Microstereolithography System Research Articles

Development of a compact micro-stereolithography (MSTL) system using a Blu-ray optical pickup unit

In this paper, a compact micro-stereolithography (MSTL) apparatus of tabletop size was designed and constructed using a Blu-ray optical pickup unit (OPU), which came from a commercial Blu-ray optical disk driver. This is the very first application of a Blu-ray OPU to a light source of a MSTL system. A three-axis stage was adopted to obtain 3D motions, and a simple optic system was added to extend the focal length of a Blu-ray OPU for avoiding the physical interference. A liquid photo-curable resin suitable for the system was recomposed by modifying previously reported one. Then, the fabrication characteristics were investigated by constructing single-line structures at varying parameters such as laser power, scan speed and aperture diameter. The cured depth and width of the single-line structures decreased as the irradiated energy, which is determined by laser power and scan speed, decreased. Interestingly, the result also showed that the aperture diameter can effectively control the aspect ratio of cured depth and width. The increase of aperture diameter brings about the decrease of cured depth and increase of cured width. Based on the results of single-line exposure experiment, various 3D micro-structures were successfully fabricated. From this study, it can be shown that the Blu-ray-based MSTL system and the resin are suitable for fabricating complicated 3D micro-structures with reproducibility.

Polymer microfabrication by scanning based microstereolithography: Optical design and material functionality

Several research groups have attempted to optimize photopolymerization parameters to increase the throughput of scanning based microstereolithography (MSL) systems through modified beam scanning techniques. Efforts in reducing the curing line width have been implemented through high numerical aperture (NA) optical setups. However, the intensity contour symmetry and the depth of field of focus have led to grossly non-vertical and non-uniform curing profiles. This work tries to review the photopolymerization process in a scanning based MSL system from the aspect of material functionality and optical design. The focus has been to exploit the rich potential of photoreactor scanning system in achieving desired fabrication modalities (minimum curing width, uniform depth profile, and vertical curing profile) even with a reduced NA optical setup and a single movable stage. The present study tries to manipulate to its advantage the effect of optimized lower [c] (photoinitiator (PI) concentration) in reducing the minimum curing width to ~10-20 μm even with a higher spot size (~21.36 μm) through a judiciously chosen "monomer-PI" system. Optimization on grounds of increasing E(max) (maximum laser exposure energy at surface) by optimizing the scan rate provides enough time for the monomer or resin to get cured across the entire resist thickness (surface to substrate ~10-100 μm), leading to uniform depth profiles along the entire scan lengths.

Bone regeneration using a microstereolithography-produced customized poly(propylene fumarate)/diethyl fumarate photopolymer 3D scaffold incorporating BMP-2 loaded PLGA microspheres

Bony defects have been three-dimensionally (3D) created in many clinical circumstances; however, many defects cannot be reconstructed because most of the current bony substitutes cannot provide the necessary exact 3D structure. Therefore, to overcome this limitation, a 3D scaffold with embedded growth factor-delivering microspheres was developed by solid free-form fabrication (SFF) technology using computer-aided design/manufacturing (CAD/CAM). In this study, BMP-2-loaded poly(DL-lactic-co-glycolic acid) (PLGA) microspheres were incorporated into a 3D scaffold that was fabricated using a microstereolithography (MSTL) system with a suspension of microspheres and a poly(propylene fumarate) (PPF)/diethyl fumarate (DEF) photopolymer. By measuring release profiles in vitro, we verified that the fabricated microsphere-containing 3D scaffold could gradually release growth factor. The effects of BMP-2 were also assessed in vitro by observing cell differentiation using MC3T3-E1 pre-osteoblasts. Finally, we confirmed that SFF scaffolds created by MSTL were superior to traditional scaffolds produced using a particulate leaching/gas foaming method. In addition, based on in vivo tests, the scaffolds that released BMP-2 promoted bone formation. Based on these results, we concluded that our 3D scaffold might be a useful tool for enhancing reconstruction quality in many complex bony defects that should be reconstructed using a customized 3D scaffold.

