Stereolithography Process Research Articles

Physical-mechanical properties and accuracy of additively manufactured resin denture bases: Impact of printing orientation.

This systematic review evaluated the effect of different printing orientations on the physical-mechanical properties and accuracy of resin denture bases and related specimens. Utilizing PRISMA 2020 guidelines, a comprehensive search of PubMed, Web of Science, Cochrane, and Scopus databases was conducted until June 2024. Included studies examined the accuracy, volumetric changes, and mechanical or physical properties of 3D-printed denture bases in various orientations. Studies without relevant data were excluded. Bias risk was assessed using a modified CONSORT checklist. This review included 24 studies on 3D-printed denture base resins, mainly based on stereolithography and digital light processing. Horizontal orientation (0°) generally enhanced flexural strength, while tilted and vertical orientations (90°) reduced it. Microhardness results varied due to differences in materials, layer thicknesses, and post-curing. Surface roughness was highest at 45°. Vertical orientation uses less material but is less time-efficient. Microbial adhesion, influenced by surface roughness, varied with printing orientation without a clear consensus on the optimal direction. Printing orientation significantly impacts the physical and mechanical properties and accuracy of 3D-printed resin dentures. A horizontal orientation (0°) improved flexural strength, while accuracy and adaptability were better at 45° and 90°. Surface roughness, translucency, and chemical stability are also affected by orientation, post-curing, and material choice. Although a 90° orientation reduces material use, it increases printing time. Standardized study designs are recommended for drawing definitive conclusions in future research.

Numerical analysis of a FE/SAV scheme for a Caginalp phase field model with mechanical effects in stereolithography

In this work, we propose a phase field model based on a Caginalp system with mechanical effects to study the underlying physical and chemical processes behind stereolithography, which is an additive manufacturing (3D printing) technique that builds objects in a layer-by-layer fashion by using an ultraviolet laser to solidify liquid polymer resins. Existence of weak solutions is established by demonstrating the convergence of a numerical scheme based on a first order scalar auxiliary variable temporal discretization and a finite element spatial discretization. We further establish uniqueness and regularity of solutions, as well as optimal error estimates for the Caginalp system that are supported by numerical simulations. We also present some qualitative two-dimensional simulations of the stereolithography processes captured by the model.

MODELING OF PHOTOPOLYMER CURING

The paper considers the process of curing a photopolymer material. The effect of light on a photopolymer material triggers a reaction that leads to the conversion of polymer chains, which leads to the release of heat and an increase of temperature, solidification or an increase of stiffness of the material, and is also accompanied by a volumetric shrinkage. Such processes cause the distortion of the initial shape of the material. With nonuniform irradiation of the material, the processes are initiated with different intensities and a certain delay causing residual stresses. Stereolithography technology has become widespread in industry, in which the material is irradiated in certain areas, the so-called masks, after which the uncured material is removed. Modern photopolymer 3d printers are focused on this effect, which cures the material in layers with various masks. In 3D printing, the curing of the upper layer is accompanied by a higher shrinkage relative to the lower one, which by this time has a higher degree of curing leading to residual stresses. Thus, each new layer in a produced part initiates a gradual accumulation of residual stresses. As a result, there is a distortion of the originally planned shape of the product and a loss of strength characteristics. Residual stresses realized during the printing process can exceed the strength of the material, which often leads to a rapid increase in cracks and damage of the printed structure. This study proposes a model of a photopolymer material and an algorithm for modeling curing. It considers the process of stereolithography based on the action of a movable laser. A comparison with the experiment is given.

Post‐Print Processing to Minimize Cytotoxicity of 3D‐Printed Photopolymer Resins for Biomedical Applications

