DLP 3D printing porous β-tricalcium phosphate scaffold by the use of acrylate/ceramic composite slurry

Digital light processing (DLP) 3D printing has been utilized to fabricate controlled porous β-tricalcium phosphate (β-TCP) scaffolds, which promote cell adhesion and angiogenesis during bone regeneration. However, the current limitation of DLP 3D printing for the fabrication of β-TCP scaffold is how to prepare a low viscosity ceramic slurry and remove the toxicity of residual non-polymerized slurry. The present study has developed a low viscosity ceramic slurry system by mixing β-TCP with photosensitive acrylate resin, and the viscosity of slurry is about 3 Pa s and the solid content of β-TCP can be as high as 60 wt%. After optimizing the ratio of slurry, printing, degreasing and sintering processes, the maximum compressive strength of the DLP printed scaffolds reaches up to 9.89 MPa, while the porosity keeps ca. 40%. According to the proliferation of cells, it confirms the preserved biocompatibility of DLP-fabricated β-TCP scaffolds. These porous scaffolds made by DLP 3D printing technology is of great significance for bone regeneration, and will also help to expand the application of DLP technology in biomedical field.     

3D打印氧化硅陶瓷的制备及性能研究

随着陶瓷3D打印技术的发展,3D打印高性能陶瓷越来越受关注,在航空航天领域得到快速应用.通过研究分散剂、浆料pH、氧化硅粉体粒径和固相含量对浆料粘度和流动性的影响,可制备出粘度低、固相含量高、流动性好的陶瓷浆料.测试了不同固相含量对SiO2陶瓷的弯曲强度、烧成收缩率、气孔率和致密度的影响.结果表明:在68vol%的固相含量条件下,烧结后SiO2陶瓷的致密度达到74.32%,烧成收缩率为0.95%.     

The fabrication of SiBCN ceramic components from preceramic polymers by digital light processing (DLP) 3D printing technology

We present a novel method to fabricate SiBCN ceramic components with complex shapes from preceramic polymers by using digital light processing (DLP) 3D printing technology in this research work. The photocurable precursor for 3D printing was prepared by blending high ceramic yield polyborosilazane with photosensitive acrylate monomers. The material formulation and printing parameters were optimized to fabricate complicated SiBCN ceramic components with high precision. The printed SiBCN ceramic materials were pyrolyzed at different temperatures, and retained their fine features after pyrolysis. Their microstructures were characterized by FTIR, XRD and TEM respectively. Furthermore, the thermal stability and mechanical properties of the SiBCN ceramic samples were investigated and discussed in detail. The 3D printed SiBCN ceramic material exhibited excellent thermal stability and resistance to high temperature oxidation up to 1500?°C.     

致密超细球形氧化铝制备性能良好的陶瓷超滤膜

热等离子体制备的超细球形氧化铝具有表面致密光滑、分散性好等特点,本工作以超细球形氧化铝为原料,通过浸渍提拉烧结法,制备了孔径分布窄、渗透通量高的陶瓷超滤膜,研究了烧结温度对陶瓷膜微孔结构的演化、孔径分布和渗透通量的影响。随后对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理,采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程。结果表明,通过调节烧结温度调控陶瓷膜的微孔结构,当烧结温度为1250℃时,陶瓷膜的孔径分布较窄,孔径大小为25?65 nm,渗透通量为986.4 L/(m2?h)。超细球形氧化铝粒径分布较窄及表面致密光滑有助于1250℃下烧结形成均匀的烧结颈,提供了陶瓷膜较窄的孔径分布。对1250℃下烧结的陶瓷膜进行了纳米硅水分散液过滤处理后其浊度下降为0.231 NTU,浊度去除率达99.96%。采用不同堵塞模型分析了陶瓷膜过滤纳米硅水分散液的膜污染过程,结果表明,纳米硅水分散液的堵塞模型是滤饼过滤,属于可逆污染。     

Evaluation of direct light processing for the fabrication of bioactive ceramic scaffolds: Effect of pore/strut size on manufacturability and mechanical performance

