Photopolymerization of Ceramic Resins by Stereolithography Process: A Review

The effect of feed mechanisms on the structural design of flexible antennas, and research on their material processing and applications

Flexible antennas are widely used in mobile communications, the Internet of Things, personalized medicine, aerospace, and military technologies due to their superior performance in terms of adaptability, impact resistance, high degree of freedom, miniaturization of structures, and cost-effectiveness. With excellent flexibility and portability, these antennas are now being integrated into paper, textiles, and even the human body to withstand the various mechanical stresses of daily life without compromising their performance. The purpose of this paper is to provide a comprehensive overview of the basic principles and current development of flexible antennas, systematically analyze the key performance factors of flexible antennas, such as structure, process, material, and application environment, and then discuss in detail the design structure, material selection, preparation process, and corresponding experimental validation of flexible antennas. Flexible antenna design in mobile communication, wearable devices, biomedical technology, and other fields in recent years has been emphasized. Finally, the development status of flexible antenna technology is summarized, and its future development trend and research direction are proposed.

Nested structure role in the mechanical response of spicule inspired fibers

Euplectella aspergillummarine sponge spicules are renowned for their remarkable strength and toughness. These spicules exhibit a unique concentric layering structure, which contributes to their exceptional mechanical resistance. In this study, finite element method simulations were used to comprehensively investigate the effect of nested cylindrical structures on the mechanical properties of spicules. This investigation leveraged scanning electron microscopy images to guide the computational modeling of the microstructure and the results were validated by three-point bending tests of 3D-printed spicule-inspired structures. The numerical analyses showed that the nested structure of spicules induces stress and strain jumps on the layer interfaces, reducing the load on critical zones of the fiber and increasing its toughness. It was found that this effect shows a tapering enhancement as the number of layers increases, which combines with a threshold related to the 3D-printing manufacturability to suggest a compromise for optimal performance. A comprehensive evaluation of the mechanical properties of these fibers can assist in developing a new generation of bioinspired structures with practical real-world applications.

Application of 4D printing in dentistry: A narrative review

4D printing is an innovative digital manufacturing technology that originated by adding a fourth dimension, i.e., time, to pre-existing 3D technology or additive manufacturing (AM). AM is a fast-growing technology used in many fields, which develops accurate 3D objects based on models designed by computers. Dentistry is one such field in which 3D technology is used for manufacturing objects in periodontics (scaffolds, local drug-delivering agents, augmentation of ridges), implants, prosthodontics (partial and complete dentures, obturators), oral surgery for reconstructing jaw, and orthodontics. Dynamism is a vital property needed for the survival of materials used in the oral cavity since the oral cavity is constantly subjected to various insults. 4D printing technology has overcome the disadvantages of 3D printing technology, i.e., it cannot create dynamic objects. Therefore, constant knowledge of 4D technology is required. 3D printing technology has shortcomings, which are discussed in this review. This review summaries various printing technologies, materials used, stimuli, and potential applications of 4D technology in dentistry.

Advanced Additive Manufacturing of Structurally-Colored Architectures

Direct ink writing (DIW) stands out as a facile additive manufacturing method, minimizing material waste. Nonetheless, developing homogeneous Bingham inks with high yield stress and swift liquid-to-solid transitions for versatile 3D printing remains a challenge. In this study, high-performance Bingham inks are formulated by destabilizing silica particle suspensions in acrylate-based resin. A colloidal network forms in the shear-free state through interparticle attraction, achieved by disrupting the solvation layer of large resin molecules using polar molecules. The network is highly dense, with evenly distributed linkage strength as monodisperse particles undergo gelation at an ultra-high fraction. Crucially, the strength is calibrated to ensure a sufficiently large yield stress, while still allowing the network to reversibly melt under shear flow. The inks immediately undergo a liquid-to-solid transition upon discharge, while maintaining fluidity without nozzle clogging. The dense colloidal networks develop structural colors due to the short-range order. This enables the rapid and sophisticated drawing of structurally-colored 3D structures, relying solely on rheological properties. Moreover, the printed composite structures exhibit high mechanical stability due to the presence of the colloidal network, which expands the range of potential applications.

