Second skin is a topically applied, skin-conforming material that mimics human skin properties and bears potential cosmetic and e-skin applications. To successfully integrate with natural skin, characteristics such as color and skin features must be matched. In this work, we prepared bio-based skin-like films from cross-linked keratin/melanin films (KMFs), using a simple fabrication method and non-toxic materials. The films retained their stability in aqueous solutions, showed skin-like mechanical properties, and were homogenous and handleable, with non-granular surfaces and a notable cross-linked structure as determined by attenuated total reflection (ATR). In addition, the combination of keratin and melanin allowed for adjustable tones similar to those of natural human skin. Furthermore, KMFs showed light transmittance and UV-blocking (up to 99%) as a function of melanin content. Finally, keratin/melanin ink (KMI) was used to inkjet-print high-resolution images with natural skin pigmented features. The KMFs and KMI may offer advanced solutions as e-skin or cosmetics platforms.
A near-perfect black solar absorber made of carbon nanotubes (CNTs) prepared by a low-cost wet-deposition method on a reflective metal surface for mid-temperature non-evacuated concentrated solar power (CSP) applications is demonstrated. The dispersed CNTs in an alumina–silica matrix exhibit an absorptance of 0.985 in the entire solar spectrum and emittance of 0.90 in the infrared (IR) region. The coating shows high durability and is super-hydrophilic (0° contact angle) after plasma treatment, without affecting the solar absorptance and excellent coating adhesion. The efficiency of the coating is evaluated by analytical models, which implies that it has higher efficiency at low temperature and at a high solar concentration ratio than that of previously reported selective coatings.
The 3D printing process enables to print objects having various functionalities at pre-designed locations in the object. Hereby, we report on the printing of superhydrophobic objects composed of patterns of micropillars. Superhydrophobicity is an important property of surfaces that has applications in various fields such as self-cleaning, drag reduction, increased buoyancy, and air conditioning. Most existing methods for the fabrication of superhydrophobic surfaces are complicated and time-consuming. Here, we performed a simple and cost-effective process for the fabrication of superhydrophobic (SH) objects by Digital Light Processing (DLP) 3D printing. To the best of our knowledge, this is the first study that has used DLP 3D printing to fabricate SH 3D objects without further coating process. We designed a novel ink, which contained non-fluorinated acrylates and Hydrophobic Fumed Silica (HFS). We studied the effects of HFS concentration and pillar-array design for imparting the SH property, which was measured in terms of the contact and rolling angle of water droplets on the surface. As proof of the concept of increased buoyancy by superhydrophobicity, we demonstrated the floatation of the printed SH objects in comparison to their non-SH counterparts even after forcefully submerging them into water.
Millions of people suffer from different types of skin diseases worldwide. In the last decade, the development of nanocarriers has been the focus of the pharmaceutical and cosmetic industries to enhance the performance of their products, and to meet consumers’ demands. Several delivery systems have been developed to improve the efficiency and minimize possible side effects. In this study, retinyl palmitate and Dead Sea water loaded nanoemulsions were developed as carriers to treat skin conditions such as photoaging, psoriasis, or atopic dermatitis. Toxicity profiles were carried out by means of viability, cell membrane asymmetry study, evaluation of oxidative stress induction (reactive oxygen species), and inflammation via cytokines production with a human keratinocyte cell line (HaCaT) and a mouse embryo fibroblasts cell line (BALB/3T3). Results showed that loaded nanoemulsions were found to be non-cytotoxic under the conditions of the study. Furthermore, no oxidative stress induction was observed. Likewise, an efficacy test of these loaded nanoemulsions was also tested on human skin organ cultures, before and after ultraviolet B light treatment. Viability and caspase-3 production assessment, in response to the exposure of skin explants to the loaded nanoemulsions, indicated non-toxic effects on human skin in culture, both with and without ultraviolet B irradiation. Further the ability of loaded nanoemulsions to protect the skin against ultraviolet B damage was assessed on skin explants reducing significantly the apoptotic activation after ultraviolet B irradiation. Our promising results indicate that the developed loaded nanoemulsions may represent a topical drug delivery system to be used as an alternative treatment for recurrent skin diseases.
