Digital Light Projector Research Articles

Effects of build conditions and angle acuteness on edge reproducibility of casting patterns fabricated using digital light projection.

The aim of the present study was to evaluate the effects of build conditions and angle acuteness on edge reproducibility of the casting patterns fabricated using a digital light process. The prism-shaped patterns with various vertex angles were fabricated in three build orientations. The height from the base to the vertex angle point of the fabricated pattern was measured and the incomplete height was calculated as the discrepancy between the original and measured heights. Two-way ANOVA revealed that the vertex angle and build orientation and their interaction were significant (p<0.05). The incomplete height significantly decreased with an increase of the vertex angle. When the vertex angle was 20° and the build-up direction was parallel to the edge of vertex angle and perpendicular to the triangular base, the incomplete height was the smallest. Therefore, build orientation and angle acuteness influenced the edge reproducibility of the casting patterns fabricated using a digital light process.

Development of polycaprolactone/hydroxyapatite composite resin for 405 nm digital light projection 3D printing

PurposeThe purpose of this study is to develop resin composite materials composed of polycaprolactone (PCL) acrylates and hydroxyapatite (HA) nanoparticles for ultraviolet digital light projection (DLP) three-dimensional (3D) printing technique.Design/methodology/approachTwo PCL-based triacrylates, namely, glycerol-3 caprolactone-triacrylate (Gly-3CL-TA) and glycerol-6 caprolactone-triacrylate (Gly-6CL-TA) were synthesized from ring-opening polymerization of ε-caprolacton monomer in the presence of glycerol and then acrylation was performed using acryloyl chloride. 3D printing resins made of Gly-3CL-TA or Gly-6CL-TA, 5% HA and 3% of photoinitiator 2,4,6-Trimethylbenzoyl-diphenyl-phosphineoxide were then formulated. The surface topography, surface element composition, flexural strength, flexural modulus, cytotoxicity and degradation of the PCL-based scaffolds were then characterized.FindingsResin composite composed of Gly-3CL-TA or Gly-6CL-TA and 5% (w/w) of HA can be printed by 405 nm DLP 3D printers. The former has lower viscosity and thus can form a more uniform layer-by-layer structure, while the latter exhibited a higher flexural strength and modulus after being printed. Both composite materials are non-cytotoxic and degradable.Originality/valueThis study provides a direction of the formulation of environment-friendly resin composite for DLP 3D printing. Both resin composites have huge potential in tissue engineering applications.

Sliding surface structure comparison of 3D printed polymers using FDM and DLP technologies

This study aims to review the surface structure of the parts that are manufactured using various techniques of 3D printing. Particularly, two different methods were employed in the current work: Fused Deposition Modelling (FDM) and digital light projection (DLP). The output of both technologies regarding the surface construction aspects was evaluated and compared. For determining the features of the surfaces, an optical microscope was utilised for taking the pictures from the cross-sectional area (upper and lower edges) and the outer face of the samples. Various magnification values have been investigated to find the best sights at the surface structure of the printed bodies. Surface roughness was examined due to its relevance to the texture properties of the fabricated pieces. The tribology of the workpieces has been tested as well. The results show that the products of the FDM technique have been characterised with a rough surface and anisotropic properties which were reflected on the examined measurements. In contrast, the DLP method has revealed objects with a very smooth surface and approximately homogeneous structure.

Investigation of Light-Induced Surface Roughness in Projection Micro-Stereolithography Additive Manufacturing (PµSLA)

Abstract Parts manufactured by PµSLA have intrinsic surface roughness on the sidewalls, which is a result of two main factors, the staircase effect and diffraction of the projected light. Each micromirror in the digital light projector acts like a micro aperture. Therefore, the projected light has a Gaussian intensity profile that is reflected in the cured geometry. Proposed here is a physics-based analytical model as a function of the exposure time and the layer thickness to predict the surface roughness of the manufactured parts. The predicted results are then assessed experimentally with parts manufactured with a combination of different process parameters values. The different lay directions of surface roughness produced by this process are identified. The effect of the process parameters on surface profile in the different lay directions is investigated experimentally.

