Search Results (27)

Microcontact stamping is a promising microfabrication technique for producing functional patterned thin films on flexible substrates; however, systematic optimization of its process parameters for thermochromic applications remains limited. In this study, we present a comprehensive parametric optimization of the microcontact stamping process to fabricate thermochromic pigment-coated thin films with rapid and reversible color responses. The effects of liquid resin type, SU-8 mold thickness, polydimethylsiloxane (PDMS) mixing ratio, and pattern size on pattern fidelity and thermochromic performance were systematically investigated. The optimal conditions were identified as a UV-curable resin, a 600 µm-thick SU-8 mold, a PDMS base-to-curing-agent ratio of 5:1, and a pattern size of 125 × 125 µm². Under these conditions, the stamped thermochromic films exhibited uniform micro-patterns, rapid response and recovery behavior, and stable reversible color changes over 20 consecutive thermal cycles. This work provides practical guidelines for parameter-controlled microcontact stamping of functional thin films and demonstrates its potential for scalable fabrication of thermochromic micro-patterns. The proposed approach is expected to contribute to the development of flexible and wearable electronic devices, smart displays, and thermally responsive sensing platforms. Full article

The increasing complexity of modern electrical substations—driven by renewable integration, advanced automation, and asset aging—necessitates a transition from reactive maintenance toward intelligent, data-driven strategies. Predictive maintenance (PdM), supported by artificial intelligence, enables early fault detection and remaining useful life (RUL) estimation, while Digital Twin (DT) technology provides synchronized cyber–physical representations for situational awareness and risk-free validation of maintenance decisions. This study proposes a five-layer DT-enabled PdM architecture integrating standards-based data acquisition, semantic interoperability (IEC 61850, CIM, and OPC UA Part 17), hybrid AI analytics, and cyber-secure decision support aligned with IEC 62443. The framework is validated using utility-grade operational data from the SS1 substation of the Badra Oil Field, comprising approximately one million multivariate time-stamped measurements and 139 confirmed fault events across transformer, feeder, and environmental monitoring systems. Fault detection is formulated as a binary classification task using event-window alignment to the 1 min SCADA timeline, preserving realistic operational class imbalance. Five supervised learning models—a Random Forest, Gradient Boosting, a Support Vector Machine, a Deep Neural Network, and a stacked ensemble—were benchmarked, with the ensemble embedded within the DT core representing the operational predictive model. Experimental results demonstrate strong performance, achieving an F1-score of 0.98 and an AUC of 0.995. The results confirm that the proposed DT–AI framework provides a scalable, interoperable, and cyber-resilient foundation for deployment-ready predictive maintenance in modern substation automation systems. Full article

Background/Objectives: Three-dimensional (3D) cell cultures are increasingly used because 3D cell aggregates better mimic tissue-level biological mechanisms and support studies of tissue physiology and drug screening. However, existing laboratory methods and commercial microwell platforms often yield inconsistent results and can be error-prone, time-consuming, or costly. The objective of this work was to develop a reproducible, high-yield, and cost-effective approach for generating homogeneous cell aggregates using custom 3D-printed microwell stamps. Methods: Custom conical and semi-spherical microwell stamps were fabricated using 3D printing. Stamp resolution was characterized by scanning electron microscopy (SEM). Negative imprints were cast in polydimethylsiloxane (PDMS), a biocompatible and hydrophobic polymer conducive to cell aggregation. These PDMS microwells were then used to generate pluripotent stem cell aggregates (embryoid bodies, EBs) and tumor spheroids from adherent cancer cell lines. Results: The 3D-printed stamps produced high-resolution conical and semi-spherical microwells in PDMS. Semi-spherical microwells enabled rapid, simple, and cost-effective formation of pluripotent stem cell aggregates that were homogeneous in size and shape. These aggregates outperformed those produced using commercial microwell plates and ultra-low attachment plates. The fabricated microwells also generated uniform tumor spheroids from adherent cancer cells, demonstrating their versatility. Conclusions: The in-house 3D-printed microwell stamps offer a reproducible, efficient, and economical platform for producing homogeneous cell aggregates. This system improves upon commercial alternatives and supports a broad range of applications, including pluripotent stem cell embryoid body formation and tumor spheroid generation. Full article

