Functionally heterogeneous porous scaffold design for tissue engineering

Most of the current tissue scaffolds are mainly designed with homogeneous porosity which does not represent the spatial heterogeneity found in actual tissues. Therefore engineering a realistic tissue scaffolds with properly graded properties to facilitate the mimicry of the complex elegance of native tissues are critical for the successful tissue regeneration. In this work, novel bio-mimetic heterogeneous porous scaffolds have been modeled. First, the geometry of the scaffold is extracted along with its internal regional heterogeneity. Then the model has been discretized with planner slices suitable for layer based fabrication. An optimum filament deposition angle has been determined for each slice based on the contour geometry and the internal heterogeneity. The internal region has been discritized considering the homogeneity factor along the deposition direction. Finally, an area weight based approach has been used to generate the spatial porosity function that determines the filament deposition location for desired biomimetic porosity. The proposed methodology has been implemented and illustrative examples are provided. The effective porosity has been compared between the proposed design and the conventional homogeneous scaffolds. The result shows a significant error reduction towards achieving the biomimetic porosity in the scaffold design and provides better control over the desired porosity level. Moreover, sample designed structures have also been fabricated with a NC motion controlled micro-nozzle biomaterial deposition system

Photocatalytic oxidation of ethanol using macroporous titania

Photocatalytic oxidation (PCO) using TiO2 is a potential means of remediating poor indoor air quality that is attributed to low levels of volatile organic compounds (VOC). In this work, ethanol is chosen as a simple compound representative of VOC’s. The aim of this research is to establish a baseline for the photocatalytic activity of TiO2 in ethanol PCO as well as the photonic efficiency of the photoreactor. The PCO conversion could then be enhanced by using photocatalyst having a macroporous structure. A flat plate photoreactor, UV light delivery and a flow system was designed in this work to accomplish ethanol PCO. Three kinds of photocatalysts were evaluated: 1) commercial Degussa P25 (in powder and slurry form), 2) unstructured sol-gel TiO2 and 3) macroporous TiO2 deposited on two substrates (optic fiber and glass slide). Titania from sol-gel hydrolysis was found to be a better photocatalyst than the commercial Degussa P25. Maximum PCO conversion found is 61% using an optimum TiO2 surface loading of 0.403 mg/cm2. A quantum efficiency of 2.3% was obtained for the photoreactor. Kinetic analysis of the experimental rate data gave an apparent reaction order of 0.45 and an approximate rate constant of 0.00144 (mol/cm3)0.55 (cm3/ gcat-s) for ethanol PCO. The photocatalyst samples were characterized using XRD and it was found that during sol-gel hydrolysis, only anatase crystalline phase was formed. From SEM images it was confirmed that the dipcoating method at low TiO2 weights resulted to a macroporous structure but only short range ordering is apparent. It was also found that colloidal crystals made from convective assembly have very good long range order and with clearly visible (111) symmetric plane. The available surface areas were measured from adsorption isotherms, for the unstructured sol-gel TiO2 it was found to have a surface area of 50 m2/g which is comparable to Degussa P25. The pore size distributions were generated from desorption isotherms, for the unstructured sol-gel TiO2 it was found to have an average pore size of 3.9 nm. A porosity of 0.21 and bulk density of 3.07 cm3/g was also found, indicating a much denser structure than Degussa P25 slurry. Lastly, an effort was made to attain higher PCO conversion for the macroporous TiO2 through higher TiO2 weights at ideal TiO2:PS weight ratio, using three different colloidal crystal templating methods and four variations of sol-gel infiltration techniques. However, no evidence that a macroporous structure was formed. Comparable PCO conversion values to unstructured sol-gel TiO2 were obtained. Additional work is needed to improve the methodology used in the fabrication of the macroporous structure

