Selective Laser Sintering 3D Printing Research Articles

Flexible Pressure Sensors with Wide Linearity Range and High Sensitivity Based on Selective Laser Sintering 3D Printing

AbstractTo achieve practical applications of flexible pressure sensors, good performance and scalable manufacturing processes are both desired. Here, flexible pressure sensors with excellent performance are fabricated via selective laser sintering (SLS). Having benefitted from the irregular microstructures generated in the powder sintering process, the sensors exhibit high sensitivity of 55 kPa−1 in a wide linearity range of 100 kPa, and they maintain decent sensitivity (>10 kPa−1) over a high‐pressure range (100–400 kPa), which is among the best results for flexible pressure sensors. The working mechanism of the sensor is finely revealed combining in situ observations and electrical simulations. The results demonstrate that electrical saturation (due to parasitic resistance) greatly affects the linearity range except for the geometric saturation of the microstructure. As a proof of concept, tactile, pulse, muscle stiffness, and plantar pressure tests are performed. The fast and stable responses of the sensor show its great potential for electronic skin, human–machine interface, and healthcare monitoring. Besides its excellent performance, the fabrication processes via SLS are compatible with fab‐scale production and flexible customization, which pave new paths for the mass manufacturing and diversified applications of flexible pressure sensors in the future.

Understanding the effects of formulation and process variables on the printlets quality manufactured by selective laser sintering 3D printing.

The focus of the study was to understand the effects of formulation and process variables on the printlets quality manufactured by selective laser sintering (SLS) 3D printing. The Box-Behnken response surface methodology was used to evaluate effects of individual variables and combinations thereof. The formulation and process variables studied were printing chamber temperature (°C, X1), laser scanning speed (mm/sec, X2) and lactose monohydrate concentration (%, X3). The responses studied were weight of printlets (mg, Y1), hardness (N, Y2), disintegration time (sec, Y3) and dissolved drug fraction in 15 min (%, Y4). The values of Y1, Y2, Y3 and Y4 varied from 170.2-257.0 mg, 5.5-32.0 N, 20-120 s and 64.4-97.5%, respectively. The studied factors showed statistically significant effects on the dependent variables (p < 0.04). The correlation coefficient between empirical and model predicted values for Y1, Y2, Y3 and Y4 were 0.999, 0.992, 0.998 and 0.983, respectively. The model was validated by an independent experiment and actual values of the responses were in close agreement with model predicted values. Fourier transformed infrared spectroscopy indicated no chemical interactions between the components of the formulation during printing process. X-ray powder diffractograms suggested a decrease in crystallinity of the drug and lactose in the printlets. Chemical images indicated uniform distribution of the drug. Scanning electron microscopy and X-ray micro-CT scanning showed a very porous microstructure of the printlets with a porosity of about 37.89%. In conclusion, the SLS method of manufacturing provides a feasible and flexible avenue for fabricating dosage forms with tailored characteristics.

Evaluation of Local Tissue Reaction After the Application of a 3D Printed Novel Holdfast Device for Left Atrial Appendage Exclusion

The left atrial appendage (LAA) is a small, finger-like extension of the left atrium and its exclusion is used as a treatment strategy to prevent ischemic stroke. Existing holdfast devices may damage the tissue, are unisized and not adjustable. A novel holdfast device for LAA exclusion devoid of these shortcomings was designed and 3D-printed using the Selective Laser Sintering (SLS) technology with polyamide powder and tested it on animal model. We selected the SLS 3D printing technology due to its wid14e availability and low production costs which could provide on-site 3D printing for specific patient. The purpose of this study was to evaluate the biocompatibility of the reported holdfast device and compare the histological results obtained for local tissue reactions to those obtained for an established grafting material. Thirty swine subdivided into two groups were examined. The LAA exclusion device was implanted and was either coated with a polyester vascular implant or not coated at all and the histological response to the device’s presence was evaluated which is a standard approach to test the device biocompatibility. In all cases, complete occlusion was seen without any pathological findings during the incubation time. In both groups, the surface of the atrium under a holdfast device was smooth and shiny and had no clots. The foreign body reaction of the LAA holdfast device made of polyamide powder was insignificantly lower compared to the polyester graft. Thus, it fulfils the parameters of biocompatibility at the highest degree, and makes it suitable material for the manufacturing of LAA holdfast devices.

Fabrication of Porous Hydrogenation Catalysts by a Selective Laser Sintering 3D Printing Technique.

Three-dimensional selective laser sintering printing was utilized to produce porous, solid objects, in which the catalytically active component, Pd/SiO2, is attached to an easily printable supporting polypropylene framework. Physical properties of the printed objects, such as porosity, were controlled by varying the printing parameters. Structural characterization of the objects was performed by helium ion microscopy, scanning electron microscopy, and X-ray tomography, and the catalytic performance of the objects was tested in the hydrogenation of styrene, cyclohexene, and phenylacetylene. The results show that the selective laser sintering process provides an alternative and effective way to produce highly active and easily reusable heterogeneous catalysts without significantly reducing the catalytic efficiency of the active Pd/SiO2 component. The ability to control the size, porosity, mechanical properties, flow properties, physical properties, and chemical properties of the catalyst objects opens up possibilities to optimize devices for different reaction environments including batch reactions and continuous flow systems.

