Stereolithography Method Research Articles

Feasible Study for Multi-photon Stereolithography Method of Electro Conductive Polymer Actuator with Complex Shape

recently, a soft actuator was developed using an electro-conducting polymer and an ionic conducting polymer. Moreover, stereolithography that uses a femtosecond laser was researched as a method of multiphoton-sensitized polymerization. In this study, we tried a more stable and more rapid stereolithography method for fabricating an electro-conducting polymer using a protein material. From the results of this study, we found that the method was 10 times faster when an aqueous solid that included an electro-conducting polymer, a catalyst, and gelatine was used. In addition, it was stable in that the temperature of the aqueous solid was controlled at 10 degree. We built a 3D shape using the newly developed method.

Surface Roughness Model for Components Created by Stereolithography Method

Rapid prototyping (RP) can fabricate complex 3D physical models without geometric limitations. The surface of the RP processed components is excessively rough (called stair-step effect) and depends on several parameters such as thickness of layer, position on the platform, etc. This paper presents several surface roughness models and results of experimental research.

Micro Rubber Structures for Passive Walking

The final goal of this work is the development of functional rubber sheets with micro rubber structures such as friction free, adhesion, and impact adsorption rubbers, etc. We report a micro rubber structure that can successfully perform flexible passive walking with 3 V-shaped units consisting of 4 legs to achieve very low friction. We show how to miniaturize and integrate this structure to produce, by means of a micro rubber molding process using the stereo lithography method, a rubber sheet with 64 legs. The prototype is designed, fabricated, and tested. Under certain conditions, the 64-legged rubber sheet successfully realizes flexible passive walking down an incline.

Multimodality vascular imaging phantoms: A new material for the fabrication of realistic 3D vessel geometries

Multimodality vascular flow phantoms provide a way of testing the geometric accuracy of clinical scanners and optimizing acquisition protocols with easy reproducibility of experimental conditions. This article presents a stereolithography method combined with a lost-material casting technique that eliminates metal residues of cerrolow (a low temperature melting point metallic alloy) left within irregular vessel lumens after casting. These residues potentially cause image artifacts especially in magnetic resonance angiography or flow disturbance. Geometrical accuracies of constructed lumens with isomalt, the proposed material, ranged from 3.3% to 5.7% for vessel diameters of 1.8-7.9 mm, which are comparable to those of lumens constructed with cerrolow that had better accuracies varying from 1.1% to 4.1% (p<0.02). Examples of geometries mimicking diseased arteries such as an aorta with stenosed renal arteries and an iliac artery with multiple stenoses are presented. This sugar-based isomalt material, combined with phantom designs having fiducial markers visible in digital subtraction angiography, computed tomography angiography, magnetic resonance angiography, and ultrasound [Med. Phys. 31, 1424-1433 (2004)], makes easier the fabrication of complex realistic and accurate replicas of pathological vessels with lumen irregularities.

2P1-D06 マイクロラバー構造体による受動歩行 : 第2報;光造形プロセスによる集積化と小型化

The final goal of this work is the development of functional rubber sheets with micro rubber structure such as friction free, adhesion, and impact adsorption rubbers, etc. In the previous report, we reported a micro rubber structure realizing flexible passive walking with 3 v-shaped units consisting of 4 legs to achieve very low friction. In this second report, we show the miniaturization and integration of this structure to realize a rubber sheet with 64 legs by micro rubber molding process using stereo lithography method. The prototype is designed and fabricated, and tested. Under some conditions, the 64 legged rubber sheet realizes flexible passive walking on a sloping road successfully.

Experimental study of the bone behaviour of the human skull bone for the development of a physical head model

The first part of this work aims to develop an experimental protocol in order to identify the monolayer behaviour of the skull (cortical and spongy bones in the model are represented by a single homogeneous layer). Experimental tests on 20 skulls from unembalmed cadavers have been performed by the LAMIH and the CEESAR. Nineteen specimens were taken from each of the human skulls following a very precise cartography (five frontal, eight parietal, two temporal, one occipital, two on the coronal suture and one on the sagittal suture). Three hundred and eighty specimens were tested in three-point bending test. In the second part, a physical head model was developed. A reference model was realized by using stereolithography method. The main point was to find a resin whose characteristics are similar to human skull bone. Then, this prototype was validated by means of experimental tests similar to Nahum et al. (test in 6 m/s by means of a cylindrical impactor of 6-kg mass).