Practical Development of Si Anodes for High-Energy Lithium Ion Batteries

Department of Energy Engineering (Battery Science and Technology)Since the first commercialization of the lithium ion battery (LIB), LIB has played a significant role as a power source for electric devices. As increasing energy demands with the emergence of the electric vehicle and the energy storage system, improving the energy density of LIB has been recognized as one of the most important issue for battery researchers. Accordingly, the high-capacity materials have been investigated to break the theoretical capacity limit of current LIB chemistry with the carbonaceous anode and the lithium metal oxide cathode. In terms of the anode, silicon (Si) has received great attention because of its low discharge potential and 10 times greater theoretical capacity than the state-of-the-art graphite. However, the intrinsic hurdle of Si anodes, which is the huge volume expansion (300%) during battery operation, retards the application to the practical LIB. Therefore, the concrete strategies for overcoming the challenge are required in order to improve the energy density with utilizing Si anodes. For over twenty years, the nanoengineering has considerably improved the electrochemical performance of the Si anode by alleviating the intensified stress and strain from the volume change. However, there is a significant gap between the nanoengineered Si anode in academic field and the commercial LIB system in terms of the synthesis of Si anode, the battery manufacturing, and the electrochemical cell design. In this regards, to implement the Si anodes in commercial LIBs, several commercial factors such as the scalability, the rational cost, and performance feasibility, should be considered at the beginning of the development. Accordingly, herein, I have covered a comprehensive review about the co-utilization of graphite and Si anodes for commercial LIBs, the development of high-capacity Si anode for commercial high energy LIB, the benchmarking comparison of industrially-developed Si anode, and finally the remaining issues regarding the practical implementation of Si anode. In the Chapter 1, the graphite Specifically, the development of the Si anodes would be presented with physicochemical analysis, and the practical utilization of Si anodes for high-energy LIB would be discussed. Furthermore, in order to compare the performance of the developed Si anodes, benchmarking with industrial samples would be conducted with the electrochemical characterization and the failure mechanism analysis. In chapter 2, the high-capacity Si anodes for commercial high energy LIB is proposed with Fe-Cu-Si composite. FeCuSi is built up with Si nanoparticles and numerous nano-sized metal silicides as a form of a secondary particle. In this design, the micron-sized secondary particle exhibits high tap density which is easy to handle in the battery manufacturing process, and the numerous voids between Si nanoparticles effectively accommodated volume expansion of Si. In addition, the metal silicides such as iron silicide and copper silicide reduced interparticle contact resistance between Si nanoparticles. To investigate the commercial feasibility, the graphite-blended electrode with FeCuSi composite was fabricated under the commercial standard. It exhibited the superior electrochemical performances compared to industrially developed SiOx and FeSi anodes. In chapter 3, the benchmark comparison of industrially developed Si anodes including Si nanolayer-embedded graphite composite, carbon-coated SiOx, Si-containing graphite/carbon composite, has been presented. The benchmarking comparison was performed in graphite-Si blending system (fixed reversible specific capacity of 420 mAh/g) under the industrial electrode density (> 1.6 g/cc), areal capacity (> 3 mAh/cm2), and a small amount of binder (3 wt%). In addition, the one-to-one comparison has included essential items of both material characterization including laser diffraction particle size analysis, BET surface area, tap density, SEM, and HR-TEM, as well as the electrochemical analysis including half-cell and full-cell tests with measuring electrode volume expansion. As a result, the Si nanolayer-embedded graphite composite exhibited a great compatibility with conventional graphite. In chapter 4, I discuss the critical issues of the practical implementation of Si anode in high-energy LIBs. The electrochemical cell design has been systematically presented with proper examples. I emphasize that the influence of the electrochemical cell design on the battery performances when aimed at high volumetric energy density. In addition, based on the electrochemical design, the limit on the electrode swelling of Si anodes in terms of energy density is suggested. Furthermore, the origin of differences in the capacity fading between in the half-cell and in the full-cell is carefully figured out. Finally, I propose the potential future direction regarding with the electrode swelling, the capacity fading, and the feasibility study.clos

