS) organ chips were fabricated using standard soft lithography. The layers of the device were separated with semi-permeable membranes that allow exchange of soluble factors. Once assembled, the upper channel was loaded with female (XX) human umbilical vein endothelial cells. Collagen hydrogels were injected into the tissue layer and the devices were cultured on a rocker to induce endothelial barrier alignment via application of an average shear stress of 5 dynes/cm2. We optimized rocking conditions by assessing endothelial layer alignment, junctional organization, and permeability. TNBC cells and XX mammary carcinoma fibroblasts were added to the hydrogel to model the effects of TME-derived signals on endothelial barrier permeability. 40 kDa FITC- Dextran was chosen to assay permeability as it can show leakage due to active disruption of the barrier. Staining for F-actin and ZO-1 allowed for quantification of junctional organization. Sex hormone modulation of proinflammatory gene expression was assessed by RT-qPCR. The presence of TNBC cells significantly increased transport of 40kDa FITC-Dextran across the endothelial barrier, disrupted intercellular junction quality, and induced the expression of inflammatory adhesion molecules including ICAM-1. Our results demonstrate that sex hormones modulate TNBC-associated changes in endothelial cell bioenergetics, junctional organization, and macromolecular barrier permeability. Ongoing work will investigate the effects of age-matched XX monocyte derived macrophages on barrier function in the model. This organ chip platform provides an assay for measuring altered vascular inflammation and permeability in the TNBC microenvironment and may provide a venue for investigating vascular-normalizing effects of various candidate therapeutics. Citation Format: Delia Carlino, Ashley Martier, Yasmin Maurice, G. Wills Kpeli, Matthew Burow, Mark Mondrinos. Investigation of sex hormone effects in an organ chip model of endothelial barrier dysfunction in the triple negative breast cancer microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6791.

Enhanced electro-actuation property of heterogeneous multi-layered polydimethylsiloxane-based dielectric elastomer composites

Due to their feature of the conversion from electrical to mechanical energy under an applied electric field, dielectric elastomers (DEs) have been widely adopted in smart devices. However, the significant electro-actuated property of DEs is always obtained under a giant driving electric field, which raises a potential safety hazard and limits their practical application range. Moreover, the traditional strategy of regulating the flexibility of DEs via physical swelling effect would result in an undesired plasticizer leakage and an irreversible reduction in both electromechanical stability and lifetime. Herein, a typical heterogeneous multi-layered polydimethylsiloxane (PDMS)-based DE composite was prepared by solution blending and the layer-by-layer casting method. Through synchronously introducing the high-permittivity BaTiO3 and the plasticizer dimethyl silicone oil in the middle layer, both the dielectric and mechanical property of the composite are effectively regulated. Not only the interlayered mechanical mismatch is eliminated but also the problem of plasticizer leakage is optimized through this reasonable structural design. The maximum electro-actuated strain obtained in the sandwiched DE composite was as large as 24.25% under 60 V/μm, which is 338.52% higher than that of pristine PDMS. Furthermore, the composite exhibits the largest driving strain (58.31%) near its breakdown electric field of 77.82 V/μm. Therefore, this study provides a promising route for the preparation of advanced DE composite with an improved low-field electro-actuated property.

Microfabrication Bonding Process Optimization for a 3D Multi-Layer PDMS Suspended Microfluidics

Microfluidic systems have received increased attention due to their wide variety of applications, from chemical sensing to biological detection to medical analysis. Microfluidics used to be fabricated by using etching techniques that required cleanroom and aggressive chemicals. However, another microfluidic fabrication technique, namely, soft lithography, is less expensive and safer compared to former techniques. Polydimethylsiloxane (PDMS) has been widely employed as a fabrication material in microfluidics by using soft lithography as it is transparent, soft, bio-compatible, and inexpensive. In this study, a 3D multi-layer PDMS suspended microfluidics fabrication process using soft lithography is presented, along with its manufacturing issues that may deteriorate or compromise the microsystem’s test results. The main issues considered here are bonding strength and trapped air-bubbles, specifically in multi-layer PDMS microfluidics. In this paper, these two issues have been considered and resolved by optimizing curing temperature and air-vent channel integration to a microfluidic platform. Finally, the suspended microfluidic system has been tested in various experiments to prove its sensitivity to different fluids and flow rates.

Hydrophilic Porous Polydimethysiloxane Sponge as a Novel 3D Matrix Mimicking Heterogeneous Pores in Soil for Plant Cultivation.

