The Impact of Particle Size and Surface Treatment of Zirconia Suspension for Photocuring Additive Manufacturing.

To prepare a photocurable ceramic suspension for use in commercialized additive manufacturing equipment, the effects of the rheological properties of zirconia particles added to a binder, and the presence or absence of a silane coupling agent on the particles was evaluated. To this end, three experimental groups (ZSs, ZMs, ZLs) and three control groups (ZS, ZM, ZL) were designed depending on the size of the underlying zirconia particles. The test-group zirconia suspensions were prepared through silanization, which was not applied to the control-group suspensions. Depending on the particle size, viscosity differences between the test and control groups were 16,842, 18,623, and 12,303 mPa·s, respectively. Compared to the other groups, the viscosity of the ZLs group suspension decreased by 70.98-88.04%. This confirmed that the viscosity of the suspensions was affected by the particle size and the presence of silane coating. The dispersion stability of the zirconia suspensions was evaluated over 20 days. A sedimentation test confirmed that the sedimentation rate of the ZLs group was slower than those of the other groups. This study aimed to optimize the suspension manufacturing method to effectively be utilized in further commercializing zirconia three-dimensional (3D) printing and could also help to develop various medical applications.

Aqueous Rechargeable Zn/ZnO Battery Based on Deposition/Dissolution Chemistry.

Recently, a novel electrochemical regulation associated with a deposition/dissolution reaction on an electrode surface has been proven to show superiority in large-scale energy storage systems (ESSs). Hence, in the search for high-performance electrodes showcasing these novel regulations, we utilized a low-cost ZnO microsphere electrode to construct aqueous rechargeable batteries (ARBs) that supplied a harvestable and storable charge through electrochemical deposition/dissolution via a reversible manganese oxidation reaction (MOR)/manganese reduction reaction (MRR), respectively, induced by the inherent formation/dissolution of zinc basic sulfate in a mild aqueous electrolyte solution containing 2 M ZnSO4 and 0.2 M MnSO4.

Effects of UV Absorber on Zirconia Fabricated with Digital Light Processing Additive Manufacturing.

This study evaluated the effect of UV absorbers on the dimensional accuracy of zirconia specimens fabricated by additive manufacturing using a digital light process. Zirconia suspension for additive manufacturing was prepared by setting the volume fractions (0, 0.005, 0.05, and 0.1%) of various UV absorbers. The effect of UV absorber content was evaluated through curing thickness, geometric overgrowth model design, linear deviation, and microstructure evaluation before and after sintering. Statistical analysis was performed by Kruskal-Wallis H and post-tested by the Bonferroni correction method. There was no significant difference in the cure depth according to the presence or absence of the UV absorber, the difference in geometric overgrowth was from 2.1 to 12.5%, and the overgrowth significantly decreased as the amount of added UV absorber increased. This result may contribute to improved precision of 3D multilayer ceramic products.

Evaluation of Physical Properties of Zirconia Suspension with Added Silane Coupling Agent for Additive Manufacturing Processes.

In this study, we have analysed the effects of a silane coupling agent on the volume fraction of zirconia for digital light processing (DLP)-based additive manufacturing processes. Zirconia suspension was prepared by the incorporation of silane-modified zirconia particles (experimental group) or untreated zirconia particles (control group). Furthermore, the control and experimental group were subdivided into three groups based on the volume fraction (52, 54, and 56 vol%) of zirconia particles. The disk-shaped zirconia samples were 3D (three-dimensional) printed using the DLP technique and their physical and mechanical properties were evaluated. The addition of a silane coupling agent to the zirconia samples was found to have influence of about 6% on the hardness and biaxial flexural strength. Moreover, the decrease in minute air gaps inside the zirconia layers significantly increased the material density (visualized from the microstructure analysis). Thus, from this study, it was established that the silane-modified zirconia particles had a positive effect on the physical properties of the zirconia parts.

Three-Dimensional Zirconia-Based Scaffolds for Load-Bearing Bone-Regeneration Applications: Prospects and Challenges.

