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Contact lenses are widely used for vision correction and cosmetic purposes. Smart contact lenses offer further opportunities as functionalized non-invasive devices capable of simultaneous vision correction, real-time health monitoring and patient specific drug delivery. Herein, a low-cost vat photopolymerization technique is developed for directly 3D printing functionalized structures on commercially available contact lenses. The process enables controlled deposition of functionalized hydrogels, in customizable patterns, on the commercial contact lens surface with negligible optical losses. Multi-functional contact lenses can also be 3D printed with multiple materials deposited at different regions of the contact lens. Herein, the functionalities of colour blindness correction and real-time UV monitoring are demonstrated, by employing three suitable dyes incorporated into 2-hydroxyethyl methacrylate (HEMA) hydrogel structures printed on contact lenses. The results suggest that 3D printing can pave the way towards simple production of low-cost patient specific smart contact lenses. [ABSTRACT FROM AUTHOR]

Metalenses on a flexible template are engineered metal‐dielectric interfaces that improve conventional imaging system and offer dynamic focusing and zooming capabilities by controlling the focal length and bandwidth through a mechanical or external stretch. However, realizing large‐scale and cost‐effective flexible metalenses with high yields in a strain‐multiplex fashion remains as a great challenge. Here, single‐pulsed, maskless light interference and imprinting technique is utilized to fabricate reconfigurable, flexible metalenses on a large‐scale and demonstrate its strain‐multiplex tunable focusing. Experiments, in accordance with the theory, show that applied stretch on the flexible‐template reconfigurable diffractive metalenses (FDMLs) accurately mapped focused wavefront, bandwidth, and focal length. The surface relief metastructures consisted of metal‐coated hemispherical cavities in a hexagonal close‐packed arrangement to enhance tunable focal length, numerical aperture, and fill factor, FF ≈ 100% through normal and angular light illumination with external stretch. The strain‐multiplex of FDMLs approach lays the foundation of a new class of large‐scale, cost‐effective metalens offering tunable light focusing and imaging. [ABSTRACT FROM AUTHOR]

High-quality optical glass diffusers have applications in aerospace, displays, imaging systems, medical devices, and optical sensors. The development of rapid and accurate fabrication techniques is highly desirable for their production. Here, a micropatterning method for the fast fabrication of optical diffusers by means of nanosecond pulsed laser ablation is demonstrated (λ=1064 nm, power=7.02, 9.36 and 11.7 W and scanning speed=200 and 800 mm s-1). The experiments were carried out by point-to-point texturing of a glass surface in spiral shape. The laser machining parameters, the number of pulses and their power had significant effect on surface features. The optical characteristics of the diffusers were characterized at different scattering angles. The features of the microscale structures influenced average roughness from 0.8 μm to 1.97 μm. The glass diffusers scattered light at angles up to 20° and their transmission efficiency were measured up to ∼97% across the visible spectrum. The produced optical devices diffuse light less but do so with less scattering and energy losses as compared to opal diffusing glass. The presented fabrication method can be applied to any other transparent material to create optical diffusers. It is anticipated that the optical diffusers presented in this work will have applications in the production of LED spotlights and imaging devices. [ABSTRACT FROM AUTHOR]

Analyte-sensitive hydrogels that incorporate optical structures have emerged as sensing platforms for point-of-care diagnostics. The optical properties of the hydrogel sensors can be rationally designed and fabricated through self-assembly, microfabrication or laser writing. The advantages of photonic hydrogel sensors over conventional assay formats include label-free, quantitative, reusable, and continuous measurement capability that can be integrated with equipment-free text or image display. This Review explains the operation principles of photonic hydrogel sensors, presents syntheses of stimuli-responsive polymers, and provides an overview of qualitative and quantitative readout technologies. Applications in clinical samples are discussed, and potential future directions are identified. [ABSTRACT FROM AUTHOR]

The wing scales of Morpho butterflies contain 3D nanostructures that produce blue iridescent colors. Incident light is diffracted from multilayered nanostructures to create interference effects and diffract narrow‐band light. The intensity of the diffracted light remains high over a wide range of viewing angles. Structural coloration originating from the scales of Morpho wing nanostructures has been studied to analyze its optical properties and to produce scalable replicas. This review discusses computational and experimental methods to replicate these nanoarchitectures. Analytical and numerical methods utilized include multilayer models, the finite element method, and rigorous coupled‐wave analysis, which enable the optimization of nanofabrication techniques involving biotemplating, chemical vapour deposition, electron beam lithography, and laser patterning to mimic the wing scale nanostructure. Dynamic tunability of the morphology, refractive index, and chemical composition of the Morpho wing scales allows the realization of a numerous applications. [ABSTRACT FROM AUTHOR]

Willemite is a zinc silicate mineral used in modern day pottery as a decorative feature within glazes. It is produced by controlled heat treatment of zinc oxide-containing ceramic glazes. The heat-treated glazes devitrify, producing thin nanoscale needle-like willemite crystals growing in spherulitic morphologies through branching of the needles. We show here that this resulting morphology of willemite crystals in an inorganic glass matrix has a previously unreported strong interaction with light, displaying remarkable optical diffraction patterns. Thin sections of such spherulites act as optical diffusers, enabling light beams to be spread up to 160° in width. Analysis of the interaction between the willemite spherulites and light suggests that the high density of willemite crystals in the spherulites and the length scales associated with both the thickness of the needles and the spacings between branches are together responsible for this optical diffusion behaviour. [ABSTRACT FROM AUTHOR]

