Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, February 2013. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 103-117). / Mesenchymal stem cells (MSCs) are derived from bone marrow, and are capable of proliferating and differentiating along multiple pathways such as osteoblasts, chondrocytes and adipocytes. MSCs offer the means for regenerative therapies not possible with conventional small molecule/antibody/ nucleic acid therapeutics. However, all MSCs are not equivalent. Adult MSCs (aMSCs) derived from infant or adult sources are heterogeneous, exhibit poor overall integration in host tissues, and their differentiation and proliferation capacities are limited by ex vivo culture. On the other hand, fetal MSCs (fMSCs) derived from fetuses are more homogeneous, plastic and grow faster than aMSCs. However, they face serious ethical and practical issues that limit their applications. For these reasons, we hypothesized that aMSC populations contain a subpopulation with similar biophysical and biological properties to fMSCs. To verify this thesis, we studied aMSC size distribution, aMSC migration velocity and aMSC mechanical properties. We explain later in this work why we chose these characteristics. We were then able to find a subpopulation of aMSCs with similar size distribution to fMSCs. We were not able to find a subpopulation of aMSCs with similar migration velocity to fMSCs. At last, we were able to prove the existence of a subpopulation of aMSCs with similar mechanical properties to fMSCs. / by Remi Jolibois-Quinot. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2014. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 147-164). / More than two billion people in the world have little or no access to electricity. To be empowered they need robust and lightweightrenewable energy conversion technologies that can be easily transported with high yield from our manufacturing centers to their (often) rural homes. Few conventional photovoltaic technologies are robust enough to fill this need, however organic photovoltaics (OPVs) are ideal candidates due to their potential to be ultra-lightweight and flexible. However, this promising technology is currently limited by its relatively low power conversion efficiencies. This doctoral dissertation seeks to speed the eming of this promising technology. As a proof of concept for the accessibility and ultra-lightweight of OPVs, we integrate vapor-processed carbon-based electrodes and sub-30nm-thin encapsulations in organic photovoltaics, leading to the demonstration of monolithic, robust solar cell arrays as well as the first ever solar cells fabricated directly on paper. Furthermore, we have developed and advanced two unconventional approaches to enhancing power conversion efficiency via conventional methods: (1) optimization of multijunction efficiency via computational optical interference modeling and subcell photocurrent balance quantization and control, and (2) novel implementation of conventional vapor processing methods in the formation of molecular semiconductor crystals. This work has confirmed the potential of carbon-based materials to enable robust, ultra-lightweight, efficient solar arrays, thus advancing their capacity to empower our brothers and sisters even at the ends of the earth. / by Jill Annette (Rowehl) Macko. / Ph. D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1999. / Includes bibliographical references (p. 237-241). / Classically, technical cost models have been constructed using commercial spreadsheet problems. Spreadsheets, however, are not well suited to construct models of industrial systems, especially those where variable configurations of operation steps arc of interest. In light of this, a methodological framework and complementary computer tool were developed to address the existing impediments to system modelinb. This tool parametrizes the components of a system model and of spreadsheet based TCMs. Here, parametrization means creating both data structures which describe each system part and procedures which emulate the behavior and interrelationship of those parts. Using this strategy, a tool was created which successfully permits definition and manipulation of any real configuration, ensures consistent application of model formulae, provides a mechanism for appropriate and conveniently audited linking of variable values, and affords extensive auditing. This modeling tool was