Browsing by Author "Bailey, Travis S., advisor"
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Item Embargo Development of bioinspired hyaluronan enhanced synthetic polymers for medical applications(Colorado State University. Libraries, 2023) Gangwish, Justin Phillip, author; James, Susan P., advisor; Bailey, Travis S., advisor; Dasi, Lakshmi Prasad, committee member; Popat, Ketul, committee member; Monnet, Eric, committee memberThe first transcatheter aortic valve replacement (TAVR) was performed in 2002, and over the past two decades has become as prevalent as surgical aortic valve replacements in America. TAVR's have significant potential to provide relief for patients with aortic valve disease, but due to their high cost remain accessible primarily in wealthy nations. Furthermore, TAVR's have limited lifespans and are radiotransparent so they can only be evaluated for function through echocardiography. Thus, an expensive medical implant with limited durability is only replaced after it has begun to fail and cause the patient further stress on their heart. To address these issues this dissertation reviews the research performed in generating a novel heart valve leaflet material that is radiopaque, made primarily out of linear low-density polyethylene (LLDPE), and incorporates the biological polymer hyaluronan (HA). These leaflets could significantly reduce the cost of TAVR's potentially allowing for global adoption of the technology. They are radiopaque and easily imaged using x-ray fluoroscopy allowing changes in leaflet shape or movement to be identified prior to when the echocardiography would have shown a deleterious effect to function. They incorporate HA which is found in the interior lumen of blood vessels and has been shown to decrease calcification and thrombosis, both of which have caused polymeric leaflets to fail in previous research. Finally, they can be easily shaped and reinforced allowing for a potentially far greater device lifespan. The leaflets are made by melt pressing in radiopaque powders of either tungsten or bismuth trioxide into sheets of LLDPE followed by treatment with HA to form an interpenetrating polymer network. The material properties of the leaflets were evaluated for their tensile mechanical properties, their hydrophilicity, their radio transparency (or lack thereof), and their hemodynamics. The biocompatibility of the leaflets was evaluated through a cytotoxicity assay, whole blood clotting on the surface of the material, and the ability for platelets to adhere and activate on the material surface. The results demonstrate the material has significant potential to function as a heart valve leaflet in a TAVR. Beyond evaluating this novel material, the process by which HA is incorporated into LLDPE was examined and optimized for commercial scale up. First, the need for solvent distillation and nitrogen blankets during treatment were determined to be unnecessary to produce an HA IPN with LLDPE. Then the rate at which the LLDPE is drawn from the HA solution as well as the vacuum pressure and temperature during this process was found to affect the amount of active HA at the surface of the material. Finally initial evidence was found that shows that HA IPN does not form through the bulk of the material, but rather in the first few microns of the LLDPE. Unrelated to TAVR's a study was performed to enhance the non-woven polypropylene used in surgical masks and N-95 masks against COVID-19 using HA and polyethylene glycol (PEG). HA was used to form a microcomposite on the surface of the non-woven polypropylene while PEG was grafted to the surface with oxygen plasma. The resulting materials were evaluated for their tensile mechanical properties, breathability, chemical composition, hydrophilicity, cytotoxicity, and ability to adsorb COVID-19 spike protein. The results indicate the material has notable potential to make masks more effective at preventing the transfer of COVID-19, however further studies using live SARS-CoV-2 virus beyond the capabilities of this laboratory are necessary before that potential can be fully confirmed.Item Open Access Development of tethered micelle hydrogel networks through sphere-forming AB/ABA block copolymer melts(Colorado State University. Libraries, 2013) Guo, Chen, author; Bailey, Travis S., advisor; Kipper, Matt J., committee member; Chen, Eugene, committee member; Wickramasinghe, S. Ranil, committee memberThe overriding theme of the work contained in this thesis is concerned with the preparation of tethered micelle hydrogel networks through the melt-state self-assembly of sphere-forming AB diblock and ABA triblock copolymer blends. The first chapter of this dissertation introduces the various projects pursued and provides background information for the reader. The second chapter of this thesis contains the