Filtern
Dokumenttyp
- Zeitschriftenartikel (13)
Sprache
- Englisch (13)
Schlagworte
- Additive manufacturing (5)
- Additive Fertigung (2)
- Ceramic (2)
- Ceramics (2)
- Keramik (2)
- Al2O3 reaction bonding (1)
- Calcium alkaline orthophosphates (1)
- Cell culture media (1)
- Cellular (1)
- Fetal bovine serum (1)
Particle size gradation is regarded as an effective method for overcoming the contradicting requirements in three-dimensional printing (3DP). In present work, particle size gradation was optimized to obtain both acceptable flowability of the powder material and high-strength 3D-printed glass-ceramic products. The effect of gradation on the printing process, sintering process and performance of the 3D-printed glass-ceramic products was investigated comprehensively. The glass-ceramic powders with three size ranges were mixed in certain proportions and applied to print parts. The result showed parts printed with powder mixed by 60 wt% 45–100 µm and 40 wt% 0–25 µm particles had satisfactory density of 1.60 g/cm³ and bending strength of 13.8 MPa. The flowability decreased with an increasing proportion of fine particles. Part density was determined by the powder bulk density in the powder bed as well as the shrinkage during sintering while strength of part was found to be dependent on the sintering degree.
Most additive manufacturing (AM) techniques have in common that material is spread out as thin layers of a dried powder/granulate by a roller or a shaker system. These layers are mostly characterized by a low packing rate. On the other hand, appreciable densities can be reached by the use of ceramic slurries. In this context, the layer-wise slurry deposition (LSD) has been developed. Specific features of the LSD process are reflected on the basis of already existing additive manufacturing technologies. The microstructure of laser-sintered bodies will be discussed, and strategies for an improved microstructure during sintering will be introduced.
Silicate bioceramics possess an excellent bioactivity; however, shaping them into complex geometries is still challenging. Therefore, this paper aims to present a new strategy for the shaping of a bioglass-ceramic with controlled geometry and properties starting from a glass powder combined with a preceramic polymer, i.e. a silicon resin, and reactive fillers. The powder-based three-dimensional (3D)-printing of wollastonite (CaSiO3)-based silicate bioceramic parts was demonstrated in this work. The resin plays a dual role, as it not only acts as a non-sacrificial binder for the filler powders in the printing process but it also reacts with the fillers to generate the desired bioceramic phases. The mechanical and physical properties, i.e. ball-on-three-balls test, density, porosity and morphology, were evaluated in 3D-printed discs. These samples possessed a total porosity around 64 vol% and a biaxial flexural strength around 6 MPa. The raw materials used in this work also enabled the 3D-printing of scaffolds possessing a designed multi-scale porosity, suitable bioceramic phase assemblage and a compressive strength of 1 MPa (for cylindrical scaffolds with total porosity ~80 vol%). Solubility in TRIS/HCl and in vitro assays, i.e. viability, cytotoxicity and apoptosis assays, were also performed. In vitro tests indicated good cell viability and no cytotoxicity effect on the cells.
Porous Al2O3 with high porosity (~45%), remarkable flexural strength (~70 MPa), and low dimensional change (~1–2%), was produced by indirect 3D printing and reaction bonding. Coarse Al with good flowability was carried out printing green body. The green body was heat treated to get fully oxidized, volume expansion during oxidation simultaneously formed strong neck bonding, not only brought good strength, but also restricted shrinkage. Porous Al2O3 with architecture of macro pores designed by 3D printing and micro pores in the strut formed by packing of particles was obtained. The near zero shrinkage can facilitate precise design of product with complex shape.
Additive manufacturing (AM) is a technology which has the potential not only to change the way of conventional industrial manufacturing processes, adding material instead of subtracting, but also to create entirely new production and business strategies. Since about three decades, AM technologies have been used to fabricate prototypes or models mostly from polymeric or metallic materials. Recently, products have been introduced into the market that cannot be produced in another way than additively. Ceramic materials are, however, not easy to process by AM technologies, as their processing requirements (in terms of feedstock and/or sintering) are very challenging. On the other hand, it can be expected that AM technologies, once successful, will have an extraordinary impact on the industrial production of ceramic components and, moreover, will open for ceramics new uses and new markets.