Development of an innovative, high speed, large-scaled, and affordable metal additive manufacturing process

This paper introduces a new additive manufacturing (AM) process which significantly improves the productivity of the current metal AM technologies by combining binder jet printing and stereolithography principles. Three dimensional objects can be printed on a powder bed system where photopolymerization takes place by selectively curing the suspensions containing metallic powder and ultraviolet curable resin in a layer-by-layer fashion. Integration of a digital light projection module allows a high-speed production with dimensional accuracy within 100 µm. Printed parts are sintered at appropriate temperatures to attain metal parts with the final density above 97% and homogenous microstructure without residual stress.

In vivo imaging of cervical precancer using a low-cost and easy-to-use confocal microendoscope.

Cervical cancer incidence and mortality rates remain high in medically underserved areas. In this study, we present a low-cost (<$5,000), portable and user-friendly confocal microendoscope, and we report on its clinical use to image precancerous lesions in the cervix. The confocal microendoscope employs digital apertures on a digital light projector and a CMOS sensor to implement line-scanning confocal imaging. Leveraging its versatile programmability, we describe an automated aperture alignment algorithm to ensure clinical ease-of-use and to facilitate technology dissemination in low-resource settings. Imaging performance is then evaluated in ex vivo and in vivo pilot studies; results demonstrate that the confocal microendoscope can enhance visualization of nuclear morphology, contributing to significantly improved recognition of clinically important features for detection of cervical precancer.

Additive Manufacturing of Bovine Serum Albumin-Based Hydrogels and Bioplastics.

Biosourced and biodegradable polymers for additive manufacturing could enable the rapid fabrication of parts for a broad spectrum of applications ranging from healthcare to aerospace. However, a limited number of these materials are suitable for vat photopolymerization processes. Herein, we report a two-step additive manufacturing process to fabricate robust protein-based constructs using a commercially available laser-based stereolithography printer. Methacrylated bovine serum albumin (MA-BSA) was synthesized and formulated into aqueous resins that were used to print complex three-dimensional (3D) objects with a resolution comparable to a commercially available resin. The MA-BSA resins were characterized by rheometry to determine the viscosity and the cure rate, as both parameters can ultimately be used to predict the printability of the resin. In the first step of patterning these materials, the MA-BSA resin was 3D printed, and in the second step, the printed construct was thermally cured to denature the globular protein and increase the intermolecular noncovalent interactions. Thus, the final 3D printed part was comprised of both chemical and physical cross-links. Compression studies of hydrated and dehydrated constructs demonstrated a broad range of compressive strengths and Young's moduli that could be further modulated by adjusting the type and amount of co-monomer. The printed hydrogel constructs demonstrated good cell viability (>95%) after a 21 day culture period. These MA-BSA resins are expected to be compatible with other vat photopolymerization techniques including digital light projection and continuous liquid interface production.

Realization of Photo-curing Gelatin Hydrogel using a Commercial Projector for Culturing Mesenchymal Cells

This paper investigates the realization of synthetic extracellular matrix with visible light photo-patterning gelatin in a simpler manner. A synthetic extracellular matrix provides an initial attachment for the seeded cells on the experimental substrate such as glass plate or multi-well until they realized their the natural extracellular matrix. Here, a commercial Digital Light Projector (DLP) was used to induce gelatin with Rose Bengal as a crosslinking agent to form the thin layer on the experimental substrate. Various gelatin concentrations from 2%-10% were exposed at different times in order to optimize the patterning process. A geometrical characterization on the patterned gelatin, such as contour measurement and resolution, were taken place. Results showed that the thickness of patterned gelatin was in the range of 10 µm - 60 µm depends on the exposure time of the DLP projector. Moreover, a visual method aided by the Fiji toolbox from NIH ImageJ image processing was used to observe the density and spatial arrangement of the cultured cells on the substrate. Ultimately, biocompatibility using MTT assay was also employed to confirm the viability of the cells on the gelatin substrate. The results show that we are able to control the physical and spatial arrangement of the gelatin substrate, and they with cell viability depend on 6 days of observation. It was found that the gelatin substrate provides faster growth on cultured cells compared to the control study. This finding leads to the possibility to realize the automation system in cell culture technology with an affordable investment.

