Conventional slicing algorithms for additive manufacturing (AM) processes slice the designed model into a set of planar layers, due to the simplicity, robustness, and generality of most geometries. However, such planar-layer-based slicing significantly limits the performance of the AM system with stair-stepping surface finishing, massive supporting structures, non-conformable to curved substrates, and reduced strength for thin shell structures. To mitigate these drawbacks of planar layer slicing, we presented a curved layer slicing method by utilizing the isothermal surfaces in heat transfer simulation. The designed part is virtually placed on a heated substrate, and the heat spread out through the part, which establishes a temperature field. The isothermal surfaces of this temperature field naturally create curved layers for the printing process. Our method successfully generated curved layers and tool paths for additive manufacturing processes with three-axis and multi-axis 3D printing. A multi-axis motion 3D printing machine is developed based on fused decomposition modeling (FDM). Several test cases were performed to verify and demonstrate our slicing method's capabilities. A discussion of future development on our general non-planar slicing system was also given.
Soil salinization, an important and increasingly prevalent issue in arid regions, influences plant growth and carbon (C): nitrogen (N): phosphorus (P) stoichiometry patterns by limiting nutrient access. Plant C:N:P stoichiometry patterns and response to soil salinity among organs (e.g., leaves, stems and roots) reflect plants' trade-offs between access to resources and their adaptation strategies to different habitats. Common in marshes of arid middle-lower reaches of the Shule River Basin, China, Phragmites australis (Cav.) Trin. Ex Steud. (P. australis), is often the dominant species. The effects of soil salinity on the C:N:P stoichiometry among organs of P. australis were investigated in this study. The average N and P concentrations in leaves (19.09 ± 0.63 and 0.98 ± 0.05 g·kg−1, respectively) were significantly greater than those in roots (3.16 ± 0.16 and 0.76 ± 0.05 g·kg−1, respectively) and stems (3.80 ± 0.16 and 0.55 ± 0.05 g·kg−1, respectively) (P < 0.05). However, the average C concentrations in leaves (406.47 ± 5.37 g·kg−1) were not significantly different from those in stems (405.63 ± 6.03 g·kg−1) and roots (402.83 ± 7.94 g·kg-1) (P > 0.05). The N:P ratio in leaves (20.89 ± 0.81) was significantly greater than those in stems (8.95 ± 0.67) and roots (5.11 ± 0.49), while C:N and C:P ratios (22.33 ± 0.82 and 469.25 ± 26.81, respectively) were significantly lower than those in stems (114.56 ± 4.93 and 1014.49 ± 86.57, respectively) and roots (144.58 ± 8.25 and 693.00 ± 74.18, respectively) (P < 0.05). N and P concentrations of leaves and C concentration of stems under high soil salinity were significantly lower than those in low and medium soil salinity, whereas C:P and N:P ratios of leaves and C:P ratio of stems were significantly greater than the others (P < 0.05). Soil salinity played a dominant role in determining leaf's and root's C:N:P stoichiometry of P. australis. This indicated that plant in arid marshes adapt to soil salinity conditions by modulating the changes in solute penetration in leaves and roots. These lead to diverse stoichiometric response patterns of C:N:P stoichiometry among organs. The information helps to understand C:N:P stoichiometry patterns, nutrient utilization strategy and carbon allocation of dominant plants and its potential responses to global changes in the marsh wetland ecosystems of arid regions.
Abstract Microfluidic devices have been widely investigated for various applications, specifically in the biomedical field, which involve manipulating cells at a sub-micron scale. However, the conventional lithography process with polydimethylsiloxane (PDMS) micro-molding process (soft lithography) involves numerous steps demanding high-end equipment and a cleanroom fueling up the cost and making it a time-consuming process. This paper presents a low-cost yet versatile way to fabricate long microfluidic channels using liquid crystal display (LCD)-based vat photopolymerization 3D printing. The accuracy, resolution and repeatability of the printing process were characterized using various parameter settings. We validated the developed process by 3D-printing four different microfluidic devices with 100 μm wide channels. Subsequently, we successfully demonstrated the formation of a single streamline of breast cancer cells in a microchannel with long and smooth edges. The scanning electron microscopy (SEM) characterization shows a high-quality fabricated channel. This proposed approach aligns with the ongoing efforts toward a versatile, flexible, and fast option for producing the diagnostic device.
A new manufacturing paradigm is showcased to exclude conventional mold-dependent manufacturing of pressure sensors, which typically requires a series of complex and expensive patterning processes. This mold-free manufacturing leverages high-resolution 3D-printed multiscale microstructures as the substrate and a gas-phase conformal polymer coating technique to complete the mold-free sensing platform. The array of dome and spike structures with a controlled spike density of a 3D-printed substrate ensures a large contact surface with pressures applied and extended linearity in a wider pressure range. For uniform coating of sensing elements on the microstructured surface, oxidative chemical vapor deposition is employed to deposit a highly conformal and conductive sensing element, poly(3,4-ethylenedioxythiophene) at low temperatures (<60 °C). The fabricated pressure sensor reacts sensitively to various ranges of pressures (up to 185 kPa-1 ) depending on the density of the multiscale features and shows an ultrafast response time (≈36 µs). The mechanism investigations through the finite element analysis identify the effect of the multiscale structure on the figure-of-merit sensing performance. These unique findings are expected to be of significant relevance to technology that requires higher sensing capability, scalability, and facile adjustment of a sensor geometry in a cost-effective manufacturing manner.
