3D Printing of Salt as a Template for Magnesium with Structured Porosity

Porosity is an essential feature in a wide range of applications that combine light weight with high surface area and tunable density. Porous materials can be easily prepared with a vast variety of chemistries using the salt‐leaching technique. However, this templating approach has so far been limited to the fabrication of structures with random porosity and relatively simple macroscopic shapes. Here, a technique is reported that combines the ease of salt leaching with the complex shaping possibilities given by additive manufacturing (AM). By tuning the composition of surfactant and solvent, the salt‐based paste is rheologically engineered and printed via direct ink writing into grid‐like structures displaying structured pores that span from the sub‐millimeter to the macroscopic scale. As a proof of concept, dried and sintered NaCl templates are infiltrated with magnesium (Mg), which is typically highly challenging to process by conventional AM techniques due to its highly oxidative nature and high vapor pressure. Mg scaffolds with well‐controlled, ordered porosity are obtained after salt removal. The tunable mechanical properties and the potential to be predictably bioresorbed by the human body make these Mg scaffolds attractive for biomedical implants and demonstrate the great potential of this additive technique.     

3D Printing of Ceramics with Controllable Green-Body Configuration Assisted by the Polyvinyl Alcohol-Based Physical Gels

Additive manufacturing of ceramics has received intense attention. In particular, 3D-printed ceramics with customized shapes are highly desirable in the chemical industry, aerospace, and biomedical engineering. Nevertheless, developing a simple and cost-effective process that shapes dense ceramics to complex geometries remains challenging because of the high hardness and low ductility of ceramic materials. Extrusion-based printing, such as direct ink writing (DIW), often requires supporting materials that pose additional difficulties during printing. Herein, a simple approach is developed to produce stretchable ceramic green bodies of zirconia and alumina for DIW. The ink is composed of polyvinyl alcohol (PVA) and an aqueous suspension of ceramic powders. Besides the colloidal network formed by the ceramic particles, PVA plays an important role in tuning the printability of the aqueous ink. Through a freeze-thaw process, PVA crystallizes to form physical networks. This strategy provides highly stretchable hydrogel green bodies that can be reprogrammed to complex geometries difficult for common DIW printing. The subsequent drying, debinding, and sintering processes produce ceramics with dense structures and fine mechanical properties. In short, this work demonstrates an efficient method for the DIW of ceramic parts that can be reprogrammed to complex geometries.     

Digital Light-Processing (DLP) 3D Printing of Magnesium Phosphate Minerals and Cements

Digital light processing (DLP) enables the fabrication of complex 3D structures based on a photopolymerizable resin usually containing a photo initiator and an UV or photo absorber. The resin and thus the final properties of the printed structures can be adjusted by adding fillers like bioceramic powders relevant for bone-regeneration applications. Herein, a water-based and biocompatible poly(ethylene glycol diacrylate) (PEGDA) resin containing the photo initiator lithium-phenyl-2,4,6-trimethylbenzoylphosphinate (LAP) enables the production of 3D structures via DLP. The addition of calcium magnesium phosphate cement (CMPC) powder, acting as photo absorber, leads to higher accuracy of the final structures. After curing the printed construct in a diammonium–hydrogen phosphate (DAHP) bath for hardening, the resulting mechanical properties can be adjusted without post-process sintering. Solid loading of up to 40 wt% CMPC powder is possible, and the resins are investigated regarding their rheological behavior and printability. The resulting constructs are analyzed in respect to their surface morphology using scanning electron microscope (SEM), porosity, phase composition using X-ray diffraction (XRD) methods, as well as mechanical properties influenced by the hardening process using DAHP for different durations.