Robocasting of advanced ceramics: ink optimization and protocol to predict the printing parameters - A review

Rheology and Printability of a Porcelain Clay Paste for DIW 3D Printing of Ceramics with Complex Geometric Structures

The modeling of ceramics with complex geometric structures currently depends on the handcrafted mode, with long cycles, high costs, and low efficiency; additive manufacturing (AM) technology can solve this problem well. Herein, the porcelain clay paste was successfully prepared for the direct ink writing (DIW) 3D printing process of ceramics with complex geometric structures, and the effects of sodium citrate (SC) content on the rheological properties and DIW 3D printability of the porcelain clay paste were investigated in detail. The SC has a vital role in the rheological behavior of porcelain clay paste. Adding SC increases the absolute zeta potential and decreases the viscosity of the paste, while a high SC content will lead to a low storage modulus of the paste. The porcelain clay paste with an SC content of 0.05% and a paste solid content of 75% possesses suitable rheological properties and a storage modulus for DIW 3D printing. The as-prepared porcelain clay paste has high DIW 3D printability at a pressure of 0.5 MPa, and a 3D-printed green body with a well-densified structure can be achieved. After being sintered, the 3D-printed ceramic exhibits high densification and mechanical properties. A green body with complex geometric structures is quickly and precisely modeled by the DIW 3D printing process with the resultant porcelain clay paste as the raw material. This work provides a practical approach to rapidly fabricating ceramics with complex geometrical structures.

An in vitro and in vivo study of electrospun polyvinyl alcohol/chitosan/sildenafil citrate mat on 3D-printed polycaprolactone membrane as a double layer wound dressing

Double-layer dermal substitutes (DS) generally provide more effective therapeutic outcomes than single-layer substitutes. The architectural design of DS incorporates an outer layer to protect against bacterial invasions and maintain wound hydration, thereby reducing the risk of infection and the frequency of dressing changes. Moreover, the outer layer is a mechanical support for the wound, preventing undue tension in the affected area. A 3D-printed polycaprolactone (PCL) membrane was utilized as the outer layer to fabricate DS wound dressing. Simultaneously, a polyvinyl alcohol/chitosan/sildenafil citrate (PVA/CS/SC) scaffold was electrospun onto the PCL membrane to facilitate cellular adhesion and proliferation. Scanning electron microscopy (SEM) analysis of the PCL filaments revealed a consistent cross-sectional surface and structure, with an average diameter of 562.72 ± 29.15 μm. SEM results also demonstrated uniform morphology and beadless structure for the PVA/CS/SC scaffold, with an average fiber diameter of 366.77 ± 1.81 nm for PVA/CS. The addition of SC led to an increase in fiber diameter while resulting in a reduction in tensile strength. However, drug release analysis indicated that the SC release from the sample can last up to 72 h. Animal experimentation confirmed that DS wound dressing positively accelerated wound closure and collagen deposition in the Wistar rat skin wound model.

3D-Printed Polycaprolactone-Based Containing Calcium Zirconium Silicate: Bioactive Scaffold for Accelerating Bone Regeneration

There is an essential clinical need to develop rapid process scaffolds to repair bone defects. The current research presented the development of calcium zirconium silicate/polycaprolactone for bone tissue engineering utilising melt extrusion-based 3D printing. Calcium zirconium silicate (CZS) nanoparticles were added to polycaprolactone (PCL) porous scaffolds to enhance their biological and mechanical properties, while the resulting properties were studied extensively. No significant difference was found in the melting point of the samples, while the crystallisation temperature points of the samples containing bioceramic increased from 36.1 to 40.2 °C. Thermal degradation commenced around 350 °C for all materials. According to our results, increasing the CZS content from 0 to 40 wt.% (PC40) in porous scaffolds (porosity about 55-62%) improved the compressive strength from 2.8 to 10.9 MPa. Furthermore, apatite formation ability in SBF solution increased significantly by enhancing the CZS percentage. According to MTT test results, the viability of MG63 cells improved remarkably (~29%) in PC40 compared to pure PCL. These findings suggest that a 3D-printed PCL/CZS composite scaffold can be fabricated successfully and shows great potential as an implantable material for bone tissue engineering applications.

Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Efficient route for preparation of Nd3+ doped Y2O3 nanoparticles at intermediate temperature

Yttrium oxide nanoparticles are one of the proper host materials for rare-earth elements. The rare-earth ions doped in yttrium oxide nanoparticles have medical applications such as biological imaging and photonic applications such as waveguides in the infrared region, laser mediums, sensitizers, LEDs, etc. The preparation of rare-earth ion-doped Y2O3 nanoparticles is usually done through the solid-state process and at a very high temperature, such as 1200 °C. In this research, using the solid-state process and during multi-step heat treatment at temperatures of 210 °C, 380 °C, and 500 °C, white nanopowders of Nd:Y2O3were prepared in 6 h. The produced nanopowders were studied using various characterization methods. The results showed that the produced nanopowders have a cubic structure and an average particle size between 22 and 65 nm.