Investigation of UV Light Intensity Distribution of Integral Micro-Stereolithography System

The non-uniformity distribution of UV light intensity in the imaging plane of integral micro-Stereolithography (µSL) System will induces serious distortion of object in building process, and the building accuracy of the SL system can not be assured. To obtain uniformity distribution of UV light intensity, experimental investigations were performed to research the relationship of UV light intensity with position (x,y) in the imaging plane and gray-scale z of the pattern in the integral µSL System. Based on the experiment results, the model of UV light intensity was established with least squares method. According to the model, for a given point in the imaging plane of the µSL system, the UV light intensity can be changed with varying the gray-scale of the pattern. As a result, Uniformity UV light intensity distribution is obtained in the imaging plane, and the difference between maximum and minimum value of UV light intensity is 0.06µW/cm2. The uniformity UV light intensity distribution provides a foundation for building accurate microstructures with the µSL system.

Multi-material microstereolithography

We have previously described the development of a microstereolithography (µSL) system using a Digital Micromirror Device (DMD) for dynamic pattern generation and an ultraviolet (UV) lamp filtered at 365 nm for crosslinking a photoreactive polymer solution. The µSL system was designed with x–y resolution of approximately 2 µm and a vertical (z) resolution of approximately 1 µm (with practical build limitations on vertical resolution of approximately 30 µm due to limitations on controlling UV penetration in z). The developed µSL system is capable of producing real three-dimensional (3D) microstructures, which can be employed in applications such as microfluidics, tissue engineering, and various functional microsystems. Many benefits will potentially be derived from producing multiple material microstructures in µSL, and one particular application area of interest is in producing multi-material microscaffolds for tissue engineering. In the present work, a method for multi-material µSL fabrication was developed using a syringe pump system to add a material to a small, removable vat designed specifically for the multi-material µSL system. Multi-material fabrication was accomplished using a material changeover process that included manually removing the vat, draining the current material, rinsing the vat, returning the vat to the system, and finally dispensing a prescribed volume in the vat using the syringe pump. Layer thicknesses of approximately 30 µm were achieved using this process. To demonstrate this system, several multi-material microstructures were produced to highlight the capability of this promising technology for fabricating 3D functional, multi-material microstructures with spatial control over placement of both material and structure.

Research of Micro-Stereolithography System with Dynamic Pattern Generator

In order to fabricate micro/meso structures, a novel micro-stereolithography (SL) system with dynamic pattern generator using digital micro-mirror device (DMD) has been investigated. The micro-stereolithography system solidifies photo-sensitive resin with image mask generated by dynamic pattern generator. The micro-stereolithography system is made up of dynamic pattern generator, recoating system and control system. The dynamic pattern generator consists of parabolic concentrator, UV lamp, collimating lens, shutter, DMD and its control, lens and computer. UV light intensity distribution in the imaging plane is investigated. Uniformity UV light intensity distribution is obtained in the imaging plane with changing small area’s gray-scale, and the difference between maximum and minimum value of UV light intensity is 0.4µW/cm2. Small size parts with intricate microstructures have been fabricated with the novel SL system. Compared with laser scanning SL system, the advantage of the novel micro-SL system is that the new SL system can build small objects having micro-structures with low cost in shorter time. The novel micro-SL system provides a solution to the problem that has hampered the progress of SL process into high resolution with low cost.

Microwave Emission from Metal Photonic Crystals Fabricated by using Stereolithography

Micro-scale photonic crystals composed of pure copper for microwave emission control were fabricated by using micro-stereolithography system and sintering process. As a crystal structure, we designed diamond lattice structure with or without stretched lattice spacing. Diamond lattices exhibited common bandgap where electromagnetic wave can not propagate at any direction. Stretched lattices showed directional transmission property. Simulated and measured transmission properties of microwave propagating through the metal photonic crystals showed good agreements.

Terahertz wave behaviours in ceramic and metal structures fabricated by spatial joining of micro-stereolithography

We have newly developed micro-stereolithography system to realize freeform fabrication of micrometer order 3D metal structures. In this process, the photo-sensitive resin paste mixed with nanometer sized ceramic and metal particles was spread on a glass substrate with 10 μm in layer thickness by using a mechanical knife edge, and two-dimensional images of UV ray were exposed using DMD (Digital Micro-mirror Device) with 2 μm in part accuracy. Through the layer by layer stacking process, micrometer order three-dimensional objects were formed. Dense metal structures could be obtained by dewaxing and successive sintering of the formed objects. In our recent investigation, micro photonic crystals with lattice structures of alumina or pure copper were fabricated in order to control electromagnetic wave propagation in a terahertz (THz) frequency range. The micro photonic crystals with a diamond structure perfectly reflected the THz wave by Bragg diffraction

