published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

published_or_final_version / Orthopaedics and Traumatology / Master / Master of Philosophy

Novel net shaping technique Laser Engineered Net shaping™ (LENS) laser based manufacturing solution (Sandia Corp., Albuquerque, NM); Laser can be used to deposit orthopedic implant alloys. Ti-35Nb-7Zr-5Ta (TNZT) alloy system was deposited using LENS. The corrosion resistance being an important prerequisite was tested electrochemically and was found that the LENS deposited TNZT was better than conventionally used Ti-6Al-4V in 0.1N HCl and a simulated body solution. A detailed analysis of the corrosion product exhibited the presence of complex oxides which are responsible for the excellent corrosion resistance. In addition, the in vitro tests done on LENS deposited TNZT showed that they have excellent biocompatibility. In order to improve the wear resistance of the TNZT system boride reinforcements were carried out in the matrix using LENS processing. The tribological response of the metal matrix composites was studied under different conditions and compared with Ti-6Al-4V. Usage of Si3N4 balls as a counterpart in the wear studies showed that there is boride pullout resulting in third body abrasive wear with higher coefficient of friction (COF). Using 440C stainless steel balls drastically improved the COF of as deposited TNZT+2B and seemed to eliminate the effect of “three body abrasive wear,” and also exhibited superior wear resistance than Ti-6Al-4V.

The polymer gels especially hydrogels have a very special structure and useful features such as unusual volume phase transition, compatibility with biological systems, and sensitivity to environmental stimuli (temperature, pH value, electric field, light and more), which lead to many potential applications in physical and biochemical fields. This research includes: (1) the theoretical and experimental studies of polymer gels on swelling kinetics, spinodal decomposition, and solution convection in gel matrix; (2) applications of polymer gels in wound dressing, tissue-simulating optical phantom and gel display. The kinetics of gel swelling has been theoretically analyzed by considering coupled motions of both solvent and polymer network. Analytical solutions of the solvent and the network movement are derived from collective diffusion equations for a long cylindrical and a large disk gel. Kinetics of spinodal decomposition of N-isopropylacrylamide (NIPA) polymer gel is investigated using turbidity and ultrasonic techniques. By probing movement of domains, a possible time-dependent gel structure in the spinodal decomposition region is presented. Theoretical studies of solution convection in gel matrix have been done and more analysis on dimensionless parameters is provided. To enhance the drug uptake and release capacity of silicone rubber (SR), NIPA hydrogel particles have been incorporated into a SR membrane. This SR/NIPA composite gel has promising attributes for wound dressing and other uses. Tissue-simulating optical phantom has been synthesized and studied using NIPA solution trapped inside a hydrogel. Polymer gels with engineered surface patterns were implemented. NIPA gel deposited on the surface of an acrylamide gel can be used as responsive gel display. A dynamically measurement technique of local shear modulus and swelling ratio of gel is presented based on an engineered periodic surface pattern as square array.

CHDS State/Local / Approved for public release; distribution is unlimited / The concept of biosecurity as it pertains to Biological Select Agents and Toxins in American biomedical research institutions is explored in some depth. Posing the research question "How can specific public biomedical research universities securely use and store biological select agents?" the thesis outlines the dynamics of the select agent and toxin list, the relevant history of the control of biological agents both in the international and domestic settings, including federal regulations pertaining to biosecurity (42CFR73). Two specific case studies are presented in the thesis. The biosecurity strategies and tactics at these two distinct biomedical research are compared. An answer to the research question is proposed and additional areas for research are outlined. / Captain, the University of Texas at Houston Police Department

Hydroxyapatite (HAp) is an ideal bioactive material that is used in orthopedics. Chemical composition and crystal structure properties of HAp are similar to the natural bone hence it promotes bone growth. However, its mechanical properties of synthetic HAp are not sufficient for major load-bearing bone replacement. The potential of improving the mechanical properties of synthetic hydroxyapatite (HAp) by incorporating carboxyl functionalized single walled carbon nanotubes (CfSWCNT) and polymerized ɛ-caprolactam (nylon) is studied. The fracture toughness, tensile strength, Young’s modulus, stiffness and fracture energy were studied for a series of HAp samples with CfSWCNT concentrations varying from 0 to 1.5 wt. % without, and with nylon addition. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were used to characterize the samples. The fracture toughness and tensile test was performed under the standard protocol of ASTM D5045 and ASTM D638-02a respectively. Reproducible maximum values of (3.60 ± 0.3) MPa.m1/2 for fracture toughness and 65.38 MPa for tensile strength were measured for samples containing 1 wt. % CfSWCNT and nylon. The Young’s modulus, stiffness and fracture energy of the samples are 10.65 GPa, 1482.12 N/mm, and 644 J/m2 respectively. These values are comparable to those of the cortical bone. Further increase of the CfSWCNT content results to a decreased fracture toughness and tensile strength and formation of a secondary phase. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

