Click‐Chemistry Based Multi‐Component Microarrays by Quill‐Like Pens

We demonstrate the generation of multi‐component spot microarrays by blotting different ink solutions via quill‐like pens. The obtained arrays are immobilized by click‐chemistry in form of the copper(I)‐catalyzed azide‐alkyne cycloaddition and remain stable against washing and immersion in aqueous solution. The average spot radius ranges from 10 to 20 μm and is about an order of magnitude smaller than in currently commercially applied arraying techniques, effectively bridging the gap to high resolution methods as dip‐pen nanolithography and polymer pen lithography. The use of the quill‐like‐pen‐generated spot microarrays as binding assay is demonstrated by capturing of streptavidin from solution and by bioactive sandwich structures from neutravidin and biotin‐labeled fibronectin. Thus, our multi‐component spot microarrays have ideal dimensions and biochemical properties to accommodate (single) cells. Additionally, the building up of the cell‐recruiting protein sandwich structure on top of the basic spot microarray allows for the highly selective adhesion of fibroblasts. This results then in ordered (single) cell arrays, demonstrating the bio‐compatibility and high throughput of this multi‐component spot microarray platform.     

Microcontact Printing: Arrays of Silicon Micro/Nanostructures Formed in Suspended Configurations for Deterministic Assembly Using Flat and Roller‐Type Stamps (Small 4/2011)

The ability to create and manipulate large arrays of inorganic semiconductor micro/nanostructures for integration on unconventional substrates provides new possibilities in device engineering. Here, simple methods are described for the preparation of structures of single crystalline silicon in suspended and tethered configurations that facilitate their deterministic assembly using transfer‐printing techniques. Diverse shapes (e.g., straight or curved edges), thicknesses (between 55 nm and 3 μm), and sizes (areas of 4000 μm² to 117 mm²) of structures in varied layouts (regular or irregular arrays, with dense or sparse coverages) can be achieved, using either flat or cylindrical roller‐type stamps. To demonstrate the technique, printing with 100% yield onto curved, rigid supports of glass and ceramics and onto thin sheets of plastic is shown. The fabrication of a printed array of silicon p⁺–i–n⁺ junction photodiodes on plastic is representative of device‐printing capabilities.     

Biochips for Cell Biology by Combined Dip‐Pen Nanolithography and DNA‐Directed Protein Immobilization

A general methodology for patterning of multiple protein ligands with lateral dimensions below those of single cells is described. It employs dip pen nanolithography (DPN) patterning of DNA oligonucleotides which are then used as capture strands for DNA‐directed immobilization (DDI) of oligonucleotide‐tagged proteins. This study reports the development and optimization of PEG‐based liquid ink, used as carrier for the immobilization of alkylamino‐labeled DNA oligomers on chemically activated glass surfaces. The resulting DNA arrays have typical spot sizes of 4–5 μm with a pitch of 12 μm micrometer. It is demonstrated that the arrays can be further functionalized with covalent DNA‐streptavidin (DNA‐STV) conjugates bearing ligands recognized by cells. To this end, biotinylated epidermal growth factor (EGF) is coupled to the DNA‐STV conjugates, the resulting constructs are hybridized with the DNA arrays and the resulting surfaces used for the culturing of MCF‐7 (human breast adenocarcinoma) cells. Owing to the lateral diffusion of transmembrane proteins in the cell's plasma membrane, specific recruitment and concentration of EGF receptor can be induced specifically at the sites where the ligands are bound on the solid substrate. This is a clear demonstration that this method is suitable for precise functional manipulations of subcellular areas within living cells.     

