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A Passive particle dispersion control technique was investigated in which longitudinal vortices were injected into a developing coaxial swirling jet with sufficient annular swirl for flow recirculation to occur. Four vortex generators, separated by 90 degrees and placed along the outside of the annular nozzle, injected vorticity opposite in sign to the mean swirl, significantly altering the structure of the swirling jet. The injected vorticity competed with the mean swirl to reduce azimuthal particle flinging and to disrupt the development of the vortex rings in the outer shear layer. Axial flow visualization showed the formation of axial structures at the forcing frequency but considerable azimuthal asymmetry. Horizontal cross sections showed a four-lobed structure which persisted in the natural jet for at least eight inner jet diameters. The particle concentration field was measured using digital processing of pulsed laser sheet images. Outward radial particle dispersion reduced while inward dispersion toward the jet centerline increased indicating that the injected vorticity sufficiently reduced particle flinging by large-scale vortices.

Recent advances in the field of 3D printing have utilized embedded electronic interconnects in order to construct advanced electronic devices. This work builds on these advances in order to construct and characterize arbitrarily formed capacitive sensors using fine-pitch copper mesh and embedded copper wires. Three varieties of sensors were fabricated and tested, including a small area wire sensor (320μm width), a large area mesh sensor (2cm2), and a fully embedded demonstration model. In order to test and characterize these sensors in FDM materials, three distinct tests were explored. Specifically, the sensors were able to distinguish between three metallic materials and distinguish salt water from distilled water. These capacitive sensors have many potential sensing applications, such as biomedical sensing, human interface devices, material sensing, electronics characterization, and environmental sensing. As such, this work specifically examines optimum mesh/wire capacitive parameters as well as potential applications such as 3D printed integrated material sensing.

Measurements of the particle/fluid velocity correlation and the dissipation of turbulent kinetic energy by particles were made in the near field of an axisymmetric jet laden with either 55 or 86 μm diameter glass beads. A digital particle-image-velocimetry system was adapted to measure simultaneously the velocity of fine tracer particles and larger dispersed particles. The particle/fluid velocity correlation was measured directly using the simultaneous measurements and indirectly using separate phase-locked measurements in an acoustically-forced jet. The direct measurements produced correlation values which were too low and the indirect measurements were too high, so the two techniques bracketed the correlation. Surprisingly, the correlation increased with increasing particle time-constant because the mean velocity of the heavier particles was closer to the convection velocity of the vortex rings in the jet. The dissipation of fluid turbulent kinetic energy by the particles was calculated using the phase-locked velocity measurements along with phase-locked particle concentration measurements. The results showed that the extra dissipation is large near the jet centerline, but quite small in the shear layer where the production is large.

The microstructures and residual hardnesses for solid components of 2-phase TiAl (Ti-48Al-2Nb-2Cr in a / o ) and Inconel 625 (Ni-19Cr-9Mo-4Nb in w / o ) fabricated by electron beam melting (EBM) were compared with a 10:1 blend of TiAl: alloy 625 pre-alloyed powders producing a complex alloy having the composition 48Ti-24Al-9Ni-8Nb-4.5Cr-4Ni (in w / o ). The blended alloy hardness (HV) reached 7.5 GPa in contrast to 1.4 GPa for the Alloy 625 and 4.0 for the 2-phase TiAl alloy. Reticulated mesh samples and stochastic foam samples prepared from the blended alloy by EBM exhibited a relative stiffness versus relative density plotted on a log-log basis consistent with other reference alloys fitted to a straight line with a slope n = 2 for ideal open cellular materials.

Ti-6Al-4V alloy with two kinds of open cellular structures of stochastic foam and reticulated mesh was fabricated by additive manufacturing (AM) using electron beam melting (EBM), and microstructure and mechanical properties of these samples with high porosity in the range of 62%∼92% were investigated. Optical observations found that the cell struts and ligaments consist of primary α' martensite. These cellular structures have comparable compressive strength (4∼113 MPa) and elastic modulus (0.2∼6.3 GPa) to those of trabecular and cortical bone. The regular mesh structures exhibit higher specific strength than other reported metallic foams under the condition of identical specific stiffness. During the compression, these EBM samples have a brittle response and undergo catastrophic failure after forming crush band at their peak loading. These bands have identical angle of ∼45° with compression axis for the regular reticulated meshes and such failure phenomenon was explained by considering the cell structure. Relative strength and density follow a linear relation as described by the well-known Gibson-Ashby model but its exponential factor is ∼2.2, which is relative higher than the idea value of 1.5 derived from the model.

This project enabled the integration of ultrasonic consolidation, direct write dispensing, and material deposition technologies into a manufacturing workcell capable of fabricating advanced, integrated Naval-relevant structures. The workcell was shown to be capable of spatial composition control and complex internal geometries - including embedded electronics, thermal management, reinforcement fibers and other features - along with the resolution, scalability, repeatability, dimensional accuracy and surface finish of milling, all within an integrated Direct Digital Manufacturing (DDM) workcell. A one-year extension led to the development of a computational modeling infrastructure for ultrasonic consolidation that has revolutionized the prediction of the effects of process parameter variations on bonding, microstructure and mechanical properties of parts made using ultrasonic consolidation.

