This thesis concerns the fabrication and modification of novel oxygen and glucose biosensors as well as the application of these biosensors in oxygen and glucose transport research in cell constructs. In Chapter 1, the principle and development of biosensors has been reviewed. Particular attention is paid to oxygen and glucose mass transport research in cell constructs which are crucial for bio-scaffold design in tissue engineering. Chapter 2 details the materials and methods in oxygen and glucose sensor fabrication, modification and characterization. Chapter 3 presents research into practical challenges in oxygen and glucose sensors. For oxygen sensor, membrane biofouling and sensitivity to stirring effect have been detected and successful progresses have been made to reduce their effects. For glucose sensor, membrane biofouling and oxygen tension reliance affect their performance. Remarkable contributions have been made to improve glucose sensors’ stability and reliability. In particular, micro-biosensors have been introduced in the interests of better sensor adaptability for further biomedical applications. Chapter 4 is the experimental section for biosensor applications, and thus provides a detailed description of the cell culture models used in the thesis. Chapter 5 describes the oxygen partial pressure and glucose concentration measurements using biosensors. 2D and 3D cell culture constructs are investigated and results are discussed in this section. It deserves to be mentioned that the modified oxygen and glucose sensor in this thesis are excellent for in vitro biomedical applications, the simultaneously investigation of PO2 and glucose concentration gradient in 3D cell constructs is also a pioneering work in this research field. Chapter 6 illustrates the overall conclusions resulting from the experiments described in the thesis and points out possible future research directions.

The increasing availability of nanopowders and nanotubes combined with new processing techniques is enabling the development of new multifunctional materials. Carbon Nanotubes (CNTs) are one of the recently discovered allotropic forms of carbon. They have exceptional mechanical, electrical and thermal properties. The application of CNTs in the reinforcement of ceramic nanocomposites has not yet been fully investigated and is the subject of this study. Alumina is the main matrix used in this study. CNTs need to be de-agglomerated and homogeneously distributed in ceramic nanocomposites. Dimethylformamide (DMF) produces fine and stable CNT and alumina dispersions. All nanocomposites were sintered by Spark Plasma Sintering (SPS). Nanocomposites prepared using DMF dispersions showed better dispersions, higher electrical conductivity and mechanical properties as compared to those prepared using ethanol dispersions. The addition of CNTs or Carbon Black (CB) to alumina significantly aids its densification. The CNTs produce significant grain growth retardation. CNTs were found to be well preserved in alumina after being SPSed up to 1900 oC. Structural preservation of CNTs in ceramic nanocomposites depends on the nature of ceramic and SPS processing conditions. The electrical conductivity of alumina – CNT nanocomposites is four times higher as compared to alumina – CB nanocomposites due to the fibrous nature and high aspect ratio of CNTs. Alumina coated CNTs were used for better interfacial adhesion with the matrix. Oxidative resistance of CNTs was increased by coating them with alumina and by decreasing the grain boundary area in alumina – CNT nanocomposites. Coated and uncoated CNTs showed higher mechanical reinforcement in alumina nanocomposite as compared to CB. The future for ceramic – CNT nanocomposites is very bright, especially for applications associated with the electrical and thermal properties. Apart from a good understanding of nanocomposites, the commercial development of CNT based technologies heavily relies on the availability and price of CNTs.

Ad hoc wireless networks have emerged as a promising communication scheme to meet the ever growing portability and infrastructureless demand of wireless services. The transmission power level affects signal quality and interference which causes congestion and thus impacts the communication performance. Hence, power control has been the focus of extensive research. In this thesis, we examine the problem of power control in wireless networks, specially in ad hoc wireless networks. Two important types of power control, which are power control with fixed SNIR targets and power control with variable SNIR targets, are discussed in the thesis. We first introduce some important techniques and results involved in the development of power control algorithms and give literature review. A PI power control approach from literature is introduced. Due to lack of stability analysis, we show there are problems in the existing algorithm. We then propose a stable Proportional-integral (PI) power control algorithm. A forgetting factor is adopted to improve the transient performance. Distributed power control algorithms for systems with fixed SNIR targets might diverge when the feasibility condition is not satisfied. Multi-objective optimisation (MO) is adopted to deal with power control with variable SNIR targets. After discussing the existing MO algorithm, we propose a quadratic multiobjective-optimisation (QMO) algorithm where a quadratic objective function and the greedy methodology are adopted for the dynamics. Theoretical and simulation results of convergence of the new algorithms are given. We also provide review of some important power control frameworks which can be used to show convergence of power control algorithms. However, the QMO algorithm does not fall into any existing framework. In order to show convergence of the QMO algorithm, we suggest a new generalised framework in this thesis.

