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The development of porous materials useful as scaffolds for the sustained three-dimensional (3D) growth of human adipose-derived stem cells (hASC) is of particular interest to facilitate healing after musculoskeletal injuries. In this study, a composite porous material obtained by blending akermanite with poly-e-caprolactone (PCL) is proposed as novel alternative to bone tissue regeneration. The objectives of this study are (1) to characterize the akermanite:PCL scaffold properties; (2) to investigate the in vitro osteogenic potential of hASC loaded to optimal akermanite:PCL scaffolds; (3) to assess the metabolic activity and osteogenesis of hASC loaded to optimal akermanite:PCL scaffolds post-thawing using optimal cryopreservation protocol; and (4) to evaluate the behavior of optimal akermanite:PCL scaffolds in vivo using an immunodeficient murine model for ectopic bone formation. We hypothesized that (1) optimal akermanite:PCL blend has mechanical properties and biocompatibility suitable for tissue engineering applications; (2) hASC loaded to optimal akermanite:PCL scaffolds has higher expression of mature osteogenic marker in scaffolds cultured in osteogenic medium for 21 days; (3) PVP-serum free medium can be used to cryopreserve hASC loaded to optimal akermanite:PCL scaffolds; and (4) hASC preloaded to optimal akermanite:PCL scaffolds would produce meaningful bone-like tissue 8 weeks post-implantation. According to the results, 75:25 akermanite:PCL composite scaffolds displayed increased mechanical (1), biological and osteogenic properties (1-3). Moreover, hASC loaded to 75:25 akermanite:PCL scaffolds and frozen at 40ᵒC/min displayed metabolic activity and osteogenesis comparable to fresh control scaffolds (3). However, in vivo implantation of akermanite-base scaffolds (akermanite and akermanite:PCL) in nude mice, sudden death within the first 48 hours of this study (4). The acute toxicity observed in all animals assigned to the akermanite scaffolds was associated to a disturbance of the phosphorus homeostasis in vivo. Specifically, akermanite and akermanite:PCL scaffolds harvested 48 hours post-implantation had comparable levels of phosphorous in the composition, indicating acute phosphorous depletion from the serum. Accumulative evidences have suggested that akermanite is biocompatible and can enhance adhesion, proliferation and osteogenic phenotype maintenance of adult/osteoprogenitor stem cells both in vitro and in vivo. As a conclusion, further studies are needed to address the akermanite dose-dependent toxicity in murine models for akermanite-assisted bone regeneration.

Indentation is a useful technique for studying the mechanical properties of a material. Measurable mechanical properties from indentation include time-dependent as well as time independent properties. Among these mechanical properties, time-dependent permanent deformation (creep) is of interest in this study. The purpose of this study is to explore the behavior of creep deformation of a solid under indentation. The main scientific research tool will be the finite element method. Existing works by others provide limited solutions that allow us to correlate uniaxial creep to indentation creep. In this study, the task is taken a step further to enhance and modify previous solutions to more realistic indentation situations. Indentations with spherical and conical indenter geometries are considered. Practical data obtained from indentation creep are usually in the form of displacement (h) – time (t) or load (P) – displacement (h). Results in this study are derived to describe this behavior and obtain fundamental creep parameters from it. Elasticity may not be ignored in the majority of indentation situations. Therefore, the effect of finite elastic deformation is considered in this study with the intention of characterizing elastic transient phenomena. From the results, certain criteria in terms of an experimentally measurable parameter will be suggested in order to avoid misinterpreting indentation data influenced by the initial elasticity. The effect of finite strain – finite deformation in indentation is investigated. Creep solutions provided by others usually assume infinitesimal strain – infinitesimal deformation. As a result, only blunt cones approaching the geometry of a flat punch indenter have been considered for the most part in previous works. In this study, the problem of finite strain – finite deformation is addressed for conical indentation. Various half-included cone angles of the indenter are considered to account for finite strain – finite deformation problems. The power law relation is the most common general description of creep deformation when strain rate and steady-state stress are involved. However, power law breakdown, due to large strain rates and stresses may occur during the initial parts of indentation, especially for conical indenters. Modeling of power law breakdown in indentation creep is presented and corresponding relations between uniaxial to indentation creep behavior are proposed in this study.

