Papers by Keyword: Stereolithography

Abstract: This study aims to evaluate the antibacterial properties of dental resin photopolymer (DRP) specimens modified with additive titanium dioxide (TiO₂) nanoparticles using stereolithography 3D printing technology. TiO₂ known for its excellent biocompatibility, making it a promising additive for enhancing bacterial resistance. Specimens were fabricated with varying compositions of TiO₂ and characterized for surface morphology using Scanning Electron Microscopy (SEM). Antibacterial activity was assessed against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative) using Kirby-Bauer disc diffusion method. SEM analysis revealed that TiO₂ particles were relatively well-dispersed on the matrix surface. Antibacterial testing showed the formation of inhibition zones, particularly in sample with composition 5%wt TiO₂, indicating increasing antibacterial performance. The activity was more pronounced against S. aureus, attributed to its less complex cell wall structure and more susceptible to reactive oxygen species (ROS) generated by TiO₂ photocatalytic conditions. These findings suggest that TiO₂-modified DRP has strong potential as an antimicrobial dental restorative material fabricated through SLA-based 3D printing.

Abstract: Lattice metamaterials with adjustable auxetic behavior are characterized by periodic configurations of interconnecting struts and nodes, allowing for precise control over their macroscopic mechanical properties. Different lattice configurations were examined, two-unit cell variants with varying void fractions were assembled into crystalline-inspired designs, specifically simple cubic and body-centered cubic. Using vat photopolymerization, fabrication was carried out using a transparent biomedical elastomeric resin that was chosen for its exceptional ductility and strain tolerance. The curing, crosslinking and thermal mechanical stability of the resin were examined using Fourier Transform Infrared Spectroscopy and Differential Scanning Calorimetry, before and after polymerization. In order to determine specific stiffness, specific yield strength, mechanical characterization involved quasi-static uniaxial compression testing. The effect of different aspects of the macroscopic structures was also observed, exploiting diverse possible applications. The combination of geometry and the behavior of the elastomeric material allowed the creation of lightweight structures that could support large reversible deformations that could be used in soft robotics and healthcare devices.

Abstract: Triply periodic minimal surface (TPMS) represents a class of porous architectures characterized with continuous curved surface and periodic repetition, demonstrating significant potential for industrial applications requiring high specific surface area. In this work, a Gyroid-type TPMS sheet has been designed and manufactured with acrylonitrile butadiene styrene (ABS) resin via stereolithography 3D printing. The printed surface microstructure was characterized by scanning electron microscopy to evaluate the printing accuracy. Both the quasi-static compression test as well as the numeric finite element analysis were performed to study the mechanical response. Compared with the strut-based Re-entrant lattice, the Gyroid TPMS demonstrated a superior combination of high load-bearing and energy-absorption properties. Comparative analysis of compressive load-displacement curves and cracking behaviors elucidated the distinct deformation mechanisms between TPMS and Re-entrant structures. To validate the practical applicability, a prototype helmet liner with Gyroid TPMS structure was successfully manufactured with ABS resin using the studied printing procedures. These findings substantiate the promising implementation potential of TPMS structures in lightweight engineering and impact protection systems requiring synergistic mechanical performance.

Abstract: This study aims to assess the morphological, thermal, chemical structure and mechanical properties of the gamma-irradiated and conventional (unirradiated) test specimens that were 3D printed using a methacrylate-based photo-curable resin and a stereolithography (SLA) 3D printer. The irradiated test specimens were exposed to 50 kGy gamma-ray dose. The morphological, thermal, chemical structure and mechanical properties of the irradiated and unirradiated test specimens were characterized using the Atomic Force Microscope (AFM), Differential scanning calorimeter (DSC), Thermogravimetric analyzer (TGA), Fourier Transform Infrared Spectrometer (FTIR) and Universal Testing Machine (UTM). Results showed that irradiated test specimens exhibited lower surface roughness compared to the unirradiated specimens. Gamma-irradiated specimens also showed improved tensile strength and modulus of elasticity by 12.2% and 12.4 %, respectively. FTIR, DSC and TGA results showed no significant changes in the chemical structure and thermal properties of the 3D printed methacrylate-based resin after subjecting to gamma irradiation.

Abstract: Stereolithography (SLA) is a 3D printing technology that stands out because of its high dimensional accuracy and resolution, excellent surface finish, versatile modification of feedstock chemistry, and low cost of its printers. SLA uses an ultraviolet laser to trace and illuminate a light pattern onto a layer of photocurable resin. However, its disadvantages are the requirement of support structures, use of hazardous resins, the feedstock is limited to curable materials, and the need for a faster curing time. This study aims to improve the curing time of acrylate-based photopolymer resin by adding nanoclay as an additive. Different concentrations of nanoclay, 1wt%, 3wt%, and 5wt%, were added to urethane dimethacrylate, and their curing behavior and mechanical properties were determined. In this study, 3wt% was the ideal concentration since it had better mechanical properties than the control and exhibited the best curing characteristic. This further confirmed that nanoclay is a favorable additive in the 3D printing of acrylate-based photopolymers, solving the concern for fabrication speed and enhancing the mechanical properties of the photopolymer.

