<p>Unreinforced masonry (URM) constitutes a large part of current building inventory worldwide, and this type of construction also represents a major seismic risk, especially in developing countries where URM is widely used. During an earthquake, URM walls are unable to dissipate seismic forces without experiencing considerable damage or collapse. Due to their lack of ductility, URM walls fail in a brittle manner, which can leads to damaged face shells becoming falling debris and a major source of hazard. The aim of this study is to investigate the applicability of using polyurethane foams as an inexpensive reinforcement technique for both retrofitting existing and new URM construction.</p> <p>Experimental testing of the reinforced masonry walls showed a large increase in the resiliency of the wall, with an increase in the out-of-plane capacity of up to 34 times over the URM specimen, and with the addition of rope reinforcement an increase in the out-of-plane capacity of up to 90 times the URM specimen was achieved. This system allows walls to experience a considerable amount of deflection before ultimate failure is reached. Within certain limits, the polyurethane foam is able to demonstrate elastic characteristics. By developing foam with higher densities, higher compressive, tensile, flexural and shear strengths can be reached. This type of reinforcement allows for less damage during low seismic events, and through the greater resiliency of the system, walls are able to remain stable and exhibit post-peak strength during a stronger seismic event. In its ultimate limit state, the wall will fail, however collapse is typically prevented – reducing the amount of hazardous debris and saving the lives of the buildings occupants.</p> / Master of Applied Science (MASc)

<p>The development of nanocomposite materials has had significant influence on modern material design. Novel properties can be achieved and controlled for a diverse range of applications. The work presented here focused on characterization of polyurethane based coatings with ITO nano-inclusions. The coatings displayed high transparency in the visible range, and UV/IR shielding properties when studied with UV-Vis spectroscopy. UV/IR shielding improved with greater ITO density, with minor affect on visible transmittance. The effective medium approximation was successfully applied to ellipsometry modeling. Coatings with varying fractions of nanoparticles were analyzed. The modeled volume percent of the nanoparticles followed a strong linear trend with the known weight percentages. SEM and TEM imaging determined that majority of the particles existed in clusters. The nanoparticles were oblong shaped, 10-20nm big, randomly distributed, with no segregation to interfaces. Agglomerates varied in size, with the largest observed agglomerate being 250nm.</p> <p>Thermal stability was studied by TGA and DSC. No degradation occurred until 238°C. DSC revealed that the matrix continued to undergo modifications with consecutive runs. It was inconclusive whether the changes were from the polyurethane or dispersive agents in the system. Electron micrographs showed that segregation did not occur post-annealing. Average surface roughness increased from 3.5nm to 5nm after annealing at 120°C for several weeks. Ellipsometry results showed that film thickness decreased 20nm and 50nm before equilibriating for the 80°C and 120°C anneals respectively. The optical and thermal measurements demonstrated that the coating has great potential for improving the PV performance.</p> / Master of Applied Science (MASc)

This dissertation research addresses the interrelationships between chemistry and network structure in epoxy networks as well as how mechanical properties of the resulting networks are affected by these relationships. The effects of chemistry and network structure on interphase morphology and performance in vinyl ester/carbon fiber composites have also been investigated on both a macro and nanoscale. Thermosets were prepared with blends of bisphenol-A and novel phosphine oxide based diepoxide oligomers using a siloxane or a novolac crosslinking agent. In the siloxane cured networks the incorporation of the phosphine oxide group yielded networks with increased glass transition temperatures, from 71°C to 92°C, and water absorption, from 1 wt % to 5.5 wt %, due to the polar nature of the phosphine oxide bond. Higher char yields were also observed with the addition of the phosphorus, 27 wt % compared to 11 wt % for bisphenol-A epoxy networks. The bisphenol-A based epoxy/siloxane network was exceptionally ductile with a fracture toughness (K1c) of 2 MPa-m1/2. In networks prepared with the novolac crosslinking agent hydrogen bonding, observed