RESOURCES

Abstract
Ceramics and metals are important materials that modern technologies are constructed from. The capability to produce such materials in a complex geometry with good mechanical properties can revolutionize the way we engineer our devices. Current curing techniques pose challenges such as high energy requirements{,} limitations of materials with high refractive index{,} tedious post-processing heat treatment processes{,} uneven drying shrinkages{,} and brittleness of green bodies. In this paper{,} a novel modified self-curable epoxide–amine 3D printing system is proposed to print a wide range of ceramics (metal oxides{,} nitrides{,} and carbides) and metals without the need for an external curing source. Through this technique{,} complex multi-material structures (with metal–ceramic and ceramic–ceramic combinations) can also be realized. Tailoring and matching the sintering temperatures of different materials through sintering additives and dopants{,} combined with a structural design providing maximum adhesion between interfaces{,} allow us to successfully obtain superior quality sintered multi-material structures. High-quality ceramic and metallic materials have been achieved (e.g.{,} zirconia with >98% theoretical density). Also{,} highly conductive metals and magnetic ceramics were printed and shaped uniquely without the need for a sacrificial support. With the addition of low molecular weight plasticizers and a multi-stage heat treatment process{,} crack-free and dense high-quality integrated multi-material structures fabricated by 3D printing can thus be a reality in the near future.

Abstract
Engineered neural tissues serve as models for studying neurological conditions and drug screening. Besides observing the cellular physiological properties, in situ monitoring of neurochemical concentrations with cellular spatial resolution in such neural tissues can provide additional valuable insights in models of disease and drug efficacy. In this work, we demonstrate the first three-dimensional (3D) tissue cultures with embedded optical dopamine (DA) sensors. We developed an alginate/Pluronic F127 based bio-ink for human dopaminergic brain tissue printing with tetrapodal-shaped-ZnO microparticles (t-ZnO) additive as the DA sensor. DA quenches the autofluorescence of t-ZnO in physiological environments, and the reduction of the fluorescence intensity serves as an indicator of the DA concentration. The neurons that were 3D printed with the t-ZnO showed good viability, and extensive 3D neural networks were formed within one week after printing. The t-ZnO could sense DA in the 3D printed neural network with a detection limit of 0.137 μM. The results are a first step toward integrating tissue engineering with intensiometric biosensing for advanced artificial tissue/organ monitoring.

Abstract
Sensors are crucial in the understanding of machines working under high temperatures and high-pressure conditions. Current devices utilize polymeric materials as electrical insulators which pose a challenge in the device’s lifespan. Ceramics, on the other hand, is robust and able to withstand high temperature and pressure. For such applications, a co-fired ceramic device which can provide both electrical conductivity and insulation is beneficial and acts as a superior candidate for sensor devices. In this paper, we propose a novel fabrication technique of complex multi-ceramics structures via 3D printing. This fabrication methodology increases both the geometrical complexity and the device’s shape precision. Structural ceramics (alumina) was employed as the electrical insulator whilst providing mechanical rigidity while a functional ceramic (alumina-doped zinc oxide) was employed as the electrically conductive material. The addition of sintering additives, tailoring the printing pastes’ solid loadings and heat treatment profile resolves multi-materials printing challenges such as shrinkage disparity and densification matching. Through high-temperature co-firing of ceramics (HTCC) technology, dense high quality functional multi-ceramics structures are achieved. The proposed fabrication methodology paves the way for multi-ceramics sensors to be utilized in high temperature and pressure systems in the near future.