Bioactive ceramic scaffolds for bone regeneration consisting of a three-dimensional mesh of interpenetrating struts with square section were fabricated via Digital Light Processing (DLP). The ability of the technique to manufacture 3D porous structures from β-tricalcium phosphate (β-TCP) powders with different dimensions of struts and pores was evaluated, identifying the possibilities and limitations of the manufacturing process. Small pore sizes were found to seriously complicate the elimination of excess slurry from the scaffold’s innermost pores. The effect of the strut/pore size on the mechanical performance of the scaffolds under compressive stresses was also evaluated, but no significant influence was found. Under compressive stresses, the structures resulted weaker when tested perpendicularly to the printing plane due to interlayer shear failure. Interlayer superficial grooves are proposed as potential failure-controlling defects, which could also explain the lack of a Weibull size effect on the mechanical strength of the fabricated DLP scaffolds.     

High-performance and high-precision Al2O3 architectures enabled by high-solid-loading,graphene-containing slurries for top-down DLP 3D printing

To date, obtaining the high-solid-loading Al₂O₃ slurry and overcoming the trade-off between high solid loading and printing accuracy and strength of printed green bodies to achieve high-performance and precision Al₂O₃ ceramic parts by DLP 3D printing remain challenging. In this study, an Al₂O₃ slurry with high solid loading of 60 vol% was developed through dispersant optimisation for top-down DLP 3D printing. Graphene was innovatively introduced during slurry fabrication to decouple the printing accuracy and strength of green bodies from such high solid loading. Simultaneously, graphene addition could considerably reduce slurry fluidity, thereby facilitating its coordination with top-down DLP. With 0.07 wt% graphene addition, the dimension deviations of printed green bodies improved from 90 to 880 µm to ≤ 70 µm, and the bending strength increased by 17.75%. High-performance and precise Al₂O₃ ceramic components with low sintering shrinkages were prepared. The density and microhardness were 99.7% and 18.61 GPa, respectively.     

Additive manufacturing of Al2O3 ceramic core with applicable microstructure and mechanical properties via digital light processing of high solid loading slurry

Ceramic cores are essential intermediate mediums in casting superalloy hollow turbine blades. The developing of additive manufacturing (AM) technology provides a new approach for the preparation of ceramic cores with complex structure. In this study, alumina oxide (Al₂O₃) ceramic cores with fine complex geometric shapes were fabricated by digital light processing (DLP) in high resolution. The maximum solid content of 70 vol% of ceramic slurry was adopted in the printing process, which is important for the regulation of deformations and mechanical properties. The effects of the printing parameters, including exposure intensity, printing layer thickness and sintering temperature on the microstructures and mechanical properties of printed samples were investigated. The decrease of residual stress and similar shrinkage in X, Y, and Z directions could be obtained by adjusting the printing parameters, which are crucial to prepare complex ceramic cores with high quality. Besides, the flexure strength and open porosity of ceramic cores reached 34.84 MPa and 26.94%, respectively, which were supposed to meet the requirement of ceramic cores for the fabrication of superalloy blades.     

大壁厚3D打印SiO2陶瓷快速制备技术研究

选用复合分散剂制备低粘度陶瓷料浆,采用自主研发的陶瓷3D打印机,以DLP(digital light processing)工艺制备出了大壁厚(>3 mm)SiO2空心内六角陶瓷部件,坯体精度均在50μm内.分析了3D打印陶瓷素坯在空气气氛和氩气气氛下的热分解过程,研究了气氛对大壁厚(>3 mm)SiO2陶瓷部件脱脂与...     

