Calcium polyphosphate (CPP) is a suitable substrate in a novel tissue-engineering strategy. The strategy aims to culture articular cartilage in vitro onto porous CPP and then implant the biphasic construct into the joint to replace damaged cartilage. CPP substrates should degrade faster to enhance repair. This project examined the structural and degradation effects of doping CPP with sodium phosphate, sodium hydroxide, and sodium carbonate. Doping concentration was narrowed to 0.01 Na2O/CaO for comparable phase composition to pure CPP. All doped groups sintered and crystallized at lower temperatures than pure CPP. Hydroxide-doped CPP did not form adequate sinter necks. At similar open porosity, Phosphate-doped CPP had similar diametral strength than pure CPP, while Carbonate-doped CPP had greater diametral strength. Degradation in vitro showed that Phosphate-doped CPP had greater strength loss, while Carbonate-doped CPP had similar strength loss, compared to pure CPP. Both doped groups degraded more slowly than pure CPP.

In vitro grown cartilage is functionally inferior to native tissue, and improvements in its quality should be attempted so it can be used therapeutically. In these studies we investigated the effects of cell shape on tissue quality through alteration of substrate geometry and application of mechanical stimuli. Articular chondrocytes were isolated and cultured on the surface Ti-6Al-4V substrates with various geometries. When cultured on fully porous titanium alloy substrates, chondrocyte spreading was enhanced over those grown on substrates with solid bases. Chondrocytes which remained round did not synthesize significant amounts of matrix and were thus unable to form cartilaginous tissue. In contrast, chondrocytes which were directed to spread to a limited amount, resulting in a polygonal morphology, accumulated significantly more matrix molecules and in time formed cartilage-like tissue. Computational fluid dynamics analyses demonstrated that cells on fully porous substrates experience time-dependent shear stresses that differ from those experienced by cells on substrates with solid bases where media flow-through is restricted. Integrin-blocking experiments revealed that integrins are important regulators of cell shape, and appeared to influence the accumulation of collagen and proteoglycans by chondrocytes. Furthermore, compressive mechanical stimulation induced a rapid, transient increase in chondrocyte spreading by 10 minutes, followed by a retraction to pre-stimulated size within 6 hours. This has been shown to be associated with increased accumulation of newly synthesized proteoglycans. Blocking the α5β1 integrin, or its β1 subunit, inhibited cell spreading and resulted in a partial inhibition of compression-induced increases in matrix accumulation, thereby substantiating the role of β1 integrins in this process. These results suggest that both fluid induced shear forces and compressive forces regulate chondrocyte matrix accumulation by altering cell morphology, which is mediated by integrins. Identifying the molecular mechanisms that influence chondrocyte shape and thus tissue formation may ultimately lead to the development of a tissue that more closely resembles native articular cartilage.

Many low dimensional structures arise from self-assembly when depositing metals on silicon surfaces, including both quantum dots and quantum wires. One class of these objects are rare earth silicide nanowires (RENW) grown on Si(001). In this dissertation, NW thermal stability, control of NW cross section, and associated surface reconstructions are studied by Scanning Tunneling Microscopy (STM). We test thulium and find for the first time that it forms NWs and these NWs are stable against prolonged annealing. We also find that the RENWs nucleate at 2×7 reconstruction domain boundaries. These results pave the way for precise control over NW size, placement, and integration with functional nanostructures and nanodevices.Another type of self-assembled NWs on Si(001) are insulating CaF2 NWs. As an ideal model system for epitaxial growth of an insulator on a semiconductor surface, CaF2 offers unique properties such as simple structure, good lattice match to silicon and congruent evaporation. In this thesis the growth behavior of CaF2 on the Si(001) surface is investigated. At low coverages CaF2 molecules randomly locate on Si(001). Features observed at this stage are explained in terms of dissociated fragments of CaF2 terminating the dangling bonds of Si dimers. Etching is observed after surface is saturated by these features with a 2×1 periodicity. A 2×n phase, grown at 750°C, suggests the dissociation of CaF2, as proved by the simulation of LEED patterns. A c(4×4) phase is observed from 0.5ML to about 1ML with deposition temperature from 600oC to 700oC. At the highest CaF2 deposition coverages studied, a stripe phase and CaF2 NWs are observed by a combination of STM, AFM and SEM. The results provide a significant expansion in the knowledge of CaF2 on Si(001). The common thread that links all these studies is the extent to which nanostructures can be controlled by careful growth conditions, not just by substrate temperature and the amount of material deposited, but also by timing of post-deposition annealing, etc. The grown nanostructures are metastable and result from a balance of energetic considerations and kinetics.