Selective laser sintering of ceramic powders is a promising technique for the additive manufacturing of complex- and delicate-shaped ceramic parts. Most techniques have in common that the powder to be sintered is spread to a thin layer as a dry powder by means of a roller or shaker system. These layers have a relatively low density. On the other hand, appreciable densities can be reached with the use of ceramic slurries as the starting material. Therefore, the layer-wise slurry deposition (LSD) process has been developed. Layer stacks, i.e. powder beds, built up by employing the LSD technology exhibit a density comparable to ceramic powder compacts processed by means of conventional forming technologies. Writing the layer information with a focused laser beam in these dense ceramic powder compacts enables the manufacture of ceramic bodies with a high density and precision in contour.
2014AbstractWollastonite/apatite glass-ceramics have been successfully prepared by a novel approach, consisting of the heat treatment of a silicone resinembedding micro-sized CaCO3particles, that act as reactive fillers, and bioactive glass powder in the SiO2–CaO–P2O5–K2O–Na2O–MgO–CaF2system. Zn-containing silicates, such as hardystonite (Ca2ZnSi2O7) and willemite (Zn2SiO4), were also developed either by directly mixing ZnOpowders with the glass, or by embedding them in the preceramic polymer, as additional fillers.
The most successful additive manufacturing (AM) technologies are based on the layer-by-layer deposition of a flowable powder. Although considered as the third industrial revolution, one factor still limiting these processes to become completely autonomous is the often necessary build-up of support structures. Besides the prevention of lateral shifts of the part during the deposition of layers, the support assures quality and stability to the built process. The loose powder itself surrounding the built object, or so-called powder-bed, does not provide this sustenance in most existent technology available. Here we present a simple but effective and economical method for stabilizing the powder-bed, preventing distortions in the geometry with no need for support structures. This effect, achieved by applying an air flow through the powder-bed, is enabling an entirely autonomous generation of parts and is a major contribution to all powder-based additive manufacturing technologies. Moreover, it makes powder-based AM independent of gravitational forces, which will facilitate crafting items in space from a variety of powdery materials.
Advancements in the fields of biocompatible materials, manufacturing processes, computational methods and medicine have led to the emergence of a new field: micro-scale scaffolds for bone replacement and regeneration. Yet most such scaffolds produced today are characterized by very basic geometry, and their microstructure differs greatly from that of the actual tissue they are intended to replace. In this paper, we propose a novel approach for generating micro-scale scaffolds based on processing actual micro-CT images and then reconstructing a highly accurate geometrical model. This model is manufactured by means of a state-of-the-art 3D additive manufacturing process from biocompatible materials. At the micro-scale level, these scaffolds are very similar to the original tissue, thus interfacing better with the surrounding tissue and facilitating more efficient rehabilitation for the patient. Moreover, the approach facilitates the design and manufacture of patient-specific scaffolds which can copy patients exact structural and mechanical characteristics, taking into account their physical condition and medical history. By means of multi-resolution volumetric modeling methods, scaffold porosity can also be adapted according to specific mechanical requirements. The process of designing and manufacturing micro-scale scaffolds involves five major stages: (a) building a volumetric multi-resolution model from micro-CT images; (b) generation of surface geometric model in STL format; (c) additive manufacturing of the scaffold; (d) scaffold shape verification relative to the geometric design; and (e) verification of mechanical properties through finite element analysis. In this research, all the proposed stages of the approach were tested. The input included micro-CT scans of porous ceramic structure, which is quite similar to commercial porous scaffolds. The results show that the proposed method is feasible for design and manufacture of micro-scale scaffolds.
Highly porous (>60% open porosity) glass–ceramic scaffolds with remarkable mechanical properties (compression strength of ~15 MPa) were produced by indirect 3D printing. Precursor glass powders were printed into 3D ordered structures and then heat treated to sinter and develop crystalline phases. The final glass–ceramic contained a β-spodumene solid solution together with a secondary phase of lithium disilicate.
The precision of the printed geometry and the density of the struts in the scaffold depended on several processing parameters (e.g. powder size and flowability, layer thickness) and were improved by increasing the binder saturation and drying time. Two types of powders with different particle size distribution (PSD) and flowability were used. Powders with a larger PSD, could be processed within a wider range of printing parameters due to their good flowability; however, the printing precision and the struts density were lower compared to the scaffolds printed using the powder in a smaller average PSD.