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Search Results (2,443)

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37 pages, 7422 KiB  
Review
Trends in Flexible Sensing Technology in Smart Wearable Mechanisms–Materials–Applications
by Sen Wang, Haorui Zhai, Qiang Zhang, Xueling Hu, Yujiao Li, Xin Xiong, Ruhong Ma, Jianlei Wang, Ying Chang and Lixin Wu
Nanomaterials 2025, 15(4), 298; https://doi.org/10.3390/nano15040298 (registering DOI) - 15 Feb 2025
Abstract
Flexible sensors are revolutionizing our lives as a key component of intelligent wearables. Their pliability, stretchability, and diverse designs enable foldable and portable devices while enhancing comfort and convenience. Advances in materials science have provided numerous options for creating flexible sensors. The core [...] Read more.
Flexible sensors are revolutionizing our lives as a key component of intelligent wearables. Their pliability, stretchability, and diverse designs enable foldable and portable devices while enhancing comfort and convenience. Advances in materials science have provided numerous options for creating flexible sensors. The core of their application in areas like electronic skin, health medical monitoring, motion monitoring, and human–computer interaction is selecting materials that optimize sensor performance in weight, elasticity, comfort, and flexibility. This article focuses on flexible sensors, analyzing their “sensing mechanisms–materials–applications” framework. It explores their development trajectory, material characteristics, and contributions in various domains such as electronic skin, health medical monitoring, and human–computer interaction. The article concludes by summarizing current research achievements and discussing future challenges and opportunities. Flexible sensors are expected to continue expanding into new fields, driving the evolution of smart wearables and contributing to the intelligent development of society. Full article
(This article belongs to the Special Issue Polymeric 3D Printing: Applications in Nanoscience and Nanotechnology)
49 pages, 3382 KiB  
Review
Recent Advances in the Fabrication of Intelligent Packaging for Food Preservation: A Review
by Tshamisane Mkhari, Jerry O. Adeyemi and Olaniyi A. Fawole
Processes 2025, 13(2), 539; https://doi.org/10.3390/pr13020539 - 14 Feb 2025
Abstract
The advancement of intelligent packaging technologies has emerged as a pivotal innovation in the food industry, significantly enhancing food safety and preservation. This review explores the latest developments in the fabrication of intelligent packaging, with a focus on applications in food preservation. Intelligent [...] Read more.
The advancement of intelligent packaging technologies has emerged as a pivotal innovation in the food industry, significantly enhancing food safety and preservation. This review explores the latest developments in the fabrication of intelligent packaging, with a focus on applications in food preservation. Intelligent packaging systems, which include sensors, indicators, and RFID technologies, offer the real-time monitoring of food quality and safety by detecting changes in environmental conditions and microbial activity. Innovations in nanotechnology, bio-based materials, and smart polymers have led to the development of eco-friendly and highly responsive packaging solutions. This review underscores the role of active and intelligent packaging components—such as oxygen scavengers, freshness indicators, and antimicrobial agents in extending shelf life and ensuring product integrity. Moreover, it highlights the transformative potential of intelligent packaging in food preservation through the examination of recent case studies. Finally, this review provides a comprehensive overview of current trends, challenges, and potential future directions in this rapidly evolving field. Full article
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<p>Classification of time–temperature indicators (TTIs) [<a href="#B47-processes-13-00539" class="html-bibr">47</a>]. Reproduced with permission from J Food Process Technol, under the terms of the Creative Commons Attribution License (Copyright, 2021).</p>
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<p>The uses of nanocomposites in food packaging [<a href="#B113-processes-13-00539" class="html-bibr">113</a>]. Reproduced with permission from Springer, copyright (2024).</p>
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<p>Potential uses of microfluidics in the field of food science as well as technology [<a href="#B152-processes-13-00539" class="html-bibr">152</a>]. Reproduced with permission from MDPI under the terms of the Creative Commons Attribution License (Copyright, 2022).</p>
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<p>Temperature-responsive polymers of (<b>A</b>) lemon essential oil [<a href="#B265-processes-13-00539" class="html-bibr">265</a>] and (<b>B</b>) cinnamon essential oil based on PNIPAm [<a href="#B266-processes-13-00539" class="html-bibr">266</a>]. Both figures are reproduced with permission from Elsevier (Copyright, 2024).</p>
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<p>Various types of pH indicators employed in intelligent packaging [<a href="#B267-processes-13-00539" class="html-bibr">267</a>]. Reproduced with permission from Taylor and Francis (Copyright, 2024).</p>
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16 pages, 4129 KiB  
Article
Nonlinear Dynamics of a Piezoelectric Bistable Energy Harvester Using the Finite Element Method
by Virgilio J. Caetano and Marcelo A. Savi
Appl. Sci. 2025, 15(4), 1990; https://doi.org/10.3390/app15041990 - 14 Feb 2025
Abstract
The conversion of ambient mechanical vibrational energy into electrical energy through piezoelectric devices has received an increasing attention in recent years. The main challenges are to develop efficient devices that operate over a wide frequency range, adapting to diverse environmental energy sources. This [...] Read more.
The conversion of ambient mechanical vibrational energy into electrical energy through piezoelectric devices has received an increasing attention in recent years. The main challenges are to develop efficient devices that operate over a wide frequency range, adapting to diverse environmental energy sources. This work presents a framework for the analysis of a nonlinear vibration-based energy harvesting devices combining the nonlinear finite element method with a reduced-order model, which provides a broader dynamical investigation. On this basis, a flexible tool is developed, allowing the multimodal analysis of nonlinear systems. A bistable piezoelectric energy harvesting device is investigated considering the influence of multimodal and nonlinear effects on the system performance. Bistability is due to magnetic interactions among magnets and the beam tip, modeled by cubic nonlinearities. Numerical simulations show the influence of vibration sources on the dynamics and performance of the device. Nonlinear effects furnish rich dynamics, presenting periodic and chaotic responses. All these effects can be combined to enhance energy harvesting capacity. Full article
(This article belongs to the Special Issue Nonlinear Dynamics and Vibration)
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<p>Schematic representation of (<b>a</b>) linear energy harvester and (<b>b</b>) bimorph beam cross section.</p>
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<p>Schematic representation of a nonlinear energy harvesting device comprising a ferromagnetic bimorph beam with magnetic interactions.</p>
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<p>Schematic of FE model of energy harvester with a magnetic force <math display="inline"><semantics> <mrow> <msub> <mrow> <mi>f</mi> </mrow> <mrow> <mi>M</mi> </mrow> </msub> </mrow> </semantics></math>, a resistive load <math display="inline"><semantics> <mrow> <mi>R</mi> </mrow> </semantics></math>, boundary displacement conditions <math display="inline"><semantics> <mrow> <mi>U</mi> </mrow> </semantics></math> and coupled voltage DOF to emulate the electrodes.</p>
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<p>Magnetic force variation with lateral displacement.</p>
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<p>Bifurcation diagram built with the reduced-order model.</p>
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<p>Reduced-order model analysis considering an excitation frequency of 70 Hz. Phase space and displacement time-history for different excitation amplitudes: (<b>a</b>) Intra-well response (0.15 mm); (<b>b</b>) chaotic response (0.4 mm); and (<b>c</b>) inter-well response (1.0 mm). The blue and gray solid lines represent the time-history, while the black and blue markers represent the Poincare’s section.</p>
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<p>FE model analysis considering an excitation frequency of 70 Hz. Phase space and output voltage time-history for different excitation amplitudes: (<b>a</b>) Intra-well response (0.15 mm); (<b>b</b>) chaotic response (0.4 mm); and (<b>c</b>) inter-well response (1.0 mm). The red and gray solid lines represent the time-history response, while the red markers represent the Poincare’s section.</p>
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<p>Frequency response curve for linear energy harvester.</p>
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<p>F Responses for frequencies smaller than the first resonant condition for base excitation of 0.2 mm. Phase space and output voltage time-history at steady-state condition for different excitation frequencies: (<b>a</b>) 35 Hz, (<b>b</b>) 48 Hz and (<b>c</b>) 50 Hz.</p>
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<p>Response for frequencies bigger than the first resonant condition for base excitation of 0.4 mm. Phase space and output voltage time-history for different excitation frequencies: (<b>a</b>) 300 Hz and (<b>b</b>) 500 Hz.</p>
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11 pages, 9905 KiB  
Proceeding Paper
Production Parameters and Thermo-Mechanical Performance of Twisted and Coiled Artificial Muscles (TCAMs)
by Salvatore Garofalo, Chiara Morano, Leonardo Pagnotta and Luigi Bruno
Eng. Proc. 2025, 85(1), 1; https://doi.org/10.3390/engproc2025085001 - 13 Feb 2025
Abstract
High-strength polymer fibers such as nylon 6, nylon 6,6, and polyethylene are utilized to produce Twisted and Coiled Artificial Muscles (TCAMs) through the twisting of low-cost fibers. These artificial muscles exhibit high displacement and specific power, particularly under electrothermal actuation, which requires conductive [...] Read more.