Silicon carbide whiskers reinforced SiOC ceramics through digital light processing 3D printing technology

Polymer derived silicon oxycarbide ceramic materials and silicon carbide whiskers reinforced ceramic composite are prepared through digital light processing (DLP) 3D printing technology in the present work. A new type of UV-curable preceramic polymer is firstly synthesized and then two types of photopolymer resins with and without SiC whiskers as reinforcement are prepared. Due to the high curing rate and good fluidity of the resins, they are applied in DLP 3D printing and various 3D objects with complicated structures and high printing resolution have been printed. The derived ceramic materials show amorphous microstructure and there is no apparent porosity and cracking throughout the whole sample surface of the ceramic materials and the SiC whiskers are uniformly embedded in the ceramic matrix and remain intact and unaffected during the pyrolysis process. The SiC whiskers reduced the shrinkage and mass loss. More importantly, it significantly improves the mechanical performance of the derived ceramic materials in which the compressive strength increases from 77.5 ± 10.2 MPa to 98.4 ± 12.3 MPa. Benefiting from the easiness of the fabrication, high printing resolution and excellent mechanical performance, the derived ceramic materials have great potential applications in various areas.     

Digital light processing-stereolithography three-dimensional printing of yttria-stabilized zirconia

Digital light processing (DLP)-stereolithography three-dimensional (3D) printing is a well known technique for fabricating components with complex geometries. However, the application of DLP 3D printing to functional ceramics such as 8 mol% yttria-stabilized zirconia (8YSZ), which is one of the most extensively used electrolyte materials for solid oxide fuel cells, is still a great challenge. Therefore, the fabrication of fully 8YSZ monoliths via DLP 3D printing was attempted herein, including the preparation of UV-curable ceramic suspensions, shaping of green bodies, and debinding and sintering. The results show that intact green bodies printed using a 30 vol% 8YSZ-photosensitive resin suspension with 0.1 wt% oleic acid as the dispersant under the optimized printing conditions was sufficiently dense without connected pores after vacuum debinding and sintering in air. The successful fabrication of 8YSZ monoliths with design flexibility via 3D printing provides a simple method for preparing functional ceramic components and may expand the application of 3D printing technology to the energy field.     

3D printing of porous scaffolds BaTiO3 piezoelectric ceramics and regulation of their mechanical and electrical properties

A series of porous scaffolds of piezoelectric ceramic barium titanate (BaTiO₃) were successfully fabricated by Digital Light Processing (DLP) 3D printing technology in this work. To obtain a high-precision and high-purity sample, the debinding sintering profile was explored and the optimal parameters were determined as 1425 °C for 2h. With the increase of scaffolds porosity from 10% to 90%, the compressive strength and piezoelectric coefficient (d₃₃) decreased gradually. The empirical formulas about the mechanical and piezoelectric properties were obtained by adjusting BaTiO₃ ceramics with different porosity. In addition, the distribution of potential and stress under 100 MPa pressure were studied by the finite element method (FEM).     

Preparation of Si3N4 ceramic based on digital light processing 3D printing and precursor infiltration and pyrolysis

The emergence of digital light processing (DLP) 3D printing technology creates favorable conditions for the preparation of complex structure silicon nitride (Si₃N₄) ceramics. However, the introduction of photosensitive resin also makes the Si₃N₄ ceramics prepared by 3D printing have low density and poor mechanical properties. In this study, high-density Si₃N₄ ceramics were prepared at low temperatures by combining DLP 3D printing with precursor infiltration and pyrolysis (PIP). The Si₃N₄ photocurable slurry with high solid content and high stability was prepared based on the optimal design of slurry components. Si₃N₄ green parts were successfully printed and formed by setting appropriate printing parameters. The debinding process of printed green parts was further studied, and the results showed that samples without defects and obvious deformation can be obtained by setting the heating rate at .1°C/min. The effect of the PIP cycle on the microstructure and mechanical properties of the Si₃N₄ ceramics was studied. The experimental results showed that the mass change and open porosity of the samples tended to be stable after eight PIP cycles, and the open porosity, density, and bending strength of the Si₃N₄ ceramics were 1.30% (reduced by 97%), 2.64 g/cm³ (increased by 43.5%), and 162.35 MPa.     

