MXene‐Reinforced Cellulose Nanofibril Inks for 3D‐Printed Smart Fibres and Textiles

Fibre‐based materials have received tremendous attention due to their flexibility and wearability. Although great efforts have been devoted to achieve high‐performance fibres over the past several years, it is still challenging for multifunctional macroscopic fibres to satisfy versatile applications. 2D transition metal carbides/nitrides (MXenes) with intriguing physical/chemical properties have been explored in broad application, and may be able to reinforce synthetic fibres. Inspired by natural materials, for the first time, flexible smart fibres and textiles are fabricated using a 3D printing process with hybrid inks of TEMPO (2,2,6,6‐tetramethylpiperidine‐1‐oxylradi‐cal)‐mediated oxidized cellulose nanofibrils (TOCNFs) and Ti₃C₂ MXene. The hybrid inks display good rheological properties, which allow them to achieve accurate structures and be rapidly printed. TOCNFs/Ti₃C₂ in hybrid inks self‐assemble to fibres with an aligned structure in ethanol, mimicking the features of the natural structures of plant fibres. In contrast to conventional synthetic fibres with limited functions, smart TOCNFs/Ti₃C₂ fibres and textiles exhibit significant responsiveness to multiple external stimuli (electrical/photonic/mechanical). TOCNFs/Ti₃C₂ textiles with electromechanical performance can be processed into sensitive strain sensors. Such multifunctional smart fibres and textiles will be promising in diverse applications, including wearable heating textiles, human health monitoring, and human–machine interfaces.     

Self‐Healing and Stretchable 3D‐Printed Organic Thermoelectrics

With the advent of flexible and wearable electronics and sensors, there is an urgent need to develop energy‐harvesting solutions that are compatible with such wearables. However, many of the proposed energy‐harvesting solutions lack the necessary mechanical properties, which make them susceptible to damage by repetitive and continuous mechanical stresses, leading to serious degradation in device performance. Developing new energy materials that possess high deformability and self‐healability is essential to realize self‐powered devices. Herein, a thermoelectric ternary composite is demonstrated that possesses both self‐healing and stretchable properties produced via 3D‐printing method. The ternary composite films provide stable thermoelectric performance during viscoelastic deformation, up to 35% tensile strain. Importantly, after being completely severed by cutting, the composite films autonomously recover their thermoelectric properties with a rapid response time of around one second. Using this self‐healable and solution‐processable composite, 3D‐printed thermoelectric generators are fabricated, which retain above 85% of their initial power output, even after repetitive cutting and self‐healing. This approach represents a significant step in achieving damage‐free and truly wearable 3D‐printed organic thermoelectrics.     

Self‐Propelled 3D‐Printed “Aircraft Carrier” of Light‐Powered Smart Micromachines for Large‐Volume Nitroaromatic Explosives Removal

Self‐propelled micro‐/nanomotors are in the forefront of materials research, for applications ranging from environmental remediation to biomedicine. However, due to their limited sizes, they can only navigate within small distances, typically in the order of millimeters, which inevitably hinder their use for large‐volume real applications. Here it is shown that a 3D‐printed millimeter‐scale motor (3DP‐motor) can act as “aircraft carrier” of TiO₂/Pt Janus micromotors and be used for enhanced large‐volume environmental remediation applications. The 3DP‐motor can move fast for tens of meters through the Marangoni effect by asymmetrically releasing ethanol. During its navigation, this 3DP‐motor can carry and slowly release in solution TiO₂/Pt Janus micromotors which can be propelled by light illumination while acting as photodegradation agents. Highly efficient degradation of nitroaromatic explosives over a large solution area is achieved. A wall‐following motion of the 3DP‐motor without external guidance is also demonstrated which is generated by the chemiosmotic flow at the wall vicinity. This can be easily tuned by changing the wettability of the wall surface and also modifying the shape of 3DP‐motor, leading to different motion behaviors. This work introduces a new concept of micromotors carried by large millimeter sized motors to traverse long distances and it should find a broad range of applications.     