The layer-by-layer building of monolithic, 3D metal components from selectively melted powder layers using laser or electron beams is a novel form of 3D printing or additive manufacturing. Microstructures created in these 3D products can involve novel, directional solidification structures which can include crystallographically oriented grains containing columnar arrays of precipitates characteristic of a microstructural architecture. These microstructural architectures are advantageously rendered in 3D image constructions involving light optical microscopy and scanning and transmission electron microscopy observations. Microstructural evolution can also be effectively examined through 3D image sequences which, along with x-ray diffraction (XRD) analysis in the x-y and x-z planes, can effectively characterize related crystallographic/texture variances. This paper compares 3D microstructural architectures in Co-base and Ni-base superalloys, columnar martensitic grain structures in 17–4 PH alloy, and columnar copper oxides and dislocation arrays in copper.

An experimental study was undertaken to determine the effect of an annular jet on the near-field vortex structure and dynamics of an incompressible axisymmetric jet issuing into a quiescent ambient fluid. The effect of varying the velocity ratio between the two streams was investigated for a single nozzle exit area ratio, a single core flow Reynolds number, and uniform density. A thin laser sheet was used to illuminate the flow for instantaneous photographs of natural and axially excited flow. Natural jet evolution results indicated the initial vortex development in the shear lagers occurred independently, but the large-scale structures in the outer layer ultimately controlled the core flow

Conductive inks are key enablers for the use of printing techniques in the fabrication of electronic systems. Focus on the understanding of aspects controlling the electrical performance of conductive ink is paramount. A comparison was made between microparticle Ag inks and an Ag nanoparticle ink. The microstructures resulting from thermal cure processes were characterized morphologically and also in terms of their effect on the resistivity of printed traces. For microparticle inks, the variability of resistivity measurements between samples as defined by coefficient of variation (CV) was greater than 0.1 when the resistivity was 10 to 50 times that of bulk Ag. When the resistivity was lower (~1.4 times that of bulk Ag) the CV of sample sets was less than 0.1. In the case of the nanoparticle ink, resistivity was found to decrease by a factor ranging from 1.2 to 1.5 after doubling the amount of layers printed prior to curing though it was expected to remain the same. Increasing the amount of layers printed also enhanced the sintering process.

The purpose of this study is to validate numerical simulations of flow and pressure in an abdominal aortic aneurysm (AAA) using phase-contrast magnetic resonance imaging (PCMRI) and an in vitro phantom under physiological flow and pressure conditions. We constructed a two-outlet physical flow phantom based on patient imaging data of an AAA and developed a physical Windkessel model to use as outlet boundary conditions. We then acquired PCMRI data in the phantom while it operated under conditions mimicking a resting and a light exercise physiological state. Next, we performed in silico numerical simulations and compared experimentally measured velocities, flows, and pressures in the in vitro phantom to those computed in the in silico simulations. There was a high degree of agreement in all of the pressure and flow waveform shapes and magnitudes between the experimental measurements and simulated results. The average pressures and flow split difference between experiment and simulation were all within 2%. Velocity patterns showed good agreement between experimental measurements and simulated results, especially in the case of whole-cycle averaged comparisons. We demonstrated methods to perform in vitro phantom experiments with physiological flows and pressures, showing good agreement between numerically simulated and experimentally measured velocity fields and pressure waveforms in a complex patient-specific AAA geometry.

In recent years, additive manufacturing (AM) or rapid prototyping (RP) technologies, initially developed to create prototypes prior to production for the automotive, aerospace, and other industries, have found applications in tissue engineering (TE) and their use is growing rapidly. RP technologies are increasingly demonstrating the potential for fabricating biocompatible 3D structures with precise control of the micro- and macro-scale characteristics. Several comprehensive reviews on the use of RP technologies, also known as solid freeform fabrication, Additive Manufacturing, direct digital manufacturing, and other names, have been published recently [1–4].

A manufacturing process for fabricating off-the-shelf multilumen poly(ethylene glycol) (PEG)-based nerve guidance conduits (NGCs) was developed that included the use of stereolithography (SL). A rapid fabrication strategy for complex 3D scaffolds incorporated postprocessing with lyophilization and sterilization to preserve the scaffold, creating an implantable product with improved suturability. SL is easily adaptable to changes in scaffold design, is compatible with various materials and cells, and can be expanded for mass manufacture. The fabricated conduits were characterized using optical and scanning electron microscopy, and measurements of swelling ratio, dimensional swelling factor, resistance to compression, and coefficient of friction were performed. Water absorption curves showed that the conduits after lyophilization and sterilization return easily and rapidly to a swollen state when placed in an aqueous solution, successfully maintaining their original overall structure as required for implantation. Postprocessed conduits at the swollen state were less slippery and therefore easier to handle than those without postprocessing. Suture pullout experiments showed that NGCs fabricated with a higher concentration of PEG were better able to resist suture pullout. NGCs having a multilumen design demonstrated a better resistance to compression than a single-lumen design with an equivalent surface area, as well as a greater force required to collapse the design. Conduits fabricated with a higher PEG concentration were shown to have compressive resistances comparable to those of commercially available NGCs. The use of SL with PEG and the manufacturing process developed here shows promise for improving the current state of the art in peripheral nerve repair strategies.

