In recent years, biodegradable polymeric systems have gained importance for design of surgical devices, artificial organs, drug delivery systems with different routes of administration, carriers of immobilized enzymes and cells, biosensors, ocular inserts, and materials for orthopedic applications. Polysaccharide-based polymers represent a major class of biomaterials, which includes agarose, alginate, dextran, and chitosan. Chitosan has found many biomedical applications, including tissue engineering, owing to its biocompatibility, low toxicity, and degradation in the body, which has opened up avenues for modulating drug release in vivo in the treatment of various diseases. These chitosan-based delivery systems range from microparticles to nanoparticles and from gels to films. In this study, chitosan (CH) and chitosan-polyethylene glycol (CH-PEG) microspheres with different compositions were prepared by oil/water emulsion method and crosslinked with gluteraldehyde. Some microspheres were loaded with a model chemotherapeutic drug, methotrexate (MTX). SEM, particle size and in vitro release analysis were performed. In vitro drug release studies showed that the release of MTX from CH-PEG microspheres was faster compared to CH microspheres. In the second part, CH-PEG microspheres were conjugated with a monoclonal antibody which is immunoglobulin G (IgG). The cytotoxicity efficiencies of entrapped drug were determined by using MCF-7 and MCF-7/MDA-MB breast cancer cell lines. In the third part, CHF-PEG films with the same compositions as in microspheres were prepared by solvent casting method. IR, DSC, mechanical and surface analysis were performed. The mechanical properties of films were improved by the presence of proper amount of PEG but higher amounts of PEG caused the deteriotion in the properties.

An experimental investigation exploring the use of wire mesh/hollow glass microsphere combination for use as thermal insulation was conducted with the aim to conclude whether or not it represents a superior insulation technology to those on the market. Three primary variables, including number of wire mesh layers, filler material, and temperature dependence were studied using an apparatus that was part of L.I.C.H.E.N (LabVIEW Integrated Conduction Heat Experiment Network), a setup whose basic components allow three vertically stacked samples to be thermally and mechanically controlled. Knowing the temperature profile in the upper and lower samples allows for determination of thermal conductivity of the middle material through the use of Fourier?s law. The numbers of layers investigated were two, four, six, and eight, with each separated by a metallic liner. The filler materials included air, s15, s35 and s60HS 3MTM hollow glass microspheres. The experiments were conducted at four temperatures of 300, 330, 366, and 400K with an interface pressure of 20 Psi. The experimental results indicated the ?number of layers? used was the primary factor in determining the effective thermal conductivity value. The addition of hollow glass microspheres as filler material resulted in statistically insignificant changes in effective thermal conductivity. Increasing the number of wire mesh layers resulted in a corresponding increase in effective thermal conductivity of the insulation. Changes in temperature had little to no effect on thermal conductivity. The effective thermal conductivity values for the proposed insulation structure ranged from 0.22 to 0.65 W/m-K, the lowest of which came from the two layer case having air as filler material. The uncertainties associated with the experimental results fell between 10 to 20 percent in all but a few cases. In the best performing cases, when compared with existing insulation technologies, thermal conductivity was approximately 3 to 10 times higher than these methods of insulation. Thus, the proposed insulation scheme with hollow glass-sphere filler material does not represent superior technology, and would be deemed uncompetitive with those readily available in the insulation market.

