Embedded 3D Printing of Architected Ceramics via Microwave-Activated Polymerization

Hybrid Formative-Additive Manufacturing

Material extrusion additive manufacturing (AM) provides extensive design flexibility and exceptional material versatility, enabling the fabrication of complex, multifunctional objects ranging from embedded electronics to soft robotics and vascularized tissues. The bottom-up creation of these objects typically requires discretization into layers and voxels. However, the voxel size, determined by the nozzle diameter, limits extrusion rate, creating a conflict between resolution and speed. To address these inherent scalability challenges, the study proposes a hybrid formative-additive manufacturing technology that combines the respective strengths of each method-speed and quality with complexity and flexibility. The approach involves 3D-printing complex geometries, multimaterial features, and bounding walls of bulky, lower-resolution volumes, which are rapidly filled via casting or molding. By precisely controlling the materials' rheological properties-while maintaining similar solidified properties and high interfacial strength-several typical AM flaws, such as bulging and internal voids, are eliminated, achieving exponentially faster production speeds for objects with varying feature sizes.

The Significance and Usage Strategies of Macromolecules in 3D Printed Ceramic Composites

3D printing technology enables the creation of complex ceramic structures and enhances the efficiency of customized ceramic production. Polymers play a crucial role in 3D-printed ceramic composites due to their unique processability, yet their significance and application strategies remain underexplored. These polymers not only enable rapid and precise 3D shaping but also offer additional advantages due to their unique and adjustable physicochemical properties. Therefore, the appropriate selection and utilization of polymers are expected to drive new breakthroughs in the field of 3D-printed ceramic composites. This review provides an overview of relevant additive manufacturing technologies and processes, with a specific focus on the strategies for using polymers in 3D-printed ceramic composites, including their roles as binders, templates, preceramics, and matrices. Highlighting the critical functionalities and potential value of these ceramic composites from a practical application perspective.

All-Aqueous Embedded 3D Printing for Freeform Fabrication of Biomimetic 3D Constructs

All-aqueous embedded 3D printing, which involves extruding inks in an aqueous bath, has emerged as a transformative platform for the freeform fabrication of 3D constructs with precise control. The use of a supporting bath not only enables the printing of arbitrarily designed 3D constructs but also broadens ink selection for various soft matters, advancing the wide application of this technology. This review focuses on recent progress in the freeform preparation of 3D constructs using all-aqueous embedded 3D printing. It begins by discussing the significance of ultralow interfacial tension in all-liquid embedded printing and highlights the fundamental concepts and properties of all-aqueous system. The review then introduces recent advances in all-aqueous embedded 3D printing and clarifies the key factors affecting printing stability and shape fidelity, aiming to guide expansion and assessment of emerging printing systems used for various representative applications. Furthermore, it proposes the potential scope and applications of this technology, including in vitro models, cytomimetic microreactors, and soft ionic electronics. Finally, the review discusses the challenges facing current all-aqueous embedded 3D printing and offers future perspectives on possible improvements and developments.

3D Printing of Metals with sub-10 µm Resolution

The ability to manufacture 3D metallic architectures with microscale resolution is greatly pursued because of their diverse applications in microelectromechanical systems (MEMS) including microelectronics, mechanical metamaterials, and biomedical devices. However, the well-developed photolithography and emerging metal additive manufacturing technologies have limited abilities in manufacturing micro-scaled metallic structures with freeform 3D geometries. Here, for the first time, the high-fidelity fabrication of arbitrary metallic motifs with sub-10 µm resolution is achieved by employing an embedded-writing embedded-sintering (EWES) process. A paraffin wax-based supporting matrix with high thermal stability is developed, which permits the printed silver nanoparticle ink to be pre-sintered at 175 °C to form metallic green bodies. Via carefully regulating the matrix components, the printing resolution is tuned down to ≈7 µm. The green bodies are then embedded in a supporting salt bath and further sintered to realize freeform 3D silver motifs with great structure fidelity. 3D printing of various micro-scaled silver architectures is demonstrated such as micro-spring arrays, BCC lattices, horn antenna, and rotatable windmills. This method can be extended to the high-fidelity 3D printing of other metals and metal oxides which require high-temperature sintering, providing the pathways toward the design and fabrication of 3D MEMS with complex geometries and functions.

Sophisticated Structural Ceramics Shaped from 3D Printed Hydrogel Preceramic Skeleton

Shaping ceramic materials into sophisticated architecture with 3D hierarchical structure is desirable in multiapplication yet remains challenge due to their brittle and stiff nature. Herein, a new method to achieve ceramic architectures with unsupported and large-spanning structure by shaping vat photopolymerization 3D printed hydrogel preceramic skeleton with unique flexible and deformable character is proposed. Specifically, the present photopolymerizable hydrogel preceramic achieves one stone, two birds: the photosensitive polymer matrix coupled with ceramic nanoparticles for the first shaping by vat photopolymerization 3D printing and the secondary plasticity of the 3D printed ceramic body through flexible shape deformation of hydrogel networks. Inorganic binder aluminum dihydrogen phosphate serves as hydrogel dispersion medium to achieve ultralow shrinkage photopolymerization ceramic. Compared with conventional polymer-derived photocuring ceramics, the linear shrinkage of lamina structure is solely 2%, and which of cubic ceramic structure is just 13.3%. More importantly, one 3D printed preceramic is conducted to reshape repeatedly myriad constructions, realizing reusability of intrinsic brittle ceramic, improving manufacturing fault tolerance rate. Finally, a variety of paradigms for ceramic structure applications are proposed toward stereo circuit, biomedicine, and catalytic applications, breaking the limitation of intrinsic brittleness of ceramic in high-precision manufacturing of complex ceramic devices.