Simultaneous realization of conductive segregation network microstructure and minimal surface porous macrostructure by SLS 3D printing

A general strategy, i.e. simultaneous realization of the conductive segregation network microstructure and minimal surface porous macrostructure by means of selective laser sintering (SLS) 3D printing is proposed for devices fabrication. For the purpose of strategy demonstration, a flexible piezoresistive sensor is fabricated by SLS 3D printing with the use of self-made single-walled carbon nanotubes (SWCNTs) wrapped thermoplastic polyurethane (TPU) powders. The SLS-printed TPU/SWCNTs composite possesses an ultra-low conductive percolation threshold and excellent mechanical strength due to the construction of electrically conductive segregation network microstructure in polymer matrix, what is a prerequisite to a flexible piezoresistive sensor. The minimal surfaces including the Schwarz, Gyroid- and Diamond-structures have been used to design a 3D-ordered porous macrostructure of the sensor. The Schwarz structure has been found to be capable of producing the best piezoresistive properties of the SWCNTs/TPU composite sensor with a gauge factor (GF) much higher than that for the Gyroid- and Diamond-structures. This phenomenon is well understood by the relationship between the piezoresistive sensitivity and the localized strain distribution revealed by Finite Element Modeling.

4D Printing of Magnetically Functionalized Chainmail for Exoskeletal Biomedical Applications

AbstractChainmail fabrics manufactured by selective laser sintering 3D printing have been magnetically functionalized to create a lightweight, 4D printed, actuating fabric. The post-processing method involves submerging the porous prints in commercial ferrofluid (oil-based magnetic liquid), followed by drying under heat. The actuation of the chainmail has been simulated using a rigid multi-body physics engine, and qualitatively matches experiment. Such magnetically actuating fabrics have potential to make thin, lightweight and comfortable wearable assistive devices.

The synthesis of epoxy resin coated Al2O3 composites for selective laser sintering 3D printing

PurposeTo prepare a new type of composite for selective laser sintering 3D printing, the surface of Al2O3 nanoparticles was modified by the coupling agent (3-methacryloxypropyl)-trimethoxy silane (KH570) before coated with thermoplastic epoxy resin (TER).Design/methodology/approachLaser diffraction confirmed that the size distribution of prepared powder materials in this study ranged between 20 to 80 µm. Thermogravimetric analysis (TGA) showed that the loading of organic matter was below 5 per cent. Fourier transform infrared spectroscopy indicated that the silane coupling agent molecule bound strongly with the alumina. X-ray diffraction confirmed the prepared powder materials to be α-alumina. Through the angle of repose (AOR) test, the AOR = 18.435º was obtained, suggesting the high flowability of prepared powder materials. Scanning electron microscopy (SEM) observation demonstrated that the shape of the prepared powder materials was sphere-like grains.FindingsMolding properties of prepared powder materials were studied on the basis of particle size distribution, particle size, sphericity, crystal structure and the reaction mode of the TER. This prepared powder materials can be well applied to the production of epoxy resin-coated Al2O3 composite parts with high precision and good mechanical performance.Originality/valueThis composite can be well applied to the production of epoxy resin-coated Al2O3 composite parts with high precision and good mechanical performance.

A dimensional compensation algorithm for vertical bending deformation of 3D printed parts in selective laser sintering

PurposeThe purpose of this study is to mitigate the dimensional inaccuracy due to vertical curling/bending deformation of three-dimensional (3D) printed parts produced by selective laser sintering (SLS) using PA12 based on dimensional compensation of the computer-aided design (CAD) model.Design/methodology/approachTo carry out this study, specially designed features are initially produced as references, and the dimensional deviations from the vertical bending deformation of the SLS process are analyzed. Next, the deformation patterns are formulated using a polynomial regression model in the global Cartesian coordinates of the building platform. Then, the compensation algorithm is implemented and the original 3D CAD file is preprocessed with an inverse transformation of the features to compensate the deformation errors.FindingsIt was found that the 3D printed parts from the SLS process have the dimensional inaccuracy due to the vertical bending pattern of the quadratic form. By implementing the compensation algorithm, it was statistically shown to effectively reduce bending deformations of various sample parts, including the automotive components, in SLS.Research limitations/implicationsThe position of samples in a batch has a direct impact on not only bending deformation but also on horizontal shape geometry error. However, the application of this algorithm is focused on the vertical bending deformation, which is estimated as a major part of dimensional inaccuracy.Practical implicationsThis paper provides a practical case study with a real vehicle part. The algorithm was shown to provide a more realistic solution to the dimensional deformation of printed products, which is not manageable by simply using the constant scale factors provided by SLS 3D printer manufacturers.Originality/valueThis paper suggests that the vertical bending deformation from SLS’s 3D printed complex parts can be improved through the proposed compensation algorithm. The compensation algorithm was constructed by using the predictive regression model created from the bending deformation patterns of reference samples. The proposed compensation algorithm can be further used and applied for other complex samples without making additional reference parts.

