3D Printing and Additive Manufacturing最新文献

Bioprinting has emerged as a powerful manufacturing platform for tissue engineering, enabling the fabrication of 3D living structures by assembling living cells, biological molecules, and biomaterials into these structures. Among various biomaterials, hydrogels have been increasingly used in developing bioinks suitable for 3D bioprinting for diverse human body tissues and organs. In particular, hydrogel blends combining gelatin and gelatin methacryloyl (GelMA; "GG hydrogels") receive significant attention for 3D bioprinting owing to their many advantages, such as excellent biocompatibility, biodegradability, intrinsic bioactive groups, and polymer networks that combine the thermoresponsive gelation feature of gelatin and chemically crosslinkable attribute of GelMA. However, GG hydrogels have poor electroactive properties, which hinder their applications in neural tissue engineering where electrical conductivity is required. To overcome this problem, in this study, a small amount of highly electroactive graphene oxide (GO) was added in GG hydrogels to generate electroactive hydrogels for 3D bioprinting in neural tissue engineering. The incorporation of GO nanoparticles slightly improved mechanical properties and significantly increased electrical conductivity of GG hydrogels. All GO/GG composite hydrogels exhibited shear thinning behavior and sufficient viscosity and hence could be 3D printed into 3D porous scaffolds with good shape fidelity. Furthermore, bioinks combining rat bone marrow-derived mesenchymal stem cells (rBMSCs) with GO/GG composite hydrogels could be 3D bioprinted into GO/GG constructs with high cell viability. GO nanoparticles in the constructs provided ultraviolet (UV) shading effect and facilitated cell survival during UV exposure after bioprinting. The GO/GG composite hydrogels appear promising for 3D bioprinting applications in repairing damaged neural tissues.

The article discusses the importance of optimizing process parameters in 3D printing to achieve better mechanical properties of printed parts. It emphasizes the material extrusion 3D printing technology and some of the most commonly used materials, acrylonitrile butadiene styrene (ABS) and polyethylene terephthalate glycol (PETG). Optimizable process parameters such as, print angle, outer layer number, extruder flow ratio, extrusion (nozzle) temperature, and layer thickness are examined. The article also highlights the importance of postprocessing techniques, specifically thermal postprocessing (annealing) and chemical postprocessing in the acetone (AC) chamber, to enhance mechanical properties of printed parts. The results show that the wall structures played a crucial role in defining mechanical properties, acting as main load-bearing elements. Adjusted flow ratios influenced mechanical properties. Samples with a 25% extruder flow rate increase demonstrated a 44% rise in elongation at break, while a 50% increase led to slight strength reduction. The ABS material AC-treated sample exhibited 58.2% lower tensile strength and 1.9% lower elongation due to stress concentration, while thermally treated showed similar results to the default, printed at manufacturer-recommended settings. The PETG material AC-treated sample exhibited 53.2% lower tensile strength, but 17.5% higher elongation, while thermally treated showed similar results to the default. Samples printed at 0° orientation exhibited plastic deformation with the highest tensile strength and elongation, while samples at 45° and 90° orientations experienced delamination, leading to brittle fracture, proving that the orientation and interlayer adhesion have a great influence on mechanical properties. While the print settings and orientation had similar effects on mechanical properties of each material, postprocessing effects are greatly influenced by the polymer matrix.

Heat accumulation due to repetitive simple laser processing paths during building up a three-dimensional structure is a well-known issue that needs to be settled to reduce the excessively high residual stress and thermal deformation in a powder bed fusion (PBF) additive manufacturing process. Because of the dependency of laser path on the thermal dispersion, it is essential to analyze the heat accumulation phenomenon during laser processing. A computational fluid dynamics (CFD) analysis based on the volume of fraction method is used to optimize the laser path for minimizing the local heating up in the PBF process. In this work, a novel spiral laser path with optimal rotation angle is proposed and compared with the commonly used scanning paths. As the results, the accumulated temperature of the optimal spiral path shows a 200.9 K less compared with that of the general repetitive path. The thermal deformation of a cantilever structure made by the optimal spiral path is experimentally evaluated. From the experimental test, we verify that the spiral laser path reduces thermal deformation by 52.3% compared with the one made by the general one-directional laser path. This work based on numerical simulations and experiments utilizes the proposed spiral laser path to obtain higher precision, less residual stress, and more uniform microstructure of an additive-manufactured structure.