initial demonstration of this novel strategy using polystyrene-poly(ethylene oxide) (PS-PEO, SO) diblock and PS-PEO-PS (SOS) triblock copolymers. Included in this chapter is a discussion of the synthetic polymerization techniques used to produce the SO and SOS block copolymers, the basic melt-state fabrication and characterization strategies used to pre-structure the tethered micelle networks, and the impact of changing both the SOS concentration and temperature on the resultant properties of the hydrogels produced. In these initial studies, the SOS triblock copolymer was constructed to be exactly double the SO diblock copolymer molecular weight, such that the preferred lattice dimensions during self-assembly were "matched". These "matched" hydrogels produced equilibrium swelling ratios (3.8-36.9 g water/g polymer) and dynamic elastic moduli (G' = 1.7-160 kPa) tunable across an impressive range of values using only temperature (10-50 °C) and SOS concentration (3.3-72.0 mol%). The third chapter of this thesis describes our efforts to influence the swelling and mechanical properties exhibited by simply modifying the PEO midblock molecular weight in the SOS tethering molecules. In doing so, we were able to show that the degree of coronal layer overlap between adjacent micelles was the primary contributing factor determining the dynamic mechanical response of the hydrogel. That is, the changes in mechanical properties produced due to altering tether concentration, tether length, or temperature, could all be understood in terms of their impact on the degree of coronal layer overlap in the system. In addition to these findings, we also discovered an interesting relationship between swelling and tether length. Increases in tether length by a factor of 1.6 compared to that of the matched system, resulted in higher swelling ratios and smaller elastic moduli (due to reduced coronal layer overlap). However, increases in tether length by a factor of 2.3 produced swelling behavior and mechanical properties nearly identical to that of the matched system. We concluded that the increase in tether length by a factor of 2.3 was sufficient to allow bridging into the second shell of the nearest neighbor micelles, negating the swelling advantage anticipated for the system. The fourth chapter of this thesis concerns our efforts to demonstrate the modification potential of the swollen hydrogel systems of Chapters 2 and 3. In this study, the terminal hydroxyl functionality present in the aforementioned SO diblock copolymers was substituted with either an azide or alkyne functionality. Cu(I) catalyzed coupling of the azide/alkyne functional diblock copolymer was then performed in the swollen state, producing a secondary network of tethers in the system. Installation of the secondary network produced dramatic improvements in the hydrogel tensile modulus, strain at break, stress at break, and toughness, while permitting swelling ratios, small strain rheological properties, and response in unconfined compression to remain largely unchanged. The fifth and final chapter of this thesis concerns a discussion of preliminary data supporting several promising directions for future work involving the further development of these tethered micelle networks.Item Open Access Elastic free-standing RTIL composite membranes for CO2/N2 separation based on sphere-forming triblock/diblock copolymer blends(Colorado State University. Libraries, 2016) Wijayasekara, Dilanji B., author; Bailey, Travis S., advisor; Fisk, John D., committee member; Kipper, Matthew, committee member; James, Susan, committee memberThe main focus of this dissertation was the development of a robust polymeric membrane material for separating CO2 from a gas mixture of CO2 and N2. Flu gas, which is mainly a mixture CO2 and N2, is the single largest form of anthropogenic CO2 emissions to the atmosphere. Capturing CO2 from flu gas is considered as a measure of controlling anthropogenic CO2 emissions. Existing CO2 capturing technologies for flu gas suffer from low efficiency and the low cost effectiveness. Adoption of membrane technology is comparatively the best route towards the economical separations. Challenges faced by existing CO2 separation membrane materials are the lack of high mechanical robustness and the processability required for fabrication of membrane units while maximizing their gas separation properties. We were able to form a novel membrane material that addresses each of these challenges. These novel membranes are based on highly swollen, self-standing films produced using sphere-forming PS-PEO diblock and PS-PEO-PS triblock copolymer blends. The intricate connectivity among spherical domains produced during melt-state assembly (prior to swelling), provides a framework that remains elastically tough even in the presence of large quantities