Mineral trioxide aggregate (MTA) can provide bioactivity to poly‐caprolactone (PCL), which is an inert polymer used to print scaffolds. However, testing all combinations of scaffold characteristics ...(e.g., composition, pore size, and distribution) to optimize properties of scaffolds is time‐consuming and costly. The Taguchi's methods can identify characteristics that have major influences on the properties of complex designs, hence decreasing the number of combinations to be tested. The objective was to assess the potential of Taguchi's methods as a predictive tool for the optimization of bioactive scaffold printed using electro‐hydro dynamic jetting. A three‐level approach assessed the influence of PCL/MTA proportion, pore size, fiber dimension and number of layers in pH, degradation rate, porosity, yield strength, and Young's modulus. Data were analyzed using Tukey's honest significant difference test, analysis of mean and signal‐to‐noise ratio (S/N) test. Cytocompatibility and differentiation potential were assessed for 5 and 30 days using dental pulp stem cells and analyzed with one‐way analysis of variance (proliferation) or Mann–Whitney (qPCR). The S/N ratio and analysis of mean showed that fiber diameter and composition were the most influential characteristics in all properties. The experimental data confirmed that the addition of MTA to PCL increased the pH and scaffold degradation. Only PCL and PCL with 4% MTA allowed cell proliferation. The latter increased the genetic expression of ALP, COL‐1, OCN, and MSX‐1. The theoretical predictions were confirmed by the experiments. The Taguchi's identified the inputs that can be disregarded to optimize 3D printed meshed bioactive scaffolds.
It is difficult to produce bulk blanks directly from metallic glass, which limits its application. Ni-based metallic-glass thin strips that can be manufactured easily were used to manufacture bulk ...metallic glass additively by ultrasonic bonding. The effects of ultrasonic vibration energy on the quality of the additive manufacturing of bulk Ni-based metallic glass were studied. The experimental results showed that a fully amorphous structure of bulk Ni-based metallic glass can be obtained with an appropriate ultrasonic vibration energy. The thermal properties were almost unchanged, and the hardness and elastic modulus of the Ni-based metallic glass were improved compared with the original material. Additive manufacturing of bulk metallic glass by ultrasonic bonding can broaden the application field of metallic glass.
•A new method to forming bulk metallic glass employed ultrasonic additive manufacturing is proposed.•The bulk Ni-based metallic glass can be formed layer-by-layer with ultrasonic vibration energy.•The internal hardness and modulus of the bulk metallic glass are higher with ultrasonic additive manufacturing.
Purpose
This study aims to further the understanding of support structures and the likely impacts on maraging steel MS1 parts fabricated by selective laser melting (SLM) at 45°, 60° and 75° building ...angles.
Design/methodology/approach
Two groups of samples, one group with support structures and the other group without support structures, were designed with the same specifications and printed under the same conditions by SLM at 45°, 60° and 75° building angles. Differences in dimensional accuracy, surface roughness, Vickers microhardness, residual stress and microstructure were compared between groups.
Findings
The results showed that with support structures, more accurate dimension and slightly higher Vickers microhardness could be obtained. Larger compressive stress dominated and was more uniformly distributed on the supporting surface. Without support structures, the dimension became more precise as the building angle increased and alternating compressive and tensile stress was unevenly distributed on the supporting surface. In addition, the surface roughness of the outer surface decreased with the increase of the built angle, regardless of the support structures. Furthermore, whether the building angle was 45°, 60° or 75°, the observed microstructures revealed that the support structures altered the orientation of the molten pool and the direction of grain growth.
Originality/value
This paper studies the influence of support structures on the workpieces printed at different building angles. Support structures affect the residual stress distribution, heat dissipation rate and microstructure of the parts, and thus affecting the printing quality. Therefore, it is necessary to balance the support strategy and printing quality to better apply or design the support structures in SLM.
Since various build defects in the Selective laser melting (SLM) process are found to be associated with the instability of melt pool, the melt pool monitoring is particularly important for the final ...product quality control. Previous studies focus on the geometric features to describe the changes of the size and shape of melt pool, which are not sufficient to characterize the dynamic variations of the melt pool during the build process monitoring. To solve this problem, a new motion feature is introduced to describe the moving melt pool. The melt pool and spatters are extracted by thresholds combined with the connected component analysis method. The distance between the centroid and the boundary of melt pool is calculated from the unfolded clockwise at a step angle, which constructs a high dimensional feature vector as the motion features. The k-means clustering algorithm is applied to cluster the motion features under varied process parameters, aiming at construct the link between the melt pool states and processing parameter for the quality control. The research results have shown that the extracted motion features can describe the variation of melt pool more accurately than the traditional geometric features, and they can distinguish the moving direction and melted states of over melting, partial melting and defects simultaneously. This research provides a new approach for intelligent online monitoring of the SLM process.