using FTIR, was evident even at temperatures above the network Tg and resulted in increased rubbery moduli with phosphine oxide incorporation. Adhesive strengths to steel increased from ~9.7 MPa with bisphenol-A epoxy to ~13.8 MPa when the phosphine oxide containing epoxy was incorporated into the network. Within carbon fiber/vinyl ester composites, a series of tough ductile thermoplastics and a series of one-phase polyurethanes were investigated as carbon fiber sizings. The three poly(hydroxyether)s resulted in different interphase morphologies due to their respective interdiffusion into the vinyl ester resin. The unmodified poly(hydroxyether) was miscible with the vinyl ester resin at the elevated cure temperatures and adhesion between the fiber and bulk matrix was increased from 28 MPa with unsized fibers to 45 MPa with sized fibers. The carboxylate modified poly(hydroxyether) was also miscible at elevated temperatures, however the interdiffused region was narrower, ~5 mm. This system showed an increase in the fiber/matrix adhesion similar to that found for the unmodified poly(hydroxyether)/vinyl ester system and composite cyclic fatigue durability was improved by ~50 %. Using a poly(hydroxyether ethanolamine) interphase material, which was not miscible with the resin, resulted in a sharp interface. While the adhesion was not improved through the use of this sizing, the composite fatigue durability was still increased by a moderate amount, ~ 25%. The one-phase polyurethanes were dispersible in water with incorporation of a minimum of 0.08 equivalents of N-methyldiethanolamine per mole of diisocyanate. Fatigue durability in composite panels was not improved by the addition of the polyurethane sizings due to the miscibility of the sizing and the matrix. / Ph. D.

An A2 + B3 polymerization for the synthesis of hyperbranched polymers was altered using oligomeric precursors in place of either one or both of the monomer pairs to synthesize highly branched macromolecules. Unique topologies that are intermediates between long-chain branched and hyperbranched structures were obtained and the term "highly branched" was used to define these novel architectures. Various types of highly branched polymers, such as polyurethanes, poly(urethane urea)s, poly(ether ester)s, and poly(arylene ether)s were synthesized using the oligomeric A2 + B3 strategy. The molar mass of the oligomeric precursor permitted the control of the molar mass between branch points, which led to interesting macromolecular properties, such as superior mechanical performance to conventional hyperbranched polymers, disrupted crystallinity, improved processibility, and a multitude of functional end groups. Highly branched poly(urethane urea)s and polyurethanes exhibited microphase-separated morphologies as denoted by dynamic mechanical analysis. The similarity in soft segment glass transition behavior and mechanical properties of the branched systems with that of the linear analogues suggested these materials have considerable promise for a variety of applications. When a polycaprolactone triol was utilized as the B3 oligomer for the synthesis of highly branched polyurethane elastomers, the high degree of branching resulted in a completely amorphous soft segment, whereas the linear analogue with equivalent soft segment molar mass retained the crystallinity of polycaprolactone segment. Oligomeric A2 + B3 methodology was further utilized to tailor the degree of branching of poly(ether ester)s that were developed based on slow addition of dilute solution of poly(ethylene glycol) (PEG) (A2) to a dilute solution of 1,3,5-benzenetricarbonyl trichloride (B3) at room temperature in the presence of triethylamine. A revised definition of the degree of branching was proposed to accurately describe the branched poly(ether ester)s and the degree of branching decreased as the molar mass of the PEG diols was increased. Moreover, branched poly(arylene ether)s were prepared via a similar oligomeric A2 + B3 polymerization of phenol endcapped telechelic poly(arylene ether sulfone) oligomers (A2) and tris(4-fluorophenyl) phosphine oxide (B3) in solution. Highly branched poly(ether ester)s were also synthesized in the melt phase using the oligomeric A2 + B3 polymerization strategy. Melt polymerization effectively limited the cyclization reactions, which are common in A2 + B3 polymerizations in solution, and overcame the need for large amounts of polymerization solvent typical of A2 + B3 systems. Finally, a new family of telechelic polyester ionomers was synthesized based on phosphonium bromide salt end groups and branching allowed the incorporation of higher levels of ionic end groups compared to linear analogues. / Ph. D.

