Thesis (Ph.D.)--University of Missouri-Columbia, 2005. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (November 15, 2006) Vita. Includes bibliographical references.

One of the challenges in tissue engineering is to fabricate scaffolds which can mimic the natural microenvironments of cells. In a cell niche, biophysical and mechanical cues are crucial factors influencing cell functions. Given the complexity of natural extracellular matrix (ECM) engineered ECMs providing controllable biophysical and mechanical cues are appealing both in enhancing the understanding of cell-matrix interaction and in controlling cell fates in vitro. The ultimate goal of our study is to establish a platform as an engineered ECM by fabricating customized solid protein microstructures from solution using two-photon photochemical crosslinking, a novel laser-based freeform fabrication technique. In this study, protein structures varying from submicron lines, 2D micropatterns and microporous matrices, to 3D micropillars were successfully fabricated, demonstrating freeform fabrication capability with two-photon photochemical crosslinking. Two-photon fluorescent imaging and scanning electron microscope (SEM)-based microstructural characterization revealed that power, scan speed, total exposure time and concentrations of protein (bovine serum albumin) and photosensitizer (rose Bengal) in the solution were crucial processing parameters in this fabrication technique. Quantitative imaging analysis showed that porosity of protein matrices was highly dependent on processing parameters including power, scan speed, number of cycles in time series scan and protein concentrations in the solution. An atomic force microscopy (AFM)-based step change nano-compression test was used to measure the reduced elastic modulus of 3D viscoelastic protein micro-pillars fabricated, as a pilot study. Microporous protein matrices and 3D micropillar arrays fabricated with two-photon photochemical crosslinking can be used as engineered ECM for future study in cell-ECM interactions. / published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy

Thesis (Ph.D.)--Drexel University, 2008. / Includes abstract and vita. Includes bibliographical references (leaves 90-100).

This article reports the recent progress of re-search made in the Droplet-Based Manufacturing Laboratory at MIT. The study has been focused on obtaining a fundamental understanding of microdroplet deposition and applying the technology to various practical applications. Specific scientific contributions include the development of an analytical model for droplet splashing/recoiling, an in situ droplet size control methodology, and a study of microstructure design for spray forming. The research per-formed in the lab provides both fundamental knowledge base and practical process developments for a range of manufacturing applications, including electronics packaging, spray forming and freeform fabrication. / Singapore-MIT Alliance (SMA)

This thesis is concerned with the design of a novel system for inserting porogen particles within internal structure of the bone scaffold. The proposed system would be integrated with a 3D printing machine to create macro-pores based on the conventional porogen leaching method. The system is capable of inserting porogens on pre-designed locations within the scaffold structure to realize the generation of macro-porosity within scaffolds. Several alternatives for such a porogen insertion mechanism are proposed based on employing a mechanical actuator for opening and closing the path of porogen particles from a porogen reservoir to the build chamber. Another possible design that offers significant advantages over its actuator-based alternatives is a pneumatic-based mechanism that picks up porogens from a porogen reservoir and places them at pre-designed locations. Among all the presented alternatives, the pneumatic-based system is selected by utilizing the value matrix method, and detail design of the different parts of this system is presented. The required pilot test setups for performing the feasibility study of the proposed method have been designed and successfully developed, and the practicality of the designed porogen insertion mechanism is proven through experiment.

This thesis is concerned with the design of a novel system for inserting porogen particles within internal structure of the bone scaffold. The proposed system would be integrated with a 3D printing machine to create macro-pores based on the conventional porogen leaching method. The system is capable of inserting porogens on pre-designed locations within the scaffold structure to realize the generation of macro-porosity within scaffolds. Several alternatives for such a porogen insertion mechanism are proposed based on employing a mechanical actuator for opening and closing the path of porogen particles from a porogen reservoir to the build chamber. Another possible design that offers significant advantages over its actuator-based alternatives is a pneumatic-based mechanism that picks up porogens from a porogen reservoir and places them at pre-designed locations. Among all the presented alternatives, the pneumatic-based system is selected by utilizing the value matrix method, and detail design of the different parts of this system is presented. The required pilot test setups for performing the feasibility study of the proposed method have been designed and successfully developed, and the practicality of the designed porogen insertion mechanism is proven through experiment.

Laser Sintering, a method of additive manufacturing, is used in the production of concept models, functional prototypes, and end-use production parts. As the technology has transitioned from a product development tool to an accepted production technique, functional qualities have become increasingly important. Tension properties reported for popular polyamide sintering materials are comparable to the molded properties with the exception of elongation. Reported strains for laser sintered polyamide are in the 15-30% range with 200-400% strains reported for molding. (CES Edupack n.d.) The primary contributors to poor mechanical properties in polyamide materials used during Selective Laser Sintering® are studied. Methods to quantify decreased mechanical properties are compared against each other and against mechanical properties of components fabricated using multiple process parameters. Of primary interest are Ultimate Tensile Strength (UTS) and Elongation at Break (EOB) of tensile specimens fabricated under conditions that produce varying degrees of ductile and brittle fracture. / text

In an effort to gain a more comprehensive and complete understanding of the thermal behaviors occurring during the selective laser sintering process, external temperature measurements were taken during the build process. To accomplish this, an infrared camera was aimed directly through a viewport on the front of the sinterstation. The temperature was monitored during the heating process which showed slightly non-uniform heating of the part bed surface. Temperatures were also recorded while the laser was sintering each layer and the subsequent cooling of the entire machine following the build. By directly capturing infrared images of the part bed’s surface, it is clearer how the temperature gradients behave and the impact such variables have on part build efficiency. / text

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