<p> This study examines whether 500 solid copper bullets fired from a 9mm firearm would have a significant effect on the individual rifling characteristics of the barrels of a Glock Model 17, a Beretta Model M9, and a Taurus Model PT 92 AF. Five silicone casts of each barrel bore were prepared over the course of this study. The casts were used to compare and evaluate the wear on the rifling of each barrel and note any changes that may have occurred during the progression of the study. The bullets were purchased as reloading components and were tested for hardness in addition to Energy Dispersive Spectroscopy (EDS) analysis. The bullets used for examination were collected at the start, throughout the experiment, and after the firearm had been cleaned following the 500 firings. The bullets, as well as barrel casts, were analyzed using a Leica FS C comparison microscope. Results from the analysis indicate the bullets do not obturate and they do not engage with the grooves of each barrel. Analysis of land impressions show striations that deteriorate or disappear completely; while others appear over the course of firing the 500 copper bullets. Regarding the influence of the bullet wear on the individual rifling characteristics, the striations of each firearm barrel were permanently changed to the point where bullet identification no longer was possible.</p><p>

This thesis is focussed on a numerical method to analyse the ballistic performance of multi-material armour system. The overall objective of this work is to develop numerical models to be used within MSC. DYTRAN capable of accurately predicting the ballistic response of multi-material composite armour, the effect of impact type on the damage and to help improve the armour design. The research presented in this thesis includes a review of the existing ceramic and composite damage models, combine, modify and optimize them to investigate the type and extent of damage response of the materials used in ballistic protection. The numerical model leads to insight into the parameters governing the penetration and deformation response of laminated composite subjected to ballistic impact. The effect of various model parameters on the predicted ballistic response of the ballistic plate is intensively investigated. It was found that the through thickness properties used in the numerical model have a large effect on the predicted ballistic response. A detailed study of the effect of mesh density on the numerical solution has shown that the numerical predictions are highly influenced by the element shape and size. The smaller the element the sooner the failure occurs, the less energy is absorbed and the smaller the time step becomes leading to a larger simulation time. The accuracy of the composite numerical model was evaluated by comparing the numerical prediction to experimental data obtained from ballistic impact trials. Very good agreement has been found between the experimental and numerical results for both observations of damage and deformation. Further, values of measured ballistic limit are in very good agreement with the values gained from the simulations. This correlation forms a verification of our finite element simulations. Fibre breakage is generally acknowledged as the main energy absorption mechanism in damage due to ballistic impact; in this work the delamination and matrix failure have been shown to increasingly contribute to the energy absorption mechanism by reducing the matrix strength. Further study of multi-layered ceramic composite armour has shown that use of ceramic tiles can improve the ballistic protection of the armour within an optimum ceramic composite ratio. Finite element simulation has been shown to be a very powerful technique to predict the behaviour of composite and ceramic panels under ballistic impact.

Skin is a complex biological composite system that serves as the outermost barrier to the environment and is mechanically robust. Understanding the mechanical properties of skin is important to improve and compare current in vitro experiments to the physiological conditions as the mechanical properties have a crucial role in determining cell behaviour. The mechanical behaviour of skin at the cellular level is expected to be dominated by the collagen fibre network within the dermis, which displays an anisotropic mechanical response to macroscopic loading. However, the three dimensional mechanical properties of skin at the nanoscale are not well understood. The aim of this work is to examine the mechanical properties of skin at the nanoscale in three dimensions and explore the links between the nanoscale and the macroscopic behaviour. Multiple sample preparation techniques are employed to expose the different layers of skin for mechanical testing and the elastic modulus of skin is evaluated by using atomic force microscopy (AFM) nanoindentation. The effect of freezing skin to cryogenic temperatures on the mechanical properties is evaluated and found to have no impact on the mechanical response of skin, indicating that the composition and structure of skin are robust enough to withstand the cryosectioning sample preparation methods used to expose the transverse layers of skin. AFM indentation was used to evaluate the elastic modulus of the dermis depending on the orientation of the sample and found to have an isotropic mechanical response. This result is opposite to anisotropy observed in macroscopic skin due to small scale mechanical testing ignoring collagen fibril orientation during strain. The variations in the elastic modulus of skin are also evaluated by AFM indentation at high spatial resolution to construct a composite model of the mechanical behaviour of skin at the nanoscale to predict the macroscopic response. The AFM nanoindentation technique was extended to evaluate the mechanical properties of a cell derived matrix deposited on an electrospun nanofibre scaffold, where the results indicate increasing the nanofibre diameter produces a cell derived matrix with an increased elastic modulus for more effective scaffolds. This work highlights the use of AFM mechanical testing to evaluate the nanoscale mechanical behaviour of skin, treated as a composite biological system, and determine the influence of the length scale and sample orientation on the observed mechanical response.