ABSTRACTLight‐based 3D printing techniques, including stereolithography (SLA) and digital light processing (DLP), are of great utility owing to their ability to create complex geometries with high speed, high spatial resolution, and often, optical transparency. These are useful for fabricating custom components and structures for various biomedical applications—scaffolds, implants, microfluidic devices, in vitro cellular experiments, etc. However, a drawback of light‐based methods is that uncured resin monomers and other additives have the potential for cytotoxic effects, adversely impacting cells and tissues. In this study, we investigate a facile method to process light‐based 3D printing to mitigate cytotoxicity. Three optically clear, photocurable resins—a commercially available acrylate‐based resin, BioMed Clear, and an ecoresin derived from soybean oil—are subjected to various post‐treatment protocols. These involve combinations of isopropanol (IPA) washing, UV curing, and water or IPA agitation. The in vitro cytotoxicity and effect on cell proliferation are characterized using two cell lines (myoblasts and fibroblasts). Compared to untreated controls, IPA or water wash, and cleaning with a commercial developer, the results indicate that a short postprint cure with double IPA wash effectively reduces cytotoxicity across all resins, particularly BioMed Clear and ecoresin, maintaining nearly 100% cell viability after 7 days and avoiding material cloudiness or brittleness. The study therefore highlights a low‐cost postprint treatment method applicable to existing commercial resins and 3D printers. The minimization in leachate and cytotoxicity of optically clear 3D‐printed parts can pave the way for broader adoption in resource‐limited settings and safer use in cell studies, microfluidics, and other biomedical applications.

Numerical simulation model for the curing of photosensitive acrylate resin in a stereolithography process

Numerical simulation model for the curing of photosensitive acrylate resin in a stereolithography process

Comprehensive Study of Stereolithography and Digital Light Processing Printing of Zirconia Photosensitive Suspensions

Zirconia ceramics are used in a wide range of applications, including dental restorations, bioimplants, and fuel cells, due to their accessibility, biocompatibility, chemical resistance, and favorable mechanical properties. Following the development of 3D printing technologies, it is possible to rapidly print zirconia-based objects with high precision using stereolithography (SLA) and digital light processing (DLP) techniques. The advantages of these techniques include the ability to print multiple objects simultaneously on the printing platform. To align with the quality standards, it is necessary to focus on optimizing processing factors such as the viscosity of the suspension and particle size, as well as the prevention of particle agglomeration and sedimentation during printing, comprising the choice of a suitable debinding and sintering mode. The presented review provides a detailed overview of the recent trends in preparing routes for zirconium oxide bodies; from preparing the suspension through printing and sintering to characterizing mechanical properties. Additionally, the review offers insight into applications of zirconium-based ceramics.

Quick-Delivery Mold Fabricated via Stereolithography to Enhance Manufacturing Efficiency.

The ever-growing demand for reducing costs and decreasing the time to market in today's plastics industry makes rapid tooling and rapid prototyping highly researched areas. Stereolithography (SLA)-manufactured injection mold inserts make it possible to produce prototype parts rapidly and cost-effectively. To utilize SLA in the injection molding industry, two steps have to be considered. The first is to identify suitable SLA process and post-thermal curing process parameters to enhance the mechanical and thermal characteristics. The second is to verify the applicability of SLA-manufactured molds for use in the injection molding industry. IA comprehensive study was performed to find the optimum process parameters for an SLA mold with excellent mechanical and thermal properties and to verify the applicability of the mold. First of all, the mechanical and thermal properties of samples manufactured based on various laser powers and heat treatment at different temperatures were analyzed with a tensile test, DSC, and TMA according to the degree of cure. On the basis of the results from those tests, an SLA mold was designed and fabricated with the optimum mechanical and thermal properties. In addition, the SLA mold was assembled into an injection machine, and an injection molding test was conducted. The SLA mold endured during the injection cycle, and 500 shots were successfully injected without damaging the mold, which resulted in reaching the quick-delivery mold standard. Finally, we demonstrate that SLA is an effective technology to produce molds for use in the injection molding industry.

Analysis of Geometrical Accuracy and Surface Quality of Threaded and Spline Connections Manufactured Using MEX, MJ and VAT Additive Technologies.

This paper presents the process of manufacturing mechanical joint components using additive manufacturing (AM) techniques such as Material Extrusion (Fused Deposition Modelling (FDM)), Material Jetting (PolyJet), and Vat Photopolymerization (VAT)/Stereolithography (SLA). Using the PolyJet technique and a photopolymer resin, spline and threaded joint components were produced. For comparative analysis, the threaded joint was also fabricated using FDM and SLA techniques. PLA material was used for the FDM technique, while photopolymer resin was utilized for the SLA process. The components produced underwent a surface analysis to evaluate the accuracy of the dimensions in relation to the nominal dimensions. For the spline connection components, the dimensional deviations recorded by a 3D scanner ranged from -0.11 to +0.18 mm for the shaft and up to 0.24 mm for the sleeve. Measurements of screw and nut diameters showed the highest accuracy for screws produced using the PolyJet technique, while the nuts exhibited the best accuracy when fabricated with the SLA method. The profile of the screw threads using a contour gauge revealed the most accurate thread profile on the screw manufactured with the PolyJet technique.