The foundational studies of this dissertation concern the characterization of segmented polyurethanes and polyureas synthesized without the use of chain extenders'molecules that are typically used to promote a microphase separated morphology that gives these materials their useful characteristics. Polyurethanes in which a single asymmetric diisocyanate comprising the whole of the hard segment were found to display poor microphase separation. Conversely, polyurethanes in which a single symmetric diisocyanate composed the hard segment were found to display good microphase separation. The more efficient packing of the symmetric hard segments also led to an increase in hard segment connectivity and hence higher values of storage moduli in these systems. When hydroxyl-terminated diisocyanates were replaced with amine-terminated diisocyanates, polyureas were formed. Here too, diisocyanate symmetry was found to play a key role with symmetric diisocyanates leading to better microphase separation. In addition, the polyurea materials displayed broader service temperature windows than their polyurethane counterparts as the relatively stronger bidentate hydrogen bonding replaced monodentate hydrogen bonding in these materials. A thread-like, microphase separated morphology was visually confirmed using atomic force microscopy. Other techniques such as ambient temperature tensile testing, and wide and small angle x-ray scattering were employed to confirm the presence of the microphase separated structure. The investigation into the effects of diisocyanate chemistry and its symmetry was broadened to incorporate non-chain extended polyurethane materials with different soft segment molecular weights, as well as polyurethanes that did contain chain extenders. Once again the effect of using symmetric versus asymmetric diisocyanates was evident in the structure–property behavior of these systems, with symmetric diisocyanates forming materials that displayed better microphase separation and more connectivity of their hard domains. Lastly, in a departure from the segmented copolymer area, a study was conducted into the influence of casting variables on the solid-state structure of synthetic polypeptide films based on glutamate chemistry. The effect of solvent evaporation was determined to play a key role in the morphology of these polypeptide films. Measured small angle light scattering patterns were compared to computer calculated patterns to reveal information about the structure, shape, and length scale of the polypeptide structure. / Ph. D.

The advancements of chemists, engineers, and material scientists has yielded an enormous and diverse library of high-performance materials with varying chemical and physical properties that can be used in a wide array of applications. A molecular-level understanding of the nature of gas–surface interactions is critical to the development of next generation materials for applications such as gas storage and separation, chemical sensing, catalysis, energy conversion, and protective coatings. Quartz crystal microbalance (QCM) and in situ infrared (IR) spectroscopic techniques were employed to probe how topological features of a material as well as structural differences of the analytes affect gas sorption. Detailed studies of the interactions of three categories of molecules: aromatic hydrocarbons, triatomic ambient gases, and chemical warfare agents, with metal-organic frameworks (MOFs) and polyurethane coatings were conducted to build structure–property relationships for the nature and energetics of gas sorption within each material. Differences in the molecular structure of the guest compounds were found to greatly influence how, and to what extent each molecule interacts with the MOF or polyurethane film. Specifically, IR studies revealed that transport of aromatic compounds within the zirconium-based MOF, UiO-66 was limited by steric restrictions as molecules passed through small triangular apertures within the pore environment of the MOF. In contrast, the smaller triatomic molecules, CO2, SO2, and NO2, were able to pass freely through the MOF apertures and instead reversibly adsorbed inside the MOF cavities. Specifically, SO2 and NO2 were observed to preferentially bind to undercoordinated zirconium sites located on the MOF nodes. In addition, uptake of CO2, SO2, and NO2 was also aided by dispersion forces within the confined pore environments and by hydrogen bond formation with μ3 OH groups of the MOFs. Dimethyl chlorophosphate (DMCP), a nerve agent simulant that contains several electronegative moieties, was also found to strongly adsorb to undercoordinated zirconium; however, unlike in the aromatic and triatomic molecule systems, DMCP remained permanently bound to the MOFs, even at high temperatures. Finally, QCM studies of mustard gas simulant uptake into polyurethane films of varying hard:soft segment compositions revealed that dipole-dipole and dipole-induced dipole interactions were responsible for favorable absorption conditions. Furthermore, the ratio of hard and soft segment components of the polyurethane had a minor impact on simulant adsorption. Higher hard-segment content resulted in a more crystalline film that reduced simulant uptake, whereas the rubbery, high soft segment polyurethane allowed for greater vapor absorption. Ultimately, molecular-level insight into how the chemical identity of a guest molecule impacts the mechanism and energetics of vapor sorption into both MOFs and polymeric films can be extended to other relevant