Microspheres are spherically shaped particles within the size range of 1-1000 μm in diameter. Due to the their small size and round shape, microspheres show many advantages in various applications such as pharmaceuticals, composites and coatings. The microspheres can be customized to fit a specific application and are manufactured in various forms such as solid, hollow and encapsulating. Encapsulating cellulose microspheres have been produced in this project by the emulsionsolvent evaporation technique. The purpose of this study was to further investigate the possibility of producing encapsulating microspheres with a size range of 10-50 μm that will have a high encapsulation. A second purpose of this study was optimizing the emulsifier system for the preparation of these spheres. This has been accomplished by varying several process parameters such as type of emulsifiers and solvents to study the effect on morphology and encapsulation efficiency. The analyses of the spheres were performed with optical microscopy, thermal gravimetric analyzer (TGA) and scanning electron microscopy (SEM). The emulsifier type and concentration affected the encapsulation and size distribution but had no direct effect on the internal and external structure, which was multi-cellular and porous, respectively. The highest encapsulation in relation to average size was obtained with 0.1 v/v- % of the emulsifier mixture Emulsifier 1 (E1)/Emulsifier 2 (E2) (70/30 %). The solvent used to dissolve the polymer had a direct effect on encapsulation, a combination of Solvent 2 (S2) and Solvent 1 (S1) proved best for the three tested cellulose derivatives with low, medium and high number average molecular weight. The solvent also had an effect on the internal structure of the microspheres, becoming more core-shell when using the S1/S2 combination.

This research studied Ho166/PLLA microspheres, a promising treatment for tumours in the liver. The Ho166 is generated through a neutron capture reaction during irradiation in a nuclear reactor. Previous work has found that neutron-irradiation in-core causes damage to microspheres and causes additional degradation to progress once suspended in media. The cause of this damage was not well understood and is the focus of this research. This research studied factors present in-core such as heat, gamma radiation, and impacts of lead shielding, for their impact on microsphere quality. Additionally, this research looked at the potential of reactive oxygen species causing damage once microspheres are suspended in liquid. Thresholds for damage were identified to correlate with the glass transition temperature of poly- l-lactic acid. Exposure to gamma radiation induces heating, as well as structural changes to the polymer which shifts the temperature where the glass transition occurs. Damage formed from gamma radiation, independent of other variables, was seen at extreme accumulated doses. Notably, exposure to gamma radiation and heat did not cause a progression of damage over time. Samples exposed only to these factors remained stable in solution for extended periods. A theory was proposed that reactive oxygen species formed by the interaction of ionizing radiation with the suspending media may be causing the progression of damage over time. This factor would only be present for microspheres having undergone neutron capture reactions, forming radioactive holmium. Testing confirmed a potential impact of radiation interactions with the suspending media contributing to damage progression. Several thicknesses of lead shielding surrounding the sample chamber were tested in-core. There were significant impacts on temperature, neutron flux, and microsphere quality. / Thesis / Master of Science (MSc) / This research studied Ho166/PLLA microspheres, a promising treatment for tumours in the liver. The preparation of this treatment includes microspheres being neutron irradiated in the core of a nuclear reactor. Irradiation in-core leads to damage of microspheres. This research studied factors present in-core such as heat, gamma radiation, and thickness of lead shielding, for their impact on microsphere quality. Additionally, this research looked at the potential of reactive oxygen species causing damage once microspheres are suspended in liquid. Thresholds for damage were identified for temperature and gamma radiation exposure. Radiation interactions in liquid suggest possible damaging effects over time. Finally changing the thickness of lead shielding in core had significant impact on temperature, neutron flux, and microsphere quality.

Switchable adhesives using stimuli-responsive systems have many applications, including transfer printing, climbing robots, and gripping in pick and place processes. Among these adhesives, electroadhesive surface can spontaneously adjust their adhesion in response to an external electric field. However, electroadhesives usually need high voltage (e.g. kV) and the adhesion disappears upon turning off the signal. These limitations make them complicated and costly. In this research, we demonstrated a gold-coated silica microsphere (GCSM) with highly switchable and memorable adhesion triggered by a relatively small voltage (<30 V). In the experiment, a silica microsphere with a diameter of 15 μm was glued to a tipless atomic force microscope (AFM) cantilever. The nanoscale thick gold coating was sprayed on the surface of the microsphere by a sputter coater. AFM was used to explore the tunable adhesion with an external voltage at different relative humidity (RH). The results revealed that when applying a positive electrical bias at high RH, the adhesive force increased dramatically while it decreased to almost zero after applying a negative potential. Even if the bias was turned off, the adhesive force state could still be kept and erased on demand by simply applying a negative voltage. The adhesive force can be altered repeatedly by an alternative electrical bias. This adhesion modulated by the external electrical signals is attributed to the electrochemical effect of the nanoscale-thick gold coating, where an oxide layer can be formed and thus becomes positively charged when applying a positive voltage, and counter electric field cancel out the applied negative voltage to decrease the adhesion force.

