Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Includes bibliographical references (p. 211-222). / Gastropod mollusk nacre tablets and Polypterus senegalus armored scales share common features such as a very complex and changing structure spanning several length scales. The smallest building blocks are single crystals, have dimensions of a from tens of nanometers to several microns and are intimately blended with an organic glue present within pores or between the crystallites. In particular, our results strongly suggest that nacre tablets possess nanoscale porosity in the form of elongated tubules that may contain the intratablet macromolecules. Their unique structure allows these materials deform in a ductile way at the nanoscale, with no cracks observed, and to confine deformation at the microscale so as to impede crack propagation. Gradient in the mechanical properties are ubiquitous at both the microscale (scales) and the nanoscale (nacre tablets), preventing stress concentration and enhancing strain distribution. The armored scales thus exhibit a unique spatial functional form of mechanical properties with regions of differing levels of gradation within and between material layers, as well as layer with an undetectable gradation. Though highly mineralized, these biomaterials also exhibit greater local heterogeneity in their mechanical properties compared to pure minerals. Materials layers have distinct morphology and mechanical properties depending on their role (resistance to abrasion for harder outer layers, resistance to fracture for tougher inner layers) and their interface are reinforced (by anchored organic fiber ligaments and corrugated interfaces that maximize contact surface., preventing propagation of cracks both through and along the interfaces. / (cont.) The heterogeneity in size and shape of the crystallites and the pores, as well as the variation in the composition (mineral / organic, crystalline amorphous) are likely responsible for the desirable variations of mechanical properties as observed in these biocomposites at the smallest length scales, resulting in more spatially distributed strains and greater energy dissipation. / Benjamin J.F. Bruet. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references. / We propose several methodologies to study and optimize the electromagnetic process for Electromagnetic Forming (EMF) and Welding (EMW), thereby lowering the necessary process energy up to a factor of three and lengthening the life-time of EMW compression coils. We present a new theoretical approach to calculate a so-called critical kinetic energy to achieve a proper EMW joint, which is related to the volume of the accelerated mass and the Vicker's Hardness of the material. Using this novel approach, welding windows for several materials are presented. Studying the circuit theory, the current discharge pulse can be optimized to the needs of the EMW process, when opting for a critically damped RLC circuit. We present MultiSIM and MATLAB models that prove the proposed optimization and reflect the experimental EMW setup and parameters. Using the models, unknown parameters, such as machine inductance and resistance can be extrapolated for EMF and EMW machinery. Furthermore, the MATLAB model can calculate the optimal gap between the outer and inner workpiece for the outer workpiece to reach the maximum velocity at impact. Good correlation was found with regards to the High-Speed Videography used to study the EMF process in further detail measuring velocities between 50 m/s and 100 m/s. Studying the mechanical properties of the outer workpiece we propose an EMF-EMW setup that would decrease the strength of the outer workpiece by introducing a controlled amount of wrinkles through an EMF step with a mandrel inside the outer workpiece, followed by a lower critical energy EMW step. / (cont.) Through a failure study, accompanied by a metallurgical analysis, of an Aluminum Bronze Bitter coil we present a materials selection of other possible coil materials, as well as a new method called Electromagnetic Fatigue (EMFA) Analysis to study the crack initiation and propagation in electromagnetic high-current applications. Finally, through two sets of EMW experiments tubular lap joints that were stronger than the base material could be produced and the EMW process parameters of increased cleanliness, gap, wall thickness and a lower taper angle, for the case of our setup, showed to increase the final joint strength. / by Daniel G. Pressl. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1988. / Vita. / Includes bibliographical references. / by Chune-Ching Young. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 111-131). / Degradable polymeric materials provide opportunities for the development of improved vaccines and immunotherapies by acting as platforms that facilitate the delivery of molecules to appropriate tissue and cellular locations to achieve therapeutic outcomes. To this end, we have designed and characterized nano-films and particles employing a hydrolytically degradable polymer for the delivery of vaccine antigens and immunotherapeutics. We first describe protein- and oligonucleotide-loaded layer-by-layer (LbL)-assembled multilayer thin films constructed based on electrostatic interactions between a cationic poly(p-amino ester) (PBAE, denoted Poly-1) with a model protein antigen, ovalbumin (OVA), and/or immunostimulatory CpG oligonucleotides for transcutaneous delivery. Linear growth of nanoscale Poly-1/OVA bilayers was observed. Dried OVA protein-loaded films rapidly deconstructed when rehydrated in saline solutions, releasing OVA as non-aggregated/non-degraded protein, suggesting that the