2008 International Solid Freeform Fabrication Symposium

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Proceedings for the 2008 International Solid Freeform Fabrication Symposium. For more information about the symposium, please see the Solid Freeform Fabrication website.

The Nineteenth Annual International Solid Freeform Fabrication (SFF) Symposium, held at The University of Texas in Austin on August 4-6, 2008, was attended by almost 120 national and international researchers from 13 countries. Papers addressed SFF issues in computer software, machine design, materials synthesis and processing, and integrated manufacturing. The diverse domestic and foreign attendees included industrial users, SFF machine manufacturers, university researchers and representatives from the government. The Symposium organizers look forward to its being a continuing forum for technical exchange among the expanding body of researchers involved in SFF.

The Symposium was again organized in a manner to allow the multi-disciplinary nature of the SFF research to be presented coherently, with various sessions emphasizing process development, design tools, modeling and control, process parameter optimization, applications and materials. We believe that documenting the changing state of SFF art as represented by these Proceedings will serve both those presently involved in this fruitful technical area as well as new researchers and users entering the field.

The special theme for this year’s conference was education. A special session on this topic was held Monday morning at the meeting and included talks spanning from associates programs to undergraduate and graduate education to the public at large.

This year’s best oral presentation was given by Kamran Mumtaz of Loughborough University. Selection is based on the overall quality of the paper, the presentation and discussion at the meeting, the significance of the work and the manuscript submitted to the proceedings. The paper title was, “Selective Laser Melting of Inconel 625 using Pulse Shaping” by K.A. Mumtaz and N. Hopkinson. Selected from 66 oral presentations, his presentation appears on Page 165 of this Proceedings. The best poster presentation selected from 20 posters was given by Kaushik Alayavalli of The University of Texas at Austin (co-author David Bourell). The paper title was, “Fabrication of Electrically Conductive, Fluid impermeable Direct Methanol Fuel Cell (DMFC) Graphite Bipolar Plates by Indirect Selective Laser Sintering (SLS)”, and the paper starts on Page 186.

The editors would like to extend a warm “Thank You” to Rosalie Foster for her detailed handling of the logistics of the meeting and the Proceedings, as well as her excellent performance as registrar and problem solver during the meeting. We are grateful to John Hall and his staff at the Cockrell School of Engineering Print Services for the final production of the Proceedings. We would like to thank the Organizing Committee, the session chairs, the attendees for their enthusiastic contributions, and the speakers both for their significant contribution to the meeting and for the relatively prompt delivery of the manuscripts comprising this volume. We look forward to the continued close cooperation of the SFF community in organizing the Symposium. We also want to thank the Office of Naval Research (N00014-08-1-0666) and the National Science Foundation (CMMI-0820114) for supporting this meeting financially. The meeting was co-organized by the University of Connecticut at Storrs, and the Mechanical Engineering Department, Advanced Manufacturing Center, and Laboratory for Freeform Fabrication at The University of Texas at Austin.

