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Abstract
In this study, WC-8.4Co-3.6Mo (wt%) cemented carbides were fabricated by laser powder bed fusion (L-PBF) and direct-ink writing (DIW). The effects of various processing parameter combinations on the consolidation of the alloys were investigated. A multi-objective response surface methodology (RSM) was employed to determine the optimal L-PBF and DIW processing parameters, utilising a fractional factorial design of experiment (DoE) approach. The RSM analysis included parameters such as scanning speed, laser power, hatch spacing, extrusion pressure and solid loading. Samples prepared by L-PBF showed alternating layers of coarse and fine WC grains, with the fine grains embedded in a binder melt pool. Increasing the laser energy density resulted in a gradual decomposition of the WC phase, accompanied by the loss of Co and the formation of ƞ phases. For DIW, feedstock filaments with powder loading content between 89.4 and 92.4 wt% were prepared using a binder system composed of Pluronic F-127 and Dolapix CE-64. These filaments exhibited steady thermoplastic behaviour with controllable extrusion, yielding samples with a linear shrinkage of approximately 20 %. The results revealed that DIW-produced samples achieved a maximum hardness of 12.69 GPa and a relative density of 95 % under optimised conditions, specifically an extrusion pressure of 0.125 MPa and a solid loading of 92.4 wt%. For L-PBF, a maximum hardness of 12.60 GPa and a relative density of 99 % were obtained at an optimised scanning speed of 485 mm/s, laser power of 197 W and hatch spacing of 90 μm. These optimisation results derived from the regression models provided new parameter sets for further refinement and enhancement.

Abstract
While available treatments have addressed a variety of complications in the dentoalveolar region, associated challenges have resulted in exploration of tissue engineering techniques. Often, scaffold biomaterials with specific properties are required for such strategies to be successful, development of which is an active area of research. This study focuses on the development of a copolymer of poly (N-isopropylacrylamide) (pNIPAM) and chitosan, used for 3D printing of scaffolds for dentoalveolar regeneration. The synthesized material was characterized by Fourier transform infrared spectroscopy, and the possibility of printing was evaluated through various printability tests. The rate of degradation and swelling was analyzed through gravimetry, and surface morphology was characterized by scanning electron microscopy. Viability of dental pulp stem cells seeded on the scaffolds was evaluated by live/dead analysis and DNA quantification. The results demonstrated successful copolymerization, and three formulations among various synthesized formulations were successfully 3D printed. Up to 35% degradability was confirmed within 7 days, and a maximum swelling of approximately 1200% was achieved. Furthermore, initial assessment of cell viability demonstrated biocompatibility of the developed scaffolds. While further studies are required to achieve the tissue engineering goals, the present results tend to indicate that the proposed hydrogel might be a valid candidate for scaffold fabrication serving dentoalveolar tissue engineering through 3D printing.

Abstract
Alumina toughened zirconia (ATZ) ceramics combine high biocompatibility with remarkable mechanical properties, making them suitable for dental and orthopedic implant applications. Producing these ATZ ceramics using slurry-based additive manufacturing necessitates homogeneous, stable suspensions with controlled particle sizes. Stabilizing such systems with the appropriate type and amount of dispersant is challenging, particularly since multi-component systems are prone to hetero-coagulation. In this study, ATZ powders with different surface areas were investigated to determine the optimum concentration of three commercially available dispersants: Darvan CN, Darvan 821 A, and Dolapix CE64, which have been successfully used to stabilize Al2O3 and 3Y-TZP suspensions. Based on zeta potential (0.01 vol% suspensions), agglomerate size (0.01 vol% suspensions), sedimentation (10 vol% slurries), and rheological (40 vol% slurries) characterization, the optimum dispersant concentrations were found to be 0.50 mg/m2 for Dolapix CE64, 0.75 mg/m2 for Darvan 821 A, and 1.50 mg/m2 for Darvan CN. Among the studied dispersants, Dolapix CE64 was the most effective in terms of reduced sedimentation, smaller agglomerate size (0.70 μm), flow behavior, and low resistance to structure breakdown. The rheological assessment showed that slurries prepared with ATZ powder featuring a smaller specific surface area (7.3 m2/g) resulted in lower viscosity, critical stress, and equilibrium storage and loss moduli compared to those prepared with higher specific surface area (13.3 m2/g) starting powder. The sedimentation analysis however revealed that the larger specific surface area ATZ powder exhibited higher slurry stability. While 38 vol% ATZ pastes without dispersant showed inhomogeneous extrusion and the presence of aggregates, the filaments extruded from 45 vol% paste with 0.50 mg/m2 Dolapix CE64 had a homogeneous and smooth structure and were free of aggregates, highlighting the importance of the dispersant addition for DIW.

