Polydimethylsiloxane Substrate Research Articles

Matrix stiffening promotes chondrocyte senescence and the osteoarthritis development through downregulating HDAC3

Extracellular matrix (ECM) stiffening is a typical characteristic of cartilage aging, which is a quintessential feature of knee osteoarthritis (KOA). However, little is known about how ECM stiffening affects chondrocytes and other molecules downstream. This study mimicked the physiological and pathological stiffness of human cartilage using polydimethylsiloxane (PDMS) substrates. It demonstrated that epigenetic Parkin regulation by histone deacetylase 3 (HDAC3) represents a new mechanosensitive mechanism by which the stiffness matrix affected chondrocyte physiology. We found that ECM stiffening accelerated cultured chondrocyte senescence in vitro, while the stiffness ECM downregulated HDAC3, prompting Parkin acetylation to activate excessive mitophagy and accelerating chondrocyte senescence and osteoarthritis (OA) in mice. Contrarily, intra-articular injection with an HDAC3-expressing adeno-associated virus restored the young phenotype of the aged chondrocytes stimulated by ECM stiffening and alleviated OA in mice. The findings indicated that changes in the mechanical ECM properties initiated pathogenic mechanotransduction signals, promoted the Parkin acetylation and hyperactivated mitophagy, and damaged chondrocyte health. These results may provide new insights into chondrocyte regulation by the mechanical properties of ECM, suggesting that the modification of the physical ECM properties may be a potential OA treatment strategy.

Flexible Strain Sensors Based on an Interlayer Synergistic Effect of Nanomaterials for Continuous and Noninvasive Blood Pressure Monitoring.

The continuous, noninvasive monitoring of human blood pressure (BP) through the accurate detection of pulse waves has extremely stringent requirements on the sensitivity and stability of flexible strain sensors. In this study, a new ultrasensitive flexible strain sensor based on the interlayer synergistic effect was fabricated through drop-casting and drying silver nanowires and graphene films on polydimethylsiloxane substrates and was further successfully applied for continuous monitoring of BP. This strain sensor exhibited ultrahigh sensitivity with a maximum gauge factor of 34357.2 (∼700% sensitivity enhancement over other major sensors), satisfactory response time (∼85 ms), wide strange range (12%), and excellent stability. An interlayer fracture mechanism was proposed to elucidate the working principle of the strain sensor. The real-time BP values can be obtained by analyzing the relationship between the BP and the pulse transit time. To verify our strain sensor for real-time BP monitoring, our strain sensor was compared with a conventional electrocardiogram-photoplethysmograph method and a commercial cuff-based device and showed similar measurement results to BP values from both methods, with only minor differences of 0.693, 0.073, and 0.566 mmHg in the systolic BP, diastolic BP, and mean arterial pressure, respectively. Furthermore, the reliability of the strain sensors was validated by testing 20 human subjects for more than 50 min. This ultrasensitive strain sensor provides a new pathway for continuous and noninvasive BP monitoring.

Optimization of polydimethylsiloxane (PDMS) surface chemical modification and formulation for improved T cell activation and expansion

Adoptive T cell therapy has undergone remarkable advancements in recent decades; nevertheless, the rapid and effective ex vivo expansion of tumor-reactive T cells remains a formidable challenge, limiting their clinical application. Artificial antigen-presenting substrates represent a promising avenue for enhancing the efficiency of adoptive immunotherapy and fostering T cell expansion. These substrates offer significant potential by providing flexibility and modularity in the design of tailored stimulatory environments. Polydimethylsiloxane (PDMS) silicone elastomer stands as a widely utilized biomaterial for exploring the varying sensitivity of T cell activation to substrate properties. This paper explores the optimization of PDMS surface modification and formulation to create customized stimulatory surfaces with the goal of enhancing T cell expansion. By employing soft PDMS elastomer functionalized through silanization and activating agent, coupled with site-directed protein immobilization techniques, a novel T cell stimulatory platform is introduced, facilitating T cell activation and proliferation. Notably, our findings underscore that softer modified elastomers (Young’ modulus E~300 kPa) exhibit superior efficacy in stimulating and activating mouse CD4+ T cells compared to their stiffer counterparts (E~3MPa). Furthermore, softened modified PDMS substrates demonstrate enhanced capabilities in T cell expansion and Th1 differentiation, offering promising insights for the advancement of T cell-based immunotherapy.

