1,721,086 research outputs found
Direct Ink Writing of AISI 316L Dense Parts and Porous Lattices
Full text linkThe focus of the present work is the development of a metallic ink that possesses controlled rheological properties: by keeping printing parameters constant both AISI 316L dense parts and porous scaffolds have been produced. Shrinkage, porosity, and mechanical properties have been studied to evaluate the link between the ink rheological properties and the final part. Depending on binder composition, linear shrinkage ranging from 9% to 22% and porosity from 34 to 7 vol% are measured. Tensile strength for specimens sintered at 1240 °C reach the value of 444 MPa and elongation at a break of 12.3%. These values are still far from additively manufactured AISI 316L parts with powder bed fusion technologies, but represent an improvement compared to previously reported data in the literature for AISI 316L parts 3D printed by DIW. Porous scaffolds with a spanning distance of 1.2 mm are printed and sintered. Porosity of 74 vol% and compression strength of 74 MPa are measured for this set of samples showing how the produced ink represents a valuable alternative to pastes already present in the literature
Enhanced mechanical properties of 3D printed alumina ceramics by using sintering aids
No full textStereolithography based 3D printing provides an efficient pathway to fabricate alumina ceramics, and the exploration on the mechanical properties of 3D printed alumina ceramics is crucial to the development of 3D printing ceramic technology. However, alumina ceramics are difficult to sinter due to their high melting point. In this work, alumina ceramics were prepared via stereolithography based 3D printing technology, and the improvement in the mechanical properties was investigated based on the content, the type and the particle size of sintering aids (TiO2, CaCO3, and MgO). The flexural strength of the sintered ceramics increased greatly (from 139.2 MPa to 216.7 MPa) with the increase in TiO2 content (from 0.5 wt% to 1.5 wt%), while significant anisotropy in mechanical properties (216.7 MPa in X-Z plane and 121.0 MPa in X–Y plane) was observed for the ceramics with the addition of 1.5 wt TiO2. The shrinkage and flexural strength of the ceramics decreased with the increase in CaCO3 content due to the formation of elongated grains, which led to the formation of large-sized residual pores in the ceramics. The addition of MgO help decrease the anisotropic differences in shrinkage and flexural strength of the sintered ceramics due to the formation of regularly shaped grains. This work provides guidance on the adjustment in flexural strength, shrinkage, and anisotropic behavior of 3D printed alumina ceramics, and provides new methods for the fabrication of 3D printed alumina ceramics with superior mechanical properties
Hybrid direct ink writing of bioglass-calcite-carbon composite scaffolds supported by novel silicone-based emulsions
No full text70S30C (70 mol% SiO2, 30 % CaO) bioglass is one of the most promising bioceramics for bone tissue engineering. We discuss the feasibility of 70S30C bioglass/calcite/carbon composites derived from novel silicone-based emulsions, leading to highly porous lattice scaffolds. These are produced by direct ink writing (DIW) 3D printing, followed by ceramic conversion at 700 degrees C in flowing nitrogen. The emulsions consisted of droplets of concentrated calcium nitrate aqueous solution incorporated into blends of H44 commercial polysiloxane and photocurable acrylate resin. This formulation offered unprecedented opportunities in both synthesis and shaping. Specifically, the homogeneous dispersion of the CaO precursor in silicone enabled a uniform SiO2/CaO distribution, favoring the formation of a glass matrix. Additionally, the acrylate component and water content allowed for tuning of the microstructure both immediately after printing and upon firing. Photopolymerization of acrylates consolidated the printed bodies (configuring a 'hybrid DIW') after extrusion, while water evaporation enhanced gas evolution during ceramic conversion, promoting pore interconnectivity
3D-printed porous mullite lattice structures by hybrid direct ink writing of silicone suspension-emulsions
Full text linkSilicones added with nano-sized alumina particles are already known as starting materials for phase pure mullite ceramics, synthesized at quite low temperatures. The present paper deals with a fundamental upgrade, based on a novel suspension-emulsion concept, for the easy fabrication of highly porous lattice structures. An aqueous suspension of γ-Al2O3 nanoparticles in water was first distributed as emulsion within an “oily phase,” consisting of a silicone/acrylates blend, with the help of a surfactant. The mixture was later employed to fabricate highly porous structures (∼80% open porosity), by direct ink writing, that is, an extrusion-based 3D printing technology requiring specific rheological behavior of the feedstock ink. Finally, the structures were rapidly stabilized through a photo-polymerization step (configuring a form of “hybrid” direct ink writing). The presence of water also allowed the application of a freeze-curing procedure, for a second series of samples. The abundant w..
