Projection Stereolithography Research Articles

Hybrid additive manufacturing of 3D electronic systems

A novel hybrid additive manufacturing (AM) technology combining digital light projection (DLP) stereolithography (SL) with 3D micro-dispensing alongside conventional surface mount packaging is presented in this work. This technology overcomes the inherent limitations of individual AM processes and integrates seamlessly with conventional packaging processes to enable the deposition of multiple materials. This facilitates the creation of bespoke end-use products with complex 3D geometry and multi-layer embedded electronic systems. Through a combination of four-point probe measurement and non-contact focus variation microscopy, it was identified that there was no obvious adverse effect of DLP SL embedding process on the electrical conductivity of printed conductors. The resistivity maintained to be less than 4 × 10−4 Ω · cm before and after DLP SL embedding when cured at 100 °C for 1 h. The mechanical strength of SL specimens with thick polymerized layers was also identified through tensile testing. It was found that the polymerization thickness should be minimised (less than 2 mm) to maximise the bonding strength. As a demonstrator a polymer pyramid with embedded triple-layer 555 LED blinking circuitry was successfully fabricated to prove the technical viability.

Environmental Performance Evaluation of a Fast Mask Image Projection Stereolithography Process Through Time and Energy Modeling

The emergence of additive manufacturing (AM) has potential for dramatic changes in labor productivity and economic welfare. With the growth of AM, understanding of the sustainability performance of relevant technologies is required. Toward that goal, an environmental impact assessment (EIA) approach is undertaken to evaluate an AM process. A novel fast mask image projection stereolithography (MIP-SL) process is investigated for the production of six functional test parts. The materials, energy, and wastes are documented for parts fabricated using this process. The EIA is completed for human health, ecosystem diversity, and resource costs using the ReCiPe 2008 impact assessment method. It is noted that process energy, in the form of electricity, is the key contributor for all three damage types. The results are used to depict the underlying relationship between energy consumed and the environmental impact of the process. Thus, to facilitate prediction of process energy utilization, a mathematical model relating shape complexity and dimensional size of the part with respect to part build time and washing time is developed. The effectiveness of this model is validated using data from real-time process energy monitoring. This work quantifies the elemental influence of design features on AM process energy consumption and environmental impacts. While focused on the environmental performance of the fast MIP-SL process, the developed approach can be extended to evaluate other AM processes and can encompass a triple bottom line analysis approach for sustainable design by predicting environmental, economic, and social performance of products.

3D printed fluidic valves for remote operation via external magnetic field

This paper reports a novel 3D-printed fluidic valve which is fabricated by projection-stereolithography (PSL) in combination with insertion of functional elements such as permanent magnets. We first constructed a PSL setup which can fabricate complicated three dimensional structures via layer-by-layer photocuring. Then, 3D fluidic valves which could be remotely controlled were designed. After the working mechanisms of proposed fluidic valves were thoroughly analyzed, they were fabricated with outlet orifice diameters of 0.5, 1, and 2 mm. The main housing of the valve assembly was printed, then, three permanent magnets were inserted into the part and the valve fabrication was completed by combining the end cap with an orifice and sealing. The completed valve was integrated within a 20-Fr (6.7-mm in diameter) medical catheter for evaluation. The flow rate through the valve could be controlled by changing positions of the inserted permanent magnets with an external magnetic field. With the applied pressure of 10 kPa, the flow rate was measured to be 131.07 mL/min that is only 8.78% lower than the system without the valve (143.68 mL/min). The results obtained in this work would be beneficial to further development of efficient fluidic valves for complicated 3D fluidic systems.

A Tubular Biomaterial Construct Exhibiting a Negative Poisson's Ratio.