applied against a real-world case study of the automobile recycling infrastructure. For this system, concerns exist regarding how it will sustain as vehicles continue to decline in mass and change in composition. To reveal this, a process-based cost model of the automobile recycling system was created and used to I) expose retiring fleet compositions which pose a problem for recyclers and 2) evaluate strategies for using the system's waste, automobile shredder residue (ASR). The system model was run against retired fleets made up of three vehicles: predominantly steel, aluminum intensive, and polymer composite intensive (CIV). Results indicated that the current recycling system maintains profitability except when presented with a 100% CIV fleet. Also, the material value within a vehicle containing an aluminum structure, closures, chassis, and engine block would be sufficient to prompt extensive dismantling, consuming the bulk of the shredder's feedstock. For a similar vehicle without the aluminum chassis, shredders would have to offer 18¢/kg. for hulks, to preserve their profitability. Of the ASR processing technologies investigated, pyrolysis seems the most promising. Pyrolysis achieves profitability at a landfill price of $50/ton. In contrast, mechanical separation and selective precipitation require landfill prices of $70/ton. / by Randolph E. Kirchain Jr. / Ph.D.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2005. / Includes bibliographical references (leaves 61-62). / The purpose of the studies carried out in this thesis was to aid in the curation of samples of solar wind returned to earth on the Genesis spacecraft. An experimental study was carried out to aid development of a set of protocols for the laser scribing and subdivision of the Genesis silicon collector array materials. Optimisation of the scribing speed and the positioning of the focal point of the laser were carried out. It was found that scribe width was independent of both factors. Slower scribing speeds were found to produce deeper scribes, while heating effects were minimised with faster speeds. Vertical movement of the stage of 5 pm/pass was found to optimise the focal point of the laser, and minimise heating effects. A procedure to measure the flexural modulus of samples was proposed to quantify the success of the optimisation of the scribing parameters. A theoretical study was carried out to develop a predictive kinetic model for the oxidation of the silicon collector arrays during flight. The mechanism proposed for the increase in oxide thickness over that present pre-flight was the formation of a less-dense suboxide at the SiO₂/Si interface. The driving force is the elevated temperature of the collectors during collection, in the vacuum of space. / (cont.) A kinetic model was developed and growth rate expressions derived for two limiting kinetic cases. It was not possible to apply these expressions to the Genesis sample conditions, as the measurement of several experimental parameters was beyond the time limits of this study. A second model was developed alongside literature models to reduce further the number of unknown variables. Finally, the maximum possible thickness of oxide that could grow on the silicon surface was calculated. This was found to be 25 A, representing a 47 % increase over the original 17A of SiO₂ present pre-flight. It was noted that there was a non-linear increase of total oxide thickness with increase in suboxide thickness to due to density differences between Si and SiO, and SiO₂ and SiO. / by Benjamin K. Jackson. / S.M.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / "May 2007." Cataloged from PDF version of thesis. / Includes bibliographical references (p. 19). / There is considerable amount of interest in the immediate treatment of personnel involved in high risk situations on the battlefield. A novel approach to drug delivery on the battlefield based on MEMS technology is discussed. By combining three separately fabricated layers, a single implantable drug delivery device capable of delivering up to 100 mm3 of a vasopressin solution was developed. In vitro release of vasopressin was observed and the I-V response of the bubble generator was characterized. Results show that the voltage at the time of release is ~11V while the current is ~0.35A, giving a power output of 3.79W. The time to total release of the drug was less than 2 minutes. / by Wang Lei. / S.B.

Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2000. / Vita. / Includes bibliographical references (p. 85-87). / Ultra-high purity titanium is used as a barrier metal in integrated circuitry. Metallothermic reduction does not produce titanium sufficiently pure for micro-electronics applications so electro refining of the metal in a molten chloride bath at temperatures above 700°C is necessary. The present study focused on the electrorefining of titanium in a bath consisting of the CsCl-NaCl-KCl eutectic as the solvent. Interfacial phenomena (multiple reaction steps and the kinetics associated with each) related to the faradaic process were investigated with electroanalytical techniques. The bulk chemistry of the electrolyte (the structure of the chlorotitanate complexes) that describes the nature of the species present during the electrorefining process was investigated using spectroscopic techniques. Recommendations were made concerning the potential for the various technologies to be used for on-line control to improve operating practices. Electrode kinetics were studied by ac voltammetry. Phase angle information was used to determine the value of the standard rate constant ([alpha) and the transfer coefficient (a) for the reduction couples Ti3+/Ti2+ and Ti2+/Ti0 at a glassy carbon electrode. The reduction from Ti2+ to metal has been identified as the slow step in the electrorefining process. The utility of electrochemical sensing to observe concentration changes has been judged poor. Industrial use of reference electrodes is recommended for controlling the overpotential in the electrorefining process and to improve efficiency. Absorption spectroscopy has established that a temperature sensitive equilibrium between TiC16 3- and TiCl4- exists in the CsCl-NaCl-KCl eutectic. Fiber optic absorption spectroscopy was shown to be capable of detecting additions of Ti2+ to melts containing Ti8+ , as well as sensing Ti3+ concentration fluctuations at a level of ±+5mM. Raman spectroscopy was found to be ill suited for investigating complexation in this system due to the deeply colored nature of the melts. / by Luis A. Ortiz. / Sc.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 162-172). / Multispectral infrared (IR) detection has been widely employed for numerous applications including hyperspectral imaging, IR spectroscopy, and target identification. Traditional multispectral detection technology is based on the combination of broadband focal plane arrays (FPA) and spectral filters, grating spectrometers, or Fourier transform spectrometers, which requires bulky, high-cost mechanical scanning instruments and have a slow response. Hybrid structures integrating FPA and silicon readout integrated circuits (Si ROIC) greatly limit the yield and result in extremely expensive devices. Single photodetectors capable of detecting multiple wavebands simultaneously and monolithic integration with Si ROIC, however, enable dramatically simplified system design with superior mechanical robustness, and thus attract a lot of interest around the world today. In this thesis, we focus on the development of novel IR sensitive material and resonant-cavity- enhanced (RCE) photodetector devices that address the emerging need in the field of IR radiation detection. Polycrystalline PbTe films have been identified as the IR absorbing layers due to their high photosensitivity and fabrication flexibility; on the device side, we have established a universal design theory for multispectral detection and demonstrated fully functional mid-IR RCE photodetectors capable of monolithic integration with Si ROIC. We have developed room-temperature-sensitized, polycrystalline PbTe films using single source thermal evaporation for detecting IR light up to 5 pm in wavelength. Thinner PbTe layers yields enhanced performance than thicker layers due to strong thickness dependence of both photo-responsivity and detectivity. Structural, electrical, and optical property studies reveal photoconductivity mechanism in the films and point out directions of further material optimization. We have established a versatile and scalable design theory for cavity-enhanced multispectral photodetectors using phase-tuned propagation. Critical coupling condition is identified as the prerequisite to achieve near unity quantum efficiency in RCE photodetectors. Coupling-matching layers are positioned between cascaded planar resonant cavities for controlling optical phase and coupling strength between incident light and resonant modes to obtain critical coupling condition. After developing another two IR transparent layers as low and high index materials, evaporated As2S3 and sputtered Ge, we design and fabricate distributed Bragg reflectors (DBR) for mid-IR resonant cavities. In our design example of dual waveband RCE photodetectors, peak quantum efficiencies over 80% have been realized in both wavebands (1.55 pm and 3.6 pm) with only 50 nm and 100 nm thick PbTe IR absorbers, and spectral cross talk as low as 0.1% is obtained. Preliminary results on our first attempt of fabricated dual waveband RCE photodetectors demonstrate the two resonant cavity modes at 1.61 pm and 3.70 pm. And quantum efficiencies as high as 92% and 68% have been achieved in two wavebands respectively. We have developed and