Vanadium dioxide (VO2) based thermochromic smart window is considered as the most promising approach for economizing building energy consumption. However, the high phase transition temperature (τc), low luminous transmission (Tlum), and solar modulation (ΔTsol) impose an invertible challenge for commercialization. Currently, smart window research surprisingly assumes that the sunlight radiates in one direction which is obviously not valid as most regions receive solar radiation at various angles in different seasons. For the first time, solar elevation angle is considered and 3D printing technology is employed to fabricate tilted microstructures for modulating solar transmission dynamically. To maximize energy-saving performance, the architecture of the structures (tilt, thickness, spacing, and width) and tungsten (W) doped VO2 can be custom-designed according to the solar elevation angle variation at the midday between seasons and tackle the issue of compromised Tlum and ΔTsol with W-doping. The energy consumption simulations in different cities prove the efficiency of such dynamic modulation. This first attempt to adaptively regulate the solar modulation by considering the solar elevation angle together with one of the best reported thermochromic properties (τc = 40 °C, Tlum(average) = 40.8%, ΔTsol = 23.3%) may open a new era of real-world-scenario smart window research.
Ordered mesoporous silica materials gain high interest because of their potential applications in catalysis, selective adsorption, separation, and controlled drug release. Due to their morphological characteristics, mainly the tunable, ordered nanometric pores, they can be utilized as supporting hosts for confined chemical reactions. Applications of these materials, however, are limited by structural design. Here, we present a new approach for the 3D printing of complex geometry silica objects with an ordered mesoporous structure by stereolithography. The process uses photocurable liquid compositions that contain a structure-directing agent, silica precursors, and elastomer-forming monomers that, after printing and calcination, form porous silica monoliths. The objects have extremely high surface area, 1900 m2/g, and very low density and are thermally and chemically stable. This work enables the formation of ordered porous objects having complex geometries that can be utilized in applications in both the industry and academia, overcoming the structural limitations associated with traditional processing methods.
4D printed objects are 3D printed structures whose shape, property, and functionality are able to self-transform when exposed to a predetermined stimulus. The emerging field of 4D printing has attracted wide interest from both academia and industry since first introduced in 2013. Stimuli-responsive hydrogels have become a competitive and versatile group of materials for 4D printed devices due to their good deformability, promising biocompatibility, simple manufacturing, and low cost. This review aims to provide a summary of the current progress of hydrogel-based 4D printed objects and devices based on their fabrication techniques, materials, and applications. Herein, presented are: the characteristics of different additive manufacturing methods such as direct ink writing, fused deposition modeling, and stereolithography; the properties of various stimuli-responsive hydrogels such as poly(N-isopropylacrylamide) and poly(N,N-dimethylacrylamide), alginate, etc.; and diverse applications of 4D printed hydrogels such as actuators, cellular scaffolds, and drug release devices. Opportunities and challenges for 4D printed hydrogels are discussed and prospects for future development are elaborated.
Privacy and energy-saving are key functionalities for next-generation smart windows, while to achieve them independently on a window is challenging. Inspired by the cephalopod skin, we have developed a versatile thermo- and mechano-chromic design to overcome such challenge and reveal the mechanism via both experiments and simulations. The design is facile with good scalability, consisted of well-dispersed vanadium dioxide (VO2) nanoparticles (NPs) with temperature-dependent localized surface plasmon resonance (LSPR) in transparent elastomers with dynamic micro wrinkles. While maintaining a fixed solar energy modulation of (ΔTsol), the design can dynamically control visible transmittance (Tvib) from 60% to 17%, adding a new dimension to VO2-based smart windows. We prove that the optical modulation relies on the microtexture-induced broadband diffraction and the plasmon-enhanced near-infrared absorbance of VO2 NPs. We further present a series of modified designs towards additional functionalities. This work opens an avenue for independent dual-mode windows and it may inspire development from fundamental material, optic, and mechanical science to energy-related applications.
