Freeform Fabrication of Biological Scaffolds by Projection Photopolymerization

This article presents a micro-manufacturing method for direct, projection printing of 3- dimensional (3D) scaffolds for applications in the field of tissue engineering by using a digital micro-mirror-array device (DMD) in a layer-by-layer process. Multi-layered scaffolds are microfabricated using curable materials through an ultraviolet (UV) photopolymerization process. The pre-patterned UV light is projected onto the photocurable polymer solution by creating the “photomask” design with graphic software. Poly (ethylene glycol) diacrylate (PEGDA), is mixed with a small amount of dye (0.3 wt %) to enhance the fabrication resolution of the scaffold. The DMD fabrication system is equipped with a purging mechanism to prevent the accumulation of oligomer, which could interfere with the feature resolution of previously polymerized layers. The surfaces of the pre-designed, multi-layered scaffold are covalently conjugated with fibronectin for efficient cellular attachment. Our results show that murine marrow-derived progenitor cells successfully attached to fibronectin-modified scaffolds.Mechanical Engineerin

Integration of Direct-Write (DW) and Ultrasonic Consolidation (UC) Technologies to Create Advanced Structures with Embedded Electrical Circuitry

In many instances conductive traces are needed in small, compact and enclosed areas. However, with traditional manufacturing techniques, embedded electrical traces or antenna arrays have not been a possibility. By integrating Direct Write and Ultrasonic Consolidation technologies, electronic circuitry, antennas and other devices can be manufactured directly into a solid metal structure and subsequently completely enclosed. This can achieve a significant reduction in mass and volume of a complex electronic system without compromising performance.Mechanical Engineerin

Processing of Bioceramic Implants Via Fused Deposition Process

Porous ceramic structures have long been a subject of investigation as bone sl..bstitute. Most of these porous structures are typically made by techniques that result .randomly arranged pores with a wide variety of pore sizes. In recent years, SFF methods are being used for the fabrication of porous bioceramic implants. Porous ceramic structures have been fabricated using indirect route where a .polymeric mold is fitst created via fused deposition process. The mold was then infiltrated with ceramic slurry, dried. and ·then subjected to a binder bum out and sintering cycle. In this paper, processing of 3D honeycomb porous alumina ceramic structures and some.initial mechanical properties for bone implants will be discussed.Mechanical Engineerin

Multiscale Design for Solid Freeform Fabrication

One of the advantages of solid freeform fabrication is the ability to fabricate complex structures on multiple scales, from the macroscale features of an overall part to the mesoscale topology of its internal architecture and even the microstructure or composition of the constituent material. This manufacturing freedom poses the challenge of designing across these scales, especially when a part with designed mesostructure is part of a larger system with changing requirements that propagate across scales. A setbased multiscale design method is presented for coordinating design across scales and reducing iterative redesign of SFF parts and their mesostructures. The method is applied to design a miniature unmanned aerial vehicle system. The system is decomposed into disciplinary subsystems and constituent parts, including wings with honeycomb mesostructures that are topologically tailored for stiffness and strength and fabricated with selective laser sintering. The application illustrates how the design of freeform parts can be coordinated more efficiently with the design of parent systems.Mechanical Engineerin

Design and Freeform Fabrication of Deployable Structures with Lattice Skins

Frontier environments—such as battlefields, hostile territories, remote locations, or outer space—drive the need for lightweight, deployable structures that can be stored in a compact configuration and deployed quickly and easily in the field. We introduce the concept of lattice skins to enable the design, solid freeform fabrication (SFF), and deployment of customizable structures with nearly arbitrary surface profile and lightweight multi-functionality. Using Duraform FLEX® material in a selective laser sintering machine, large deployable structures are fabricated in a nominal build chamber by either virtually collapsing them into a condensed form or decomposing them into smaller parts. Before fabrication, lattice sub-skins are added strategically beneath the surface of the part. The lattices provide elastic energy for folding and deploying the structure or constrain expansion upon application of internal air pressure. Nearly arbitrary surface profiles are achievable and internal space is preserved for subsequent usage. In this paper, we present the results of a set of experimental and computational models that are designed to provide proof of concept for lattice skins as a deployment mechanism in SFF and to demonstrate the effect of lattice structure on deployed shape.Mechanical Engineerin

Manufacturing Metallic Parts with Designed Mesostructure via Three-Dimensional Printing of Metal Oxide Powder

Cellular materials, metallic bodies with gaseous voids, are a promising class of materials that offer high strength accompanied by a relatively low mass. In this paper, the authors investigate the use of ThreeDimensional Printing (3DP) to manufacture metallic cellular materials by selectively printing binder into a bed of metal oxide ceramic powder. The resulting green part undergoes a thermal chemical post-process in order to convert it to metal. As a result of their investigation, the authors are able to create cellular materials made of maraging steel that feature wall sizes as small as 400 µm and angled trusses and channels that are 1 mm in diameter.Mechanical Engineerin

Tunable Digital Material Properties of 3D Voxel Printers

Digital materials are composed of many discrete voxels placed in a massively parallel layer deposition process, as opposed to continuous (analog) deposition techniques. We explore the material properties attainable using a voxel-based freeform fabrication process and simulate how the properties can be tuned for a wide range of applications. By varying the precision, geometry, and material of the individual voxels, we obtain continuous control over the density, elastic modulus, CTE, ductility, and failure mode of the material. Also, we demonstrate the effects of several hierarchical voxel “microstructures”, resulting in interesting properties such as negative poisson’s ratio. This implies that digital materials can exhibit widely varying properties in a single desktop fabrication process.Mechanical Engineerin

Structurally Embedded Electrical Systems Using Ultrasonic Consolidation (UC)

Current research has demonstrated the use of Ultrasonic Consolidation (UC) to embed several USB-based sensors into aluminum, and is working toward embedding suites of sensors, heaters and other devices, connected via USB hubs, which can be monitored and controlled using an embedded USB capable processor. Additionally, the research has shown that electronics can be embedded at room temperature, but with some inter-layer delamination between the ultrasonically bonded aluminum layers. Embedding sensors and electronics at 300o F to overcome the delamination issues resulted in optimal bonding, and the sensors used thus far have functioned normally. Future investigation will explore other UC parameter combinations to ascertain the quality of embedding at lower temperatures.Mechanical Engineerin

A continues multi-material toolpath planning for tissue scaffolds with hollowed features

This paper presents a new multi-material based toolpath planning methodology for porous tissue scaffolds with multiple hollowed features. Ruled surface with hollowed features generated in our earlier work is used to develop toolpath planning. Ruling lines are reoriented to enable continuous and uniform size multi-material printing through them in two steps. Firstly, all ruling lines are matched and connected to eliminate start and stops during printing. Then, regions with high number of ruling lines are relaxed using a relaxation technique to eliminate over deposition. A novel layer-by-layer deposition process is progressed in two consecutive layers: The first layer with hollow shape based zigzag pattern and the next layer with spiral pattern deposition. Heterogeneous material properties are mapped based on the parametric distances from the hollow features

Novel Ceramics and Metal-Ceramic Composites via Fused Deposition Process

Indirect fused·· deposition process is utilized.·.. to ·fabricate controlled porosity ceramic structures using alumina, mullite, zirconia, LSCF-perovskite, tricalcium phosphate and hydroxyapatite, where pore size, pore shape and pore connectivity are varied from one end to the other end of the parts. Some of these porous ceramics are then infiltrated with metals via pressureless reactive metal infiltration to form novel metal-ceramic composites. Thispaper will describe processing, structures of various porous and metal-infiltrated composites and their physical and mechanical properties.Mechanical Engineerin