Effect of binder system on the thermophysical properties of 3D-printed zirconia ceramics

Fabrication of 3D-printed ceramic parts with high complexity and high spatial resolution often demands low wall thickness as well as high stiffness at the green state, whereas printing simpler geometries may tolerate thicker, more compliant walls with the advantage of a rapid binder-burn-out and sintering process. In this work, the influence of the binder system on the thermophysical properties of 3D-printed stabilized zirconia ceramics was investigated. Samples were fabricated with the lithography-based ceramic manufacturing (LCM) technology using two different photosensitive ceramic suspensions (LithaCon 3Y230 and LithaCon 3Y210), with the same ZrO₂ powder. A significant difference in stiffness in the green state (~3 MPa vs. ~32 MPa for LithaCon 3Y230 and LithaCon 3Y210, respectively) was measured, associated with a rather loose or a linked network formed in the binder due to photopolymerization. Both materials reached high relative densities, that is, >99%, exhibiting a homogeneous fine-grained microstructure. No significant differences on the coefficient of thermal expansion (11.18 ppm/K vs. 11.17 ppm/K) or Young's modulus (207 GPa vs. 205 GPa) were measured, thus demonstrating the potential of tailoring binder systems to achieve the required accuracy in 3D-printed parts, without detrimental effects on material's microstructure and thermophysical properties at the sintered state.     

The hydromorphology index IHM based on fish requirements

Stream ecosystems are diverse and dynamic habitats that are strongly influenced by the direct and indirect consequences of human interventions. Several initiatives have been started all over Europe to satisfy the European guidelines for the protection of local water bodies, but a standardised procedure across national borders fulfilling all relevant aspects and parameters of the Water Framework Directive (WFD) does not exist. In this context, we propose a new methodical approach based on salmonid fish populations to assess stream quality to increase the comparability of individual assessments due to standardized survey and evaluation methods for hydromorphology. Our approach is based on the Austrian and Italian methods, which account for the European standards, and it has been tested in 81 stream sections representative of different site and anthropogenic use conditions in the European Alps. The assessment procedure is composed of a set of 11 indicators, which were selected to evaluate longitudinal and lateral morphological and temporal dynamics of morphological and hydrological conditions. The indicators were combined into three indices, the morphology (I_M), hydrology (I_H), and hydromorphology indices (I_HM), to obtain a holistic picture with as few parameters as possible. The definition of indicators and indices, their methodical implementation and practical testing in the field, were carried out by an interdisciplinary team of international experts. The resulting and tested field manual is included with this publication as Supplementary material. The applicability, strengths, and weaknesses of the approach are discussed in the present paper.     

Nanoparticles Targeted to Fibroblast Activation Protein Outperform PSMA for MRI Delineation of Primary Prostate Tumors

Accurate delineation of gross tumor volumes remains a barrier to radiotherapy dose escalation and boost dosing in the treatment of solid tumors, such as prostate cancer. Magnetic resonance imaging (MRI) of tumor targets has the power to enable focal dose boosting, particularly when combined with technological advances such as MRI-linear accelerator. Fibroblast activation protein (FAP) is overexpressed in stromal components of >90% of epithelial carcinomas. Herein, the authors compare targeted MRI of prostate specific membrane antigen (PSMA) with FAP in the delineation of orthotopic prostate tumors. Control, FAP, and PSMA-targeting iron oxide nanoparticles were prepared with modification of a lymphotropic MRI agent (FerroTrace, Ferronova). Mice with orthotopic LNCaP tumors underwent MRI 24 h after intravenous injection of nanoparticles. FAP and PSMA nanoparticles produced contrast enhancement on MRI when compared to control nanoparticles. FAP-targeted MRI increased the proportion of tumor contrast-enhancing black pixels by 13%, compared to PSMA. Analysis of changes in R2 values between healthy prostates and LNCaP tumors indicated an increase in contrast-enhancing pixels in the tumor border of 15% when targeting FAP, compared to PSMA. This study demonstrates the preclinical feasibility of PSMA and FAP-targeted MRI which can enable targeted image-guided focal therapy of localized prostate cancer.     