In this work, a citric acid monohydrate (CAM)-templated polydimethylsiloxane (PDMS) sponge was proposed to mimic heterogeneous pore structures in the soil for plant cultivation. The porosity of the PDMS sponges was tuned by adjusting the CAM template. The water intake capability of the sponge was improved by (3-Aminopropyl) triethoxysilane (APTES) functionalization. The pore size and pore distribution were characterized by SEM and micro-computed tomography (micro-CT). The effect of pore structures on Oryzasativa (O. sativa) growth was investigated. Also, a 3D multi-layer PDMS sponge assembling was proposed to mimic the heterogeneous pore distribution at the different soil depth. The different growth rates of O. sativa and Nicotiana tabacum L. (N. tabacum) seeds on porous PDMS sponge indicated the impact of physical obstacles (pores) and chemical (water content) conditions on plant development. It is anticipated that this PDMS sponge could serve as a 3D matrix to mimic soil and provide a new idea for plant cultivation.

A 0.9m Long 0.5gf Resolution Catheter-based Force Sensor for Real-Time Force Monitoring of Cardiovascular Surgery.

This paper presents a 0.9m long capacitive force sensor for a catheter integration, which measures a contact force to inner vessel wall or organs with a resolution of 0.5gf. The force sensor is implemented with a thin flexible printed circuit board (FPCB) encapsulated by a force sensitive medium, multilayer polydimethylsiloxane (PDMS). The parasitic capacitance $( \mathrm {C}_{P})$ inherent in long catheters significantly degrades the sensing accuracy of capacitive force sensors. To account for this, this work proposes a sensor interface with $\mathrm {C}_{P}$ canceller. By removing the 348pF (91.5%) of $\mathrm {C}_{\mathrm{P}}$with the $\mathrm {C}_{\mathrm{P}}$ canceller, the capacitive force sensor achieves a capacitance resolution of 16aF equivalent to a force error of 0.5gf, which is a $10 \times $ improvement compared to the conventional sensor interface. The proposed force sensor offers great potential for real-time force monitoring of cardiovascular surgery.

Inkjet printed polyethylene glycol as a fugitive ink for the fabrication of flexible microfluidic systems

This paper demonstrates a novel and simple processing technique for the realization of scalable and flexible microfluidic microsystems by inkjet-printing polyethylene-glycol (PEG) as a sacrificial template, followed by embedding in a structural layer (e.g. soft elastomers). The printing technology allows production of an array of PEG droplets simultaneously, reducing cost and manufacturing time. The PEG can be removed through heating above its phase-change temperature after the formation of the structural layer, with hydraulic flow removing the material. The developed technique allows easy modulation of the shape and dimensions of the pattern with the ability to generate complex architectures without using lithography. The method produces robust planar and multilayer microfluidic structures that can be realized on wide range of substrates. Moreover, microfluidics can be realized on other systems (e.g. electrodes and transducers) directly without requiring any bonding or assembling steps, which often limit the materials selection in conventional microfluidic fabrication. Multilayer Polydimethylsiloxane (PDMS) microfluidic channels were created using this technique to demonstrate the capability of the concept to realize flexible microfluidic electronics, drug delivery systems, and lab-on-a-chip devices. By utilizing conductive liquid metals (i.e. EGaIn) as the filling material of the channels, flexible passive resistive components and sensors have been realized.

Design of a Tri-Axial Force Measurement Transducer for Plantar Force Measurements.

Transducers for spatial plantar force measurements have numerous applications in biomechanics, rehabilitation medicine, and gait analysis. In this work, the design of a novel, tri-axial transducer for plantar force measurements was presented. The proposed design could resolve both the normal and the shear forces applied at the foot's sole. The novelty of the design consisted in using a rotating bump to translate the external loads into axial compressive forces which could be measured effectively by conventional pressure sensors. For the prototype presented, multilayer polydimethylsiloxane (PDMS) thin-film capacitive stacks were manufactured and used as sensing units, although in principle the design could be extended to various types of sensors. A quasi-static analytic solution to describe the behavior of the transducer was also derived and used to optimize the design. To characterize the performance of the transducer, a 3 cm diameter, 1 cm tall prototype was manufactured and tested under various combination of shear and normal loading scenarios. The tests confirmed the ability of the transducer to generate strong capacitive signals and measure both the magnitude and direction of the normal and shear loads in the dynamic range of interest.

An automated microfluidic system for screening Caenorhabditis elegans behaviors using electrotaxis.