Femtosecond Laser Fabrication of High-Linearity Liquid Metal-Based Flexible Strain Sensor.

Liquid metal (LM) is widely used in flexible electronic devices due to its excellent metallic conductivity and ductility. However, the fabrication of LM flexible strain sensors with high sensitivity and linearity is still a huge challenge, since the resistance of LM does not change much with strain. Here, a highly sensitive and linear fully flexible strain sensor with a resistive sensing function is proposed. The sensor comprises an Fe-doped liquid metal (Fe-LM) electrode for enhanced performance. The design and manufacturing of flexible strain sensors are based on the technology of controlling surface wettability by femtosecond laser micro/nano-processing. A supermetalphobic microstructure is constructed on a polydimethylsiloxane (PDMS) substrate to achieve the selection adhesion of Fe-LM on the PDMS substrate. The Fe-LM-based flexible strain sensor has high sensitivity and linearity, a gauge factor (GF) up to 1.18 in the strain range of 0-100%, excellent linearity with an R2 of 0.9978, a fast response time of 358 ms, and an excellent durability of more than 2400 load cycles. Additionally, the successful monitoring of human body signals demonstrates the potential of our developed flexible strain sensor in wearable monitoring applications.

Extrusion Printing of Surface-Functionalized Metal-Organic Framework Inks for a High-Performance Wearable Volatile Organic Compound Sensor.

Wearable sensors hold immense potential for real-time andnon-destructive sensing ofvolatile organic compounds (VOCs), requiring both efficient sensing performance and robust mechanical properties. However, conventional colorimetric sensor arrays, acting as artificial olfactory systems for highly selective VOC profiling, often fail to meet these requirements simultaneously. Here, a high-performance wearable sensor array for VOC visual detection is proposed by extrusion printing of hybrid inks containing surface-functionalized sensing materials. Surface-modified hydrophobic polydimethylsiloxane (PDMS) improves the humidity resistance and VOC sensitivity of PDMS-coated dye/metal-organic frameworks (MOFs) composites. It also enhances their dispersion within liquid PDMS matrix, thereby promoting the hybrid liquid as high-quality extrusion-printing inks. The inks enable direct and precise printing on diverse substrates, forming a uniform and high particle-loading (70 wt%) film. The printed film on a flexible PDMS substrate demonstrates satisfactory flexibility and stretchability while retaining excellent sensing performance from dye/MOFs@PDMS particles. Further, the printed sensor array exhibits enhanced sensitivity to sub-ppm VOClevels, remarkable resistance to high relative humidity (RH) of 90%, and the differentiation ability for eight distinct VOCs. Finally, the wearable sensor proves practical by in situ monitoring of wheat scab-related VOC biomarkers. This study presents a versatile strategy for designing effective wearable gas sensors with widespread applications.

The large-range strength-switchable circular dichroism in a mechanically reconfigurable chiral metasurface

The strength-switchable circular dichroism (CD) is crucial in the fields of biological detection, analytical chemistry, etc. In this paper, we achieved large-range strength-switchable CD by mechanically stretching polydimethylsiloxane (PDMS) substrate. With normal incidence, the traditional C4 rotation symmetric 卍-shaped chiral array could exhibit obvious optical activity but near-zero CD. However, we found that the giant CD could be gained by breaking the period symmetry in x- and y-directions in the 卍-shaped array. By mechanically stretching PDMS substrate in x-direction, the magnitude of CD is dynamically switched from 0.99 to 0 at 1314.5 nm. Essentially, the giant CD originates from the circular polarization selective excitations of magnetic dipole and electric quadrupole resonances, which is demonstrated by quantitative multipole decomposition and electric and magnetic field analysis. The giant and large-range strength-switchable CD has great potentials in the next generation optical devices.