Hierarchically porous ceria with tunable pore structure from particle-stabilized foams

We firstly fabricated CeO₂ ceramic foams with tunable structure by using particle-stabilized bubbles as template, and designed their interconnected porous structure and even hierarchically porous structure, which endows them the penetration ability for gases or liquids. Hollow spheres with single-layer shell were innovatively selected as the pore-former, which allows for the formation of open pores on the cell wall. Moreover, 3D printing CeO₂ particle-stabilized foams are realized with the aid of direct ink writing, which enables the production of CeO₂ ceramic foams with complex shape. Highly porous CeO₂ with relatively high compressive strength have been fabricated, the porosity of which varies from 81.0% to 92.0% while their excellent compressive strength ranges from 5.0 MPa to 20.0 MPa. Attributed to the hierarchical porous structure, uniform pore size distribution as well as densely assembled cell wall, 3D printing CeO₂ ceramic foams possess superior mechanical performance at high porosity level.     

A review of 3D printed porous ceramics

Three-dimensional (3D) printing of ceramics has gained widespread attentions in recent years. Many excellent reviews have reported the printing of ceramics. However, most of them focus on printing of dense ceramics or general ceramic aspects, there is no systematical review about 3D printing of porous ceramics. In this review paper, the 3D printing technologies for fabricating of porous ceramic parts are introduced, including binder jetting, selective laser sintering, direct ink writing, stereolithography, laminated object manufacturing, and indirect 3D printing processes. The techniques to fabricate hierarchical porous ceramics by integrating 3D printing with one or more conventional porous ceramics fabrication approaches are reviewed. The main properties of porous ceramics such as pore size, porosity, and compressive strength are discussed. The emerging applications of 3D printed porous ceramics are presented with a focus on the booming application in bone tissue engineering. Finally, summary and a perspective on the future research directions for 3D printed porous ceramics are provided.     

Fabrication and Characterization of Dual-Channeled Zirconia Ceramic Scaffold

A novel porous ceramic with a structure containing two three-dimensional (3D) pore channels in a tetragonal zirconia polycrystals (TZP) ceramic was fabricated using a combination of a CNC-machining method and slurry coating process. A graphite scaffold with a single interconnected 3D channel as a template was prepared using CNC machining and lamination. The surfaces of the graphite scaffold were then coated uniformly with the TZP slurry, followed by heat treatment at 900°C for 3 h in air to remove the graphite material completely via thermal oxidation and at 1400°C for 3 h in air to sinter the TZP walls. This process produced a dual-channeled TZP scaffold with an additional 3D channel, which replicated the 3D graphite structure with the pre-existing channel. The fabricated scaffold showed ultra-high porosity (91%), high surface area, and high compressive strength (2.04 MPa), as well as a tightly controlled pore structure.     

Effect of the preparation techniques of photopolymerizable ceramic slurry and printing parameters on the accuracy of 3D printed lattice structures

Digital Light Processing (DLP) technology demonstrates the potential for manufacturing parts with complex structures for various engineering applications. The purpose of this study is to evaluate Al₂O₃ ceramic slurry preparation techniques, establish optimal processing window and assess the manufacturability and dimensional accuracy of lattice structures with CAD strut diameters of up to 500 μm. Two preparation techniques of the ceramic slurry were investigated. The slurry with the pre-treated powder showed appropriate rheological and photopolymerization behaviour. Full factorial Design of Experiments (DOE) was conducted to generate an experimental plan and assess the influence of the printing parameters on the dimensional accuracy. Analysis of Variance (ANOVA) revealed the exposure time, the exposure power, and the interaction effect of both had a significant influence on the dimensional accuracy of lattice strut diameters. The excess cure width was found to be dependent on the feature size, the energy dose and the layer thickness.     

Study of alumina ceramic parts fabricated via DLP stereolithography using powders with different sizes and morphologies

Selecting suitable ceramic powders for the preparation of UV-curable ceramic suspensions, which are well suited for printing processes and production of high-performance ceramic components, is a crucial factor in the practical industrial application of digital light processing (DLP) stereolithography. Therefore, this study aims to provide a comprehensive evaluation of alumina ceramic parts fabricated via DLP stereolithography using a variety of alumina powders with varying sizes and morphologies. Experiments were conducted to examine the rheological response, recoating performance, and curing behavior of UV-curable alumina suspensions. Additionally, the thermal decomposition behavior of three-dimensional (3D)-printed green-bodies, as well as the physical and mechanical properties of 3D-printed sintered alumina components were thoroughly investigated. The best physical and mechanical performances were achieved by printing 55 vol% suspensions prepared using near-spherical AA04 alumina powders (median diameter .4 μm). This study elucidates the effects of ceramic particle size and morphology on the entire technological process of DLP-based ceramic stereolithography, thereby establishing the guidelines for the fabrication of high-performance 3D-printed ceramic objects in industrial and engineering production by selecting appropriate ceramic powders.     