Flow‐Through Microbial Capture by Antibody‐Coated Microsieves

A new flow‐through method for rapid capture and detection of microorganisms is developed using optically‐flat microengineered membranes. Selective and efficient capture of Salmonella is demonstrated with antibodies coated on membranes (microsieves) having a pore size much larger than the microorganism itself. The silicon‐nitride membranes are first photochemically coated with 1,2‐epoxy‐9‐decene yielding stable Si–C and N–C linkages. The resultant epoxide‐terminated microsieves are subsequently biofunctionalized with anti‐Salmonella antibodies. The capture efficiency of antibody‐coated microsieves with different pore sizes (2.0–5.0 μm) is studied with Salmonella enterica enterica serotype Typhimurium suspensions (10⁷ cfu mL^–1). The antibody‐coated microsieves capture 52% (2 μm microsieves), 30% (3.5 μm microsieves), and 12% (5 μm microsieves) of Salmonella from the suspension. The influence of flow rate (0.8–16 μL min^–1 mm^–2) on the capture efficiency of antibody‐coated 3.5 μm microsieves is investigated. The capture efficiency increases from ≈30% to ≈70% when the flow‐rate decreases from 16 to 0.8 μL min^–1 mm^–2. Antibody‐coated 3.5 μm microsieves can capture Salmonella rapidly and directly from fresh milk suspension (capture 35% at concentration of 80 cfu mL^–1). The use of antibody‐coated microsieves as microbial selective capture devices is thus shown to be highly promising for the direct capture of microorganisms.     

Rapid,Controllable Fabrication of Regular Complex Microarchitectures by Capillary Assembly of Micropillars and Their Application in Selectively Trapping/Releasing Microparticles

A simple strategy to realize new controllable 3D microstructures and a novel method to reversibly trapping and releasing microparticles are reported. This technique controls the height, shape, width, and arrangement of pillar arrays and realizes a series of special microstructures from 2‐pillar‐cell to 12 cell arrays, S‐shape, chain‐shape and triangle 3‐cell arrays by a combined top down/bottom up method: laser interference lithography and capillary force‐induced assembly. Due to the inherent features of this method, the whole time is less than 3 min and the fabricated area determined by the size of the laser beam can reach as much as 1 cm², which shows this method is very simple, rapid, and high‐throughput. It is further demonstrated that the ‘mechanical hand’‐like 4‐cell arrays could be used to selectively trap/release microparticles with different sizes, e.g., 1.5, 2, or 3.5 μm, which are controlled by the period of the microstructures from 2.5 to 4 μm, and 6 μm. Finally, the ‘mechanical hand’‐like 4‐cell arrays are integrated into 100 μm‐width microfluidic channels prepared by ultraviolet photolithography, which shows that this technique is compatible with conventional microfabrication methods for on‐chip applications.     

Scalable Fabrication of Highly Crystalline Organic Semiconductor Thin Film by Channel‐Restricted Screen Printing toward the Low‐Cost Fabrication of High‐Performance Transistor Arrays

Control over the morphology and crystallinity of small‐molecule organic semiconductor (OSC) films is of key importance to enable high‐performance organic optoelectronic devices. However, such control remains particularly challenging for solution‐processed OSC devices because of the complex crystallization kinetics of small‐molecule OSC materials in the dynamic flow of inks. Here, a simple yet effective channel‐restricted screen‐printing method is reported, which uses small‐molecule OSCs/insulating polymer to yield large‐grained small‐molecule OSC thin‐film arrays with good crystallization and preferred orientation. The use of cross‐linked organic polymer banks produces a confinement effect to trigger the outward convective flow at two sides of the channel by the fast solvent evaporation, which imparts the transport of small‐molecule OSC solutes and promotes the growth of small‐molecule OSC crystals parallel to the channel. The small‐molecule OSC thin‐film array produced by screen printing exhibits excellent performance characteristics with an average mobility of 7.94 cm² V^?1 s^?1 and a maximum mobility of 12.10 cm² V^?1 s^?1, which are on par with its single crystal. Finally, screen printing can be carried out using a flexible substrate, with good performance. These demonstrations bring this robust screen‐printing method closer to industrial application and expand its applicability to various flexible electronics.     

Pattern formation of cytochrome c by microcontact printing and dip-pen nanolithography

We report the results of fabricating micrometer and submicrometer-scale patterns of cytochrome c on gold surfaces. We used direct micro-contact printing (μCP) and indirect dip-pen nanolithography (DPN) for fabricating cytochrome c arrays. The protein dots were formed in diameters of 2 μm by μCP and of ∼200 nm by DPN, respectively. We analyzed the pattern size and height of protein arrays with atomic force microscopy (AFM). We expect that these methods will be potentially useful for developing small-scale biosensors and protein chip microarrays.     