systems and may help identify how specific characteristics of each material, such as size, shape, and chemical functionality impact their potential use in targeted applications. / Doctor of Philosophy / The nature in which specific gases interact with materials will largely dictate how the material can be utilized. By understanding where and how strongly gas molecules interact with a material, scientists and engineers can rationally design new and improved systems for targeted applications. In the research described in this thesis, we examined how the chemical structure of three different groups of compounds, which have relevance in many industrial, environmental, and defense-related applications, affected the type and strength of interaction between the gas and material of interest. From these studies, we have identified how key properties and features within the examined materials such as size, shape, and chemical composition, lead to significant differences in how vapor molecules interacted with the materials. For example, benzene, toluene, and xylene, which are incredibly important chemicals in industry, were found to be restricted by narrow passageways as they moved through materials with small pores. In contrast, small gases present in the environment from combustion exhaust such as CO₂, SO₂, and NO₂ were able to freely traverse through the passageways, and instead weakly interacted with specific chemical groups inside the cavities of the material. On the same material however, a third class of compounds, organophosphorus-containing chemical warfare agent mimics, irreversibly reacted with chemical groups of the surface, and remained bound even after exposure to high temperatures. Ultimately, the work presented in this thesis is aimed at providing key fundamental insights about specific classes of materials on how, and how strongly they interact with targeted hazardous vapors, which can be utilized by synthetic chemists to design next generation materials.

This thesis is concerned with fused filament fabrication (FFF) of cellulose nanocrystal (CNC) and thermoplastic polyurethane (TPU) nanocomposites, focusing on preliminary optimization of a processing window for 3D printing of mechanically responsive composites and the influence of temperature on mechanical adaptivity, thermal stability, and rheology. CNC thermoplastic nanocomposites are a water responsive, mechanically adaptive material that has been gaining interest in additive manufacturing for 4D-printing applications. Using a desktop FlashForge Pro 3D printer, we first established a viable processing window for a nanocomposite comprising 10 wt% CNCs in a thermoplastic urethane (TPU) matrix, formed into a filament through the combination of masterbatch solvent casting and single screw extrusion. Printing temperatures of 240, 250, and 260°C and printing speeds of 600, 1100, and 1600 mm/min instituted a consistent 3D-printing process that produced characterizable CNC/TPU nanocomposite samples. To distinguish the effects of these parameters on the mechanical properties of the printed CNC/TPU samples, a design of experiments (DOE) with two factors and three levels was implemented for each combination of printing temperature and speed. Dynamic mechanical analysis (DMA) highlighted 43 and 66% increases in dry-state storage moduli values as printing speed increases for 250 and 260°C, respectively. 64 and 23% increases in dry-state storage moduli were also observed for 600 and 1100 mm/min, respectively, as temperature decreased from 260 to 250°C. For samples printed at 240°C and 1600 mm/min, it was determined that that parameter set may have fallen out of the processing window due to inconsistent deposition and lower dry-state storage moduli than what the slower speeds exhibited. As a result, the samples printed at 240°C did not follow the same trends as 250 and 260°C. Further analysis helped determine that the thermal energy experienced at the higher end printing temperatures coupled with the slower speeds decreased the dry-state storage moduli by nearly 50% and lead to darker colored samples, suggesting CNC degradation. Isothermal thermogravimetric analyses (TGA) demonstrated that the CNC/TPU filament would degrade at relative residence times in the nozzle for all the chosen printing temperatures. However, degradation did not eliminate the samples' ability to mechanically adapt to a moisture-rich environment. DMA results verified that mechanical adaptivity was persistent for all temperature and speed combinations as samples were immersed in water. However, for the higher temperatures and slower speeds, there was about a 15% decrease in adaptability. Optimal parameters of 250°C and 1600 mm/min provided the highest dry-state storage modulus of 49.7 +/- 0.5 MPa and the highest degree of mechanical adaptivity of 51.9%. To establish the CNC/TPU nanocomposite's use in 4D printing applications, shape memory analysis was conducted on a sample printed at the optimal parameters. Multiple wetting, straining, and drying steps were conducted to highlight 76% and 42% values for shape fixity and shape recovery, respectively. Furthermore, a foldable box was printed to serve as an example of a self-deployable structure application. The box displayed shape fixity and recovery values of 67% and 26%, respectively, further illustrating significant promise and progress for CNC/TPU nanocomposites in 4D-printed, shape adaptable structures. Further analysis of the effect of degradation during FFF of the CNC/TPU nanocomposite was conducted using rotational rheometry, Fourier-Transform Infrared Spectroscopy (FTIR), and polymer swelling experiments. A temperature ramp from 180 to 270°C showed a significant increase in complex viscosity (h*) at the chosen printing temperatures (240, 250, and 260°C). Moreover, h* of neat TPU suddenly increases at 230°C, indicating a potential chemical crosslinking reaction taking place. 