Complex 3D‐Printed Microchannels within Cell‐Degradable Hydrogels

3D‐printing is emerging as a technology to introduce microchannels into hydrogels, for the perfusion of engineered constructs. Although numerous techniques have been developed, new techniques are still needed to obtain the complex geometries of blood vessels and with materials that permit desired cellular responses. Here, a printing process where a shear‐thinning and self‐healing hydrogel “ink” is injected directly into a “support” hydrogel with similar properties is reported. The support hydrogel is further engineered to undergo stabilization through a thiol‐ene reaction, permitting (i) the washing of the ink to produce microchannels and (ii) tunable properties depending on the crosslinker design. When adhesive peptides are included in the support hydrogel, endothelial cells form confluent monolayers within the channels, across a range of printed configurations (e.g., straight, stenosis, spiral). When protease‐degradable crosslinkers are used for the support hydrogel and gradients of angiogenic factors are introduced, endothelial cells sprout into the support hydrogel in the direction of the gradient. This printing approach is used to investigate the influence of channel curvature on angiogenic sprouting and increased sprouting is observed at curved locations. Ultimately, this technique can be used for a range of biomedical applications, from engineering vascularized tissue constructs to modeling in vitro cultures.     

3D‐Printed Microrobotic Transporters with Recapitulated Stem Cell Niche for Programmable and Active Cell Delivery

Poor retention rate, low targeting accuracy, and spontaneous transformation of stem cells present major clinical barriers to the success of therapies based on stem cell transplantation. To improve the clinical outcome, efforts should focus on the active delivery of stem cells to the target tissue site within a controlled environment, increasing survival, and fate for effective tissue regeneration. Here, a remotely steerable microrobotic cell transporter is presented with a biophysically and biochemically recapitulated stem cell niche for directing stem cells towards a pre‐destined cell lineage. The magnetically actuated double‐helical cell microtransporters of 76 µm length and 20 µm inner cavity diameter are 3D printed where biological and mechanical information regarding the stem cell niche are encoded at the single‐cell level. Cell‐loaded microtransporters are mobilized inside confined microchannels along computer‐controlled trajectories under rotating magnetic fields. The mesenchymal stem cells are shown retaining their differentiation capacities to commit to the osteogenic lineage when stimulated inside the microswimmers in vitro. Such a microrobotic approach has the potential to enable the development of active microcarriers with embedded functionalities for controlled and precisely localized therapeutic cell delivery.     

3D‐Printed All‐Fiber Li‐Ion Battery toward Wearable Energy Storage

Conventional bulky and rigid power systems are incapable of meeting flexibility and breathability requirements for wearable applications. Despite the tremendous efforts dedicated to developing various 1D energy storage devices with sufficient flexibility, challenges remain pertaining to fabrication scalability, cost, and efficiency. Here, a scalable, low‐cost, and high‐efficiency 3D printing technology is applied to fabricate a flexible all‐fiber lithium‐ion battery (LIB). Highly viscous polymer inks containing carbon nanotubes and either lithium iron phosphate (LFP) or lithium titanium oxide (LTO) are used to print LFP fiber cathodes and LTO fiber anodes, respectively. Both fiber electrodes demonstrate good flexibility and high electrochemical performance in half‐cell configurations. All‐fiber LIB can be successfully assembled by twisting the as‐printed LFP and LTO fibers together with gel polymer as the quasi‐solid electrolyte. The all‐fiber device exhibits a high specific capacity of ≈110 mAh g^?1 at a current density of 50 mA g^?1 and maintains a good flexibility of the fiber electrodes, which can be potentially integrated into textile fabrics for future wearable electronic applications.     

Helical 3D‐Printed Metal Electrodes as Custom‐Shaped 3D Platform for Electrochemical Devices

3D‐printing represents an emerging technology that can revolutionize the way object and functional devices are fabricated. Here the use of metal 3D printing is demonstrated to fabricate bespoke electrochemical stainless steel electrodes that can be used as platform for different electrochemical applications ranging from electrochemical capacitors, oxygen evolution catalyst, and pH sensor by means of an effective and controlled deposition of IrO₂ films. The electrodes have been characterized by scanning electrode microscopy and energy dispersive X‐ray spectroscopy before the electrochemical testing. Excellent pseudocapacitive as well as catalytic properties have been achieved with these 3D printed steel‐IrO₂ electrodes in alkaline solutions. These electrodes also demonstrate Nernstian behavior as pH sensor. This work represents a breakthrough in on‐site prototyping and fabrication of highly tailored electrochemical devices with complex 3D shapes which facilitate specific functions and properties.     