Electrochromic smart windows, with the ability to dynamically modulate thermal radiation transmission, are the key technologies to preserve energy expenditure for indoor lighting and air-conditioning. Despite receiving numerous exertions on design and fabrication technique, smart windows have rarely been commercially employed in the building industry due to unreliable lifetime, poor heat switching performance as well as high fabrication costs. Herein, we introduce a novel strategy in designing smart glass device, which focuses on the development of functionalized MxSnO2 nano-frameworks for electrochromic coating. The hybrid structures based on such nano-frameworks do not change the amorphous nature of electrodeposited tungsten trioxide (ɑ-WO3) layer and therefore are able to preserve its excellent electrochromic properties. Novel hybrid nano-structures of MxSnO2/ɑ-WO3 are able to encompass all desired features of a smart window, including the ability to block more than 95% NIR radiation in colored state while still allow about 80% of visible light transmittance in bleached state, rapid electro-optical response time of about 10 s and improved coloration efficiencies. More importantly, the advanced MxSnO2/ɑ-WO3 nanostructures can also retain their structure and functionality for at least 1000 switching cycles due to the enhanced binding strength. In addition, the synthetic recipe of such functionalized nano-framework is facile and cost-effective, enabling the fabrication on any template type and size.
Three-dimensional (3D) printing has recently been introduced into the field of chemistry as an enabling tool employed to perform reactions, but so far, its use has been limited due to material and structural constraints. We have developed a new approach for fabricating 3D catalysts with high-complexity features for chemical reactions via digital light processing printing (DLP). PtO2-WO3 heterogeneous catalysts with complex shapes were directly fabricated from a clear solution, composed of photo-curable organic monomers, photoinitiators, and metallic salts. The 3D-printed catalysts were tested for the hydrogenation of alkynes and nitrobenzene, and displayed excellent reactivity in these catalytic transformations. Furthermore, to demonstrate the versatility of this approach and prove the concept of multifunctional reactors, a tungsten oxide-based tube consisting of three orderly sections containing platinum, rhodium, and palladium was 3D printed.
We report a method for the design and fabrication of 3D printed bioanodes for Biophotovotaic (BPV) applications. Electrodes were fabricated in 5 different thicknesses, from 0.2 mm to 1.0 mm with a 0.2 mm increment and the electrodes were coated with multi-wall carbon nanotubes (MWCNTs). Electrochemical characterisation of these electrodes was performed and the performance tested alongside a bare carbon paper electrode in a bespoke designed membrane electrode assembly (MEA)-type BPV device. All of the MWCNTs-coated 3D printed electrodes outperformed the bare carbon paper electrode. The best performing one (1.0 mm) showed a 40 times increment in power density and a 20 times reduction of the internal resistance. The successful development of the 3D printed bioanode can be used as a standardised platform for the comparison of similar materials. The development of the electrodes and MEA-type BPV device will serve as the initial step towards the development of a monolithic 3D printed BPV platform.
Coordination polymers (CPs) and coordination network solids such as metal-organic frameworks (MOFs) have gained increasing interest during recent years due to their unique properties and potential applications. Preparing 3D printed structures using CP would provide many advantages towards utilization in fields such as catalysis and sensing. So far, functional 3D structures were printed mostly by dispersing pre-synthesized particles of CPs and MOFs within a polymerizable carrier. This resulted in a CP active material dispersed within a 3D polymeric object, which may obstruct or impede the intrinsic properties of the CP. Here, we present a new concept for obtaining 3D free-standing objects solely composed of CP material, starting from coordination metal complexes as the monomeric building blocks, and utilizing the 3D printer itself as a tool to in situ synthesize a coordination polymer during printing, and to shape it into a 3D object, simultaneously. To demonstrate this, a 3D-shaped nickel tetra-acrylamide monomeric complex composed solely of the CP without a binder was successfully prepared using our direct print-and-form approach. We expect that this work will open new directions and unlimited potential in additive manufacturing and utilization of CPs.