Zirconia specimens printed by vat photopolymerization: Mechanical properties, fatigue properties, and fractography analysis.

The mechanical and fatigue properties of zirconia specimens printed by vat photopolymerization (VPP) were evaluated and compared with those of zirconia specimens milled by computer numerical control (CNC). Bar-shaped specimens were printed by stereolithography (SL) and digital light processing (DLP). CNC-milled specimens were used as control samples. The fracture toughness, hardness, and flexural strength properties of the zirconia specimens were evaluated via single edge V-notch beam tests, Vickers hardness tests, and 3-point bending tests. Dynamic fatigue tests were carried out in distilled water using a step-stress test. After static bending and dynamic step-stress testing, fractography analysis was performed. Statistical analysis was carried out to compare the fracture toughness, hardness, flexural strength, and fatigue cycle results of each group (α = 0.05). The fracture toughness values did not significantly differ among the groups (p>0.05). The flexural strength was 894.10MPa for SL, 831.46MPa for DLP, and 1140.39MPa for CNC. The flexural strength of CNC was greater than that of SL and DLP (p<0.01). The mean fatigue cycles were 23498.07 for SL, 19858.60 for DLP, and 31566.80 for CNC. The mean fatigue failure strength was 643.13MPa for SL, 530.63MPa for DLP, and 903.75MPa for CNC. The fatigue failure strength of CNC was greater than that of SL and DLP (p<0.05). Fractography analysis revealed material defects at the fracture origin for each group. A partially fused structure of the incompletely debonded resin could be observed in SL, and a porous region of incompletely sintered zirconia grains could be observed in CNC. The fracture toughness and hardness of zirconia printed by VPP are comparable to those of zirconia milled by CNC. However, zirconia milled by CNC has superior static flexural strength and dynamic fatigue resistance. Further studies are needed to explore the clinical applications of VPP-printed zirconia.

Additive Manufacturing of Ceramic Reference Spheres by Stereolithography (SLA)

Additive Manufacturing (AM) is advancing technologically towards the production of components for high-demand mechanical applications with stringent dimensional accuracy, leveraging metallic and ceramic raw materials. The AM process for ceramic components, known as Ultraviolet Laser Stereolithography (SLA), enables the fabrication of unique parts or small batches without substantial investments in molds and dies, and avoids the problems associated with traditional manufacturing, which involves multiple stages and final machining for precision. This study addresses the need to produce reference elements or targets for metrological applications, including verification, adjustment, or calibration of 3D scanners and mid- to high-range optical sensors. Precision spheres are a primary geometry in this context due to their straightforward mathematical definition, facilitating rapid and accurate error detection in equipment. Our objective is to exploit this novel SLA process along with the advantageous optical properties of technical ceramics (such as being white, matte, lightweight, and corrosion-resistant) to materialize these reference objects. Specifically, this work involves the fabrication of alumina hemispheres using SLA. The manufacturing process incorporates four design variables (wall thickness, support shape, fill type, and orientation) and one manufacturing variable (the arrangement of spheres on the printing tray). To evaluate the impact of the design variables, dimensional and geometric parameters (GD&amp;T), including diameters, form errors, and their distribution on the surface of the sphere, have been characterized. These measurements are conducted with high accuracy using a Coordinate Measuring Machine (CMM). The study also examines the influence of these variables in the dimensional and geometric accuracy of the spheres. Correlations between various parameters were identified, specifically highlighting critical factors affecting process precision, such as the position of the piece on the print tray and the wall thickness value. The smallest diameter errors were recorded at the outermost positions of the tray (rear and front), while the smallest shape errors were found at the central position, in both cases with errors in the range of tens of micrometers. In any case, the smallest deformations were observed with the highest wall thickness (2 mm).

Optimized vascular network by stereolithography for tissue engineered skin.