Integrated treatment of brackish groundwater

As freshwater resources become more limited, Australian coastal cities have begun building seawater desalination plants, and inland communities have begun investigating the option of treating brackish groundwater to supplement their water supply. Membrane reverse osmosis (RO) is the leading technology applied in municipal desalination. Despite the advances in technology, membrane scaling is a common problem causing membrane failure, decline in membrane flux and deterioration of product water quality. Since inland plants cannot dispose of RO concentrate into the ocean, they operate at high water recovery in order to minimize the volume of RO concentrate. Antiscalants (AS) are often added during RO pretreatment to prevent membrane scaling. Water recovery percentages (Rw) are then limited by AS efficacy and yet large volumes of RO concentrate are frequently disposed of in evaporation ponds. Therefore, it is important to find novel technologies to combat scaling issues. The integration of a ‘High-pH pretreatment’ in inland desalination plants is a promising choice for facilitating the removal of scale-forming precursors and other contaminants negatively affecting the desalination process. In a comprehensive project, this study investigated the efficacy of ‘High-pH pretreatment’ for membrane scale control and the removal of specific pollutants such as boron. The first phase of the project highlighted the differences between inland and seawater desalination and critically reviewed the existing strategies for RO concentrate minimization towards zero liquid discharge (ZLD) in inland desalination. In contrast to previous studies, the groundwater and RO concentrate collected for these experiments had a magnesium concentration higher than the calcium concentration. Furthermore, no previous studies evaluated the ‘High-pH pretreatment’ on magnesium-dominated water as this study does. The investigation continued further to assess the efficacy and utilization of two scale control technologies: acid/AS addition and ‘High-pH pretreatment’. Therefore, the second phase of this study evaluated ‘High-pH pretreatment’ of a RO concentrate followed by secondary RO to increase overall water Rw in an existing inland desalination system. The results showed that the lime and soda ash softening treatment followed by pH readjustment and AS addition, allowed the overall water Rw to increase from 80 to 97%. Experimental trials also confirmed CaCO3 and CaO recovery from the precipitated sludge through CO2 gas injection to selectively dissolve magnesium. This success provided a further opportunity to explore ‘High-pH pretreatment’ of RO concentrate followed by other advanced desalination technologies such as air-gap membrane distillation (AGMD). In the third phase of the study, two scale control strategies, ‘High-pH pretreatment’ and AS addition, for RO concentrate minimization were further investigated in a labscale AGMD system. The results indicated that the first option was more efficient in terms of preventing scale build up in the AGMD system. Following ‘High-pH pretreatment’, pH readjustment and AS addition, the use of AGMD minimized the existing RO concentrate with a TDS level of 10.8 g/L by a concentration factor of 3.2. In addition, the ‘High pH-pretreatment’, using lime and soda ash, facilitated the operation of the AGMD system at a higher temperature, thus permeate flux also increased. Boron can also be present in groundwater due to natural or anthropogenic sources. It can produce harmful effects on human health depending on both the frequency and extent of exposure. Boron removal is considered to be very complex. In fact, it is largely unclear whether softening pretreatments can enhance boron removal in groundwater desalination systems. Therefore, the final phase of this study investigated the feasibility of ‘High-pH pretreatment’ for boron removal from magnesiumdominated groundwater samples obtained from an existing inland desalination facility. Before commencing the experiments, the brackish groundwater was spiked with 5 mg/L of boron. The results revealed that the lime and soda ash softening treatment achieved 33% boron removal by sorption of hydroxyborate ions onto precipitated magnesium silicate. An additional 9% boron removal was achieved with magnesium chloride addition before the softening treatment, or by a secondary polishing treatment by means of adsorption with MgO. This solution can safely facilitate compliance with strict boron standards in inland desalination plants using RO or electrodialysis technology. This study evaluated the efficacy of integrating a ‘High-pH pretreatment’ in inland desalination plants treating magnesium-dominated groundwater. The novel approach overcame AS limitations and increased freshwater Rw in the inland desalination plant. It also enabled partial removal of other contaminants such as boron. Since groundwater quality is site-specific, selection and optimization of the most suitable treatment for every single process must be based on raw water characteristics

Designing heterogeneous porous tissue scaffolds for additive manufacturing processes

A novel tissue scaffold design technique has been proposed with controllable heterogeneous architecture design suitable for additive manufacturing processes. The proposed layer-based design uses a bi-layer pattern of radial and spiral layers consecutively to generate functionally gradient porosity, which follows the geometry of the scaffold. The proposed approach constructs the medial region from the medial axis of each corresponding layer, which represents the geometric internal feature or the spine. The radial layers of the scaffold are then generated by connecting the boundaries of the medial region and the layer's outer contour. To avoid the twisting of the internal channels, reorientation and relaxation techniques are introduced to establish the point matching of ruling lines. An optimization algorithm is developed to construct sub-regions from these ruling lines. Gradient porosity is changed between the medial region and the layer's outer contour. Iso-porosity regions are determined by dividing the subregions peripherally into pore cells and consecutive iso-porosity curves are generated using the isopoints from those pore cells. The combination of consecutive layers generates the pore cells with desired pore sizes. To ensure the fabrication of the designed scaffolds, the generated contours are optimized for a continuous, interconnected, and smooth deposition path-planning. A continuous zig-zag pattern deposition path crossing through the medial region is used for the initial layer and a biarc fitted isoporosity curve is generated for the consecutive layer with C-1 continuity. The proposed methodologies can generate the structure with gradient (linear or non-linear), variational or constant porosity that can provide localized control of variational porosity along the scaffold architecture. The designed porous structures can be fabricated using additive manufacturing processes

Augmenting Functional Adaptation: Does Obesity have a Systemic Effect on Bone Strength Properties in Humans?

