a new active dimension of "time" has evolved, leading to the new concept of 4D printing, which refers to the ability of 3D printed structures to actively transform over time in response to environmental stimuli. [5] Smart or stimuliresponsive materials have the unique ability to return from a temporary deformed state, induced by heat, light, pH, ultrasound, chemical substances, [6][7][8][9][10][11][12][13] etc., to their permanent, i.e., original, shape, thus exhibiting advantages for applications in numerous sectors, such as sensors and actuators, [14] tissue engineering, [15] bio-separation devices, and controlled drug delivery. [16][17][18][19][20][21] To date, two main types of materials have been considered to realize 4D printing: shape memory polymers (SMPs) and hydrogels. SMP-based 4D printing offers structural modification and recovery in response to temperature, which are established through complex functionalities of multiple or reversible shape switching, and such printing may provide inspiration for the molecular architecture of shape memory hydrogels (SMHs). However, SMPs cannot completely replace hydrophilic soft materials due to the limitations arising from their sustainability in wet environments, rigidity, material permeability, and biological compatibility. [22] Therefore, mechanically active, self-shaping hydrogels that undergo desired, programmable 3D shape transformations and execute mechanical tasks as soft robots under an external trigger have recently attracted growing interest. The use of a hydrogel system in soft robotic counterparts offers distinct advantages: simple designs, low cost, processability at low temperatures and in aqueous environments, and the possibility to mimic human functionality. [23,24] Directed movement of hydrogels can be obtained by expansion/contraction, for example, by isotropic volume expansion or shrinkage of homogeneous hydrogels or by the bending/unbending approach, which represents an anisotropic deformation and often involves fabrication of a hydrogel structure with two layers with different swellability values. [25][26][27][28][29] The first hydrogel-based bilayer actuation system composed of pNIPAM and acrylamide, obtained through conventional mold techniques, was demonstrated by Hu et al.; [25] after that, a range of self-assembled, origami-inspired structures were reported, [27,[30][31][32][33][34][35][36][37][38] but only a few works successfully realized 4D printing with hydrogels. [28,29] Some noteworthy Hydrogel actuators with soft-robotic functions and biomimetic advanced materials with facile and programmable fabrication processes remain scarce. A novel approach to fabricating a shape-memory-hydrogel-(SMG)-based bilayer system using 3D printing to yield a soft actuator responsive to the methodical application of swelling and heat is introduced. Each layer of the bilayer is composed of poly(N,N-dimethyl acrylamide-co-stearyl acrylate) (P(DMAAm-co-SA))-based hydrogels with different concentrations of the crystalline monomer SA within the SMG network...

Ionic liquids (ILs) are molten salts that are entirely composed of ions and have melting temperatures below 100 °C. When immobilized in polymeric matrices by sol–gel or chemical polymerization, they generate gels known as ion gels, ionogels, ionic gels, and so on, which may be used for a variety of electrochemical applications. One of the most significant research domains for IL-based gels is the energy industry, notably for energy storage and conversion devices, due to rising demand for clean, sustainable, and greener energy. Due to characteristics such as nonvolatility, high thermal stability, and strong ionic conductivity, IL-based gels appear to meet the stringent demands/criteria of these diverse application domains. This article focuses on the synthesis pathways of IL-based gel polymer electrolytes/organic gel electrolytes and their applications in batteries (Li-ion and beyond), fuel cells, and supercapacitors. Furthermore, the limitations and future possibilities of IL-based gels in the aforementioned application domains are discussed to support the speedy evolution of these materials in the appropriate applicable sectors.

Multi-walled carbon nanotubes (MWCNTs) without and with adsorbed silver nanoparticles (Ag-NPs), are used to detect acetone vapour. MWCNTs are grown on SiO2/Si substrates and silver (Ag) nanoparticles (NPs) are deposited onto some of these MWCNTs using electron beam evaporation method. The sensitivity of CNT based sensors (with and without NPs) increases with the concentration of acetone vapour (50 ppm to 800 ppm) while a substantial rise in sensitivity is obtained from MWCNTs with Ag NPs. Band diagrams of the MWCNTs, with and without NPs, are analyzed to understand the gas molecules adsorption phenomena. This study is the first to establish that such sensors can operate at 27 °C rather than the 180 °C–450 °C used elsewhere, thus offering significant advantages over existing methods. To investigate the sensors’ dependability, they’re exposed to three cycles of 50 ppm acetone gas. These tests show that the devices’ responses remain unchanged, indicating their reliability. The effects of humidity upon MWCNT acetone sensors within 100 ppm of acetone vapour are also studied and improved performance towards stability and response/recovery is observed for the sensors with Ag-NPs. Furthermore, higher selectivity is observed for the Ag-coated sensors for acetone against various target gases (acetone, ethanol, NO2, ammonia, and acetone with water).