This paper demonstrates the essential and efficient methods to design, and fabricate optimal vascular network for tissue engineering structures based on their physiological conditions. Comprehensive physiological requirements in both micro and macro scales were considered in developing the optimisation design for complex vascular vessels. The optimised design was then manufactured by stereolithography process using materials that are biocompatible, elastic and surface bio-coatable. The materials are self-developed photocurable resin consist of BPA-ethoxylated-diacrylate, lauryl acrylate and isobornylacrylate with Irgacure® 184, the photoinitiator. The optimised vascular vessel offers many advantages: 1) it provides the maximum nutrient supply; 2) it minimises the recirculation areas and 3) it allows the wall shear stress on the vessel in a healthy range. The stereolithography manufactured vascular vessels were then embedded in the hydrogel seeded with cells. The results of in vitro studies show that the optimised vascular network has the lowest cell death rate compared with a pure hydrogel scaffold and a hydrogel scaffold embedded within a single tube in day seven. Consequently, these design and manufacture routes were shown to be viable for exploring and developing a high range complex and specialised artificial vascular networks.

Impact of Printing Orientation on the Accuracy of Additively Fabricated Denture Base Materials: A Systematic Review.

Printing orientation is one of the printing parameters that affect the properties of three-dimensional (3D)-printed resins. Different printing orientations and directions have been suggested; however, no clear and specific orientations are recommended in the literature in terms of the printing orientation effect on the accuracy and fit of 3D-printed removable dental prostheses. This review aimed to evaluate the effect of printing orientation on the fit and accuracy of 3D-printed removable dental prostheses. The PubMed, Scopus, and Web of Science databases were searched for published articles that investigated the effect of printing orientations on the accuracy and fit of the 3D-printed denture base. Full-length English published articles were searched between January 2010 and December 2023, which examined topics related to printing orientations, building angles, 3D printing, printing technology, accuracy, dimensional changes, internal fit, marginal integrity, marginal discrepancies, trueness, precision, and adaptation. Of the ten included studies, one investigated maxillary and mandibular denture bases, seven assessed maxillary denture bases, and two evaluated mandibular bases. Different printing orientations, ranging from 0° to 315°, were explored, with a higher prevalence of 0°, 45°, and 90°. The included studies utilized stereolithography and digital light processing printing technologies. High accuracy was observed at 45°, followed by 90. Additional struts and bars on the cameo surface increased the accuracy of the 3D-printed denture base. These results shows that printing orientation has a significant effect on the accuracy of 3D-printed resin, with 45° exhibiting the highest accuracy. In addition to the support structure, the density and position can impact the accuracy.

Advances in 4D printing of biodegradable photopolymers

AbstractOver the past decade, 4D printing has revolutionized the field of advanced manufacturing by fabricating structures that dynamically respond to environmental stimuli. During this process, shape‐memory polymers (SMPs) stand out, enabling transformations triggered by temperature, light, or other environmental factors, and show great potential for applications in biomedicine and beyond. Notably, biodegradable SMPs offer a compelling advantage in medical devices due to their ability to adapt within the body's temperature range and to be absorbed by tissues, reducing the risks associated with permanent implants. While extrusion techniques have laid the groundwork for 4D printing in biomedicine, vat photopolymerization methods like stereolithography and digital light processing are now at the forefront, favored for their high printing resolution and flexibility in material design. However, the search for suitable biodegradable materials for these advanced techniques continues, with current research focusing on developing systems that meet both the mechanical demands and degradation profiles required for medical applications. This review aims to critically analyze the advancements in biodegradable 4D photopolymers, particularly biodegradable elastomers, and discuss the challenges that lie ahead for their clinical translation.