Developing highly efficient microcavities with predictive narrow-band resonance frequencies using the least amount of material will allow the applications in nonlinear photonic devices. We have developed a microcavity array that comprised multi-walled carbon nanotubes (MWCNT) organized in a biconvex pattern. The finite element model allowed designing microcavity arrays with predictive transmission properties and assessing the effects of the microarray geometry. The microcavity array demonstrated negative index and produced high Q factors. 2-3 im tall MWCNTs were patterned as biconvex microcavities, which were separated by 10 im in an array. The microcavity was iridescent and had optical control over the diffracted elliptical patterns with a far-field pattern, whose properties were predicted by the model. It is anticipated that the MWCNT biconvex microcavities will have implications for the development of highly efficient lenses, metamaterial antennas, and photonic circuits. [ABSTRACT FROM AUTHOR]

We computationally and experimentally demonstrate enhanced reflection effects displayed by silicon-based inverted nanocone arrays. A 3D finite element model is used to characterize the optical properties of the nanocone arrays with respect to the change in polarization and incident angles. The nanocone arrays are fabricated by e-beam lithography in hexagonal and triangular geometries with a lattice constant of 300 nm. The fabricated devices show a two-fold increase in reflection compared with bare silicon surface, as well as a strong diffraction within the visible and nearinfrared spectra. The nanocone arrays may find a variety of applications from optical devices to energy conservation technologies. [ABSTRACT FROM AUTHOR]

Flexible photonic devices based on soft polymers enable real-time sensing of environmental conditions in various industrial applications. A myriad of fabrication techniques have been established for producing optical devices, including photo and electron-beam lithography, nano/femtosecond laser writing, and surface imprinting or embossing. However, among these techniques, surface imprinting/embossing is simple, scalable, convenient to implement, can produce nanoscale resolutions, and is cost-effective. Herein, we utilize the surface imprinting method to replicate rigid micro/nanostructures onto a commonly available PDMS substrate, enabling the transfer of rigid nanostructures into flexible forms for sensing at a nanometric scale. The sensing nanopatterned sheets were mechanically extended, and the extension was remotely monitored via optical methods. Monochromatic light (450, 532, and 650 nm) was transmitted through the imprinted sensor under various force/stress levels. The optical response was recorded on an image screen and correlated with the strain created by the applied stress levels. The optical response was obtained in diffraction pattern form from the flexible grating-based sensor and in an optical-diffusion field form from the diffuser-based sensor. The calculated Young's modulus in response to the applied stress, measured through the novel optical method, was found in a reasonable range compared to the reported range of PDMS (360–870 kPa) in the literature. [ABSTRACT FROM AUTHOR]

A fundamental study of visible diffraction effects from patterned graphene layers is presented. By patterning graphene into optical gratings, visible diffraction from graphene is experimentally measured as a function of the number of layers and visible wavelengths. A practical application of these effects is also presented, by demonstrating an optical hologram based on graphene. A high resolution (pixel size 400 nm) intensity hologram is fabricated which, in response to incident laser light, generates a visible image. These findings suggest that visible diffraction in graphene can find practical application in holograms and should also be considered during the design and characterisation of graphene‐based optical applications. [ABSTRACT FROM AUTHOR]

We report the remarkable diffraction effects produced from circular patterned arrays of multiwalled carbon nanotubes (MWCNTs). Highly ordered circular arrays of multiwalled carbon nanotubes (with inter-nanotube spacings of 633 nm) display optical dispersion effects similar to compact discs. These arrays display remarkable diffraction patterns in the far field which are spatially continuous. High quality diffraction patterns were obtained experimentally which are in excellent agreement with the theoretical calculations. The achieved continuous diffraction patterns pave the way towards the utilization of engineered carbon nanotube arrays in applications like three dimensional holograms. [ABSTRACT FROM AUTHOR]

The forests of carbon nanotubes have been termed as the darkest man-made materials. Such materials exhibit near-perfect optical absorption (reflectance ∼ 0.045%) due to low reflectance and nanoscale surface roughness. We have demonstrated the utilization of these perfectly absorbing forests to produce binary amplitude cylindrical Fresnel lenses. The opaque Fresnel zones are defined by the dark nanotube forests and these lenses display efficient focusing performance at optical wavelengths. Lensing performance was analyzed both computationally and experimentally with good agreement. Such nanostructure based lenses have many potential applications in devices like photovoltaic solar cells. [ABSTRACT FROM AUTHOR]

We demonstrate metamaterials operating in the near-visible regime based on two-dimensional arrays of gold-coated silicon nanopillars. The nanopillar arrays demonstrate a cutoff response at the metamaterial plasma frequency in accordance with theory and can be utilized for filtering applications. A plasma frequency in the near visible region of λ = 1 μm is calculated numerically for an array with a lattice constant of 300 nm and wire radius of 50 nm, with reflection measurements in agreement with numerical calculations. Such structures can be utilized for achieving negative-index based metamaterials for the visible spectrum. [ABSTRACT FROM AUTHOR]