Caenorhabditis elegans (C. elegans) is a widely used animal model to study mechanisms of biological processes and human diseases. To facilitate manipulations of C. elegans in the laboratory, researchers have developed various tools that permit careful monitoring of behavior and changes in cellular processes. Earlier, we had reported a novel microfluidic assay device to study the neuronal basis of movement and to investigate the effects of cellular and environmental factors that can induce degeneration in certain neurons leading to movement disorder. The system involved the use of an electric field to perform electrotaxis assays, which allows detailed examination of movement responses of animals. One of the potential uses of this system is to perform genetic and chemical screenings for neuroprotective factors; however, it could not be done due to manual operations and low throughput. In this paper, we present an integrated microfluidic system that automates screening of C. elegans behavioral response using electrotaxis. The core component of system is a multilayer poly dimethyl siloxane (PDMS) device, which enables C. elegans loading, capture, flush, release, electrotaxis, and clean sequentially with the help of other components. The system is capable of screening C. elegans, at a throughput of more than 20 worms per hour, automatically and continually without human intervention. To demonstrate the effectiveness of the system, C. elegans neuronal mutants were screened, and the phenotype data were extracted and analyzed. We envision that the automatic screening potential of the system will accelerate the study of neuroscience, drug discovery, and genetic screens in C. elegans.

Assessment of PDMS Technology in a MIMO Antenna Array

This letter assesses the use of a flexible multilayered polydimethylsiloxane (PDMS) substrate in a multiple-input- multiple-output (MIMO) antenna array for WLAN applications at 5.8 GHz. The use of the innovative polymer-based PDMS technology features favorable mechanical properties such as flexibility, water/dust resistance, and optical transparency. Besides that, PDMS also has a relatively low loss tangent. All these properties are very relevant for future (wearable) WLAN MIMO antennas. The proposed 2 × 4 antenna array and its rear ground plane are embedded in a multilayered PDMS substrate and fed by two 50Ω coaxial ports. It is found that the multilayered PDMS substrate may yield a design with excellent MIMO parameters. The mutual coupling is better than -30 dB, the envelope correlation coefficient (ρ) is in the order of 0.001, and the efficiency is 72%. A high gain of 11.5 dB is achieved.

A 3-D Overbridge-Shaped Micromixer for Fast Mixing Over a Wide Range of Reynolds Numbers

This paper reports the development of a 3-D passive micromixer named the overbridge-shaped micromixer (OBM), which can achieve fast mixing by taking advantage of the splitting, recombination, and chaotic advection mechanisms simultaneously. A scheme with the splitting channels of unequal widths is proposed for tremendously enhancing the mixing uniformity in the regions closing to the side walls. The channel depth-to-width ratio is the key factor to mixing performance. A four-unit OBM has been successfully fabricated via a multilayer polydimethylsiloxane process, and the total length of the OBM is <2 mm. Up to a 90% efficiency has been achieved within a Reynolds number (Re) range from 0.01 to 200 by numerical analysis, and the same mixing efficiency was also proven experimentally within a Re range from 0.01 to 50. A high efficiency of 90% was also obtained when mixing two fluids with different flow rates at the two inlets ranging from a ratio of 1:9 to 9:1. [2014-0186]

Desktop aligner for fabrication of multilayer microfluidic devices.

Multilayer assembly is a commonly used technique to construct multilayer polydimethylsiloxane (PDMS)-based microfluidic devices with complex 3D architecture and connectivity for large-scale microfluidic integration. Accurate alignment of structure features on different PDMS layers before their permanent bonding is critical in determining the yield and quality of assembled multilayer microfluidic devices. Herein, we report a custom-built desktop aligner capable of both local and global alignments of PDMS layers covering a broad size range. Two digital microscopes were incorporated into the aligner design to allow accurate global alignment of PDMS structures up to 4 in. in diameter. Both local and global alignment accuracies of the desktop aligner were determined to be about 20 μm cm(-1). To demonstrate its utility for fabrication of integrated multilayer PDMS microfluidic devices, we applied the desktop aligner to achieve accurate alignment of different functional PDMS layers in multilayer microfluidics including an organs-on-chips device as well as a microfluidic device integrated with vertical passages connecting channels located in different PDMS layers. Owing to its convenient operation, high accuracy, low cost, light weight, and portability, the desktop aligner is useful for microfluidic researchers to achieve rapid and accurate alignment for generating multilayer PDMS microfluidic devices.