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 95-97). / Computational studies in kinetic transport are of great use in micro and nanotechnologies. In this work, we focus on Monte Carlo methods for phonon transport, intended for studies in microscale heat transfer. After reviewing the theory of phonons, we use scientific literature to write a Monte Carlo code solving the Boltzmann Transport Equation for phonons. As a first improvement to the particle method presented, we choose to use the Boltzmann Equation in terms of energy as a more convenient and accurate formulation to develop such a code. Then, we use the concept of control variates in order to introduce the notion of deviational particles. Noticing that a thermalized system at equilibrium is inherently a solution of the Boltzmann Transport Equation, we take advantage of this deterministic piece of information: we only simulate the deviation from a nearby equilibrium, which removes a great part of the statistical uncertainty. Doing so, the standard deviation of the result that we obtain is proportional to the deviation from equilibrium. In other words, we are able to simulate signals of arbitrarily low amplitude with no additional computational cost. After exploring two other variants based on the idea of control variates, we validate our code on a few theoretical results derived from the Boltzmann equation. Finally, we present a few applications of the methods. / by Jean-Philippe M. Péraud. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2007. / Includes bibliographical references (p. 201-215). / This thesis explored the incorporation of iptycenes into polymers as a means to enhance the mechanical properties. Iptycene structures were targeted because they possess a unique structural property called internal molecular free volume. When these bulky pendant groups are incorporated into the backbone of a polymer chain, they produce a novel chain architecture called molecular barbed wire. This molecular barbed wire architecture not only influences individual polymer chain dynamics but also induces lateral interactions between polymer chains through the minimization of internal molecular free volume. Work began by developing the concepts of internal molecular free volume and how to exploit its minimization. A formal definition for this property was created along with methods to identify and quantify its existence. Experimental results document the effects of introducing this property into polyesters and polycarbonates. Two specific novel inter-chain interactions were established: molecular threading and molecular interlocking. These steric interactions between polymers chains generate a non-bonded, network morphology and actively enhance the mechanical properties during deformation. / (cont.) It was demonstrated that the stiffness, strength and ductility of polymers could be enhanced simultaneously through this method. Mechanical properties were observed in tension at quasistatic deformation rates and in compression at both quasistatic and ballistic deformation rates. Improved mechanical performances were related back to structural properties through x-ray scattering experiments. Concepts of internal molecular free volume were necessary to explain the structure-property relationships observed. In addition, a prototype of enhanced polycarbonate was successfully developed for possible use in protective armor applications. This work provides a new pathway for the continued research and development in the field of ballistic protection. / by Nicholas T. Tsui. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2008. / Vita. / Includes bibliographical references (leaves 64-69). / Many potentially powerful therapeutic strategies for the treatment of disease require the delivery of drugs into the cytosolic or nuclear compartments of cells. Members of the Irvine laboratory have developed a novel pH-responsive core-shell nanoparticle system that can achieve efficient and non-cytotoxic drug delivery into the cytosol. Another advantage is that the shell can be easily modified to bind to different types of drug agents and incorporate ligands for specific cell targeting. Experimental analysis of the newly synthesized nanoparticles with various shell structures has demonstrated that modification of the shell does not compromise their cytosolic delivery. These nanoparticles, if successful, will improve the therapeutic potential of a wide range of drugs. However, critical issues on the research side need to be resolved, and an appropriate intellectual property strategy should be initiated in the near future. Applications to siRNA delivery and vaccines have been examined in depth, as cytosolic delivery is one of the main challenges in these fields. Partnerships with large pharmaceutical companies are critical in order to acquire key patents on siRNA/antigen. Even though the market is competitive, there is a strong demand for innovative delivery platforms; provided that the overall profile of the core-shell nanoparticles is comparable to that of emerging drug delivery systems, and a strong intellectual property portfolio is developed, the Irvine technology should be able to compete in the market. After analyzing risks on the business side, including the FDA approval process, a suggested business strategy is outlined, through which value can be successfully obtained throughout the existing pharmaceutical supply chain from the novel drug delivery system. / (cont.) The Irvine technology company will develop formulations, contract manufacturers will produce the nanoparticles, and pharmaceutical companies will concentrate on clinical trials, late-stage development and sales and marketing. A case study on the liver cancer market has demonstrated that commercial development of the Irvine nanoparticles can be a financially successful endeavor. / by Eun Chol Cho. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1990. / Includes bibliographical references (leaves 190-194). / by Ng, Lee Hong. / Ph.D.