of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTf2N) - a room temperature ionic liquid (RTIL) that has high selectivity for CO2 over N2. Further investigations on improving the robustness of these membranes and the gas separation properties were carried out based on two scenarios. First, potential of improving the thermal stability of these membranes by replacing the thermoplastic polystyrene with a thermoset moiety such as a chemically cross-linked polyisoprene (PI) was researched. Cross-linking chemistry utilized required a post-polymerization modification of PI and it was found that this oxidation modification of olefins on PI caused the decoupling of triblock copolymer in the blend and also substantially hindered melt-state self assembly. The membranes formed with this modification turned out to have inferior mechanical properties compared to the polystyrene based ones, most likely due to the above mentioned complications. Due to the time restrictions, this study was limited to just the identification of the existing challenges in the proposed strategy. Recommendations for addressing the challenges identified are also presented later in the dissertation. The second scenario for improving the performance of these membranes was to increase their productivity by improving both the CO2 permeability and maximizing the trans-membrane pressure differentials possible during operation. To accomplish this we focused on the development of an alternative matrix material (alternative for PEO) enriched with ionic groups. The goal was to increase matrix solubility in the RTIL (improved CO2 permeability) while simultaneously strengthening matrix-RTIL interactions for reduced leaching under higher pressure differentials. Synthetic routes to achieve this task involved a sequential polymerization of isoprene and ethoxy ethyl glycidyl ether (EEGE) monomers. Polymerization of EEGE to yield high molecular weight linear blocks proved to be extremely challenging due to the undesirable chain transfer reaction tendency of EEGE monomer. A great deal of research effort was spent characterizing various anionic reaction conditions and developing measures aimed at suppressing chain transfer. While ultimately unsuccessful, the results of these studies provide significant insight into the challenges of forming high molecular weight linear polyglycidols and will hopefully provide inspiration for the development of future synthetically successful strategies. A series of proof of concept experiments for transforming alcohol functionalities on this polymer system to imidazolium was also completed successfully. The dissertation concludes with a final project completed outside the main objective of the dissertation - a morphological characterization of a series of thermoplastic elastomers with unique molecular architectures. This work is reported separately in the appendix I.Item Open Access Engineering effective fibrocartilage replacement technologies using nanostructure-driven replication of soft tissue biomechanics in thermoplastic elastomer hydrogels(Colorado State University. Libraries, 2018) Lewis, Jackson Tyler, author; Bailey, Travis S., advisor; Haut Donahue, Tammy L., advisor; James, Susan P., committee member; Popat, Ketul C., committee member; Li, Yan, committee memberSynthesis of hydrogel networks capable of accurately replicating the biomechanical demands of musculoskeletal soft tissues continues to present a formidable materials science challenge. Current systems are hampered by combinations of limited moduli at biomechanically relevant strains, inefficiencies driven by undesirable hysteresis and permanent fatigue, and recovery dynamics too slow to accommodate rapid cycling prominent in most biomechanical loading profiles. This dissertation presents a new paradigm in hydrogel design based on prefabrication of an efficient nanoscale network architecture using the melt-state self-assembly of amphiphilic block copolymers. Rigorous characterization and preliminary mechanical testing reveal that swelling of these preformed networks produce hydrogels with physiologically relevant moduli and water compositions, negligible hysteresis, sub-second elastic recovery rates, and unprecedented resistance to fatigue over hundreds of thousands of compressive cycles. By relying only on simple thermoplastic processing to form these nanostructured networks, the synthetic complexities common to most solution-based hydrogel fabrication strategies are completely avoided. Described within this dissertation are a range of efforts, broadly focused on refining synthetic and post-synthetic processing techniques to improve the modulus, surface hydrophilicity, fatigue resistance and cytocompatibility of these thermoplastic elastomer hydrogels, with the ultimate goal of producing a material viable as a meniscal