Developing functional small-diameter vascular grafts is an important objective in tissue engineering research. In this study, we address the problem of compliance mismatch by designing and developing a 3D tubular construct that has a negative Poisson’s ratio νxy (NPR). NPR constructs have the unique ability to expand transversely when pulled axially, thereby resulting in a highly-compliant tubular construct. In this work, we used projection stereolithography to 3D-print a planar NPR sheet composed of photosensitive poly(ethylene) glycol diacrylate biomaterial. We used a step-lithography exposure and a stitch process to scale up the projection printing process, and used the cut-missing rib unit design to develop a centimeter-scale NPR sheet, which was rolled up to form a tubular construct. The constructs had Poisson’s ratios of -0.6 ≤ νxy ≤ -0.1. The NPR construct also supports higher cellular adhesion than does the construct that has positive νxy. Our NPR design offers a significant advance in the development of highly-compliant vascular grafts.

Fabrication of conductive gelatin methacrylate–polyaniline hydrogels

Hydrogels with inherently conductive properties have been recently developed for tissue engineering applications, to serve as bioactive scaffolds to electrically stimulate cells and modulate their function. In this work, we have used interfacial polymerization of aniline monomers within gelatin methacrylate (GelMA) to develop a conductive hybrid composite. We demonstrate that as compared to pure GelMA, GelMA–polyaniline (GelMA–Pani) composite has similar swelling properties and compressive modulus, comparable cell adhesion and spreading responses, and superior electrical properties. Additionally, we demonstrate that GelMA–Pani composite can be printed in complex user-defined geometries using digital projection stereolithography, and will be useful in developing next-generation bioelectrical interfaces. Statement of SignificanceWe report the fabrication of a conductive hydrogel using naturally-derived gelatin methyacrylate (GelMA) and inherently conductive polyaniline (Pani). This work is significant, as GelMA-Pani composite has superior electrical properties as compared to pure Gelma, all the while maintaining biomimetic physical and biocompatible properties. Moreover, the ability to fabricate conductive-GelMA in complex user-defined micro-geometries, address the significant processing challenges associated with all inherently conductive polymers including Pani. The methodology described in this work can be extended to several conductive polymers and hydrogels, to develop new biocompatible electrically active interfaces.

Fabrication of Polymer Micro Needles for Transdermal Drug Delivery System Using DLP Based Projection Stereo-lithography

Fabrication of micro needles, which reduce pain during insertion and lessen tissue injury, has recently attracted great interest. Different manufacturing systems have been utilized for the advancement of micro needles such as two-photon photo polymerization, bulk lithography, droplet-borne air blowing and injection molding [1]. This paper proposes a micro fabrication process for polymer micro needles, using DLP based projection-based stereo lithography that is capable of fabricating micro-needles using biocompatible polymers. The fabrication in the experimental setup is performed with continuous movement of the platform in the vertical direction hence good surface quality is obtained. The influence of polymerization time, light intensity of DLP projector and chemical composition of the resins on the production speed and the geometrical accuracy of the micro needles have been studied. The length and the tip diameter of the micro needle are shown to be controlled through these factors. The length and tip diameter of the fabricated micro needles were observed using SEM and optical microscope and measured to be around 520μm and 40μm, respectively. The results indicate that polymer micro needles with appropriate geometry can be fabricated using this technique.

High-Resolution Projection Microstereolithography for Patterning of Neovasculature.

To gain a quantitative understanding of the way cells sense, process, and respond to dynamic environmental signals in real-time requires developing in vitro model systems that accurately replicate the 3D structure and function of native tissue. A high-resolution projection stereolithography apparatus (μSLA) capable of multimaterial and grayscale 3D patterning of cells and biomaterials at <5 μm resolution is presented. Murine cells (fibroblasts, myoblasts, endothelial, and bone marrow stromal cells) encapsulated within photosensitive hydrogels using the μSLA remain viable up to two weeks after fabrication. Harnessing the high-resolution fabrication capabilities of this machine, sub-millimeter scale angiogenic cell-encapsulating patches designed to promote targeted growth of neovasculature are printed, as assessed in vitro via enzyme-linked immunosorbent assay (ELISA) and in ovo via a chick chorioallantoic membrane assay (CAM). This application establishes the μSLA as an enabling technology that is widely adaptable to any application that requires high-resolution patterning of cells and cells signals. By providing an efficient and robust method of engineering microscale tissues with encapsulated cells, this apparatus has a range of applications including fundamental studies of extracellular matrix interactions, high throughput drug testing of physiologically relevant substitutes for native tissue, and programmable tissue engineering for applications in regenerative medicine.