Inkjet printing of triethylene glycol monomethyl ether (TEGMME)-based ink droplet on oxygen plasma treated PDMS substrate for flexible circuit

Circuits fabricated by inkjet printing on polydimethylsiloxane (PDMS) substrate is a promising direction of flexible electronics. Oxygen plasma treatment is a commonly used method to modify PDMS from hydrophobic to hydrophilic, which is prerequisite before inkjet printing. In this study, inkjet printing of triethylene glycol monomethyl ether (TEGMME)-based silver dispersion nanoparticle droplets on oxygen plasma treated PDMS was investigated by molecular dynamics simulations and experiments. It is revealed that the improved hydrophilicity of PDMS surface is contributed to the replacement of hydrophilic groups (-OH and -C=O) from hydrophobic groups (-CH3) on the PDMS molecular chains. Considering the existence of hydroxyl groups in TEGMME molecules, more hydrogen bonds are formed at the interface between the treated PDMS and TEGMME-based droplets during printing process. These significantly optimize the merging of droplets and the distribution of silver nanoparticles. Moreover, too short plasma treatment will lead to poor circuit morphology caused by weak hydrophilicity, while too long treatment will lead to defects caused by coffee ring effect. The suggested process parameter is treating PDMS for 30 s at a radio-frequency power of 45 W. The morphology of printed circuit is greatly improved and the resistivity decreased to 2.5 Ω/mm. A PDMS-based pressure sensor is designed and fabricated by the proposed inkjet printing process, which shows a sensitivity of 1.8 Ω/kPa and R2 of 0.98.

High-performance, large-area flexible SERS substrates prepared by reactive ion etching for molecular detection

In the realm of molecular detection, the surface-enhanced Raman scattering (SERS) technique has garnered increasing attention due to its rapid detection, high sensitivity, and non-destructive characteristics. However, conventional rigid SERS substrates are either costly to fabricate and challenging to prepare over a large area, or they exhibit poor uniformity and repeatability, making them unsuitable for inspecting curved object surfaces. In this work, we present a flexible SERS substrate with high sensitivity as well as good uniformity and repeatability. First, the flexible polydimethylsiloxane (PDMS) substrate is manually formulated and cured. SiO2/Ag layer on the substrate can be obtained in a single process by using ion beam sputtering. Then, reactive ion etching is used to etch the upper SiO2 layer of the film, which directly leads to the desired densely packed nanostructure. Finally, a layer of precious metal is deposited on the densely packed nanostructure by thermal evaporation. In our proposed system, the densely packed nanostructure obtained by etching the SiO2 layer directly determines the SERS ability of the substrate. The bottom layer of silver mirror can reflect the penetrative incident light, the spacer layer of SiO2 and the top layer of silver thin film can further localize the light in the system, which can realize the excellent absorption of Raman laser light, thus enhancing SERS ability. In the tests, the prepared substrates show excellent SERS performance in detecting crystalline violet with a detection limit of 10−11 M. The development of this SERS substrate is anticipated to offer a highly effective and convenient method for molecular substance detection.

Broadband and strong visible-light driven photocatalytic enhancement utilizing two-dimensional plasmonics of Au/Cu-modified SrTiO3 perovskite nanostructures

Addressing limited access to clean drinking water demands innovative solutions to energy and environmental crises. Photocatalysis offers promise without eliciting secondary pollution, yet traditional metal oxide semiconductor photocatalysts encounter impediments in solar energy utilization and charge carrier recombination rates. To overcome these limitations, we present for the first time, a novel design, fabrication, and characterization of two-dimensional plasmonic noble metal/perovskite nanostructure hybrids for photocatalysis, combining Au as the plasmonic material with Cu-modified SrTiO3 as the semiconductor, fabricated on elastomeric polydimethylsiloxane substrates. Integrating localized surface plasmon resonance and Schottky junction-related band-bending significantly extends optical absorption into the ultraviolet-visible-infrared bands and enhances the effective carrier lifetimes, ensuring state-of-the-art photocatalytic efficiency. Exceptional photocatalytic performance in a 5-ppm aqueous methylene blue solution can be attained with 72.69-wt% Cu incorporation in the perovskite oxide, reaching a visible light-mediated photodegradation efficiency of 26% - an astounding 62.5-% efficiency increase compared to previous experiments without Cu modification. This advancement underscores the synergistic potential of noble metals and photocatalytic semiconductors in managing water purification challenges.