structure of biomolecules integrated into these multilayer films are preserved during release. Using confocal fluorescence microscopy and an in vivo murine ear skin model, we demonstrated delivery of OVA from LbL films into barrier-disrupted skin, uptake of the protein by skin-resident antigen-presenting cells (Langerhans cells), and transport of the antigen to the skin-draining lymph nodes. Dual incorporation of OVA and CpG oligonucleotides into the nanolayers of LbL films enabled dual release of the antigen and adjuvant with distinct kinetics for each component; OVA was rapidly released while CpG was released in a relatively sustained manner. Applied as skin patches, these films delivered OVA and CpG to Langerhans Cells in the skin. To our knowledge, this is the first demonstration of LbL films applied for the delivery of biomolecules into skin. This approach provides a new route for storage of vaccines and other immunotherapeutics in a solid-state thin film for subsequent delivery into the immunologically-rich milieu of the skin. In parallel, we also developed biodegradable core-shell nanoparticles with a PBAE core enveloped by a phospholipid bilayer shell for cytosolic delivery, with a view towards delivery of messenger RNA (mRNA)-based vaccines. The pH-responsive PBAE component was chosen to promote endosome disruption, while the lipid surface layer was selected to minimize toxicity of the polycation core. mRNA was efficiently adsorbed via electrostatic interactions onto the surface of these net positively charged nanoparticles. In vitro, mRNA-loaded particle uptake by dendritic cells led to mRNA delivery into the cytosol with low cytotoxicity, followed by translation of the encoded protein in these difficult-to-transfect cells at a frequency of -30%. Particles also promoted cytosolic uptake of co-delivered anti-tumor toxins in tumor cells resulting in synergistic killing, demonstrating potential for cancer therapy. In vivo, particles loaded with mRNA administered intranasally or intratracheally in mice led to the enhanced expression of the reporter protein luciferase compared to naked mRNA. This system may thus be promising for noninvasive delivery of mRNA-based vaccines. / by Xingfang Su. / Ph.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001. / Includes bibliographical references (p. 151-154). / The factors dictating the minimum feature size in Slurry-based Three Dimensional Printing (S-3DPTM) of ceramics have been examined, focusing on effects related to the polymeric binder system polyacrylic acid (PAA, MW 60000) and its interaction with the ceramic powder bed. Methods for retrieving structures characteristic of the minimum feature, referred to as the "binder primitive," and for characterizing the size and shape of the binder primitive have been developed. Impact-related spreading of the printed binder droplets has been found to play little or no role on the primitive structure. Two dominant factors controlling primitive width were however identified. The first is wetting-induced spreading of the printed binder solution on the surface of the powder bed. The spreading process is halted prior to completion by infiltration of the printed liquid into the pore space. The role this factor plays thus depends on wetting properties and the relative rates of spreading and infiltration. The spreading and infiltration rates were modeled, and a means of predicting the maximum extent of spreading was developed. The second factor controlling minimum feature size is adsorption of the polymeric binder molecules from solution onto the surface of the ceramic particles during infiltration of the printed binder solution. This effectively filters the polymer from solution, resulting in a progressive decrease in concentration as the binder solution penetrates deeper into the pore space of the powder bed, which serves to limit the primitive size. / (cont.) This was confirmed via the generation of adsorption isotherms for PAA on A1203, SiO2, and TiO2 surfaces and correlating adsorption to measured primitive size in each of these systems, and by correlating the trend of primitive size with specific surface area of the powder in the high affinity A1203 - PAA system. A general model for predicting the combined effects of spreading and adsorption in the PAA-A1203 system was developed, and suggestions for future directions based on this research have been made. / by Richard K. Holman. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 68-70). / The crude oil supply crisis the world is facing today along with the disastrous global warming caused primarily as a result the green house gases, has heightened the need for an eco-friendly and renewable energy technology. Solar cells, with their ability to convert the free and gigantic energy supply of the sun into electricity, are one such attractive choice. In this thesis, a study of the use of new technologies for enhanced solar cell performance based on conversion efficiency is carried out by first understanding the mechanism of selected major solar cell types, followed by an analysis of external or internal factors that affect their performance. One new technology under investigation to boost solar cell efficiency is the introduction of nanorod/wire structures into existing designs. This report discusses this approach in detail, highlighting beneficial characteristics offered and also looking into the structure realization through advanced nanostructure processing techniques. Finally, having a complete technology background at hand, various potential markets for new solar cell technologies are examined. / by Bertha Tan. / M.Eng.