High-strength polymer fibers such as nylon 6, nylon 6,6, and polyethylene are utilized to produce Twisted and Coiled Artificial Muscles (TCAMs) through the twisting of low-cost fibers. These artificial muscles exhibit high displacement and specific power, particularly under electrothermal actuation, which requires conductive elements. An experimental setup was developed to produce, thermally treat, and characterize commercially available nylon 6,6 fibers coated with silver. The results demonstrate that TCAMs can contract by over 15% and generate forces up to 2.5 N with minimal energy input. Key factors such as motor speed, applied load, and fiber geometry affect the overall performance. Full article
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<p>Manufacturing process of TCAM: twisting and coiling are necessary to create the structure of the artificial muscle; annealing and training allow to relax stress during the previous steps and set the geometry; plying is needed when multi-plies geometries are required.</p>
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<p>SEM analysis performed on the precursor fibers: (<b>a</b>) SEM image obtained of the Shieldex 235/36x4 HCB precursor fiber; (<b>b</b>) SEM magnification of (<b>a</b>).</p>
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<p>Micrographs taken of the precursor fibers and determination of their average diameters: (<b>a</b>) Shieldex 117/17x2 HCB; (<b>b</b>) Shieldex 235/36x2 HCB; (<b>c</b>) Shieldex 235/36x4 HCB.</p>
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<p>Schematic representation of the experimental setup (on the <b>left</b>) and its prototyping (on the <b>right</b>).</p>
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<p>Results of percentage displacement obtained for TCAMs made from the Shieldex 235/36x4 HCB fiber at the three rotational speeds during production: <span class="html-italic">ω</span> = 300 rpm (red curve); <span class="html-italic">ω</span> = 600 rpm (blue curve); <span class="html-italic">ω</span> = 900 rpm (black curve). The tests were conducted with a supply current of 0.6 A.</p>
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<p>Results of percentage displacement obtained for TCAMs made from the Shieldex 235/36x2 HCB fiber at the three rotational speeds during production: <span class="html-italic">ω</span> = 300 rpm (red curve); <span class="html-italic">ω</span> = 600 rpm (blue curve); <span class="html-italic">ω</span> = 900 rpm (black curve). The tests were conducted with a supply current of 0.35 A.</p>
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<p>Results of percentage displacement obtained for TCAMs made from the Shieldex 117/17x2 HCB fiber at the three rotational speeds during production: <span class="html-italic">ω</span> = 300 rpm (red curve); <span class="html-italic">ω</span> = 600 rpm (blue curve); <span class="html-italic">ω</span> = 900 rpm (black curve). The tests were conducted with a supply current of 0.15 A.</p>
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<p>Experimental results in terms of displacement obtained for TCAMs produced with a DC motor rotational speed of <span class="html-italic">ω</span> = 300 rpm, using increasing supply currents. The graphs refer to the following precursor fibers: (<b>a</b>) Shieldex 235/36x4 HCB; (<b>b</b>) Shieldex 235/36x2 HCB; (<b>c</b>) Shieldex 117/17x2 HCB.</p>
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13 pages, 8457 KiB  
Article
Electromagnetic Properties of Natural Plant Leaves for Eco-Friendly and Biodegradable Substrates for Wireless IoT Devices
by Nikolay Todorov Atanasov, Blagovest Nikolaev Atanasov and Gabriela Lachezarova Atanasova
Sensors 2025, 25(4), 1118; https://doi.org/10.3390/s25041118 - 12 Feb 2025
Abstract
Today, innovative engineering solutions, including IoT devices, enable the precise monitoring of plant health and the early detection of diseases. However, the lifespan of IoT devices used for the real-time monitoring of environmental or plant parameters in precision agriculture is typically only a [...] Read more.
Today, innovative engineering solutions, including IoT devices, enable the precise monitoring of plant health and the early detection of diseases. However, the lifespan of IoT devices used for the real-time monitoring of environmental or plant parameters in precision agriculture is typically only a few months, from planting to harvest. This short lifespan creates challenges in managing the e-waste generated by smart agriculture. One potential solution to reduce the volume and environmental impact of e-waste is to use more environmentally friendly and biodegradable materials to replace the non-degradable components (substrates) currently used in the structure of IoT devices. In this study, we estimate the electromagnetic properties at 2565 MHz of the leaves from three widely grown crops: winter wheat, corn, and sunflower. We found that winter wheat and sunflower leaves have values of the real part of relative permittivity ranging from about 33 to 69 (wheat) and 13 to 32 (sunflower), respectively, while corn exhibits a value of about 33.5. Our research indicates that the position of a leaf on the plant stem and its distance from the soil significantly affect the relative permittivity of winter wheat and sunflower. These relationships, however, are not evident in the electromagnetic properties of corn leaves. Full article
(This article belongs to the Special Issue Electromagnetic Waves, Antennas and Sensor Technologies)
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<p>Application example of a wearable antenna on a substrate from a <span class="html-italic">ZZ plant</span> leaf: (<b>a</b>) photo of the antenna prototype; (<b>b</b>) measured reflection coefficient |S<sub>11</sub>| and 3D radiation pattern.</p>
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<p>Locations of agricultural fields and their GPS coordinates.</p>
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<p>Photos of the sample preparation procedure.</p>
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<p>Block diagram of the experimental setup.</p>
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<p>Results from measurements of winter wheat leaves during three growth stages (from Feekes 8 to Feekes 10.5) in the agriculture field near Blagoevgrad: (<b>a</b>) Real part of the relative permittivity; (<b>b</b>) Imaginary part of the relative permittivity; (<b>c</b>) Leaf length; (<b>d</b>) Plant height, soil relative humidity and temperature.</p>
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<p>Results from measurements of winter wheat leaves in the agriculture field near Stoyanovtci: (<b>a</b>) Real and imaginary parts of the relative permittivity; (<b>b</b>) Leaf length, plant height, soil relative humidity and temperature.</p>
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<p>Results from measurements of corn leaves during the R5 growth stage: (<b>a</b>) Mean value and standard deviation of real and imaginary parts of corn leaf relative permittivity measured in agricultural fields near Mezdra; (<b>b</b>) Mean value and standard deviation of real and imaginary parts of corn leaf relative permittivity measured in agricultural fields near Dabrava; (<b>c</b>) Leaf length, plant height, soil relative humidity and temperature for measurements in agricultural fields near Mezdra; (<b>d</b>) Leaf length, plant height, soil relative humidity and temperature for measurements in agricultural fields near Dabrava.</p>
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<p>Results from measurements of sunflower leaves during the seed development stage in the agriculture field near Kameno pole: (<b>a</b>) Real part of the relative permittivity; (<b>b</b>) Imaginary part of the relative permittivity; (<b>c</b>) Leaf area, plant height, soil relative humidity and temperature; (<b>d</b>) Photos.</p>
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34 pages, 1230 KiB  
Review
Advanced Hydrogel Systems for Local Anesthetic Delivery: Toward Prolonged and Targeted Pain Relief
by Jin-Oh Jeong, Minjoo Kim, Seonwook Kim, Kyung Kwan Lee and Hoon Choi
Gels 2025, 11(2), 131; https://doi.org/10.3390/gels11020131 - 12 Feb 2025
Abstract
Local anesthetics (LAs) have been indispensable in clinical pain management, yet their limitations, such as short duration of action and systemic toxicity, necessitate improved delivery strategies. Hydrogels, with their biocompatibility, tunable properties, and ability to modulate drug release, have been extensively explored as [...] Read more.