This study considers the mechanical and neuroendocrine-metabolic effects of obesity on cortical bone and joint morphology throughout the human skeleton. Obesity has primarily been associated with changes in lower limb bone morphology, attributed to local mechanical responses; however, it is known that systemic metabolic shifts concomitant with obesity also influence bone turnover and cell signaling. Thus, the interaction of these mechanical and metabolic effects should be considered, rather than either factor in isolation. The presented research addresses this interaction by examining skeletal data obtained the William M. Bass Donated Collection (University of Tennessee), a modern collection with documentation representing obese and non-obese individuals. Much of the collection has also undergone x-ray computer tomographic (CT) scanning, providing the means to assess bone morphologies beyond the external surface. The scans of 114 individuals are used here to test the hypothesis that obese individuals have increased cortical bone strength properties throughout the skeleton due to both mechanical and systemic effects, while the linear joint dimensions remain unaffected. A total of 22 cross-sections from six skeletal elements (cranial vault, humerus, radius, femur, tibia, fibula), representing three mechanically disparate regions (cranial vault, upper limb, lower limb), and linear dimensions from three articulations (shoulder, hip, and knee) are examined for each individual. Results indicate that obese individuals exhibit larger cross-sectional geometric properties for the humerus, femur, tibia, and fibula relative to normal mass individuals, and the load bearing bones display the greatest magnitudes of difference. Furthermore, whole-diaphyses data indicate that variability in bone robusticity decreases along a proximal-to-distal gradient. Equivocal cranial vault results require further investigation, although the present study suggests that there are minute, if any, macroscopic differences in cranial vault properties between obese and normal mass individuals. Articular dimensions are found to be constrained relative to the diaphyseal cross-sectional measures. Both biomechanical and systemic stimuli are known to affect bone and adipose tissues in known capacities but are rarely examined together. The study presented here applies conclusions from the experimental literature to a human skeletal sample with known demographics, finding that both biomechanical and neuroendocrine-metabolic factors influence macroscopic bone morphology throughout the skeleton

Spanish Missionization and Maya Social Structure: Skeletal Evidence for Labor Distribution at Tipu, Belize

The cultural and human biological outcomes of Spanish colonization of the Americas were diverse. This dissertation examines the effects of Spanish colonization on Maya social structure using skeletal evidence for the distribution of labor at Tipu, a mission site in west central Belize. Skeletal remains of indigenous Maya buried in the context of a church, and in accordance with European Catholic burial customs, were examined for enthesis development and the cross-sectional morphology (CSG) of upper and lower limb long bones. Nothing besides burial placement in relation to the church (inside or outside the walls) denotes social status among individuals. Bone functional adaptations were used to examine the distribution of labor at Tipu and determine whether activity patterns varied by burial placement, and therefore social status. The bone functional adaptations of samples of pre-contact Maya elite and non-elites were also examined to determine whether the activity patterns of high and low status individuals at Tipu varied in the same way as those of Classic/Postclassic Maya of different social tiers. A 3D laser scanner was used to measure the surface areas of entheses on the humerus, radius and ulna, as well as CSG of the humerus (at 35% of length), femur and tibia (at midshaft). Detailed in this dissertation are: 1) a pilot study testing the reliability of the new 3D method for quantifying enthesis development, 2) an investigation of the distribution of labor at Tipu using entheses as indicators of habitual upper limb muscle use, and 3) an investigation of labor distribution at Tipu using CSG as indication of habitual upper limb use and mobility patterns. The pilot study presented in Chapter 2 supports the use of the 3D method for quantifying enthesis development. Chapters 3 and 4 demonstrate that both patterns of enthesis development and CSG at Tipu suggest Maya social structure changed with missionization. The activity patterns of high and low status individuals did not replicate those of pre-contact elites and non-elites. In general, the activity patterns of Tipuans of different social status were more similar. There were no drastic differences in the bone functional adaptations of inside and outside burial groups. However, some notable exceptions to this finding in both enthesis development and CSG suggest there may have been some task specialization among higher status Tipu men and women