Lithography-based Ceramic Manufacturing Research Articles

Mid-infrared optical coherence tomography and machine learning for inspection of 3D-printed ceramics at the micron scale

IntroductionIn this paper, recent developments in non-destructive testing of 3D-printed ceramics and monitoring of additive manufacturing of ceramics are presented.MethodsIn particular, we present the design and use of an inline mid-infrared optical coherence tomography (MIR-OCT) system to evaluate printed and micro-structured specimens in lithography-based ceramic manufacturing (LCM).ResultsThe proposed system helps with the detection of microdefects (e.g., voids, inclusions, deformations) that are already present in green ceramic components, thereby reducing the energy and costs incurred.DiscussionThe challenges during integration are discussed. Especially, the prospects for MIR-OCT imaging combined with machine learning are illustrated with regard to inline inspection during LCM of printed ceramics.

Effect of artificial aging on fracture toughness and hardness of 3D-printed and milled 3Y-TZP zirconia.

This study aimed to evaluate the impact of artificial aging on the fracture toughness and hardness of three-dimensional (3D)-printed and computer-aided design and computer-aided manufacturing (CAD-CAM) milled 3 mol% yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP). Forty bar-shaped specimens (45 × 4 × 3mm) were prepared using two manufacturing technologies: 3D printing (LithaCon 3Y 210, Lithoz GmbH, Vienna, Austria; n = 20) and milling (Initial Zirconia ST, GC, Japan; n = 20) of 3Y-TZP. The chevron-notch beam method was used to assess the fracture toughness according to ISO 24370. Specimens from each 3Y-TZP group were divided into two subgroups (n = 10) based on the artificial aging process (autoclaving): nonaged and aged. Nonaged specimens were stored at room temperature, while aged specimens underwent autoclave aging at 134°C under 2bar-pressure for 5 h. Subsequently, the specimens were immersed in absolute 99% ethanol using an ultrasonic cleaner for 5 min. Each specimen was preloaded by subjecting it to a 4-point loading test, with a force of up to 200 N applied for three cycles. Further 4-point loading was conducted at a rate of 0.5mm/min under controlled temperature and humidity conditions until fracture occurred. The maximum force (Fmax) was recorded and the chevron notch was examined at 30 × magnification under an optical microscope for measurements before the fracture toughness (KIc) was calculated. Microhardness testing was also performed to measure the Vickers hardness number (VHN). A scanning electron microscope (SEM) coupled with an energy dispersive X-ray unit (EDX) was used to examine surface topography and chemical composition. X-ray diffraction (XRD) was conducted to identify crystalline structure. Data were statistically analyzed using two-way ANOVA and Student's t-test with a significance level of 0.05. The nonaged 3D-printed 3Y-TZP group exhibited a significantly higher fracture toughness value (6.07MPam1/2) than the milled 3Y-TZP groups (p < 0.001). After autoclave aging, the 3D-printed 3Y-TZP group maintained significantly higher fracture toughness (p < 0.001) compared to the milled 3Y-TZP group. However, no significant differences in hardness values (p = 0.096) were observed between the aged and nonaged groups within each manufacturing process (3D-printed and milled) independently. The findings revealed that the new 3D-printed 3Y-TZP produced by the lithography-based ceramic manufacturing (LCM) technology exhibited superior fracture toughness after autoclave aging compared to the milled 3Y-TZP. While no significant differences in hardness were observed between the aged groups, the 3D-printed material demonstrated greater resistance to fracture, indicating enhanced mechanical stability.