Microstereolithography (microSL) technology can fabricate complex, three-dimensional (3D) microstructures, although microSL has difficulty producing macrostructures with micro-scale features. There are potentially many applications where 3D micro-features can benefit the overall function of the macrostructure. One such application involves a medical device called a coaxial phacoemulsifier where the tip of the phacoemulsifier is inserted into the eye through a relatively small incision and used to break the lens apart while removing the lens pieces and associated fluid from the eye through a small tube. In order to maintain the eye at a constant pressure, the phacoemulsifier also includes an irrigation solution that is injected into the eye during the procedure through a coaxial sleeve. It has been reported, however, that the impinging flow from the irrigation solution on the corneal endothelial cells in the inner eye can damage these cells during the procedure. As a result, a method for reducing the impinging flow velocities and the resulting shear stresses on the endothelial cells during this procedure was explored, including the design and development of a complex, 3D micro-vane within the sleeve. The micro-vane introduces swirl into the irrigation solution, producing a flow with rapidly dissipating flow velocities. Fabrication of the sleeve and fitting could not be accomplished using microSL alone, and thus, a two-part design was accomplished where a sleeve with the micro-vane was fabricated with microSL and a threaded fitting used to attach the sleeve to the phacoemulsifier was fabricated using an Objet Eden 333 rapid prototyping machine. The new combined device was tested within a water container using particle image velocimetry, and the results showed successful swirling flow with an ejection of the irrigation fluid through the micro-vane in three different radial directions corresponding to the three micro-vanes. As expected, the sleeve produced a swirling flow with rapidly dissipating streamwise flow velocities where the maximum measured streamwise flow velocities using the micro-vane were lower than those without the micro-vane by 2 mm from the tip where they remained at approximately 70% of those produced by the conventional sleeve as the flow continued to develop. It is believed that this new device will reduce damage to endothelial cells during cataract surgery and significantly improve patient outcomes from this procedure. This unique application demonstrates the utility of combining microSL with a macro rapid prototyping technology for fabricating a real macro-scale device with functional, 3D micro-scale features that would be difficult and costly to fabricate using alternative manufacturing methods.

Numerical methods have become a powerful tool to quantify hemodynamic forces in the cardiovascular system. Studying these forces enables us to understand cardiovascular disease mechanisms, as well as better evaluate and design cardiovascular medical devices. However, much work remains to validate numerical methods against experimental data. Vignon-Clementel and colleagues have shown that the boundary conditions (BCs) prescribed at the outlets of numerical domains dramatically influence the flow and pressure computational results [1]. While many in-vitro studies have implemented simple BCs to allow for acceptable validations of numerical methods, none has implemented BCs that provide physiologically realistic flows and pressures.Copyright © 2010 by ASME

In this paper, we examine prospects for the manufacture of patient-specific biomedical implants replacing hard tissues (bone), particularly knee and hip stems and large bone (femoral) intramedullary rods, using additive manufacturing (AM) by electron beam melting (EBM). Of particular interest is the fabrication of complex functional (biocompatible) mesh arrays. Mesh elements or unit cells can be divided into different regions in order to use different cell designs in different areas of the component to produce various or continually varying (functionally graded) mesh densities. Numerous design elements have been used to fabricate prototypes by AM using EBM of Ti-6Al-4V powders, where the densities have been compared with the elastic (Young) moduli determined by resonant frequency and damping analysis. Density optimization at the bone–implant interface can allow for bone ingrowth and cementless implant components. Computerized tomography (CT) scans of metal (aluminium alloy) foam have also allowed for the building of Ti-6Al-4V foams by embedding the digital-layered scans in computer-aided design or software models for EBM. Variations in mesh complexity and especially strut (or truss) dimensions alter the cooling and solidification rate, which alters the α -phase (hexagonal close-packed) microstructure by creating mixtures of α / α ′ (martensite) observed by optical and electron metallography. Microindentation hardness measurements are characteristic of these microstructures and microstructure mixtures ( α / α ′) and sizes.

The development of the Digital Micromirror Device (DMD) by Texas Instruments has made a significant breakthrough in 3D micro-manufacturing, and in particular, in the area of additive layer-based manufacturing. One area of particular interest for using DMD technology is microstereolithography; a technology that builds 3D shapes through successive photopolymerization of individual thin 2D layers that are stacked vertically. A DMD-based projection microstereolithography system and a robust micro-manufacturing process have been developed. This system and various micro-fabricated 3D structures with features on the order of 10 microns, including recent advancements in multimaterial micro-fabrication, will be presented and described.

