Macroporous ceramics with pore sizes from 400 nm to 4 mm and porosity within the range 20%–97% have been produced for a number of well‐established and emerging applications, such as molten metal ...filtration, catalysis, refractory insulation, and hot gas filtration. These applications take advantage of the unique properties achieved through the incorporation of macropores into solid ceramics. In this article, we review the main processing routes that can be used for the fabrication of macroporous ceramics with tailored microstructure and chemical composition. Emphasis is given to versatile and simple approaches that allow one to control the microstructural features that ultimately determine the properties of the macroporous material. Replica, sacrificial template, and direct foaming techniques are described and compared in terms of microstructures and mechanical properties that can be achieved. Finally, directions to future investigations on the processing of macroporous ceramics are proposed.
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Hierarchical porous materials are widespread in nature and find an increasing number of applications as catalytic supports, biological scaffolds and lightweight structures. Recent advances in ...additive manufacturing and 3D printing technologies have enabled the digital fabrication of porous materials in the form of lattices, cellular structures and foams across multiple length scales. However, current approaches do not allow for the fast manufacturing of bulk porous materials featuring pore sizes that span broadly from macroscopic dimensions down to the nanoscale. Here, ink formulations are designed and investigated to enable 3D printing of hierarchical materials displaying porosity at the nano-, micro- and macroscales. Pores are generated upon removal of nanodroplets and microscale templates present in the initial ink. Using particles to stabilize the droplet templates is key to obtain Pickering nanoemulsions that can be 3D printed through direct ink writing. The combination of such self-assembled templates with the spatial control offered by the printing process allows for the digital manufacturing of hierarchical materials exhibiting thus far inaccessible multiscale porosity and complex geometries.
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4D printing has a great potential for the manufacturing of soft robotics and medical devices. The alliance of digital light processing (DLP) 3D printing and novel shape-memory photopolymers allows ...for the fabrication of smart 4D-printed medical devices in high resolution and with tailorable functionalities. However, most of the reported 4D-printed materials are nondegradable, which limits their clinical applications. On the other hand, 4D printing of biodegradable shape-memory elastomers is highly challenging, especially when transition points close to physiological temperature and shape fixation under ambient conditions are required. Here, we report the 4D printing of biodegradable shape-memory elastomers with tailorable transition points covering physiological temperature, by using poly(D,L-lactide-co-trimethylene carbonate) methacrylates at various monomer feed ratios. After the programming step, the high-resolution DLP printed stents preserved their folded shape at room temperature, and showed efficient shape recovery at 37 °C. The materials were cytocompatible and readily degradable under physiological conditions. Furthermore, drug-loaded devices with tuneable release kinetics were realized by DLP-printing with resins containing polymers and levofloxacin or nintedanib. This study offers a new perspective for the development of next-generation 4D-printed medical devices.
Digital light 4D printing of biodegradable drug-eluting elastomeric devices with tailorable thermal response at the physiological temperature and tunable drug release. Display omitted
•Biodegradable shape-memory elastomers were DLP printed.•The materials displayed elasticity below and above their transition temperatures.•4D printed elastomeric stents showed efficient shape recovery at 37 °C.•4D printed drug-loaded devices showed tuneable release kinetics.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Additive manufacturing (AM) technologies offer an attractive pathway towards the fabrication of functional materials featuring complex heterogeneous architectures inspired by biological systems. In ...this paper, recent research on the use of AM approaches to program the local chemical composition, structure and properties of biologically-inspired materials is reviewed. A variety of structural motifs found in biological composites have been successfully emulated in synthetic systems using inkjet-based, direct-writing, stereolithography and slip casting technologies. The replication in synthetic systems of design principles underlying such structural motifs has enabled the fabrication of lightweight cellular materials, strong and tough composites, soft robots and autonomously shaping structures with unprecedented properties and functionalities. Pushing the current limits of AM technologies in future research should bring us closer to the manufacturing capabilities of living organisms, opening the way for the digital fabrication of advanced materials with superior performance, lower environmental impact and new functionalities.
Analogous to the layer-by-layer and site-specific deposition of building blocks carried by living organisms during biomineralization (left), additive manufacturing technologies offer a compelling route for the fabrication of bioinspired heterogeneous architectures for next generation composite materials (right).