Study of Nano-Stereolithography Using Evanescent Light (2nd report)

Micro-fabrication technologies have recently developed dramatically and fabrication methods have become much-needed with which devices on the order of micrometer can be fabricated precisely. In particular, methods of fabricating MEMS and microscopic optical devices as typified by a photonic crystal are in huge demand. In this study, we propose a novel stereolithography method using evanescent light instead of propagating light to realize a 100-nanometer resolution. With this method, we intend to establish the nano-stereolithography with higher accuracy and flexibility. In the second report, we performed the fabrication of in-plane lattice structures, which is strongly required as diffraction grating, diffractive optics, photonic crystals, etc. Theoretical and experimental analyses suggest that the proposed stereolithography method using evanescent light has a potential to fabricate micro three-dimensional objects with a resolution of sub-micrometer.

Icosahedral quasicrystals for visible wavelengths by optical interference holography

Quasicrystals, realized in metal alloys, are a class of lattices exhibiting symmetries that fall outside the usual classification for periodic crystals. They do not have translational symmetry and yet the lattice points are well ordered. Furthermore, they exhibit higher rotational symmetry than periodic crystals. Because of the higher symmetry (more spherical), they are more optimal than periodic crystals in achieving complete photonic bandgaps in a new class of materials called photonic crystals in which the propagation of light in certain frequency ranges is forbidden. The potential of quasicrystals has been demonstrated in two dimensions for the infrared range and, recently, in three-dimensional icosahedral quasicrystals fabricated using a stereo lithography method for the microwave range and direct laser writing for the IR range. Here, we report the fabrication and optical characterization of icosahedral quasicrystals using a holographic lithography method for the visible range. The icosahedral pattern, generated using a novel 7-beam optical interference holography, is recorded on photoresists and holographic plates. Electron micrographs of the photoresist samples show clearly the symmetry of the icosahedral quasicrystals in the submicron range, while the holographic plate samples exhibit bandgaps in the angular-dependent transmission spectra in the visible range. Calculations of the bandgaps due to reflection planes inside the icosahedral quasicrystal show good agreement with the experimental results.

Study of Nano-Stereolithography Using Evanescent Light (1st report)

Micro-fabrication technologies have recently developed dramatically and fabrication methods have become much-needed with which devices on the order of micrometer can be fabricated precisely. In particular, methods of fabricating MEMS and microscopic optical devices as typified by a photonic crystal are in huge demand. In this study, we propose a novel stereolithography method using evanescent light instead of propagating light to realize a 100-nanometer resolution. With this method, we intend to establish the nano-stereolithography with higher accuracy and flexibility. In the first report, we carry out theoretical and experimental analyses to verify the feasibility of the method. The analyses show that evanescent light energy is sufficient for curing photosensitive resin and that it is possible to fabricate micro three-dimensional objects with a 100-nanometer resolution by laminating resin layers cured by evanescent light exposure.

Laser‐layered microfabrication of spatially patterned functionalized tissue‐engineering scaffolds

Understanding cell behavior inside complex, three-dimensional (3D) microenvironments with controlled spatiotemporal patterning of physical and biochemical factors would provide significant insights into the basic biology of organ development and tissue functions. One of the fundamental limitations in studying such behavior has been the inability to create patterned microenvironments within 3D scaffold structures. Here a simple, layer-by-layer stereolithography (SL) method that can precisely pattern ligands, extracellular-matrix (ECM) components, and growth factors, as well as controlled release particles inside a single scaffold, has been developed. The process also allows fabrication of predesigned internal architectures and porosities. Photocrosslinkable poly(ethylene glycol) dimethacrylate (PEGDMA) was used as the basic structural component of these microfabricated scaffolds. PEG acrylates, covalently modified with the cell adhesive peptide arginine-glycine-aspartic acid (RGD) or the ECM component heparan sulfate, was incorporated within the scaffolds to facilitate cell attachment and to allow spatial sequestration of heparan-binding growth factors. Fluorescently labeled polymer microparticles and basic fibroblast growth factor (FGF-2) were chosen to illustrate the capability of SL to spatiotemporally pattern scaffolds. The results demonstrate that a precise, predesigned distribution of single or multiple factors within a single 3D structure can be created, and specific internal architectures can be fabricated. Functionalization of these scaffolds with RGD is demonstrated, and heparan sulfate allows efficient cell attachment and spatial localization of growth factors. Such patterned scaffolds might provide effective systems to study cell behavior in complex microenvironments and could eventually lead to engineering of complex, hybrid tissue structures through predesigned, multilineage differentiation of a single stem-cell population.

DESIGN AND FABRICATION OF MICRO FLUID POWER SYSTEM BY STEREOLITHOGRAPHY

Neither high accumulation nor densification on micro mechatronics are so advanced comparing with semiconductor devices. Our research aims at the establishment of design and fabrication to perform miniaturization, high accumulation and high densification by integrating mechano-micro elements. In difficult assembly of these elements, a stereolithography method is used to form the entire micro fluid power systems in all-in-one design including actuators, pumps and valves. In this paper, prototype models based on a bourdon type and diaphragm type of micro fluid power devices are fabricated and experimentally investigated. Some problems regarding design and fabrication of micro fluid power systems are discussed.