PurposeTo operate a multiple material stereolithography (MMSL) system, a material build schedule is required. The purpose of this paper is to describe a scheduling and process‐planning software system developed for MMSL and designed to minimize the number of material changeovers by using low‐viscosity resins that do not require sweeping.Design/methodology/approachThis paper employs the concept of using low‐viscosity resins that do not require sweeping to minimize the number of material changeovers required in MMSL fabrication. A scheduling and process‐planning software system specific to MMSL is introduced that implements four simple rules. Two rules are used to select the material to be built in the current layer, and two rules are used to determine at which layer a material changeover is required. The schedule for the material to be built depends on the material properties stored in a user‐defined materials library. The developed algorithm produces sliced loop data for each material using the predetermined layer thickness from an input CAD model, and the four rules are applied at each layer. The algorithm then determines the build order for each material, the material‐specific number of layers to be built, and whether or not sweeping is required. Output data from the program are the scheduling and process‐planning report and the partitioned computer‐aided design models to be built before changing a material according to the process planning. Two examples of the algorithm applied to multiple material parts are provided.FindingsThe MMSL scheduling and process‐planning software system is developed using Microsoft Visual C++7.0. For verification, a simple demonstration is conducted on a two material part where the process plan could be easily determined through intuition. A more complex multiple material part is also tested that consisted of four subparts. Several cases of resin assignment are tested showing that the ultimate scheduling and process planning vary significantly depending on the material combinations and specifications. These examples demonstrate that the strategy, method, and software developed in this paper can be successfully applied to prepare for MMSL fabrication.Research limitations/implicationsAlthough the software system is demonstrated on two multiple material parts, more extensive work will be performed in the future on fabricating multiple material parts using the MMSL machine. It is expected that additional rules will be developed as additional limitations of MMSL are identified. It is also anticipated that particular emphasis will be placed on building without sweeping as well as development of advanced non‐contact recoating processes.Originality/valueAs designs incorporating multiple materials increase in the future and additive manufacturing (AM) technologies advance in both building out of multiple materials and fabricating production parts, the scheduling and process‐planning concepts presented here can be applied to virtually any AM technology.

Next generation electronics will be painted onto plastic substrates providing both functionality and physical flexibility. The corresponding manufacturing process will lead to significantly reduced cost; however the performance of the resulting circuits will not match many existing high-performance electronic circuits fabricated with traditional technology today. High performance is not always necessary, but when required, Printed Electronics may still be a viable solution. The future of Printed Electronics is bright and will eventually include sophisticated function, but until that time, a Printed Hybrid option will simultaneously provide the cost savings of printing and the high performance of silicon and printed circuit boards. An interim contribution is to use state-of-the-art silicon devices and print the supporting conductive patterns and passives on substrates for flexible systems integration. This paper describes and demonstrates a hybrid circuit technology, which can manufacture circuits more easily adapted to complex shapes and diverse sizes. Additionally, a number of printed components and devices are reviewed and a demonstration of two circuits is provided: an RF antenna and the supporting substrate design of a Field Programmable Gate Array.

Porous coatings, notably thin, porous bead coatings, sintered mesh arrays, thermal-spray coatings and metallic foams have been incorporated into biomedical devices and appliances for several decades to improve bone compatibility, stability, and bone ingrowth. In this research program, we are concerned with the fabrication of reticulated mesh arrays as integral components of monolithic products using Ti-6Al-4V powder to build complex, 3D structures by electron beam melting (EBM). Utilizing software capable of building lattice-truss or cellular lattices with high symmetry, 3D-periodic reticulated arrangements such as hip stem and knee component prototypes have been fabricated with complete mesh arrays or with solid stems with a surrounding mesh structure completely fabricated as a monolithic product. The 3D mesh structures begin with so-called lattice elements which can be designed, computed, and attached to a CAD program for additive layered manufacturing by EBM. Mesh arrays with cortical bone density (1.9 g/cm3) can be fabricated with various lattice-truss structures and truss dimensions tailored to stress-strain and stiffness properties to optimize porous bone-replacement implants, including craniofacial replacements, etc. Mesh-to-mesh structures and functionally graded structures are also explored. Metallographic analysis of these structures using optical and electron microscopies illustrate their microstructural characteristics in association with measured mechanical properties such as microindentation hardness which can be related linearly to residual stress.

A procedure for manufacturing cardiovascular system models using patient-specific data, rapid prototyping, and a multistep dip-spin coating process is presented here. Improvements to a previously developed process permitted the fabrication of flexible complex vascular replicas. The primary improvement included the development of a two-axis rotation mechanism that enabled a pseudorandom rotation of the coated mold in space, providing uniform coats. Other improvements included the use of a low viscosity (1500–2000cP) silicone solution that allowed for complete coverage of the mold, and developing a procedure for fixing defects. The dip-spin coating procedure was shown to be effective for the manufacture of compliant cardiovascular membranes, such as an arterial bypass graft with an internal flow passage and an abdominal aorta with nonuniform radial geometry, tapered diameters, bifurcations, and small branches. Results from a design of experiments comparing two dipping setups demonstrated that horizontally dipping the model produced coatings with more uniform thicknesses along the length of the model when compared to vertical dipping. For a 250-mm-long model, the difference in thickness between the top and bottom of the membrane was 0.42±0.069mm and 0.09±0.077mm for vertical and horizontal dippings, respectively. Mold diameter also affected the thickness of the membrane, with membrane thickness increasing as mold diameter decreased. Thickness data comparing locations at approximately the same height of the mold but with different diameters showed thicknesses of 2.54±0.198mm and 1.95±0.140mm for 7.85mm and 15.20mm diameters, respectively. Moreover, the differences in thickness between these locations were 0.60±0.128mm and 0.58±0.231mm for vertical and horizontal dippings, respectively; thus, membrane thickness variations occurred with mold diameter irrespective of the dipping setup. Depending on the prescribed tolerance for membrane thickness, the vertical dipping setup may be recommended for use because (1) it was easier to use since only the mold was immersed in the coating solution and no special protection of the dipping mechanism was required and (2) it produced fewer defects in the coatings since the solution always dripped from downfacing surfaces of the mold. Using this dip-spin coating procedure, patient-specific cardiovascular membranes can be manufactured and used in the development of medical devices, research requiring accurate anatomical models, and education and training.