Abstract All-ceramic dental restorations exhibit enhanced esthetics and biocompatibility as compared to traditional metal-based prosthesis. However, long-term fatigue and subcritical crack growth in ...the presence of water and cyclic loading can decrease the strength of ceramic components over time. We investigated the cyclic fatigue in water of three dental materials currently used as frameworks in all-ceramic restorations: a 3 mol%-yttria partially stabilized zirconia (3Y-TZP, Cercon, Degudent GmbH), a Al2 O3 –ZrO2 –Glass composite (Inceram-Zirconia, Vita Zahnfabrik GmbH) and a Li2 O·2SiO2 glass ceramic (Empress 2, Ivoclar Vivadent AG). Fatigue and fast fracture tests were performed to determine the Weibull distribution of lifetime and initial mechanical strength for each framework component. In spite of its noticeable susceptibility to fatigue in water, the 3Y-TZP material was found to be particularly suitable for the preparation of posterior all-ceramic bridges due to its high initial mechanical strength. Guidelines are provided for the selection of materials and the design of all-ceramic posterior bridges exhibiting lifetime longer than 20 years under severe wet and cyclic loading conditions.
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Fibre-reinforced polymer structures are often used when stiff lightweight materials are required, such as in aircraft, vehicles and biomedical implants. Despite their very high stiffness and strength
..., such lightweight materials require energy- and labour-intensive fabrication processes
, exhibit typically brittle fracture and are difficult to shape and recycle
. This is in stark contrast to lightweight biological materials such as bone, silk and wood, which form by directed self-assembly into complex, hierarchically structured shapes with outstanding mechanical properties
, and are circularly integrated into the environment. Here we demonstrate a three-dimensional (3D) printing approach to generate recyclable lightweight structures with hierarchical architectures, complex geometries and unprecedented stiffness and toughness. Their features arise from the self-assembly of liquid-crystal polymer molecules into highly oriented domains during extrusion of the molten feedstock material. By orienting the molecular domains with the print path, we are able to reinforce the polymer structure according to the expected mechanical stresses, leading to stiffness, strength and toughness that outperform state-of-the-art 3D-printed polymers by an order of magnitude and are comparable with the highest-performance lightweight composites
. The ability to combine the top-down shaping freedom of 3D printing with bottom-up molecular control over polymer orientation opens up the possibility to freely design and realize structures without the typical restrictions of current manufacturing processes.
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We report the assembly of monodisperse colloidosomes containing a wide range of functional nanoparticles in the outer shell using a double emulsion templating method in a microfluidic device. By ...selecting nanoparticles of specific functionalities, hollow capsules with inert, magnetic, photocatalytic, and potentially biocompatible and piezoelectric shells are easily obtained. Proper control over the surface chemistry of the nanoparticles forming the shell and of the liquid interfaces involved is key to enable the assembly of colloidosomes using this double emulsification route.
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Direct foaming of colloidal suspensions is a simple and versatile approach for the fabrication of macroporous ceramic materials. Wet foams produced by this method can be stabilized by long‐chain ...surfactants or by colloidal particles. In this work, we investigate the processing of particle‐stabilized wet foams into crack‐free macroporous ceramics. The processing steps are discussed with particular emphasis on the consolidation and drying process of wet foams. Macroporous alumina ceramics prepared using different consolidation and drying methods are compared in terms of their final microstructure, porosity, and compressive strength. Consolidation of the wet foam by particle coagulation before drying resulted in porous alumina with a closed‐cell structure, a porosity of 86.5%, an average cell size of 35 μm, and a remarkable compressive strength of 16.3 MPa. On the other hand, wet foams consolidated via gelation of the liquid within the foam lamella led to porous structures with interconnected cells in the size range from 100 to 150 μm. The tailored microstructure and high mechanical strength of the macroporous ceramics can be of interest for the manufacture of bio‐scaffolds, thermal insulators, impact absorbers, separation membranes, and light weight ceramics.
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We present a novel direct‐foaming method to produce macroporous ceramics using particles instead of surfactants as stabilizers of the wet foams. This method allows for the fabrication of ultra‐stable ...wet foams that resist coarsening upon drying and sintering. Macroporous ceramics of various chemical compositions with open or closed cells, average cell sizes ranging from 10 to 300 μm and porosities within 45% and 95%, can be easily prepared using this new approach. The sintered foams show high compressive strengths of up to 16 MPa in alumina foams with porosities of 88%.
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Bioinspired spring origami Faber, Jakob A; Arrieta, Andres F; Studart, André R
Science,
03/2018, Volume:
359, Issue:
6382
Journal Article
Peer reviewed
Open access
Origami enables folding of objects into a variety of shapes in arts, engineering, and biological systems. In contrast to well-known paper-folded objects, the wing of the earwig has an exquisite ...natural folding system that cannot be sufficiently described by current origami models. Such an unusual biological system displays incompatible folding patterns, remains open by a bistable locking mechanism during flight, and self-folds rapidly without muscular actuation. We show that these notable functionalities arise from the protein-rich joints of the earwig wing, which work as extensional and rotational springs between facets. Inspired by this biological wing, we establish a spring origami model that broadens the folding design space of traditional origami and allows for the fabrication of precisely tunable, four-dimensional-printed objects with programmable bioinspired morphing functionalities.
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