Calcium polyphosphate (CPP) is a suitable substrate in a novel tissue-engineering strategy. The strategy aims to culture articular cartilage in vitro onto porous CPP and then implant the biphasic construct into the joint to replace damaged cartilage. CPP substrates should degrade faster to enhance repair. This project examined the structural and degradation effects of doping CPP with sodium phosphate, sodium hydroxide, and sodium carbonate. Doping concentration was narrowed to 0.01 Na2O/CaO for comparable phase composition to pure CPP. All doped groups sintered and crystallized at lower temperatures than pure CPP. Hydroxide-doped CPP did not form adequate sinter necks. At similar open porosity, Phosphate-doped CPP had similar diametral strength than pure CPP, while Carbonate-doped CPP had greater diametral strength. Degradation in vitro showed that Phosphate-doped CPP had greater strength loss, while Carbonate-doped CPP had similar strength loss, compared to pure CPP. Both doped groups degraded more slowly than pure CPP.

Doctor of Philosophy / Department of Grain Science and Industry / Xiuzhi Susan Sun / Soy protein is one of the most promising bio-degradable adhesives as an alternative to synthetic petroleum-based adhesives for wood composite industries. In this study, soy protein was modified to improve adhesion properties and water resistance, which could facilitate the industrialization of soy protein-based adhesives. Furthermore, we attempted to identify a reliable indicator to predict the adhesion properties of soy protein by establishing the correlation of physical and mechanical properties with adhesion properties of soy protein. One of the objectives in this work was to investigate if inorganic calcium silicate hydrate (CSH) hybrids could improve adhesion properties of soy protein-based adhesives. 3-aminopropyltriethoxysilane (APTES) was used as a crosslinking agent between organic soy protein and inorganic CSH phases. APTES helped to form a crosslinked interface between soy protein and CSH, which was confirmed by changes in thermal, rheological, spectroscopic, and morphological properties with aging effect. More entangled structure and reduction of water-sensitive functional groups could lead to improvements in adhesion strength compared to unmodified soy protein-based adhesives. The second objective was to identify reliable indicators to predict shear adhesion properties by building the correlation between physical properties and adhesion properties of enzymatically modified soy protein-based adhesives (ESP). ESP was prepared with three independent variables (X1: trypsin concentration, X2: incubation time, and X3: glutaraldehyde (GA) concentration as a crosslinker) using a response surface methodology (RSM) called a central composite design (CCD). The important physical properties of viscosity (Y1), tacky force (Y2), and water resistance (Y3) were measured and investigated their relationship with adhesion strength. Viscosity, tacky force and water resistance showed solid correlation with adhesion strength of ESP and they were used to predict adhesion performance of soy protein modification system in this work. In addition, we studied the correlation between film strength and adhesion strength of another soy protein system. Because cohesion among protein molecules plays an important role in film and bonding mechanisms, we assumed that the film strength may be a reliable indicator to predict the adhesion strength of soy protein. The mechanical properties of the film and adhesion properties of soy protein on cherry wood were measured in terms of different concentrations of plasticizer (poly (propylene glycol) bis (2-aminopropyl ether) (H2N–PPG–NH2)). The results found out the low correlation between film and adhesion strength of soy protein in the presence of the plasticizer. We believe this might be caused by different curing conditions for film and adhesive applications of soy protein. Curing conditions greatly affect the thermal and curing behavior as well as mechanical properties of final materials. Thus, similar or comparable curing conditions should be required to obtain the information on the relationship between film and adhesion strength of soy protein.

The mechanisms underlying the effect of alterations in Type I collagen on bone mechanical properties are not well defined. Clinical tools for evaluating fracture risk, such as dual energy x-ray absorptiometry (DXA) and quantitative ultrasound (QUS) focus on bone mineral and cannot detect changes in the collagen matrix. The mechanical response tissue analyzer (MRTA) is a potential tool for evaluating fracture risk. Thus, the focus of this work was to investigate the effects of collagen degradation on bone mechanical properties and examine whether clinical tools can detect these changes. Female and male emu tibiae were endocortically treated with 1 M potassium hydroxide (KOH) solution for 1-14 days and then either mechanically tested in three-point bending, fatigued to failure or fatigued to induce stiffness loss. Computed Tomography scans, DXA, QUS, MRTA and three-point bend testing in the elastic region were performed on emu tibiae before and after either KOH treatment or fatigue to induce stiffness loss. Fracture surfaces were examined to determine failure mechanisms. Bone mineral and bone collagen were characterized using appropriate techniques. Bone mineral-collagen interface was investigated using Raman spectroscopy and atomic force microscopy (AFM). Endocortical KOH treatment does not affect bone mineral however, it causes in situ collagen degradation, rather than removal and may be weakening the mineral-collagen interface. These changes result in significantly compromised mechanical properties. Emu tibiae show significant decreases in failure stress and increased failure strain and toughness, with increasing KOH treatment time. The significant increase in toughness of KOH treated bones is due to structural alterations that enhance the ability of the microstructure to dissipate energy during the failure process, thereby slowing crack propagation, as shown by fracture surface analysis. KOH treated samples exhibit a lower fatigue resistance compared to untreated samples at high stresses only for both sexes. Partial fatigue testing results in similar decreases in modulus for all groups and sexes. The MRTA detected these changes whereas DXA and QUS did not. MRTA detects changes in bone mechanical properties induced by changes in collagen quality and fatigue and could be a more effective tool for predicting fracture risk.