Digital manufacturing techniques and the in vitro biocompatibility of acrylic-based occlusal device materials

ObjectivesMaterial chemistry and workflow variables associated with the fabrication of dental devices may affect the biocompatibility of the dental devices. The purpose of this study was to compare digital and conventional workflow procedures in the manufacturing of acrylic-based occlusal devices by assessing the cytotoxic potential of leakage products.MethodsSpecimens were manufactured by 3D printing (stereolithography and digital light processing), milling, and autopolymerization. Print specimens were also subjected to different post-curing methods. To assess biocompatibility, a human tongue epithelial cell line was exposed to material-based extracts. Cell viability was measured by MTT assay while Western blot assessed the expression level of selected cytoprotective proteins.ResultsExtracts from the Splint 2.0 material printed with DLP technology and post-cured with the Asiga Flash showed the clearest loss of cell viability. The milled and autopolymerized materials also showed a significant reduction in cell viability. However, by storing the autopolymerized material in dH2O for 12 h, no significant viability loss was observed. Increased levels of cytoprotective proteins were seen in cells exposed to extracts from the print materials and the autopolymerized material. Similarly to the effect on viability loss, storing the autopolymerized material in dH2O for 12 h reduced this effect.Conclusions/Clinical relevanceBased on the biocompatibility assessments, clinical outcomes of acrylic-based occlusal device materials may be affected by the choice of manufacturing technique and workflow procedures.

Auxetic fixation devices can achieve superior pullout performances compared to standard fixation concepts

Despite bone screws being the most commonly inserted implant in orthopaedic surgery, 10% of fracture fixation failure is a result of screw migration or pullout. In this study, the effect of four auxetic structures on the pullout performance of a novel unthreaded bone fastener was investigated through experiments and numerical simulations. The auxetic fasteners included the re-entrant, rotating squares, missing rib, and tetrachiral structures. Parametric CAD models were developed for each, and polymer samples manufactured using a stereolithography process. Pullout testing using bone analogue material found the rotating squares fastener to achieve superior pullout resistance 2.5 times that of the non-auxetic control sample. With a pullout to push-in force ratio of 33.7, this fastener achieved high pullout resistance with a low insertion force improving ease of installation. The Poisson’s ratio of the structure was determined using image analysis to be −1.31, similar to the missing rib and re-entrant types. The low axial stiffness of 12.1 N mm−1 for the rotating squares fastener was the reason for superior performance, allowing axial and resulting transverse strain to be initiated at relatively low load. The effect of increased diametral interference was investigated, and the re-entrant structure found to be superior with pullout resistance improved by 342%. This work provides a foundation for further development of unthreaded auxetic bone fasteners, which have the potential to replace screws for some orthopaedic applications and significantly reduce the prevalence of pullout as a failure mode.

Development of recyclable bio-based epoxy/acrylate blends for liquid crystal display 3D printing

AbstractBio-based epoxy resins are widely utilized in various application fields such as adhesives, coatings, composites, and electrical components, offering comparable performance characteristics to conventional epoxy resins, including high strength, durability, and chemical resistance. The use of bio-based materials in 3D printing has been receiving increasing attention as a means of reducing the environmental impact of this technology, because most formulations available for stereolithography and digital light processing are generally non-renewable. This study aimed to explore the potential of blending a bio-based epoxy resin with a commercial daylight-curable resin at various msss percentages to enhance the thermomechanical properties of 3D-printed parts while adhering to the working principle of liquid crystal display (LCD) printers. The prepared formulations were initially characterized in terms of their thermo-mechanical properties both before and after post-treatments like photo- and thermal-curing. This procedure facilitated a comparison of the various blends based on their mechanical strength, glass transition temperature, and other pertinent properties. Upon identifying the optimal formulation, 3D-printed samples were produced using LCD printing technology. Calorimetric and morphological tests were then carried out to evaluate the thermal stability and microstructure of the printed parts. Overall, the findings of this study indicate that blending recyclable bio-based epoxy resins with commercial ones can lead to enhanced properties in additive manufactured parts. This approach has the potential to promote sustainability in 3D printing by reducing the consumption of non-renewable resources, while still meeting the standard performance required for numerous applications.

Energy Absorption Capability of Graded Hybrid Triply Periodic Minimal Surface Structures Based on Fracture Zone Controlling

A novel design strategy of the graded hybrid energy‐absorbing lattice structure is proposed by controlling fracture zone. The primitive (P) and iWP (W) structures are two kinds of triply periodic minimal surface structures with typical deformation and failure modes. Thus, taking the P (stretching‐dominated) and the W structures (bending‐dominated) as object, the deformation and failure mechanisms of two structures are studied. Then, the PWP (i.e., the fracture zone of the P structure filling with the W structure) and WPW (i.e., the fracture zone of the P structure filling with the W structure) structures with uniform and gradient change are designed. The structures are fabricated using stereolithography appearance process and compressed under quasistatic conditions. And the energy absorption capacity comparison of these structures is studied. The experimental results show that the maximum energy absorption efficiency of the PWP structure is 38.85% higher than that of the P structure and the densification energy absorption of the WPW structure is 66.67% higher than that of the W structure. Additionally, gradient design can effectively improve the densification energy absorption of lattice structure. The novel structural design greatly contributes to customized energy absorption design of lattice structures.