Transparent ceramics are usually polycrystalline materials, which are wildly used in many optical applications, such as lasers. As of today, the fabrication of transparent ceramic structures is still limited to conventional fabrication methods, which do not enable the formation of complex structures. A new approach for 3D printing of micrometer-size, transparent ceramic structures is presented. By using a solution of metal salts that can undergo a sol–gel process and photopolymerization by two-photon printing, micrometer-sized yttrium aluminum garnet (YAG) structures doped with neodymium (Nd) are fabricated. The resulting structures are not only transparent in the visible spectrum but can also emit light at 1064 nm due to the doping with Nd. By using solution-based precursors, without any particles, the sintering can be performed under air at ambient pressure and at a relatively low temperature, compared to conventional processes for YAG. The crystalline structure is imaged at atomic resolution by ultrahigh-resolution scanning transmission electron microscopy (STEM), indicating that the doped Nd atoms are located at the yttrium positions. Such miniaturized structures can be used for diverse applications, e.g., optical components in high-intensity laser systems, which require heat resistance, or as light sources in optical circuits.
Graphene and its derivatives have been reported as materials with excellent electrical and thermal conductivity, allowing for various promising applications. In particular, the large-scale surface coating of graphene-based materials can be employed to minimize cross-sectional heat transfer through the glass window. This study introduces a facile and cost-effective method to fabricate graphene quantum dots (GQDs) thin film on Fluorine-doped Tin Oxide (FTO) glass via casting of the GQDs dispersion and stabilizing with poly-vinyl-pyrrolidone (PVP). The thin film possesses excellent optical properties of GQDs and allows more than 80% of visible transmittance. The presence of the GQDs thin film shows effective reduction in the cross-sectional thermal diffusivity of FTO glass, from 0.55 mm2/s to zero when measured with laser flash over a 4-second period. This low cost and eco-friendly GQDs thin film will be a promising material for heat management in smart window applications.
Shape memory polymers are attractive smart materials that have many practical applications and academic interest. Three-dimensional (3D) printable shape memory polymers are of great importance for the fabrication of soft robotic devices due to their ability to build complex 3D structures with desired shapes. We present a 3D printable shape memory polymer, with controlled melting and transition temperature, composed of methacrylated polycaprolactone monomers and N-Vinylcaprolactam reactive diluent. Tuning the ratio between the monomers and the diluents resulted in changes in melting and transition temperatures by 20, and 6 °C, respectively. The effect of the diluent addition on the shape memory behavior and mechanical properties was studied, showing above 85% recovery ratio, and above 90% fixity, when the concentration of the diluent was up to 40 wt %. Finally, we demonstrated multi-material printing of a 3D structure that can be activated locally, at two different temperatures, by two different stimuli; direct heating and light irradiation. The remote light activation was enabled by utilizing a coating of Carbon Nano Tubes (CNTs) as an absorbing material, onto sections of the printed objects.
The selective removal of radioactive cationic species, specifically 137Cs+ and 90Sr2+, from contaminated water is critical for nuclear waste remediation processes and environmental cleanup after accidents, such as the Fukushima Daiichi Nuclear Power Plant disaster in 2011. Nanoporous silicates, such as zeolites, are most commonly used for this process but in addition to acting as selective ion exchange media must also be deployable in a correct physical form for flow columns. Herein, Digital Light Processing (DLP) three-dimensional (3D) printing was utilized to form monoliths from zeolite ion exchange powders that are known to be good for nuclear wastewater treatment. The monoliths comprise 3D porous structures that will selectively remove radionuclides in an engineered form that can be tailored to various sizes and shapes as required for any column system and can even be made with fine-grained powders unsuitable for normal gravity flow column use. 3D-printed monoliths of zeolites chabazite and 4A were made, characterized, and evaluated for their ion exchange capacities for cesium and strontium under static conditions. The 3D-printed monoliths with 50 wt% zeolite loadings exhibit Cs and Sr uptake with an equivalent ion-capacity as their pristine powders. These monoliths retain their porosity, shape and mechanical integrity in aqueous media, providing a great potential for use to not only remove radionuclides from nuclear wastewater, but more widely in other aqueous separation-based applications and processes.