We report enhanced reflection displayed by arrays of silicon based inverted nanocones. Theoretical studies suggest that such arrays display enhanced reflection and photonic band gaps within the optical and near infrared regions. Measured results show three to four fold enhancement in reflection and agree well with calculations. Such arrays can be used to enhance infrared reflection in photovoltaic devices which mostly contribute towards heating. [ABSTRACT FROM AUTHOR]

In this manuscript, we demonstrate metamaterials based on two-dimensional high density arrays of metallic multiwalled carbon nanotubes. They demonstrate a cutoff response toward electromagnetic waves and can be utilized for filtering applications. The plasma frequency, where the metamaterial displayed a sharp change in the reflection and transmission, depends on the geometry of their two-dimensional cubic lattice. A plasma frequency in the near infrared region of 1.5 μm was calculated numerically, for an array consisting of multiwalled nanotubes, having radius of 50 nm and lattice constant of 400 nm. Reflection experiments conducted on the nanoscale structures were in excellent agreement with numerical calculations. [ABSTRACT FROM AUTHOR]

Diabetes mellitus (DM) presents a substantial global health concern due to elevated blood glucose levels, necessitating an affordable, rapid, and reliable continuous glucose monitoring (CGM) solution. In this pursuit, a pioneering approach is introduced utilizing optical fiber (OF) sensors based on nanocomposite photonic hydrogel functionalized with phenylboronic acid (PBA) for precise CGM. The fabrication of OF sensors involves a streamlined process, involving one‐step polymerization of PBA‐based hydrogel onto a commercial fiber tip and the integration of gold nanoparticles (AuNPs) via a simple dipping process. These sensors offer robust performance within the physiological glucose range (0–20 mm), exhibiting a remarkable 25% increase in transmission intensity and a 4 nm blue shift in the surface plasmon resonance with increasing glucose concentration. Additionally, there is a noticeable elevation in reflection intensity, affirming the sensor's suitability for remote sensing applications. These results are further validated using a green laser, underlining the method's reliability. The sensors exhibit a swift 30 s response time, followed by a 5 min saturation period, for all measurements. Practicality is demonstrated through smartphone readouts, utilizing the phone's photodiode to measure optical power changes concerning various glucose concentrations. These OF sensors hold great promise for CGM integration, enhancing diabetic management. [ABSTRACT FROM AUTHOR]

Colour vision disorders, pose challenges in perceiving and distinguishing specific colours. To address these challenges, technologies such as colour-filtering glasses and contact lenses have been developed. However, customisation of eyewear for individual patients remains a challenge. This research aims to design multifunctional contact lenses combining colour filtering and pH sensing capabilities for personalised colour vision correction. A pH-responsive, Neutral red dye-doped hydrogel was developed and optimised for the vat photo polymerization-based 3D printing process. A novel in-house multimaterial 3D printing technique was employed for printing lenses exhibiting both colour filtering and pH sensing capabilities. 3D printed samples contained outer radial rings, made from porous and pH-responsive polymer. The optically tunable dye-doped resin was also applied to the central part of the lenses to achieve customised wavelength blockage. The lenses demonstrate potential for customised colour vision correction and pH monitoring of the tear film. [ABSTRACT FROM AUTHOR]

Wearable medical devices (WMDs) will advance point-of-care diagnostics and therapeutics. This article analyses the market and patents for wearable devices. Activity monitors have the largest market share, and the intellectual property landscape is dominated by electronics corporations. However, the majority of these patents have not been realized in commercial products. [ABSTRACT FROM AUTHOR]

Optical fiber (OF) sensors are critical optical devices with excellent sensing capabilities and the capacity to operate in remote and hostile environments. However, integrating functional materials and micro/nanostructures into the optical fiber systems for specific sensing applications has limitations of compatibility, readiness, poor control, robustness, and cost-effectiveness. Herein, we have demonstrated the fabrication and integration of stimuli-responsive optical fiber probe sensors using a novel, low-cost, and facile 3D printing process. Thermal stimulus–response of thermochromic pigment micro-powders was integrated with optical fibers by incorporating them into ultraviolet-sensitive transparent polymer resins and then printed via a single droplet 3D printing process. Hence, the thermally active polymer composite fibers were grown (additively manufactured) on top of the commercial optical fiber tips. Then, the thermal response was studied within the temperature range of (25–35 °C) and (25–31 °C) for unicolor and dual color pigment powders-based fiber-tip sensors, respectively. The unicolor (with color to colorless transition) and dual color (with color to color transition) powders-based sensors exhibited substantial variations in transmission and reflection spectra by reversibly increasing and decreasing temperatures. The sensitivities were calculated from the transmission spectra where average change in transmission spectra was recorded as 3.5% with every 1 °C for blue, 3% for red and 1% for orange-yellow thermochromic powders based optical fiber tip sensors. Our fabricated sensors are cost-effective, reusable, and flexible in terms of materials and process parameters. Thus, the fabrication process can potentially develop transparent and tunable thermochromic sensors for remote sensing with a much simpler manufacturing process compared to conventional and other 3D printing processes for optical fiber sensors. Moreover, this process can integrate micro/nanostructures as patterns on the optical fiber tips to increase sensitivity. The developed sensors may be employed as remote temperature sensors in biomedical and healthcare applications. [ABSTRACT FROM AUTHOR]