Bioengineered dermal–epidermal composites (DECs) have demonstrated promise initiating skin regeneration and hair follicle neogenesis after injury. DECs in our work comprise a collagen matrix embedded with human dermal papilla cells (HDPCs) overlaid with human keratinocytes. HDPCs, as three-dimensional spheroids, enhance hair follicle formation, working in tandem with keratinocytes. Herein, 3D printed stamped PDMS microwell arrays were used as a strategy for spatially patterning dermal papilla spheroids in the dermal components of the DEC. DECs were transferred to cell culture media for 5 days followed by air–liquid interface culture for 2 days. Spheroid diameter, cell viability, and qPCR gene expression analyses were conducted. DECs were surgically grafted on immunocompromised mice, and healing was followed for 10 weeks. HDPCs cultured in the microwell arrays formed patterned viable spheroids and successfully transferred to the collagen dermal matrix. RNA analysis using qPCR showed upregulation of key HDPC markers (VCAN and BMP6) in DC microwell patterned HDPC spheroids compared to monolayers. This work represents a novel 3D printing strategy optimizing designing patterned HDPC spheroids in the extracellular matrix to regenerate functional human skin instead of scar tissue after injury. Full article

This study addresses the persistence of avoidable failures and efficiency losses in HVAC plants by introducing a field-validated predictive maintenance (PdM) framework that estimates component-level RUL from multiyear BMS telemetry and translates forecasts into schedule-aware maintenance actions. The objective was to determine whether an LSTM ensemble with mode-aware segmentation and isotonic calibration could yield decision-quality RUL forecasts that reduce unplanned outages, downtime, and electricity use in a large Riyadh office building. Two years of 1 min BMS data from chillers, primary pumps, and AHU fans were cleaned, standardized, and segmented by operating mode; RUL labels were derived from time-stamped work orders and failure confirmations; the LSTM produced per-minute RUL estimates trained with a Huber loss, calibrated to lower quantiles, and converted to sustained triggers compared against a fixed-interval program. On the held-out test set, the model achieved a weighted MAE of 19.8 ± 2.1 h and RMSE of 29.1 ± 3.3 h, with quantile calibration error (QCE) $\le 0.06$ and lead-time accuracy (LTA; fraction of triggers whose calibrated lower-quantile RUL is $\ge$ the planning threshold) of 0.79 at a 10-day threshold. When deployed in counterfactual evaluation, triggers reduced unplanned outages by 47.6% (paired bootstrap p = 0.008) and total downtime by 41.3% (p = 0.012), and yielded a 10.6% reduction in HVAC electricity (95% CI: 7.7–13.2%) and a 9.7% decrease in total operating cost. The findings indicate that calibrated sequence models coupled to simple sustained triggers can convert routine BMS data into reliable maintenance schedules with quantifiable reliability and energy benefits. Practically, conservative calibration (q approximately 0.25) with thresholds of 10–12 days provided stable lead windows; future work should assess transferability across climates and facility types using transfer learning and integrate uncertainty-aware triggering with MPC for joint operational and maintenance optimization. Full article

Lung cancer remains one of the deadliest cancers worldwide, which highlights the urgent need for new diagnostic tools to detect reliable biomarkers. To enable scalable and cost-effective production, we developed reusable PDMS stamps patterned with electrodes to print flexible electrodes on PET substrates using a microcontact printing (µCP) approach. PET was chosen not only for its flexibility but also as a more sustainable alternative to conventional rigid materials. On these electrodes, three sensing platforms were tested for neuron-specific enolase (NSE) detection: APTES-based monolayers, electrospun PVA/alginate nanofibers, and electropolymerized polypyrrole (PPy) films. Voltammetric and fluorescence/AFM analyses confirmed that all three platforms could recognize the target analyte, with the PPy-CdTe configuration showing the strongest signal variation. Impedance spectroscopy further supported this finding, revealing a clear linear correlation between charge transfer resistance (RCT) and NSE concentration. The PPy-CdTe sensor demonstrated high sensitivity and consistent performance for NSE detection, achieving a detection limit (LOD) of 8.05 pg·µL⁻¹ and a quantification limit (LOQ) of 26.84 pg·µL⁻¹. Full article

This study evaluates the tribological properties of poly-DL-lactic acid (PDLLA) nanosheets attached to shark-skin surfaces with varying textures. The main goal was to assess friction reduction in samples with different surface textures and investigate the influence of PDLLA nanosheets on tribological behaviors. Biomimetic shark skin was created using a polydimethylsiloxane (PDMS)-embedded stamping method (PEES) that replicates shark skin’s unique texture, which reduces friction and drag in aquatic environments. PDLLA nanosheets, with a controlled thickness of several tens of nanometers, were fabricated and attached to the PDMS surfaces. The morphological characteristics of the materials were analyzed before and after attaching the PDLLA nanosheets using scanning electron microscopy (SEM), revealing the uniformity and adherence of the nanosheets to the PDMS surfaces. Friction tests were conducted using force transducers to measure the friction coefficients of biomimetic shark skin, biological models, and flat PDMS and silicon substrates, allowing a comprehensive comparison of frictional properties. Additionally, sliding tests with human fingers were performed to assess friction coefficients between various fingerprint shapes and sample surfaces. This aspect of the study is critical for understanding how human skin interacts with biomimetic materials in real-world applications, such as wearable devices. These findings clarify the relationship between surface texture, nanosheets, and their tribological performance against human skin, thereby contributing to the development of materials with enhanced friction-reducing properties for applications such as surface coatings, substrates for wearable devices, and wound dressings. Full article