Local anesthetics (LAs) have been indispensable in clinical pain management, yet their limitations, such as short duration of action and systemic toxicity, necessitate improved delivery strategies. Hydrogels, with their biocompatibility, tunable properties, and ability to modulate drug release, have been extensively explored as platforms for enhancing LA efficacy and safety. This narrative review explores the historical development of LAs, their physicochemical properties, and clinical applications, providing a foundation for understanding the integration of hydrogels in anesthetic delivery. Advances in thermoresponsive, stimuli-responsive, and multifunctional hydrogels have demonstrated significant potential in prolonging analgesia and reducing systemic exposure in preclinical studies, while early clinical findings highlight the feasibility of thermoresponsive hydrogel formulations. Despite these advancements, challenges such as burst release, mechanical instability, and regulatory considerations remain critical barriers to clinical translation. Emerging innovations, including nanocomposite hydrogels, biofunctionalized matrices, and smart materials, offer potential solutions to these limitations. Future research should focus on optimizing hydrogel formulations, expanding clinical validation, and integrating advanced fabrication technologies such as 3D printing and artificial intelligence-driven design to enhance personalized pain management. By bridging materials science and anesthetic pharmacology, this review provides a comprehensive perspective on current trends and future directions in hydrogel-based LA delivery systems. Full article
(This article belongs to the Special Issue Advances in Functional Hydrogels and Their Applications)
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<p>Hydrogel Systems for Local Anesthetic Delivery.</p>
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<p>Key Mechanisms of Drug Release from Hydrogels: (<b>A</b>) Diffusion-controlled, (<b>B</b>) Degradation-controlled, (<b>C</b>) Stimuli-response.</p>
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15 pages, 3735 KiB  
Article
Development of Smart Material Identification Equipment for Sustainable Recycling in Future Smart Cities
by Gaku Manago, Tadao Tanabe, Kazuaki Okubo, Tetsuo Sasaki and Jeongsoo Yu
Polymers 2025, 17(4), 462; https://doi.org/10.3390/polym17040462 - 10 Feb 2025
Abstract
Waste recycling is critical for the development of smart cities. Local authorities are responsible for the disposal of waste plastics, but the extent of material recycling is insufficient, and much of the waste generated is incinerated. This conflicts with the trend of decarbonisation. [...] Read more.
Waste recycling is critical for the development of smart cities. Local authorities are responsible for the disposal of waste plastics, but the extent of material recycling is insufficient, and much of the waste generated is incinerated. This conflicts with the trend of decarbonisation. Of particular note are the effects of the COVID-19 pandemic, during and after which large quantities of waste plastics, such as plastic containers and packaging, were generated. In order to develop a sustainable smart city, we need an effective scheme where we can separate materials before they are taken to the local authorities and recyclers. In other words, if material identification can be performed at the place of disposal, the burden on recyclers can be reduced, and a smart city can be created. In this study, we developed and demonstrated smart material identification equipment for waste plastic materials made of PET, PS, PP, and PE using GaP THz and sub-THz wavelengths. As basic information, we used a GaP terahertz spectrometer to sweep frequencies from 0.5 THz to 7 THz and measure the spectrum, and the transmittance rate was measured using the sub-THz device. The sub-THz device used a specific frequency below 0.14 THz. This is a smaller, more carriable, and less expensive semiconductor electronic device than the GaP. Moreover, the sub-terahertz device used in the development of this equipment is compact, harmless to the human body, and can be used in public environments. As a result, smart equipment was developed and tested in places such as supermarkets, office entrances, and canteens. The identification of materials can facilitate material recycling. In this study, we found that measuring devices designed to identify the PET and PS components of transparent containers and packaging plastics, and the PP and PE components of PET bottle caps, could effectively identify molecular weights, demonstrating new possibilities for waste management and recycling systems in smart cities. With the ability to collect and analyse data, these devices can be powerful tools for pre-sorting. Full article
(This article belongs to the Special Issue Polymer Composites in Municipal Solid Waste Landfills)
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Graphical abstract
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<p>Research background and methodology.</p>
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<p>Broadband terahertz spectroscopic equipment (the right picture was adopted from [<a href="#B30-polymers-17-00462" class="html-bibr">30</a>]).</p>
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<p>Terahertz spectra of polyethylene terephthalate (<b>a</b>) and polystyrene (<b>b</b>).</p>
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<p>Terahertz spectra from 0.5 THz to 5 THz of (<b>a</b>) a polypropylene plate, (<b>b</b>) a polyethylene plate, and (<b>c</b>) PE and PP bottle caps [<a href="#B15-polymers-17-00462" class="html-bibr">15</a>].</p>
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<p>Terahertz transmission distribution of PET and PS at frequencies of 0.1 THz and 0.075 THz.</p>
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<p>The z-scores for the transmittance rates of each sample.</p>
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<p>Bottle caps’ transmittance rates after being subjected to 0.14THz irradiation.</p>
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<p>The design of the smart identification equipment for identifying waste plastic containers used in the demonstration (<b>a</b>), and the implementation of the demonstration (<b>b</b>).</p>
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<p>The design of the smart identification equipment for identifying waste bottle caps used in the demonstration (<b>a</b>), and the implementation of the demonstration (<b>b</b>).</p>
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15 pages, 5050 KiB  
Article
A Comparison of the Resistance- and Capacitance-Based Sensing of Geopolymer and Cement Composites with Graphite Filler Under Compression
by Pavel Rovnaník, Ivo Kusák, Pavel Schmid and Patrik Bayer
Materials 2025, 18(4), 750; https://doi.org/10.3390/ma18040750 - 8 Feb 2025
Abstract
Aluminosilicate binders, such as Portland cement or geopolymers, are generally considered electrical insulators. In order to decrease their electrical resistance, electrically conductive fillers are added. This brings new application possibilities, such as the self-sensing and self-monitoring of smart structures. In this study, three [...] Read more.
Aluminosilicate binders, such as Portland cement or geopolymers, are generally considered electrical insulators. In order to decrease their electrical resistance, electrically conductive fillers are added. This brings new application possibilities, such as the self-sensing and self-monitoring of smart structures. In this study, three different aluminosilicate composites with the same amount of fine graphite filler (6% with respect to the basic aluminosilicate raw material) were tested for resistance- and capacitance-based self-sensing properties. Portland cement and two geopolymer binders were used as the basic matrices for the conductive composites. The composites were tested for self-sensing properties in repeated compression in the elastic area, static mechanical properties, and microstructure using scanning electron microscopy and mercury intrusion porosimetry. The results showed that alkali-activated materials are less stiff than Portland cement composite; however, they provide better self-sensing properties, regardless of the measured electrical parameters. The highest capacitance-based gauge factor 74.5 was achieved with the blended slag/fly ash geopolymer composite, whereas the cement composite showed very poor sensitivity, with a gauge factor of 10.2. The study showed a new possibility of self-sensing based on the measurement of capacitance, which is suitable for geopolymers and alkali-activated composites; however, in the case of cement composites, it is very limited. Full article
(This article belongs to the Special Issue Advances in Function Geopolymer Materials)
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<p>Experimental setup for self-sensing measurements during compressive loading tests [<a href="#B24-materials-18-00750" class="html-bibr">24</a>].</p>
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<p>Mechanical properties of tested composites at the age of 7 and 28 days: (<b>a</b>) compressive strength; (<b>b</b>) flexural strength.</p>
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<p>Distribution of pores determined by means of mercury intrusion porosimetry in range of pore diameters 0.006–60 μm: (<b>a</b>) cumulative intruded volume; (<b>b</b>) differential intruded volume.</p>
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<p>Self-sensing properties of CEM G6 composite during repeated compressive loading with constant amplitude recorded as (<b>a</b>) fractional change in resistance; (<b>b</b>) fractional change in capacitance.</p>
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<p>Self-sensing properties of AAS G6 composite during repeated compressive loading with constant amplitude recorded as (<b>a</b>) fractional change in resistance; (<b>b</b>) fractional change in capacitance.</p>
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<p>Self-sensing properties of FAS G6 composite during repeated compressive loading with constant amplitude recorded as (<b>a</b>) fractional change in resistance; (<b>b</b>) fractional change in capacitance.</p>
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<p>Electrical response of the tested composites vs. compressive strain recorded for (<b>a</b>) resistance-based sensing; (<b>b</b>) capacitance-based sensing. Linear fits for the self-sensing sensitivity dependence are depicted.</p>
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<p>Calculated gage factors for resistance- and capacitance-based self-sensing properties.</p>
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<p>Morphology of tested composites depicted by SEM: (<b>a</b>) CEM G6; (<b>b</b>) AAS G6; (<b>c</b>) FAS G6. Microcracks are present in AAS and FAS matrices.</p>
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17 pages, 974 KiB  
Review
Current Research Status and Prospects of Electrode Boilers Under the Background of the “Dual Carbon” Goals
by Zheng Zhao, Rui Hu, Yu Zhang, Heming Dong and Qian Du
Energies 2025, 18(4), 769; https://doi.org/10.3390/en18040769 - 7 Feb 2025
Abstract
In the context of “dual carbon” goals, energy structures are rapidly shifting towards cleaner, low-carbon solutions. The clean and efficient electrode boiler, with its unique heat generation mechanism, is well aligned with this trend. This review begins by outlining the operating principles of [...] Read more.
