Strategies to enhance properties of 3D-printed ceramics

Technologies of additive manufacturing (AM) impress with the ability of fabricating ceramic parts of high precision and complexity. However, their mechanical performance may be affected by printing process-related parameters as compared to conventionally processed ceramics. To improve strength and damage tolerance of 3D-printed alumina-based ceramics, two different approaches have been investigated, focusing on microstructural and architectural design. (i) High strength alumina based on a multilayer design: A-B-A laminates of (A) alumina and (B) alumina-zirconia materials were additive manufactured using the 2K-lithography-based ceramic manufacturing (LCM) technology. Through mismatching thermal expansions of the different materials, compressive residual stresses were induced into the surface alumina layers during cooling after sintering. A biaxial strength of 1 GPa was obtained, in comparison to 650 MPa on 3D-printed bulk alumina.[1] (ii) Damage tolerance alumina: Textured alumina ceramics were 3D-printed by applying the method of templated grain growth. Through shear forces, occurring during the printing process, aligned high aspect ratio templates grew due to the dissolution and precipitation of surrounding submicron-sized powder particles. As a result, anisotropic crystallographic properties as well as the morphology of the textured grains led to a biaxial strength of 670 MPa, compared to 570 MPa measured on equiaxed alumina sintered under the same conditions. Additionally, toughening mechanisms as crack deflection, bifurcation and even crack arrest could be observed, leading to an enhanced damage tolerance.[2] These two strategies may be applied to other 3D-printed ceramic materials and systems of more complex geometry to enhance their structural properties

Lithography-based ceramic manufacture (LCM) of auxetic structures: present capabilities and challenges

Auxetic metamaterials are known for having a negative Poisson's ratio (NPR) and for displaying the unexpected properties of lateral expansion when stretched and densification when compressed. Even though a wide set of micro-manufacturing resources have been used for the development of auxetic metamaterials and related devices, additional precision and an extension to other families of materials is needed for their industrial expansion. In addition, their manufacture using ceramic materials is still challenging. In this study we present a very promising approach for the development of auxetic metamaterials and devices based on the use of lithography-based ceramic manufacturing. The process stands out for its precision and complex three-dimensional geometries attainable, without the need of supporting structures, and for enabling the manufacture of ceramic auxetics with their geometry controlled from the design stage with micrometric precision. To our knowledge it represents the first example of application of this technology to the manufacture of auxetic geometries using ceramic materials. We have used a special three-dimensional auxetic design whose remarkable NPR has been previously highlighted

Digital light processing stereolithography of hydroxyapatite scaffolds with bone-like architecture, permeability, and mechanical properties

AbstractThis work deals with the additive manufacturing and characterization of hydroxyapatite scaffolds mimicking the trabecular architecture of cancellous bone. A novel approach was proposed relying on stereolithographic technology, which builds foam‐like ceramic scaffolds by using three‐dimensional (3D) micro‐tomographic reconstructions of polymeric sponges as virtual templates for the manufacturing process. The layer‐by‐layer fabrication process involves the selective polymerization of a photocurable resin in which hydroxyapatite particles are homogeneously dispersed. Irradiation is performed by a dynamic mask that projects blue light onto the slurry. After sintering, highly‐porous hydroxyapatite scaffolds (total porosity ~0.80, pore size 100‐800 µm) replicating the 3D open‐cell architecture of the polymeric template as well as spongy bone were obtained. Intrinsic permeability of scaffolds was determined by measuring laminar airflow alternating pressure wave drops and was found to be within 0.75‐1.74 × 10−9 m2, which is comparable to the range of human cancellous bone. Compressive tests were also carried out in order to determine the strength (~1.60 MPa), elastic modulus (~513 MPa) and Weibull modulus (m = 2.2) of the scaffolds. Overall, the fabrication strategy used to print hydroxyapatite scaffolds (tomographic imaging combined with digital mirror device [DMD]‐based stereolithography) shows great promise for the development of porous bioceramics with bone‐like architecture and mass transport properties

Lithography-based addtive manufacture of ceramic biodevices with design-controlled surface topographies

The possibility of manufacturing textured materials and devices, with surface properties controlled from the design stage, instead of being the result of machining processes or chemical attacks, is a key factor for the incorporation of advanced functionalities to a wide set of micro- and nanosystems. High-precision additive manufacturing (AM) technologies based on photopolymerization, together with the use of fractal models linked to computer-aided design tools, allow for a precise definition of final surface properties. However, the polymeric master parts obtained with most commercial systems are usually inadequate for biomedical purposes and their limited strength and size prevents many potential applications. On the other hand, additive manufacturing technologies aimed at the production of final parts, normally based on layer-by-layer melting or sintering ceramic or metallic powders, do not always provide the required precision for obtaining controlled micro-structured surfaces with high-aspect-ratio details. Towards the desired degree of precision and performance, lithography-based ceramic manufacture is a remarkable option, as we discuss in the present study, which presents the development of two different micro-textured biodevices for cell culture. Results show a remarkable control of the surface topography of ceramic parts and the possibility of obtaining design-controlled micro-structured surfaces with high-aspect-ratio micro-metric details

