Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007. / Includes bibliographical references (p. 157-166). / Endothelial cells play a central role in maintaining vascular integrity. Lesions in the endothelial layer may allow the invasion of leukocytes into the artery wall and promote inflammatory responses that could possibly lead to atherosclerosis. Over the past decade, a series of studies have demonstrated the presence of a delicate surface layer, named the glycocalyx, decorating the endothelial membrane and associated with a number of physiological implications in the vasculature. This thesis studies the flow-induced dynamics of the endothelial glycocalyx layer and reports the first direct measurement of the in vitro mechanical properties as well as the thickness of the glycocalyx through a novel optical imaging approach. Here, we have developed an optical imaging system that tracks the position of single particles in three-dimensional (3D) space with high precision, typically 1~4 nm in the XY plane and 15 ~ 40nm in the Z-direction along the optical axis of the microscope. With the use of quantum dots (QDs), semiconducting nanoparticles of superior optical characteristics, this method provides the opportunity to investigate biological subjects in living cells that can be neither spatially resolved nor continuously traced over minutes by conventional optical microscopy techniques. Therefore, by 3D mapping of both the glycocalyx layer and the membrane using quantum dots of different colors, the in vitro thickness of the endothelial glycocalyx layer is found to be - 350nm. With QDs attached to the glycocalyx layer, we track the flow-induced motion of this thin structure at multiple levels of oscillating shear stresses from 5 to 20 dynes/cm2. The displacement of each QD ranges from 80 - 400 nm and varies from cell to cell and point to point on a single cell. / (cont.) The estimated Young's modulus is thus~6.7Pa, for a 3D matrix with a measured thickness of ~ 350nm. The QD motion, staying in phase with the applied shear stress up to the 1Hz limit of the present study, confirms the highly elastic gel nature for the glycocalyx layer in which major deformations occur at physiological level of fluid shear stress. / by Yu Yao. / Ph.D.

Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 101). / The project work presented in this thesis has proposed solutions related to the control of production and work-in-process inventory in a multi-item multi-stage manufacturing system. A suitable base-stock inventory control policy is recommended to ensure that the desired service levels are maintained between production stages and for the final customers. Concept of coupling the production lines though coupling-stock under suitable assumptions is then introduced to reduce the stock levels at certain consecutive production stages. A framework for demand seasonality and characteristic analysis is also established to enable the inventory control policy to respond to seasonal variations. Monte Carlo simulation was performed on a model of chain of production stages controlled under base-stock policy for the verification of results and to study the effects of stock-outs on base-stock levels. The results of simulation study showed that overall system performance is satisfactory and desired service levels were achieved. Simulation work was also carried out to validate the line coupling concept and its performance under certain conditions. A novel Kanban based visual management system design, which is aligned with the requirements of inventory control policy, along with the material transfer batch sizes between production stages is proposed to facilitate the implementation of inventory control policy. Furthermore, capacitated shipment planning approach is proposed and implemented in form of a spreadsheet-based interface to aid planning personnel in shipment planning under the constraints provided by the inventory control policy. / by Syed Zia Abbas Rizvi. / M.Eng.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 327-332). / MEMS fabricated electrical contacts consist of two MEMS fabricated surfaces which are physically separated and brought together for the purpose of carrying current. MEMS fabricated electrical contacts are used in a wide variety of applications including MEMS relays, wafer probing applications, and the packaging and assembly of MEMS devices. In all of these devices, low, stable contact resistance is desired. Modeling these contacts is difficult because much of traditional contact resistance theory was derived for macro scale contacts and relies on assumptions not valid at the MEMS scale. A large variety of factors affect contact resistance including contact force, contact scrub, contact material, and contact geometry. Additionally, electrical characteristics of these contacts can change over many cycles. The result of this is that the MEMS fabricated electrical contacts used in a variety of devices are often designed using a trial and error approach to determine which contact materials and geometries work best. Since these devices are often expensive and timely to manufacture, this method of design is far from ideal. The objective of my research is to develop a system for measuring and characterizing a wide variety of MEMS fabricated electrical contacts. The system consists of two silicon coupons which can be assembled and disassembled with a positional repeatability of less than one micron. This system allows any combination of contact force and contact scrub to be imparted on a pair of MEMS fabricated electrical contacts. The contacts themselves can consist of a wide variety of materials fabricated in a wide variety of ways including sputtering contact material, plating contact material, unconventional contact materials, plated tips, and three-dimensional tips. The repeatable assembly and disassembly of the coupons allows the contacts to be tested, observed using metrology such as an SEM or AFM, and then reassembled for further testing. This allows