Focus of this research is on developing cotton-based nonwoven mattress pads with flame retardant (FR) properties by blending cotton with other commercially available fibers, binders, and followed by chemical treatments; offering a cost-effective recipe to meet the upcoming flammability standards. Furthermore this research explores the opportunities taking advantage of possible synergistic effects to achieve maximum performance. Recent changes in the flammability regulations require improvements in the flame resistance of cotton-containing consumer goods such as upholstered furniture, mattresses, and pillows. Cotton, synthetic fibers, fabrics, and foam are the basic constituents of these goods that are often the first to be engulfed by fire. Hence there is a need to impart certain degree of flame resistance based on their end use. In case of real fires, these improvements in flame retardancy would provide more time for people to escape from a fire with fewer injuries, and result in savings of life as well as property. Cotton being a highly flammable fiber, to achieve higher degree of flame resistance, it is necessary to incorporate additional fibers and chemicals into cotton products. Choice of appropriate materials can help to achieve a synergistic role in the combustion process to slow down burning, reduce flame spread, or even extinguish the fire. Many of these chemicals are expensive and lead to a spike in the product cost. Moreover there are certain FR chemicals that are likely to pose environmental and health hazards. The FR chemicals used in this research are halogen free and have been considered safe. Finally, a cost effective recipe for constructing mattress pads that passes the latest flammability tests was developed. As planned, these nonwoven pads were produced by blending cotton with other commercially available fibers, binders, and followed by chemical treatments that take advantages of various synergistic effects to achieve maximum performance at low cost. The product of this research is a good candidate for mattress pads as well as other products such as upholstered furniture, mattress ticking, and pillows, which are required to comply with the open flame standards.

A high resolution x-ray tomography system was used to study chopped fiber polymeric composites made of polypropylene resin, nickel coated carbon fiber and Eglass fiber. Procedures are developed to obtain micro-structured features of importance. In-situ tensile testing system was developed and integrated into the existing hardware for tomography equipment to study the evolution of damage and micro-structural features as a function of mechanical stress. High resolution x-ray tomographic images of glass fiber were collected and viewed on a micron scale. The radiographs were reconstructed to visualize the fiber content of the samples in three dimensional volume. In addition, glass fiber dogbone specimens were tested on a miniature tensile machine using x-ray tomography to view deformation of the samples in high resolution. Fractures in the chopped glass composite were observed for x-ray microscopy showing the dominant failure mechanism of the sample are low interfacial strength and adhesion between the fiber and matrix. Cracks were not observed until after failure by fiber pull-out using the digital microscopy method. Using SEM microscopy method, resin cracking and fiber debonding was observed for a carbon fiber with vinyl ester resin while under tensile loading. Important micro-structural information relationship with and mechanical behavior including variation modulus, yield and ultimate strength are discussed.

Within the scope of this thesis, an experimental system has been designed, developed and manufactured for the determination of the wetting behavior of liquids and polymer melts with solid surfaces (coated and uncoated) at high temperatures (> 200 ºC). The measurement system incorporates a modified Wilhelmy plate technique, using a precision weighing module, a vertical linear stage, custom developed application software using LabView with suitable hardware and a high temperature furnace with thermocouple feedback control. Experiments have been performed and are reported to evaluate the performance of the testing system, using liquids of known wetting properties. A suitable testing procedure based on dynamic Wilhelmy plate theory is proposed, involving investigation of advancing and receding liquid-probe interactive forces and hysteresis loops. Interfacial wetting and wicking behavior of polystyrene melt with clay based refractory coatings, as used in the lost-foam casting (LFC) process, are presented a function of temperature using this measurement system. Experiments of particular interest were performed for two different types of refractory coating and for polymer melts at processing temperatures between 220°C and 300°C, where they show pronounced viscoelastic behavior. Different variables, obtained from the hysteresis loops, were utilized as quantitative indicators for comparison, including the area under the loop from contact onwards, the slope of advancing and receding lines in the force-displacement domain, the force hysteresis at zero displacement and Fast Fourier Transform (FFT) analysis of the hysteresis loop.

Objective. To perform frequency response analysis of passive intact and rneniscectomized human knee joints under body mass. The knee dynamic system parameters and their alterations with different preloads and displacement amplitudes will be determined. Design. Using an Instron Mechanical Testing System, specially designed fixtures, and the following softwares: WaveMaker, Excel, LabView, and Matlab, the knees were dynamically tested and analyzed. Background. Studies have been performed to analyze the dynamic behavior of the human knee. However, no experimental study has investigated the dynamic response of the knee joint under an axial compressive dynamic loading condition considering the effect of the upper body mass. Methods. Ten human knee joints were each placed in fixtures and secured in the Instron equipment, with an added mass to simulate body weight. The dynamic testing sequence consisted of creep tests, a series of frequency sweeps at increasing amplitudes, and relaxation tests. This testing series was performed with the knee in full extension, and at a 25-degree flexion angle. A meniscectomy was performed on each specimen, and the testing trial was performed again. The data from testing was then analyzed, and the joint response was obtained. Results. The results indicated that the resonance frequency is significantly affected by change in preload and flexion angle. Increase in preload resulted with an increase in resonant frequency, but flexing the knee resulted in a decreased resonant frequency. The stiffness also decreased significantly when the knee was flexed. The joint compliance response increased up to two fold at resonant frequency compared with that of 1 Hz frequency at different joint conditions. Conclusion. The compliance graphs had similar shapes and had interesting trends that yielded results that can be used as reference data for future studies and rehabilitation means. The analysis indicated that there is a range in the dynamic factors depending on the testing conditions. The meniscectomy had a significant effect on the joint response as well.