The microstructure and mechanical behavior of simple product geometries produced by layered manufacturing using the electron beam melting (EBM) process and the selective laser melting (SLM) process are compared with those characteristic of conventional wrought and cast products of Ti-6Al-4V. Microstructures are characterized utilizing optical metallography (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and included alpha (hcp), beta (bcc) and alpha(') (hcp) martensite phase regimes which give rise to hardness variations ranging from HRC 37 to 57 and tensile strengths ranging from 0.9 to 1.45 GPa. The advantages and disadvantages of layered manufacturing utilizing initial powders in custom building of biomedical components by EBM and SLM in contrast to conventional manufacturing from Ti-6Al-4V wrought bar stock are discussed.

Pedicle screw insertion is an orthopaedic spinal fixation procedure involving the placement of screws through individual spine pedicles and secured in spinal vertebrae. Pedicle anatomy varies widely within and across the patient population, and many complications have been reported with the surgical technique. To reduce complications, an automated procedure was developed that utilizes patient-specific medical imaging data to predetermine optimum pedicle screw size, length, and trajectory. The procedure involves importing medical imaging scans into the software, creating uniform voxel data for algorithm simplicity, segmenting the bony anatomy of the spine and defining its boundary, and identifying the pedicle using a search algorithm. The operations are performed in two-dimensions in the coordinate system of the medical imaging data. For each image slice, the minimum pedicle width is identified, and examining all slices identifies the overall minimum pedicle width. The optimum trajectory is determined using a 3D linear least squares fit to the array of minimum pedicle width midpoints. With the optimum trajectory determined, the maximum screw size and length are determined.

Drug-loaded microneedle arrays for transdermal delivery of a chemotherapeutic drug were fabricated using multi-material microstereolithography (μSL). These arrays consisted of twenty-five poly(propylene fumarate) (PPF) microneedles, which were precisely orientated on the same polymeric substrate. To control the viscosity and improve the mechanical properties of the PPF, diethyl fumarate (DEF) was mixed with the polymer. Dacarbazine, which is widely used for skin cancer, was uniformly blended into the PPF/DEF solution prior to crosslinking. Each microneedle has a cylindrical base with a height of 700 μm and a conical tip with a height of 300 μm. Compression test results and characterization of the elastic moduli of the PPF/DEF (50:50) and PPF/drug mixtures indicated that the failure force was much larger than the theoretical skin insertion force. The release kinetics showed that dacarbazine can be released at a controlled rate for five weeks. The results demonstrated that the PPF-based drug-loaded microneedles are a potential method to treat skin carcinomas. In addition, μSL is an attractive manufacturing technique for biomedical applications, especially for micron-scale manufacturing.

Quality assurance is an important topic for additive manufacturing (AM) and often seen as a requirement for the transition and adoption of the technology toward fabrication of end use applications. As AM technologies are used for production, it is necessary to ensure high quality, repeatable, and reproducible components are manufactured. Various nondestructive examination techniques have been used to evaluate AM-fabricated parts to determine part quality post-fabrication (e.g. scanning and/or microstructural characterization). In situ monitoring methods have been developed for AM technologies to enable defect detection and have potential to be used for in situ monitoring and correction of fabrication anomalies (e.g. undesired temperature gradients and porosity). In this research, defects (e.g. pores) were seeded into parts fabricated using the powder bed fusion AM process, electron beam melting, and monitored using in situ infrared (IR) thermography. Results from layerwise thermography were compared with results obtained using computer tomography (CT) scanning techniques. Although the measured geometry of the seeded defects between IR thermography and CT was substantially different (area difference of ~60%), the thermographs did provide a good indication of defects present within a fabricated part. Furthermore, defect correction methods were evaluated including post-processing methods such as hot isostatic pressing as well as in situ correction methods such as layer re-melting. Re-melting a porous layer successfully corrected defects and demonstrates a potential method for in situ defect correction if implemented in future systems equipped with automatic feedback control of powder bed fusion processes.