the changes in the contact surface to be observed as the contact is cycled. The instrumentation to impart force, scrub and measure contact resistance has also been developed. This system is used to measure the contact resistance between flat-on-flat contacts, plated tip contacts, and spherical contacts. The results of these tests offer fundamental (cont.) insights into the contact resistance between two thin films as well as compile a variety of data regarding multiple contact materials and contact geometries. / The results of these tests are used to create guidelines for designers of MEMS fabricated electrical contacts. Additionally, this platform can be used as a method of measurement and characterization for designers of MEMS fabricated electrical contacts to test any new contact geometries and materials in a quick cost effective manner. This method can also be used by research scientists investigating the fundamental physics of MEMS scale electrical contacts. / by Melissa B. Read. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references. / Arthroplasty, the practice of rebuilding diseased biological joints using engineering materials, is often used to treat severe arthritis of the knee and hip. Prosthetic joints have been created in a "biomimetic" manner to reconstruct the shape of the biological joint. We are at a disadvantage, however, in that metals and polymers used to replace bone and articular cartilage often wear out too soon, leading to significant morbidity. This thesis explores the use of kinetic-mimicry, instead of bio-mimicry, to design prosthetic rolling contact joints, including knee braces, limb prosthetics, and joint prostheses, with the intent of reducing morbidity and complications associated with joint/tissue failure. A deterministic approach to joint design is taken to elucidating six functional requirements for a prosthetic tibiofemoral joint based on anatomical observations of human knee kinetics and kinematics. Current prostheses have a high slide/roll ratio, resulting in unnecessary wear. A rolling contact joint, however, has a negligible slide/roll ratio; rolling contact prostheses would therefore be more efficient. A well-established four-bar linkage knee model, in a sagittal plane that encapsulates with the knee's flexion/extension degree of freedom, is used to link human anatomy to the shape of rolling cam surfaces. The first embodiment of the design is a flexure coupling-based joint for knee braces. Failure mode analysis, followed by cyclic failure testing, has shown that the prototype joint is extremely robust and withstood half a million cycles during the first round of tests. Lubrication in the joint is also considered: micro- and nano-textured porous coatings are investigated for their potential to support the formation of favorable lubrication regimes. Hydrodynamic lubrication is optimal, as two surfaces are separated by a fluid gap, thus mitigating wear. Preliminary results have shown that shear stress is reduced by more than 60% when a coating is combined with a shear thinning lubricant like synovial fluid. These coatings could be incorporated into existing joint prostheses to help mitigate wear in current technology. This thesis seeks to describe improvements to the design of prosthetic joints, both existing and future, with the intent of increasing the overall quality of care delivered to the patient. / by Alexander Henry Slocum, Jr. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1991. / Includes bibliographical references (leaves 136-141). / by Jong Hyeon Park. / Ph.D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 243-245). / Product development cycles have consistently become shorter, but the timeline for designing and developing manufacturing equipment has changed little. In some cases the time do design manufacturing equipment can be several times longer than the development cycle for the product it will produce. Consequently, manufacturing equipment development is under growing pressure to efficiently produce equipment solutions in reduced time. Building upon lessons from microelectronics design tools and trends in specialized digital design tools, this thesis examines the potential for a platform of modular design tools targeted at the design, analysis, and fabrication of process and manufacturing equipment through the development of the platform's first design tool: a web-based tool for the design and analysis of Cartesian positioning systems. This thesis documents the codification of positioning system design into physical and functional representative models that enable a systematic, yet flexible workflow focused on decreasing development cycle time, reducing error and oversight, and diminishing barriers in the product selection process. In the positioning system design tool, the user first configures a system architecture using rules based on common architectures and defines inputs for work envelope and payloads. The user is then able to search for, compare, and select products from a vendor-submitted part library based upon performance measures and target specifications. The product selections and resulting design are then validated using force and moment analysis, motion path time analysis, and precision analysis. The development effort associated with the tool emphasized the importance of appropriate levels of representation for different tool functions and resulted in a guiding methodology for the development of future design tool modules. / by Andrew Turner Kriebel. / S.M.