20-minute time sweeps further verified that h* increases along with steady increases in storage (G') and loss (G'') moduli. From these results, it was hypothesized that crosslinking is occurring between CNCs and TPU. Preliminary characterization with FTIR was used to probe the molecular structure of thermally crosslinked samples. At 1060 and 1703 cm-1, there are significant differences in intensities (molecular vibrations) as the temperature increases from 180 to 260°C related to primary alcohol formation and hydrogen bonded carbonyl groups, respectively. The hypothesis is the disassociation of TPU carbamate bonds into soft segments with primary alcohols and hard segments with isocyanate groups. The subsequent increasing peaks at 1060 and 1703 cm-1 may indicate crosslinking of CNCs with these disassociated TPU segments. To quantify potential crosslinking, polymer swelling experiments were implemented. After being submerged in dimethylformamide (DMF) for 24 hours, CNC/TPU samples thermally aged for 15 minutes at 240, 250, and 260°C retained their filament shape and did not dissolve. The 240 and 250°C aged samples had relatively similar crosslink densities close to 900 mole/cm3. However, from 250 to 260°C, there was about a 36% increase in crosslink density. These results suggest that crosslinking is occurring at these printing temperatures because both CNCs and TPU are thermally degrading into reactive components that will lead to covalent crosslinks degradation. Additional characterization is needed to further verify the chemical structure of these CNC/TPU nanocomposites which would provide significant insight for CNC/TPU processing and 3D printing into tunable printed parts with varying degrees of crosslinking. / Master of Science / This thesis is concerned with the development of a processing window for mechanically adaptive cellulose nanocrystal (CNC) and thermoplastic polyurethane (TPU) nanocomposites with fused filament fabrication (FFF) and, evaluating the influence of elevated temperatures on the mechanical, thermal, and rheological properties of said nanocomposite. CNC thermoplastic nanocomposites are a water responsive, mechanically adaptive material that has been gaining interest in additive manufacturing for 4D-printing. Using a desktop 3D-printer, an initial processing window for a 10 wt% CNC in TPU was established with printing temperatures of 240, 250, and 260°C and printing speeds of 600, 1100, and 1600 mm/min. A design of experiments (DOE) was implemented to determine the effects of these parameters on the mechanical properties and mechanical adaptability of printed CNC/TPU parts. Dynamic mechanical analysis (DMA) suggests that combinations of higher temperatures and lower speeds result in reduced storage moduli values for printed CNC/TPU parts. However, mechanical adaptation, or the ability to soften upon water exposure, persists for all the printed samples. Additionally, there was significant discolorations of the printed samples at the higher temperature and slower speed combinations, suggesting thermal degradation is occurring during the printing process. The decrease in storage moduli and discoloration is attributed to thermal energy input, as thermogravimetric analysis indicated thermal degradation was indeed occurring during the printing process regardless of printing temperature. Using the parameters (250°C and 1600 mm/min) that displayed the superior mechanical properties, as well as mechanical adaptivity, shape memory analysis was conducted. The optimal printed part was able to hold 76% of the shape it was strained to, while recovering 42% of the original unstrained shape once immersed in water, indicating potential for shape memory and 4D-printing applications. Furthermore, a foldable box was printed with the optimal parameters and it displayed similar shape memory behavior, illustrating promise for CNC/TPU self-deployable shape adaptable structures. To further study the effect of degradation on the CNC/TPU system, melt flow properties, molecular structure, and polymer swelling were investigated. At the printing temperatures (240, 250, and 260°C), the complex viscosity of the CNC/TPU filament experienced an exponential increase, indicating potential network formation between the CNCs and TPU. Fourier-Transform Infrared Spectroscopy (FTIR) highlighted changes in the molecular structure for the CNC/TPU filament as temperature increased from 240 to 260°C, which suggests that chemical structure changes are occurring because of degradation. The hypothesis is TPU is disassociated into free soft and hard segments that the CNCs can covalently crosslink with, which can potentially be explained by the increases in the FTIR intensities relating to TPU and CNC's chemical structure. To further quantify potential crosslinking between CNCs and TPU, polymer swelling experiments were implemented. The results from these experiments suggest that increasing printing temperatures from 240 to 260°C will lead to higher degrees of crosslinking. Further investigation could yield the validity of this crosslinking and additional optimization of FFF printing with CNC/TPU nanocomposites.