Color blindness or color vision deficiency (CVD) is a congenital ocular deficiency that hampers patients' daily life activities. CVD patients rely mostly on using wearable visual aids that enhance color distinction by blocking problematic wavelengths of light. Contributing to that, this study examines the fabrication of 3D‐printed colored contact lens for color blindness management. A vat photopolymerization based 3D printing technology is utilized to fabricate the contact lenses for CVD patients. An in‐house prepared resin is mixed with a low‐cost colored ink to attain the desired blocking range (520–580 nm). The fabricated lens blocks more than 50% of light at the problematic wavelengths, along with exhibiting minimal leakage when stored and examined in water and contact lens storage solution. Average contact angle and water content values are 48° and 56%, respectively. Mechanical properties demonstrate the physical adequacy of the contact lens. The CVD filtering efficacy of the tinted contact lens and its potential as a CVD wearable is evaluated by comparing its optical performance with that of commercial products. Finally, cytotoxicity analysis of the lens to dermal fibroblast cells reveals the biocompatibility of the lens as the cell viability remains greater than 75% after 24 h. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) is a widely used additive manufacturing process that can be used for printing of intricate three dimensional (3D) metallic structures. Here we demonstrate the fabrication of titanium alloy Ti–6Al–4V alloy based 3D meshes with nodally-connected diamond like unit cells, with lattice spacing varying from 400 to 1000 microns. A Concept Laser M2 system equipped with laser that has a wavelength of 1075 nm, a constant beam spot size of 50μm and maximum power of 400W was used to manufacture the 3D meshes. These meshes act as optical shutters / directional transmitters and display interesting optical properties. A detailed optical characterisation was carried out and it was found that these structures can be optimised to act as scalable rotational shutters with high efficiencies and as angle selective transmission screens for protection against unwanted and dangerous radiations. The efficiency of fabricated lattice structures can be increased by enlarging the meshing size. [ABSTRACT FROM AUTHOR]

Additive manufacturing has revolutionised the production of intricate and complex structures, offering numerous applications across diverse industries. Among the additive manufacturing techniques, VAT photopolymerisation (VP) is a promising method for fabricating intricate structures with smooth surface finishes. However, the inherent limitations of 3D printed structures, such as compromised mechanical strength and conductivity, necessitate the incorporation of filler materials. Graphene, a remarkable two-dimensional carbon material renowned for its exceptional mechanical and electrical properties, emerges as a highly desirable filler of various applications. The review addresses the critical parameters that affect the quality and properties of graphene composites fabricated using VP, including the choice of photopolymer resin, exposure parameters, and pre and post-processing techniques. It also explores the functionalisation of graphene materials, multi-material printing and hybrid composite systems. The resulting graphene composites find applications in various fields, including electronics, aerospace, biomedicine and energy storage. This review presents a comprehensive survey of these applications, highlighting the unique advantages of VP-derived graphene composites. The challenges and future prospects in the field of VP for graphene composites are discussed. These encompass improving printability, achieving enhanced graphene dispersion, and exploring novel hybrid materials and innovative applications. [ABSTRACT FROM AUTHOR]

The benefits of enclosing pH sensors into wound dressings include treatment monitoring of wounded skin and early detection of developing chronic conditions, especially for diabetic patients. A 3D printed re-entrant auxetic hydrogel wound dressing, doped with pH indicator phenol red dye, was developed and characterized. The re-entrant auxetic design allows wound dressing adhesion to complex body parts, such as joints on arms and legs. Tensile tests revealed a yield strength of 140 kPa and Young's modulus of 78 MPa. In addition, the 3D-printed hydrogel has a swelling capacity of up to 14%, limited weight loss to 3% in six days, and porosity of near 1.2%. A reasonable pH response resembling human skin pH (4–10) was obtained and characterized. The integration of color-changing pH indicators allows patients to monitor the wound's healing process using a smartphone. In addition to the above, the mechanical properties and their dependence on post-processing were studied. The results show that the resin composition and the use of post-treatments significantly affect the quality and durability of the wound dressings. Finally, a poly (acrylic acid) (PAA) and water-based adhesive was developed and used to demonstrate the performance of the auxetic wound dressing when attached to moving body joints. [ABSTRACT FROM AUTHOR]

Titanium oxides have a wide range of applications in industry, and they can be formed on pure titanium using different methods. Laser-induced oxidation is one of the most reliable methods due to its controllability and selectivity. Colour marking is one of the main applications of the oxidation process. However, the colourizing process based on laser scanning strategies is limited by the relative large processing area in comparison to the beam size. Single spot oxidation of titanium substrates is proposed in this research in order to increase the resolution of the processed area and also to address the requirements of potential new applications. The method is applied to produce oxide films with different thicknesses and hence colours on titanium substrates. High resolution colour image is imprinted on a sheet of pure titanium by converting its pixels’ colours into laser parameter settings. Optical and morphological periodic surface structures are also produced by an array of oxide spots and then analysed. Two colours have been coded into one field and the dependencies of the reflected colours on incident and azimuthal angles of the light are discussed. The findings are of interest to a range of application areas, as they can be used to imprint optical devices such as diffusers and Fresnel lenses on metallic surfaces as well as for colour marking. [ABSTRACT FROM AUTHOR]