A multi-layered polydimethylsiloxane structure for application in low-excitation, broadband and low frequency energy harvesting

Vibrational kinetic energy is a promising energy source that can be harvested due to its abundance in daily life, especially from human motion. This low frequency vibration poses a challenge in achieving a small device that is practical and wearable. Further, the effective energy harvesting of a linear structure is very limited to a narrow range of frequencies around the resonance. These two limitations call for the development of wide bandwidth energy harvesters that can work at a wider low frequency range. Using low Young's modulus material is a common technique to achieve a low resonant frequency energy harvester. Nonlinear bistability is a potential solution for bandwidth broadening. In this paper, a broadband low frequency vibrational energy harvester using multi-layered soft polydimethylsiloxane (PDMS) will be presented. First, a multi-layered PDMS structure was created by sandwiching a thicker PDMS with two thinner pre-stressed PDMS films. After releasing the prestresses, the multi-layered PDMS structure can settle into two cylindrical configurations. An analytical model that can predict the shapes of this multi-layered structure has been developed using classical lamination theory along with Rayleigh–Ritz approximation technique. Through this model, PDMS shapes can be easily predicted by changing various parameters such as the ratio of side length to thickness, prestrain levels, and Young's modulus. A multi-layered PDMS structure has been further proposed to be used as a bistable energy harvester. The soft PDMS allows working frequencies of lower than 15Hz. The dynamic response of this harvester under small input excitation shows a softening spring system, before the strong nonlinear ‘snap through’ effect occurs. This softening spring system is able to broaden the bandwidth of the energy harvesting device.

Enzyme-functionalized electrochemical immunosensor based on electrochemically reduced graphene oxide and polyvinyl alcohol-polydimethylsiloxane for the detection of Salmonella pullorum &amp; Salmonella gallinarum

A novel and ultrasensitive electrochemical enzyme immunosensor based on electrochemically reduced graphene oxide (ERGO) and a polyvinyl alcohol (PVA)-multilayer polydimethylsiloxane (PDMS) film modified screen-printed carbon electrode (SPCE) for the rapid detection of Salmonella pullorum (S. pullorum) & Salmonella gallinarum (S. gallinarum) was proposed in this study. The electrochemical characteristics of the stepwise modified electrodes and the determinations of S. pullorum & S. gallinarum were investigated by cyclic voltammetry (CV). PVA-PDMS was characterized by Fourier transform infrared spectroscopy (FTIR). The conductivity of the electrode was promoted by electrochemically reduced graphene oxide, and the sensitivity of the immunosensor was enhanced and strengthened. The binding capacity and biocompatibility of the ERGO modified electrode was elevated considerably by the PVA-PDMS film. Under optimized working conditions, the sensor showed a good performance with a linear response range from 101 CFU mL−1 to 109 CFU mL−1, and the detection limit was 1.61 × 101 CFU mL−1 (S/N = 3). The proposed enzyme immunosensor had high sensitivity, good specificity, acceptable accuracy and reproducibility, and low detection limit characteristics and could be a promising analytical tool in the detection of S. pullorum & S. gallinarum in practical samples.

Multiplexed microfluidic enzyme assays for simultaneous detection of lipolysis products from adipocytes.

Microfluidics has enabled new cell biology experiments. Incorporating chemical monitoring of cellular secretion into chips offers the potential to increase information content and utility of such systems. In this work, an integrated, multilayer polydimethylsiloxane microfluidic chip was developed to simultaneously measure fatty acids and glycerol secreted from cultured adipocytes on chip in near real time. Approximately 48,000 adipocytes were loaded into a cell chamber in a reversibly sealed chip. Cells were perfused at 0.75 μL/min. Cell perfusate was split and directed to separate, continuously operating fluorescent enzyme assay channel networks. The fluorescent assay products were detected simultaneously near the outlet of the chip. The fatty acid and glycerol assays had linear dynamic ranges of 150 and 110 μM and limit of detection (LOD) of 6 and 5 μM, respectively. Surface modifications including pretreatment with sodium dodecyl sulfate were utilized to prevent adsorption of fatty acids to the chip surface. Using the chip, basal fatty acid and glycerol concentrations ranged from 0.18 to 0.7 nmol × 10(6) cell(-1) min(-1) and from 0.23 to 0.85 nmol × 10(6) cell(-1) min(-1), respectively. Using valves built into the chip, the perfusion solution was switched to add 20 μM isoproterenol, a β-adrenergic agonist, which stimulates the release of glycerol and fatty acids in adipocytes. This manipulation resulted in a rapid and stable 1.5- to 6.0-fold increase of non-esterified fatty acid (NEFA) and glycerol. The ratio of NEFA:glycerol released increased with adipocyte age. These experiments illustrate the potential for performing multiple real-time assays on cells in culture using microfluidic devices.