Abstract Diffractive optical elements (DOEs) are important optics that can manipulate the light by diffraction, which could be used in optical systems where compactness and lightweight matter. As one of the typical DOEs, diffractive gratings have widely application and their fabrication requires high precision and a clean environment. In this paper, we designed and fabricated diffraction gratings with different dimensions for visible light using the two-photon polymerization technique. The optical path differences and distances between diffraction fringes were measured and compared with the theoretical ones. The results showed that the precision across the printing direction was good while the height differences in the printing direction were around 20% smaller than the designed ones. Another problem was that the gratings were printed by small blocks and the borders of the blocks could serve as secondary gratings to generate smaller diffraction fringes, which need to be fixed for future fabrication of precise gratings and other complex DOEs by two-photon polymerization.
The aim of this study was to prescreen the expression of ALK-positive in signet-ring cell gastric carcinoma by IHC assay. We selected 84 FFPE samples with signet-ring cell gastric carcinoma (55 cases of GC, 29 cases of EGJ) and performed the detection of ALK-positive using IHC. The correlation of ALK-positive and clinicopathologic characteristics was statistically analyzed. The results showed, of 84 cases prescreened, 11 (13.09%) were ALK-positive. For the 6 cases with IHC 2+ (7.14%), and the 5 cases with IHC 1+ (5.95%). We noted that 8 (72.73%) cases were never smoker, 8 (72.73%) cases were >5 cm tumor size and 9 (81.82%) cases were T4 in invasive depth. All of the 11 cases were III of pathologic TNM stage. The ALK-positive patients showed significantly statistical difference in lymph node metastasis (p=0.0285) and TNM stage (p=0.0497), compared with the ALK-negative patients. In conclusion, the expression of ALK fusion is found in signet-ring cell gastric carcinoma by IHC assay.
Abstract Spin coating on flat substrates is a well-understood fluid phenomenon, creating uniform thin films with microscale and nanoscale thicknesses. It is widely used in the microscale and nanoscale fabrication of functional devices. Beyond flat substrates, there is an increasing manufacturing demand for fabricating micro/nanoscale thin films on non-flat substrates, such as spherical and freefrom surfaces. However, it is still challenging to model spin coating on a non-flat substrate. This paper numerically models the spin coating on a freeform substrate as a laminar flow. The centrifugal force from spinning was modeled as a volume force proportional to the spin coating speed square and radius. Various initial thicknesses were simulated and compared. A two-way sinusoidal surface was used as the freeform surface. The simulation results showed that the coating thickness converged to an asymptotic solution, regardless of the initial coating conditions. Also, similar to the spin coating on a flat surface, we found the thickness of the spin coating on a non-flat surface was halved when the spin coating time was increased to four times. These surprising results produce a predictable thin film coating on the freeform surfaces, which enables microfabrication on the freeform substrate.
Abstract Real-time and in-situ printing performance diagnostic in vat photopolymerization is critical to control printing quality, improve process reliability, and reduce wasted time and materials. This paper proposed a low-cost smart resin vat to monitor the printing process and detect the printing faults. Built on a conventional vat photopolymerization process, we added equally spaced thermistors along the edges of the resin vat. During printing, polymerization heat transferred to the edges of the resin vat, which increased thermistors’ temperature and enhanced resistances. The heat flux received at each thermistor varied with the distance to the place of photopolymerization. The temperature profiles of all thermistors were determined by the curing image pattern in each layer, and vice versa. Machine learning algorithms were leveraged to infer the printing status from the measured temperatures of these thermistors. Specifically, we proposed a simple and robust Failure Index to detect if the printing was active or terminated. Gaussian process regression was utilized to predict the printing area using the temperature recordings within a layer. The model was trained, validated, and tested using the data set collected by printing six parts. Different printing abnormalities, including printing failures, manual printing pause, and missing features (incorrect printing area), were successfully detected. The proposed approach modified the resin vat only and could be easily applied to all vat photopolymerization processes, including SLA, DLP, and LCD based 3D printing. The limitation and future work are also highlighted.
The drop-on-demand (DOD) based three-dimensional (3D) printing methods can fabricate an object with a high level of accuracy and shape complexity using multiple materials. However, a key limitation of the DOD approaches such as ink jetting is only the inks with low viscosity can be used. Such low-viscosity restriction severely limits the material options for the DOD-based 3D printing methods. To address the viscosity issue, we have developed a novel drop-on-demand 3D printing method called direct droplet writing (DDW) for highly viscous material. One main idea of the DDW process is to use direct droplet-punching to enable the printing of materials that may have a viscosity over 190,000 mPa·s; and another main idea of the DDW process is to use capillary-splitting to avoid common issues of various ink-jetting approaches, including splashing, droplet deflection, and satellite droplets. The DDW process can reliably fabricate 3D structures using a wide range of materials that are challenging for the jetting-based and extrusion-based methods. Analytical models to characterize the DDW process are presented. A set of test cases have been conducted using the in-house developed prototype system to characterize the relationship between droplet size and process parameters such as droplet punching speed and dispensing gap. Various materials, including high-loading photocurable tricalcium phosphate (TCP) ink and polyurethane (PU) leather ink, were successfully used in the DDW process. In addition to a much broader range of 3D printable materials, the DDW process is robust, without ink clogging or leaking, and can achieve consistent printing results using digitally controlled droplets.
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