Comparison of Additively Manufactured Polymer-Ceramic Parts Obtained via Different Technologies

This paper aims to compare two ceramic materials available for additive manufacturing (AM) processes-vat photopolymerization (VPP) and material extrusion (MEX)-that result in fully ceramic parts after proper heat treatment. The analysis points out the most significant differences between the structural and mechanical properties and the potential application of each AM technology. The research revealed different behaviors for the specimens obtained via the two mentioned technologies. In the case of MEX, the specimens exhibited similar microstructures before and after heat treatment. The sintering process did not affect the shape of the grains, only their size. For the VPP specimens, directly after the manufacturing process, irregular grain shapes were registered, but after the sintering process, the grains fused, forming a solid structure that made it impossible to outline individual grains and measure their size. The highest compression strength was 168 MPa for the MEX specimens and 81 MPa for the VPP specimens. While the VPP specimens had half the compression strength, the results for the VPP specimens were significantly more repeatable.

Effect of exposure energy dose on lateral resolution and flexural strength of three-dimensionally printed dental zirconia

PURPOSE

This study aims to evaluate the effects of exposure energy on the lateral resolution and mechanical strength of dental zirconia manufactured using digital light processing (DLP).

MATERIALS AND METHODS

A zirconia suspension and a custom top-down DLP printer were used for in-office manufacturing. The viscosity of the suspension and uniformity of the exposed light intensity were controlled. Based on the exposure energy dose delivered to each layer, the specimens were classified into three groups: low-energy (LE), medium-energy (ME), and high-energy (HE). For each energy group, a simplified molar cube was used to measure the widths of the outline (Xo and Yo) and isthmus (Xi and Yi), and a bar-shaped specimen of the sintered body was tested. A Kruskal-Wallis test for the lateral resolution and one-way analysis of variance for the mechanical strength were performed (α = .05).

RESULTS

The zirconia green bodies of the ME group showed better lateral resolution than those of the LE and HE groups (both P < .001). Regarding the flexural strength of the sintered bodies, the ME group had the highest mean value, whereas the LE group had the lowest mean value (both P < .05). The ME group exhibited fewer agglomerates than the LE group, with no distinctive interlayer pores or surface defects.

CONCLUSION

Based on these findings, the lateral resolution of the green body and flexural strength of the sintered body of dental zirconia could be affected by the exposure energy dose during DLP. The exposure energy should be optimized when fabricating DLP-based dental zirconia.

Additive Manufacturing of Advanced Ceramics Using Preceramic Polymers

Ceramic materials are used in various industrial applications, as they possess exceptional physical, chemical, thermal, mechanical, electrical, magnetic, and optical properties. Ceramic structural components, especially those with highly complex structures and shapes, are difficult to fabricate with conventional methods, such as sintering and hot isostatic pressing (HIP). The use of preceramic polymers has many advantages, such as excellent processibility, easy shape change, and tailorable composition for fabricating high-performance ceramic components. Additive manufacturing (AM) is an evolving manufacturing technique that can be used to construct complex and intricate structural components. Integrating polymer-derived ceramics and AM techniques has drawn significant attention, as it overcomes the limitations and challenges of conventional fabrication approaches. This review discusses the current research that used AM technologies to fabricate ceramic articles from preceramic feedstock materials, and it demonstrates that AM processes are effective and versatile approaches for fabricating ceramic components. The future of producing ceramics using preceramic feedstock materials for AM processes is also discussed at the end.

Investigation and Optimization of the Impact of Printing Orientation on Mechanical Properties of Resin Sample in the Low-Force Stereolithography Additive Manufacturing

The mechanical properties of resin samples in low-force stereolithography additive manufacturing were affected by the printing orientation, and were investigated and optimized to achieve excellent single or comprehensive tensile strength, compressive strength, and flexural modulus. The resin samples were fabricated using a Form3 3D printer based on light curing technology according to the corresponding national standards, and they were detected using a universal testing machine to test their mechanical properties. The influence of the printing orientation was represented by the rotation angle of the resin samples relative to the x-axis, y-axis and z-axis, and the parameters was selected in the range 0°-90° with an interval of 30°. The multiple regression models for the mechanical properties of the prepared resin samples were obtained based on least square estimation, which offered a foundation from which to optimize the parameters of the printing orientation by cuckoo search algorithm. The optimal parameters for the tensile strength, compressive strength and flexural modulus were 'α = 45°, β = 25°, γ = 90°', 'β = 0°, β = 51°, γ = 85°' and 'α = 26°, β = 0°, γ = 90°', respectively, which obtained the improvements of 80.52%, 15.94%, and 48.85%, respectively, relative to the worst conditions. The mechanism was qualitatively discussed based on the force analysis. The achievements obtained in this study proved that optimization of the printing orientation could improve the mechanical properties of the fabricated sample, which provided a reference for all additive manufacturing methods.