replacement.Item Embargo Failure analysis and durability enhancement of polymeric heart valve leaflets(Colorado State University. Libraries, 2024) Khair, Nipa, author; James, Susan P., advisor; Bailey, Travis S., advisor; Li, Vivian, committee member; McGilvray, Kirk, committee memberRheumatic and calcified aortic heart valve disease is prevalent globally among all aged people, and the number is rapidly increasing. Clinically accepted, minimally invasive xenograft-based transcatheter aortic heart valve replacement (TAVR) shows limited durability (<10 years). Hyaluronic acid (HA) enhanced polyethylene polymeric TAVR shows excellent in vitro and in vivo anti-calcific, anti-thrombotic, and hydrodynamic performance, making it a suitable candidate for heart valve leaflets. The main problem, however, is during durability testing, cyclic impact loading causes premature failure in a consistent fashion related to TAVR assembly. This dissertation investigates leaflet premature failure mechanisms and provides two plausible solutions to upgrade heart valve durability without sacrificing performance. With regard to the failure mechanism, representative areas of retrieved failed leaflets are examined under electron microscopy and small angle x-ray scattering. The investigation finds abrasive wear, wear polishing, fine scratching, and imprints of the metal stent of the leaflet surface, indicating surface wearing from soft plastic rubbing against hard metal. A strong permanganate oxidizer etches away low-energy amorphous domain to unveil stable spherulitic structures of approximately 3 µm, bridging and tie molecular domains of pristine LLDPE. The oxidizer partially etches away polymeric buildups of failed leaflets only to reveal thinned-out and fractured spherulites beneath them, identifying the buildups as stress precursors. SAXS study reports local lamellar disruption further confirming the SEM results. Most. Notably, this is the first study that, to our knowledge, to directly image stable craze cross-tie microstructure that formed due to chain disentanglement from high amplitude cyclic stress. The SEM images validate previous theoretical and computational molecular dynamics models of cross-tie structure architecture. Therefore, leaflet premature failures are the compound effect of cyclic fatigue-initiated crazing and surface wear. Heart valve leaflet durability can be upgraded by controlling crazing and surface wearing. Both the crazing and surface wearing can be controlled by crosslinking of randomly folded amorphous chains. Because they are direct impacts of chain disentanglement under high amplitude cyclic stress. Crosslinked covalent bonds of polymer limit chain movements. LLDPE thin sheets are crosslinked at 50, 70, 100, and 150 kGy doses using 200 KeV (low energy) and 4 MeV (low energy) electron beams at room temperature in the air. Their effects are characterized by measuring gel content percentage, tensile testing, Differential Scanning Calorimetry (DSC), nanoindentation, and nano scratch test. Crosslinked LLDPE heart valve leaflet tested in in vitro flow loop and wear tester to determine valve performance and durability, respectively. Low energy electron beam (LEEB) forms 28% xylene insoluble gel whereas high energy electron beam (HEEB) forms 58 % gel at 100 kGy doses. LEEB does not affect mechanical properties, but HEEB significantly increases stiffness and yield strength. A slight reduction of melting temperature is found for LLDPE crosslinked by both of the energy sources. Nanomechanical tests show crosslinking improves hardness and coefficient of friction, an indication of improving surface wear resistance, which can explain durability improvement. Heart valve durability can also be improved by strengthening the leaflet with fiber reinforcement. A thin plastic sheet is assembled into a cylindrical form by welding two ends, which never fails. The weld at the commissure post is found to be mechanically stronger than the rest of the leaflet, which protected this region. Braided fibers are embedded on the leaflet regions of the commissure post perpendicular to the valve circumference, mimicking the weld but at a much higher strength. Leaflet durability skyrockets from a few million ISO 5840-2005 cycles to 73 million. The entire cardiac cycle of the heart valve with embedded fibers of varying angles, lengths, and numbers is simulated in Finite Element Analysis (FEA) to study their effects on leaflet maximum principal stress and leaflet opening dynamics. Horizontal fibers wrap the leaflet 360° to relax the leaflet completely during peak diastolic. However, the leaflet has a higher coaptation gap and delayed opening. The heart valve with embedded horizontal fibers is physically manufactured and tested in an in vitro flow loop and wear tester, which showed improved durability, but compromised