3D Printed High‐Loading Lithium‐Sulfur Battery Toward Wearable Energy Storage

Wearable electronic devices are the new darling of consumer electronics, and energy storage devices are an important part of them. Here, a wearable lithium‐sulfur (Li‐S) bracelet battery using three‐dimensional (3D) printing technology (additive manufacturing) is designed and manufactured for the first time. The bracelet battery can be easily worn to power the wearable device. The “additive” manufacturing characteristic of 3D printing provides excellent controllability of the electrode thickness with much simplified process in a cost‐effective manner. Due to the conductive 3D skeleton providing interpenetrating transmission paths and channels for electrons and ions, the 3D Li‐S battery can provide 505.4 mAh g^?1 specific capacity after 500 cycles with an active material loading as high as 10.2 mg cm^?1. The practicality is illustrated by wearing the bracelet battery on the wrist and illuminating the red light‐emitting diode. Therefore, the bracelet battery manufactured by 3D printing technology can address the needs of the wearable power supply.     

Metallic Architectures from 3D‐Printed Powder‐Based Liquid Inks

A new method for complex metallic architecture fabrication is presented, through synthesis and 3D‐printing of a new class of 3D‐inks into green‐body structures followed by thermochemical transformation into sintered metallic counterparts. Small and large volumes of metal‐oxide, metal, and metal compound 3D‐printable inks are synthesized through simple mixing of solvent, powder, and the biomedical elastomer, polylactic‐co‐glycolic acid (PLGA). These inks can be 3D‐printed under ambient conditions via simple extrusion at speeds upwards of 150 mm s^–1 into millimeter‐ and centimeter‐scale thin, thick, high aspect ratio, hollow and enclosed, and multi‐material architectures. The resulting 3D‐printed green‐bodies can be handled immediately, are remarkably robust, and may be further manipulated prior to metallic transformation. Green‐bodies are transformed into metallic counterparts without warping or cracking through reduction and sintering in a H₂ atmosphere at elevated temperatures. It is shown that primary metal and binary alloy structures can be created from inks comprised of single and mixed oxide powders, and the versatility of the process is illustrated through its extension to more than two dozen additional metal‐based materials. A potential application of this new system is briefly demonstrated through cyclic reduction and oxidation of 3D‐printed iron oxide constructs, which remain intact through numerous redox cycles.     

3D‐Printed Biomimetic Scaffold Simulating Microfibril Muscle Structure

In the human body, microfibril structures can be found in several types of tissue, such as muscles, nerves, and even tendons. However, most micropatterned fabrication methods have focused on 2D surface patterned configurations, which imitate the alignment and fusion of cardiac and skeletal muscle cells. Despite the development of these 2D methods, it has continued to be a challenge to fabricate realistic 3D microfibril structures. The goal of this study is to develop a micropatterned polycaprolactone (PCL) microfiber strut. This process uses a microfibrillation/leaching process of poly(vinyl alcohol) (PVA) from a PVA/PCL mixture to imitate skeletal muscle cell alignment and fusion in vitro. To attain the optimal processing conditions, a variety of parameters—including a mixture ratio, processing temperature, and pneumatic pressure—are considered. To increase biocompatibility of a microfibrous PCL bundle, the fabricated structure is supplemented with type‐I collagen. The myoblasts (C2C12 cells) are used to determine the cellular responses of the fabricated structure. By analyzing cell proliferation and myogenic differentiation, it can be confirmed that the hybrid microfibrillated structure can be an important potential platform to obtain efficient regeneration of muscle cells.     

All‐Printed Flexible and Stretchable Electronics with Pressing or Freezing Activatable Liquid‐Metal–Silicone Inks

Liquid‐metal (LM)‐based flexible and stretchable electronics have attracted widespread interest in wearable computing, human–machine interaction, and soft robotics. However, many current examples are one‐off prototypes, whereas future implementation requires mass production. To address this critical challenge, an integrated multimaterial 3D printing process composed of direct ink writing (DIW) of sealing silicone elastomer and special LM‐silicone (LMS) inks for manufacturing high‐performance LM‐based flexible and stretchable electronics is presented. The LMS ink is a concentrated mixture of LM microdroplets and silicone elastomer and exhibits excellent printability for DIW printing. Guided by a verified theoretical model, a printing process with high resolution and high speed can be easily implemented. Although LMS is not initially conductive, it can be activated by pressing or freezing. Activated LMS possesses good conductivity and significant electrical response to strain. Owing to LMS's unique structure, LMS‐embedded flexible electronics exhibit great damage mitigation, in that no leaking occurs even when damaged. To demonstrate the flexibility of this process in fabricating LM‐based flexible electronics, multilayer soft circuits, strain sensors, and data gloves are printed and investigated. Notably, utilizing LMS's unique activating property, some functional circuits such as one‐time pressing/freezing‐on switch can be printed without any structural design.     

