Encapsulation Layer Research Articles

Controlling release from encapsulated drug-loaded devices: insights from modeling the dissolution front propagation.

Dissolution of drug from its solid form to a dissolved form is an important consideration in the design and optimization of drug delivery devices, particularly owing to the abundance of emerging compounds that are extremely poorly soluble. When the solid dosage form is encapsulated, for example by the porous walls of an implant, the impact of the encapsulant drug transport properties is a further confounding issue. In such a case, dissolution and diffusion work in tandem to control the release of drug. However, the interplay between these two competing processes in the context of drug delivery is not as well understood as it is for other mass transfer problems, particularly for practical controlled-release considerations such as an encapsulant layer around the drug delivery device. To address this gap, this work presents a mathematical model that describes controlled release from a drug-loaded device surrounded by a passive porous layer. A solution for the drug concentration distribution is derived using the method of eigenfunction expansion. The model is able to track the dissolution front propagation, and predict the drug release curve during the dissolution process. The utility of the model is demonstrated through comparison against experimental data representing drug release from a cylindrical drug-loaded orthopedic fixation pin, where the model is shown to capture the data very well. Analysis presented here reveals how the various geometrical and physicochemical parameters influence drug dissolution and, ultimately, the drug release profile. It is found that the non-dimensional initial concentration plays a key role in determining whether the problem is diffusion-limited or dissolution-limited, whereas the nature of the problem is largely independent of other parameters including diffusion coefficient and encapsulant thickness. We expect the model will prove to be a useful tool for those designing encapsulated drug delivery devices, in terms of optimizing the design of the device to achieve a desired drug release profile.

Multifunctional Titanium Oxide Layers in Silicon Heterojunction Solar Cells Formed via Selective Anodization

Herein, a novel strategy is introduced to reduce the consumption of scarce materials in silicon heterojunction solar cells by combining approaches for Ag replacement in the metallization and a reduction of the indium tin oxide layer thickness: a Ti layer deposited by physical vapor deposition serves both as the contact layer of a copper‐based metallization and after electrochemical oxidation as capping layer enabling the use of a thinner transparent conductive oxide. Further, the TiOx layer can build an encapsulation layer. While oxygen evolution and metal dissolution are found to be critical side reactions, a nonaqueous electrolyte is found in which these reactions can be avoided. The application on silicon heterojunction solar cells shows promising first results, exhibiting a short circuit current density of 35 mA cm−2 and a cell efficiency of close to 21% despite nonoptimized layer thicknesses.

An intrinsically stretchable multi-biochemical sensor for sweat analysis using photo-patternable ecoflex

AbstractEcoflex is widely used in bioelectronics due to its outstanding properties of low modulus and large stretchability. For its use as an encapsulation layer in multi-channel wearable devices, a patterning procedure is essential. However, conventional patterning strategies for Ecoflex, such as soft lithography, punching, and laser ablation, lack sufficient quality and process compatibility. To address this, we propose a process-compatible method of patterning Ecoflex by developing Photo-patternable Ecoflex (PPE). The PPE layer, used as an encapsulation layer, effectively dissipates strain energy at homogeneous interfaces, resulting in a 50% increase in electrical conductance under 250% strain. Using PPE, we fabricated intrinsically stretchable multi-sensors that monitor bio-signals like glucose, lactate, pH, and humidity in sweat. These sensors maintain durable sensitivity under strain up to 50% and for 1000 cycles at 20% strain. Finally, we mounted these stretchable multi-chemical sensors on an arm to monitor glucose and lactate levels in sweat.

Strain-Driven Negative Resistance Switching of Conductive Fibers with Adjustable Sensitivity for Wearable Healthcare Monitoring Systems with Near-Zero Standby Power.