In the context of “dual carbon” goals, energy structures are rapidly shifting towards cleaner, low-carbon solutions. The clean and efficient electrode boiler, with its unique heat generation mechanism, is well aligned with this trend. This review begins by outlining the operating principles of electrode boilers, emphasizing their advantages in terms of energy efficiency and environmental sustainability. It then examines the current status of electrode boiler applications within the framework of the “dual carbon” objectives, addressing key challenges and technological barriers. The review concludes that electrode boilers hold significant potential for clean heating, grid peak-shaving, and the integration of renewable energy. However, research on electrode materials, boiler-based water treatment, electric field distribution within boilers, and corrosion issues remains insufficient. To address these gaps, this paper proposes several recommendations, including fostering cross-regional scientific collaboration, advancing the development of new electrode materials and coatings, and leveraging smart internet technologies to optimize electrode boiler performance and applications. Full article
(This article belongs to the Section B: Energy and Environment)
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<p>Structural schematic of an immersion-type electrode boiler [<a href="#B26-energies-18-00769" class="html-bibr">26</a>].</p>
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<p>Variation in the number of electrode boiler patents over the years.</p>
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<p>Combined heat and power (CHP) system for electrode boiler [<a href="#B58-energies-18-00769" class="html-bibr">58</a>].</p>
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7 pages, 4149 KiB  
Proceeding Paper
Empowering Smart Surfaces: Optimizing Dielectric Inks for In-Mold Electronics
by Priscilla Hong, Gibson Soo Chin Yuan, Yeow Meng Tan and Kebao Wan
Eng. Proc. 2024, 78(1), 8; https://doi.org/10.3390/engproc2024078008 - 6 Feb 2025
Abstract
Dielectric materials have gained traction for their energy-storage capacitive and electrically insulating properties as sensors and in smart surface technologies such as in In-Mold Electronics (IME). IME is a disruptive technology that involves environmentally protected electronics in plastic thermoformed and molded structures. The [...] Read more.
Dielectric materials have gained traction for their energy-storage capacitive and electrically insulating properties as sensors and in smart surface technologies such as in In-Mold Electronics (IME). IME is a disruptive technology that involves environmentally protected electronics in plastic thermoformed and molded structures. The use of IME in a human–machine interface (HMI) provides a favorable experience to the users and helps reduce production costs due to a smaller list of parts and lower material costs. A few functional components that are compatible with one another are crucial to the final product’s properties in the IME structure. Of these components, the dielectric layers are an important component in the smart surface industry, providing insulation for the prevention of leakage currents in multilayered printed structures and capacitance sensing on the surface of specially designed shapes in IME. Advanced dielectric materials are non-conductive materials that impend and polarize electron movements within the material, store electrical energy, and reduce the flow of electric current with exceptional thermal stability. The selection of a suitable dielectric ink is an integral stage in the planning of the IME smart touch surface. The ink medium, solvent, and surface tension determine the printability, adhesion, print quality, and the respective reaction with the bottom and top conductive traces. The sequence in which the components are deposited and the heating processes in subsequent thermoforming and injection molding are other critical factors. In this study, various commercially available dielectric layers were each printed in two to four consecutive layers with a mesh thickness of 50–60 µm or 110–120 µm, acting as an insulator between conductive silver traces overlaid onto a polycarbonate substrate. Elemental mapping and optical analysis on the cross-section were conducted to determine the compatibility and the adhesion of the dielectric layers on the conductive traces and polycarbonate substrate. The final selection was based on the functionality, reliability, repeatability, time-stability, thickness, total processing time, appearance, and cross-sectional analysis results. The chosen candidate was then placed through the final product design, circuitry design, and plastic thermoforming process. In summary, this study will provide a general guideline to optimize the selection of dielectric inks for in-mold electronics applications. Full article
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<p>Process flow for printing conductive layers and dielectric layers through thermoforming in IME technology.</p>
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<p>Manufacturing process flow for in-mold electronics (IME).</p>
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<p>(<b>a</b>) Screen-printing by transfer of ink through open mesh to the substrate with a squeegee; (<b>b</b>) multimeter; (<b>c</b>) Keyence VHX-7000 Microscope.</p>
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<p>(<b>a-1</b>) Thermoforming in a female mold; (<b>a-2</b>) Thermoforming of printed circuitry in a female mold; (<b>b</b>) thermoforming in a male mold; (<b>c</b>) printing on flat polycarbonate substrate and thermoformed into cone-shape; (<b>d</b>) graphics with thermoforming; (<b>e</b>) thermoform equipment Formech, Singapore.</p>
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<p>(<b>a</b>) Illustration of preparation process; (<b>b</b>) comparison performance in dielectric inks in quality, appearance, and functionality. Green text indicates ”acceptable”; red text indicates “unacceptable”; blue text indicates “for consideration”.</p>
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<p>No delamination and no gap found at the intersection of dielectric ink and conductive trace in (<b>a</b>) Dielectric A or (<b>b</b>) Dielectric B. (<b>c</b>) Cross-sectioning position at the red line and polish at the green line. (<b>d</b>) Gap was found at the intersection of Dielectric C and the conductive trace; (<b>e</b>) silver was found to have seeped into the dielectric layer (Spectrums 7, 9). (<b>f</b>) “Gap” and thrusting of silver/delamination beyond the dielectric ink created an “unknown” area—analysis shows it is not Si-rich dielectric ink.</p>
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<p>No delamination and no gap found at the intersection of dielectric ink and conductive trace in (<b>a</b>) Dielectric A or (<b>b</b>) Dielectric B. (<b>c</b>) Cross-sectioning position at the red line and polish at the green line. (<b>d</b>) Gap was found at the intersection of Dielectric C and the conductive trace; (<b>e</b>) silver was found to have seeped into the dielectric layer (Spectrums 7, 9). (<b>f</b>) “Gap” and thrusting of silver/delamination beyond the dielectric ink created an “unknown” area—analysis shows it is not Si-rich dielectric ink.</p>
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<p>(<b>a</b>) Samples printed in different dielectric types and thicknesses. (<b>b</b>) Width contraction % by dielectric thicknesses; (<b>c</b>) width % change in best performing dielectric at 6 months. (<b>d</b>) Appearance and performance of Dielectric A at 6 months.</p>
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26 pages, 12669 KiB  
Review
Recent Progress in Intrinsically Stretchable Sensors Based on Organic Field-Effect Transistors
by Mingxin Zhang, Mengfan Zhou, Jing Sun, Yanhong Tong, Xiaoli Zhao, Qingxin Tang and Yichun Liu
Sensors 2025, 25(3), 925; https://doi.org/10.3390/s25030925 - 4 Feb 2025
Abstract
Organic field-effect transistors (OFETs) are an ideal platform for intrinsically stretchable sensors due to their diverse mechanisms and unique electrical signal amplification characteristics. The remarkable advantages of intrinsically stretchable sensors lie in their molecular tunability, lightweight design, mechanical robustness, solution processability, and low [...] Read more.