Photocrosslinking-based 3D printing of unsaturated polyesters from isosorbide: A new material for resorbable medical devices

Clinically used tissue-engineered devices are few and far between. The search for biocompatible materials has been a great focus for the field for the past 30 years. The ones that exist are hard to work with when manufacturing patient-specific shapes with complex external and internal pore geometries because of their material and mechanical properties. Photo-cross-linkable polymers have arisen as a potential 3D printable solution for this problem. Here we present a new sugar-based polymer, isosorbide-derived polyester as a potential candidate to help fill this gap.Isosorbide-derived polyesters containing different amount of double bonds were synthesized to allow the material to be crosslinked or functionalized. Three resin formulations with different amounts of double bonds available (5, 12 and 17%) were used. After initial thermal and photo-crosslinking studies, Isosorbide-derived unsaturated polyesters were then mixed with a photoinitiator, co-crosslinker, and solvent to form a 3D printable resin formulation. Thin films of that resin were then cured using a Digital Light Projection (DLP) printer and analyzed. An attempt was made to modulate the cured thickness by adding HMB as a photoattenuator. We assessed 3D printing success and tensile green strength for the 3 resin formulations.We were able to 3D print unsaturated polyesters from isosorbide with a DLP printer when enough double bonds were present to facilitate crosslinking and curing of the material. Finally, thin films were then seeded with fibroblasts following the ISO 10993-5 protocol. These coupons were found safe (i.e., non-cytotoxic and biocompatible), potentially marking the beginning of a new approach to preparing resorbable implants for tissue engineering uses.

High Speed 3D Shape Measurement with Temporal Fourier Transform Profilometry

A novel high-speed 3D shape measurement technology called temporal Fourier transform profilometry (TFTP for short) is proposed by combining the merits of Fourier transform profilometry (FTP) and phase-measuring profilometry (PMP). Instead of using the digital light projector, a mechanical projector is employed to generate multi-period phase-shifting fringe patterns sequentially. During the reconstruction process, the phase value of each pixel is calculated independently along the temporal axis and no spectrum filtering operation is performed in a spatial domain. Therefore, high-frequency components containing the detailed information of the measured object effectively remain. The proposed method is suitable for measuring isolated dynamic objects. Only one frame of deformed fringe pattern is required to retrieve one 3D shape of the measured object, so it has the obvious advantage if measuring the dynamic scene at a high speed. A low-cost self-made mechanical projector with fast projection speed is developed to execute the principle-proof experiments, whose results demonstrate the feasibility of measuring isolated dynamic objects.

Simple differential digital confocal aperture to improve axial response of line-scanning confocal microendoscopes.

Line-scanning confocal microendoscopy offers video-rate cellular imaging of scattering tissue with relatively simple hardware, but its axial response is inferior to that of point-scanning systems. Based on Fourier optics theory, we designed differential confocal apertures with a simple subtraction technique to improve the line-scanning sectioning performance. Taking advantage of digital slit apertures on a digital light projector and a CMOS rolling shutter, we demonstrate real-time optical sectioning performance comparable to point scanning in a dual-camera microendoscope (<$6,000). We validate the background rejection capability when imaging porcine columnar epithelium stained with fluorescent contrast agents with different uptake mechanisms and staining properties.

360-deg shape measurement system based on three-dimensional orientation target

We present a system for 360-deg shape measurement based on three-dimensional (3-D) orientation target. The measurement system mainly includes a CCD camera, digital light projector, 3-D orientation target, and the measured object. The global coordinates for all chessboard corners of the target are calculated based on close-range photogrammetry, for which the relative orientation between camera stations is discussed in detail. According to the homography matrix between the checkerboard and its image plane, the position and orientation of the measuring camera relative to the target are determined. A dot-matrix structured light is designed and projected onto the measured object surface. In each image of the structured light deformed by the object shape, the pixel coordinates of the dot-centers are accurately calculated by the ellipse-fitting algorithm, and then they are all sorted in the same order by the beads-stringing matching method. In the experiment, the designated front, rear, left, and right surfaces of a reference object are measured, and their separate point clouds are automatically stitched together by the 3-D orientation target. Compared with coordinate measurement machine data, the accuracy of the system is demonstrated; the maximum deviations are +1.257 / − 0.977 mm, and the standard deviation is 0.124 mm.