The development of nanostructures that can be reversibly arranged and assembled into 3D patterns may enable optical tunability. However, current dynamic recording materials such as photorefractive polymers cannot be used to store information permanently while also retaining configurability. Here, we describe the synthesis and optimization of a silver nanoparticle doped poly(2-hydroxyethyl methacrylate-co-methacrylic acid) recording medium for reversibly recording 3D holograms. We theoretically and experimentally demonstrate organizing nanoparticles into 3D assemblies in the recording medium using optical forces produced by the gradients of standing waves. The nanoparticles in the recording medium are organized by multiple nanosecond laser pulses to produce reconfigurable slanted multilayer structures. We demonstrate the capability of producing rewritable optical elements such as multilayer Bragg diffraction gratings, 1D photonic crystals, and 3D multiplexed optical gratings. We also show that 3D virtual holograms can be reversibly recorded. This recording strategy may have applications in reconfigurable optical elements, data storage devices, and dynamic holographic displays. [ABSTRACT FROM AUTHOR]

A sensor for monitoring of the external corrosion of small-diameter aboveground oil and gas pipelines (called flowlines), based on fiber-optic strain sensing, is proposed. The working principle of our proposed sensor relies on the use of a pre-stressed sacrificial structure made of the same material as the pipeline and monitoring changes in the measured strain that occur due to deterioration caused by corrosion to the structure. We present the development of analytical equations that allow designing the sensor structure to achieve the desired strain values. The analysis was verified using commercial finite element analysis (FEA) software. The proposed sensor is simple and cost-effective and can be easily manufactured. It can be deployed on existing overground pipelines without any modification to the pipeline structure. While it is not capable of measuring the corrosion rate continuously, it can provide a measurement of the average corrosion rate over the life span of its sacrificial metal structure. [ABSTRACT FROM AUTHOR]

Computational chemistry, molecular docking, and drug design approaches, combined with the biochemical evaluation of the antitumor activity of selected derivatives of the thiouracil-based dihydroindeno pyrido pyrimidines against topoisomerase I and II. The IC50 of other cell lines including the normal human lung cell line W138, lung cancer cell line, A549, breast cancer cell line, MCF-7, cervical cancer, HeLa, and liver cancer cell line HepG2 was evaluated using biochemical methods. The global reactivity descriptors and physicochemical parameters were computed, showing good agreement with the Lipinski and Veber's rules of the drug criteria. The molecular docking study of the ligands with the topoisomerase protein provides the binding sites, binding energies, and deactivation constant for the inhibition pocket. Various biochemical methods were used to evaluate the IC50 of the cell lines. The QSAR model was developed for colorectal cell line HCT as a case study. Four QSAR statistical models were predicted between the IC50 of the colorectal cell line HCT to correlate the anticancer activity and the computed physicochemical and quantum chemical global reactivity descriptors. The predictive power of the models indicates a good correlation between the observed and the predicted activity. [ABSTRACT FROM AUTHOR]

ABSTRACT A mixture of two polymer materials, poly (9,9-dioctylfluorene) (F8), and one of the poly( para-phenylenevinylene) derivatives, superyellow (SY) have been used to make F81− x:SY x polymer blend system. Under a 3-5 ns pulsed-laser excitation, this system showed excellent optical properties with low threshold values of ≈14 µJ/cm2 and ≈8 µJ/cm2 for amplified spontaneous emission and optically pumped lasing, respectively. The proposed system was also electroluminescent and an interesting candidate for future research on polymer injection lasers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 15-21 [ABSTRACT FROM AUTHOR]

We propose a sensor design for measurement of large strains where direct application of a fiber optic strain gauge is impossible due to the stiffness mismatch between the optical fiber and the structure under test. The sensor design is based on a rhombus type compliant mechanism, which functions to attenuate input strain and transfer it to the ends of the sensing beam with the mounted optical strain gauge. We developed an analytical model of the sensor, which allows us to relate actuation forces, input displacement/strain, and output strain. The analytical model was verified with the finite element analysis and validated against an experimental prototype. The prototype sensor was able to handle input strains exceeding ±2.5 × 105 µε. Potential application areas of the proposed sensor include compliant elastomeric structures, wearables, and soft robotics. [ABSTRACT FROM AUTHOR]

Surface functionalization of metallic nanoparticles (NPs) with external groups can be engineered to fabricate sensors that are responsive to various stimuli like temperature, pH, and numerous ions. Herein, we report the synthesis of gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (GNPs-MPA) and the doping of these nanoparticles into hydrogel materials using the breathing-in/breathing-out (BI-BO) method. MPA has a carboxyl group that becomes protonated and, thus, ionized at a pH below its pKa (4.32); hence, the GNPs-MPA solutions and gels were mostly pH-responsive in the range of 3–5. Optical properties were assessed through ultraviolet-visible (UV-Vis) spectroscopy, namely: transmission and absorption, and the parameters used to quantify the pH changes were the full width at half maximum (FWHM) and position of surface plasmon resonance (SPR). The solutions and gels gradually changed their colors from red to indigo with pH decrementation from 5 to 3, respectively. Furthermore, the solutions' and doped gels' highest FWHM sensitivities towards pH variations were 20 nm and 55 nm, respectively, while the SPR's position sensitivities were 18 nm and 10 nm, respectively. Also, transmission and scanning electron microscopy showed synchronized dispersion and aggregation of NPs with pH change in both solution and gel forms. The gel exhibited excellent repeatability and reversibility properties, and its response time was instantaneous, which makes its deployment as a colorimetric pH-triggered sensor practical. To the best of our knowledge, this is the first study that has incorporated GNPs into hydrogels utilizing the BI-BO method and demonstrated the pH-dependent optical and colorimetric properties of the developed nanocomposites. [ABSTRACT FROM AUTHOR]