Selective Laser Sintering 3D Printing: A Way to Construct 3D Electrically Conductive Segregated Network in Polymer Matrix

AbstractSelective laser sintering (SLS), which can directly turn 3D models into real objects, is employed to prepare the flexible thermoplastic polyurethane (TPU) conductor using self‐made carbon nanotubes (CNTs) wrapped TPU powders. The SLS printing, as a shear‐free and free‐flowing processing without compacting, provides a unique approach to construct conductive segregated networks of CNTs in the polymer matrix. The electrical conductivity for the SLS processed TPU/CNTs composite has a lower percolation threshold of 0.2 wt% and reaches ≈10−1 S m−1 at 1 wt% CNTs content, which is seven orders of magnitude higher than that of conventional injection‐molded TPU/CNTs composites at the same CNTs content. The 3D printed TPU/CNTs specimen can maintain good flexibility and durability, even after repeated bending for 1000 cycles, the electrical resistance can keep at a nearly constant value. The flexible conductive TPU/CNTs composite with complicated structures and shapes like porous piezoresistors can be easily obtained by this approach.

3D 프린팅법으로 제조한 티타늄 시편의 물성 평가

The interest of the additive manufacturing technology, commonly called 3D printing, is rapidly increasing. Selective laser sintering (SLS) is the one of the method for 3D printing that has potential to produce metallic prostheses in dentistry. The purpose of this study was to evaluate physical properties of titanium specimen fabricated by SLS for dental implant system. Specimens were fabricated from Ti6Al4V alloy powder with median particle size (D50) of 34 μm. The SLS 3D printing was carried out using YAG laser with wavelength of 1075 nm with power of 190 W, and thickness of each layer was 30 μm. Machined specimens with sandblasting treatment were used as control group. Density, porosity, yield strength (30o compression), elastic modulus and fatigue limit were estimated. Density measurement and microCT analysis gave valuable informations about impurity inclusions and manufacturing defects. Yield strength and elastic modulus of 3D printing dense specimen showed similar value with the machined specimens. However, fatigue limit of 3D printing dense specimens was significantly lower than the machined specimen. 3D printing porous specimen showed lower yield strength and elastic modulus than the 3D printing dense specimens. Before 3D printing porous dental prosthesis application in clinic, fatigue limit should be evaluated carefully.

Improving PEEK bioactivity for craniofacial reconstruction using a 3D printed scaffold embedded with mesenchymal stem cells.

Polyetheretherketone (PEEK) is a bioinert thermoplastic that has been investigated for its potential use in craniofacial reconstruction; however, its use in clinical practice is limited by a poor integration with adjacent bone upon implantation. To improve the bone-implant interface, two strategies have been employed: to modify its surface or to impregnate PEEK with bioactive materials. This study attempts to combine and improve upon the two approaches by modifying the internal structure into a trabecular network and to impregnate PEEK with mesenchymal stem cells. Furthermore, we compare the newly designed PEEK scaffolds' interactions with both bone-derived (BMSC) and adipose (ADSC) stem cells. Customized PEEK scaffolds were designed to incorporate a trabecular microstructure using a computer-aided design program and then printed via selective laser sintering (SLS), a 3D-printing process with exceptional accuracy. The scaffold structure was evaluated using microCT. Scanning electron microscopy (SEM) was used to evaluate scaffold morphology with and without mesenchymal stem cells (MSCs). Adipose and bone marrow mesenchymal cells were isolated from rats and cultured on scaffolds. Cell proliferation and differentiation were assessed using alamarBlue and alkaline phosphatase assays, respectively. Cell morphology after one week of co-culturing cells with PEEK scaffolds was evaluated using SEM. SLS 3D printing fabricated scaffolds with a porosity of 36.38% ± 6.66 and density of 1.309 g/cm(2). Cell morphology resembled viable fibroblasts attaching to the surface and micropores of the scaffold. PEEK scaffolds maintained the viability of both ADSCs and BMSCs; however, ADSCs demonstrated higher osteodifferentiation than BMSCs (p < 0.05). This study demonstrates for the first time that SLS 3D printing can be used to fabricate customized porous PEEK scaffolds that maintain the viability of adipose and bone marrow-derived MSCs and induce the osteodifferentiation of the adipose-derived MSCs. The combination of 3D printed PEEK scaffolds with MSCs could overcome some of the limitations using PEEK biopolymers for load-bearing bone regeneration in craniofacial reconstruction.