Ceramic parts manufactured by lithography‐based ceramic manufacturing (LCM) excel in resolution and surface quality. The material for LCM is a photosensitive ceramic particle‐filled slurry which ...needs to have homogeneous properties over time and during each processing step. The goal of this study was to use “mechanical” stabilization for a tricalcium phosphate‐filled slurry done by increasing slurry viscosity, solids loading, or inducing thixotropic behavior. The modified slurries were compared with a nonstable reference slurry. While all methods lead to increased storage stability, only the stabilized slurry with 0.5 wt% fumed silica is stable during the printing process.
Bioactive glasses and glass ceramics like the 45S5 formulation have been studied toward biocompatibility and biodegradability for years. Nevertheless, clinical applications as bone substitute or ...scaffold material are highly limited because of the often poor mechanical behavior of bioactive glasses. In this study, we are able to provide a new production alternative for 45S5 bioactive glass structures resulting in parts with high density and strength. Using the stereolithographic ceramic manufacturing (SLCM) process, it is possible to additively produce solid bulk glass ceramics as well as delicate scaffold structures. Recent developments in SLCM slurry preparation together with an appropriate selection of raw materials led to 3D parts with a very homogeneous microstructure and a density of about 2.7 g/cm³. Due to the low number and small size of defects, a high biaxial bending strength of 124 MPa was achieved. Weibull distribution also underlines good process control showing a Weibull modulus of 8.6 and a characteristic strength of 131 MPa for the samples tested here. By reaching bending strength values of natural cortical bone, bioactive glasses processed with SLCM could eventually advance to be an interesting bone substitute material even in load‐bearing applications, valuing the huge efforts undertaken to understand their bioactive behavior.
Lithography-based additive manufacturing technologies have become a valuable tool in tissue engineering for the fabrication of biocompatible and biodegradable bone regeneration scaffolds. Currently ...employed photopolymers based on (meth)acrylates, vinyl esters, or vinyl carbonates display undesirable properties such as irritancy or cytotoxicity of residual monomers, degradation via autocatalytic bulk erosion leading to implant failure, or insufficient degradation speed in vivo. This work investigates monomers containing boronic ester bonds as a potential alternative to these state-of-the-art compounds. Next to a facile synthesis, significantly lower cytotoxicity was shown for this generation of biocompatible allyl ether monomers compared to commonly utilized (meth)acrylates. Photopolymerization via the thiol–ene reaction showed that rigid boronic esters led to sufficient photoreactivity for 3D structuring, and materials with reduced shrinkage and excellent mechanical properties can be obtained. Additionally, degradation studies revealed significantly accelerated degradation via the desired surface erosion under physiological and acidic conditions. Ultimately, a 3D test structure out of a boronic ester-based formulation was successfully stereolithography-printed, showing the great potential of these monomers as precursors for photopolymers used for 3D-printed implants with improved degradation behavior without forfeiting good mechanical properties.
Hydrogels are polymeric materials with water contents similar to that of soft tissues. Due to their biomimetic properties, they have been extensively used in various biomedical applications including ...cell encapsulation for tissue engineering. The utilization of photopolymers provides a possibility for the temporal and spatial controlling of hydrogel cross-links. We produced three-dimensional (3-D) hydrogel scaffolds by means of the two-photon polymerization (2PP) technique. Using a highly efficient water-soluble initiator, photopolymers with up to 80 wt.% water were processed with high precision and reproducibility at a writing speed of 10 mm/s. The biocompatibility of the applied materials was verified using Caenorhabditis elegans as living test organisms. Furthermore, these living organisms were successfully embedded within a 200×200×35 μm³ hydrogel scaffold. As most biologic tissues exhibit a window of transparency at the wavelength of the applied femtosecond laser, it is suggested that 2PP is promising for an in situ approach. Our results demonstrate the feasibility of and potential for bio-fabricating 3-D tissue constructs in the micrometre-range via near-infrared lasers in direct contact with a living organism.
Polymer components fabricated by additive manufacturing typically show only moderate strength and low temperature stability, possibly leading to severe wear and short lifetimes especially under dry ...tribological sliding. To tackle these shortcomings, we investigated the combination of single- and multi-scale textures directly fabricated by digital light processing with amorphous diamond-like carbon (DLC) coatings. The topography of the samples and conformity of the coatings on the textures are assessed and their tribological behaviour under dry conditions is studied. We demonstrate that the surface textures have a detrimental tribological effect on the uncoated samples. This changes with the application of DLC coatings since friction substantially reduces and wear of the textures is not observed anymore. These trends are attributed to the protection of the underlying polymer substrate by the coatings and a reduced contact area. The best tribological performance is found for a coating with highest hardness and hardness-to-elasticity ratios. Moreover, multi-scale textures perform slightly better than single-scale textures due to a smaller real contact area. Summarizing, we verified that the high flexibility and low production costs of 3D printing combined with the excellent mechanical and tribological properties of DLC results in synergistic effects with an excellent performance under dry sliding conditions.