Production of high-quality temporary crowns and bridges by stereolithography

Introduction: Temporary crowns and bridges are the main elements in the treatment with fixed partial dentures. They are usually manufactured from methacrylate polymers and composites by heat-curing or CAD/CAM milling. Additive technologies (ATs) offer a number of advantages in the production of temporary dental restorations. However, there is a lack of information about the application of AT for manufacturing of provisional prostheses due to the multiple variants and complexity of their design as well as the wide variety of the 3D printing processes. Aim: The aim of the present paper was to establish the peculiarities in the production of high-quality temporary crowns and bridges by stereolithography (SLA) with digital light projection (DLP). Materials and Methods: Two groups of samples - cubic (5 mm x 5 mm x 5 mm) and four-part dental bridges (1-st premolar to 2-nd molar) were printed with different layer thickness - 35 µm and 50 µm from NextDent C+B polymer using RapidShape D30 . Results and Discussion: It was established that for effective production of temporary crowns and bridges with high dimensional accuracy and surface smoothness, it is necessary to take into account the peculiarities of the 3D printing process and to make corrections still at the stage of virtual model generation. Individual corrections of the dimensions along the separate axes of the virtual model have to be done with correction coefficients, depending on the construction type - crown or bridge. In order to obtain high smoothness, the construction should be positioned with the vertical axes of the teeth parallel to the printing direction (Z-axis). The number of the supports has to be increased (≥4 per tooth) for reduction of the deformations during 3D printing and final photopolymerization. Conclusion: The findings in the present study could be very helpful in the development of proper construction design and technological process for improving the quality of temporary restorations.

Application of grayscale expansion for accuracy improvement in phase-measuring profilometry

A method based on grayscale expansion for improving measurement accuracy in phase-measuring profilometry (PMP) is proposed. Digital light projector (DLP) has been widely used for projecting phase-shifting sinusoidal grating in PMP. However, due to its international standardization, DLP can only project at most 256 grayscales for all gray patterns. Moreover, the gray digitalization error may cause lower fidelity for the projected sinusoidal grating. In order to reduce the gray digitalization error, the sinusoidal grating can thus be designed as a 10-bit static pattern with 766 grayscales at most and then is split into three 8-bit static patterns to synthesize a repeated video. While this repeated video, rather than the static pattern, is projected onto the measured object by strictly controlling CCD camera integral time to be an integral multiple of three video refresh cycles, the captured deformed patterns are of 766 grayscales and can provide much more detailed information in phase calculation than those with 256 grayscales. Experimental results demonstrate the feasibility and validity of the proposed method. Both the measuring precision and the repeatability of PMP are improved efficiently.

A flexible geometry for panoramic visual and optogenetic stimulation during behavior and physiology

BackgroundTo study visual processing, it is necessary to precisely control visual stimuli while recording neural and behavioral responses. It can be important to present stimuli over a broad area of the visual field, which can be technically difficult. New MethodWe present a simple geometry that can be used to display panoramic stimuli. A single digital light projector generates images that are reflected by mirrors onto flat screens that surround an animal. It can be used for behavioral and neurophysiological measurements, so virtually identical stimuli can be presented. Moreover, this geometry permits light from the projector to be used to activate optogenetic tools. ResultsUsing this geometry, we presented panoramic visual stimulation to Drosophila in three paradigms. We presented drifting contrast gratings while recording walking and turning speed. We used the same projector to activate optogenetic channels during visual stimulation. Finally, we used two-photon microscopy to record responses in direction-selective cells to drifting gratings. Comparison with Existing Method(s)Existing methods have typically required custom hardware or curved screens, while this method requires only flat back projection screens and a digital light projector. The projector generates images in real time and does not require pre-generated images. Finally, while many setups are large, this geometry occupies a 30 × 20 cm footprint with a 25 cm height. ConclusionsThis flexible geometry enables measurements of behavioral and neural responses to panoramic stimuli. This allows moderate throughput behavioral experiments with simultaneous optogenetic manipulation, with easy comparisons between behavior and neural activity using virtually identical stimuli.

Compressive optical steganography via single-pixel imaging.