Master of Science / Department of Diagnostic Medicine/Pathobiology / Ying Fang / The Porcine Disease Complex (PDC) results in major economic problems for swine producers. PDC outbreaks result in increased mortality, decreased feed efficiency, higher cull rates, prolonged days to market and increased treatment costs. This disease involves the interaction and participation of many multifactorial etiologies including both bacterial and viral organisms playing a role in disease initiation and progression. The most common viral pathogens associated with the PDC include porcine reproductive and respiratory syndrome virus (PRRSV), porcine circovirus (PCV2) and swine influenza virus (swIV). The recent outbreak of porcine epidemic diarrhea virus (PEDV) in the US swine herd has made the PDC even more complicated. In aid of the prevention and control of the PDC, veterinarians and producers require fast and efficient diagnostic tests for controlling the disease. In this study, we have generated recombinant nucleocapsid antigens to these viruses for use in a Luminex™ technology-based fluorescent microsphere immunoassay (FMIA). Utilizing these recombinant nucleocapsid antigens, the FMIA was developed to simultaneously detect antibodies in serum from animals infected with PEDV, PRRSV, SwIV and PCV2. The FMIA was developed based on testing experimentally derived standard positive and negative control sera, and the diagnostic specificity and sensitivity were compared to that generated from the classical enzyme-linked immunosorbent assay (ELISA) or hemagglutination inhibition (HI) test. Based on an evaluation of 4147 serum samples with known serostatus, the multiplex FMIAs reached greater than 97.5% sensitivity and 92.3 % specificity. Results showed that multiplexing did not affect the diagnostic sensitivity or specificity of each individual assay. This work provides a platform for the development of multiplex assays for detecting various swine pathogens simultaneously and aids in preventing and controlling the PDC.

Microspheres (< 1000 μm) have applications in various fields (e.g., drug delivery, cosmetics, food, etc.). Microspheres can be generated by the micro-fluidic technique, in which microspheres are produced from one fluid under the action of another immiscible fluid in a network of channels. There are four performance indexes associated with a microsphere generation process with a device, namely (1) the size of microspheres (as small as possible), (2) the uniformity of size distributions (as high as possible), and (3) the flexibility of devices (i.e., the size range of microspheres that can be generated with one device), and (4) the efficacy of the microspheres generation process (mass production or not). Two operating principles along with their corresponding devices, the modified T-junction device and membrane emulsification device, are studied in this dissertation, because of their unique features, with the former having an excellent task flexibility and the latter having an excellent efficacy. The study defined three objectives, namely (1) understanding the mechanism of the microsphere generation process with the modified T-junction by both numerical investigation and experimental investigation, (2) optimizing the microsphere generation process with any micro-fluidic device in general and the modified T-junction device in particular (optimization: the size and uniformity), and (3) designing and fabricating a new emulsification membrane by tackling the shortcoming (i.e., fragile with the membrane) with the existing emulsification membrane. For objective (1), a simulation model was built first, validated by the experiment, and then the simulation model was employed to study the regimes. For objective (2), a new optimization procedure was first proposed for general micro-fluidic systems and then applied to the modified T-junction system. For objective (3), a new membrane was designed and fabricated and tested. The following conclusions can be drawn from the study: (1) the modified T-junction device works based on a combined operating principle (flow focusing and conventional T-junction) and there are three regimes (instead of the four regimes in the conventional T-junction) in the flow; (2) the optimization of the microsphere generation process makes sense for the micro-fluidic device in general and the modified T-junction in particular (the optimal modified T-junction is: the mean size: 16.1 μm and 24.8 μm, and the uniformity (Standard Deviation (SD)): 0.2 μm and 0.7 μm); (3) the shortcoming with emulsification membrane can be overcome with a multi-layer membrane architecture. There are several contributions made by this dissertation in the field of micro-fluidic. First is the provision of an accurate Computational Fluid Dynamics (CFD) model for the modified T-junction. Second is the new knowledge discovered regarding the mechanism of microsphere generation with the modified T-junction device. Third is the provision of an effective optimization approach for any micro-fluidic device in general and for the modified T-junction device in particular. Fourth is the design with the successful fabrication of the membrane emulsification device based on new system architecture (i.e., multi-layer structure). From an application’s perspective, this dissertation has provided evidence that with the micro-fluidic technique, the smallest size of microspheres can be 2.3 μm; the highest uniformity (SD) can be 0.8 μm. Further, if an application puts emphasis on the task flexibility, the modified T-junction device is an excellent choice, and if an application puts emphasis on the mass production, the multi-layer membrane device is an excellent choice.