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 128-135). / Skeletal muscle wasting disorders such as sarcopenia affect the daily mobility of millions of aging people globally due to decreased muscle mass and decreased muscle efficiency. In this study we discover a novel target to improve the efficiency of skeletal muscle by targeting the dynamic f-actin cytoskeleton. Using two model systems, an ex-vivo mouse muscle model and a novel in vitro optogenetic skeletal muscle micro-tissue model, we show that disruption of the dynamic f-actin cytoskeleton using small molecule actin dynamics inhibitors leads to a persistent 2-fold improvement in muscle active contractility. We explored possible drawbacks of f-actin disruption, including loss of mechanical integrity, cell death, and intracellular organelle damage. None of these downsides actually present themselves with f-actin disruption. Muscle fatigue resistance however does seem to be slightly affected. We performed a detailed characterization of the cytoskeletal modifications that occur during f-actin disruption using dose-response-recovery studies, live f-actin imaging, fluorescence recovery after photobleaching and more targeted f-actin disruption. Using these studies we conclude that treatments which shorten f-actin filaments seem to improve contraction. We also uncovered previously unidentified roles of branched and tropomyosin stabilized f-actin in force transmission. Biomechanical testing at the cell level using AFM and at the tissue level using a micro-tensile test shows a drop in mechanical stiffness that correlates well with a corresponding improvement in muscle force. We ruled out a range of alternate hypotheses involving changes to sarcomeric proteins and energetic activity, that could explain the force improvement, concluding that the force improvement due to f-actin disruption is due to mechanical softening of the cells which pose to a lower resistance to their own contraction. As a potential application, we show that a weak 3D printed muscle powered biological robot starts walking with f-actin disruption. This target has significant therapeutic potential in muscle disorders due to its disease non-specificity. We conclude by discussing possible future experiments that could reveal the best therapeutic applications. Key words: Muscle strength, f-actin, cytoskeleton, Skeletal Muscle Tissue Engineering, Muscle Disorders. / by Vivek Sivathanu. / Ph. D.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Cataloged from student-submitted PDF version of thesis. / Includes bibliographical references (pages 103-105). / Integrated supply chain models provide an opportunity to optimize costs and production times in the supply chain while taking into consideration the many steps in the production and delivery process and the many constraints on time, shared resources, and throughput capabilities. In this work, mixed integer linear programming (MILP) models are developed to describe the manufacturing plant, consolidation transport, and distribution center components of the supply chain. Initial optimization results are obtained for each of these models. Additionally, an integrated model including a single plant, multiple consolidation transport vehicles, and a single distribution center is formulated and initial results are obtained. All models are implemented and optimized for their given objectives using a standard MILP solver. Initial optimization results suggest that it is intractable to solve problems of relevant scale using standard MILP solvers. The natural hierarchical structure in the supply chain problem lends itself well to application of decomposition techniques intended to speed up solution time. Exact techniques, such as Benders decomposition, are explored as a baseline. Classical Benders decomposition is applied to the manufacturing plant model, and results indicate that Benders decomposition on its own will not improve solve times for the manufacturing plant problem and instead leads to longer solve times for the problems that are solved. This is likely due to the large number of discrete variables in manufacturing plant model. To improve upon solve times for the manufacturing plant model, an approximate decomposition technique is developed, applied to the plant model, and evaluated. The approximate algorithm developed in this work decomposes the problem into a three-level hierarchical structure and integrates a heuristic approach at two of the three levels in order to solve abstracted versions of the larger problem and guide towards high-quality solutions. Results indicate that the approximate technique solves problems faster than those solved by the standard MILP solver and all solutions are within approximately 20% of the true optimal solutions. Additionally, the approximate technique can solve problems twice the size of those solved by the standard MILP solver within a one hour timeframe. / by Lindsay Sanneman. / S.M.

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2018. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 173-175). / The MIT Education and Practice Factory was launched with support from the Massachusetts Manufacturing Innovation Initiative as part of the education and workforce development program of American Institute of Manufacturing Photonics. It is an advanced manufacturing facility integrated in an academic environment, and is designed to be utilized by three different groups, including researchers, students, and professional manufacturing staff from industry. The current capability of the MIT Education and Practice Factory offers equipment and process solutions for packaging photonics products, including chip packaging and testing. These capabilities fit very well with the research and commercial needs of research groups and industrial partners. The manufacturing scale-up requirements associated with technologies for Test, Assembly and Packaging (TAP) are significant for the photonics industry, and contribute to about seventy percent of the entire production cost. Advances in manufacturing technologies are critical to the value-add supply chain. In this thesis, the creation process of the MIT Education and Practice Factory will be reviewed. Three major stages of the project will be covered in detail, including (1) factory setup, (2) pilot products development, and (3) production ramp up. / by Mingxiu Sun. / S.M.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1990. / Includes bibliographical references (p. 236-257). / by Allen Morely Lush. / Ph.D.