optimized a multi-step lift-off patterning technique to fabricate RCE photodetectors on a Si platform. Single waveband RCE photodetectors for mid-IR (3.5 pm) have been designed according to critical coupling condition to achieve near unity quantum efficiency. The fabricated devices show high quantum efficiency (90%) and peak responsivity at the resonant wavelength of 3.5 pm, which is 13.4 times higher than blanket PbTe film of the same thickness. We demonstrate detectivity as high as 0.72x0 cmHzmW~l, comparable with commercial polycrystalline mid-IR photodetectors. As low temperature processing (150 'C) is accomplished in the entire fabrication process, this demonstration paves the way for monolithic integration of RCE photodetectors with Si ROIC. Lastly, for the first time, we fabricate and test integrated devices of single waveband (3.6 pm) RCE photodetectors and Si ROIC. Both hybrid and monolithic integration structures are investigated. We have developed the fabrication process to accommodate Si ROIC chips of only 3 mm x 5 mm in area, and successfully integrated RCE photodetectors on Si ROIC directly. Our preliminary results show high promise for monolithic integration of RCE photodetectors and Si ROIC in the future. / by Jianfei Wang. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references. / This thesis explores the creation of thin film responsive hydrogel coatings via Layer-by Layer assembly (LbL) of temperature (T) responsive block copolymer - polyelectrolyte multilayers (PEMs). First, the LbL conditions that allow for temperature driven, large, reversible swelling transitions of multilayer constructs are determined. Use of weak polyelectrolyte components and selection of an appropriate deposition pH were found to be the critical factors that allowed large scale reversible swelling. These factors were the missing pieces that explain the lack of temperature response reported in prior literature. A series of block copolymer (BCP) molecules were subsequently synthesized to expose the influence of BCP architecture on the temperature responses of these micelle-PEMs. Diblock architectures that lack connectivity in the Tresponsive poly(propylene oxide) block disintegrate quickly at low temperature. Triblock copolymers on the other hand allow access to a wide range of reversible swelling behavior. The dynamic interplay of various pH, salt concentration and T effects on the swelling and stability of these hydrogels are also further explored. In particular a critical ratio of charged block to Tresponsive block length is necessary for film stability at low temperature. As a whole these systems can be customized to either swell reversibly (by up to 6 times their dry thickness) or disintegrate under specific sets of pH, time, temperature, and salt conditions, making them useful for a wide range of smart applications. The application of these conformal temperature responsive coatings to T-gating of membranes; creation of nanotube structures; T-enabled loading and release of proteins; as well as their tunable disintegration, useful for triggered release, is discussed and demonstrated. On a separate note, the utility of inorganic nanoparticle LbL assembly in creating conformal thin UV anti-reflection coatings for PMMA Fresnel lenses is demonstrated. Key features of thin porous nanoparticle coating assembly via LbL is discussed, including how particle size and deposition pH can tune the coating porosity and refractive index. In addition, we develop several strategies for stabilization of these inherently weak systems largely composed of air. In particular, a novel means to generate stable inversely structured surface nanoporosity in thermoplastic materials is developed. / by Wui Siew Tan. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1993. / Includes bibliographical references (v. 2, leaves 369-375). / by Christophe G.E. Mangin. / Ph.D.

Thesis: S.B., Massachusetts Institute of Technology, Department of Materials Science and Engineering, February 2013. / Page 30 blank. Cataloged from PDF version of thesis. / Includes bibliographical references. / Additively manufactured (3D-printed) refractory alumina-silica ceramics were mechanically tested to ascertain their ultimate tensile strengths and observed to determine their dimensional consistency over the printing and post-printing process. The equipment used to perform tensile testing was designed and built for use with custom-designed tensile test samples. Two ceramic powders, V18 (electronic-grade alumina, colloidal silica, and organic content) and 403C (200-mesh mullite, organic content, and magnesium oxide), were printed into test samples on ZCorporation ZPrinter® 310 and 510 machines, before being infiltrated with tetraethylorthosilicate (TEaS), and in some cases infiltrated again with a 40% by weight suspension of silica in water (Ludox). Ludox-infiltrated V18 proved to be the strongest medium, with a UTS of 4.539 ± 1.008 MPa; non-Ludox-infiltrated V18 had a UTS of 2.071 ± 0.443 MPA; Ludox-infiltrated 403C was weakest with a UTS of 1.378 ± 0.526 MPa. Within V18, greater silica content lead to greater tensile strength, but this did not hold true for 403C. 403C displayed volumetric shrinkage of about 1.5%, while V18's volumetric shrinkage ranged from 7% to 14%. / by Rachel Martin. / S.B.