In this work, Ti-incorporated carbon coatings were used as substrates for modification with one- and two-component self-assembled monolayers of organosilane compounds using a polydimethylsiloxane (PDMS) stamp. This enabled the selective functionalization of surfaces with micrometric dimensions. The topography of the modified surfaces was defined using an atomic force microscope (AFM). The effectiveness of the modification was confirmed by measurements of the water contact angle and surface free energy using the Oss and Good method. Using a T-23 microtribometer with counterparts in the shape of balls that were made of steel, silicon nitride (Si₃N₄), and zirconium dioxide (ZrO₂), the tribological properties of the obtained coatings were tested. These investigations showed that modification by using a PDMS stamp makes it possible to produce two-component ultrathin silane layers on Ti-containing carbon substrates. Two-component organosilane layers had higher hydrophobicity, a lower friction coefficient, and a smaller width of wear tracks than the one-component analogs. It was also found that the work of adhesion of the created surfaces had a significant influence on the value of the friction coefficient and the percentage value of the growth inhibition of bacteria. Full article

Microfluidic paper-based analytical devices (μPADs) have been developed for use in a variety of diagnosis and analysis fields. However, conventional μPADs with an open-channel system have limitations for application as analytical platforms mainly because of the evaporation and contamination of the sample solution. This study demonstrates the design and fabrication of an enclosed three-dimensional(3D)-μPAD and its application as a primary early analysis platform for ionic contaminants. To generate the hydrophobic PDMS barrier, double-sided patterning is carried out using a PDMS blade-coated stamp mold that is fabricated using 3D printing. The selective PDMS patterning can be achieved with controlled PDMS permeation of the cellulose substrate using 3D-designed stamp molds. We find the optimal conditions enabling the formation of enclosed channels, including round shape pattern and inter-pattern distance of 10 mm of stamp design, contact time of 0.5 min, and spacer height of 300 µm of double-sided patterning procedure. As a proof of concept, this enclosed 3D-μPAD is used for the simultaneous colorimetric detection of heavy metal ions in a concentration range of 0.1–2000 ppm, including nickel (Ni²⁺), copper (Cu²⁺), mercury (Hg²⁺), and radioactive isotope cesium-137 ions (Cs⁺). We confirm that qualitative analysis and image-based quantitative analysis with high reliability are possible through rapid color changes within 3 min. The limits of detection (LOD) for 0.55 ppm of Ni²⁺, 5.05 ppm of Cu²⁺, 0.188 ppm of Hg²⁺, and 0.016 ppm of Cs+ are observed, respectively. In addition, we confirm that the analysis is highly reliable in a wide range of ion concentrations with CV values below 3% for Ni²⁺ (0.56%), Cu²⁺ (0.45%), Hg²⁺ (1.35%), and Cs⁺ (2.18%). This method could be a promising technique to develop a 3D-μPAD with various applications as a primary early analysis device in the environmental and biological industries. Full article

Microscale elastomeric valves are an integral part of many lab-on-chip applications. Normally closed valves require lower actuation pressures to form tight seals, making them ideal for portable devices. However, fabrication of normally closed valves is typically more difficult because the valve structure must be selectively bonded to its substrate. In this work, an oligomer stamping technique for selective bonding of normally closed valves is optimized for bonding of PDMS devices on glass substrates. Contact angle and blister bursting testing measurements are used to quantitatively characterize the oligomer stamping process for the first time, and recommendations are made for plasma treatment conditions, microstamping technique, and valve construction. Glass–PDMS devices are ideal for lab-on-chip systems that integrate electrodes on the rigid glass substrate. Here, integrated electrodes are used to assess valve performance, demonstrating electrical isolation in excess of 8 M$\mathsf{\Omega }$ over the biologically relevant frequency range in the closed state. Further, electrical measurement is used to demonstrate that the valve design can operate under a pulsed actuation scheme, sealing to withstand fluid pressures in excess of 200 mbar. Full article