Production of Ceramic Investment Casting Shells Using Lithography-Based Ceramic Manufacturing and Binder Jetting Technology

Production of Ceramic Investment Casting Shells Using Lithography-Based Ceramic Manufacturing and Binder Jetting Technology

Mechanical properties of additively manufactured lattice structures composed of zirconia and hydroxyapatite ceramics

Ceramic lattices hold great potential for bone scaffolds to facilitate bone regeneration and integration of native tissue with medical implants. While there have been several studies on additive manufacturing of ceramics and their osseointegrative and osteoconductive properties, there is a lack of a comprehensive examination of their mechanical behavior. Therefore, the aim of this study was to assess the mechanical properties of different additively manufactured ceramic lattice structures under different loading conditions and their overall ability to mimic bone tissue properties.Eleven different lattice structures were designed and manufactured with a porosity of 80% using two materials, hydroxyapatite (HAp) and zirconium dioxide (ZrO2). Six cell-based lattices with cubic and hexagonal base, as well as five Voronoi-based lattices were considered in this study. The samples were manufactured using lithography-based ceramic additive manufacturing and post-processed thermally prior to mechanical testing. Cell-based lattices with cubic and hexagonal base, as well as Voronoi-based lattices were considered in this study. The lattices were tested under four loading conditions: compression, four-point bending, shear and tension.The manufacturing process of the different ceramics leads to different deviations of the lattice geometry, hence, the elastic properties of one structure cannot be directly inferred from one material to another. ZrO2 lattices prove to be stiffer than HAp lattices of the same designed structure. The Young’s modulus for compression of ZrO2 lattices ranges from 2 to 30GPa depending on the used lattice design and for HAp 200MPa to 3.8GPa. The expected stability, the load where 63.2% of the samples are expected to be destroyed, of the lattices ranges from 81 to 553MPa and for HAp 6 to 42MPa.For the first time, a comprehensive overview of the mechanical properties of various additively manufactured ceramic lattice structures is provided. This is intended to serve as a reference for designers who would like to expand the design capabilities of ceramic implants that will lead to an advancement in their performance and ability to mimic human bone tissue.

Design, In Vitro Evaluation and In Vivo Biocompatibility of Additive Manufacturing Three-Dimensional Printing of β beta-Tricalcium Phosphate Scaffolds for Bone Regeneration

The reconstruction of bone deficiencies remains a challenge due to the limitations of autologous bone grafting. The objective of this study is to evaluate the bone regeneration efficacy of additive manufacturing of tricalcium phosphate (TCP) implants using lithography-based ceramic manufacturing (LCM). LCM uses LithaBone TCP 300 slurry for 3D printing, producing cylindrical scaffolds. Four models of internal scaffold geometry were developed and compared. The in vitro studies included cell culture, differentiation, seeding, morphological studies and detection of early osteogenesis. The in vivo studies involved 42 Wistar rats divided into four groups (control, membrane, scaffold (TCP) and membrane with TCP). In each animal, unilateral right mandibular defects with a total thickness of 5 mm were surgically performed. The animals were sacrificed 3 and 6 months after surgery. Bone neoformation was evaluated by conventional histology, radiology, and micro-CT. Model A (spheres with intersecting and aligned arrays) showed higher penetration and interconnection. Histological and radiological analysis by micro-CT revealed increased bone formation in the grafted groups, especially when combined with a membrane. Our innovative 3D printing technology, combined with precise scaffold design and efficient cleaning, shows potential for bone regeneration. However, further refinement of the technique and long-term clinical studies are crucial to establish the safety and efficacy of these advanced 3D printed scaffolds in human patients.

Machine learning assisted material development for lithography-based additive manufacturing of porous alumina ceramics

The transition of applying ceramic additive manufacturing (AM) from prototyping to mass production and from monolithic to multi-material (MM) components can be supported by continual development in materials and processes. Lithography-based ceramic manufacturing (LCM) can be used for MM printing of ceramics with high accuracy by introducing different approaches that enable discrete/smooth multidirectional material transitions. Adaptation of ceramic slurries plays important role for the successful printing and co-sintering. Especially for co-sintering, the shrinkage of the materials must be adapted so that no internal residual stresses occur. Machine learning (ML) offers promising opportunities for development of new materials and optimization of processes in AM by introducing relations between input features and output responses. In this article, ML algorithms were used for the prediction of shrinkage and porosity of alumina samples dependent on input features including material, printing, and thermal processing parameters so that defect-free porous/dense alumina combination can be achieved.