Transition metal oxide thin films are commonly used in organic electronics devices to improve charge-injection between electrodes and organic semiconductors. Some oxides are good hole-injectors, while others are good electron-injectors. Transition metal oxides are materials with many diverse properties. Many transition metals have more than one stable oxidation state and can form more than one oxide. Each oxide possesses its own unique properties. For example, transition metal oxide electronic band structures can range from insulating to conducting. They can exhibit a wide range of work functions. Some oxides are inert, while others are catalytically active. Such properties are affected by numerous factors, including cation oxidation state and multiple types of defects. Currently it is not fully understood which oxide properties are the most important to their performance in organic electronics. In the present thesis, photoemission spectroscopy is used to examine how changes in certain oxide properties–such as cation oxidation states and defects—are linked to the oxide properties that are relevant to organic electronics devices—such as an oxide’s work function and electron band structure. In order to unravel correlations between these properties, we controllably change one property and measure how it changes affects another property. By performing such tests on a wide range of diverse transition metal oxides, we can discern broadly-applicable relationships. We establish a relationship between cation oxidation state, work functions and valence band structures. We determine that an oxide’s electron chemical potential relative to an organic’s donor and acceptor levels governs energy-level alignment at oxide organic interfaces. We establish how interfacial reactivity at electrode/oxide interfaces dictates an oxide’s work function and electronic structure near the interface. iii These findings demonstrate some of the very interesting fundamental relationships that exist between chemical and electronic properties at interfaces. These findings should assist in the future development and understanding of the functional interfaces of organic semiconductors and transition-metal oxides.

The effects of crosslinking on EVA foaming are studied in this thesis. A fundamental approach was applied to describe the influences of crosslinking on EVA/gas viscosities, gas solubility and diffusivity in EVA, EVA foaming nucleation and early stage of bubble growth, which leads to a better understanding of the plastic foaming mechanism. Although crosslinked polyolefin foaming technology has been well applied in industry, more fundamental and thorough studies are demanded to understand the mechanism, which can serve to improve the present technology. The shear and extensional viscosities have been measured for the chemically crosslinked EVA with dissolved gas which could not be found from literature. Furthermore, by controlling the crosslinking agent amount, the polymer melt strength/viscosity can be controlled, so as to obtain optimum foam morphology. The crosslinking also has effects on the diffusivity and solubility of a blowing agent inside EVA. The solubility and the diffusivity of the blowing agent in the EVA decrease with the crosslinking degree increases. The diffusivity decrease makes more gas is utilized for the foaming rather than leak out of the polymer matrix quickly. This thesis also presents the fundamental studies on the effects of crosslinking on cell nucleation and early bubble growth. Theoretical work and in-situ visualization experimental results indicate that partial crosslinking leads to higher cell nucleation density and slower bubble growth, both of which benefit a fine-cell foam morphology generation. Last but not least, an optimized foaming process was conducted to produce chemically crosslinked EVA foams with large expansion ratios in a batch system, using a chemical blowing agent. The results determine that an optimal crosslinking degree is critical for the crosslinked EVA foaming with maximum expansion ratio. Furthermore, all research results not only benefit the foaming of crosslinked EVA, but also serve the better production of other crosslinked polyolefin foams.

Organic light emitting diodes (OLEDs) are being commercialized in display applications, and will be potentially in lighting applications in the near future. This thesis is about the design of high performance OLEDs, which includes both the electrical and optical design of OLEDs. In particular, the following work is included in this thesis: i) Energy level alignment and charge injection at metal/organic interfaces have been systematically studied. ii) Transition metal oxide anodes have been developed to inject sufficient holes into the OLEDs due to their high work function. The oxide anodes have also been used to systematically study the transport properties in organic semiconductors. iii) Highly simplified OLED devices with unprecedentedly high efficiency have been realized using both fluorescent and phosphorescent emitters. The high performance was enabled by using a high work function metal oxide anode and a hole transport material with very a deep highest occupied molecular orbital (HOMO). iv) An optical model has been developed to describe the optical electric field across the OLED device. By using the model, a high performance flexible OLED using metal anode was designed and realized.

Aluminum Doped Zinc Oxide (AZO) produced by radio frequency (RF) magnetron sputtering is thought to be the prospective replacement of the de facto standard indium tin oxide (ITO) anode in organic solar cells. In order to achieve a proper resistivity and transmittance of AZO thin film compared to ITO, a systematic study was done to optimize the sputtering conditions. In this work, two primary parameters: target-substrate distance and sputtering power, were optimized, and a optimized film thickness was determined. A poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM) bulk-heterojunction organic solar cell was fabricated based on the optimized parameters and the power conversion efficiency reached 0.83%. A theoretical analysis is given to explain the optimization process. This work provides a clear pathway to substitute AZO for ITO in organic solar cells for future mass production.