Experimental investigation on Stereolithography process parameter optimization and its influence on smooth surface finish for ABS Accura-60 material

Rapid Prototyping Technique (RPT) is a method that involves directly translating CAD models into physical parts, making it easier to produce prototypes. These 3D prototype printers have found applications in various fields, where there's a demand for prototypes with higher strength, smoother surface finishes, and overall quality. One of the newer techniques, SLA (Stereolithography), has significantly impacted part manufacturing, as well as research and development processes. To meet the growing demands for improved surface properties, especially in polymers and plastics, standardized specimen profiles like ASTM D638 Type I are utilized for surface finishing testing. This study is focused on optimizing SLA parameters specifically for Accura-60 prototypes, with a particular emphasis on enhancing surface finish for ASTM D638 Type I specimens. The experiments conducted in this research delve into variations in parameters such as hatch angle, layer thickness, and hatch spacing to better understand their impact on surface properties. The ultimate goal is to effectively control and optimize SLA parameters to enhance surface finish, thereby improving the overall quality of the prototypes.

Stereolithography and gelcasting of Li2TiO3 block breeders with a Gyroid structure: Slurry optimization and performance evaluation

This study proposes porous block structures as a viable alternative to conventional pebble bed structures, aiming to overcome the structural drawbacks including low packing fractions, extensive stress concentrations, and low thermal conductivity. To validate the feasibility of the porous block structures, Gyroid Li2TiO3 block breeders were prepared by the hybrid process of stereolithography and gelcasting. The resulting Gyroid Li2TiO3 block breeders, measuring ∼18.8 × 18.8 × 18.8 mm3, achieved a high packing fraction of ∼78.8% through optimized slurry and sintering at 1100 °C for 3 h. These Gyroid Li2TiO3 block breeders exhibited clear contours, integrated channels, a compressive strength of 8.78 MPa, and a low isotropic sintering shrinkage of ∼6%. The hybrid process demonstrated enormous advantages over the reported 3D printing for the preparation of porous block breeders with low shrinkage and large-sized dimensions. This study offers an effective avenue for the manufacture of porous block breeders with tunable tritium-releasing channels and large-sized configurations.

Experimental investigation of stereolithography and digital light processing additive manufactured pallets

Abstract Pallets are a tertiary form of packaging used for stacking, storing, protecting, or transporting goods in supply chains. They are utilized as a base for the unitization of goods for logistics and warehousing. Moreover, pallets can be manufactured using wood, plastic, metal, and corrugated paper, which can be used as material-handling equipment. With several products being transported worldwide and with year-on-year growth, it would be beneficial to make lightweight pallets. Such pallets are recyclable, easy to clean, cheap, and durable to maintain and store. Though most of the pallets are widely available for basic purposes, applications involving high-end bio-packings and transportation of special chemicals require specialized pallets to be manufactured like polymers to ensure a negligible chemical reaction, light in weight, and attenuation in freight capacity, thereby widespread reduction in wastage. With advancements, job to job and immediate requirements, additive manufacturing has the potential to close the gap for jobs with short lead times. If the design process of new pallets has limits the creation of specific codes, the transitions will be smoother in rapid prototyping. This work describes the development of polymer pallets by taking advantage of stereolithography (SLA) and digital light processing (DLP) technology for 3D printing pallets in correlation to injection moulding. After the pallets are designed and manufactured, AM technologies can be applied to specified standards, and the pallets then undergo tensile strength, elongation, and hardness tests. The analysis was carried out for configurable geometries adapting to fork lifting, conveyor, racking, and stacking conditions. Analytical and numerical solutions were carried out to understand the stress and deflections for each geometry and its wide range of applications for pallets.