A compressive optical steganography based on single-pixel imaging (SPI) is proposed. The SPI system, which employs a digital light projector to illuminate the host image with modulated patterns, is similar to a wireless broadcast system. Therefore, it is suitable for covert communication naturally. By leveraging the compressive sensing technique and a generalized phase retrieval algorithm, the secret message is sparse-sampled and then encoded into the illumination patterns, which are projected onto the host image in an SPI architecture. The resulting reflected light signals travel in the free space as a broadcast system, and the signals would be captured by the authorized receivers and the potential eavesdroppers. By implementing an inverse Fourier transform, a stegoimage will be received, which is almost the same as the host image. However, only the authorized receivers, who possess the secret key, could extract the desired data from the stegoimage and then reconstruct the secret message by using a convex optimization algorithm. Because the secret message is sparse-sampled before embedding, the imperceptibility is well preserved while the capacity also be kept in a high level. A series of simulation and experimental results verifies the validity and feasibility of the proposed method.

3D Face Profilometry Based on Galvanometer Scanner with Infrared Fringe Projection in High Speed

Structured light 3D shape metrology has become a very important technique and one of the hot research topics in 3D face recognition. However, it is still very challenging to use the digital light projector (DLP) in a 3D scanner and achieve high-speed, low-cost, small-size, and infrared-illuminated measurements. Instead of using a DLP, this paper proposes to use a galvanometer scanner to project phase-shifted fringes with a projection speed of infrared fringes up to 500 fps. Moreover, the measurement accuracy of multi-frequency (hierarchical) and multi-wavelength (heterodyne) temporal phase unwrapping approaches implemented in this system is analyzed. The measurement accuracy of the two methods is better than 0.2 mm. Comparisons are made between this method and the classical DLP approach. This method can achieve a similar accuracy and repeatability compared to the classical DLP method when a face mask is measured. The experiments on real human face indicate that this proposed method can improve the field of 3D scanning applications at a lower cost.

Comparison the fit of three-unit metal framework fabricated by wax milling method and digital light projection method

Comparison the fit of three-unit metal framework fabricated by wax milling method and digital light projection method

Dynamic Phase Measuring Profilometry Based on Tricolor Binary Fringe Encoding Combined Time-Division Multiplexing

A dynamic phase measuring profilometry (PMP) based on tricolor binary fringe combined time-division multiplexing principle is proposed. Only one tricolor binary fringe combined by red (R), green (G), and blue (B) binary fringes with the same fringe width but without any color overlapping one another is needed and sent into the flash memory of a high-speed digital light projector (HDLP) in advance. A specialized time-division multiplexing timing sequence is designed to control the HDLP to project the tricolor binary fringe saved in the flash memory onto the measured dynamic object separately and sequentially at 234 fps, at the same time, the projected light source mode is set as monochrome mode which means that all the RGB LEDs remain lighting. Meanwhile, it also triggers a high frame rate monochrome camera synchronized with the HDLP to capture the corresponding deformed patterns in R, G and B channels. By filtering, the nearly unbroken phase-shifting sinusoidal deformed patterns for three-step PMP can be extracted from the captured deformed patterns. It is equivalent to the three-dimensional (3D) shape reconstruction of the measured dynamic object at 78 fps. Experimental results verify the feasibility and the validity of the proposed method. It is effective for measuring the dynamic object and can avoid the color cross-talk effectively.

High Throughput Nanoliposome Formation Using 3D Printed Microfluidic Flow Focusing Chips

AbstractThe use of additive manufacturing to fabricate microfluidic devices capable of high throughout synthesis of nanoscale liposomes with tunable dimensions is demonstrated. Employing a high‐resolution 3D printing process based on stereolithography and digital light projection, microchannel geometries and printing parameters are optimized to enable reliable patterning of channel features with critical dimensions of 200 µm, supporting the production of lipid vesicles below 100 nm in diameter by microfluidic flow focusing. The additive manufacturing approach enables the fabrication of flow focusing microchannels with high aspect ratios, together with seamless fabrication of high‐pressure fluidic ports for world‐to‐chip interfacing, supporting large volumetric flow rates and high‐throughput nanoparticle synthesis, with demonstrated production rates for optimized liposomes as high as 4 mg min−1 from a single device.