UV-Curing Assisted Direct Ink Writing of Dense, Crack-Free, and High-Performance Zirconia-Based Composites With Aligned Alumina Platelets

Additive manufacturing (AM) of high-performance structural ceramic components with comparative strength and toughness as conventionally manufactured ceramics remains challenging. Here, a 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% are developed to fabricate dense and crack-free alumina-toughened zirconia (ATZ) containing 3 wt% alumina platelets. Importantly, a non-reactive diluent is 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 reveals even better mechanical properties than that processed by a conventional pressing. This is 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 four-point bending strength of the DIW ATZ (1009 ± 93 MPa) is also higher than that of the conventionally manufactured equivalent (861 ± 68 MPa). Besides homogeneous ceramic, laminate structures are demonstrated. This work provides a valuable hybrid approach to additively manufacture tough and strong ceramic components.

Development of TiO2/ZrO2 Multi-Material Obtained from Ceramic Pastes for Material Extrusion

The application of additive manufacturing method such as material extrusion (MEX) allows the successful fabrication of ceramic products, including multi-ceramic products. Promising materials in this research area are TiO2 and ZrO2 ceramics, which can be used in electrical and electronic engineering. The aim of this work is to investigate the possibility of fabricating TiO2/ZrO2 multi-materials from ceramic pastes that can be used in the MEX. In this work, defects, chemical and phase composition, and microhardness were analyzed in multi-ceramic samples after sintering. Multi-ceramic TiO2/ZrO2 samples after the sintering process without interlayer could not be fabricated due to a too large difference in shrinkage between TiO2 and ZrO2. The samples with one and three interlayers also have defects, but they are less significant and can be fabricated. The average hardness for the TiO2 zone was 636.7 HV and for the ZrO2 zone was 1101 HV. In the TiO2 zone, only TiO2 phase in rutile is observed, while in the interlayer zones, in addition to rutile, ZrO2 and ZrTiO4 are also present, as is a small amount of Y2O3. In the zone ZrO2, only the ZrO2 phase is observed. The chemical analysis revealed that the interlayers comprise sintered ZrO2 granules enveloped by TiO2, ZrO2, and ZrTiO4.

Straightforward Design Strategy toward 3D Near-Net-Shape Stoichiometric SiC Parts

Fused deposition modeling (FDM), traditionally reserved for thermoplastics, is modified here with a granule-based extrusion head to be extended to advanced nonoxide ceramics via a straightforward design strategy that considers the shaping opportunities and the chemical richness offered by preceramic polymers. Specifically, 3D near-net-shape stoichiometric silicon carbide (SiC) objects are designed by manipulating the key features of a commercially available polycarbosilane (fusibility, high carbon content, relatively high SiC yield). In the early stage of the process, the carbon-rich polycarbosilane is first mixed with Si and SiC fillers and then thermolyzed at 120 °C to increase polymer branching while offering tailored rheological properties during the subsequent extrusion process at 90 °C and adequate shape retention once extruded. This allows for the design of tailored and complex 3D complex polycarbosilane-based architectures with features down to 400 µm. Polymer-based parts are further converted into 3D stoichiometric SiC objects with quasi-near-net-shape-a volume shrinkage reduced to 9.1% is measured-by heat treatment at a temperature as low as 1400 °C (argon flow). Given the flexibility to tune the preceramic polymer chemical and rheological properties, a new combined design approach is leveraged to generate bespoke advanced ceramics with a high freedom in geometry complexity.

Special Issue: Porous Ceramics, Glasses and Composites, Volume II

This Special Issue, titled "Porous Ceramics, Glasses and Composites, Volume II", aims to present an up-to-date overview of the synthesis/fabrication, characterization, and applications of porous materials, with a special focus on ceramics, glasses, and composites [...].

Additive Manufacturing of Polymer/Bioactive Glass Scaffolds for Regenerative Medicine: A Review

Tissue engineering (TE) is a branch of regenerative medicine with enormous potential to regenerate damaged tissues using synthetic grafts such as scaffolds. Polymers and bioactive glasses (BGs) are popular materials for scaffold production because of their tunable properties and ability to interact with the body for effective tissue regeneration. Due to their composition and amorphous structure, BGs possess a significant affinity with the recipient's tissue. Additive manufacturing (AM), a method that allows the creation of complex shapes and internal structures, is a promising approach for scaffold production. However, despite the promising results obtained so far, several challenges remain in the field of TE. One critical area for improvement is tailoring the mechanical properties of scaffolds to meet specific tissue requirements. In addition, achieving improved cell viability and controlled degradation of scaffolds is necessary to ensure successful tissue regeneration. This review provides a critical summary of the potential and limitations of polymer/BG scaffold production via AM covering extrusion-, lithography-, and laser-based 3D-printing techniques. The review highlights the importance of addressing the current challenges in TE to develop effective and reliable strategies for tissue regeneration.