Abstract: In this study, we used Stereolithography to develop tricalcium phosphate-based scaffolds. The feedstock for the process consisted of a UV-curable resin, synthetic tricalcium phosphate, and silicon oxide. The viscosity and curability of the resins are carefully controlled to enable the fabrication of complex-shaped scaffolds. Following stereolithography, the ceramic-resin scaffolds were heat treated. The first step was debinding process followed by a sintering step. The resulting sintered samples underwent microstructure, chemical, and mechanical analysis to assess their properties. The optimized samples were then subjected to biodegradability and cytotoxicity tests to evaluate their suitability for use as tissue engineering scaffolds.

Abstract: Heat exchangers have traditionally been produced on mass using metal alloys and complex manufacturing processes. This work proposes an alternative production via for the additive manufacturing of a cost-effective air-to-air heat exchanger, based on the use of the stereolithography technology. The element has been produced on a FormLabs Form3 printer using standard photosensitive resin. The dimensions of the heat exchanger were 100 × 100 × 100 mm³ and the wall thickness was 0.5 mm. The manufacturing cost of the element was 53.11 €. The heat exchanger was experimentally tested in an air handling laboratory under different climatic conditions. The thermal power of the equipment was 200 W, which is equivalent to a power-volume ratio equal to 200 kW/m³. The experimental energy efficiency was equal to 0.54 (for a number of heat transfer units equal to 1.4) and an overall energy transfer coefficient (U) equal to 1823 W/m²K. In addition, the results showed that the thermal conductivity of the material was less influential the smaller the thickness of the heat exchanger channels. The obtained results show that stereolithography is an economical alternative to obtain customized and high compactness heat exchangers, on demand and just in time.

Abstract: Hydroxyapatite (HA) ceramic scaffolds are commonly used as bone graft substitutes. Design of such scaffolds is a challenge to improve biological properties and extend the applications of HA ceramics in the field of bone tissue engineering. In this work, we investigated the processing and the in vitro properties of HA ceramic scaffolds mimicking human trabecular bone architecture. Samples of human tibial trabecular bone were collected (University Hospital Center of Limoges) and scanned by X-Ray μ-computed tomography (μ-CT) to generate 3D model database. From this computer-aided design, HA ceramic scaffolds were shaped layer-by-layer by additive manufacturing using laser stereolithography (SLA). Then, green parts were sintered to obtain dense ceramic scaffolds. The shaped parts were compared to the model (wall thickness, size, and geometry of the porous network) using image analysis. A good agreement was found. Only small differences were detected due to a light overpolymerization or to some unprinted very small details that were not linked to a polymerized area of the previous layer. Due to part shrinkage during sintering a magnifying factor has to be applied to the scanned CAO model to match the real dimensions of the trabecular bone sample. Human mesenchymal stem cell (hMSC) cultures were performed to investigate the biological properties of these scaffolds (cell attachment and proliferation of hMSC). These preliminary biological evaluations show the good biocompatibility and cell adhesion of the HA substitute. This work evidences the efficiency of SLA to produce ceramic scaffold architectures mimicking that of the natural trabecular bone with promising biological behavior.

Abstract: In this study, stereolithography (SLA) 3D printing was used to prepare toughened composites by facile blending of chemically compatible nanoscale polyhedral oligomeric silsesquioxanes (POSS) to commercial photoreactive resin. Due to the complex nature of 3D printing, the mechanical performance of the final parts cannot be simply determined or even estimated until they are manufactured and tested. Thus, response surface methodology (RSM) and artificial neural network (ANN) were used to build regression models for determining the toughness of fabricated composites as function of toughener (POSS) amount and printing conditions (layer thickness and annealing temperature). The influence of the mentioned process parameters on toughness were investigated through a 17-run three-factor three-level Box-Behnken RSM design (BBD). The same experimental design was also used to acquire a data set for ANN. Finally, both the modeling methodologies were compared by coefficient of determination (R²) and residual distribution values. Results reveal that ANN possesses a better data fitting and predictive power as compared to RSM.

Abstract: In recent years, the diffusion of additive manufacturing (AM) or 3D printing (3DP) techniques for polymers have been boosted by the expiration of earlier patents from the last century and the development of low-cost machines. Since these technologies become more widespread, there is a need to assess the capability and accuracy of low-cost machines in terms of dimensional and geometric tolerance. To this aim, this work proposes an innovative reference part for benchmarking layerwise processes that involve the curing of photopolymers. The geometry of the part is conceived to include several classical shapes that are easily measurable for defining the part accuracy in terms of ISO IT grades and GD&T values. Two replicas of the reference part were fabricated by stereolithography (SLA) and digital light processing (DLP) using two machines and related proprietary materials by Sharebot Company. The replicas were printed with a layer thickness of 50 μm for the DLP process and 100 μm for the SLA one. The results of dimensional measurements of the replicas, that were carried out using a Coordinate Measuring Machine (CMM), show that the geometric accuracy of the time-consuming DLP process is slightly better than that of stereolithography.