Recently, one of the primary concerns in e-textile-based healthcare monitoring systems for chronic illness patients has been reducing wasted power consumption, as the system should be always-on to capture diverse biochemical and physiological characteristics. However, the general conductive fibers, a major component of the existing wearable monitoring systems, have a positive gauge-factor (GF) that increases electrical resistance when stretched, so that the systems have no choice but to consume power continuously. Herein, a twisted conductive-fiber-based negatively responsive switch-type (NRS) strain-sensor with an extremely high negative GF (resistance change ratio ≈ 3.9× 108 ) that can significantly increase its conductivity from insulating to conducting properties is developed. To this end, a precision cracking technology is devised, which could induce a difference in the Young's modulus of the encapsulated layer on the fiber through selective ultraviolet-irradiation treatment. Owing to this technology, the NRS strain-sensors can allow for effective regulation of the mutual contact resistance under tensile strain while maintaining superior durability for over 5000 stretching cycles. For further practical demonstrations, three healthcare monitoring systems (E-fitness pants, smart-masks, and posture correction T-shirts) with near-zero standby power are also developed, which opens up advancements in electronic textiles by expanding the utilization range of fiber strain-sensors.

Correlating Optical Microspectroscopy with 4×4Transfer Matrix Modeling for Characterizing Birefringent Van der Waals Materials.

Van der Waals materials exhibit intriguing properties for future electronic and optoelectronic devices. As those unique features strongly depend on the materials' thickness, it has to be accessed precisely for tailoring the performance of a specific device. In this study, a nondestructive and technologically easily implementable approach for accurate thickness determination of birefringent layered materials is introduced by combining optical reflectance measurements with a modular model comprising a 4×4 transfer matrix method and the optical components relevant to light microspectroscopy. This approach is demonstrated being reliable and precise for thickness determination of anisotropic materials like highly oriented pyrolytic graphite and black phosphorus in a range from atomic layers up to more than 100nm. As a key feature, the method is well-suited even for encapsulated layers outperforming state of-the-art techniques like atomic forcemicroscopy.

Thermoplastic Elastomers for Wireless, Skin‐Interfaced Electronic, and Microfluidic Devices

AbstractWireless, skin‐interfaced electronic and microfluidic devices have the potential to replace wired, bulky, and cumbersome technologies for personal and clinical health monitoring, allowing care to extend from hospital settings to the home. For use on skin, these devices commonly employ silicone‐based thermoset elastomers (TSEs) as layers that encapsulate the electronics or serve as molded microchannels for biofluid (e.g., sweat) capture, storage, and analysis. Barriers to commercial adoption of such devices include difficulties in use of these elastomers in conventional practices for mass manufacturing. Their relatively high cost and inability to allow for recycling represent additional disadvantages. By contrast, thermoplastic elastomers (TPEs) are fully compatible with industrial‐scale manufacturing processes, low in cost, and recyclable. Like TSEs, TPEs are soft, stretchable, flexible, and optically transparent, while possessing other properties well‐suited for applications in wireless, skin‐interfaced devices. Herein, the characteristics, processing, and application techniques for three commercially available TPEs, including two thermoplastic polyurethanes as encapsulation layers for a wireless skin hydration sensor and one thermoplastic styrenic block copolymer for a microfluidic sweat analysis platform, are reported. The results demonstrate that TPEs can be effectively integrated into these classes of devices, as a compelling alternative to TSEs, as a mass‐manufacturable, sustainable materials option.

State‐of‐the‐Art Electronic Materials for Thin Films in Bioelectronics

AbstractThis review is dedicated to electronics materials enabling thin‐film‐based neural interface and bioelectronics devices. First‐generation bioelectronic medicine devices feature hand‐crafted bulk interface electrodes, wires and interconnects, and insulators. This review discusses how modern materials science, especially know‐how repurposed from semiconductor and microdevice technologies, enables next‐generation bioelectronics. Those are divided into two subgroups: second and third generation. The former refers to rigid microscaled devices, while the latter is defined as soft, ultrathin, and flexible microdevices. A critical assessment of different biointerface electrodes, conductors for interconnects, and insulators for substrates, passivation, and encapsulation layers is made. The goal is not to give an exhaustive account of every use‐example of given materials, but to point out specific aspects that are relevant to making the right choices for materials for a given device or application. Unique advantages of specific materials are highlighted, while also focusing on weaker points and caveats that those materials may have. The goal is to have an up‐to‐date handbook for persons entering the field which also points out tips and tricks as well as challenging problems that researchers can be inspired to confront and overcome.