New Materials and Methods for Hierarchically Structured Tissue Scaffolds

ABSTRACTThe overall goal of our work is to develop new methods and materials for the fabrication of hierarchically structured, three-dimensional (3D) tissue scaffolds. Conventional scaffolds commonly lack substantial mechanical strength, and there is difficulty in controlling porosity, pore distribution, and pore interconnectivity. Additionally, the chemical nature of these scaffolds is typically homogenous. The ability to chemically modify selected areas on a scaffold is one method to direct cell growth in deliberate patterns; which could aid in the engineering of complex, functioning tissues. The general aim of this work is to address these issues through the application of stereolithography (SL) to the fabrication of hierarchically structured scaffolds.In order to achieve this goal, photopolymerizable materials must be developed that are both compatible with cell growth and with SL processing. SL methods are designed to produce arbitrary control over the physical structure of the part. In addition to physical structure control, control over the local surface chemistry of the scaffold is also desired. This would permit the use of both physical and chemical cues to control cell behavior in a tissue engineering construct. Chemical control could be achieved in SL methods by using photopolymerizable materials that can also be selectively chemically modified during the SL part building process. This paper provides an update on our work directed at using combined photoradical initiated polymerization and photoacid generator based chemical modification of a polymeric scaffold via multi-wavelength SL to produce hierarchically structured scaffolds.

Part shrinkage anomilies from stereolithography injection mould tooling

The use of stereolithography (SL) tooling allows plastic parts to be produced by injection moulding in a very short time due to the speed of mould production. One of the supposed advantages of the process is that it provides a low volume of parts that are the same as parts that would be produced by the conventional hard tooling in a fraction of the time and cost. However, this work demonstrates different rates of polymer shrinkage are developed by parts produced by SL and conventional tooling methods. These revelations may counter the greatest advantages of the SL injection moulding tooling process as the parts do not replicate those that would be produced by conventional hard tooling. This work identifies the different shrinkage that occurs in mouldings produced by an SL mould as compared to those produced from an aluminium mould. The experiments utilise two very different types of polymers and two mould geometries, which are processed in the same manner so that the heat transfer characteristics of the moulds are isolated as the only experimental variable. The work demonstrates how the two mould materials exhibit very different rates of expansion due to the temperature profiles experienced during moulding. This expansion must be compensated for to establish the total amount of shrinkage incurred by moulded parts. The compensation is derived by a mathematical approach and by modelling using finite element analysis. Both techniques depend upon knowledge of the thermal conditions during moulding. Knowledge of these thermal conditions are obtained by real-time data acquisition and simulated by FEA modeling. The application of the findings provide knowledge of the complete shrinkage values relating to the mould material and polymer used which would enable the production of geometrically accurate parts.

A novel stereolithography technology with conventional UV light

Stereolithography (SL) is a kind of rapid prototyping technology which uses the laminate manufacturing to fabricate parts. With the development of RP, some new RP processes have boomed rapidly. Compact prototyping system (CPS) is a kind of novel stereolithography method which utilizes conventional UV light as the light source. After transmitting by optic fiber and focusing through lens set, the light is intensified and can be used to cure the photopolymer. Compared with the laser SL prototyping apparatus, this apparatus has unique characteristics on its driving system and light path system. Discusses the characteristics and corresponding consequences of the driving system and light path system, and analyzes the light energy distribution and the corresponding line shapes. Since each layer is constructed from a serial of lines, the scanning parameters, especially scanning speed and hatch gap, will influence the overall light intensity which determines the layer thickness, section shape and ultimately the prototyping accuracy. The driving system, due to the non‐uniform moving speeds, could cause the shape error of the lines. A light shutter, keeping the light only illuminating on resin surface within given curing areas, is employed to solve this deficiency.

Thermal-expansion and fracture toughness properties of parts made from liquid crystal stereolithography resins

Stereolithography is a layered manufacturing technique that uses a laser to selectively polymerize a thermosetting resin to form complex three-dimensional parts. This rapid prototyping technique has evolved over the years from a model maker to a rapid fabrication technique for soft-tooling and parts for in-service testing. With this evolution in applications has come increased demand for high-performance resins. Liquid crystal (LC) resins can be processed by stereolithography methods to provide parts with superior and in some cases unique properties compared with conventional resins. LC resins consist of rod-like molecules that can be aligned prior to cure resulting in anisotropic mechanical and physical properties. A magnet outside the resin vat can be used to control the molecular alignment. Alignment can be varied within a layer or from layer-to-layer to achieve desired properties much as is done with fiber reinforced plastics. Two properties that are important for many applications are toughness and thermal dimensional-stability. Initial studies showed that fracture toughness values of LC coupons were about twice that of isotropic coupons manufactured from the same resin. Also, we have demonstrated that the in-plane thermal expansion of LC parts can be minimized over a wide temperature range by rotating the molecular alignment 90° from one layer to the next.