Organic field-effect transistors (OFETs) are an ideal platform for intrinsically stretchable sensors due to their diverse mechanisms and unique electrical signal amplification characteristics. The remarkable advantages of intrinsically stretchable sensors lie in their molecular tunability, lightweight design, mechanical robustness, solution processability, and low Young’s modulus, which enable them to seamlessly conform to three-dimensional curved surfaces while maintaining electrical performance under significant deformations. Intrinsically stretchable sensors have been widely applied in smart wearables, electronic skin, biological detection, and environmental protection. In this review, we summarize the recent progress in intrinsically stretchable sensors based on OFETs, including advancements in functional layer materials, sensing mechanisms, and applications such as gas sensors, strain sensors, stress sensors, proximity sensors, and temperature sensors. The conclusions and future outlook discuss the challenges and future outlook for stretchable OFET-based sensors. Full article
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<p>Schematic illustration of intrinsically stretchable OFET-based sensors.</p>
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<p>Schematic diagram of OFET structure and operating mechanism.</p>
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<p>Four typical device structures of stretchable OFETs, including (<b>a</b>) bottom-gate top-contact structure, (<b>b</b>) bottom-gate bottom-contact structure, (<b>c</b>) top-gate top-contact structure, and (<b>d</b>) top-gate bottom-contact structure. (S: source electrode, D: drain electrode, G: gate electrode).</p>
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<p>Schematic illustration of an intrinsically stretchable transistor, including intrinsically stretchable conductor, semiconductor, and dielectric materials. Reproduced with permission from [<a href="#B20-sensors-25-00925" class="html-bibr">20</a>], copyright 2018, Springer Nature.</p>
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<p>Schematic illustration, AFM, and conductive AFM images of intrinsically stretchable electrodes of (<b>a</b>–<b>c</b>) SWCNT and (<b>d</b>–<b>f</b>) PEDOT:PSS/SWCNT. Reproduced with permission from [<a href="#B25-sensors-25-00925" class="html-bibr">25</a>], copyright 2019, RSC publishing.</p>
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<p>(<b>a</b>) Mechanism of lithography of PEDOT:PSS and PEGDMA. Reproduced with permission from [<a href="#B28-sensors-25-00925" class="html-bibr">28</a>], copyright 2021, AAAS Science. (<b>b</b>) Chemical structure of PR-PEGMA. (<b>c</b>) Schematic diagram illustrating PR and PEDOT:PSS for enhanced conductivity. Reproduced with permission, copyright [<a href="#B29-sensors-25-00925" class="html-bibr">29</a>] AAAS Science.</p>
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<p><b>Low-voltage stretchable OFETs.</b> (<b>a</b>) Device structure and tri-layer insulators. (<b>b</b>) Typical transfer curves of the OFETs. (<b>c</b>) Optical image of the low-voltage stretchable OFET array. Reproduced with permission from [<a href="#B63-sensors-25-00925" class="html-bibr">63</a>], copyright 2023, AAAS Science.</p>
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<p>(<b>a</b>) Fabrication illustration of intrinsically stretchable transistor-based gas sensors. (<b>b</b>) Photographs of the fully intrinsically stretchable OFET-based sensors stretched to 100% strain. (<b>c</b>) The excellent conformability of the OFET-based sensors can conform on human skin. (<b>d</b>,<b>e</b>) Typical transfer curves, on and off currents, and mobilities under 0–90% strains. (<b>f</b>) The transfer characteristics of stretchable sensors show mechanical robustness, as the device can function well under 30% strain for 2000 cycles. Reproduced with permission from [<a href="#B67-sensors-25-00925" class="html-bibr">67</a>], copyright 2013, John Wiley and Sons.</p>
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<p>Intrinsically stretchable pressure sensors based on OFETs. (<b>a</b>) A 10 × 10 stretchable active matrix transistor array (scale bar: 1 mm). (<b>b</b>) A diagram of the tactile sensor array based on the OFET array. (<b>c</b>) The array can be adhered to a human palm and accurately detect the position of a synthetic ladybug with six conductive legs. (<b>d</b>) Current mapping of the ladybug on the OFET array. Reproduced with permission from [<a href="#B20-sensors-25-00925" class="html-bibr">20</a>], copyright 2018, Spring Nature.</p>
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<p>Electro-oculo-gram (EOG) sensor based on stretchable OFETs. (<b>a</b>) Diagram of the stretchable OFETs. (<b>b</b>) Schematic circuit diagram of the transistor amplifier. (<b>c</b>) Output voltage (<span class="html-italic">V</span><sub>out</sub>) and gain (<span class="html-italic">A</span>v) curves of the amplifier. (<b>d</b>) EOG signals of the amplifier under alternate upward and downward movement of the eyeball. Reproduced with permission from [<a href="#B46-sensors-25-00925" class="html-bibr">46</a>], copyright 2018, John Wiley and Sons.</p>
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<p>Strain sensors based on OFETs. (<b>a</b>) Schematic illustration of rubrene single-crystal OFET strain sensors. (<b>b</b>) Optical microscopy image and AFM image of rubrene single crystals. (<b>c</b>) <span class="html-italic">I–V</span> curves of the rubrene single-crystal device under compressive and tensile strains. (<b>d</b>) Real-time current response of the strain sensors during index finger motion under compressive and tensile strains. Reproduced with permission from [<a href="#B76-sensors-25-00925" class="html-bibr">76</a>], copyright 2017, IEEE.</p>
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<p>Stretchable proximity sensors based on OFETs. (<b>a</b>) Schematic fabrication procedures of PAM-dc-fGO conductive films. (<b>b</b>) Schematic illustration of the test methods, including (i) stomping or jumping, (ii) hand movements, and (iii) walking back and forth on a straight line. Reproduced with permission from [<a href="#B90-sensors-25-00925" class="html-bibr">90</a>], copyright 2018, ACS publishing.</p>
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<p>(<b>a</b>) Schematic structure of the stretchable temperature sensor. (<b>b</b>) Monitoring neck skin temperature and muscle movement. (<b>c</b>) IR thermograms of the neck before and after drinking hot water. Reproduced with permission from [<a href="#B93-sensors-25-00925" class="html-bibr">93</a>], copyright 2018, John Wiley and Sons.</p>
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<p>(<b>a</b>) Schematic structure of a stretchable temperature sensor based on an OFET array, with SEBS serving as the encapsulation layer, dielectric layer, and substrate; Ag serving as the source, drain, and gate electrodes; and DPPT-TT/SEBS as the active layer. (<b>b</b>,<b>c</b>) Optical and digital images of the stretchable temperature OFET array conforming to human skin. (<b>d</b>) Mobilities and threshold voltages of the OFET array. (<b>e</b>,<b>f</b>) Three-dimensional NS-current mapping and thermographic images of the OFET array temperature sensor on cold and hot metal balls. Reproduced with permission from [<a href="#B98-sensors-25-00925" class="html-bibr">98</a>], copyright 2024, John Wiley and Sons.</p>
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17 pages, 3645 KiB  
Article
Advanced Approaches to Material Processing in FFF 3D Printing: Integration of AR-Guided Maintenance for Optimized Manufacturing
by Jakub Kaščak, Marek Kočiško, Jozef Török and Peter Gabštur
J. Manuf. Mater. Process. 2025, 9(2), 47; https://doi.org/10.3390/jmmp9020047 - 3 Feb 2025
Abstract
The field of additive manufacturing increasingly demands innovative solutions to optimize material processing, improve equipment efficiency, and address maintenance challenges in high-utilization environments. This study investigates the operation and management of an FFF 3D printing production line comprising eight remotely controlled printers. The [...] Read more.
The field of additive manufacturing increasingly demands innovative solutions to optimize material processing, improve equipment efficiency, and address maintenance challenges in high-utilization environments. This study investigates the operation and management of an FFF 3D printing production line comprising eight remotely controlled printers. The system supports custom manufacturing and educational activities, focusing on processing a range of thermoplastics and composite materials. A key contribution of this work lies in addressing the impact of frequent hardware servicing caused by shared use among users. Augmented reality (AR)-guided assembly and disassembly workflows were developed to ensure uninterrupted operations. These workflows are accessible via smart devices and provide step-by-step guidance tailored to specific material and equipment requirements. The research evaluates the effectiveness of AR-enhanced maintenance in minimizing downtime, extending equipment lifespans, and ensuring consistent material performance during manufacturing processes. Furthermore, it explores the role of AR in maintaining the mechanical, thermal, and chemical properties of processed materials, ensuring high-quality outputs across diverse applications. This paper highlights the integration of advanced material processing methodologies with emerging technologies like AR, aligning with the focus on enhancing manufacturing schemes. The findings contribute to improving process efficiency and adaptability in additive manufacturing, offering insights into scalable solutions for remote-controlled and multi-user production systems. Full article
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<p>Data based on market reports, a statistical analysis of AR/VR spending trends in Europe 2019–2023, and further predictions.</p>
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<p>Example of the maintenance sequence creation in PTC Illustrate.</p>
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<p>Ender 3v2 additive device and 3D printing farm.</p>
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<p>Modeled hot-end components (details of the print head components: PTFE tube (<b>a</b>), heating element (<b>b</b>), thermistor (<b>c</b>), and connecting components: clamp (<b>d</b>), with (<b>e</b>) representing the screw).</p>
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<p>Example of the created AR Workflow.</p>
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<p>AR interface design and preview in Vuforia Studio.</p>
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<p>Example of AR sequence tracking.</p>
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<p>AR workflow preview in Vuforia Studio.</p>
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<p>The resulting display of the introduction of the AR sequence (details of the individual parts of the sequence: start of the sequence (<b>a</b>), removal of the print head cover (<b>b</b>), with (<b>c</b>) showing a detailed view of the print head).</p>
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<p>Visualization of an AR-assisted press arm adjustment using HoloLens 2.</p>
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24 pages, 20675 KiB  
Review
Cathodes for Zinc-Ion Micro-Batteries: Challenges, Strategies, and Perspectives
by Ling Deng, Qunfang Lin, Zeyang Li, Juexian Cao, Kailing Sun and Tongye Wei
Batteries 2025, 11(2), 57; https://doi.org/10.3390/batteries11020057 - 2 Feb 2025
Abstract
The sustainable development of high-performance micro-batteries, characterized by miniaturized size, portability, enhanced safety, and cost-effectiveness, is crucial for the advancement of wearable and smart electronics. Zinc-ion micro-batteries (ZIMBs) have attracted widespread attention for their high energy density, environmental friendliness, excellent safety, and low [...] Read more.