This paper describes improvements that enable engineers to create three-dimensional MEMS in a variety of materials. It also provides a means for selectively adding three-dimensional, high aspect ratio features to pre-existing PMMA micro molds for subsequent LIGA processing. This complimentary method involves in situ construction of three-dimensional micro molds in a stand-alone configuration or directly adjacent to features formed by x-ray lithography. Three-dimensional micro molds are created by micro stereolithography (MSL), an additive rapid prototyping technology. Alternatively, three-dimensional features may be added by direct femtosecond laser micro machining. Parameters for optimal femtosecond laser micro machining of PMMA at 800 nanometers are presented. The technical discussion also includes strategies for enhancements in the context of material selection and post-process surface finish. This approach may lead to practical, cost-effective 3-D MEMS with the surface finish and throughput advantages of x-ray lithography. Accurate three-dimensional metal microstructures are demonstrated. Challenges remain in process planning for micro stereolithography and development of buried features following femtosecond laser micro machining.

The use of modern microstreolithography (MSL) technology gives optics developers the freedom to integrate mounting and positioning structures directly into an optical mask structure. We have created Hadamard spectrometer masks with increments of 150 μm and less using the Sony SCS-6000 microstereolithography apparatus (MSLA). Due to laser over cure and other parameters, adjustments were made iteration by iteration until appropriate mask tolerances were met. A mounting structure was integrated with the mask for testing and application. At the computer aided design (CAD) model level, the mounting geometry can be adjusted to fit any specific mounting apparatus. By using the MSLA, features as small as 75 μm and larger than 300 mm can be created in the same build. Additionally, the conceptual design of an entire positioning system constructed using layer additive MSLA microfabrication is underway. This positioning system may be built as an integrated assembly, encapsulating necessary components. Optical characterization results are presented.

Research in rapid prototyping of high-density circuitry (RPHDC) involves integrating direct write (DW) conductive ink dispensing technology with stereolithography (SL) to manufacture smart structural members with integrated three-dimensional electronics. A significant challenge in this effort is realizing practical three-dimensional interconnect for discrete electronic packages encapsulated within a SL matrix. This paper presents research into SL-encapsulated DW three-dimensional interconnect. Results suggest that robust three-dimensional electronics are possible within an integrated DWSL structure. A power supply circuit is demonstrated that converts a 28 VDC input to a 5 VDC output with electromagnetic interference filtering capability. Additional work is necessary to improve resistance of DW interconnect, and planarity of device planes. Strategies for improving resistance of DW ink through localized laser curing and thermal curing are discussed in addition to the encapsulation performance of advanced SL resins. Future work in this area may impact the widely accepted MCM-L and MCM-C multichip module technologies.

Peripheral nerve regeneration conduits available today are single lumen conduits. Multi-lumen conduits offer advantages over currently available conduits in that multiple lumen better mimic the natural structure of the nerve, provide a greater surface area for neurite extension, and allow for more precisely located growth factors or support cells within the scaffold. This work describes and demonstrates the use of the stereolithography (SL) rapid prototyping technique for fabricating multi-lumen nerve guidance conduits (NGCs) out of photopolymerizable poly(ethylene glycol) (PEG). NGCs were fabricated from PEG-dimethacrylate (PEG-dma) molecular weight 1000 with 30% (w/v) aqueous solution and 0.5% (w/v) of the photoinitiator Irgacure 2959. The selection of the PEG-dma and photoinitiator concentration was based on previous work [13]. A 3D Systems 250/50 SL machine with a 250 μm laser beam diameter was used for the experiments in a slightly modified process where the NGCs were fabricated on a glass slide within a small flat-bottom cylindrical container placed on top of the SL machine’s original build platform. SL successfully manufactured three-dimensional, multi-layered and multi-material NGCs with varying overall NGC lengths and lumen sizes. Minimum lumen size, spacing, and geometric accuracy were constrained by the laser beam diameter and path, curing characteristics of the polymer solution, and UV transmission properties of the polymer solution and cured PEG-dma. Overall lengths of the NGCs were constrained by the ability of the conduit to self-support its own construction. Multiple material conduits were demonstrated by varying the build solution during the layering process. In summary, SL shows promise for fabrication of bioactive NGCs using PEG hydrogels, and the use of SL in this application offers the additional advantage of easily scaling up for mass production.Copyright © 2005 by ASME

Layered manufacturing (LM) using stereolithography (SL) of aqueous polymer solutions was accomplished so three-dimensional (3D) tissue engineered scaffolds with complex distributions of bioactive agents could be produced. Successful LM with embedded channel architectures required investigation of hydrogel thickness or cure depth as a function of photoinitiator type and concentration, energy dosage, and polymer concentration in solution. Poly(ethylene glycol) dimethacrylate (PEG-dma) with an average molecular weight of 1000 in quantities of 20% and 30% (w/v) was prepared in distilled water. Different concentrations of two photoinitiators (PIs), Sarcure1121 (2-hydroxy-2-methyl-1-phenyl-1-propanone) and Irgacure 2959 (2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone), were used to vary gel thickness at select energy dosages by controlling the scan speed of the SL machine's ultraviolet scanning system. Gel thickness was a strong function of PI type and concentration, energy dosage, and PEG-dma concentration, especially at the low PI concentrations required for implantation. The gel thickness curves were utilized to demonstrate LM for two construct geometries where different layer thicknesses were required to successfully fabricate the constructs. This work demonstrates the effective use of SL as a processing technique for complex 3D tissue scaffolds and addresses some practical considerations associated with the use of hydrogels in LM.