Wood‐Inspired 3D‐Printed Helical Composites with Tunable and Enhanced Mechanical Performance

Helical fibers are versatile building blocks used by Nature to improve mechanical performance and to tune local behavior of load‐bearing materials. Helicoidal biocomposites are arranged in multiple layers with different fiber orientations. Such heterogeneity, not matched in synthetic materials, provides biological structures with superior properties. This is the case of the multilayer tube‐like structure of the wood cell wall, where each ply features a compliant matrix reinforced by stiff helicoidal microfibrils. Here, 3D polyjet printing and computer simulations are combined to investigate wood‐inspired helix‐reinforced cylinders. Composites with a main layer containing helicoidal fibers, bordered by inner and outer plies having thinner fibrils are considered. It is shown how the mechanical functionalities of the synthetic structures can be programmed by varying fibers/fibrils orientation and matrix compliance. It is demonstrated that failure resistance can be enhanced by enclosing the main helicoidal layer with a minimum amount of thin fibrils oriented perpendicular to the applied load, as observed in wood. Finite element simulations are used to highlight the critical role of the matrix in load‐transfer mechanisms among stiff elements. These structures have the potential to be assembled into larger systems, leading to graded composites with region‐specific properties optimized for multiple functionalities.     

Tunable Room‐Temperature Synthesis of ReS2 Bicatalyst on 3D‐ and 2D‐Printed Electrodes for Photo‐ and Electrochemical Energy Applications

The advancement in 3D‐printing technologies conveniently offers boundless opportunities for the customization of a practical substrate or electrode for diverse functionalities. ReS₂ is an attractive transition metal dichalcogenide (TMD), showing strong photoelectrochemical activities. Two advanced systems are merged for the next step in electrochemistry—the limits of the prevailing synthesis techniques of TMDs operating at high temperature or low pressure, which are not compatible with 3D‐printed polymer electrodes that can withstand only comparatively low temperatures, are overcome. A unique NH₄ReS₄ precursor is separately prepared to conduct subsequent ReS₂ electrodeposition at room temperature on 3D‐printed carbon and 2D‐printed carbon electrodes. The deposited ReS₂ is investigated as a dual‐functional electro‐ and photocatalyst in hydrogen evolution reaction and photoelectrochemical oxidation of water. Moreover, the electrodeposition conditions can be adjusted to optimize the catalytic activities. These encouraging outcomes demonstrate the simplicity yet versatility of TMDs based on electrodeposition technique on a rationally designed conductive platform, which creates numerous possibilities for other TMDs and on other low‐temperature substrates for electrochemical energy devices.     

Highly Elastic,Transparent, and Conductive 3D‐Printed Ionic Composite Hydrogels

Despite extensive progress to engineer hydrogels for a broad range of technologies, practical applications have remained elusive due to their (until recently) poor mechanical properties and lack of fabrication approaches, which constrain active structures to simple geometries. This study demonstrates a family of ionic composite hydrogels with excellent mechanical properties that can be rapidly 3D‐printed at high resolution using commercial stereolithography technology. The new material design leverages the dynamic and reversible nature of ionic interactions present in the system with the reinforcement ability of nanoparticles. The composite hydrogels combine within a single platform tunable stiffness, toughness, extensibility, and resiliency behavior not reported previously in other engineered hydrogels. In addition to their excellent mechanical performance, the ionic composites exhibit fast gelling under near‐UV exposure, remarkable conductivity, and fast osmotically driven actuation. The design of such ionic composites, which combine a range of tunable properties and can be readily 3D‐printed into complex architectures, provides opportunities for a variety of practical applications such as artificial tissue, soft actuators, compliant conductors, and sensors for soft robotics.     

3D‐Printed MOF‐Derived Hierarchically Porous Frameworks for Practical High‐Energy Density Li–O2 Batteries

Aprotic Li–O₂ batteries are promising candidates for next‐generation energy storage technologies owing to their high theoretical energy densities. However, their practically achievable specific energy is largely limited by the need for porous conducting matrices as cathode support and the passivation of cathode surface by the insulating Li₂O₂ product. Herein, a self‐standing and hierarchically porous carbon framework is reported with Co nanoparticles embedded within developed by 3D‐printing of cobalt‐based metal–organic framework (Co‐MOF) using an extrusion‐based printer, followed by appropriate annealing. The novel self‐standing framework possesses good conductivity and necessary mechanical stability, so that it can act as a porous conducting matrix. Moreover, the porous framework consists of abundant micrometer‐sized pores formed between Co‐MOF‐derived carbon flakes and meso‐ and micropores formed within the flakes, which together significantly benefit the efficient deposition of Li₂O₂ particles and facilitate their decomposition due to the confinement of insulating Li₂O₂ within the pores and the presence of Co electrocatalysts. Therefore, the self‐standing porous architecture significantly enhances the cell's practical specific energy, achieving a high value of 798 Wh kg^?1_cell. This study provides an effective approach to increase the practical specific energy for Li–O₂ batteries by constructing 3D‐printed framework cathodes.     