The sustainable development of high-performance micro-batteries, characterized by miniaturized size, portability, enhanced safety, and cost-effectiveness, is crucial for the advancement of wearable and smart electronics. Zinc-ion micro-batteries (ZIMBs) have attracted widespread attention for their high energy density, environmental friendliness, excellent safety, and low cost. The key to designing high-performance ZIMBs lies in improving their volumetric capacity and cycle stability. This review focuses on material design, electrode fabrication, and the structural configuration of micro-batteries, providing a comprehensive analysis of the challenges and strategies associated with cathodes in ZIMBs. Additionally, the application of ZIMBs, which provide energy for electronics such as wearable devices, tiny robots, and sensors, is introduced. Finally, future perspectives on cathodes for ZIMBs are discussed, offering key insights into their design and fabrication in order to facilitate the successful integration of ZIMBs into practical applications. Full article
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<p>(<b>a</b>) Structural transformation of MnO<sub>2</sub> during discharge/charge cycles. Reprinted with permission from ref. [<a href="#B18-batteries-11-00057" class="html-bibr">18</a>]. Copyright 2018, Springer Nature. (<b>b</b>) Pourbaix diagram for (<b>b</b>) manganese and (<b>c</b>) vanadium, oxides. Reprinted with permission from ref. [<a href="#B19-batteries-11-00057" class="html-bibr">19</a>]. Copyright 2023, John Wiley and Sons.</p>
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<p>(<b>a</b>) SEM and (<b>b</b>) TEM images of a-H-MnFeO. Reprinted with permission from ref. [<a href="#B25-batteries-11-00057" class="html-bibr">25</a>]. Copyright 2023, Elsevier. (<b>c</b>) SEM and (<b>d</b>) TEM images of Pr/Mn-MIL-100. Reprinted with permission from ref. [<a href="#B26-batteries-11-00057" class="html-bibr">26</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>e</b>) SEM and (<b>f</b>) TEM images of MnO<sub>2</sub>-NRs@HsGDY. Reprinted with permission from ref. [<a href="#B29-batteries-11-00057" class="html-bibr">29</a>]. Copyright 2023, Elsevier. Morphology of V<sub>2</sub>O<sub>5</sub>@LIG with different composite amounts of LIG: (<b>g</b>) 0%, (<b>h</b>) 22%. Reprinted with permission from ref. [<a href="#B30-batteries-11-00057" class="html-bibr">30</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>i</b>) SEM and (<b>j</b>) TEM images of MnO<sub>2</sub>@PANI nanowires. (<b>k</b>) Nyquist plots of MnO<sub>2</sub>@PANI and MnO<sub>2</sub> electrodes and (<b>l</b>) the corresponding linear plots of Z′ vs. ω<sup>−1/2</sup>. Reprinted with permission from ref. [<a href="#B31-batteries-11-00057" class="html-bibr">31</a>]. Copyright 2023, Elsevier. (<b>m</b>) SEM, (<b>n</b>) TEM, and (<b>o</b>) HRTEM images of the MOP-5 microsphere. (<b>p</b>) Nyquist plots of MOP-5 and MnO<sub>2</sub> electrodes. Reprinted with permission from ref. [<a href="#B32-batteries-11-00057" class="html-bibr">32</a>]. Copyright 2023, Elsevier.</p>
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<p>(<b>a</b>) SEM, (<b>b</b>) TEM, and (<b>c</b>) HRTEM images of 3D-NPG@S-NVO@CTAB. The PDOS and TDOS of 3D (<b>d</b>) NPG@NVO, (<b>e</b>) NPG@S-NVO, and (<b>f</b>) NPG@S-NVO@CTAB. Reprinted with permission from ref. [<a href="#B48-batteries-11-00057" class="html-bibr">48</a>]. Copyright 2024, Elsevier. Schematic illustrations of (<b>g</b>) Zn<sup>2+</sup> adsorption/desorption and (<b>h</b>) Zn<sup>2+</sup> storage on MnO<sub>2</sub>. (<b>i</b>) The calculated Zn<sup>2+</sup> adsorption energies. Reprinted with permission from ref. [<a href="#B49-batteries-11-00057" class="html-bibr">49</a>]. Copyright 2019, Wiley-VCH GmbH.</p>
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<p>Electrode architectures of MBs and their typical characteristics: (<b>a</b>) 2D stacked; (<b>b</b>) 2D planar; (<b>c</b>) 3D stacked; (<b>d</b>) 3D planar; (<b>e</b>) fiber-shaped. Reprinted with permission from ref. [<a href="#B51-batteries-11-00057" class="html-bibr">51</a>]. Copyright 2022, American Chemical Society.</p>
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<p>(<b>a</b>) The scheme of the fabrication of 3D P-ZIMBs. (<b>b</b>) A schematic demonstration of the 3D in-plane diffusion. (<b>c</b>) Digital images of the obtained electrodes. (<b>d</b>) 2D and 3D profilometer images of 3D P-ZIMB. GCDs of the C-ZIMB and 3D P-ZIMB at different current densities of (<b>e</b>) 50 μA cm<sup>−2</sup> and (<b>f</b>) 1000 μA cm<sup>−2</sup>. (<b>g</b>) The cycling performance of the C-ZIMB and 3D P-ZIMB. Reprinted with permission from ref. [<a href="#B54-batteries-11-00057" class="html-bibr">54</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>h</b>) Photos of the interdigital electrodes with 1, 3, and 5 layers, respectively. (<b>i</b>) A photo of the mass fabrication of MBs in a 4 × 4 layout. (<b>j</b>) Photos of the fabricated MBs in various sizes and their attachment to fingers. (<b>k</b>) Viscosity of the inks as a function of shear rate. Reprinted with permission from ref. [<a href="#B55-batteries-11-00057" class="html-bibr">55</a>]. Copyright 2023, American Chemical Society. (<b>l</b>) The fabrication scheme of a 3D-printed electrode. (<b>m</b>) An SEM of a 3D-printed electrode at different magnifications and deposition times. Reprinted with permission from ref. [<a href="#B56-batteries-11-00057" class="html-bibr">56</a>]. Copyright 2019, Elsevier. (<b>n</b>) A dispersion consisting of the V<sub>2</sub>O<sub>5</sub>·nH<sub>2</sub>O and soybean oil. (<b>o</b>) Photos of 3D-printed emulsified V<sub>2</sub>O<sub>5</sub>·nH<sub>2</sub>O. Scale bars: 5 mm. Reprinted with permission from ref. [<a href="#B57-batteries-11-00057" class="html-bibr">57</a>]. Copyright 2023, Wiley-VCH GmbH.</p>
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<p>(<b>a</b>) The scheme of the 3D printing process. (<b>b</b>) Discharge curves of PZIMBs with different surface areas at 2 mA cm<sup>-2</sup>. (<b>c</b>) A photo of and (<b>d</b>) the sheet resistance of the printed electrode. (<b>e</b>) Cross-sectional and (<b>f</b>) surface SEMs of printed cathode. Reprinted with permission from ref. [<a href="#B59-batteries-11-00057" class="html-bibr">59</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>g</b>) A coaxial device via direct ink writing. (<b>h</b>,<b>i</b>) The various printed device. Scale bar, 10 mm. Reprinted with permission from ref. [<a href="#B62-batteries-11-00057" class="html-bibr">62</a>]. Copyright 2021, the Authors. (<b>j</b>) Zn//MnO<sub>2</sub> MBs connected: 5 series × 3 parallel. (<b>k</b>) Photos of four concentric circle shapes under a bending state. Reprinted with permission from ref. [<a href="#B60-batteries-11-00057" class="html-bibr">60</a>]. Copyright 2019, Oxford University Press.</p>