Abstract
Direct ink writing (DIW) is a promising additive manufacturing technique for fabricating structural ceramics, including alumina-toughened zirconia (ATZ), heavily reliant on the rheological properties of the paste. The rheological properties of aqueous ATZ pastes with 25 wt% Pluronic® F127 hydrogel and solid loadings of 28–44 vol% were investigated, complemented by characterization of the parts, including relative density and shrinkage measurements, to assess the printability. The 42 vol% paste was identified as most suitable for producing high-density parts with minimal shrinkage. A controlled drying process gradually decreased humidity from 90% to 30% while raising temperature from 25 to 60°C over 4 days to prevent drying defects. Mechanical testing showed DIW-printed high-density (97.2±2.2%) parts with a mean flexural strength of 670±270 MPa, Vickers hardness of 13.6±2.8 GPa, and fracture resistance of 4.4±0.2 MPa, highlighting the potential for DIW to create high-density ATZ ceramic parts with favorable mechanical properties.

Abstract
Abstract Additive manufacturing (AM) of high-performance structural ceramic components with comparative strength and toughness as conventionally manufactured ceramics remains challenging. Here, an UV-curing approach is integrated in direct ink writing (DIW), taking advantage from DIW to enable an easy use of high solid-loading pastes and multi-layered materials with compositional changes, while avoiding drying problems. UV-curable opaque zirconia-based slurries with a solid loading of 51 vol% were developed to fabricate dense and crack-free alumina-toughened zirconia (ATZ) containing 3 wt% alumina platelets. Importantly, a non-reactive diluent was added to relieve polymerization-induced internal stresses, avoid subsequent warping and cracking, and facilitate the de-binding. For the first time, UV-curing assisted DIW-printed ceramic after sintering revealed even better mechanical properties than that processed by a conventional pressing. This was attributed to the aligned alumina platelets, enhancing crack deflection and improving the fracture toughness from 6.8 ± 0.3 MPa m0.5 (compacted) to 7.4 ± 0.3 MPa m0.5 (DIW). The 4-point bending strength of the DIW ATZ (1009 ± 93 MPa) was also higher than that of the conventionally manufactured equivalent (861 ± 68 MPa). Beside homogeneous ceramic, laminate structures were demonstrated. This work has provided a valuable hybrid approach to additively manufacture tough and strong ceramic components. This article is protected by copyright. All rights reserved

Abstract
Methacryloyl gelatin (GelMA) is a versatile material for bioprinting because of its tunable physical properties and inherent bioactivity. Bioprinting of GelMA is often met with challenges such as lower viscosity of GelMA inks due to higher methacryloyl substitution and longer physical gelation time at room temperature. In this study, a tunable interpenetrating polymer network (IPN) hydrogel was prepared from gelatin-hyaluronan dialdehyde (Gel-HDA) Schiff’s polymer, and 100% methacrylamide substituted GelMA for biofabrication through extrusion based bioprinting. Temperature sweep rheology measurements show a higher sol-gel transition temperature for IPN (30 °C) compared to gold standard GelMA (27 °C). Furthermore, to determine the tunability of the IPN hydrogel, several IPN samples were prepared by combining different ratios of Gel-HDA and GelMA achieving a compressive modulus ranging from 20.6 ± 2.48 KPa to 116.7 ± 14.80 KPa. Our results showed that the mechanical properties and printability at room temperature could be tuned by adjusting the ratios of GelMA and Gel-HDA. To evaluate cell response to the material, MC3T3-E1 mouse pre-osteoblast cells were embedded in hydrogels and 3D-printed, demonstrating excellent cell viability and proliferation after 10 d of 3D in vitro culture, making the IPN an interesting bioink for the fabrication of 3D constructs for tissue engineering applications.