Revealing the interlayer orientations for bilayer graphene grown on hexagonal boron nitride by c-AFM measurement

Owing to its excellent properties in optical and electronic applications, twisted bilayer graphene (TBG) has attracted extensive research attention. As an encapsulation layer, hexagonal boron nitride (h-BN) is indispensable for fabricating TBG devices. Because h-BN and graphene exhibit similar lattice structures, TBG on h-BN exhibits periodic moiré patterns, which enable interlayer orientations to be revealed for bilayer graphene on h-BN. Herein, we used two-step chemical vapor deposition to synthesize TBG exhibiting multiple twist angles on h-BN. Conductive atomic force microscopy measurements revealed that the conductivity distribution was different for the graphene/h-BN and TBG moiré patterns. Using the characteristics of the moiré patterns formed by these layers, h-BN and graphene interlayer orientations were precisely determined. This provides a feasible method for investigating the turbostratic arrangement of few-layer van der Waals heterostructures.

Amorphous nickel hydroxide shell tailors local chemical environment on platinum surface for alkaline hydrogen evolution reaction.

In analogy to natural enzymes, an elaborated design of catalytic systems with a specifically tailored local chemical environment could substantially improve reaction kinetics, effectively combat catalyst poisoning effect and boost catalyst lifetime under unfavourable reaction conditions. Here we report a unique design of 'Ni(OH)2-clothed Pt-tetrapods' with an amorphous Ni(OH)2 shell as a water dissociation catalyst and a proton conductive encapsulation layer to isolate the Pt core from bulk alkaline electrolyte while ensuring efficient proton supply to the active Pt sites. This design creates a favourable local chemical environment to result in acidic-like hydrogen evolution reaction kinetics with a lowest Tafel slope of 27 mV per decade and a record-high specific activity and mass activity in alkaline electrolyte. The proton conductive Ni(OH)2 shell can also effectively reject impurity ions and retard the Oswald ripening, endowing a high tolerance to solution impurities and exceptional long-term durability that is difficult to achieve in the naked Pt catalysts. The markedly improved hydrogen evolution reaction activity and durability in an alkaline medium promise an attractive catalyst material for alkaline water electrolysers and renewable chemical fuel generation.

Flexible strain sensor based on PU film with three-dimensional porous network

Flexible strain sensors are widely used in wearable applications such as human motion and health detection, but it is challenging to prepare sensors with excellent performance, such as a wide sensing range and high sensitivity with a simple process and low cost. By taking the advantages of the electrostatic spinning technique that can prepare micro-structured films with fibrous porous networks, and this paper investigated the effect of the distance between the electrostatic spinning needle and the collection drum on the mechanical properties of the PU films produced. Then, the most mechanically excellent three-dimensional porous PU fiber film was selected as the substrate, and Carbon Black (CB) particles were selected as the conductive filler to prepare the CB/PU/Ecoflex strain sensor (CPESS) with a three-dimensional porous fiber network structure by spraying CB on the PU fiber film for the sensitive layer and applying a layer of biocompatible Ecoflex on the surface as the encapsulation layer. Owing to the substrates of this three-dimensional network microstructure with excellent mechanical properties such as high Young's modulus and elongation at break, the CPESS has an excellent sensing performance, with a detection range of 200 %, a sensitivity of up to 1443.95, rapid dynamic response of 50 ms, a low detection limit of (0.3 % strain), favorable repeatability, and excellent dynamic response at a large-scale tensile strain of 150 % − 200 %. The CPESS can be used to detect human joint movements and fine motion changes, and it exhibits great potential for smart wearable applications.