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2008 International Solid Freeform Fabrication Symposium Table of Contents
(2008) Laboratory for Freeform Fabrication and University of Texas at Austin
Rapid Manufacturing in Biomedical Materials: Using Subtractive Rapid Prototyping for Bone Replacement
(University of Texas at Austin, 2008-09-10) Frank, Matthew C.; Hunt, Christopher V.; Anderson, Donald D.; McKinley, Todd O.; Brown, Thomas D.
This paper presents methods for the rapid manufacturing of replacement bone fragments using a Subtractive Rapid Prototyping process called CNC-RP. The geometry of segmental defects in bone, resulting from traumatic injury or cancerous tumor resection, can be reverse-engineered working from medical images (such as CT scans), and then accurate defect fillers can be automatically generated in advanced synthetic biomaterials and other bioactive/biocompatible materials. The research provides evidence that suitable bone geometries can be created using subtractive RP from a variety of materials including Trabecular Metal® (porous tantalum), polymers, ceramics, and actual bone allografts. The research has implications in the orthopaedic treatment of segmental bone defects, as custom prototyped bone fillers should aid in bone growth and improve recovery.
Improved Quality of 3D-Printed Tissue Constructs Through Enhanced Mixing of Alginate Hydrogels
(University of Texas at Austin, 2008-09-10) Cohen, Daniel L.; Tsavaris, Andrew M.; Lo, Winifred M.; Bonassar, Lawrence J.; Lipson, Hod
While alginate hydrogel is a desirable material platform for Solid Freeform Fabrication (SFF) of cell-seeded tissue engineering scaffolds, achieving consistently high-quality results can be challenging. Local variations in the material properties cause inconsistent material deposition behavior and consequently decrease the resultant geometric fidelity of the construct. The effects of gel mixing on material property consistency, geometric fidelity, and cell viability were characterized in an attempt to improve the formulation’s compatibility with SFF processing. Material homogeneity was quantified through a novel experimental setup composed of an EnduraTEC mechanical test-frame and custom syringe-extrusion jig. Cell viability and geometric fidelity were assessed using standard protocol. The baseline mechanical stiffness of the printed samples was 16±3 kPa (n=6). We found that increasing mixing reduced material inconsistency and improved geometric fidelity, without adversely affecting cell viability: the printed construct quality was drastically improved by increasing mixing well beyond previously established limits.
Optimised Polymerization Conditions for Inkjetting of Caprolactam to Produce Polyamide Parts
(University of Texas at Austin, 2008-09-10) Khodabakhshi, K.; Gilbert, M.; Dickens, P.; Hague, R.; Fathi, S.
Rapid Manufacturing (RM) techniques have been developed to shorten the processing cycle, and lead to efficient production of ready-to-use complex items. This project aims to manufacture three dimensional parts, directly from monomer, using a 3D Printing process based on ink-jet printing technology. A fast polymerization and high monomer conversion are essential. This work describes conditions for the rapid anionic polymerization of caprolactam after inkjetting to produce polyamide (nylon 6) parts. The effect of polymerization temperature and different catalyst/initiator types and concentrations on the rate of reaction were studied. Results show that, although increasing polymerization temperature results in quicker polymerization, the highest polymerization rate is achievable with 0.38g of sodium hydride and 320µl of N-acetylcaprolactam.
Fabrication of Complex 3D Micro-Scale Scaffolds and Drug Delivery Devices using Dynamic Mask Projection Microstereolithography
(University of Texas at Austin, 2008-09-10) Choi, Jae-Won; Park, In-Baek; Wicker, Ryan; Lee, Seok-Hee; Kim, Ho-Chan
Microstereolithography (μSL) technology can fabricate three-dimensional (3D) tissue engineered scaffolds with controlled biochemical and mechanical micro-architectures. A μSL system for tissue engineering was developed using a Digital Micromirror Device (DMDTM) for dynamic pattern generation and an ultraviolet (UV) lamp filtered at 365 nm for crosslinking the photoreactive polymer solution. The μSL system was designed with x-y resolution of ~2 μm and a vertical (z) resolution of ~1 μm. To demonstrate the use of μSL in tissue engineering, poly(propylene fumarate) (PPF) was synthesized with a molecular weight of ~1200 Da. The viscosity of the PPF was reduced to ~150 cP (at 50 o C) by mixing with diethyl fumarate (DEF) in the ratio of 7:3 (w/w). Finally, ~2 % (w/w) of (bis(2,4,6- trimethylbenzoyl) phenylphosphine oxide (BAPO) was added to the solution to serve as a photoinitiator. Cure depth experiments were performed to determine the curing characteristics of the synthesized PPF, and the resulting system and photopolymer were used to construct a variety of 3D porous scaffolds with interconnected pores between 100 and 150 μm and a micro-needle array with height of ~800 μm and individual tip diameters of ~20 μm. SEM and microscope images of the micro-architectures illustrate that the developed μSL system is a promising technology for producing biodegradable and biocompatible microstructures.
Fabrication of Embedded Horizontal Micro-Channels Using Line-Scan Stereolithogrpahy
(University of Texas at Austin, 2008-09-10) Choi, Jae-Won; Quintana, Rolando; Wicker, Ryan B.