Wounds are a major health concern affecting the lives of millions of people. Some wounds may pass a threshold diameter to become unrecoverable by themselves. These wounds become chronic and may even lead to mortality. Recently, 3D printing technology, in association with biocompatible hydrogels, has emerged as a promising platform for developing smart wound dressings, overcoming several challenges. 3D printed wound dressings can be loaded with a variety of items, such as antibiotics, antibacterial nanoparticles, and other drugs that can accelerate wound healing rate. 3D printing is computerized, allowing each level of the printed part to be fully controlled in situ to produce the dressings desired. In this review, recent developments in hydrogel-based wound dressings made using 3D printing are covered. The most common biosensors integrated with 3D printed hydrogels for wound dressing applications are comprehensively discussed. Fundamental challenges for 3D printing and future prospects are highlighted. Additionally, some related nanomaterial-based hydrogels are recommended for future consideration. [ABSTRACT FROM AUTHOR]

Nanotube forest behaves as highly absorbent material when they are randomly placed in sub-wavelength scales. Furthermore, it is possible to create diffractive structures when these bulks are patterned in a substrate. Here, we introduce an alternative to fabricate intensity holograms by patterning fringes of nanotube forest on a substrate. The result is an efficient intensity hologram that is not restricted to sub-wavelength patterning. Both the theoretical and experimental analysis was performed with good agreement. The produced holograms show a uniform behaviour throughout the visible spectra. [ABSTRACT FROM AUTHOR]

Dual detection systems are of interest for rapid, accurate data collection in sensing systems and in vitro testing. We introduce an IrIII complex with a boronic acid receptor site attached to the 2‐phenylpyridine ligand as an ideal probe with photo‐ and electrochemical signals that is sensitive to monosaccharide binding in aqueous solution. The complex displays orange luminescence at 618 nm, which is reduced by 70 and 40 % upon binding of fructose and glucose, respectively. The electro‐chemiluminescent signal of the complex also shows a direct response to monosaccharide binding. The IrIII complex shows the same response upon incorporation into hydrogel matrices as in solution, thus demonstrating the potential of its integration into a device, as a nontoxic, simple‐to‐use tool to observe sugar binding over physiologically relevant pH ranges and saccharide concentrations. Moreover, the complex's luminescence is responsive to monosaccharide presence in cancer cells. [ABSTRACT FROM AUTHOR]

Contact lenses can be functionalized to offer advanced capabilities transcending their primary applications in vision correction and cosmetics. Herein, 40 and 60 nm spherical silver nanoparticles (SNPs) are integrated within poly(2‐hydroxyethyl methacrylate) (pHEMA) contact lenses toward fabrication of SNP‐loaded contact lenses with excellent optical and material properties as wearables for blue‐yellow color vision deficiency (CVD) patients. The morphology and optical properties of the SNPs are characterized prepolymerization using the transmission electron microscopy (TEM) and an optical spectrophotometer. Then, the transmission spectra of the SNP‐loaded contact lenses at different concentrations along with the wettability and water content are measured, to demonstrate the effect of NPs' addition on the lenses' optical and material characteristics. Results indicate that the transmission spectra of SNP‐loaded contact lenses, with optimum concentrations, filter out problematic wavelengths of visible light (485–495 nm), which will facilitate better color distinction for blue‐yellow CVD patients. The contact lenses' optical properties are analogous to the commercial colorblind glasses, indicating their effectiveness as color filtering wearables. Finally, the cytobiocompatability analysis of the contact lenses to RAW 264.7 culture of cells shows that they are biocompatible, and the cell viability remains higher than 75% after 24 h in contact with the lenses. [ABSTRACT FROM AUTHOR]

A hybrid liquid crystal and carbon nanotube‐based device which shows the capacity to perform as a switchable diffraction grating is demonstrated. A liquid crystal layer was sandwiched between two electrodes (patterned into gratings). The bottom electrode consists of a two dimensional square array of carbon nanotubes, while the top electrode comprises an ITO‐based in‐plane switching electrode on glass. The carbon nanotubes, due to their high aspect ratios, produce defects within the liquid crystal layer, producing a two dimensional grating. The device displays distinct voltage‐dependent diffraction patterns due to the two different electrodes. The diffraction patterns are studied both computationally and experimentally, with good agreement between the results obtained. Both the diffraction pattern and efficiency from the device could be switched by varying the applied voltage across the liquid crystal layer. [ABSTRACT FROM AUTHOR]