전사방식 광조형 시스템의 해상도 최적화를 통한 출력물의 정밀도 향상

Article history: Projection stereolithography is an additive manufacturing method that uses beam projection to cure the photo-reactive resin used. The light source of a crosssection layer-form illuminates photo-curable resin for building a threedimensional (3D) model. This method has high accuracy and a fast molding speed because the processing unit is a face instead of a dot. This study describes a Scalable Projection Stereolithography 3D Printing System for improving the accuracy of the stereolithography. In a conventional projection 3D printer, when printing a small sized model, many pixels are not used in the projection or curing. The proposed system solves this problem through an optical adjustment, and keeps using the original image as possible as filling the whole projection area. The experimental verification shows that the proposed system can maintain the highest level of precision regardless of the output size.

LCD와 UV-LED 를 사용한 고성능, 저비용의 3D Printer 개발

3D Printing has a great advantage for its capabilities in manufacturing complicated structures in a reasonable manufacturing time, and thus is widely used in various fields. Due to the high cost of the equipment and material, a fairly acceptable equipment, the Projection Stereolithography Apparatus (PSLA), has been developed, using the projection pattern approach for the purpose of quick manufacturing. We evaluated its surface quality, as compared with that of other systems. The result is the development of a high-performance, low-cost 3D Printer and its operating software, using LCD and UV LED. Working materials for an optimal manufacturing are suggested in the research, along with some suggestions of basic approaches for enhancing the accuracy and quality of the manufactured structures.

3D printing antagonistic systems of artificial muscle using projection stereolithography

The detailed mechanical design of a digital mask projection stereolithgraphy system is described for the 3D printing of soft actuators. A commercially available, photopolymerizable elastomeric material is identified and characterized in its liquid and solid form using rheological and tensile testing. Its capabilities for use in directly printing high degree of freedom (DOF), soft actuators is assessed. An outcome is the ∼40% strain to failure of the printed elastomer structures. Using the resulting material properties, numerical simulations of pleated actuator architectures are analyzed to reduce stress concentration and increase actuation amplitudes. Antagonistic pairs of pleated actuators are then fabricated and tested for four-DOF, tentacle-like motion. These antagonistic pairs are shown to sweep through their full range of motion (∼180°) with a period of less than 70 ms.

Projection Stereolithographic Fabrication of Human Adipose Stem Cell-Incorporated Biodegradable Scaffolds for Cartilage Tissue Engineering.

The poor self-healing ability of cartilage necessitates the development of methods for cartilage regeneration. Scaffold construction with live stem cell incorporation and subsequent differentiation presents a promising route. Projection stereolithography (PSL) offers high resolution and processing speed as well as the ability to fabricate scaffolds that precisely fit the anatomy of cartilage defects using medical imaging as the design template. We report here the use of a visible-light-based PSL (VL-PSL) system to encapsulate human adipose-derived stem cells (hASCs) into a biodegradable polymer [poly-d,l-lactic acid/polyethylene glycol/poly-d,l-lactic acid (PDLLA-PEG)]/hyaluronic acid (HA) matrix to produce live cell constructs with customized architectures. After fabrication, hASCs showed high viability (84%) and were uniformly distributed throughout the constructs, which possessed high mechanical properties with a compressive modulus of 780 kPa. The hASC-seeded constructs were then cultured in control or TGF-β3-containing chondrogenic medium for up to 28 days. In chondrogenic medium-treated group (TGF-β3 group), hASCs maintained 77% viability and expressed chondrogenic genes Sox9, collagen type II, and aggrecan at 11, 232, and 2.29 × 105 fold increases, respectively compared to levels at day 0 in non-chondrogenic medium. The TGF-β3 group also produced a collagen type II and glycosaminoglycan-rich extracellular matrix, detected by immunohistochemistry, Alcian blue staining, and Safranin O staining suggesting robust chondrogenesis within the scaffold. Without chondroinductive addition (Control group), cell viability decreased with time (65% at 28 days) and showed poor cartilage matrix deposition. After 28 days, mechanical strength of the TGF-β3 group remained high at 240 kPa. Thus, the PSL and PDLLA-PEG/HA-based fabrication method using adult stem cells is a promising approach in producing mechanically competent engineered cartilage for joint cartilage resurfacing.