In an effort to directly and rapidly manufacture micro-fluidic devices with embedded horizontal micro-channels on the order of tens of microns, a method was developed for using current commercially available line-scan stereolithography (SL) technology. The method consisted of inserting a wire of specified diameter during the build, building around the inserted wire, and removing the wire once fabricated leaving a channel with a circular cross-sectional geometry equivalent to the wire diameter. Demonstration of the technique using 31.6 µm, 57.2 µm and 83.5 µm wire was performed using a 3D Systems Viper si2TM SL system and DSM Somos® WaterShedTM resin. By embedding the wire and building around the insert, the down-facing surfaces were supported during fabrication enabling successful and accurate fabrication of embedded micro-channel geometries. A method for successful fabrication was developed that involved first building an open micro-channel, interrupting the SL process and inserting the wire, and then capping over the wire with multiple layers. After fabricating a part with a micro-wire, the micro-channel was produced by simply pulling the wire out of the part. Scanning electron microscope (SEM) images were used to examine and measure the geometries of the fabricated micro-channels, and a statistical design of experiments was performed to show that the process was capable of producing accurate horizontal micro-channels. It is expected that this process will enable unique micro-fluidic and other applications of micro-channel fabrication to be pursued using commercial line-scan SL.
Process Resolution of Laser Sintering Process Using Plastic Powder Containing Inorganic Filler at a High Rate
(2008-09-10) Niino, Toshiki; Oizumi, Shunsuke; Sato, Kazuki
Research is being performed on a laser sintering process in which inorganic filler is employed as porogen at a high content to fabricate highly porous three dimensional tissue engineering scaffold. Previously, the scaffold, which included capillary like flow channel network, was used in cell culture test, but obtained cell density was limited due to insufficient fineness of the network structure. In the scaffold fabrication the author experienced degradation of process resolution when inorganic filler was introduced at a high content, but reasons for the low resolution has not been cleared. This paper investigates the dominating cause of the low resolution. Discussion is focused on effect of optical and thermal properties of filler. Experiments using transparent and opaque fillers are performed, and existence of dominating effect of difference in the optical property is denied. Experiments using thermally conductive solid filler and insulating hollow filler is performed, and it is concluded that temperature conductivity is dominating on process resolution.
Solid Freeform Fabrication of Calcium Polyphosphate Dual-Porous Structure Osteochondral Scaffold
(2008-09-10) Shanjani, Yaser; Toyserkani, Ehsan; Pilliar, Robert
In this work the solid freeform fabrication (SFF) of dual-porous structure scaffolds using the 3D-printing method is investigated. The structure, including a cartilage substrate and a bone scaffold with different porosities and pore sizes, provide a suitable facility for repairing the osteochondral tissues in the implanted site. Calcium polyphosphate (CPP), with distinct particle sizes for each portion, was utilized as the biomaterial. Polyvinyl alcohol (PVA), as a biocompatible polymer was also used as a binder to adhere the CPP particles upon injecting of a solvent through the 3D-printing process. The prototyped parts are finally post-processed in the controlled furnace to obtain the required bio-mechanical properties. The biomechanical properties of the fabricated samples are also characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), and density analysis.
Developing printable content: A repository for printable teaching models
(2008-09-10) Knapp, Mary E.; Wolff, Ryan; Lipson, Hod
Alongside the development of RP technology, there is an increasing need to develop and share printable content. Like digital photography and digital music, content drives technology as much as technology drives content. This paper describes the development and population of an open wiki-style website (3Dprintables.org) that houses an archive of printable models for education. Teaching models were chosen as the initial focus for this effort for two key reasons. First, quality educational models are difficult for teachers to obtain due to high prices, limited availability, and limited customization options; and second, many studies have demonstrated that learning is enhanced when students interact with physical models. Such models are also indispensible tools for teaching the visually impaired and those with spatial reasoning difficulties. At present, the website contains models relevant to mechanical engineering, aerospace, biochemistry, mathematics, anatomy, and archaeology (e.g. proteins, airfoils, kinematics models, cuneiform tablets). These models are intended to serve as "seeds" to encourage educators to further develop and share printable models and the associated curricular materials.
Object Augmentation for the Visually Impaired Using RP
(2008-09-10) Chung, Marilyn; Malone, Evan; Tolley, Michael T.; Chepaitis, Andrew J.; Lipson, Hod
We demonstrate the application of rapid prototyping technology to augment every-day objects for the visually impaired. A freeform fabricator was used to print a tactile alphabet on multiple surfaces including paper, plastic, and metal. We have identified and experimented with multiple non-toxic materials and analyzed the dimensional tolerance, repeatability, and adhesion characteristics on multiple surfaces. Printing time for 1x1cm embossed letters varied from 14 to 52 seconds. More broadly, these experiments open the door to RP applications that involve custom product adaptation to address disabilities.

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