Periodic highly dense multi-wall carbon nanotube (MWCNT) arrays can act as photonic materials exhibiting band gaps in the visible regime and beyond terahertz range. MWCNT arrays in square arrangement for nanoscale lattice constants can be configured as a microcavity with predictable resonance frequencies. Here, computational analyses of compact square microcavities (≈0.8x0.8 µm²) in MWCNT arrays were demonstrated to obtain enhanced quality factors (≈170-180) and narrow-band resonance peaks. Cavity resonances were rationally designed and optimized (nanotube geometry and cavity size) with finite element method. Series (1x2 and 1x3) and parallel (2x1 and 3x1) combinations of microcavities were modeled and resonance modes were analyzed. Higher order MWCNT microcavities showed enhanced resonance modes, which were red shifted with increasing Q-factors. Parallel microcavity geometries were also optimized to obtain narrow-band tunable filtering in low-loss communication windows (810, 1336, and 1558 nm). Compact series and parallel MWCNT microcavity arrays may have applications in optical filters and miniaturized optical communication devices. [ABSTRACT FROM AUTHOR]

Corrosion in the oil and gas industry represents one of the major problems that affect oil production and transportation processes. Several corrosion-inspection technologies are in the market to detect internal and external corrosion of oil storage tanks, but inspection of storage tanks occurs every 3 to 7 years. In between inspection interval, aggressive corrosion can potentially occur, which makes the oil and gas industry vulnerable to accidents. This study proposes a new internal corrosion detection sensor based on the magnetic interaction between a rare-earth permanent magnet and the ferromagnetic nature of steel, used to manufacture oil storage tanks. Finite element analysis (FEA) software was used to analyze the effect of various sensor parameters on the attractive force between the magnet and the steel. The corrosion detection sensor is designed based on the FEA results. The experimental testing of the sensor shows that it is capable of detecting internal metal loss due to corrosion in oil storage tanks within approximately 8 mm of the internal surface thickness. The sensor showed more than two-fold improvement in the detection range compared to previous sensor proposed by the authors. Furthermore, the sensor of this paper provides a monitoring rather than occasional inspection solution. [ABSTRACT FROM AUTHOR]

Color blindness or color vision deficiency (CVD) affects around 4.5% of the population in Europe. There have been several attempts to assist color‐blind individuals using color filter glasses. Here, contact lenses are developed to assist individuals suffering from color blindness. Two dyes (Atto 488 and 565) that provide the desired absorption wavelength ranges are selected to be immobilized in soft contact lenses. The chosen dyes have absorption bands in wavelength ranges of 480–500 and 550–580 nm. Both dyes are individually immobilized in contact lenses, and over 95% of the light in the undesired ranges are blocked. The dyes do not diffuse out from lenses in artificial tears and contact lens storage solution. Performances of the developed contact lenses are compared to commercial color‐blind glasses. The contact lenses are tested in color vision deficient patients using Ishihara test. Participants indicate enhancement in the visibility of the colors and their contrast in a color rich environment. The proposed contact lenses show enhanced results as compared to commercial color‐blind glasses in indoors and achieved similar outcomes outdoors. [ABSTRACT FROM AUTHOR]

In this article, using the integration of paper microfluidics within laser-inscribed commercial contact lenses, we demonstrate the multiplexed detection of clinically relevant analytes including hydrogen ions, proteins, glucose, nitrites and L -ascorbic acid, all sampled directly from model tears. In vitro measurements involved the optimization of colorimetric assays, with readouts collected, stored and analyzed using a bespoke Tears Diagnostics smartphone application prototype. We demonstrate the potential of the device to perform discrete measurements either for medical diagnosis or disease screening in the clinic or at the point-of-care (PoC), with future applications including monitoring of ocular infections, uveitis, diabetes, keratopathies and assessing oxidative stress. [ABSTRACT FROM AUTHOR]

Color vision deficiency (CVD) or color blindness is an ocular disorder that hinders the patients from distinguishing shades of certain colors. Color blind patients are often not considered for critical occupations (e.g., military, police) and cannot differentiate colors in public places or media (i.e., watching TV). The most common form of color blindness is red‐green, which is a result of either a missing or defective red or green photoreceptor cone. Since no cure for this disorder exists, sufferers opt for methods to enhance their color perception. The products and methods that have been developed to aid CVD patients are discussed. These technologies include contemporary work on gene therapy, tinted glasses, lenses, optoelectronic glasses, and advanced features developed on smartphones and computers. Among these wearables, tinted glasses, developed by companies such as Enchroma, are the most widely used by CVD patients. [ABSTRACT FROM AUTHOR]

Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3′,5,5′‐tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L−1. The dermal albumin sensor consisted of 3′,3′′,5′,5′′‐tetrachlorophenol‐3,4,5,6‐tetrabromosulfophthalein to measure concentrations up to 5.0 g L−1. The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid–base homeostasis, diabetes, and liver failure in point‐of‐care settings. [ABSTRACT FROM AUTHOR]