Microfluidic channel systems can be used for various biomedical applications, including drug administration, wound healing, cell culture research, and many others. A 3D microfluidic channel system has enormous potential over conventional microfluidic channel systems, including the capacity to simulate biological events in a laboratory setting. This system has the ability to recreate biological phenomena such as concentration gradient generators (CGGs). Microfluidic CGGs have complex fabrication when built into a 3D channel system. These complex systems can be built with complicated processes such as plasma bonding, which requires expensive setup and fine equipment. Therefore, in this study, a smart additive manufacturing technique is applied for an enormous review of the design and fabrication process, which is optimized for different operating conditions. This study employs a 3D printed removable channel mold to avoid the complex fabrication technique of microfluidic channels, allowing the direct casting of polydimethylsiloxane without extra bonding stages. The proposed design comprises dual mixing stages, incorporating a 3D mixer configuration and a converging output to attain the desired gradient outcome. Optimization is performed to achieve the best operating conditions by using response surface methodology, with channel dimension $\left(L_C\right)$ and operating volumetric flow rate $\left(Q_C\right)$ as individual variables to minimize the gradient gap value $\left(G_{val}\right)$ . As a result, the optimal operating conditions are the combinations of 640 $\mu m$ channel dimensions and ${242}^{\mathrm{mL}{/}_{\mathrm{hr}}}$ operating volumetric flow rates, generating a stable and linear gradient value raise. A cost analysis was conducted to assess the fabrication expenses, revealing that the production cost of a sole 3D microfluidic channel is merely 1.42 USD.

The large amount of unfused powder that remains on the surface of Ti6AL4V porous scaffolds prepared by selective laser melting technology is a common problem. Therefore, this article investigated the effects of three different chemical polishing processes on the surface state, pore structure, and mechanical properties of small pore size scaffold materials at different polishing times in the field of implantable medical devices. The results show that the overall treatment effect of the simple chemical polishing process is poor, the internal treatment depth of porous support is insufficient and uneven, and the overall mechanical properties of the sample with the same porosity are average. The outer structure during the electrochemical polishing process showed an obvious treatment effect. However, the internal treatment depth and uniformity were significantly lower compared with the simple chemical polishing process, and the overall mechanical properties of the sample with the same porosity were inferior. The overall treatment effect, depth, and uniformity of the inner and outer structure of the sample using a dynamic chemical polishing process were significantly optimized, and the overall mechanical properties of the sample with the same porosity were superior to the other two methods. Furthermore, the main reasons for the nonuniform treatment effect between the inner and outer layers during the chemical polishing of porous scaffolds were observed to be related to the restricted exchange of etchant caused by the complex internal structure of porous scaffolds and the gas generated by the chemical reaction.

Direct ink writing of multiple mineral materials (M³) coupled with simulation analysis is an optimization solution in accordance with low-carbon and sustainable manufacturing. It improves the ability to imitate natural biological iterative optimization, and accurately obtained data for geological model tests to effectively help prevent natural disasters. This article investigates the effects of equivalent materials on the direct ink writing and permeability behaviors through geological simulation models. The mineral compositions provide adjustable cohesion and compression coefficient properties and considerably improve the stability and dispersion of slurry by adjusting parameters such as the viscosity, filling ratio, and deposition height. The upper limit of the permeability depends on the designed macropores and the printing accuracy because macro features provide pathways for rapid water infiltration into the printed specimen. This research establishes guidelines for the fabrication of components with tailored and designed-pore-dependent permeability properties that are primarily for slope geotechnical engineering applications.