Bio-inspired monomers functionalized with nucleobase or ionic group allowed synthesis of supramolecular polymers using free radical polymerization and controlled radical polymerization techniques. Comprehensive investigations for the structure-property-morphology relationships of these supramolecular polymers elucidated the effect of noncovalent interactions on polymer physical properties and self-assembly behaviors. Reverse addition-fragmentation chain transfer (RAFT) polymerization afforded acrylic ABC and ABA triblock copolymers with nucleobase-functionalized external blocks and a low-Tg central block. The hard-soft-hard triblock polymer architecture drove microphase-separation into a physically crosslinked hard phase in a low Tg matrix. Hydrogen bonding in the hard phase enhanced the mechanical strength and maintained processability of microphase-separated copolymers for thermoplastics and elastomers. A thermodynamically favored one-to-one stoichiometry of adenine and thymine yielded the optimal thermomechanical performance. Intermolecular hydrogen bonding of two thymine units and one adenine unit allowed the formation of base triplets and directed self-assembly of ABC triblock copolymers into remarkably well-defined lamellae with long-range ordering. Acetyl protected cytosine and guanine-containing random copolymers exhibited tunable cohesive strength and peel strength as pressure sensitive adhesives. Post-functionalization converted unprotected cytosine pendent groups in acrylic random copolymers to ureido-cytosine units that formed quadruple self-hydrogen bonding. Ureido-cytosine containing random copolymers self-assembled into nano-fibrillar hard domains in a soft acrylic matrix, and exhibited enhanced cohesive strength, wide service temperature window, and low moisture uptake as soft adhesives. A library of styrenic DABCO salt-containing monomers allowed the synthesis of random ionomers with two quaternized nitrogen cations on each ionic pendant group. Thermomechanical, morphological, and rheological analyses revealed that doubly-charged DABCO salts formed stronger ionic association and promoted more well-defined microphase-separation compared to singly-charged analogs with the same charge density. Bulkier counterions led to enhanced thermal stability, increased phase-mixing, and reduced water uptake for DABCO salt-containing copolymers, while alkyl substituent lengths only significantly affected water uptake of DABCO salt-containing copolymers. Step growth polymerization of plant oil-based AB monomer and diamines enabled the synthesis of unprecedented isocyanate-free poly(amide hydroxyurethane)s, the first examples of film-forming, linear isocyanate-free polyurethanes with mechanical integrity and processability. Successful electrospinning of segmented PAHUs afforded randomly orientated, semicrystalline fibers that formed stretchable, free-standing fiber mats with superior cell adhesion and biocompatibility. / Ph. D.