Carp-inspired self-regulating marine antifouling coating: Featuring robust controlled release of eugenol and high-efficiency self-healing performance

The practical application of low surface energy polydimethylsiloxane (PDMS) in marine antifouling is significantly limited due to its inadequate static antifouling capability. Herein, integrating a strategy inspired by carps to release antifouling agents with the fouling release properties of low surface energy materials, an innovative self-regulating marine antifouling coating (named PDMS-Pun-x) was developed, which demonstrates remarkable robust ability of controlled release of eugenol and efficient self-healing performance. Under seawater, the coating regulates its inherent hydrophilicity and the content of the surface anti-fouling agent to obtain the ability of controlled releasing eugenol. Compared with other self-renewal coatings, there proves non-heavy metal leaching and no internal self-hydrolysis existing. Moreover, based on the synergistic action of disulfide bonds and hydrogen bonds, the coating demonstrated a notable self-healing performance, with a self-healing rate of 94.06%. Additionally, the substrate of PDMS modified with polyurea provides the coating with excellent resistance against corrosion. This study introduces a highly promising approach towards the advancement of environmentally-friendly and durable marine antifouling coatings.

Additive Blending Effects on PEDOT:PSS Composite Films for Wearable Organic Electrochemical Transistors.

Organic electrochemical transistors (OECTs) employing conductive polymers (CPs) have gained remarkable prominence and have undergone extensive advancements in wearable and implantable bioelectronic applications in recent years. Among the diverse arrays of CPs, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a common choice for the active-layer channel in p-type OECTs, showing a remarkably high transconductance for the high amplification of signals in biosensing applications. This investigation focuses on the novel engineering of PEDOT:PSS composite materials by seamlessly integrating several additives, namely, dimethyl sulfoxide (DMSO), (3-glycidyloxypropyl)trimethoxysilane (GOPS), and a nonionic fluorosurfactant (NIFS), to fine-tune their electrical conductivity, self-healing capability, and stretchability. To elucidate the intricate influences of the DMSO, GOPS, and NIFS additives on the formation of PEDOT:PSS composite films, theoretical calculations were performed, encompassing the solubility parameters and surface energies of the constituent components of the NIFS, PEDOT, PSS, and PSS-GOPS polymers. Furthermore, we conducted a comprehensive array of material analyses, which reveal the intricacies of the phase separation phenomenon and its interaction with the materials' characteristics. Our research identified the optimal composition for the PEDOT:PSS composite films, characterized by outstanding self-healing and stretchable capabilities. This composition has proven to be highly effective for constructing an active-layer channel in the form of OECT-based biosensors fabricated onto polydimethylsiloxane substrates for detecting dopamine. Overall, these findings represent significant progress in the application of PEDOT:PSS composite films in wearable bioelectronics and pave the way for the development of state-of-the-art biosensing technologies.

Hollow-microsphere-integrated optofluidic immunochip for myocardial infarction biomarker microanalysis

This work developed an optofluidic immunochip that uses whispering gallery mode with fiber laser enhancement, for the rapid detection of a key biomarker cardiac troponin I for acute myocardial infarction (AMI). The immunochip adopted an innovative design, using perforated hollow glass microspheres (HGMS) as carriers, with antibodies immobilized on the inner surface of the HGMS, thereby achieving ultra-low sample consumption. The performance of the immunochip was improved by fiber laser, including spectral width compression to 0.019 nm, optical signal-to-noise ratio amplification to 63.17 dB, and an enhancement in the limit of detection to 5 pg/mL. Moreover, this immunochip can provide results within 15 minutes, making it highly suitable for early AMI risk management. Compared to the standard electrochemiluminescence detection method, although some differences exist in the results of the immunochip due to the principle of detection and differences in antibody affinity, its positive reference value can be calculated as 0.0754 ng/mL, with a successful recognition rate of 88% for positive patients. The immunosensor is integrated on a polydimethylsiloxane substrate, with a compact size suitable for use in point-of-care devices and AMI self-screening, as well as rapid disease screening and microanalysis of various biomarkers, offering new possibilities for applications in these fields.