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<p>(<b>a</b>) A schematic diagram of the fabrication of MBs. (<b>b</b>) Photos of an MB with planar and bending. (<b>c</b>) An MB on the thumb-scale bar: 5 mm. (<b>d</b>) The various shapes of MBs by all DLP-scale bar: 3 mm. Reprinted with permission from ref. [<a href="#B63-batteries-11-00057" class="html-bibr">63</a>]. Copyright 2023, Wiley-VCH GmbH. (<b>e</b>) A schematic diagram and photo of GP-LTMSs. Reprinted with permission from ref. [<a href="#B64-batteries-11-00057" class="html-bibr">64</a>]. Copyright 2017, Wiley-VCH GmbH. (<b>f</b>) The scheme for fabricating fibrous batteries. (<b>g</b>–<b>i</b>) An SEM of the fibrous MnO<sub>2</sub> electrodes. Reprinted with permission from ref. [<a href="#B65-batteries-11-00057" class="html-bibr">65</a>]. Copyright 2022, American Chemical Society. (<b>j</b>) Schematic diagrams of the processes for Zn-PANI MB. Reprinted with permission from ref. [<a href="#B68-batteries-11-00057" class="html-bibr">68</a>]. Copyright 2020, Wiley-VCH GmbH. (<b>k</b>) A schematic diagram of the manufacturing of an MnO<sub>2</sub>@CFs electrode. Reprinted with permission from ref. [<a href="#B69-batteries-11-00057" class="html-bibr">69</a>]. Copyright 2023, American Chemical Society.</p>
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<p>(<b>a</b>) A photo of a textile woven with the fiber-shaped ZIMBs. Reprinted with permission from ref. [<a href="#B71-batteries-11-00057" class="html-bibr">71</a>]. Copyright 2022, Elsevier. (<b>b</b>) A photo of an LED illuminated by a coaxial device. Reprinted with permission from ref. [<a href="#B62-batteries-11-00057" class="html-bibr">62</a>]. Copyright 2021, the authors. (<b>c</b>) A photo of a wearable self-power integrated system. Reprinted with permission from ref. [<a href="#B72-batteries-11-00057" class="html-bibr">72</a>]. Copyright 2021, Copyright 2022, Wiley-VCH GmbH. (<b>d</b>) The preparation process of a multifunctional battery. (<b>e</b>) A photo of the fiber-shaped device. (<b>f</b>) A photo of an electronic watch driven by two fiber-shaped devices in series. Reprinted with permission from ref. [<a href="#B73-batteries-11-00057" class="html-bibr">73</a>]. Copyright 2022, American Chemical Society. (<b>g</b>) A schematic illustration of the fiber-shaped battery. (<b>h</b>) A photo of the fiber-shaped battery woven into a textile. (<b>i</b>) Robotic locomotion under magnetic actuation. Reprinted with permission from ref. [<a href="#B74-batteries-11-00057" class="html-bibr">74</a>]. Copyright 2022, Elsevier. (<b>j</b>) A schematic diagram of the fabricated fiber electrode and fiber-shaped ZIMBs. (<b>k</b>) A photo of the integrated device used to monitor the movement. (<b>l</b>) The dynamic response of the sensor with the finger moving. Reprinted with permission from ref. [<a href="#B75-batteries-11-00057" class="html-bibr">75</a>]. Copyright 2022, Elsevier.</p>
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<p>(<b>a</b>) A schematic diagram of a stacked ZIB. (<b>b</b>) A photo of a ZIB providing power for LED under bending. Reprinted with permission from ref. [<a href="#B78-batteries-11-00057" class="html-bibr">78</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>c</b>–<b>f</b>) The resistance variation of the cathode before cutting and after self-healing. Reprinted with permission from ref. [<a href="#B79-batteries-11-00057" class="html-bibr">79</a>]. Copyright 2022, Elsevier. (<b>g</b>,<b>h</b>) A photo of on-body trial setup with the Zn/MoS<sub>2</sub>-MnO<sub>2</sub> batteries mounted on the arm while riding an exercise bike. Reprinted with permission from ref. [<a href="#B82-batteries-11-00057" class="html-bibr">82</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>i</b>) A photo of an interactive integrated system resembling electronic skin. Reprinted with permission from ref. [<a href="#B59-batteries-11-00057" class="html-bibr">59</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>j</b>) Photos of ZIMBs while stretched up to 5 cm. (<b>k</b>) LED illumination using a ZIMB in water and ice. Reprinted with permission from ref. [<a href="#B83-batteries-11-00057" class="html-bibr">83</a>]. Copyright 2023, Wiley-VCH GmbH.</p>
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<p>(<b>a</b>) A photo of four devices, in series, lighting an LED. Reprinted with permission from ref. [<a href="#B57-batteries-11-00057" class="html-bibr">57</a>]. Copyright 2023, Wiley-VCH GmbH. (<b>b</b>) A module with four individual devices powers a miniature rotary motor. Reprinted with permission from ref. [<a href="#B55-batteries-11-00057" class="html-bibr">55</a>]. Copyright 2023, American Chemical Society. (<b>c</b>) A watch is powered by three MBs in series. Reprinted with permission from ref. [<a href="#B68-batteries-11-00057" class="html-bibr">68</a>]. Copyright 2020, Wiley-VCH GmbH. (<b>d</b>) Photo and (<b>e</b>) cycle performance of all printed AZIBs. Reprinted with permission from ref. [<a href="#B84-batteries-11-00057" class="html-bibr">84</a>]. Copyright 2024, Wiley-VCH GmbH. (<b>f</b>) Temperature change test of conformal temperature measurement circuit. Reprinted with permission from ref. [<a href="#B85-batteries-11-00057" class="html-bibr">85</a>]. Copyright 2024, Wiley-VCH GmbH.</p>
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15 pages, 4052 KiB  
Article
Viscoelastic, Shape Memory, and Fracture Characteristics of 3D-Printed Photosensitive Epoxy-Based Resin Under the Effect of Hydrothermal Ageing
by Mohamad Alsaadi, Tamer A Sebaey, Eoin P. Hinchy, Conor T. McCarthy, Tielidy A. de M. de Lima, Alexandre Portela and Declan M. Devine
J. Manuf. Mater. Process. 2025, 9(2), 46; https://doi.org/10.3390/jmmp9020046 - 1 Feb 2025
Abstract
Using 3D-printed (3DPd) polymers and their composites as shape memory materials in various smart engineering applications has raised the demand for such functionally graded sustainable materials. This study aims to investigate the viscoelastic, shape memory, and fracture toughness properties of the epoxy-based ultraviolet [...] Read more.