The synthetic biodegradable polymer poly(lactide-co-glycolide) (PLGA) has been widely explored as substrate biomaterials for controlled drug delivery and tissue engineering. ECM component heparin and bone mineral hydroxyapatite (HA) are attractive biomaterials which can functionalize the PLGA surface to improve cell cell response and to bring in the dual growth factor delivery, because heparin and HA both can improve cell responses and bind with various proteins. To combine the osteoconductivity of HA and the controlled drug release of PLGA microspheres, HA coated PLGA microspheres were developed by a 3 hour rapid HA precipitation on the PLGA microsphere surface. Effects of various fabrication parameters on microsphere and HA coating morphology were evaluated. This core-shell composite worked as a dual drug delivery device and demonstrated better cell cell response than PLGA microspheres without HA coating. Three different methods, including osmogen, extractable porogen and gas-foaming porogen, were evaluated to fabricate porous microspheres as injectable cell scaffolds in the tissue engineering. The gas-foaming method produced covered porous PLGA microspheres, on which a skin layer covered all the surface pores. The skin layer was hydrolysed by NaOH to control the surface porosity. The modified open porous microspheres have large continued surface areas between pores, which provided more continued areas for cell adhesion. The porous microspheres with controllable surface porosity and large surface continuity between pores could be novel injectable cell scaffolds. Heparin was immobilized on the open porous PLGA microspheres by a facile layer-by-layer assemble to combine the advantages of porous structure and the protein binding from heparin. The heparin-coated porous microspheres promoted cell adhesion, spreading, proliferation and osteogenic differentiation. Growth factor-like protein lactoferrin was immobilized on the heparin coated porous microspheres, which further enhanced MG-63 proliferation and osteogenic differentiation. The heparin-coated porous microspheres are promising multi-functional devices for controlled drug delivery and injectable cell delivery.