The effect of processing temperature on the crystal structure properties of the Fe-substituted Hydroxyapatite (Fe-HAp) was studied by using the Rietveld refinement method of powder x-ray (XRD) and neutron diffraction (NPD) patterns. Superconducting QUantum Interference Device (SQUID) magnetometry, transmission electron microscopy (TEM) and x-ray fluorescence spectroscopy (XRF) were used to study the magnetic properties, particle morphology and chemical composition of the prepared samples. Two sets of samples of chemical formula Ca5-xFex(PO4)3OH were prepared with x = 0, 0.05, 0.1, 0.2 and 0.3 by using processing temperatures of 37°C and 80°C, following a two-step co-precipitation method. A single phase HAp was identified in samples with x = 0 and 0.05. Processing temperature affects the type and percentage of secondary phases: hematite was detected in samples prepared at 37°C with x ≥ 0.1, hematite and maghemite were detected in samples prepared at 80°C with x = 0.2 and 0.3. Rietveld refinements of NPD and XRD patterns showed that the a lattice constants are greater in Fe-substituted samples prepared at 37°C, whereas the c lattice constants are greater in the 80°C samples for x ≥ 0.05. Fe preferentially substitutes at the Ca2 site in the 80°C samples, whereas Ca1 is the preferred substitution site in the 37°C samples. Fe substitution results to a decrease of the lattice constants at both preparation temperatures. The ratios Fe/(Fe + Ca) of the refined atomic fractions of the samples prepared at 80°C are greater than those of the 37°C samples. Further, more secondary phases form in samples prepared at 37°C compared to 80°C samples. The magnetic measurements reveal that pure HAp is diamagnetic, whereas samples with x = 0.05 and 0.1 are paramagnetic. Samples with x = 0.3 showed superparamagnetic behavior based on ZFC and FC measurements. Similar hysteresis loops in samples x = 0.2 and 0.3 indicate that the samples with x = 0.2 may show superparamagnetic properties. For x = 0.2 and 0.3, the samples prepared at 80°C showed higher magnetization compared to the 37°C samples, because of the maghemite secondary phase. Based on the TEM images, Fe substituted HAp nanoparticles prepared at 37°C are mainly spherically shaped, and the 80°C particles are mainly elongated. Increase of the Fe concentration favors formation of elongated particles and larger spherical particles. The XRF measurements confirm the Fe for Ca substitution in the HAp structure based on the decrease of the Ca/P and the increase of the Fe/(Fe + Ca) atomic ratios with the Fe concentration. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

Thesis submitted in fulfilment of the requirements for the degree of Master of Technology: Chemistry in the Faculty of Applied Sciences at the Cape Peninsula University of Technology, 2012 / Batch experiments were conducted to assess the removal of Ni(II) from aqueous solutions and landfill leachates using low cost adsorbents eggplant peel (EGP), sweet potato peel (SWP) and banana peel (BNP). Preliminary studies were carried out to optimize biosorbent mass, pH, Ni(II) concentration, temperature and contact time for Ni(II) removal. The optimized conditions were then applied to landfill leachates using the selected low cost adsorbents. Ni(II) removal efficiency for each biosorbent was investigated for each parameter. Results indicated that biosorbents masses, pH, initial concentration as well as solution temperature were important factors influencing Ni(II) removal from aqueous solutions. Percentage Ni(II) removal was 66±0.30, 38±3.97 and 33±1.20 using EGP, SWP and BNP, respectively. Ni(II) removal efficiency increased significantly (P ≤ 0.05) with increasing biosorbent mass, pH and Ni(II) initial concentration while it decreased significantly (P ≤ 0.05) with increasing temperature. Although Ni(II) removal efficiency varied significantly with time and the biosorbents no significant (P 0.05) difference was observed between the time interval whether the experiment was conducted in batch or semi batch mode. Results of FTIR studies indicated that several binding and chelating functional groups such as carboxyl, carbonyl and hydroxyl groups on the biomaterials surfaces could be responsible for Ni(II) biosorption. The optimum biosorbent mass for EGP and SWP was 0.4 g and for BNP was 0.05 g. The values for initial concentration, pH, temperature and contact time were 100 mg/L, 5, 22oC and 2 hours, respectively. Ni(II) removal efficiencies using EGP, SWP and BNP were 66, 38 and 33%, respectively. Taking into account the result and optimum condition obtained on Ni(II) removal efficiency from aqueous solution using EGP, SWP and BNP, the Ni(II) removal efficiency using these biosorbents from landfill leachate was investigated. It was found to be significantly (P ≤ 0.05) lower than what was found from aqueous solution.