Combined 3D printing technologies and material for fabrication of tactile sensors

Recently, 3D printing technology has taken the spotlight internationally with the recognition of the importance of the manufacturing industry. Currently, there are many mature 3D printing processes and materials. However, an absence of fabrication capability of smart structures such as sensors and actuators remains. In this research, we present a hybrid manufacturing process including directprint/cure (DPC) and projection-based stereolithography, along with printable materials for stretchable tactile sensors. The suggested DPC system consists of a robotically controlled micro-dispensing head, and a light curing module combined with projection stereolithography (PSL) retrofitted from a commercial projector. The materials developed in this research are based on a photocurable and stretchable liquid resin filled with multi-walled carbon nanotubes (MWNTs); this polymer/nanocomposite exhibits the piezoresistive property used in tactile sensing. We also used another hybrid process to develop a tactile sensor using a commercial machine to build the sensor body while a dispensing system was used to create the sensing elements. We have characterized the fabricated sensors with several experiments to detect the locations where forces are applied to the surfaces of the sensors. It is concluded that the suggested processes and materials are promising in developing accurate and reliable stretchable tactile sensors.

Development of a 3D printer using scanning projection stereolithography

We have developed a system for the rapid fabrication of low cost 3D devices and systems in the laboratory with micro-scale features yet cm-scale objects. Our system is inspired by maskless lithography, where a digital micromirror device (DMD) is used to project patterns with resolution up to 10 µm onto a layer of photoresist. Large area objects can be fabricated by stitching projected images over a 5cm2 area. The addition of a z-stage allows multiple layers to be stacked to create 3D objects, removing the need for any developing or etching steps but at the same time leading to true 3D devices which are robust, configurable and scalable. We demonstrate the applications of the system by printing a range of micro-scale objects as well as a fully functioning microfluidic droplet device and test its integrity by pumping dye through the channels.

An analytical model for scanning-projection based stereolithography

There is a growing need for effective small scale production methods. Projection stereolithography (PSL) is a technological response to such a demand. In PSL, Experience shows a decrease in resolution as area of exposure increases. A relatively novel hybrid method, scanning-projection stereolithography (SPSL) is presented in this work. This method is based on previous work by a number of authors, utilizing a combination of scanning and projection to manufacture large parts with relatively high-resolution.A modelling method to investigate the total energy received by individual pixels on resin surface is considered for both PSL and SPSL. The modelling shows near identical energy distribution for both methods. The modelling results were attempted to verify experimentally. Four patterns with circular and rectangular features were exposed with both methods. The resulting cured layers were compared via microscopic observation and measurements. Sample measurements show SPSL has a slightly better resolution using an inherently non-uniform exposure system. In large area exposure, SPSL provided less stitching and overlap issue.

Advanced projection image generation algorithm for fabrication of a tissue scaffold using volumetric distance field

Advanced additive manufacture (AM) techniques have been developed to generate three-dimensional (3D) tissue scaffolds with complex topography and controlled internal pore architecture. Among the various AM methods, projection stereolithography (PSL) can be used to fabricate intricate 3D tissue scaffolds that can be engineered to mimic the microarchitecture of tissues. PSL system offers the advantages of enhanced fabrication speed and accuracy compared with conventional stereolithography system. To design and fabricate a complex 3D scaffold, we propose a new projection image generation algorithm that automatically and robustly generates 2D projection image data. The method uses the volumetric distance field (VDF) and triply periodic minimal surface (TPMS) pore morphology. By the creative combination of VDF and TPMS-based pore architecture, we can easily and rapidly generate projection image data for PSL system without using complicated 3D scaffold models. An effective Boolean operation based on VDF was utilized to improve the efficiency of geometrical manipulations required in the scaffold projection image generation. The design results demonstrated that the proposed algorithm can completely alleviate all the limitations and problems of the previous approaches mostly based on time-consuming and error-prone slicing process.