Hierarchically porous 3D-printed akermanite scaffolds from silicones and engineered fillers
Full text linkThe present investigation is dedicated to the manufacturing of reticulated three-dimensional akermanite scaffolds, developed by direct reaction between silica, from the oxidation of a commercial silicone resin and oxide fillers, forming pastes for direct ink writing. Crack-free scaffolds, with dense and regular struts, were due to the use of CaCO3 (micro) and MgO nano-particles as reactive fillers. An excellent phase purity was obtained, with the help of the liquid phase provided by anhydrous sodium borate (Na2B4O7), upon firing. The structure of the scaffolds, finally, was successfully modified by using Mg(OH)2 and hydrated sodium borate: besides macro-porosity from direct ink writing, the new scaffolds exhibited homogenous ‘spongy’ struts (owing to water vapor release in the heating step), with no crack. Both types of scaffolds (with dense or porous struts) exhibited remarkable strength-to-density ratios
Metabolons and the biosynthesis of Gerbera hybrida flavonoids
Full text linkThe formation of protein complexes, metabolons, and the channeling of intermediates of secondary metabolism has
been discussed for at least 30 years. Metabolons and channeling enable plants to perform a highly effective synthesis of specific natural products without or with
reduced metabolic interference and avoiding accumulation of toxic intermediates. In spite of a long tradition of the concept, precise examples of complete metabolons are very scarce.
Our aim is to define flavone and anthocyanidin specific metabolons in the ornamental plant Gerbera hybrida. Our earlier data shows that specific genes are expressed early in development PAL and CHS3 and others late PAL, CHS1 and DFR, possibly correlating with flavone and anthocyanin
biosynthesis. Furthermore, transformation of the pelargonidin type Gerbera cultivar Terra Regina with a MYB-type regulatory gene induces cyanidin biosynthesis without interfering with the background pelargonidin biosynthesis. Using our large set of EST, the expanding genomic sequence resource of Gerbera and new data from Illumina sequences for wild type of Regina and MYB transgenic lines, we are establishing correlations in expression and patterns of protein-protein
interactions for the whole flavonoid metabolism isoenzyme complex in our model plant
Embedded direct ink writing of freeform ceramic components
No full textDirect ink writing, a widely used additive manufacturing technique, has some disadvantages in fabricating suspended ceramic structures due to instabilities in the ink caused by surface tension and gravity forces, requiring a strict optimization of the rheology of the feedstock. To overcome this problem, freeform 3D printing was achieved in this work by performing printing inside a supporting medium composed of vegetable oil and fumed silica. The rheological properties of the supporting medium as well as the printability of the ink as a function of the solid content were investigated. Printing parameters such as gas pressure and nozzle movement speed were optimized for a selected diameter of the printed filament. With this method, several suspended structures were fabricated, such as coils with different pitches, hollow cylinders and 3D letters, showing no shape distorting both after printing and the thermal treatment. A preceramic polymer was used as the primary material for the tests, but we also demonstrated that with this approach it is possible to print using inks containing either metal or ceramic powders, thereby showcasing the large potential of this approach for being used in different applications
Additive manufacturing of SiOC scaffolds with tunable structure-performance relationship
No full textAiming at optimizing the performance of porous ceramics through structural optimization, this work explored the properties variation achieved by designing different patterns in SiOC log-pile structures fabricated by direct ink writing. Specifically, we investigated the effect of filament diameter, spacing between filaments and angle of deflection between adjacent layers on the compression strength and gas permeability of these structures. Results confirm that mechanical performance could be tuned by designing the structures’ architectural features, such as the spacing between filaments and the angle of deflection between layers, leading to changes in the contact area of filaments belonging to adjacent layers. Permeability decreased with varying angle of deflection from 90 ° to 15 °, due to the higher tortuosity of the flow paths. This enables to optimize the strength and permeability of the structure without reducing the porosity of the component
Comparative Analysis of Wollastonite-Diopside Glass-Ceramic Structures Fabricated via Stereo-Lithography
No full textOne key feature of digital light processing consists of the high flexibility in the design of highly porous reticulated scaffolds. In the present paper, the authors report recent experiences concerning two glasses, both converted into wollastonite‐diopside (CaSiO3–CaMgSi2O6) glass‐ceramics by viscous flow sintering of fine powders (<45 μm) with concurrent crystallization. Glass particles are homogeneously dispersed in a photosensitive polymer, selectively hardened, layer‐by‐layer, by exposure to visible light, forming diamond cell lattices. The printing accuracy is slightly influenced by the glass chemistry, whereas the shape maintenance, after firing at 1100 °C, is observed for both compositions. The newly developed scaffolds are compared to other glass‐ceramic scaffolds, previously developed on the basis of the starting glass: the adoption of a new design does not determine any substantial degradation of mechanical properties
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