Designing complex internal cooling passages is extremely difficult without detailed information about the flow behavior due to the presence of separated flow zones and strong secondary flows. This paper describes a new approach to designing internal flow passages called Rapid Iterative Design Using Experimentation (RIDUE). RIDUE utilizes rapid prototyping (RP) manufacturing to quickly build an accurate model of a complex internal flow passage and magnetic resonance velocimetry (MRV) to measure the full three dimensional velocity field. Because both techniques offer very fast turnaround, it is feasible to conduct iterative design with a cycle time of 1–2 days. RIDUE is demonstrated using a generic turbine blade internal cooling passage with four serpentine channels. Two channels have rectangular cross-section and two are square. In each channel, two of the four walls have ribs (also called turbulators) angled at 45 degrees to the main flow direction. Two models based on the generic geometry are studied, each with different turbulator cross-sections, one square and one rounded. Both models were built using a stereo lithography apparatus. MRV provided three-component velocity vectors for flow at a Reynolds number of 10,000 based on the hydraulic diameter of the first passage. Sample vector fields are presented to illustrate the detail with which the flow can be investigated. Although little difference is seen in the flows between the two models, it is demonstrated that through its use of RP processes and the MRV measurement technique, RIDUE is a viable technique for modern internal passage design.Copyright © 2003 by ASME

A throttle control system has been developed for a small V-twin engine used in a hybrid AC power generation system that incorporates two time variable power sources: a wind turbine and an internal combustion engine-generator combination. The control system utilizes a throttle actuator, a proportional integral derivative (PID) controller and software that determines desired power outputs (engine speeds) based on real-time measurements. A parallel approach to the design of the PID controller for system stability and proper performance is described. Transient response tests were performed from which suitable PID gain settings were selected by trial and error. In addition, frequency response tests were performed to develop models of the engine (system identification) at different operating points, which can then be used to analytically design the gains of the PID controller.

The correct address for Materials Science, University of Texas at El Paso is 500 W. University Avenue, El Paso, TX 79968, USA. As specified in the original article, the data for UTS, elongation to break and Young’s modulus for the ABS loaded with TiO2, jute fiber and TP elastomer were based on three specimens instead of five specimens. Tables 3 and 4 are updated with the correct data. The data for ABS remains the same. Table 3 Values of UTS and UFS for XYZ specimens

A hybrid stereolithography (SL)/direct print (DP) system has been developed and previously described that fabricates three-dimensional (3D) structural electronic devices in which component placement, interconnect routing, and system boundaries are not confined to two dimensions as is the case with traditional printed circuit boards (PCBs). The resulting increased level of design and fabrication freedom provides potential for a reduction in both volume and weight as well as the capability of fabricating systems in arbitrary and complex shapes as required to conform to unique application requirements (e.g., human anatomy, airframe structures, and other volumetrically-constrained mechanical systems). The fabrication of these devices without intermediate part removal between SL and DP processes requires in situ curing of DP-dispensed silver-based inks to sufficiently cure the inks prior to continuing additional SL fabrication. This paper describes investigations into the laser curing process using the two laser wavelengths, 355nm and 325nm, which have been used in commercial SL machines. Various laser curing parameters, including energy (laser power and scan speed), scanning location, and laser wavelength were investigated. The trace resistances and structural changes in the SL substrate and printed trace were compared for each experiment to determine the most preferred laser ink curing method. Furthermore, oven curing of partially laser cured ink traces was investigated as a means for minimizing the number of in situ laser passes required to embed ink traces during SL fabrication. The laser curing process was repeated for a wide variety of conductive inks, having different structure, composition, and curing properties to determine if certain inks were more responsive to laser curing and if the ink curing results could be generalized. A statistical study was conducted under the hypothesis that laser curing of inks at 325nm wavelength would be better, due to lower silver reflectance, as compared to 355nm wavelength. Results indicated that particulate silver based conductive inks can be successfully cured in situ using SL lasers with various laser curing parameters. Curing ink traces at high laser power and slow scan speeds with the laser beam located on the substrate adjacent to the ink channel resulted in the most effective ink curing but resulted in discoloration of the ink and/or charring of the SL substrate. Comparatively, when laser power was reduced sufficiently to eliminate the charring, lower effective ink curing was achieved. Irradiating the laser directly on the ink did not damage the ink or the substrate, while providing low trace resistances, and represents the most viable laser curing alternative to achieve acceptable trace resistance without charring the SL substrate. The results further indicated that partial laser curing of ink using a reduced number of laser passes with subsequent oven cure seem to work effectively and may decrease overall manufacturing time. SL lasers with low power (