Influence of glazing and aging on the marginal, axial, axio-occlusal, and occlusal fit of 3-unit monolithic zirconia restorations fabricated using additive and subtractive techniques

Studies are sparse on how glazing and aging influence the fit of additively fabricated monolithic zirconia restorations. The purpose of this in vitro study was to assess the effect of glazing and aging on the fit of 3-unit monolithic zirconia restorations fabricated using different techniques. A total of 32 monolithic zirconia restorations were fabricated for a typodont model by using 4 distinct techniques (subtractive fabrication [SF], stereolithography [SLA], digital light processing [DLP], and lithography-based ceramic manufacturing [LCM]). The silicone replica approach was adopted to measure the discrepancy values for premolar and molar abutments after sintering, glazing, and 1 year of aging. The silicone replicas were sliced into mesiodistal and buccopalatal cross-sections, and digital micrographs of the cross-sections were made with a ×80 stereomicroscope. An inherent measuring program was run to record the discrepancy values (µm). Repeated-measures 2-way ANOVAs with the Bonferroni post hoc test were used to statistically analyze the acquired data. (α=.05). From the repeated measures 2-way ANOVAs, both the glazing×fabrication technique and the aging×fabrication technique interactions were not statistically significant (P>.05). Glazing significantly influenced premolar abutment marginal (P=.022) and occlusal (P=.007) discrepancy values, as well as molar abutment marginal discrepancy values (P=.047). Aging had a statistically significant effect on premolar abutment marginal (P=.008) and occlusal (P=.011) discrepancy values, as well as molar abutment occlusal discrepancy values (P=.039). In both the glazing and aging data, for all areas of interest, statistically significant differences were detected among the fabrication techniques (P<.05). The LCM group had the lowest discrepancy values, followed by the SLA, SF, and DLP groups. The LCM and SLA groups outperformed the other groups in terms of fit accuracy. The glazing and aging procedures altered the discrepancy values. The marginal discrepancy values of all groups were below the threshold of clinical acceptability (<120µm).

3D printing of ultra-thin veneers made of lithium disilicate using the LCM method in a digital workflow: A feasibility study.

This article highlights the feasibility of the additive fabrication of ultra-thin veneers made of lithium disilicate using the lithography-based ceramic manufacturing (LCM) method. An esthetical appealing restoration of anterior teeth with thin ceramic veneers is considered one of the ultimate challenges in restorative dental prosthetics. These sophisticated restorations can be fabricated in different ways. Both analog and digital subtractive manufacturing processes have been used to date. Either of the methods is highly demanding for the dental technician and dental engineering due to the required low ceramic layer thickness. Modern additive manufacturing methods, for example LCM technology, enable the production of ultra-thin lithium disilicate veneers with layer thicknesses of down to 0.2 mm and could therefore represent a viable alternative for this indication in the future. Digital technologies can help streamline workflows, make the outcome more predictable and reproducible, and even further optimize therapeutic restorative options such as highly esthetic veneers for anterior teeth. The reduced material thickness allows for a true non-prep solution or minimally invasive preparation.

Machine learning-based design for additive manufacturing in biomedical engineering

While ceramic additive manufacturing (AM) technologies have shown great promise to create functional scaffolds with tailored biomechanical properties, the true potential of these advanced techniques has not been fully exploited yet due to lack of practical design optimisation approaches. To address this challenge, a machine learning (ML)-based design approach is proposed herein where ceramic 3D printing techniques are combined to fabricate functionally graded tissue scaffolds composed of Triply Periodic Minimal Surfaces (TPMS), aiming to fulfil the anticipated biomechanical requirements for the target bone regeneration outcomes. The proposed ML based design strategy couples a Bayesian optimisation (BO) algorithm to enable time-dependent mechano-biological optimisation of the 3D printed ceramic scaffolds at a reasonably low computational cost. For a representative example relating to bone scaffolding in a segmental defect of sheep tibia, the simulated results demonstrate that the optimised functionally graded scaffolds significantly enhance bone ingrowth outcomes. Furthermore, a Lithography-based Ceramic Manufacturing (LCM) technique is employed to fabricate the optimised scaffolds based on the proposed ML-based design framework, followed by micro-CT analyses of the additively manufactured ceramic scaffolds to assess their geometric qualities. This study is expected to gain new insights into mechanical sciences on design for varying material conditions and provide an effective design tool for ceramic additive manufacturing.