Critical quality issues such as high porosity, cracks, and delamination are common in current selective laser melting (SLM) manufactured components. This study provides a flexible and integrated ...method for in situ process monitoring and melted state recognition during the SLM process, and it is useful for process optimization to decrease part quality issues. The part qualities are captured by images obtained from an off-axis setup with a near-infrared (NIR) camera. Plume and spatter signatures are closely related to the melted states and laser energy density, and they are employed for the SLM process monitoring in an adapted deep belief network (DBN) framework. The melted state recognition with the improved DBN and original NIR images requires little signal preprocessing, less parameter selection and feature extraction, obtaining the classification rate 83.40% for five melted states. Compared to the other methods of neural network (NN) and convolutional neural networks (CNN), the proposed DBN approach is identified to be accurate, convenient, and suitable for the SLM process monitoring and part quality recognition.
•Developed a novel in-situ monitoring method for typical additive manufacturing process.•Provided a flexible and integrated method for in situ process monitoring with plume and spatter signatures.•Developed a novel Deep Belief Network based approach for melted state recognition during the SLM process.•Verified the effectiveness of the proposed approach with experimental studies and comparisons with other methods.
The aim of this study is to investigate the possibility of a freeform fabrication of porous ceramic parts through selective laser sintering (SLS). SLS was proposed to manufacture ceramic green parts ...because this additive manufacturing technique can be used to fabricate three-dimensional objects directly without a mold, and the technique has the capability of generating porous ceramics with controlled porosity. However, ceramic printing has not yet fully achieved its 3D fabrication capabilities without using polymer binder. Except for the limitations of high melting point, brittleness, and low thermal shock resistance from ceramic material properties, the key obstacle lies in the very poor absorptivity of oxide ceramics to fiber laser, which is widely installed in commercial SLS equipment. An alternative solution to overcome the poor laser absorptivity via improving material compositions is presented in this study. The positive effect of carbon additive on the absorptivity of silica powder to fiber laser is discussed. To investigate the capabilities of the SLS process, 3D porous silica structures were successfully prepared and characterized.
Additive manufacturing of metallic glass has attracted great attentions from researchers owing to the prospect of free-form fabricating high-performance bulk amorphous alloy parts. The ...characteristics of additive manufacturing from points to tracks, tracks to layers, and layers to parts are suitable for forming complex bulk metallic glass parts, which are difficult to achieve with other processing technologies. Herein, the forming principles used in metallic glass additive manufacturing are reviewed, with an emphasis on the manufacturing processes, material systems, forming part properties and potential applications. The properties of forming bulk metallic glass via selective laser melting, laser-directed energy deposition, and laser foil printing technologies are summarized. In addition, certain newly explored metallic glass additive manufacturing technologies, such as fused filament fabrication, ultrasonic consolidation, thermal spraying, and pneumatic injection, are briefly introduced. Finally, the trends in metallic glass additive manufacturing and perspectives for this emerging field are discussed.
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The prevalence of peripheral nerve injuries resulting in loss of motor function, sensory function, or both, is on the rise. Artificial Nerve Guide Conduits (NGCs) are considered an effective ...alternative treatment for autologous nerve grafts, which is the current gold-standard for treating peripheral nerve injuries. In this study, Polycaprolactone-based three-dimensional porous NGCs are fabricated using Electrohydrodynamic jet 3D printing (EHD-jetting) for the first time. The main advantage of this technique is that all the scaffold properties, namely fibre diameter, pore size, porosity, and fibre alignment, can be controlled by tuning the process parameters. In addition, EHD-jetting has the advantages of customizability, repeatability, and scalability. Scaffolds with five different pore sizes (125 to 550 μm) and porosities (65 to 88%) are fabricated and the effect of pore size on the mechanical properties is evaluated. In vitro degradation studies are carried out to investigate the degradation profile of the scaffolds and determine the influence of pore size on the degradation rate and mechanical properties at various degradation time points. Scaffolds with a pore size of 125 ± 15 μm meet the requirements of an optimal NGC structure with a porosity greater than 60%, mechanical properties closer to those of the native peripheral nerves, and an optimal degradation rate matching the nerve regeneration rate post-injury. The in vitro neural differentiation studies also corroborate the same results. Cell proliferation was highest in the scaffolds with a pore size of 125 ± 15 μm assessed by the PrestoBlue assay. The Reverse Transcription-Polymerase Chain Reaction (RT-PCR) results involving the three most important genes concerning neural differentiation, namely β3-tubulin, NF-H, and GAP-43, confirm that the scaffolds with a pore size of 125 ± 15 μm have the highest gene expression of all the other pore sizes and also outperform the electrospun Polycaprolactone (PCL) scaffold. The immunocytochemistry results, expressing the two important nerve proteins β3-tubulin and NF200, showed directional alignment of the neurite growth along the fibre direction in EHD-jet 3D printed scaffolds.
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