Using 3D-printed (3DPd) polymers and their composites as shape memory materials in various smart engineering applications has raised the demand for such functionally graded sustainable materials. This study aims to investigate the viscoelastic, shape memory, and fracture toughness properties of the epoxy-based ultraviolet (UV)-curable resin. A UV-based DLP (Digital Light Processing) printer was employed for the 3D printing (3DPg) epoxy-based structures. The effect of the hydrothermal accelerated ageing on the various properties of the 3DPd components was examined. The viscoelastic performance in terms of glass transition temperature (Tg), storage modulus, and loss modulus was evaluated. The shape memory polymer (SMP) performance with respect to shape recovery and shape fixity (programming the shape) were calculated through dynamic mechanical thermal analysis (DMTA). DMTA is used to reveal the molecular mobility performance through three different regions, i.e., glass region, glass transition region, and rubbery region. The shape-changing region (within the glass transition region) between the Tg value from the loss modulus and the Tg value from the tan(δ) was analysed. The temperature memory behaviour was investigated for flat and circular 3DPd structures to achieve sequential deployment. The critical stress intensity factor values of the single-edge notch bending (SENB) specimens have been explored for different crack inclination angles to investigate mode I (opening) and mixed-mode I/III (opening and tearing) fracture toughness. This study can contribute to the development of highly complex shape memory 3DPd structures that can be reshaped several times with large deformation. Full article
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<p>Schematic diagram of the thermomechanical SMP cycle [<a href="#B4-jmmp-09-00046" class="html-bibr">4</a>].</p>
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<p>The programming/recovery process: (<b>a</b>) schematic diagram and (<b>b</b>) images of the 3DPd specimens under the programming/recovery process.</p>
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<p>Schematic diagram of the geometrical configuration of the SENB specimen.</p>
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<p>(<b>a</b>) DSC analysis before and after thermal post-curing; (<b>b</b>) the change in water uptake versus ageing time of the 3DP-Ep objects.</p>
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<p>Viscoelastic properties of the 3DP-Ep before and after the hydrothermal ageing: (<b>a</b>) <span class="html-italic">E’</span>, (<b>b</b>) (<span class="html-italic">tan(δ)</span>), and (<b>c</b>) <span class="html-italic">E</span>”.</p>
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<p>Thermomechanical SMP cycle of 3DPd samples using 4-step DMTA test, (<b>a</b>) Ep-135 °C, Ep-170 °C and Me-100 °C samples, (<b>b</b>) EP0h, EP600h, and EP1800 h samples.</p>
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<p>3DPd epoxy-based structures demonstrate temporary and recovery shapes.</p>
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<p>Mode I and mixed mode I/III critical stress intensity factors of the 3DP-Ep beams.</p>
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<p>(<b>i</b>) SENB specimens under test, and (<b>ii</b>) the samples and fracture surfaces of the (<b>a</b>) mode I θ = 90°, (<b>b</b>) mixed-mode I/III θ = 60°, and (<b>c</b>) mixed-mode I/III θ = 30°.</p>
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<p>SEM micrographs of the tensile test specimen fracture surface (red frame represents the location of the 50 µ image).</p>
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17 pages, 7656 KiB  
Review
Supramolecular Adhesives Inspired by Nature: Concept and Applications
by Abhishek Baral and Kingshuk Basu
Biomimetics 2025, 10(2), 87; https://doi.org/10.3390/biomimetics10020087 - 1 Feb 2025
Abstract
Supramolecular chemistry, a relatively newly grown field, has emerged as a useful tool to fabricate novel smart materials with multiple uses. Adhesives find numerous uses, from heavy engineering to biomedical science. Adhesives are available in nature; inspired by them and their mechanism of [...] Read more.
Supramolecular chemistry, a relatively newly grown field, has emerged as a useful tool to fabricate novel smart materials with multiple uses. Adhesives find numerous uses, from heavy engineering to biomedical science. Adhesives are available in nature; inspired by them and their mechanism of adhesion, several supramolecular adhesives have been developed. In this review, supramolecular chemistry for the design and fabrication of novel adhesives is discussed. The discussion is divided into two segments. The first one deals with key supramolecular forces, and their implication is designing novel adhesives. In the second part, key applications of supramolecular adhesives have been discussed with suitable examples. This type of review casts light on the current advancements in the field along with the prospects of development. Full article
(This article belongs to the Special Issue Adhesives Inspired by Nature: When Bionics Boost Adhesive Innovation)
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<p>(<b>a</b>) Catechol-based molecular robust adhesives inspired by nature. Catechol forms a bidentate H-bonding network to form adhesion. H-bonding interaction and hydrophobicity make catechol groups protected from oxidation [<a href="#B28-biomimetics-10-00087" class="html-bibr">28</a>]. (Reproduced with permission from the American Chemical Society). (<b>b</b>) β-cyclodextrin (CD)- and 2,2’-bipyridyl (bpy)-based adhesive. The host–guest interaction provides stable adhesion, whereas the metal ion coordination site makes the adhesion dynamic. The dynamic nature also endows the gels with stimuli responsiveness (adapted from [<a href="#B29-biomimetics-10-00087" class="html-bibr">29</a>]).</p>
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<p>(<b>a</b>) Appending ionic liquid-like motifs can provide significant electrostatic interaction sites for an adhesive. PMBT, (poly(1–[2–methacryloylethyl]–3–methylimidazolium bis(trifluoromethane)-sulfonamide)), is a nice example of such a moiety where H-bond is hampered at the cost of electrostatic gain. The adhesion is stable at a higher temperature range (adapted from [<a href="#B35-biomimetics-10-00087" class="html-bibr">35</a>]). (<b>b</b>) Incorporating positive or negative charges into PHEMA-based adhesive on quartz (PEI to blue quartz; PAA to red quartz), and the molecular self-assembly produces a strong adhesion in the adhered solids [<a href="#B36-biomimetics-10-00087" class="html-bibr">36</a>]. (reproduced with permission from the American Chemical Society) (<b>c</b>) π–π stacking interaction between graphene and polydopamine provides adhesion in conductive composite hydrogels [<a href="#B37-biomimetics-10-00087" class="html-bibr">37</a>] (reproduced with permission from the American Chemical Society).</p>
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<p>Underwater adhesive hydrogels. (<b>a</b>) Schematic illustration of the fabrication of the underwater adhesive hydrogels. The hydrogel (PAM-C-M) created from MBAA-crosslinked poly(acrylamideco-C18) was immersed in an aqueous Fe<sup>3+</sup> solution followed by a water-washing process to obtain a hydrogel (Fe-PAM-C-M) with a hydrophobic surface. DI water was used, and MBAA is N,N′-methylenebisacrylamide. (<b>b</b>) Schematic illustration of the self-hydrophobization process for the formation of firm underwater adhesion between the hydrogel and substrate. When the hydrogel is compressed to achieve contact with the substrate underwater, the hydrophobic interactions form and grow at the interface and repel water away from the interface. (<b>c</b>) Demonstration of underwater adhesion. The as-prepared hydrophilic PAM-C-M hydrogel was nonadhesive and slipped away from the metal block surface underwater, while the hydrophobic Fe-PAM-C-M hydrogel firmly adhered to the metal block surface and was able to lift the block (200 g) up underwater. (<b>d</b>) Photograph showing that the adhesion between the hydrogel and substrate is strong enough to resist water blasting for 10 s (adapted from reference [<a href="#B40-biomimetics-10-00087" class="html-bibr">40</a>]). (<b>e</b>) Crown ether-appended hydrophobic moisture-proof adhesive, formation of glassy appearance upon heating and cooling with moldable shape formation properties (right side upper panel), and macroscopic adhesion with different substances with strong adhesion value (right lower panel) [<a href="#B41-biomimetics-10-00087" class="html-bibr">41</a>] (reproduced with permission from the American Chemical Society).</p>
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<p>Modification of the carboxylic acid end with the acylhydrazine group increases the H-bonding interaction in thioctic acid, branched bonding interaction (lower left panel); (<b>A</b>–<b>C</b>) show the mechanism of robust adhesion (adapted from [<a href="#B43-biomimetics-10-00087" class="html-bibr">43</a>]).</p>
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<p>Photopolymerization of a Fe<sup>3+</sup>-coordinated catechol-based dynamic hydrogel. Healing of the stretched hydrogel holds potential promise for bioadhesion (right panel) [<a href="#B47-biomimetics-10-00087" class="html-bibr">47</a>] (reproduced with permission from the American Chemical Society).</p>
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<p>(<b>a</b>) PDMAPS-co-PMA-Ade/chitosan hydrogel as a wound dressing in a full-thickness skin defect. The left panel shows molecular structures and the right panel shows photographs of wounds treated by the control, gauze, PDMAPS-co-PMA-Ade (Gel 1), and PDMAPS-co-PMA-Ade/chitosan (Gel 2) hydrogel samples on days 0, 3, 7, 10, and 14 [<a href="#B39-biomimetics-10-00087" class="html-bibr">39</a>] (reproduced with permission from the American Chemical Society). (<b>b</b>) Illustration of preparing HA-PG hydrogel patches incorporated with inorganic particles (HAP, WKT) and BMP-2 and intermolecular complex formation through the coordination of oxidized PG moieties with ions released from HAP and WKT particles [<a href="#B55-biomimetics-10-00087" class="html-bibr">55</a>] (reproduced with permission from Elsevier).</p>
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