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 76-80). / The possible use of programmable integrated circuit interconnect vias using an indirectly heated phase change material is evaluated. Process development and materials investigations are examined. Devices capable of multiple cycles between on/off states for reconfigurable applications have been successfully demonstrated in a standard CMOS-compatible technology. Building computer chips with these vias would create a new kind of field programmable gate array (FPGA), whereby the design can be reconfigured depending on its application. The phase change reprogrammable-via is nonvolatile, unlike SRAM-based technology. It also has a relatively low on-state resistance and occupies less real estate on the chip. As the "switches" are placed at the metallization level, it provides flexibility for the designer to place them. Programmable-via can operate at a relatively low voltage compared to FLASH-based technology. Similar to the case of antifuses, programmable-via interconnect structures are projected to be radiation hard. However, the most challenging part of implementation is the circuit design. Issues such as integration of materials and design with current tools need to be overcome. A lack of expert personnel in this area also makes the implementation of programmable-via FPGAs complicated. The market for FPGA is promising due to the attraction of the programmable logic market. An intellectual Property (IP) analysis indicates there exist a significant new space for exploration in this area. The best-suited business model is as a new start-up that demonstrates feasibility and develops intellectual property. The potential commercialization of such technology is also discussed. Although this concept is promising result, more research is needed to show the reliability and feasibility of such a technology in complex circuits. It will take some time before this approach can be considered for production. / by Chee Ying Khoo. / M.Eng.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1994. / Includes bibliographical references (leaves 151-153). / by Rizwan Mahmood Gul. / M.S.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Vita. / Includes bibliographical references (p. 93-103). / Essential to the emergence of spin-based electronics is a source of highly polarized electron spins. Conventional ferromagnets have at best a spin polarization P-50%. Europium monoxide is a novel material capable of generating a highly spin-polarized current when used as a tunnel barrier. EuO is both a Heisenberg ferromagnet (Tc=69 K) and a semiconductor. Exchange splitting of the conduction band creates different tunnel barrier heights for spin-up and spin-down electrons, thus filtering the spins during tunneling. High-quality EuO films at the monolayer level is necessary for efficient spin-filtering. Because non-ferromagnetic, insulating Eu20 forms more readily, growth of an ultra-thin, high-quality film is quite challenging, which restricted previous studies of EuO to bulk form. EuO films were grown by reactive thermal evaporation, and various thin film characterization techniques were employed to determine the structural, optical, and magnetic properties, even on the thickness scale needed for tunneling (<3 nm). The film properties closely matched those of bulk EuO, though the Tc for ultra-thin films was found to be reduced from bulk value, in agreement with theoretical prediction. / (cont.) Controlling the smoothness and chemical nature of the inter-faces between EuO and metallic electrodes was found to be of critical importance, as proven by careful interfacial chemical and magnetic analysis at the monolayer level, using x-ray absorption spectroscopy, magnetic circular dichroism, and diffuse x-ray resonance scattering techniques. EuO was successfully prepared as the barrier in Al/2.5 nm EuO/Y tunnel junctions. By fitting the current-voltage characteristics of these junctions to tunneling theory, exchange splitting in an ultra-thin layer of EuO was quantitatively determined for the first time, and complete spin filtering yielded total spin polarization, P=100%. In an alternative approach, P was directly measured using the superconducting Al electrode as a spin detector. Spin-filtering in EuO barriers was also observed in magnetic tunnel junctions (MTJs), in which a ferromagnetic electrode was the spin detector. In Cu/EuO/Gd MTJs a tunnel magnetoresistance (TMR) of 280% was measured by changing the relative alignment of magnetization of EuO and Gd, which is the largest TMR measured using a spin-filter barrier. Co/A1203/EuO/Y junctions, in which the A1203 barrier magnetically decoupled Co and EuO, also showed substantial TMR. Its matching band gap (1.1 eV) and compatibility with Si open up the novel possibility of using EuO to inject highly polarized spins into Si-based semiconductors. / by Tiffany S. Santos. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 45-47). / A stamped nanoparticle array patterning technology integrating interference lithography, self assembly and soft lithography is assessed. This technology is capable of parallel patterning of nanoparticles at a large scale. Among several possible applications of this technology, potential for Deoxyribonucleic Acid detection is specifically investigated. Attaching DNA to nanoparticles through a probe molecule changes the local dielectric environment and hence affects surface plasmon resonance. However, the projected plasmon peak shift is not significant. Another detection method is described here to create a visible optical DNA sensor with a tolerable increase in cost relative to existing technologies. Intellectual property issues are also discussed for this technology. / by Zongbin Wang. / M.Eng.