Direct Laser‐Patterned Micro‐Supercapacitors from Paintable MoS2 Films

Micrometer‐sized electrochemical capacitors have recently attracted attention due to their possible applications in micro‐electronic devices. Here, a new approach to large‐scale fabrication of high‐capacitance, two‐dimensional MoS₂ film‐based micro‐supercapacitors is demonstrated via simple and low‐cost spray painting of MoS₂ nanosheets on Si/SiO₂ chip and subsequent laser patterning. The obtained micro‐supercapacitors are well defined by ten interdigitated electrodes (five electrodes per polarity) with 4.5 mm length, 820 μm wide for each electrode, 200 μm spacing between two electrodes and the thickness of electrode is ～0.45 μm. The optimum MoS₂‐based micro‐supercapacitor exhibits excellent electrochemical performance for energy storage with aqueous electrolytes, with a high area capacitance of 8 mF cm^?2 (volumetric capacitance of 178 F cm^?3) and excellent cyclic performance, superior to reported graphene‐based micro‐supercapacitors. This strategy could provide a good opportunity to develop various micro‐/nanosized energy storage devices to satisfy the requirements of portable, flexible, and transparent micro‐electronic devices.     

Ultra‐High Optical Absorption Efficiency from the Ultraviolet to the Infrared Using Multi‐Walled Carbon Nanotube Ensembles

The optical absorption efficiencies of vertically aligned multi‐walled (MW)‐carbon nanotube (CNT) ensembles are characterized in the 350?7000 nm wavelength range where CNT site densities > 1 × 10¹¹/cm² are achieved directly on metallic substrates. The site density directly impacts the optical absorption characteristics, and while high‐density arrays of CNTs on electrically insulating and non‐metallic substrates have been commonly reported, achieving high site‐densities on metals has been challenging and remains an area of active research. These absorber ensembles are ultra‐thin (<10 μm) and yet they still exhibit a reflectance as low as ～0.02%, which is 100 times lower than the reference; these characteristics make them potentially attractive for high‐sensitivity and high‐speed thermal detectors. In addition, the use of a plasma‐enhanced chemical vapor deposition process for the synthesis of the absorbers increases the portfolio of materials that can be integrated with such absorbers due to the potential for reduced synthesis temperatures. The remarkable ruggedness of the absorbers is also demonstrated as they are exposed to high temperatures in an oxidizing ambient environment, making them well‐suited for extreme thermal environments encountered in the field, potentially for solar cell applications. Finally, a phenomenological model enables the determinatiom of the extinction coefficients in these nanostructures and the results compare well with experiment.     

Flexible,Printable Soft‐X‐Ray Detectors Based on All‐Inorganic Perovskite Quantum Dots

Metal halide perovskites represent a family of the most promising materials for fascinating photovoltaic and photodetector applications due to their unique optoelectronic properties and much needed simple and low‐cost fabrication process. The high atomic number (Z) of their constituents and significantly higher carrier mobility also make perovskite semiconductors suitable for the detection of ionizing radiation. By taking advantage of that, the direct detection of soft‐X‐ray‐induced photocurrent is demonstrated in both rigid and flexible detectors based on all‐inorganic halide perovskite quantum dots (QDs) synthesized via a solution process. Utilizing a synchrotron soft‐X‐ray beamline, high sensitivities of up to 1450 µC Gy_air^?1 cm^?2 are achieved under an X‐ray dose rate of 0.0172 mGy_air s^?1 with only 0.1 V bias voltage, which is about 70‐fold more sensitive than conventional α‐Se devices. Furthermore, the perovskite film is printed homogeneously on various substrates by the inexpensive inkjet printing method to demonstrate large‐scale fabrication of arrays of multichannel detectors. These results suggest that the perovskite QDs are ideal candidates for the detection of soft X‐rays and for large‐area flat or flexible panels with tremendous application potential in multidimensional and different architectures imaging technologies.     

Cancer Cell Membrane Camouflaged Nanoprobe for Catalytic Ratiometric Photoacoustic Imaging of MicroRNA in Living Mice

Herein, a cancer cell (MCF‐7 cell) membrane‐encapsulated dendritic mesoporous silica nanoparticle simultaneously functionalized with DNA‐photoacoustic (DNA‐PA) probes and glutathione (GSH)‐responsive DNA fuel strands for PA imaging of tumor‐related miRNA in living mice with signal amplification ability is developed. It is demonstrated that one target miRNA can trigger disassembly of multiple PA fluorophore probes from the quencher with the aid of GSH‐responsive DNA fuel strands via the entropy‐driven process, resulting remarkable amplified change of PA signal ratio. Using oncogenic miRNA‐21 as a model, a linear relationship between miRNA‐21 concentrations and PA ratio in a dynamic range from 10 × 10^?12 m to 100 × 10^?9 m and a limit of detection down to 11.69 × 10^?12 m are established. The accurate PA signal observation related to miRNA‐21s in the tumor area in living mice is demonstrated, and the PA signal ratio increases significantly via the injection of miRNA‐21. It is anticipated that the catalytic ratiometric PA imaging system can be applied to an array of molecular detection in living system by rational detection probe design.     