Effect of slight short fiber aluminosilicate proportion on alumina slurry devoted to additive manufacturing: Rheological behaviour and final properties of sintered materials

Lithography based additive manufacturing (L-AMT) is a widely used additive manufacturing technique for the fabrication of ceramics like Al2O3. Al2O3 shows many favorable properties e.g. high temperature resistance, high hardness, and good corrosion and erosion resistance As a drawback, ceramics are generally brittle, limiting the achievable strength and toughness of the material. One approach to increase fracture toughness is by short fiber reinforcements. The scope of this work focuses on the processing of short aluminosilicate fiber reinforced alumina by lithography based ceramic manufacturing (LCM). As fibers tend to agglomerate when incorporating them into a ceramic slurry, different dispersing additives and amounts were investigated. Using 5 wt% Disperbyk 2155, a slurry containing 1 wt% of aluminosilicate fibers could be processed, showing a viscosity of 11 Pa s at 10 s−1 and agglomerates of maximal (45 ± 17) μm. This viscosity makes the material processable in L-AMT.

Highly textured 3D-printed translucent alumina through pressure-assisted sintering

Templated grain growth is a promising method for the fabrication of translucent alumina ceramics and a possible way to circumvent light scattering due to birefringence. In the present paper the effect of temperature, heating rate and dwell time on grain size, orientation, hardness and in-line transmittance is investigated on 3D-printed textured alumina. The samples were prepared by lithography-based ceramic manufacturing (LCM) of suspensions with fine-grained alumina, seeded by high aspect ratio templates and sintered by spark plasma sintering (SPS). A fully developed textured microstructure was achieved at 1600 °C for 1 h, whereas sufficient in-line transmittance of 54.6 % at 550 nm was achieved at 1700 °C for 3 h, albeit at the cost of considerable grain growth and loss of microstructural texturing.

Wear behaviour of lithography ceramic manufactured dental zirconia

ObjectiveThe study aims to evaluate the wear surface using 3D surface roughness and other material characterization of zirconia fabricated using photopolymerization based Lithography-based Ceramic Manufacturing (LCM).MethodLCM technology was used to fabricate zirconia specimens of size 10 × 10 × 2mm3. Scanning Electron Microscope, 3D–profilometer, X-ray Diffraction, and hardness test characterized the samples before and after wear and Coefficient of friction (COF) was monitored.ResultThe COF was around 0.7 and did not differ much between the horizontally and vertically printed specimens. However, the surface roughness after wear for horizontally printed specimen was 0.567 ± 0.139 μm, while that for vertically printed specimen was 0.379 ± 0.080 μm. The reduced valley depth and the dale void volume were low for the vertically printed zirconia specimen, indicating lesser voids and low fluid retention. In addition, it was observed that the hardness value of the vertically printed sample was better. The scanning electron microscopic images and 3D surface profiles of the zirconia specimens depicted the surface topography and revealed the wear track.ConclusionThe study shows that zirconia fabricated using LCM technology possesses surface roughness of about 0.5 μm with no machining scars that are usually associated with CAD/CAM dentistry and also indicating agreement with clinically acceptable values for minimal surface roughness of dental restorations. Dental restorations using LCM fabricated zirconia redues the requirement of post-processing work flow that is part of CAD/CAM dentistry.

Hybridizing Lithography-Based Ceramic Additive Manufacturing with Two-Photon-Polymerization