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•3D printed PMMA with single- and multi-scale surface textures and DLC coatings•Tribological ball-on-disk characterization under dry sliding conditions•Detrimental effects on friction and wear for surfaces textures without coating•Improved tribological behaviour for DLC coatings with high hardness and elasticity•Synergetic effects for DLC coating on perpendicular oriented multi-scale textures
Additive manufacturing (AM) alias 3D printing translates computer-aided design (CAD) virtual 3D models into physical objects. By digital slicing of CAD, 3D scan, or tomography data, AM builds objects ...layer by layer without the need for molds or machining. AM enables decentralized fabrication of customized objects on demand by exploiting digital information storage and retrieval via the Internet. The ongoing transition from rapid prototyping to rapid manufacturing prompts new challenges for mechanical engineers and materials scientists alike. Because polymers are by far the most utilized class of materials for AM, this Review focuses on polymer processing and the development of polymers and advanced polymer systems specifically for AM. AM techniques covered include vat photopolymerization (stereolithography), powder bed fusion (SLS), material and binder jetting (inkjet and aerosol 3D printing), sheet lamination (LOM), extrusion (FDM, 3D dispensing, 3D fiber deposition, and 3D plotting), and 3D bioprinting. The range of polymers used in AM encompasses thermoplastics, thermosets, elastomers, hydrogels, functional polymers, polymer blends, composites, and biological systems. Aspects of polymer design, additives, and processing parameters as they relate to enhancing build speed and improving accuracy, functionality, surface finish, stability, mechanical properties, and porosity are addressed. Selected applications demonstrate how polymer-based AM is being exploited in lightweight engineering, architecture, food processing, optics, energy technology, dentistry, drug delivery, and personalized medicine. Unparalleled by metals and ceramics, polymer-based AM plays a key role in the emerging AM of advanced multifunctional and multimaterial systems including living biological systems as well as life-like synthetic systems.
Within the large variety of different additive manufacturing technologies stereolithography excels in high precision and surface quality. Using the Digital Light Processing (DLP) Technology a ...stereolithography-based system was developed, which is specifically designed for the processing of highly filled photopolymers.The powder-filled suspension enables the 3D-fabrication of a so called ceramic green part. In order to get a dense ceramic structure, subsequent thermal processing steps after the 3D-printing process are necessary. First, the polymer-ceramic composites heated up to 400°C. During this processing step, called debinding, the organic components are burned out. The resulting part, consisting of powder particles stabilized by physical interactions, is further heated to sinter the particles together, and the final, fully dense ceramic part is obtained.The debinding step is the most critical process. The used components have different evaporation or decomposition temperatures and behaviors. Thereby a reduction in weight and also in dimension occurs, which depends on the portion and composition of the organic components and especially on the temperature cycle. Furthermore, the physical characteristics of the ceramic powder, such as the particle size and the size distribution influence the debinding behavior. To measure the changes in weight and dimension a thermo-gravimetric (TGA) and a thermo-mechanical analysis (TMA) can be used. To avoid too high internal gas pressures inside the green parts a preferably constant gas evolution rate is seeked. Also the ‘surface-to-volume ratio’ affects the debinding characteristics. Therefore, optimized debinding cycles for specific geometries allow the crack-free debinding of parts with a wall thickness up to 20 mm.
Additive Manufacturing (AM) received a lot of attention in the last years. Organizations are using AM systems for a range of applications such as prototypes for fitting an assembly, tooling ...components, patterns for prototype tooling, functional parts and many more. Nearly a third is applied for functional parts 12. Hence, the SL method provides a smoother surface finish than other AMT3. Not only is the smoother surface a benefit but the good precision is also a positive feature. The ongoing development of new material systems and applications make them suitable alternatives for conventional series production like injection molding or machined-core fabrication for foundry use. Small to middle series cores for faucets with quantities from around 50,000 pieces produced using AM methods are already a reality 1. From the economical point of view, the SL is a cheap and fast process in comparison to AM systems. The SL technology used in this work is based on an active mask exposure, the digital light processing (DLP). The term DLP refers to the digital mirror devices which are used for selectively tuning individual mirrors on and off in order to selectively expose a photosensitive resin with visible or ultraviolet light. The resin contains a photoinitiator which triggers radical polymerization when irradiated with light. The polymerization process leads to a solidification of the resin, leading finally to a solid polymer part 4. A digital Mirror Device (DMD) chip acts as a dynamic mask to expose a defined area on the bottom of a transparent material vat above the optical system. The generated picture enables layer-wise polymerization of the photosensitive resin resulting in a 3-dimensional object. The light source radiates light with a wavelength of 460 nm which means blue visible light. At this wavelength the curing takes place. At the Institute of Materials Science and Technology at the Vienna University of Technology six generations of these Blueprinter machines have been developed and built to date. The largest parts that a Blueprinter can currently generate are 110 x 110 x 80 mm3 with a resolution of 25 x 25 x 25 μm3. The wall thickness can go down to four pixels which means one tenth of a millimetre.
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