Abstract
Dentoalveolar tissue engineering is an emerging yet challenging field, considering the lack of suitable materials and difficulty to produce patient-specific hydrogel scaffolds. The present paper aims to produce a 3D printable and tuneable biomaterial by copolymerizing a synthesized water-soluble chitosan derivative called maleic anhydride grafted chitosan (MA-C) with gelatin using genipin, a natural crosslinking agent. Development and testing of this material for 3D printing, degradation, and swelling demonstrated the ability to fabricate scaffolds with controlled physical properties based on pre-determined designs. The MA-C-gelatin copolymer demonstrated excellent biocompatibility, which was verified by analyzing the viability, growth and proliferation of human dental pulp stem cells seeded on MA-C-gelatin constructs through live/dead, alamar blue and DNA quantification assays. Based on the present findings, the proposed material might be a suitable candidate for dentoalveolar tissue engineering, while further research is required to achieve this goal.

Abstract
Abstract In hybrid bioprinting of cartilage tissue constructs, spheroids are used as cellular building blocks and combined with biomaterials for dispensing. However, biomaterial intrinsic cues can deeply affect cell fate and to date, the influence of hydrogel encapsulation on spheroid viability and phenotype has received limited attention. This study assesses this need and unravels 1) how the phenotype of spheroid-laden constructs can be tuned through adjusting the hydrogel physico–chemical properties and 2) if the spheroid maturation stage prior to encapsulation is a determining factor for the construct phenotype. Articular chondrocyte spheroids with a cartilage specific extracellular matrix (ECM) are generated and different maturation stages, early-, mid-, and late-stage (3, 7, and 14 days, respectively), are harvested and encapsulated in 10, 15, or 20 w/v% methacrylamide-modified gelatin (gelMA) for 14 days. The encapsulation of immature spheroids do not lead to a cartilage-like ECM production but when more mature mid- or late-stage spheroids are combined with a certain concentration of gelMA, a fibrocartilage-like as well as a hyaline cartilage-like phenotype can be induced. As a proof of concept, late-stage spheroids are bioprinted using a 10 w/v% gelMA–Irgacure 2959 solution with the aim to test the processing potential of the spheroid-laden bioink.

Abstract
To date, the treatment of articular cartilage lesions remains challenging. A promising strategy for the development of new regenerative therapies is hybrid bioprinting, combining the principles of developmental biology, biomaterial science, and 3D bioprinting. In this approach, scaffold-free cartilage microtissues with small diameters are used as building blocks, combined with a photo-crosslinkable hydrogel and subsequently bioprinted. Spheroids of human bone marrow-derived mesenchymal stem cells (hBM-MSC) are created using a high-throughput microwell system and chondrogenic differentiation is induced during 42 days by applying chondrogenic culture medium and low oxygen tension (5%). Stable and homogeneous cartilage spheroids with a mean diameter of 116 ± 2.80 μm, which is compatible with bioprinting, were created after 14 days of culture and a glycosaminoglycans (GAG)- and collagen II-positive extracellular matrix (ECM) was observed. Spheroids were able to assemble at random into a macrotissue, driven by developmental biology tissue fusion processes, and after 72 h of culture, a compact macrotissue was formed. In a directed assembly approach, spheroids were assembled with high spatial control using the bio-ink based extrusion bioprinting approach. Therefore, 14-day spheroids were combined with a photo-crosslinkable methacrylamide-modified gelatin (gelMA) as viscous printing medium to ensure shape fidelity of the printed construct. The photo-initiators Irgacure 2959 and Li-TPO-L were evaluated by assessing their effect on bio-ink properties and the chondrogenic phenotype. The encapsulation in gelMA resulted in further chondrogenic maturation observed by an increased production of GAG and a reduction of collagen I. Moreover, the use of Li-TPO-L lead to constructs with lower stiffness which induced a decrease of collagen I and an increase in GAG and collagen II production. After 3D bioprinting, spheroids remained viable and the cartilage phenotype was maintained. Our findings demonstrate that hBM-MSC spheroids are able to differentiate into cartilage microtissues and display a geometry compatible with 3D bioprinting. Furthermore, for hybrid bioprinting of these spheroids, gelMA is a promising material as it exhibits favorable properties in terms of printability and it supports the viability and chondrogenic phenotype of hBM-MSC microtissues. Moreover, it was shown that a lower hydrogel stiffness enhances further chondrogenic maturation after bioprinting.