This research examines rapidly solidified, atomized pure iron powder and solid and reticulated mesh components fabricated by electron beam melting (EBM) from this powder precursor. Especially significant was the characterization of associated microstructures and corresponding mechanical properties. Atomized Fe powder was used to fabricate solid and reticulated mesh components by EBM. Powder and component microstructures and phase structures were examined by light (optical) metallography, scanning electron microscopy, X-ray diffractometry, and transmission electron microscopy. Corresponding Vickers microindentation hardness measurements were also made and compared to tensile data along with measurements of dynamic stiffness for mesh components having varying densities. The atomized Fe powder was observed to contain δ-Fe which was retained in the solid, EBM-fabricated components where it was observed to be homogeneously distributed in equiaxed α-Fe grains as δ-phase platelets measuring ∼0.5 μm to 2 μm in length and ∼40 nm thick; coincident with the α-Fe matrix {1 0 0} or {1 1 0} planes. A log–log plot of E / E s versus ρ / ρ s resulted in ( E / E s ) = ( ρ / ρ s ) 2.8 . Novel, δ-Fe phase platelets have been observed in α-Fe components fabricated by EMB.

The development of improved hemodynamic impedance models can greatly aid the understanding of arterial disease progression and its remediation. This paper leverages the recent progress in advanced manufacturing techniques to engage in in-vitro experimentation with physiologically relevant geometries and flows that correspond to arterial stenosis. The measurements of pressures and flow obtained by these experiments were then used to estimate flow-to-pressure transfer functions, aimed at determining a lumped-parameter impedance model of the physical system, by applying conventional descent as well as recently developed Genetic Algorithm methods. The resulting transfer functions can now be utilized for further studies with regard to the hemodynamics relevant to arterial stenosis.

Fabricating entire systems with both electrical and mechanical content through on-demand 3D printing is the future for high value manufacturing. In this new paradigm, conformal and complex shapes with a diversity of materials in spatial gradients can be built layer-by-layer using hybrid Additive Manufacturing (AM). A design can be conceived in Computer Aided Design (CAD) and printed on-demand. This new integrated approach enables the fabrication of sophisticated electronics in mechanical structures by avoiding the restrictions of traditional fabrication techniques, which result in stiff, two dimensional printed circuit boards (PCB) fabricated using many disparate and wasteful processes. The integration of Additive Manufacturing (AM) combined with Direct Print (DP) micro-dispensing and robotic pick-and-place for component placement can 1) provide the capability to print-on-demand fabrication, 2) enable the use of micron-resolution cavities for press fitting electronic components and 3) integrate conductive traces for electrical interconnect between components. The fabrication freedom introduced by AM techniques such as stereolithography (SL), ultrasonic consolidation (UC), and fused deposition modeling (FDM) have only recently been explored in the context of electronics integration and 3D packaging. This paper describes a process that provides a novel approach for the fabrication of stiff conformal structures with integrated electronics and describes a prototype demonstration: a volumetrically-efficient sensor and microcontroller subsystem scheduled to launch in a CubeSat designed with the CubeFlow methodology.

Implementing electronics systems that are conformal with curved and complex surfaces is difficult if not impossible with traditional fabrication techniques, which require stiff, two dimensional printed circuit boards (PCB). Flexible copper based fabrication is currently available commercially providing conformance, but not simultaneously stiffness. Consequently, these systems are susceptible to reliability problems if bent or stretched repeatedly. The integration of Additive Manufacturing (AM) combined with Direct Print (DP) micro-dispensing can provide shapes of arbitrary and complex form which incorporate 1) miniature cavities for insetting electronic components and 2) conductive traces for electrical interconnect between components. The fabrication freedom introduced by AM techniques such as stereolithography (SL), ultrasonic consolidation (UC), and fused deposition modeling (FDM) have only recently been explored in the context of electronics integration. Advanced dispensing processes have been integrated into these systems allowing for the introduction of conductive inks to serve as electrical interconnect within intricately-detailed dielectric structures. This paper describes a process that provides a novel approach for the fabrication of stiff conformal structures with integrated electronics and describes several prototype demonstrations: a body conformal helmet insert for detection of Traumatic Brain Injury (TBI), a 3D magnetic flux sensor with LED indicators for magnitude and direction and a floating sensor capable of detecting impurities in water while maintaining orientation through density gradients.

This research focused on extending the applications of fused deposition modeling (FDM) by extrusion and deposition of low melting temperature metal alloys to create three-dimensional metal structures and single-layer contacts which may prove useful for electronic interconnects. Six commercially available low melting temperature solder alloys (Bi36Pb32Sn31Ag1, Bi58Sn42, Sn63Pb37, Sn50Pb50, Sn60Bi40, Sn96.5Ag3.5) were tested for the creation of a fused deposition modeling for metals (FDMm) system with special attention given to Sn–Bi solders. An existing FDM 3000 was used and two alloys were successfully extruded through the system's extrusion head. Deposition was achieved through specific modifications to system toolpath commands and a comparison of solders with eutectic and non-eutectic compositions is discussed. The modifications demonstrate the ability to extrude simple single-layer solder lines with varying thicknesses, including sharp 90 deg angles and smooth curved lines and showing the possibility of using this system for printed circuit board applications in which various connections need to be processed. Deposition parameters altered for extrusion and the deposition results of low melting temperature metal alloys are introduced.