Toward Multiscale, Multimaterial 3D Printing

Biological materials and organisms possess the fundamental ability to self-organize, through which different components are assembled from the molecular level up to hierarchical structures with superior mechanical properties and multifunctionalities. These complex composites inspire material scientists to design new engineered materials by integrating multiple ingredients and structures over a wide range. Additive manufacturing, also known as 3D printing, has advantages with respect to fabricating multiscale and multi-material structures. The need for multifunctional materials is driving 3D printing techniques toward arbitrary 3D architectures with the next level of complexity. In this paper, the aim is to highlight key features of those 3D printing techniques that can produce either multiscale or multimaterial structures, including innovations in printing methods, materials processing approaches, and hardware improvements. Several issues and challenges related to current methods are discussed. Ultimately, the authors also provide their perspective on how to realize the combination of multiscale and multimaterial capabilities in 3D printing processes and future directions based on emerging research.

Architected Poly(ionic liquid) Composites with Spatially Programmable Mechanical Properties and Mixed Conductivity

Structural electrolytes present advantages over liquid varieties, which are critical to myriad applications. In particular, structural electrolytes based on polymerized ionic liquids or poly(ionic liquids) (pILs) provide wide electrochemical windows, high thermal stability, nonvolatility, and modular chemistry. However, current methods of fabricating structural electrolytes from pILs and their composites present limitations. Recent advances have been made in 3D printing pIL electrolytes, but current printing techniques limit the complexity of forms that can be achieved, as well as the ability to control mechanical properties or conductivity. We introduce a method for fabricating architected pIL composites as structural electrolytes via embedded 3D (EMB3D) printing. We present a modular design for formulating ionic liquid (IL) monomer composite inks that can be printed into sparse, lightweight, free-standing lattices with different functionalities. In addition to characterizing the rheological and mechanical behaviors of IL monomer inks and pIL lattices, we demonstrate the self-sensing capabilities of our printed structural electrolytes during cyclic compression. Finally, we use our inks and printing method to spatially program self-sensing capabilities in pIL lattices through heterogeneous architectures as well as ink compositions that provide mixed ionic-electronic conductivity. Our free-form approach to fabricating structural electrolytes in complex, 3D forms with programmable, anisotropic properties has broad potential use in next-generation sensors, soft robotics, bioelectronics, energy storage devices, and more.

Conformable Multifunctional Space Fabric by Metal 3D Printing for Collision Hazard Protection and Self-Powered Monitoring

The monitoring of space debris assumes paramount significance to ensure the sustainability and security of space activities as well as underground bases in outer space. However, designing a wide range monitoring system with easy fabrication, low power, and high precision remains an urgent challenge under the scarcity of materials and extreme environment conditions of outer space. Here, we designed a one-piece, robust, but flexible, and repairable 3D metal-printed triboelectric nanogenerator (FR-TENG) by incorporating the advantages of standardization and customization of outer space 3D metal printing. Inspired by the structure of hexagonal and pangolin scales, a curved structure is ingeniously applied in the design of 3D printed metal to adapt different curved surfaces while maintaining superior compressive strength, providing excellent flexibility and shape adaptability. Benefiting from the unique structural design, the FR-TENG has a minimum length of 1 cm with a weight of only 3.5 g and the minimum weight resolution detected of 9.6 g, with a response time of 20 ms. Furthermore, a multichannel self-powered collision monitoring system has been developed to monitor minor collisions, providing warnings to determine potential impacts on the space station and bases surfaces. The system may contribute to ensuring the successful completion of space missions and providing a safer space environment for the exploration of extraterrestrial life and the establishment of underground protective bases.

Straightforward Design Strategy toward 3D Near-Net-Shape Stoichiometric SiC Parts

Fused deposition modeling (FDM), traditionally reserved for thermoplastics, is modified here with a granule-based extrusion head to be extended to advanced nonoxide ceramics via a straightforward design strategy that considers the shaping opportunities and the chemical richness offered by preceramic polymers. Specifically, 3D near-net-shape stoichiometric silicon carbide (SiC) objects are designed by manipulating the key features of a commercially available polycarbosilane (fusibility, high carbon content, relatively high SiC yield). In the early stage of the process, the carbon-rich polycarbosilane is first mixed with Si and SiC fillers and then thermolyzed at 120 °C to increase polymer branching while offering tailored rheological properties during the subsequent extrusion process at 90 °C and adequate shape retention once extruded. This allows for the design of tailored and complex 3D complex polycarbosilane-based architectures with features down to 400 µm. Polymer-based parts are further converted into 3D stoichiometric SiC objects with quasi-near-net-shape-a volume shrinkage reduced to 9.1% is measured-by heat treatment at a temperature as low as 1400 °C (argon flow). Given the flexibility to tune the preceramic polymer chemical and rheological properties, a new combined design approach is leveraged to generate bespoke advanced ceramics with a high freedom in geometry complexity.