Ultrasensitive and ultrastretchable metal crack strain sensor based on helical polydimethylsiloxane.

The majority of crack sensors do not offer simultaneously both a significant stretchability and an ultrahigh sensitivity. In this study, we present a straightforward and cost-effective approach to fabricate metal crack sensors that exhibit exceptional performance in terms of ultrahigh sensitivity and ultrahigh stretchability. This is achieved by incorporating a helical structure into the substrate through a modeling process and, subsequently, depositing a thin film of gold onto the polydimethylsiloxane substrate via sputter deposition. The metal thin film is then pre-stretched to generate microcracks. The sensor demonstrates a remarkable stretchability of 300%, an exceptional sensitivity with a maximum gauge factor reaching 107, a rapid response time of 158 ms, minimal hysteresis, and outstanding durability. These impressive attributes are attributed to the deliberate design of geometric structures and careful selection of connection types for the sensing materials, thereby presenting a novel approach to fabricating stretchable and highly sensitive crack-strain sensors. This work offers a universal platform for constructing strain sensors with both high sensitivity and stretchability, showing a far-reaching significance and influence for developing next-generation practically applicable soft electronics.

Substrate elasticity does not impact DNA methylation changes during differentiation of pluripotent stem cells

Background aimsSubstrate elasticity may direct cell-fate decisions of stem cells. However, it is largely unclear how matrix stiffness affects the differentiation of induced pluripotent stem cells (iPSCs) and whether this is also reflected by epigenetic modifications. MethodsWe cultured iPSCs on tissue culture plastic (TCP) and polydimethylsiloxane (PDMS) with different Young's modulus (0.2 kPa, 16 kPa or 64 kPa) to investigate the sequel on growth and differentiation toward endoderm, mesoderm and ectoderm. ResultsImmunofluorescence and gene expression of canonical differentiation markers were hardly affected by the substrates. Notably, when we analyzed DNA methylation profiles of undifferentiated iPSCs or after three-lineage differentiation, we did not see any significant differences on the three different PDMS elasticities. Only when we compared DNA methylation profiles on PDMS-substrates versus TCP we did observe epigenetic differences, particularly on mesodermal differentiation. ConclusionsStiffness of PDMS substrates did not affect directed differentiation of iPSCs, whereas the moderate epigenetic differences on TCP might also be attributed to other chemical parameters.

Water droplet impact dynamics comparison on solid and hollow square micropillared substrates

Water droplet impact dynamics comparison on solid and hollow square micropillared substrates

Quantitative investigation on the Young's modulus of ultrathin amorphous PS films attached to different substrates

AbstractIn this work, a method combining nanomechanical characterization and finite element analysis (FEA) was applied to reveal the influence mechanism and quantify the effects of the substrate on the mechanical properties of the ultrathin polystyrene (PS) film. SiOx, polylactic acid (PLA), and polydimethylsiloxane (PDMS), respectively, were chosen as the substrate. Results show that PS film exhibits a Young's modulus that is completely different from that of the bulk when the thickness is lower than the end‐to‐end distance of PS, and the value is directly related to the substrate to which the film is attached. The equivalent Young's moduli of the 20 nm PS films attached to SiOx, PLA, and PDMS substrates are 4.9, 3.4, and 1.0 GPa, respectively, which is positively correlated with the Young's modulus of the substrates. It suggests that the substrate has non‐negligible and important influences on the mechanical properties of supported polymer ultrathin films. The results provide new insight into the unique physical properties of polymer ultrathin films and favor the design of polymer‐based nanodevices.

Single-step fabrication of liquid gallium nanoparticles via capillary interaction for dynamic structural colours.