Fabrication of a hydroxyapatite scaffold for bone tissue regeneration using microstereolithography and molding technology

Recently, many groups have researched the reconstruction of bone tissue and the development of bone scaffolds using solid freeform fabrication technology. However, the capacity to produce three-dimensional hydroxyapatite (HA) scaffolds with a very accurate architecture is limited by difficulties in the manufacturing process. In this study, a HA scaffold with an accurate pore size of 300 ± 10 μm was fabricated using a microstereolithography (MSTL) system and molding technology. In addition, an agar-overlay test was performed to investigate the cytotoxicity of the fabricated scaffold.

Cure depth control for complex 3D microstructure fabrication in dynamic mask projection microstereolithography

PurposeThe paper's aim is to explore a method using light absorption for improving manufacturing of complex, three‐dimensional (3D) micro‐parts with a previously developed dynamic mask projection microstereolithography (MSL) system. A common issue with stereolithography systems and especially important in MSL is uncontrolled penetration of the ultraviolet light source into the photocrosslinkable resin when fabricating down‐facing surfaces. To accurately fabricate complex 3D parts with down‐facing surfaces, a chemical light absorber, Tinuvin 327™ was mixed in different concentrations into an acrylate‐based photocurable resin, and the solutions were tested for cure depths and successful micro‐part fabrication.Design/methodology/approachTinuvin 327 was selected as the light absorber based on its high absorption characteristics (∼0.4) at 365 nm (the filtered light wavelength used in the MSL system). Four concentrations of Tinuvin 327 in resin were used (0.00, 0.05, 0.10, and 0.15 percent (w/w)), and cure depth experiments were performed. To investigate the effects of different concentrations of Tinuvin 327 on complex 3D microstructure fabrication, several microstructures with overhanging features such as a fan and spring were fabricated.FindingsResults showed that higher concentrations of Tinuvin 327 reduced penetration depths and thus cure depths. For the resin with 0.15 percent (w/w) of the Tinuvin 327, a cure depth of ∼30 μm was achieved as compared to ∼200 μm without the light absorber. The four resin solutions were used to fabricate complex 3D microstructures, and different concentrations of Tinuvin 327 at a given irradiance and exposure energy were required for successful fabrication depending on the geometry of the micro‐part (concentrations of 0.05 and 0.1 percent (w/w) provided the most accurate builds for the fan and spring, respectively).Research limitations/implicationsAlthough two different concentrations of light absorber in solution were required to demonstrate successful fabrication for two different micro‐part geometries (a fan and spring), the experiments were performed using a single irradiance and exposure energy. A single solution with the light absorber could have possibly been used to fabricate these micro‐parts by varying irradiance and/or exposure energy, although the effects of varying these parameters on geometric accuracy, mechanical strength, overall manufacturing time, and other variables were not explored.Originality/valueThis work systematically investigated 3D microstructure fabrication using different concentrations of a light absorber in solution, and demonstrated that different light absorption characteristics were required for different down‐facing micro‐features.

Micro/Nano Three-Dimensional Fabrication Using Fine Particles Aggregation in Elastic Resin

A novel nano micro/nano fabrication process using functional nano particles is developped. Functional particle photsensitive resin is made by mixing functional micro and nanoparticles with photosensitive resin uniformly. Fundamental shape of micro parts are fabricated by using microstereolithography system: low temperature annealing procedure is applied to shrink the resin body of micro parts: during the annealing process, functional particles are moved and aggregated slowly in the elastic resin to inside via surface: functional particle are gathered on the surface of the micro parts. Micro 3D structure of functional particles are fabricated based on the proportional shrinkage of fundamental shape. In this report, we investigate the fabrication mechanism of 3D structures made of fine functional particles, and describe a fundamental experiment to form the micro electrode made of Ag nanoparticles.