Stereolithography processes such as lithography-based ceramic manufacturing (LCM) are technologies that can produce centimeter-sized structures in a reasonable time frame. However, for some parts specifications, they lack resolution. Two-photon-polymerization (2PP) ensures the highest geometric accuracy in additive manufacturing so far. Nevertheless, building up parts in sizes as large as a few millimeters or even centimeters is a time-consuming process, which makes the production of 2PP printed parts very costly. Regarding feedstock specification, the requirements for 2PP are different to those for LCM, and generally, feedstocks are designed to meet requirements for only one of these manufacturing technologies. In an attempt to fabricate highly precise ceramic components of a rather large size, it is necessary to develop a feedstock that suits both light-based technologies, taking advantage of LCM’s higher productivity and 2PP’s accuracy. Hybridization should bring the desired precision to the region of interest on reasonably large parts without escalating printing time and costs. In this study, specimens gained from a transparent feedstock with yttria stabilized zirconia (YSZ) particles of 5 nm at 70 wt% were presented. The resin was originally designed to suit 2PP, while being also printable with LCM. This work demonstrates how hybrid parts can be sintered into full YSZ ceramics.

The design and evaluation of additively manufactured piezoelectric acoustic transducers

Ceramic additive manufacturing (AM) has been demonstrated as a capable method to fabricate piezocomposite acoustic transducers that exhibit augmented sensitivity, increased bandwidth, and controlled directivity by virtue of geometry. These improvements are intrinsic to the novel piezoelectric ceramic structure, which may be printed in forms that cannot be fabricated through conventional manufacturing methods. The AM process allows for functionally-graded apertures, 3-3 piezocomposite structures, and auxetic lattices which have been simulated, printed, and measured with compelling results. This presentation expands upon previous work completed through a collaboration between Lithoz America, LLC (Lithoz), MSI Transducers Corp. (MSI), and the MITRE Corporation (MITRE) to produce novel piezoelectric structures and validate acoustic and hydrostatic pressure performance of 1-3 piezocomposite structures under operationally relevant conditions. The presentation will encompass a discussion of Finite Element Analysis (FEA) of piezoelectric metamaterials conducted at MITRE, the lithography-based ceramic manufacturing (LCM) process of said structures at Lithoz, and empirical measurements of piezoelectric and acoustical specifications of the printed structures conducted at MSI. Finally, test data recorded at Woods Hole Oceanographic Institute (WHOI) will be shown, demonstrating the resilience of AM 1-3 piezocomposite under 10 000 PSI of hydrostatic pressure derived by means of in-situ electrical impedance measurements.

Functionally graded ceramics by lithography-based ceramic manufacturing (LCM)

Functionally graded ceramics by lithography-based ceramic manufacturing (LCM)

CHARACTERISATION OF BONE-REGENERATING SCAFFOLDS PRODUCED THROUGH LITHOGRAPHY-BASED CERAMIC MANUFACTURING

Lithography-based ceramic manufacturing (LCM) is an additive manufacturing (AM) technology that builds custom-designed, three-dimensional ceramic parts layer by layer. The level of precision of the process allows for the printing of custom-made interconnected lattices and designs suitable for bone implants. This study investigated the LCM printability of various lattice structures with the hydroxyapatite (HA480) supplied by Lithoz. Different lattice structures were characterised. The microscopic structure, the composition, and the surface roughness of the test specimens were determined. To obtain the mechanical properties of the structures, compression tests were performed. The observed micropores of ±3 µm and the macropores of ±320 µm were suitable for bone cell growth. The measured microhardness of HA480 was 556±25 HV in the built direction and 559±27 HV perpendicular to the built direction. The compressive strength of the rhombic dodecahedron lattice structure was 4±0.5 MPa, and was superior to other tested lattices. From the results it was concluded that lattice structures produced through LCM have the potential to be used to produce customised bone-regenerating scaffolds.

Characterization of biomaterials with reference to biocompatibility dedicated for patient-specific finger implants

Purpose The research was focused on determining basic mechanical properties, surface and phase structure taking into consideration basic cytotoxicity analysis towards human cells. Methods Biological tests were performed on human C-12302 fibroblasts cells using 3D-printed Ti6Al4V alloy (Ti64), produced by laser-based powder bed fusion (LB-PBF) and Alumina Toughened Zirconia 20 (ATZ20), produced by lithography-based ceramic manufacturing (LCM). Surface modifications included electropolishing, and hydroxyapatite or hydroxyapatite/zinc coating. Structure analysis was carried out using a variety of techniques such as X-Ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and confocal laser scanning microscopy (CLSM), followed by mechanical properties evaluation using nanoindentation testing. Results Samples subjected to surface modifications showed diversity among surface and phase structure and mechanical properties. However, the cytotoxicity towards tested cells was not significantly higher than the control. Though, a trend was noted among the materials analysed, indicating that HAp/Zn coating on Ti64 and ATZ20 resulted in the best biological performance Conclusions Hydroxyapatite coating on Ti64 and ATZ20 resulted in the best biological properties. Tested materials are suitable for in vivo toxicity testing.