L’embolisation thérapeutique est devenu le traitement de choix pour l’hémorragie, les malformations artériovéneuses ou certains types de cancer. Parmi différents agents d’embolisation,les microsphères non dégradables (Embozene®, Bead BlockTM,…) sont les plus utilisées. Leur forme bien sphérique et leur taille calibrée permettent un meilleur ciblage dans les vaisseaux et une bonne qualité de l’occlusion. Dans certains cas cliniques, l’embolisation temporaire, envisageable avec l’utilisation des microsphères résorbables peut être bénéfique pour les patients. Le but du travail réalisé au cours de cette thèse a été le développement de microsphères résorbables satisfaisant les différents critères pour être employées comme matériaux d’embolisation (taille calibrée,biocompatibles, élastique pour être injectée au travers des cathéters mais suffisamment rigide pour résister à la pression sanguine). Dans cet objectif, nous avons développé une méthode de synthèse de microsphères constituées d’hydrogels hydrolysables par polymérisation en suspension. Une large gamme de microsphères ont été synthétisées en modulant la nature du réticulant et/ou la composition des milieux de polymérisation. Les expériences in vitro ont démontré que les microsphères obtenues sont satisfaisantes pour permettre leur injection au travers des cathéters. La dégradation rapide des ponts de réticulation a été confirmée à travers la diminution du module élastique G’ et du pH du surnageant, accompagnée d’une augmentation du taux de gonflement.Malgré une dégradation partielle des microsphères (due à une réaction secondaire formant des liaisons de réticulation non dégradables), le temps de l’hydrolyse a répondu parfaitement au cahier de charges (entre 7 et 49 jours). Des études complémentaires pour optimiser la réaction de polymérisation vont permettre le développement de microsphères totalement dégradables. / Therapeutic embolization is nowadays a first line treatment for haemorrhage, arteriovenous malformation or tumors. Among different embolization agents, non degradable microspheres(Embozene®, Bead BlockTM,…) are the most employed thanks to their well calibrated spherical shape which allows good occlusion. In some cases including treatment of uterine fibroids or chemo-sensitive tumors, it may be interesting to achieve a temporary embolization to avoid definitive destruction of the tissue. Temporary embolization would be possible using biodegradable microspheres. The aim of our work was to develop degradable microspheres having all requiredcharacteristics to be used as embolization material (well calibrated in size, biocompatible, rigide enough to resist blood pressure but elastic enough to remain intact during injection through catheter). To this purpose, we have developed hydrolysable hydrogel based microspheres by suspension polymerization. A wide range of microspheres was synthesized by varying the type of crosslinker and composition of the polymerization medium. In vitro test showed that the microspheres have suitable characteristics to pass through catheter. Degradation studies revealed a rapid diminution of G’ modulus and the pH of the supernatants, accompanied by an increase of swelling ratio due to the hydrolysis of the crosslinkings. Although microspheres were not totally degradable as expected (since a side reaction had created non degradable crosslinking during the polymerisation), characterisations showed promising results that the degradation did occur within a suitable time scale requirements for temporal embolization.

"Topographical and mechanical properties of adhesive substrates provide important biological cues that affect cell spreading, migration, growth, and differentiation. The phenomenon has led to the increased use of topographically patterned and flexible substrates in studying cultured cells. However, these studies may be complicated by various limitations. For example, the effects of ligand distribution and porosity are affected by topographical features of 3D biological constructs. Similarly, many studies of mechanical cues are compounded with cellular deformation from external forces, or limited by comparative studies of separate cells on different substrates. Furthermore, understanding cell responses to mechanical input is dependent upon reliable measurements of mechanical properties. This work addresses each of these issues. To determine how substrate topography and focal adhesion kinase (FAK) affect cell shape and movement, I studied FAK-null (FAK -/-) and wild type mouse 3T3 fibroblasts on chemically identical polystyrene substrates with either flat surfaces or micron-sized pillars, I found that, compared to cells on flat surfaces, those on pillar substrates showed a more branched shape, an increased linear speed, and a decreased directional stability, which were dependent on both myosin-II and FAK. To study the dynamic responses to changes in substrate stiffness without other confounding effects, I developed a UV-modulatable substrate that softens upon UV irradiation. As atomic force microscopy (AFM) proved inadequate to detect microscale changes in stiffness, I first developed and validated a microsphere indentation method that is compatible with fluorescence microscopy. The results obtained with this method were comparable to those obtained with AFM. The UV-modulatable substrates softened by ~20-30% with an intensity of irradiation that has no detectable effect on 3T3 cells on control surfaces. Cells responded to global softening of the substrate with an initial retraction followed by a gradual reduction in spread area. Precise spatial control of softening is also possible - while there was little response to posterior softening, anterior softening elicited a pronounced retraction and either a reversal of cell polarity or a significant decrease in spread area if the cells move into the softened region. In conclusion, these techniques provide advances in gaining mechanistic insight into cellular responses to topographical and mechanical cues. Additionally, there are various other potential applications of the novel UV-softening substrate, particularly in regenerative medicine and tissue engineering. "