An ultrasound-responsive smart nanoplatform leads to mitochondrial apoptosis of tumor cells from multiple levels

Mitochondria, the energy suppliers of cells, are crucial for cell survival and proliferation. Tumor therapy based on mitochondrial apoptosis holds good promise. Currently utilized strategies, such as the production of CO and ROS and Ca2+ overload, are not highly selective and have limited effectiveness. In this study, a smart nanoplatform (V-Mn@Ca) controlled by ultrasound (US) and with high therapeutic efficacy was designed, which can specifically target the tumor site and activate mitochondrial apoptosis at multiple levels. Specifically, VS4, featuring a narrow band gap, are utilized to generate a Fenton-like effect. Loading Mn(CO)5Br enables a US-induced release of CO and depletion of GSH, which would further enhance ROS-mediated mitochondrial apoptosis. Finally, an encapsulated CaCO3 shell layer disrupts Ca2+ homeostasis in tumor cells. Overall, our study shows that the V-Mn@Ca platform triggers CO, ROS, and Ca2+ production in a controlled manner. Thus, providing sonodynamic therapy and CO therapy on a timed-targeted basis for enhanced mitochondrial apoptosis and subsequent tumor cell death, which inhibits tumor growth.

Materials, Device Structures, and Applications of Flexible Perovskite Light‐Emitting Diodes

AbstractThe flexible type of displays, which can alter their shape freely (e.g., bendable or foldable displays) according to situational demands, is under an intense spotlight due to applications in human‐friendly mobile electronics. Among various types of light‐emitting diodes (LEDs), meanwhile, perovskite‐based LEDs (PeLEDs) have garnered particular attention in recent years as next‐generation optoelectronic devices due to their exceptional optical characteristics, such as high efficiency (up to theoretical limits), high color purity, wide color gamut over the entire visible range, and ultrathin form factor. By integrating perovskite materials on an ultrathin flexible substrate with a proper encapsulation layer, the flexible PeLEDs, which can conform to various curved surfaces and be stably operated in an ambient condition, have been developed. Here, recent advances of the flexible PeLEDs are reviewed. First, light‐emitting materials and device structures for the PeLEDs are introduced. Then, research progress on the flexible PeLEDs, either with and without the encapsulation layer are summarized. Next, some representative application examples of the flexible PeLEDs are briefly discussed. Finally, this review includes a brief discussion on future prospects.

Hardmask engineering by mask encapsulation for enabling next generation reactive ion etch scaling

Miniaturization and scaling of semiconductor devices require development of innovative techniques to sustain advancements. A promising trend is the migration from 2D to 3D device architectures that necessitate fabrication of high-aspect-ratio narrow features through layers of different materials. Reactive ion etching can achieve this but poses unique challenges due to the requirement of etch chemistries capable of etching dissimilar materials with varying etch rates while maintaining high productivity. The choice of hardmask is also crucial, as it plays a critical role in determining efficacy of the etch process and the final shape of the feature being etched. To address these challenges, we introduce a new concept of hardmask engineering that involves a bilayer hardmask scheme consisting of a patterned conventional hardmask encapsulated with a thin layer of etch-resistant ruthenium (Ru) layer. Experimental results for etching multilayer stacks consisting of alternating pairs of SiO2 and Mo show that this engineered hardmask results in improved hardmask remaining and etch profile with smaller critical dimensions (CDs). Technology computer-aided design simulations with the Ru encapsulation layer on conventional carbon hardmask demonstrate increased poly-Si etch depth with reduced bow CD. This concept can be extended to any semiconductor nanofabrication step involving high-aspect-ratio etching where precise control of CDs is essential in the vertical direction.

P41: 4D Manufacturing: Immunoprotective Materials for Islet Tissue Patches in Cell-Based Diabetes Treatments

Purpose: In order to cure diabetes on a large scale, researchers are working to develop insulin-producing cells differentiated from human pluripotent stem cells, encapsulating the tissues to protect the cells from immune attack, and implanting the cells for regulated insulin secretion. This project explored the synthesis and in vivo performance of a 4D biomaterial intended to protect implanted insulin-producing cells in the body. 3D printing of insulin-producing cells encapsulated within the biomaterial with additional timed-release anti-inflammatory agents enabled complex, personalized shapes and a 4D functional material. Methods: Anti-inflammatory agents were functionalized with varying permanent and degradable linkages to achieve a range of timed-release therapeutics to prevent immune system-mediated rejection. The molecules were crosslinked with a multi-arm polyethylene glycol (PEG) material in the subcutaneous space of immunocompetent C57BL/6 mice. After 30 days, tissue slices of the explant were examined using H&E staining revealing the thickness of biological encapsulation compared to alginate controls. Results: PEG-based implants with acetal linkages enabling the slow release (~30 days) of anti-inflammatory agents achieved the thinnest layer of biological encapsulation compared to the controls. Summary: Collectively, the described 4D biomaterial with other novel approaches and tools will enable the investigation of survival and function of a stem cell-based therapy for diabetes that could ultimately allow patients to live a diabetes-free lifestyle.