Multiple fabrications of sacrificial layers to enhance the dimensional accuracy of microstructures in maskless projection microstereolithography

Microstereolithography (MSL) is a promising technology for producing fully three-dimensional microstructures with overhanging features and high-aspect ratios. In conventional stereolithography (SL), a layer thickness of ≈50–100 μm is obtained by using a recoater. However, a recoater cannot be used in MSL, where the layer thickness is typically ≈10 μm or less, since resin flow may break or distort the pre-fabricated layers. In most MSL systems, the resin surface (or layer thickness) is controlled by a free surface technique that employs resin gravity to refresh the resin surface over a given settling time. In addition, a sacrificial layer must be fabricated in MSL to create a flat initial surface and provide support, just as in SL. In this paper, the fabrication methodology and functionality of the sacrificial layer is investigated for microstereolithography microstructures fabricated using the free surface technique. Experimental data are presented that indicate the greater the number of sacrificial layers, the sharper the dimensional accuracy of the microstructures in the building direction. This is because multiple fabrications of the sacrificial layer affect the resin ‘wetting’ status on the substrate or pre-cured surfaces. Several microstructures were fabricated to verify the effect of multiple fabrications of the sacrificial layer on dimensional accuracy in the building direction.

Development of Three-Dimensional Alginate Encapsulated Chondrocyte Hybrid Scaffold Using Microstereolithography

Hydrogels are useful materials because of their chemical similarity to extracellular matrix and their ability to rapidly diffuse hydrophilic nutrients and metabolites. Using rapid prototyping methods, we fabricated freeform three-dimensional (3D) scaffolds with chondrocytes encapsulated in an alginate hydrogel. The 3D hybrid scaffold was developed as combination of two components, a trimethylene carbonate (TMC)/trimethylolpropane (TMP) framework and an alginate hydrogel within an encapsulation of chondrocytes. To develop 3D hybrid scaffolds, we employed a microstereolithography system. The biodegradable, photopolymerizable liquid prepolymer was prepared by the polymerization of TMC with TMP and subsequently end capped with an acrylate group. The meshed framework of scaffolds withstood mechanical loading effectively. The line depth and linewidth could be controlled by varying laser power, scan path, and scan speed. Results of cell culture indicate that the biomimetic nature of these encapsulated chondrocyte scaffolds effectively retain the phenotypic function of chondrocytes within the scaffold structure. The proposed 3D hybrid scaffolds can be used for cartilage regeneration.

Mass production of 3-D microstructures using projection microstereolithography

Microstereolithography (MSL) technology is derived from the conventional stereolithography process and can meet the demands for fabricating complex 3-D microstructures with high resolution. This technology can be divided into scanning and projection methods, which have different levels of precision and fabrication speeds. Scanning MSL fabricates very fine 3-D microstructures by controlling the position of the laser spot on the resin surface. Projection MSL quickly fabricates one layer with one exposure using a mask. In this paper, we propose a projection MSL system with uniform illumination and image formation based on optical design for fabricating microstructure arrays. This system can realize mass production of 3-D microstructures in the meso-range, which falls between micro-and macro-ranges, with a resolution of a few microns. Microstructure arrays were fabricated to verify the performance of the proposed system.

Development of a bone scaffold using HA nanopowder and micro-stereolithography technology

A novel approach to manufacturing biocompatible ceramic scaffolds for tissue engineering using a micro-stereolithography system is introduced. Micro-stereolithography is a new technology that enables the manufacture of three-dimensional (3D) microstructures with complex, accurate shapes within an error of a few microns. Tissue-engineering may be a potential alternative for treating patients with serious bone defects, and many techniques for designing and fabricating 3D scaffolds have been developed. Nevertheless, scaffold imperfections, such as random pore size and porosity, limit the development of optimum scaffolds. Therefore, scaffold production with a controllable pore size and a fully interconnected shape is needed. This paper introduces and describes a bone scaffold that applies micro-stereolithography to mold technology. The scaffold material used was hydroxyapatite (HA) nanopowder. In the near future, bone scaffolds made from HA should become effective therapy for bone defects.

Development of a scaffold fabrication system using an axiomatic approach

To generate complex cartilage/bone tissues, scaffolds must possess several structural features that are difficult to create using conventional scaffold design/fabrication technologies. Successful cartilage/bone regeneration depends on the ability to assemble chondrocytes/osteoblasts into three-dimensional (3D) scaffolds. Therefore, we developed a 3D scaffold fabrication system that applies the axiomatic approach to our microstereolithography system. The new system offers a reduced machine size by minimizing the optical components, and shows that the design matrix is decoupled. This analysis identified the key factors affecting microstructure fabrication and an improved scaffold fabrication system was constructed. The results demonstrate that precise, predesigned 3D structures can be fabricated. Using this 3D scaffold, cell adhesion behavior was observed. The use of 3D scaffolds might help determine key factors in the study of cell behavior in complex environments and could eventually lead to the optimal design of scaffolds for the regeneration of various tissues, such as cartilage and bone.