Tattooing is a ubiquitous body modification involving the injection of ink and/or dye pigments into the dermis. Biosensors in the form of tattoos can be used to monitor metabolites in interstitial fluid. Here, minimally invasive, injectable dermal biosensors were developed for measuring pH, glucose, and albumin concentrations. The dermal pH sensor was based on methyl red, bromothymol blue, and phenolphthalein, which responded to a pH range from 5.0 to 9.0. The dermal glucose sensor consisted of glucose oxidase, 3,3′,5,5′‐tetramethylbenzidine, and peroxidase that detected concentrations up to 50.0 mmol L−1. The dermal albumin sensor consisted of 3′,3′′,5′,5′′‐tetrachlorophenol‐3,4,5,6‐tetrabromosulfophthalein to measure concentrations up to 5.0 g L−1. The sensors were multiplexed in ex vivo skin tissue and quantitative readouts were obtained using a smartphone camera. These sensors can be used to manage of acid–base homeostasis, diabetes, and liver failure in point‐of‐care settings. [ABSTRACT FROM AUTHOR]

Continuous glucose monitoring facilitates the stringent control of blood glucose concentration in diabetic and intensive care patients. Optical fibers have emerged as an attractive platform; however, their practical applications are hindered due to lack of biocompatible fiber materials, complex and non-practical readout approaches, slow response, and time-consuming fabrication processes. Here, we demonstrate the quantification of glucose by smartphone-integrated fiber optics that overcomes existing technical limitations. Simultaneously, a glucose-responsive hydrogel was imprinted with an asymmetric microlens array and was attached to a multimode silica fiber's tip during photopolymerization, and subsequent interrogated for glucose sensing under physiological conditions. A smartphone and an optical power meter were employed to record the output signals. The functionalized fiber showed a high sensitivity (2.6 μW mM−1), rapid response, and a high glucose selectivity in the physiological glucose range. In addition, the fiber attained the glucose complexation equilibrium within 15 min. The lactate interference was also examined and it was found minimal ∼0.1% in the physiological range. A biocompatible hydrogel made of polyethylene glycol diacrylate was utilized to fabricate a flexible hydrogel fiber to replace the silica fiber, and the fiber's tip was functionalized with the glucose-sensitive hydrogel during the ultraviolet light curing process. The biocompatible fiber was quickly fabricated by the molding, the readout approach was facile and practical, and the response to glucose was comparable to the functionalized silica fiber. The fabricated optical fiber sensors may have applications in wearable and implantable point-of-care and intensive-care continuous monitoring systems. • Fiber optic probes are demonstrated for continuous glucose monitoring. • A smartphone is exploited for detecting the probe's output signals. • The optical technique simplifies the fabrication and readout of the fiber optic probes. • The probe shows a high sensitivity in the physiological glucose range. • Biocompatible hydrogel fiber probe enables implantable applications. [ABSTRACT FROM AUTHOR]

The applications of optical fibers are impeded in implantable medical diagnostics due to incompatibility with biological tissues, and immune reaction in vivo. The utilization of biocompatible materials to construct a photonic sensing platform can reduce the immune response in in vivo medical diagnostics. Here, we developed real-time optical fiber sensors to determine the volumetric modulation of stimuli-responsive polymers. Asymmetric microlens structures were replicated on stimuli-sensitive hydrogels as stand-alone sensors and were chemically attached to the tips of silica and biocompatible optical fibers. Quantitative measurements were carried out using a smartphone to demonstrate the ease, simplicity, and practicality of the readout methodology. To demonstrate the utility in real-time sensing, the fiber probe was investigated in various concentrations of ethanol, propan-2-ol, and dimethyl sulfoxide. Also, the fiber probe showed a rapid response to pH in the acidic region with a sensitivity of 40 nW pH−1. To develop biocompatible probes for physiological applications, a microlens array-imprinted polymer was attached to the tip of a hydrogel optical fiber. The optical fiber probe in the refection configuration showed a sensitivity of 7 nW pH−1. The developed hydrogel fiber probes may have application in point-of-care diagnostics, continuous biomarker monitoring, and critical care sensing devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fiber-optic sensor for real-time monitoring glucose concentration. • Three hydrogel-based glucose sensors have been developed with smartphone readout. • The sensors have been tested in reflection and transmission mode. • The sensors have showed robust performance and high sensitivity along with a rapid response. Diabetes has become one of the leading deaths causes worldwide. Developing low-cost, rapid, and reusable sensors can provide a solution for continuous glucose monitoring to reduce the diabetic complications that could be fatal. Here, Phenylboronic acid (PBA)-based hydrogel sensors with embedded photonic nanostructures were developed for rapid and continuous glucose quantification within the physiological range. The photonic nanostructures were imprinted on the PBA-based hydrogel using simple and rapid process. Three different sensors: free-standing (FS), stand-alone (SA), and optical fiber (OF) were fabricated and tested in the glucose concentration range of 0–50 mM. A sensitivity of 6, 3, and 1.2 µW/mM was documented for FS, SA, and OF sensors, respectively. A rapid response time of 20 s and saturation time of 3 min were recorded along with a limit of detection of 1 mM. The sensing capabilities of these sensors were examined in both transmission and reflection configurations. Practicality of the sensors was tested using smartphone readout. The optical power was measured using a smartphone exploiting its photodiode and the power changes were correlated with glucose concentrations. These developed sensors may have applications in remote, continuous, and real-time glucose monitoring systems. [ABSTRACT FROM AUTHOR]