Microbial infections of medical implants occur in 10% of the more than 20 million surgical procedures carried out annually in the United States. The additional treatments required to address these infections generate more than $11 billion in additional patient costs, increase recovery time, and decrease overall patient quality of life. As the population ages, the number of necessary and voluntary surgical procedures increases; The rate of infection increases proportionately. While treatments are available, the biofilm mode of growth confers resistance to antimicrobial therapies up to 500 times greater than that of planktonic microbes. Currently, the only guaranteed method of removing an established microbial implant infection is through surgical excision of the implant and surrounding tissues. While removing the original infection, additional colonization and pathogenesis may take place. This research explores the a priori assumption that a medical implant infection cannot occur unless a microbial cell is capable of adhering to the implant surface. From that assumption, the following sections will focus primarily on identifying the necessary and sufficient factors influencing microbial adhesion, discretizing those factors into measurable quantities, and developing methods by which those factors may be mitigated or eliminated. Following is a brief summary of each major topic treated within this research period. Development of a Benchmark System: We have characterized the interactions between Pseudomonas aeruginosa ATCC 10145 and Candida parapsilosis ATCC 90018 using a novel method of cellular immobilization, which emphasizes minimal chemical modification of the cell surface. This research describes the very different force-separation interactions seen between C. parapsilosis and both a common medical implant material (viz., silicone rubber) and a nascent P. aeruginosa biofilm grown on the same material. This study was the first step in developing an ab initio technique which may be used to determine the relative affinity of a microbial cell for an implant material surface. The Role of the Substrate: Microbial adhesion to a medical implant device involves two major components, being the microbe itself, and the substrate to which it adheres. Each of the two has specific and unique surface chemical and textural characteristics which, when combined, allow for microbial colonization and subsequent infection. The goal of this study was to identify correlations between the adhesive strength of Staphylococcus epidermidis to a variety of chemically and texturally distinct substrates, and common surface characterization parameters (e.g., surface roughness and water contact angle). Relationships to adhesive strength did not demonstrate statistically significant or consistent trends. To extend upon the correlation parameters, we have employed a Discrete Bonding Model, which characterizes the surface texture according to Mandelbrot fractal theory. Correlations between the adhesive strength and the observational scale show stronger relationships, indicating a significant contribution of the surface texture to a microbe's ability to colonize a surface. Finding a Surface That Cannot Be Touched: Historically, AFM force-separation curves demonstrating only repulsive behavior on extension of the piezoactuator have been largely ignored, in terms of quantitative modeling of the interactions. In bacterial systems, such behavior describes the majority of the force profiles recorded by the instrument. As a result of the former lack of study, the latter data sets have remained unanalyzed and unanalyzable. Building on existing mathematical models, we have developed an analytical method by which the point of zero separation between a surface (viz., the microbial cell wall) coated with a polymer brush and an AFM probe may be quantitatively identified.

The evaluation of the remodeling of soft biomaterial implants often involves surgical removal of the implant for subsequent histological assessment. This approach is very resource intensive, often destructive, and imposes practical limitations on how effectively these materials can be evaluated. Magnetic resonance imaging (MRI) has the potential to non-invasively monitor the remodeling of collagen sponges, specifically the biodegradation, cellular infiltration, extracellular matrix deposition and angiogenesis within the sponge. This project involves the development of an in vivo model system for the evaluation of collagen-sponge remodeling using MRI and conventional histological techniques. Collagen sponges made using insoluble bovine collagen, and subjected various crosslinking treatments, were implanted subcutaneously into rats. Changes in water T2 relaxations times, water apparent diffusion coefficients (ADC), and MRI contrast agent uptake/washout were collected using spin-echo and diffusion-weighted MRI pulse sequences. These measurements were compared with histological assessments of sponge remodeling. Regions of differential cellularity were distinguished using calculated T2 maps and confirmed by histology. Calculated ADC maps corroborated these results and showed a decreasing trend with increased tissue in-growth. Results from MRI-contrast-agent studies were consistent with the development of angiogenesis within the sponge over time. The MRI approach allows for longitudinal studies that significantly reduce the resources required to evaluate these materials as well as improves the quality of the statistical information obtained from these studies.