The design of zirconia-based scaffolds using conventional techniques for bone-regeneration applications has been studied extensively. Similar to dental applications, the use of three-dimensional (3D) zirconia-based ceramics for bone tissue engineering (BTE) has recently attracted considerable attention because of their high mechanical strength and biocompatibility. However, techniques to fabricate zirconia-based scaffolds for bone regeneration are in a stage of infancy. Hence, the biological activities of zirconia-based ceramics for bone-regeneration applications have not been fully investigated, in contrast to the well-established calcium phosphate-based ceramics for bone-regeneration applications. This paper outlines recent research developments and challenges concerning numerous three-dimensional (3D) zirconia-based scaffolds and reviews the associated fundamental fabrication techniques, key 3D fabrication developments and practical encounters to identify the optimal 3D fabrication technique for obtaining 3D zirconia-based scaffolds suitable for real-world applications. This review mainly summarized the articles that focused on in vitro and in vivo studies along with the fundamental mechanical characterizations on the 3D zirconia-based scaffolds.

Hybrid porous zirconia scaffolds fabricated using additive manufacturing for bone tissue engineering applications.

For the formation of new bone in critical-sized bone defects, bioactive scaffolds with an interconnected porous network are necessary. Herein, we fabricated three-dimensional (3D) porous hybrid zirconia scaffolds to promote hybrid functionality, i.e., excellent mechanical properties and bioactive performance. Specifically, the 3D printed scaffolds were subjected to Zn-HA/glass composite coating on glass-infiltrated zirconia (ZC). In addition, to pertain the extracellular matrix of bone, biopolymer (alginate/gelatine) was embedded in a developed 3D construct (ZB and ZCB). A zirconia-printed scaffold (Z) group served as a control. The structural and mechanical properties of the constructed scaffolds were studied using essential characterization techniques. Furthermore, the biological performance of the designed scaffolds was tested by a sequence of in vitro cell tests, including the attachment, proliferation, and osteogenic differentiation of dental pulp cells (DPCs). The ZC and ZCB scaffolds exhibited 20% higher compression strength than the zirconia (Z) scaffolds. More importantly, the ZC constructs exhibited superior cell-adhesion, distribution, and osteogenic differentiation ability due to the synergistic effects of the composite coating. In addition, the biopolymer-embedded scaffolds (ZB, ZCB) showed an excellent biological and mechanical performance. Thus, our results suggest that the Zn-HA/glass composite-coated glass-infiltrated zirconia (ZC, ZCB) scaffolds are a dynamic approach to designing bioactive 3D scaffolds for the load-bearing bone regeneration applications.

Two-Step Sintering of Partially Stabilized Zirconia for Applications in Ceramic Crowns.

Partially-stabilized zirconia is used in ceramic crowns due to its excellent mechanical properties and bio-inertness but does not match the natural color and translucency of tooth enamel. To reduce scattering of light and improve translucency, the grain size of zirconia ceramics should be less than the wavelength of visible light (0.4-0.7 µm), and porosity should be eliminated. The aim of the present work was to study the effect of two-step sintering of a commercial powder (Zpex Smile, Tosoh Corp., Tokyo, Japan) on the grain size and translucency of zirconia for use in ceramic crowns. Samples were sintered at a first step temperature (T1) of 1300, 1375 and 1400 °C for 5 min, followed by a decrease to the second step temperature (T2) and holding at T2 for 5-20 h. Samples were also conventionally sintered at 1450 °C for 2 h for comparison. Two-step sintered samples with an almost equal density, smaller grain size and narrower grain size distribution compared to conventionally sintered samples could be sintered. However, the translucency of two-step sintered samples had lower values compared to conventionally sintered samples. This is due to the slightly higher porosity in the two-step sintered samples. Density and translucency of both conventionally and two-step sintered samples could be increased further by using a ball milled powder.

Fabrication and Characterization of 45S5 Bioactive Glass/Thermoplastic Composite Scaffold by Ceramic Injection Printer.

45S5 bioactive glass (45S5) scaffolds were fabricated using a novel additive-manufacturing (AM) technology. A ceramic injection printer (CIP) was designed by combining injection molding and fused deposition modeling, for the fabrication of three-dimensional constructs of ceramic materials. A high fraction (50 vol%) of 45S5 powder was mixed with the thermoplastic polymer. The synthesized 45S5 composites were subjected to Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD) analysis, and field-emission scanning electron microscopy (FE-SEM). The BET results of prepared 45S5 powder were confirmed to have a mean pore diameter of 11.402 nm, and specific surface area is 0.966 m²/g. The prepared 45S5/thermoplastic composite powder was subjected to Thermogravimetric/Differential thermal analysis (TG/DTA). The debinding process of polymer occurred at 192.5, 360.8, and 393 °C. The elastic modulus and ultimate stress of these scaffolds were measured to be 312.49±87.36 MPa and 21.83±6.67 MPa, respectively. The XRD results revealed the presence of Na6Ca3Si6O18 phases. The presence of Si, Ca, P, and Na was confirmed via energy-dispersive X-ray spectroscopy (EDS). The printed scaffold exhibited amorphous calcium phosphate (ACP) expression after immersion in simulated body fluid (SBF) and also it was observed that the intensity of the crystalline phase of 45S5 was decreased, as the immersion time increases. Bioactive glass composites with the high volume fraction can be able to construct 3D complex porous scaffolds using CIP.