Stability of self-encapsulated CsPbX3@PbX(OH)(X=Cl,Br) perovskite quantum dots in polar solvents

Inorganic halide perovskite quantum dots has excellent optical and photoelectric properties, so it has great potential in photovoltaic, photoelectric devices, display lighting, medical detection and other fields. However, its commercial application is hampered by its instability. In this paper, the perovskite quantum dots encapsulated by PbX (OH)(X = Cl,Br) can obtain hexahedral CsPbBr3@PbBr(OH), cube CsPbCl3@PbCl(OH) and spindle CsPbCl3@PbBr(OH) between hexahedron and cube. The core-shell encapsulation and interchange combination are realized. Before and after encapsulation, the color coordinates of CsPbX3 (X = Cl,Br) perovskite quantum dots basically did not change, no other crystal phases were found in the XRD lines, which indicatied that the PbX (OH) (X = Cl,Br) encapsulation layer did not change the crystal structure of perovskite quantum dots. PbX (OH) (X = Cl,Br) encapsulation layer plays the role of water-blocking layer and protective layer, which greatly improves the stability of CsPbX3 (X = Cl,Br) perovskite quantum dots in polar solvents. After encapsulation, the photoluminescence quantum yield (PLQY) and time-resolved photoluminescence decay performance of CsPbX3 (X = Cl,Br) perovskite quantum dots are greatly improved. The surface passivation and trap density of perovskite nanocrystals can be reduced by PbX (OH) (X = Cl,Br) wrapping, which extends the fluorescence life of CsPbX3 (X = Cl,Br) and improving the PL stability of perovskite structure. Room temperature (RT) crystallization method does not require inert gas protection, high temperature and high pressure conditions. It also has good repeatability, which provides a better alternative to hot injection. Meanwhile, the improvement of package stability provides a broader prospect for the application and promotion of lead halide perovskite.

High light extraction performance using evanescent waves for top emission OLED applications with thin film encapsulation.

We report high light extraction from the top emission OLED (TEOLED) device structure by improving mainly the waveguide mode loss in the atomic layer deposition processed thin film encapsulation (TFE) layer. A novel structure incorporating the light extraction concept using evanescent waves and the hermetic encapsulation of a TEOLED device is presented here. When the TEOLED device is fabricated using the TFE layer, a substantial amount of generated light is trapped inside the device due to the difference in refractive index (RI) between the capping layer (CPL) and the aluminum oxide (Al2O3) layer. By inserting a low RI layer at the interface between the CPL and Al2O3, the direction of the internal reflected light is changed by the evanescent waves. The high light extraction with the low RI layer is attributed to the presence of evanescent waves and an electric field in the low RI layer. The novel fabricated TFE structure, CPL/ low RI layer/ Al2O3/ polymer/ Al2O3, is reported here. The current efficiency of the fabricated blue TEOLED device using this low RI layer is improved by about 23% and the blue index value is enhanced by about 26%. This new approach for light extraction will be applicable to future encapsulation technology for flexible optoelectronic devices.

A Flexible Sensor with Excellent Environmental Stability Using Well-Designed Encapsulation Structure.

The hydrogel-based sensors suffer from poor stability and low sensitivity, severely limiting their further development. It is still "a black box" to understand the effect of the encapsulation as well as the electrode on the performance of the hydrogel-based sensors. To address these problems, we prepared an adhesive hydrogel that could robustly adhere to Ecoflex (adhesive strength is 4.7 kPa) as an encapsulation layer and proposed a rational encapsulation model that fully encapsulated the hydrogel within Ecoflex. Owing to the excellent barrier and resilience of Ecoflex, the encapsulated hydrogel-based sensor can still work normally after 30 days, displaying excellent long-term stability. In addition, we performed theoretical and simulation analyses on the contact state between the hydrogel and the electrode. It was surprising to find that the contact state significantly affects the sensitivity of the hydrogel sensors (the maximum difference in sensitivity was 333.6%), indicating that the reasonable design of the encapsulation and electrode are indispensable parts for fabricating successful hydrogel sensors. Therefore, we paved the way for a novel insight to optimize the properties of the hydrogel sensors, which is greatly favorable to developing hydrogel-based sensors to be applied in various fields.