Paste Development for an Optimized Filament Stretching Effect during Parallel Dispensing on Transparent Conductive Oxide Layers for Solar Cell Metallization

The availability of silver as an electrically conductive filler material in printing pastes for solar cell metallization is becoming a more crucial issue for multiterawatt-scale production due to its global constraints. Therefore, the silver consumption for solar cell production needs to be reduced drastically by substituting silver with alternative conductive filler materials or utilizing process-specific phenomena. The phenomenon of filament stretching during microextrusion allows significantly lower paste laydowns. The magnitude of filament stretching is paste-dependent and therefore further knowledge of the pastes’ impact to the filament stretching is required. This study presents nine low-temperature curing pastes differing in the particle system and binder resin. The rheological and thermal behavior of these suspensions are investigated and printing tests onto silicon heterojunction (SHJ) precursors are carried out. Additionally, scanning electron microscopy (SEM)-based microstructure analyses of printed electrodes are performed. Based on these experimental results, the impact of paste compositions regarding the paste behavior during microextrusion and the SHJ solar cell performances are analyzed. The developed paste formulations exhibit a strong filament stretching, leading to a reduced silver laydown of down to Δm_Ag = −60%_rel. and an absolute efficiency gain of up to Δη = +0.75%_abs. due to less shading losses.     

High-temperature carbothermal synthesis and characterization of graphite/h-BN bimaterials

Hexagonal boron nitride (h-BN) and graphite have similar crystal structures, comparable lattice parameters, and coefficients of thermal expansion, but vastly different electrical and thermal transport. Despite their key differences, it is possible to couple h-BN and graphite in a bimaterial system allowing the unique properties of both materials to be utilized in a single component. Through a carbothermal reduction of B₂O₃ in nitrogen, the surface of graphite can be converted to h-BN. This results in a layered system that is electrically insulating on the surface due to h-BN, and more compliant as well as conductive within the substrate due to the graphite structural body. We discuss the high-temperature synthesis and characterization of this layered material, focusing on the processing–microstructure relationship as well as the interface of graphite/h-BN to assess the chemical and mechanical adhesion of the layers, and to establish how such properties are contingent on the reacting phase of B₂O₃. This is achieved by investigating the origin of h-BN formation and the unwanted side reaction of boron carbide formation, through the evaluation of the thermochemistry and kinetics governing the carbothermic reactions. We establish that a reaction temperature and holding time of 1700°C for 18 h produced the thickest h-BN layers which exhibited the highest fracture toughness over all lower temperature synthesis conditions.     

The Cyanobacterial “Nutraceutical” Phycocyanobilin Inhibits Cysteine Protease Legumain

The blue biliprotein phycocyanin, produced by photo-autotrophic cyanobacteria including spirulina (Arthrospira) and marketed as a natural food supplement or “nutraceutical,” is reported to have anti-inflammatory, antioxidant, immunomodulatory, and anticancer activity. These diverse biological activities have been specifically attributed to the phycocyanin chromophore, phycocyanobilin (PCB). However, the mechanism of action of PCB and the molecular targets responsible for the beneficial properties of PCB are not well understood. We have developed a procedure to rapidly cleave the PCB pigment from phycocyanin by ethanolysis and then characterized it as an electrophilic natural product that interacts covalently with thiol nucleophiles but lacks any appreciable cytotoxicity or antibacterial activity against common pathogens and gut microbes. We then designed alkyne-bearing PCB probes for use in chemical proteomics target deconvolution studies. Target identification and validation revealed the cysteine protease legumain (also known as asparaginyl endopeptidase, AEP) to be a target of PCB. Inhibition of this target may account for PCB's diverse reported biological activities.     

Stereolithographic 3D Printing of Ceramics: Challenges and Opportunities for Structural Integrity

This article reviews the current activities at the Montanuniversität Leoben on the design, processing, and characterization of 3D printed advanced ceramics using the lithography-based manufacturing technology. An overview of the challenges and the opportunities offered to improve the mechanical properties of printing ceramics is given. Their brittle failure is analyzed within the framework of linear elastic fracture mechanics, considering specific aspects of additive manufacturing. Several issues associated with the printing process are addressed, such as surface quality, geometry control, influence of printing directions, as well as the need to establish testing protocols for 3D printed parts. Based on the layer-by-layer capabilities of the stereolithographic process, bio-inspired material design concepts are discussed aiming to enhance the mechanical resistance of 3D-printed ceramics. By tailoring the layer architecture and microstructure of the parts, high strength and fracture resistance may be achieved.