Fabrication of cancellous-bone-mimicking β-tricalcium phosphate bioceramic scaffolds with tunable architecture and mechanical strength by stereolithography 3D printing

It is highly challenging to fabricate bioceramic scaffolds mimicking architecture and mechanical strength of cancellous bone. Gyroid structure, which is based on triply periodic minimal surface, highly resembles the architecture of cancellous bone. Herein, β-tricalcium phosphate (β-TCP) bioceramic scaffolds with gyroid structure were fabricated by stereolithography (SLA) 3D printing. The SLA 3D printing ensured high precision of ceramic part. The porosity (51–87%), pore size (250 – 2400 µm), pore wall thickness (< 300 µm) and compressive strength (0.6 – 16.8 MPa) of gyroid bioceramic scaffolds were readily adjusted to match various sites of cancellous bone. The gyroid bioceramic scaffolds were more favorable for cell proliferation than the grid-like bioceramic scaffolds. The cancellous-bone-mimicking gyroid bioceramic scaffolds with tunable architecture and mechanical strength were expected to efficiently repair the target bone defects.     

Digital light processing additive manufacturing of in situ mullite-zirconia composites

Digital light processing (DLP) can produce small series ceramic parts with complex geometries and tiny structures without the high cost of molds usually associated with traditional ceramic processing. However, the availability of feedstock of different ceramics for the technique is still limited. Mullite-zirconia composites are refractory materials with diverse applications, nevertheless, their 3D printing has never been reported. In this work, alumina and zircon were used as raw materials for additive manufacturing by DLP followed by in situ mullite and zirconia formation. Thus, coarse zircon powder was milled to submicrometric size, alumina-zircon photosensitive slurries were prepared and characterized, parts were manufactured in a commercial DLP 3D printer, debound, and sintered at different temperatures. The printed parts sintered at 1600 °C completed the reaction sintering and reached a flexural strength of 84 ± 13 MPa. The process proved capable of producing detailed parts that would be unfeasible by other manufacturing methods.     

Anisotropy management on microstructure and mechanical property in 3D printing of silica-based ceramic cores

Ceramic core is an essential component in the precise casting of hollow turbine blades, and the investigation on 3D printing of silica-based ceramic cores is crucial to the development of aviation industry; however, they are suffered from difficulty in high-temperature strength and structural anisotropy. In present work, silica-based ceramic cores were prepared via DLP stereolithography 3D printing, and the anisotropy management on microstructures and properties were explored based on the particle size of fused silica powders. In 3D printed ceramic cores with coarse powders, significant anisotropy was displayed exhibiting multilayer structure with large gaps in horizontal printing and uniform porous microstructure in the vertical direction, which was further explained by the particle deposition in printing. With finer silica powders, the uniformity in the microstructures was highly improved, attributed to the enhanced particle dispersion in ceramic slurries and promoted interlayer particle rearrangement during sintering. To evaluate the anisotropy in mechanical property, the ratio of vertical strength to horizontal strength (σ_V/σ_H) was proposed, which rose from 0.48 to 0.86 as the particle size decreased from 35 µm to 5 µm, suggesting enhanced mechanical uniformity. While the average particle size of silica powders was 5 µm, the flexure strengths of ceramic cores in different directions were up to 18.5 MPa and 16.3 MPa at 1540 °C with σ_V/σ_H ratio of 0.88, which well satisfied the demands for the casting of turbine blades. This work inspires new guidance on the anisotropy management in ceramic cores prepared by 3D printing, and provides new technology for fabrication of silica-based ceramic cores with superior high temperature mechanical properties.