Controlling Penetration Depth in Projection Stereolithography by Adjusting the Operation Wavelength

In projection stereolithography, the cure depth and thereby the layer thickness in the manufacturing process may be varied by changing the operation wavelength. The change can be made even in the middle of the manufacturing process, which opens up possibilities for additional flexibility and speed-up of the process.In this paper, we investigate how the penetration depth of the curing light in the resin depends on the wavelength. The measurements were performed for wavelengths between 400 nm and 550 nm using a standard commercial resin. The penetration depth was found to almost double when moving from the short wavelengths to the long ones.

Cost-Effective Three-Dimensional Printing of Visibly Transparent Microchips within Minutes

One-step fabrication of transparent three-dimensional (3D) microfluidic to millifluidic devices was demonstrated using a commercial 3D printer costing $2300 with 500 mL of clear resin for $138. It employs dynamic mask projection stereolithography, allowing fast concept-to-chip time. The fully automated system allows fabrication of models of up to 43 mm × 27 mm × 180 mm (x × y × z) at printing speeds of 20 mm/h in height regardless of the design complexity. The minimal cross sectional area of 250 μm was achieved for monolithic microchannels and 200 μm for positive structures (templates for soft lithography). The colorless resin's good light transmittance (>60% transmission at wavelengths of >430 nm) allows for on-chip optical detection, while the electrically insulating material allows electrophoretic separations. To demonstrate its applicability in microfluidics, the printer was used for the fabrication of a micromixer, a gradient generator, a droplet extractor, and a device for isotachophoresis. The mixing and gradient formation units were incorporated into a device for analysis of nitrate in tap water with standard addition as a single run and multiple depth detection cells to provide an extended linear range.

20am2-E5 3次元光造形装置ナノスクライブによる蚊の口針を模擬したマイクロニードルの作製

20am2-E5 3次元光造形装置ナノスクライブによる蚊の口針を模擬したマイクロニードルの作製

Relative impact of uniaxial alignment vs. form-induced stress on differentiation of human adipose derived stem cells

ADSCs are a great cell source for tissue engineering and regenerative medicine. However, the development of methods to appropriately manipulate these cells in vitro remains a challenge. Here the proliferation and differentiation of ADSCs on microfabricated surfaces with varying geometries were investigated. To create the patterned substrates, a maskless biofabrication method was developed based on dynamic optical projection stereolithography. Proliferation and early differentiation of ADSCs were compared across three distinct multicellular patterns, namely stripes (ST), symmetric fork (SF), and asymmetric fork (AF). The ST pattern was designed for uniaxial cell alignment while the SF and AF pattern were designed with altered cell directionality to different extents. The SF and AF patterns generated similar levels of regional peak stress, which were both significantly higher than those within the ST pattern. No significant difference in ADSC proliferation was observed among the three patterns. In comparison to the ST pattern, higher peak stress levels of the SF and AF patterns were associated with up-regulation of the chondrogenic and osteogenic markers SOX9 and RUNX2. Interestingly, uniaxial cell alignment in the ST pattern seemed to increase the expression of SM22α and smooth muscle α-actin, suggesting an early smooth muscle lineage progression. These results indicate that geometric cues that promote uniaxial alignment might be more potent for myogenesis than those with increased peak stress. Overall, the use of these patterned geometric cues for modulating cell alignment and form-induced stress can serve as a powerful and versatile technique towards controlling differentiation in ADSCs.

LCD 와 가시광선 LED 기반의 광조형 시스템을 위한 수지의 경화 특성

Stereolithography can be classified into two main categories according to the cross-sectional shape: scanning type and projection type. Projection stereolithography has significant advantages when making a layer using a single patterned beam, and results in improved speed and accuracy. To implement relatively low-cost projection stereolithography, we developed a system using a commercially available resin, which cures on exposure to visible light. The optimum photoinitiator was investigated, as well as the mixing ratio. The viscosity, shrinkage, curing depth and tensile strength were evaluated through several experiments on fabricated three-dimensional structures, and thus an optimal resin selection system was developed.