Processing and characterising photo-sensitive polymer in the rapid prototyping process

Abstract The curability of an acrylic-based photo-polymer used in building rapid prototypes has been studied. Differential scanning calorimeter (DSC) was used to monitor the degree of curing after laser scanning. Rapid prototypes formed using the Stereolithography (SL) method have to undergo post-curing for increasing their strength and rigidity. This study attempts to reduce, if not eliminate, post-cure distortion by characterising curing behaviours. The curing characteristics of the photo-polymer at the micro-level were studied using Raman spectrum analysis. Specimens of single photo-polymer lines were created using a SL machine. Raman spectroscopy was used to quantify the curing percentage at different areas on the cross-section of these lines. Curing percentages before and after post-curing were also obtained from the experiments for analysis. The difference in the percentage of post curing gives an indication to the distortions faced. It was found that uncured and partially cured resins trapped within the photo-polymer resulted in in-homogeneity of curing in the specimens, causing shrinkage and distortion.

Curing characteristics of acrylic photopolymer used in stereolithography process

Rapid prototypes formed using stereolithography (SL) method have to undergo post‐curing to increase their strength and rigidity. This study attempts to reduce, if not eliminate, post‐cure distortion by characterising curing behaviours. Curing (both heat and UV initiated) characteristics of an acrylic‐based photopolymer under actual fabrication conditions were studied using Raman spectroscopy as well as differential scanning calorimetry (DSC) and differential scanning photo‐calorimetry (DSP). Specimens of single photopolymer lines were created using a SL machine. Raman spectroscopy was used to quantify the curing percentage at different areas on the cross‐section of these lines. Curing percentages before and after post‐curing were also obtained from the experiments. Difference in percentage of post‐curing gave an indication of the distortions faced. It was found that uncured and partially cured resins trapped within the photopolymer resulted in inhomogeneity of curing in the specimens causing shrinkage and distortion.

Development of Plane Irradiation Type Micro Stereolithography Equipment using Optical Fibers

The conventional stereolithography method has a weak point which is necessary to long time to fabricate because of exposing resin along the each point of the structure. New type micro stereolithography equipment, which is plane irradiation type micro stereolithography with optical fibers, has been developed in order to overcome this problem. The developed system consists of ultraviolet light source, shutters and five optical fibers in a line arrangement as a variable shape mask. The variable shape mask is enable to copy desired shape on the resin. This paper describes the design of the mask using simulation analysis of light power distribution from optical fiber and confirmation of availability of this equipment from curing experiments of resin. As a result of the curing experiment, the time required to fabricate a shape of star structure in the proposed method is two times as fast as the conventional method.

A New Method of Casting Human Respiratory Tract for Aerosol Deposition Study

A new method of casting the human respiratory tract was developed for aerosol deposition studies. Anatomical data of the tract were translated to three-dimensional CAD (Computer Aided Design) numerical data, and the stereo-lithography method using photo-curable resin was used for casting. The larynx region and tracheobronchial region with generation numbers from 0 to 8 (called BB in new ICRP 66 model) were modelled with slices of 0.178 mm thickness. Preliminary deposition measurements for the BB region cast model were made using monodisperse NaCl aerosols ranging from 0.008 to 0.3 µm in diameter. To date, experimental deposition data have been obtained at low respiratory flow rates below 10.1.min-1. Deposition efficiency increased with decreasing particle size and flow rate. Experimental deposition efficiencies were close to the theoretical deposition curve derived from a simple diffusion model for successive straight tubes.

Stereolithography in Resin by Using Laser-Irradiation through a Bubble.

In conventional stereolithography methods, the solidified photopolymer layers are stacked one by one in resin. As a result, these methods have such disadvantages as time consumption to recoat new resin layer and to remove the surface roughness caused by steps on the models. This paper proposes a new method of fabricating 3-D models in a resin. An air bubble is formed at the end of a pipe under the surface of the resin. A laser beam is introduced through the bubble so as to solidify the resin on the bubble surface. As the solidified parts have no mechanical interference with the pipe, it is free to move the exposing point in the 3-dimensional space. The resolution and sensitibity of the method were measured, and some objects were fabricated. Through these experiments, the possibility of making 3-D models without processes of lamination and recoating was demonstrated.