Publisher's Note: “High yield fabrication of multilayer polydimethylsiloxane devices with freestanding micropillar arrays” [Biomicrofluidics 7, 056503 (2013)

[This corrects the article on p. 056503 in vol. 7.].

A microscale anisotropic biaxial cell stretching device for applications in mechanobiology

A multi-layered polydimethylsiloxane microfluidic device with an integrated suspended membrane has been fabricated that allows dynamic and multi-axial mechanical deformation and simultaneous live-cell microscopy imaging. The transparent membrane’s strain field can be controlled independently along two orthogonal directions. Human foreskin fibroblasts were immobilized on the membrane’s surface and stretched along two orthogonal directions sequentially while performing live-cell imaging. Cyclic deformation of the cells induced a reversible reorientation perpendicular to the direction of the applied strain. Cells remained viable in the microdevice for several days. As opposed to existing microfluidic or macroscale stretching devices, this device can impose changing, anisotropic and time-varying strain fields in order to more closely mimic the complexities of strains occurring in vivo.Electronic supplementary materialThe online version of this article (doi:10.1007/s10529-013-1381-5) contains supplementary material, which is available to authorized users.

High yield fabrication of multilayer polydimethylsiloxane devices with freestanding micropillar arrays

A versatile method to fabricate a multilayer polydimethylsiloxane (PDMS) device with micropillar arrays within the inner layer is reported. The method includes an inexpensive but repeatable approach for PDMS lamination at high compressive force to achieve high yield of pillar molding and transfer to a temporary carrier. The process also enables micropillar-containing thin films to be used as the inner layer of PDMS devices integrated with polymer membranes. A microfluidic cell culture device was demonstrated which included multiple vertically stacked flow channels and a pillar array serving as a cage for a collagen hydrogel. The functionality of the multilayer device was demonstrated by culturing collagen-embedded fibroblasts under interstitial flow through the three-dimensional scaffold. The fabrication methods described in this paper can find applications in a variety of devices, particularly for organ-on-chip applications.

Optical-Based Artificial Palpation Sensors for Lesion Characterization

Palpation techniques are widely used in medical procedures to detect the presence of lumps or tumors in the soft breast tissues. Since these procedures are very subjective and depend on the skills of the physician, it is imperative to perform detailed a scientific study in order to develop more efficient medical sensors to measure and generate palpation parameters. In this research, we propose an optical-based, artificial palpation sensor for lesion characterization. This has been developed using a multilayer polydimethylsiloxane optical waveguide. Light was generated at the critical angle to reflect totally within the flexible and transparent waveguide. When a waveguide was compressed by an external force, its contact area would deform and cause the light to scatter. The scattered light was captured by a high-resolution camera and saved as an image format. To test the performance of the proposed system, we used a realistic tissue phantom with embedded hard inclusions. The experimental results show that the proposed sensor can detect inclusions and provide the relative value of size, depth, and Young's modulus of an inclusion.

Microfluidic platforms for RNA interference screening of virus–host interactions

RNA interference (RNAi) is a powerful tool for functional genomics with the capacity to comprehensively analyze host-pathogen interactions. High-throughput RNAi screening is used to systematically perturb cellular pathways and discover therapeutic targets, but the method can be tedious and requires extensive capital equipment and expensive reagents. To aid in the development of an inexpensive miniaturized RNAi screening platform, we have developed a two part microfluidic system for patterning and screening gene targets on-chip to examine cellular pathways involved in virus entry and infection. First, a multilayer polydimethylsiloxane (PDMS)-based spotting device was used to array siRNA molecules into 96 microwells targeting markers of endocytosis, along with siRNA controls. By using a PDMS-based spotting device, we remove the need for a microarray printer necessary to perform previously described small scale (e.g. cellular microarrays) and microchip-based RNAi screening, while still minimizing reagent usage tenfold compared to conventional screening. Second, the siRNA spotted array was transferred to a reversibly sealed PDMS-based screening platform containing microchannels designed to enable efficient cell loading and transfection of mammalian cells while preventing cross-contamination between experimental conditions. Validation of the screening platform was examined using Vesicular stomatitis virus and emerging pathogen Rift Valley fever virus, which demonstrated virus entry pathways of clathrin-mediated endocytosis and caveolae-mediated endocytosis, respectively. The techniques here are adaptable to other well-characterized infection pathways with a potential for large scale screening in high containment biosafety laboratories.