Coupling PEDOT on Mesoporous Vanadium Nitride Arrays for Advanced Flexible All‐Solid‐State Supercapacitors

Tailored construction of advanced flexible supercapacitors (SCs) is of great importance to the development of high‐performance wearable modern electronics. Herein, a facile combined wet chemical method to fabricate novel mesoporous vanadium nitride (VN) composite arrays coupled with poly(3,4‐ethylenedioxythiophene) (PEDOT) as flexible electrodes for all‐solid‐state SCs is reported. The mesoporous VN nanosheets arrays prepared by the hydrothermal–nitridation method are composed of cross‐linked nanoparticles of 10–50 nm. To enhance electrochemical stability, the VN is further coupled with electrodeposited PEDOT shell to form high‐quality VN/PEDOT flexible arrays. Benefiting from high intrinsic reactivity and enhanced structural stability, the designed VN/PEDOT flexible arrays exhibit a high specific capacitance of 226.2 F g^?1 at 1 A g^?1 and an excellent cycle stability with 91.5% capacity retention after 5000 cycles at 10 A g^?1. In addition, high energy/power density (48.36 Wh kg^?1 at 2 A g^?1 and 4 kW kg^?1 at 5 A g^?1) and notable cycling life (91.6% retention over 10 000 cycles) are also achieved in the assembled asymmetric flexible supercapacitor cell with commercial nickel–cobalt–aluminum ternary oxides cathode and VN/PEDOT anode. This research opens up a way for construction of advanced hybrid organic–inorganic electrodes for flexible energy storage.     

High‐Speed 3D Printing of Millimeter‐Size Customized Aspheric Imaging Lenses with Sub 7 nm Surface Roughness

Advancements in three‐dimensional (3D) printing technology have the potential to transform the manufacture of customized optical elements, which today relies heavily on time‐consuming and costly polishing and grinding processes. However the inherent speed‐accuracy trade‐off seriously constrains the practical applications of 3D‐printing technology in the optical realm. In addressing this issue, here, a new method featuring a significantly faster fabrication speed, at 24.54 mm³ h^?1, without compromising the fabrication accuracy required to 3D‐print customized optical components is reported. A high‐speed 3D‐printing process with subvoxel‐scale precision (sub 5 µm) and deep subwavelength (sub 7 nm) surface roughness by employing the projection micro‐stereolithography process and the synergistic effects from grayscale photopolymerization and the meniscus equilibrium post‐curing methods is demonstrated. Fabricating a customized aspheric lens 5 mm in height and 3 mm in diameter is accomplished in four hours. The 3D‐printed singlet aspheric lens demonstrates a maximal imaging resolution of 373.2 lp mm^?1 with low field distortion less than 0.13% across a 2 mm field of view. This lens is attached onto a cell phone camera and the colorful fine details of a sunset moth's wing and the spot on a weevil's elytra are captured. This work demonstrates the potential of this method to rapidly prototype optical components or systems based on 3D printing.     

Monolithic Flexible Vertical GaN Light‐Emitting Diodes for a Transparent Wireless Brain Optical Stimulator

Flexible inorganic‐based micro light‐emitting diodes (µLEDs) are emerging as a significant technology for flexible displays, which is an important area for bilateral visual communication in the upcoming Internet of Things era. Conventional flexible lateral µLEDs have been investigated by several researchers, but still have significant issues of power consumption, thermal stability, lifetime, and light‐extraction efficiency on plastics. Here, high‐performance flexible vertical GaN light‐emitting diodes (LEDs) are demonstrated by silver nanowire networks and monolithic fabrication. Transparent, ultrathin GaN LED arrays adhere to a human fingernail and stably glow without any mechanical deformation. Experimental studies provide outstanding characteristics of the flexible vertical μLEDs (f‐VLEDs) with high optical power (30 mW mm^?2), long lifetime (≈12 years), and good thermal/mechanical stability (100 000 bending/unbending cycles). The wireless light‐emitting system on the human skin is successfully realized by transferring the electrical power f‐VLED. Finally, the high‐density GaN f‐VLED arrays are inserted onto a living mouse cortex and operated without significant histological damage of brain.     