Utilization of soft material like hydrogels for task-specific applications such as in soft robotics requires freedom in the manufacturing process and designability. Here, we have developed highly robust thermoresponsive poly(dimethyl acrylamide-co-stearyl acrylate and/or lauryl acrylate) (PDMAAm-co-SA and/or LA)-based shape memory gels (SMGs) using a customized optical 3D gel printer. This process enabled rapid and moldless fabrication of SMGs with a variety of shapes and sizes. By varying the compositions of the constituent monomers, a wide variety of SMGs with tunable mechanical, thermal, optical and swelling properties have been obtained. Printed SMGs with excellent fixity and recovery ratios have exhibited a wide range of values of Young's modulus (0.04-17.35 MPa) and strain (612-2363%) at room temperature when the acrylate co-monomer (SA and LA) content was varied and the value of strain has been found to be enhanced at elevated temperatures. Thermogravimetric analysis (TGA) of the SMGs shows one step peak degradation (407-417 °C) regardless of composition after an initial mass loss due to water evaporation. Dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC) revealed variable transition temperatures (29-49.5 °C) depending on the SA and LA content. SMGs with all of the composition ratios possess high transparency with variable swelling degrees in water and different organic solvents and exhibit refractive index values in the range of intraocular lenses, making them suitable for applications in the optical field. These unique properties of 3D printed SMGs with free formability and tunable properties are expected to generate rapid demand in a variety of sectors in biomedicine, robotics and sensing applications.

Wide band gap semiconductors such as ZnO are characterized by unique optoelectronic properties, which have led to numerous applications in the field of sensors and optoelectronics. These components are commonly fabricated on rigid substrates. However, the same synthesis method cannot be used to fabricate these components on flexible substrates. In this work, we present a method to fabricate metal−semiconductor−metal ultraviolet photodetectors with ZnO nanorods on flexible substrates. It is observed that the overall characteristics of the fabricated ZnO nanorod photodetector are greatly enhanced by doping with gallium (Ga). The nanorods are grown on a flexible substrate (poly(ethylene 2,6-naphthalate)) at a low temperature of 80 °C. The performance of Ga-doped ZnO nanorods (GZO) shows a significant improvement in electrical measurements compared to pure ZnO nanorods. The photocurrent-to-dark current ratios of both ZnO and GZO nanorod-based photodetectors are approximately 8.5 and 570.2 under a 1 V bias, respectively. The dark current and photocurrent are substantially improved by the addition of the Ga dopant. Transient response measurements indicated that the GZO nanorod photodetectors are stable and reproducible, and no change in the current−voltage characteristics is noted after multiple bending cycles. These results indicate that Ga-doping can improve the ZnO nanorod optical and electric characteristics; this proposed method is useful for device fabrication on low-melting-point substrates to produce flexible costeffective devices.

We have developed conductive microstructures using micropatternable and conductive hybrid nanocomposite polymer. In this method carbon fibers (CFs) were blended into polydimethylsiloxane (PDMS). Electrical conductivities of different compositions were investigated with various fiber lengths (50–250 μm), and weight percentages (wt%) (10–60 wt%). Sample composites of 2 cm × 1 cm × 500 μm were fabricated for 4-point probe conductivity measurements. The measured percolation thresholds varied with length of the fibers: 50 wt% (307.7 S/m) for 50 µm, 40 wt% (851.1 S/m) for 150 µm, and 30 wt% (769.23 S/m) for 250 μm fibers. The conductive composites showed higher elastic modulus when compared to that of PDMS.

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3D food printing sectors require comprehensive knowledge on viscoelastic and mechanical properties of diverse food materials in order to effectively utilize them in rapid and customized 3D production for supply and manufacturing chains. In this work, we present mechanical and rheological properties of Agar and Konjac based edible gels at different Agar and Konjac weight ratio and discuss their 3D printing performance. Gel samples with higher Konjac content positively contributed to the viscoelastic properties of the gel samples which in return has been found viable for extrusion-based 3D printing. By choosing appropriate printing parameters, different shapes are printed to demonstrate printing resolution. We expect, this study will add potential scope for evaluating and optimizing soft-gel materials for 3D food printing sector.