Design of microstereolithography system based on dynamic image projection for fabrication of three-dimensional microstructures

As demands for complex microstructures with high aspect ratios have increased, the existing methods, MEMS and LIGA, have had difficulties coping with the number of masks and fabricable heights. A microstereolithography technology can meet these demands because it has no need of masks and is capable of fabricating high aspect ratio microstructures. In this technology, 3D part is fabricated by stacking layers, 2D sections, which are sliced from STL file, and the Dynamic Image Projection process enables the resin surface to be cured by a dynamic image generated with DMD™ (Digital Micromirror Device) and one irradiation. In this paper, we address optical design process for implementing this microstereolithography system that takes the light path based on DMD operation and image-formation on the resin surface using an optical design program into consideration. To verify the performance of this implemented microstereolithography system, complex 3D microstructures with high aspect ratios were fabricated.

Development of micro-stereolithography technology using metal powder

Micro-stereolithography is a new technology that can be used to fabricate free-form 3D microstructures by dividing a desired shape into many slices of a given horizontal thickness, hardening each slice with a focused laser beam, and then stacking them together. However, a method of providing electrical conductivity in the final product has not yet been developed. Therefore, this study developed a new suspension consisting of a photopolymer and metal powder mix, to which dispersant was added to obtain laser light scattering and stabilizing effects. A layer-recoating device was also developed to flatten the highly viscous mixed suspension. 3D microstructures were then manufactured using the recoating and micro-stereolithography systems. The fabricated products were sintered to obtain the desired electrical conductivity. This new process for fabricating electrically conductive metal microstructures is expected to broaden the range of applications for micro-stereolithography technology.

A digital micro‐mirror device‐based system for the microfabrication of complex, spatially patterned tissue engineering scaffolds

Our ability to create precise, pre-designed, spatially patterned biochemical and physical microenvironments inside polymer scaffolds could provide a powerful tool in studying progenitor cell behavior and differentiation under biomimetic, three-dimensional (3D) culture conditions. We have developed a simple and fast, layer-by-layer microstereolithography system consisting of an ultra-violet light source, a digital micro-mirror masking device, and a conventional computer projector, that allows fabrication of complex internal features along with precise spatial distribution of biological factors inside a single scaffold. Photo-crosslinkable poly(ethylene glycol) diacrylates were used as the scaffold material, and murine bone marrow-derived cells were successfully encapsulated or seeded on fibronectin-functionalized scaffolds. Fluorescently-labeled polystyrene microparticles were used to show the capability of this system to create scaffolds with complex internal architectures and spatial patterns. We demonstrate that precisely controlled pore size and shapes can be easily fabricated using a simple, computer-aided process. Our results further indicate that multi-layered scaffolds with spatially distributed factors in the same layer or across different layers can be efficiently manufactured using this technique. These microfabricated scaffolds are conducive for osteogenic differentiation of marrow-derived stem cells, as indicated by efficient matrix mineralization.

Investigations on an electronic tongue with polymer microfluidic cell for liquid sensing andidentification

Design and experimental results of a surface acoustic wave (SAW) microsensorwith polymer microfluidic cell for the sensing and identification of liquids ispresented in this paper. This microsensor, which is a part of a smart tongue–nosesystem, uses a horizontally polarized SAW (SH-SAW) for the detectionand identification of liquids. The SH-SAW microsensors are fabricated on36°-rotatedY-cutX-propagating LiTaO3 (36YX.LT) substrate. This design consists of a dual-delay-line configuration in which one line isfree and other one is metallized and shielded. Polymer microfluidic cells weredesigned and fabricated on top of it using a microstereolithography system toavoid dielectric loading of the IDTs by liquid which leads to unwanted dielectricsensitivity to the sensor. Due to the high electromechanical coupling of the36YX.LT substrate, it could detect differences in electrical properties and hence distinguishdifferent liquids. It is clear from these results that the microsensor based on36YX.LT is an effective liquid identification system for the electronic tongue application.