Radar Cross-Section of Ceramic Corner Reflectors in the W-Band Fabricated With the LCM-Method

Corner reflectors (CR), especially when combined with information coding, are potential candidates for radar beacon applications, which could be used for the self-localization of autonomous vehicles. In order to further improve the radar cross-section (RCS) of such devices, additively manufactured filled corner reflectors (FCR) made of ceramics in comparison to classical metal based CRs in the W-Band, were evaluated. The ceramic CRs were implemented using Lithography-based Ceramic Manufacturing (LCM), which is a novel high quality, high-resolution technology gaining traction in the RF community.

Lithography-based additive manufacturing of porosity graded alumina

• In recent years, alumina ceramics exhibiting gradient in porosity, i.e., porosity graded alumina ceramics (PGACs), with a controlled amount of both open/closed or macro/micro pores is of high interest for several applications such as thick barrier coating, cores for precision casting, biocompatible implants, membranes/filters, and fabrication of functionally graded metals through infiltration. • Lithography-based Ceramic Manufacturing (LCM) offers high quality and near-net manufacturing of complex ceramic components with high resolution. • Two-vat system in the newly developed multi-material LCM printer setup enables not only assigning one material to any desired layer but also use of different materials in each layer by assigning the respective materials to selected pixels of the layer image. • This article introduces methodologies for the fabrication of porosity gradient alumina with continuous and discrete porosity transitions zones by combining sacrificial templating and LCM. With the developments in manufacturing technologies, interest on porosity graded alumina ceramics has increased for applications such as thick barrier coating, cores for precision casting and biocompatible implants. Lithography-based Ceramic Manufacturing (LCM) offers high quality and near-net manufacturing of complex ceramic components with high resolution. Multi-material LCM printing setup can overcome the main problems of conventional manufacturing techniques for fabrication of porosity graded alumina with desired microstructure and gradient architecture (i.e., gradient direction, fraction, type). Two-vat system in the newly developed multi-material LCM printer setup enables not only assigning one material to any desired layer but also use of different materials in each layer by assigning the respective materials to selected pixels of the layer image. This article introduces methodologies for the fabrication of porosity graded alumina ceramics (PGACs) with continuous and discrete porosity transitions zones by combining sacrificial templating and LCM. It is illustrated how the properties of the slurry and the desired gradient architecture play an important role for the selection of suitable method.

Additive Manufacturing of Lithium Disilicate with the LCM Process for Classic and Non-Prep Veneers: Preliminary Technical and Clinical Case Experience.

Background: ceramic veneers, crowns, and other types of restorations are often made using either the press heating technique or the subtractive method. The advent of lithography-based ceramic manufacturing (LCM) allows for the manufacturing of such restorations in an additive way. Methods: this concept paper describes the first clinical experience in the application of LCM lithium disilicate restorations in vivo for the manufacturing of classic veneers for a patient with severe tooth wear. The applied restorations were analyzed in terms of their marginal fit in metrology software (Geomagic Control X, 3D Systems). Furthermore, the feasibility of 3D printing of non-prep veneers with a 0.1 mm thickness was tested. Results: the classic LCM lithium disilicate veneers were tried in the mouth cavity and demonstrated adequate esthetics and a sufficient marginal fit of 100 µm. Furthermore, the non-prep veneers with a 0.1 mm thickness could be successfully printed using LCM technology and also demonstrated an adequate fit on the model in vitro. Conclusions: the described technical approach of lithium disilicate 3D printing with LCM technology may pose a valid alternative to subtractive and analog manufacturing and be a game-changing option with the use of additive chairside ceramic fabrication.