Die Sandvegetation am Seedamm im Nationalpark Neusiedlersee-Seewinkel

Im Rahmen dieser Masterarbeit wurden ausgewählte Sandflächen entlang des Seedamms im Nationalpark Neusiedlersee-Seewinkel dokumentiert. Die Flächen zeigten eine unterschiedliche Vegetationsbedeckung, zwischen 25 - 74%. Die Vegetationsaufnahmen wurden im August 2010 sowie im April, Mai und August 2011 durchgeführt. Drei unterschiedliche Methoden (Line-Point Methode, Abundanz Methode, modifizierte Methode nach Braun-Blanquet) wurden angewandt. Die untersuchten Flächen wiesen zum Teil sehr unterschiedliche Artenspektren auf. Auf den allermeisten Flächen zeigte sich die Dominanz von 2 Arten (Cynodon dactylon, Artemisia campestris), doch hatte dies relativ wenig Auswirkung auf das Vorkommen anderer, zum Teil gefährdeter Arten. Einzelne Arten waren allerdings nur mit wenigen Individuen auf den Probeflächen vertreten, wobei es andererseits gelegentlich zu Massenvorkommen einzelner, teils gefährdeter Arten kam (z.B. Plantago arenaria, Erysimum diffusum, seltener auch Silene conica). Insgesamt wurden 64 Arten gefunden, inklusive 18 Rote-Liste-Arten, darunter auch besonders vom Aussterben gefährdete Arten (Chondrilla juncea, Silene conica und Trigonella procumbens). Die biogeographische Verbreitung der im Untersuchungsgebiet angetroffenen Arten entsprach dem im pannonischen Raum Ostösterreichs typischen Muster, mit Schwerpunkt (sub)mediterran bzw. (sub)kontinental. Ein Vergleich mit älteren Daten von Bojko, der 1934 ähnliche Flächen entlang des Seedammes untersuchte, ergab zum Teil sehr deutliche Veränderungen. Einerseits ist Onobrychis arenaria verschwunden, andererseits treten neue, zum Teil sehr seltene Arten hinzu (Trigonella procumbens, Medicago minima, Medicago monspeliaca). Auffällig ist, dass Bojko Artemisia campestris auf den Sandflächen nicht erwähnte, und nur Cynodon dactylon als dominierende Art auswies. Zum nachhaltigen Schutz der noch vorhandenen wertvollen Sandflächen im Nationalpark Neusiedlersee-Seewinkel sollten auch weiterhin entsprechende Managementprogramme weiterlaufen, wobei das Offenhalten der Sandflächen durch Beweidung oder anderer Maßnahmen von zentraler Bedeutung ist

Modelling the Mechanical Properties of Hydroxyapatite Scaffolds Produced by Digital Light Processing-Based Vat Photopolymerization

Porosity is a key feature in dictating the overall performance of biomedical scaffolds, with special relevance to mechanical properties. Usually, compressive strength and elastic modulus are the main parameters used to determine the potential mechanical suitability of porous scaffolds for bone repair. However, their assessment may not be so easy from an experimental viewpoint and, especially if the porosity is high, so reliable for brittle bioceramic foams. Hence, assessing the relationship between porosity and mechanical properties based only on the constitutive parameters of the solid material is a challenging and important task to predict the scaffold performance for optimization during design. In this work, a set of equations was used to predict the compressive strength and elastic modulus of bone-like hydroxyapatite scaffolds produced by digital light processing-based vat photopolymerization (total porosity about 80 vol.%). The compressive strength was found to depend on total porosity, following a power-law approximation. The relationship between porosity and elastic modulus was well fitted by second-order power law, with relative density and computational models obtained by numerical simulations

Additive Fertigung keramischer Schneidstoffe

Die additive Fertigung von Schneidstoffen hat das Potenzial, leistungsfähigere Zerspanungswerkzeuge zu ermöglichen. Das Lithography-based Ceramic-Manufacturing-(LCM)-Verfahren erlaubt die Fertigung hochbelastbarer Bauteile aus Keramik. Dieser Beitrag stellt zum einen das LCM-Verfahren und zum anderen die Entwicklung additiv herstellbarer Wendeschneidplatten vor. Zuletzt erfolgt die Überprüfung der Funktions‧tauglichkeit von additiv hergestellten keramischen Wendeschneidplatten in Außenlängsdrehversuchen mit vermicularem Gusseisen (GJV-450)

Making foam-like bioactive glass scaffolds by vat photopolymerization

This study explores the feasibility of bioactive glass scaffolds by using a stereolithographic technology (digital light processing-based vat photopolymerization) as fabrication method and the micro-tomographic reconstruction of an open-cell polymeric sponge as input virtual model to the printing system, in the attempt to replicate the trabecular architecture of cancellous bone. Additively-manufactured scaffolds were investigated from morphological (scanning electron microscopy), microstructural (X-ray diffraction), mechanical (compressive tests) and bioactive viewpoints (immersion studies in simulated body fluid (SBF)). Well-densified foam-like glass scaffolds were obtained after sintering, provided with suitable mechanical properties (compressive strength 21.9 ± 6.2 MPa, elastic modulus 4.8 ± 0.1 GPa, Weibull modulus 3.9) for bone-contact applications. The formation of a hydroxyapatite layer on scaffold struts after soaking in SBF also demonstrated the in vitro bioactivity of the printed structures