Programmed Deformations of 3D‐Printed Tough Physical Hydrogels with High Response Speed and Large Output Force

Shape‐morphing hydrogels have emerging applications in biomedical devices, soft robotics, and so on. However, successful applications require a combination of excellent mechanical properties and fast responding speed, which are usually a trade‐off in hydrogel‐based devices. Here, a facile approach to fabricate 3D gel constructs by extrusion‐based printing of tough physical hydrogels, which show programmable deformations with high response speed and large output force, is described. Highly viscoelastic poly(acrylic acid‐co‐acrylamide) (P(AAc‐co‐AAm)) and poly(acrylic acid‐co‐N‐isopropyl acrylamide) (P(AAc‐co‐NIPAm)) solutions or their mixtures are printed into 3D constructs by using multiple nozzles, which are then transferred into FeCl₃ solution to gel the structures by forming robust carboxyl–Fe³⁺ coordination complexes. The printed gel fibers containing poly(N‐isopropyl acrylamide) segment exhibit considerable volume contraction in concentrated saline solution, whereas the P(AAc‐co‐AAm) ones do not contract. The mismatch in responsiveness of the gel fibers affords the integrated 3D gel constructs the shape‐morphing ability. Because of the small diameter of gel fibers, the printed gel structures deform and recover with a fast speed. A four‐armed gripper is designed to clamp plastic balls with considerable holding force, as large as 115 times the weight of the gripper. This strategy should be applicable to other tough hydrogels and broaden their applications.     

Multifunctional Up‐Converting Nanocomposites with Smart Polymer Brushes Gated Mesopores for Cell Imaging and Thermo/pH Dual‐Responsive Drug Controlled Release

Multifunctional nanocarriers based on the up‐conversion luminescent nanoparticles of NaYF₄:Yb³⁺/Er³⁺ core (UCNPs) and thermo/pH‐coupling sensitive polymer poly[(N‐isopropylacrylamide)‐co‐(methacrylic acid)] (P(NIPAm‐co‐MAA)) gated mesoporous silica shell are reported for cancer theranostics, including fluorescence imaging, and for controlled drug release for therapy. The as‐synthesized hybrid nanospheres UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) show bright green up‐conversion fluorescence under 980 nm laser excitation and the thermo/pH‐sensitive polymer is active as a “valve” to moderate the diffusion of the embedded drugs in‐and‐out of the pore channels of the silica container. The anticancer drug doxorubicin hydrochloride (DOX) can be absorbed into UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) nanospheres and the composite drug delivery system (DDS) shows a low level of leakage at low temperature/high pH values but significantly enhanced release at higher temperature/lower pH values, exhibiting an apparent thermo/pH controlled “on‐off” drug release pattern. The as‐prepared UCNPs@mSiO₂‐P(NIPAm‐co‐MAA) hybrid nanospheres can be used as bioimaging agents and biomonitors to track the extent of drug release. The reported multifunctional nanocarriers represent a novel and versatile class of platform for simultaneous imaging and stimuli‐responsive controlled drug delivery.     

Reusable HEVC Design in 3D‐HEVC

This paper proposes a reusable design for the merging process used in three‐dimensional High Efficiency Video Coding (3D‐HEVC), which can significantly reduce the implementation complexity by eliminating duplicated module redundancies. The majority of inter‐prediction coding tools used in 3D‐HEVC are utilized through a merge mode, whose extended merging process is based on built‐in integration to completely wrap around the HEVC merging process. Consequently, the implementation complexity is unavoidably very high. To facilitate easy market implementation, the design of a legacy codec should be reused in an extended codec if possible. The proposed 3D‐HEVC merging process is divided into the base merging process of reusing HEVC modules and reprocessing process of refining the existing processes that have been newly introduced or modified for 3D‐HEVC. To create a reusable design, the causal and mutual dependencies between the newly added modules for 3D‐HEVC and the reused HEVC modules are eliminated, and the ineffective methods are simplified. In an application of the proposed reusable design, the duplicated reimplementation of HEVC modules, which account for of the 3D‐HEVC merging process, can be eliminated while maintaining the same coding efficiency. The proposed method has been adopted as a normative coding tool in the 3D‐HEVC international standard.