Evanescent field excitation is a powerful means to achieve a high surface-to-bulk signal ratio for bioimaging and sensing applications. However, standard evanescent wave techniques such as TIRF and SNOM require complex microscopy setups. Additionally, the precise positioning of the source relative to the analytes of interest is required, as the evanescent wave is critically distance-dependent. In this work, we present a detailed investigation of evanescent field excitation of near-surface waveguides written using femtosecond laser in glass. We studied the waveguide-to-surface distance and refractive index change to attain a high coupling efficiency between evanescent waves and organic fluorophores. First, our study demonstrated a reduction in sensing efficiency for waveguides written at their minimum distance to the surface without ablation as the refractive index contrast of the waveguide increased. While this result was anticipated, it had not been previously demonstrated in the literature. Moreover, we found that fluorescence excitation by waveguides can be enhanced using plasmonic silver nanoparticles. The nanoparticles were also organized in linear assemblies, perpendicular to the waveguide, with a wrinkled PDMS stamp technique, which resulted in an excitation enhancement of over 20 times compared to the setup without nanoparticles. Full article

In the present study, a functional template made up of in situ synthesised gold nanoparticles (AuNPs) is prepared on polydimethylsiloxane (PDMS) for patterning of target protein onto the desired solid substrates. Unlike previous studies in which bioreceptor probes are randomly attached to the PDMS stamp through electrostatic interactions, herein, we propose an AuNPs–PDMS stamp, which provides a surface for the attachment of thiol-modified biorecognition probes to link to the stamp surface through a dative bond with a single anchoring point based on thiol chemistry. By using this platform, we have developed the ability for microcontact printing (µCP) to selectively capture and transfer target protein onto solid surfaces for detection purposes. After µCP, we also investigated whether liquid crystals (LCs) could be used as a label-free approach for identifying transfer protein. Our reported approach provides promise for biosensing of various analytes. Full article

Microcontact printing using PDMS embossing tools and its variations have aroused the interest of a wide spectrum of research fields, hence the feasibility of defining micro and nanoscale patterns. In this work, we have proposed and demonstrated a novel lithography method based on grayscale patterns printed in a flexographic photopolymer mold and transferred to epoxy resin and a single PDMS stamp to obtain different microprint pattern structures. The geometry of the patterns can be modified by adjusting the layout and grayscale of the stamp patterns. The functionality of this contact printing methodology was validated by generating human induced pluripotent stem cells (hiPSC) patterns. These specific micropatterns can be very useful for achieving complex differentiation in cell lines such as hiPSC. Microfabrication through the new technique provides a promising alternative to conventional lithography for constructing complex aligned surfaces; these structures could be used as components of biological patterns or microfluidic devices. Full article

The increasing use of rapidly fluctuating renewable energy sources, such as sunlight, has necessitated the use of supercapacitors, which are a type of energy storage system with high power. Chemically exfoliated graphene oxide (GO) is a representative starting material in the fabrication of supercapacitor electrodes based on reduced GO (rGO). However, the restacking of rGO sheets driven by π–π stacking interactions leads to a significant decrease in the electrochemically active surface area, leading to a loss of energy density. Here, to effectively inhibit restacking and construct a three-dimensional wrinkled structure of rGO (3DWG), we propose an agarose gel-templating method that uses agarose gel as a soft and removable template. The 3DWG, prepared via the sequential steps of gelation, freeze-drying, and calcination, exhibits a macroporous 3D structure and 5.5-fold higher specific capacitance than that of rGO restacked without the agarose template. Further, we demonstrate a “gel-stamping” method to fabricate thin-line patterned 3DWG, which involves the gelation of the GO–agarose gel within micrometer-sized channels of a customized polydimethylsiloxane (PDMS) mold. As an easy and low-cost manufacturing process, the proposed agarose gel templating method could provide a promising strategy for the 3D structuring of rGO. Full article

Silicon nano-film is essential for the rapidly developing fields of nanoscience and flexible electronics, due to its compatibility with the CMOS process. Viscoelastic PDMS material can adhere to Si, SiO₂, and other materials via intermolecular force and play a key role in flexible electronic devices. Researchers have studied many methods of transfer printing silicon nano-films based on PDMS stamps with pyramid microstructures. However, only large-scale transfer printing processes of silicon nano-films with line widths above 20 $\mathsf{\mu }\mathrm{m}$ have been reported, mainly because the distribution of pyramid microstructures proposes a request on the size of silicon nano-films. In this paper, The PDMS base to the curing agent ratio affects the adhesion to silicon and enables the transfer, without the need for secondary alignment photolithography, and a flat stamp has been used during the transfer printing, with no requirement for the attaching pressure and detaching speed. Transfer printing of 20 $\mathsf{\mu }\mathrm{m}$ wide structures has been realized, while the success rate is 99.3%. The progress is promising in the development of miniature flexible sensors, especially flexible hydrophone. Full article