Wear Behavior of the Human Enamel Antagonist to Different Glazed Zirconia.

In this study, the wear behavior of glazed zirconia was investigated to the antagonist with human enamel after simulated mastication. Twenty Y-TZP specimens were divided into 4 groups: untreated zirconia (Z), glazed zirconia with IPS e.max Ceram (GZE), glazed zirconia with VITA AKZENT® Plus (GZV), and glazed zirconia with glass (GZG). Glazing glass was mainly composed of SiO2, B2O3, Al2O3, Na2O and K2O (nearly 91 wt%). The surface roughness of the specimens was evaluated using roughness profiler. The maxillary premolar teeth were selected as the antagonist. The wear of human enamel against human enamel was used as a control. Five-disc specimens per group were subjected to chewing stimulation CS-4 (SD Mechatronic GmbH, Germany) for 240,000 cycles against human enamel. The wear loss of antagonistic teeth was calculated using a three-dimensional profiling system and the volume loss of the tooth was scanned using a 3D scanner. 3D data obtained before and after testing were overlapped using 3D software (Dentacian Software, EZplant, Korea). The wear loss of glazed zirconia GZE, GZV and GZG groups showed significantly lower than that of human enamel. Whereas, the zirconia (Z) group exhibits significantly lower volume loss than glazed zirconia and enamel. These results show that the wear of the glazing glass is comparable to other commercial glazing materials. Glazing materials are both more susceptible to wear the antagonist relative to zirconia.

The Influence of Electron Beam Sterilization on In Vivo Degradation of ß-TCP/PCL of Different Composite Ratios for Bone Tissue Engineering.

We evaluated the effect of electron beam (E-beam) sterilization (25 kGy, ISO 11137) on the degradation of ß-tricalcium phosphate/polycaprolactone (ß-TCP/PCL) composite filaments of various ratios (0:100, 20:80, 40:60, and 60:40 TCP:PCL by mass) in a rat subcutaneous model for 24 weeks. Volumes of the samples before implantation and after explantation were measured using micro-computed tomography (micro-CT). The filament volume changes before sacrifice were also measured using a live micro-CT. In our micro-CT analyses, there was no significant difference in volume change between the E-beam treated groups and non-E-beam treated groups of the same ß-TCP to PCL ratios, except for the 0% ß-TCP group. However, the average volume reduction differences between the E-beam and non-E-beam groups in the same-ratio samples were 0.76% (0% TCP), 3.30% (20% TCP), 4.65% (40% TCP), and 3.67% (60% TCP). The E-beam samples generally had more volume reduction in all experimental groups. Therefore, E-beam treatment may accelerate degradation. In our live micro-CT analyses, most volume reduction arose in the first four weeks after implantation and slowed between 4 and 20 weeks in all groups. E-beam groups showed greater volume reduction at every time point, which is consistent with the results by micro-CT analysis. Histology results suggest the biocompatibility of TCP/PCL composite filaments.

Evaluation of Cure Depth and Geometrical Overgrowth Depending on Zirconia Volume Fraction Using Digital Light Processing.

The optical properties of zirconia photopolymer suspension for DLP (Digital Light Processing) were evaluated. The light source and intensity were set to 395 nm and 30 mW/cm². Experimental groups were divided into 48, 50, 52, 54, 56 and 58 vol% according to the zirconia volume fraction. The cure depth of all groups was at least 47.35 um when cured for 1 sec, which was higher than layer parameter values of the 3D printer. The geometrical overgrowth showed 28.55% at 48 vol% and 36.94% at 58 vol%. As the volume fraction of zirconia increased, the geometrical overgrowth increased and the cure depth reduced.