Microscale Electro‐Hydrodynamic Cell Printing with High Viability

Cell printing has gained extensive attentions for the controlled fabrication of living cellular constructs in vitro. Various cell printing techniques are now being explored and developed for improved cell viability and printing resolution. Here an electro‐hydrodynamic cell printing strategy is developed with microscale resolution (<100 µm) and high cellular viability (>95%). Unlike the existing electro‐hydrodynamic cell jetting or printing explorations, insulating substrate is used to replace conventional semiconductive substrate as the collecting surface which significantly reduces the electrical current in the electro‐hydrodynamic printing process from milliamperes (>0.5 mA) to microamperes (<10 µA). Additionally, the nozzle‐to‐collector distance is fixed as small as 100 µm for better control over filament deposition. These features ensure high cellular viability and normal postproliferative capability of the electro‐hydrodynamically printed cells. The smallest width of the electro‐hydrodynamically printed hydrogel filament is 82.4 ± 14.3 µm by optimizing process parameters. Multiple hydrogels or multilayer cell‐laden constructs can be flexibly printed under cell‐friendly conditions. The printed cells in multilayer hydrogels kept alive and gradually spread during 7‐days culture in vitro. This exploration offers a novel and promising cell printing strategy which might benefit future biomedical innovations such as microscale tissue engineering, organ‐on‐a‐chip systems, and nanomedicine.     

A General Approach for Lab‐to‐Manufacturing Translation on Flexible Organic Solar Cells

The blossoming of organic solar cells (OSCs) has triggered enormous commercial applications, due to their high‐efficiency, light weight, and flexibility. However, the lab‐to‐manufacturing translation of the praisable performance from lab‐scale devices to industrial‐scale modules is still the Achilles' heel of OSCs. In fact, it is urgent to explore the mechanism of morphological evolution in the bulk heterojunction (BHJ) with different coating/printing methods. Here, a general approach to upscale flexible organic photovoltaics to module scale without obvious efficiency loss is demonstrated. The shear impulse during the coating/printing process is first applied to control the morphology evolution of the BHJ layer for both fullerene and nonfullerene acceptor systems. A quantitative transformation factor of shear impulse between slot‐die printing and spin‐coating is detected. Compelling results of morphological evolution, molecular stacking, and coarse‐grained molecular simulation verify the validity of the impulse translation. Accordingly, the efficiency of flexible devices via slot‐die printing achieves 9.10% for PTB7‐Th:PC₇₁BM and 9.77% for PBDB‐T:ITIC based on 1.04 cm² . Furthermore, 15 cm² flexible modules with effective efficiency up to 7.58% (PTB7‐Th:PC₇₁BM) and 8.90% (PBDB‐T:ITIC) are demonstrated with satisfying mechanical flexibility and operating stability. More importantly, this work outlines the shear impulse translation for organic printing electronics.     

Single‐Crystalline,Metallic TiC Nanowires for Highly Robust and Wide‐Temperature Electrochemical Energy Storage

Customized electrode materials with good temperature adaptability and high‐rate capability are critical to the development of wide‐temperature power sources. Herein, high‐quality TiC nanowires are uniformly grown on flexible carbon cloth as free‐standing electric‐double‐layer supercapacitor electrode. The TiC nanowires, 20–40 nm wide and 3–6 µm long, are single‐crystalline and highly conductive that is close to typical metal. Symmetric supercapacitors are constructed with ionic liquid electrolyte and TiC nanowires electrodes as wide‐temperature and long‐cycle stable power source. Ultrastable high‐rate cycling life of TiC nanowire arrays electrodes is demonstrated with capacitance retention of 96.8% at 60 °C (≈440 F g^?1), 99% at 25 °C (≈400 F g^?1), and 98% at ?25 °C (≈240 F g^?1) after 50 000 cycles at 10 A g^?1. Moreover, due to high electrical conductivity, the TiC nanowire arrays show ultrafast energy release with a fast response time constant of ≈0.7 ms. The results demonstrate the viability of metal carbide nanostructures as wide‐temperature, robust electrode materials for high‐rate and ultrastable supercapacitors.     