hemodynamics. Finally, strategically crosslinked leaflet was simulated in FEA where leaflet regions of the commissure post and stent line are assigned with stiff crosslinked LLDPE material property, but the rest of the cusps undergo maximum bending are assigned with uncrosslinked LLDPE material property. Results show that strategically crosslinked leaflets open more easily than fully crosslinked leaflets. The final chapter discusses 3D shaped LLDPE leaflet bio enhancement process. Leaflets are 3D shaped in a vacuum thermoformer followed by the HA enhancement. Whole blood clotting resistance, platelet adhesion, activation, and cytotoxicity studies are conducted to determine at 10-4 µmol/mm2 ranged HA population density is required to achieve the best biocompatibility. Generally, water contact angle, Toluidine Blue O (TBO) elution assays, ATR-FTIR are used to determine overall HA presence on the leaflet. This study reports TBO staining and elution is the most effective and accurate measurement tool for determining HA population density. Fiber-reinforced LLDPE, and crosslinked LLDPE are HA-treated, and TBO staining predicts heavily populated HA surface density.Item Open Access Functional nanostructured ionic liquid-based block copolymer systems for energy applications(Colorado State University. Libraries, 2021) May, Alyssa Winter, author; Bailey, Travis S., advisor; Reynolds, Melissa, committee member; Sambur, Justin, committee member; Lear, Kevin, committee memberRoom-temperature ionic liquids (RTILs) are pure molten salts that have zero vapor pressure, a wide range of thermal stability, negligible flammability, and high ionic conductivity. These qualities make them desirable as electrolyte replacements for the more common lithium salt-doped carbonate solvents which are ubiquitous in current battery technology despite being exceptionally flammable. Use of liquid electrolytes, even non-flammable ones, has its drawbacks and challenges, like preventing leakage of the electrolyte and maintaining good contact with electrode surfaces, particularly when the battery electrodes or container become physically warped. With the emergence of flexible electronics technologies like foldable phones, bendable displays, and "wearables," interest has grown in developing solid electrolytes that are mechanically robust and sufficiently good ionic conductors, as they greatly expand the design possibilities for batteries. Block copolymers (BCPs) are an ideal platform from which to develop solid electrolyte materials as the variety of polymerizable blocks and physical properties that can be derived from them are nearly limitless. In this dissertation, we explore two methods for incorporating ionic liquid components into solid BCP materials, and thoroughly delve into their interesting chemical, physical, and mechanical properties to demonstrate their potential as functional materials. The first method is the direct, sequential polymerization of both ionic liquid-based and traditional monomers to create poly(ionic liquid) (PIL) BCPs that can microphase separate to form ordered nanostructures. We report on the synthesis of both cobalt-containing and imidazolium-based PIL BCPs and provide a comprehensive examination of their melt-state phase behavior, including the observation of all four equilibrium morphologies available to diblock copolymers: lamellae (Lam), bicontinuous gyroid (Gyr), hexagonally packed cylinders (Hex), and spheres (S). From the morphological phase behavior, we were able to build two phase diagrams and extract critical information about the materials, such as block density of the methyl-imidazolium PIL block. This is an essential parameter for BCP design that enables researchers to target specific morphologies when creating similar materials in the future. The morphology of solid-state conductive materials like PIL BCPs has direct implications on their transport properties, as only certain morphologies (Gyr, S) can have fully continuous domains in which ions can flow, so fully understanding the spectrum of phase behavior in a BCP material is incredibly important for creating truly functional materials from them. The second method is the integration of RTIL into amphiphilic, non-ionic BCPs as a selective swelling solvent to create ion gels, or gel polymer electrolytes (GPEs). We have designed these BCPs, based on melt-state phase separating blends of polystyrene-b-poly(ethylene oxide) (SO) and polystyrene-b-poly(ethylene oxide)-polystyrene (SOS) in which the hydrophilic O block is the majority component, to form hydrophobic spherical domains of S that form a tethered, physically crosslinked networked that acts like an elastic solid when swollen. We demonstrate that SOS BCPs swollen in the RTIL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, or [EMIM][TFSI], have exceptional ionic