Incorporating structural coloured materials in flexible and stretchable elastomeric substrates requires numerous steps that compromise their scalability and economic viability for prospective applications in visual sensors and displays. Here we describe a one-step approach for fabricating plasmonic Ga nanostructures embedded in a polydimethylsiloxane substrate exhibiting tunable chromaticity, in response to mechanical stimuli. The process exploits the capillary interactions between uncrosslinked oligomeric chains of the substrate and Ga metal deposited by thermal evaporation, as elucidated by a theoretical model that we developed. By tuning the oligomer content in polydimethylsiloxane, we attain a range of colours covering a substantial gamut in CIE (Commission Internationale de l'Éclairage) coordinates. This mechanochromic flexible substrate shows reversible response to external mechanical stimuli for ~80,000 cycles. We showcase the capabilities of our processing technique by presenting prototypes of reflective displays and sensors for monitoring body parts, smart bandages and the capacity of the nanostructured film to map force in real time.

All-organic transparent plant e-skin for noninvasive phenotyping.

Real-time in situ monitoring of plant physiology is essential for establishing a phenotyping platform for precision agriculture. A key enabler for this monitoring is a device that can be noninvasively attached to plants and transduce their physiological status into digital data. Here, we report an all-organic transparent plant e-skin by micropatterning poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) on polydimethylsiloxane (PDMS) substrate. This plant e-skin is optically and mechanically invisible to plants with no observable adverse effects to plant health. We demonstrate the capabilities of our plant e-skins as strain and temperature sensors, with the application to Brassica rapa leaves for collecting corresponding parameters under normal and abiotic stress conditions. Strains imposed on the leaf surface during growth as well as diurnal fluctuation of surface temperature were captured. We further present a digital-twin interface to visualize real-time plant surface environment, providing an intuitive and vivid platform for plant phenotyping.

Fabrication of a Low Cost Superhydrophobic Substrate for Surface Enhanced Laser-Induced Breakdown Spectroscopy and Its Utility through Identification of Electrolyte Variation for Oral Cancer Detection.

Ultratrace elemental detections from a limited volume of samples can offer significant benefits in biomedical fields. However, it can be challenging to concentrate the particles being analyzed in a small area to improve the accuracy of detection. Ring-like deposits on the edges of colloidal droplets are a vexing problem in many applications. Herein, we report ultratrace elemental detection using a superhydrophobic surface-enhanced laser-induced breakdown spectroscopy (SELIBS) substrate fabricated by laser ablation followed by a soft lithography technique. In this work, the SELIBS spectra on a superhydrophobic polydimethylsiloxane (PDMS) substrate replicated from a laser-patterned master Teflon substrate are investigated. This work highlights the application of this newly created superhydrophobic substrate for detecting trace elements in body fluids using SELIBS. The developed PDMS substrate was successfully adopted to investigate the electrolyte variation in serum samples of oral cancer patients and normal volunteers. Principal component analysis (PCA) and match-no-match analysis were used to distinguish the elemental variation in cancer and control groups.

Eliminating surface cracks in metal film-polymer substrate for reliable flexible piezoelectric devices

In a flexible piezoelectric-metal-polymer device, the occurrence of surface cracks in metal-polymer interface may cause unstable metal connections, unreliable piezoelectric yield, poor passivation behaviour and metal electrode delamination. In this study, the properties of polydimethylsiloxane (PDMS) polymer substrate are optimised, and the sputter-deposition of aluminium (Al) and molybdenum (Mo) metal film layer is controlled to eradicate cracks and promote only surface wrinkles on large area metal-polymer interface. The PDMS substrate thickness of ∼123.8 µm, 20:1 prepolymer base to curing agent weight ratio, 50 °C PDMS curing temperature and 30 min of Al sputtering time have been discovered to produce crack-free wrinkle-only Al thin film layer on PDMS substrate. The Al thin film is 100 % conductive over large area and adhere well on PDMS with 0 % of Al removal. The grown zinc oxide (ZnO) and aluminium nitride (AlN) piezoelectric layer on the improved Al-PDMS are of good crystal quality, generating low leakage current and decent piezoelectric voltage. The attained crack-free wrinkled-only metal film-polymer substrate interface is vital for flexible piezoelectric-metal-polymer device to perform well as an acoustic sensor, energy harvester, or even as an insulation/buffer layer in stretchable electronics.