The goal of this research study was to create an artificial annulus fibrosus similar to that of the natural intervertebral disc, as well as find preliminary results for vertebral endplate connection and nucleus pulposus internal pressure, for the correction of disc degeneration in the spine. The three-part composite samples needed to demonstrate good shock absorption and load distribution while maintaining strength and flexibility, and removing the need for metal in the body, something of which no current total disc replacement or spinal fusion surgery can offer. For this study, the spinal disc was separated into its three different components, the annulus fibrosus, the nucleus pulposus, and the vertebral endplates, each playing a vital role in the function of the disc. Two low-cost materials were selected, a Covestro polyurethane and cellulose nanocrystals, for the purpose of creating a polymer composite spinal disc implant. A methodology was established for creating the cast composite material for use as an annulus fibrosus, while also investigating its mechanical properties. The same composite material was used to acquire preliminary results for vertebral endplate connection to the synthesized annulus, however no additional material was used to determine or mimic the mechanical properties of these endplates, due to time constraints. Also because of time constraints, the nucleus used in this study was only comprised of water with no other additives for preliminary testing since the natural nucleus is comprised of about 80-90% water. These properties were then compared to the mechanical properties of the natural disc, so that they could be finely tuned to emulate the natural disc. It is shown in this study that the composite material, when swelled in water, was able to mimic the annulus fibrosus in tensile strength and modulus, however showed higher compressive strength and modulus than ideal. The samples also did not undergo any permanent deformation within the realm of force actually introduced to the natural disc. The vertebral endplates showed decent adhesion to the synthesized annulus, however there were slight defects that became failure concentrators during compression testing. The nucleus showed promising results maintaining good internal pressure to the system causing better compressive load distribution, with barreling of the samples. / Master of Science / Spinal disc degeneration is a very prevalent problem in today’s society, effecting anywhere from 12% to 35% of a given population. It usually occurs in the lumbar section of the spine, and when severe enough, can cause bulging and herniation of the intervertebral disc itself. This can cause immense lower back pain in individual’s stricken with this disease, and in the US, medical costs associated with lower back pain to exceed $100 billion. Current solutions to this problem include multiple different treatment options of which, spinal fusion surgery and total disc replacement (TDR) are among the most common. Although these treatments cause pain relief for the majority of patients, there are multiple challenges that come with these options. For example, spinal fusion surgery severely limits the mobility of its patients by fusing two vertebrae together, disallowing any individual movement, and TDR can cause hypermobility in among the vertebrae and offer little to no shock absorption of loads. Therefore, a better treatment option is needed to relieve the pain of the patients, as well as maintain equal motion, shock absorption, and load cushioning to that of the normal intervertebral disc and remaining biocompatible. The goal of this research study was to create a three-component system, like that of the natural intervertebral disc, for the use of spinal disc replacement and to replace current options. The fabricated system was comprised of the three components found in the natural intervertebral disc; the annulus fibrosus, the nucleus pulposus, and the vertebral endplates. Because the system will need to go in-body, the materials used were all characterized as biocompatible materials; the polyurethane currently being used in medical devices and implants, and the cellulose nanocrystals (CNCs) coming from natural cellulose in sources such as wood and plants. The results determined that the mechanical properties of the system can be fine-tuned in order to mimic the natural strength and cushioning capabilities of the natural disc, based on CNC content added to the polyurethane, and when all three components of the system are added together, the compressive stress-strain is most similar to the natural disc in compression. However, the system did show failure in the connection between the annulus fibrosus and vertebral endplates, causing herniation of the nucleus similar to the initial problem attempting to be solved. For this, more ideal fabrication methods should be researched in the future including 3D printing techniques, injection molding, and roll milling. As well as alternate fabrication techniques, cell grow and viability should be determined to show that cells don’t die once the system in implanted.

Yes / Highly branched poly(N-isopropylacrylamide) (HB-PNIPAM), functionalized with vancomycin at the chain ends, acted as a bacterial adhesive and was incorporated into polyurethane foams to form semi-interpenetrating networks. The poly(N-isopropylacrylamide) was labelled with a solvatochromic dye, Nile red. It was found that the thermal response of the polymer was dependent on architecture and temperature dependent color changes were observed within the foam. The foams had open pore structures and the presence of the HB-PNIPAM substantially reduced the shrinkage of the foam as the temperature was increased upto 20 °C. The foams were selectively adhesive for Staphylococcus aureus (Gram-positive bacteria) compared to Pseudomonas aeruginosa (Gram-negative bacteria) and the presence of S. aureus was indicated by increased fluorescence intensity (590 to 800 nm).