Combinatorial Synthesis of Macromolecular Arrays by Microchannel Cantilever Spotting (µCS)

Surface‐bound microarrays of multiple oligo‐ and macromolecules (e.g., peptides, DNA) offer versatile options in biomedical applications like drug screening, DNA analysis, or medical diagnostics. Combinatorial syntheses of these molecules in situ can save significant resources in regard to processing time and material use. Furthermore, high feature densities are needed to enable high‐throughput and low sample volumes as generally regarded in combinatorial chemistry. Here, a scanning‐probe‐lithography‐based approach for the combinatorial in situ synthesis of macromolecules is presented in microarray format. Feature sizes below 40 µm allow for the creation of high‐density arrays with feature densities of 62 500 features per cm². To demonstrate feasibility of this approach for biomedical applications, a multiplexed array of functional protein tags (HA‐ and FLAG‐tag) is synthesized, and selective binding of respective epitope recognizing antibodies is shown. This approach uses only small amounts of base chemicals for synthesis and can be further parallelized, therefore, opening up a route to flexible, highly dense, and cost‐effective microarrays.     

Precise Patterning of Laterally Stacked Organic Microbelt Heterojunction Arrays by Surface‐Energy‐Controlled Stepwise Crystallization for Ambipolar Organic Field‐Effect Transistors

Ambipolar organic field‐effect transistors (OFETs) combining single‐crystalline p‐ and n‐type organic micro/nanocrystals have demonstrated superior performance to their amorphous or polycrystalline thin‐film counterparts. However, large‐area alignment and precise patterning of organic micro/nanocrystals for ambipolar OFETs remain challenges. Here, a surface‐energy‐controlled stepwise crystallization (SECSC) method is reported for large‐scale, aligned, and precise patterning of single‐crystalline laterally stacked p–n heterojunction microbelt (MB) arrays. In this method, the p‐ and n‐type organic crystals are precipitated via a stepwise process: first, the lateral sides of prepatterned photoresist stripes provide high‐surface‐energy sites to guide the aligned growth of p‐type organic crystals. Next, the formed p‐type crystals serve as new high‐surface‐energy positions to induce the crystallization of n‐type organic molecules at their sides, thus leading to the formation of laterally stacked p–n microbelts. Ambipolar OFETs based on the p–n heterojunction MB arrays exhibit balanced hole and electron mobilities of 0.32 and 0.43 cm² V^?1 s^?1, respectively, enabling the fabrication of complementary‐like inverters with large voltage gains. This work paves the way toward rational design and construction of single‐crystalline organic p–n heterojunction arrays for high‐performance organic, integrated circuits.     

MoS2 Negative‐Capacitance Field‐Effect Transistors with Subthreshold Swing below the Physics Limit

The Boltzmann distribution of electrons induced fundamental barrier prevents subthreshold swing (SS) from less than 60 mV dec^‐1 at room temperature, leading to high energy consumption of MOSFETs. Herein, it is demonstrated that an aggressive introduction of the negative capacitance (NC) effect of ferroelectrics can decisively break the fundamental limit governed by the “Boltzmann tyranny”. Such MoS₂ negative‐capacitance field‐effect transistors (NC‐FETs) with self‐aligned top‐gated geometry demonstrated here pull down the SS value to 42.5 mV dec^‐1, and simultaneously achieve superior performance of a transconductance of 45.5 μS μm and an on/off ratio of 4 × 10⁶ with channel length less than 100 nm. Furthermore, the inserted HfO₂ layer not only realizes a stable NC gate stack structure, but also prevents the ferroelectric P(VDF‐TrFE) from fatigue with robust stability. Notably, the fabricated MoS₂ NC‐FETs are distinctly different from traditional MOSFETs. The on‐state current increases as the temperature decreases even down to 20 K, and the SS values exhibit nonlinear dependence with temperature due to the implementation of the ferroelectric gate stack. The NC‐FETs enable fundamental applications through overcoming the Boltzmann limit in nanoelectronics and open up an avenue to low‐power transistors needed for many exciting long‐endurance portable consumer products.