The optimization of slurry content and forming process parameters has a significant effect in slurry microextrusion direct forming method. In this article, magnesium sulfate monohydrate (MgSO₄) and polyvinylpyrrolidone (PVP) were used as raw materials to prepare the slurry, and the component ratios of the slurry and the optimization of its forming process were discussed. The optimum slurry content is 64 wt.% by mass of magnesium sulfate monohydrate and 36 wt.% by mass of binder consisting of PVP-EtOH. The process parameters that include printing speed, extrusion pressure, and the ratio of printing layer height to extrusion diameter were selected as influencing factors. The orthogonal experiment results show that a printing speed of 850 mm/min, an extrusion pressure of 250 kPa, and a layer height of 510 μm of the extrusion diameter are the optimized process parameters. Under the optimized printing parameters, the surface roughness of the prepared samples is 23.764 μm, with dimensional deviations of 0.71%, 0.77%, and 2.56% in the X, Y, and Z directions, respectively.

A novel shear test method on shear bond behavior of 3D printed interlayer interfaces and interstrip interfaces was proposed in this study. Thereafter, the effect of different replacement ratios of recycled sand, printing intervals, and surface treatments were investigated. The test results showed that under the same printing condition, the interfacial shear strengths of interlayer interface and interstrip interface were similar to each other. The interfacial shear strength slightly decreased with the increase of the replacement ratio of recycled sand, while it sharply decreased with the extension of printing interval time. The interfaces in 3D printed recycled mortar had higher time sensitivity compared with 3D printed natural mortar. Considering that discontinuous construction will introduce inferior interfaces in 3D printed concrete components, effective surface treatments should be conducted. According to the test results, the improvement effect of surface treatments was epoxy paste > cement paste > surface wetting > no treatment.

In this work, we propose a methodology to develop printability maps for the laser powder bed fusion of AISI 316L stainless steel. Regions in the process space associated with different defect types, including lack of fusion, balling, and keyhole formation, have been considered as a melt pool geometry function, determined using a finite element method model containing temperature-dependent thermophysical properties. Experiments were performed to validate the printability maps, showing a reliable correlation between experiments and simulations. The validated simulation model was then applied to collect the data by varying laser scanning speed, laser power, powder layer thickness, and powder bed preheating temperature. Following this, the collected data were used to train and test the adaptive neuro-fuzzy interference system (ANFIS)-based machine learning model. The validated ANFIS model was used to develop printability maps by correlating the melt pool characteristics to the defect types. The smart printability maps produced by the proposed methodology can be used to identify the processing window to attain defects-free components, thus attaining dense parts.

Moisture absorption into hygroscopic/hydrophilic materials used in fused deposition modeling (FDM) can diminish desired mechanical properties. Sensitivity to moisture is dependent on material properties and environmental factors and needs characterization. In this article, moisture sensitivity of four grades of polylactic acid (PLA) filaments and four different ratios of PLA/polybutylene succinate (PBS) blended filaments were characterized through FDM printed American society for testing and materials (ASTM-D638) test samples after conditioning the filaments at different relative humidity levels. The tensile testing and scanning electron microscopy (SEM) of the samples' fracture surfaces revealed that PLA 4043D was the most moisture-sensitive among the chosen grades of PLA filaments. Through filament tension test and melt flow index (MFI) testing it was observed that moisture had a significant detrimental effect (20% reduction in tensile strength and 50% increase in MFI) on PLA 4043D filaments. Samples from moisture-conditioned PLA/PBS 75/25 blended filaments displayed a significant reduction (10%) in tensile strength. Moreover, the MFI of 75/25 filaments was increased with subsequent increases in moisture level. Investigation of tensile properties of ASTM samples made from four grades of PLA filaments exposed to room temperature and humidity conditions for 3 months showed an even more significant decrease in strength (ranging from 24% to 36%).