Universal visualization of crystalline orientation for black phosphorus by angle-resolved polarized photoacoustic microscopy.

Anisotropic two-dimensional (2D) materials, such as black phosphorus (BP), normally possess unique directional in-plane electrical, optical, and thermal properties that are highly correlated with their crystalline orientations. Nondestructive visualization of their crystalline orientation is an indispensable premise for the 2D materials to harness their distinctive strengths in optoelectronic and thermoelectric applications. Here, by photoacoustically recording the anisotropic optical absorption variation under linearly polarized laser beams, an angle-resolved polarized photoacoustic microscopy (AnR-PPAM) is developed, capable of non-invasively determining and visualizing BP's crystalline orientation. We theoretically deduced the physical relationship between the crystalline orientation and polarized photoacoustic (PA) signals, and experimentally proved the ability of AnR-PPAM to universally visualize BP's crystalline orientation regardless of its thickness, substrate, and encapsulation layer. This method provides a new, to the best of our knowledge, strategy for crystalline orientation recognition of 2D materials with flexible measurement conditions, prefiguring important potential for the applications of anisotropic 2D materials.

Parylene C as a Multipurpose Material for Electronics and Microfluidics.

Poly(p-xylylene) derivatives, widely known as Parylenes, have been considerably adopted by the scientific community for several applications, ranging from simple passive coatings to active device components. Here, we explore the thermal, structural, and electrical properties of Parylene C, and further present a variety of electronic devices featuring this polymer: transistors, capacitors, and digital microfluidic (DMF) devices. We evaluate transistors produced with Parylene C as a dielectric, substrate, and encapsulation layer, either semitransparent or fully transparent. Such transistors exhibit steep transfer curves and subthreshold slopes of 0.26 V/dec, negligible gate leak currents, and fair mobilities. Furthermore, we characterize MIM (metal-insulator-metal) structures with Parylene C as a dielectric and demonstrate the functionality of the polymer deposited in single and double layers under temperature and AC signal stimuli, mimicking the DMF stimuli. Applying temperature generally leads to a decrease in the capacitance of the dielectric layer, whereas applying an AC signal leads to an increase in said capacitance for double-layered Parylene C only. By applying the two stimuli, the capacitance seems to suffer from a balanced influence of both the separated stimuli. Lastly, we demonstrate that DMF devices with double-layered Parylene C allow for faster droplet motion and enable long nucleic acid amplification reactions.

Asymmetric “Janus” Biogel for Human‐Machine Interfaces

AbstractHuman‐machine interfaces (HMIs) are essential for effective communication between machines and tissues. However, mechanical and biological mismatches, along with weak adhesion between rigid electronic devices and soft tissue, often cause unreliable responses and affect the signal recording of HMIs. In this study, an asymmetrical “Janus” biogel patch with one side firmly adhering to tissues, and the other surface having little adhesion and minimal interactions with surrounding environments has been developed. A series of analytical, mechanical, and electrical tests are performed to investigate the “Janus” biogel patch as a functional and biocompatible HMI. It is found that the gallic acid‐modified gelatin adhesive surface on one side exhibits body temperature‐dependent tissue adhesion, enabling low modulus and seamless skin contact. The other side is a tough gelatin/glycerol gel layer, which is thermally welded into the adhesive layer and functions as an encapsulant to prevent external interference due to adhesion. The encapsulation layer also exhibits a low friction coefficient when wet and proves to be a reliable alternative barrier to conventional encapsulation materials. The scientific insights and engineering principles revealed in this type of “Janus” biogel will be applicable to a broad range of biomedical applications, such as epidermal adhesive electrodes or skin‐adhesive wearable devices.