conductivity, elasticity, distensibility, recovery rates, bulk toughness, and fracture toughness. This rare combination of multiple excellent mechanical properties and high ionic conductivity makes SOS GPEs auspicious candidates as solid electrolytes in energy transport and storage applications.Item Open Access Part I - Access to UV photocured nanostructures via selective morphological trapping of block copolymer melts. Part II - Morphological phase behavior of poly(RTIL) containing block copolymer melts(Colorado State University. Libraries, 2012) Scalfani, Vincent F., author; Bailey, Travis S., advisor; Finke, Richard G., committee member; Henry, Charles S., committee member; Kipper, Matt J., committee member; Prieto, Amy L., committee memberA thermally stable photocuring system was developed for high fidelity translation of block copolymer based melt-state morphologies into their equivalent solid analogs. Cationic photoacids were combined with partially epoxidized polyisoprene-b-poly(ethylene oxide) (PI-PEO) block copolymers, forming composite blends that allow for extended thermal processing prior to cure, in addition to precise trapping of selected morphologies, a consequence of the temperature independent UV curing mechanism. The parent PI-PEO block copolymer exhibited multiple melt-state morphologies including crystalline lamellae (Lc), hexagonally packed cylinders (C), bicontinuous gyroid (G), and an isotropic disordered state (Dis). Modification of the PI-PEO backbone with epoxy groups and addition of a UV cationic photoacid acted only to shift transition temperatures quantitatively, leaving the overall morphological behavior completely unmodified. UV irradiation exposure of the composite blends directly in the melt-phase at selected temperatures resulted in permanent trapping of both the cylinder and gyroid morphologies from a single block copolymer sample. The studied photocuring chemistry was extended to produce spherical nanostructured hydrogel networks. Fabricated hydrogel networks are built from a pre-structured lattice of body-centered cubic spheres (SBCC), produced via melt-state self-assembly of blended AB diblock and ABA triblock copolymers. Added ABA triblock serves to produce active tethered junction points between the AB diblock spherical micelles. The integrated thermally stable photocuring chemistry allows for in situ trapping of these spherical domains directly in the melt phase, independent from the required thermal processing necessary to achieve the tethered BCC lattice. Specifically, the hydrogel networks were fabricated from partially epoxidized blends of polybutadiene-b-poly(ethylene oxide) diblock (PB-PEO) and PB-PEO-PB triblock copolymers. UV cured samples of composite copolymer disks containing an added amount of UV activated cationic photoinitiator samples retained the SBCC structure with high fidelity, which serves to pre-structure the hydrogel network prior to swelling. Photocured disks preserved their original shape when swollen in water or organic media, were highly elastic and had excellent mechanical properties. Control experiments with uncured samples immediately dissolved or dispersed when swollen. Simple photopatterning of the cross-linked hydrogel system is also explored. The developed pre-structured hydrogel network was then adapted to incorporate light sensitive anthracene groups into the spherical forming AB diblock copolymer for in situ generation of tethering ABA triblock. Pressed disks of anthracene terminated poly(styrene)-b-poly(ethylene oxide) diblock (PS-PEO-An) were photocoupled with UV 365 nm filtered light directly in the melt-phase, post the necessary thermal self-assembly process. Photocoupled disks swelled in water, were highly elastic, had tunable mechanical properties (based on UV irradiation time), and showed complete preservation of initial shape. Swollen photocoupled disks were found to exhibit similar properties to pre-blended PS-PEO/PS-PEO-PS hydrogels with slight differences likely resulting from an asymmetric distribution of triblock in the photocoupled gels. The PS-PEO-An based hydrogels are proposed to be possible future candidates for the development of new asymmetric hydrogels because of their simple fabrication and excellent mechanical properties. In part II of this dissertation, a new poly(room temperature ionic liquid) (RTIL) BCP platform was developed based on the sequential, living ring-opening metathesis polymerization (ROMP) of a hydrophobic non-charged dodecyl ester norbornene monomer followed by a cationic imidazolium norbornene ionic liquid (RTIL) monomer. The synthesized BCPs were found to exhibit surfactant behavior in solution and form highly periodic nanoscale melt morphologies. Extensive control experiments with homopolymer blends do not show any surfactant behavior in solution nor microphase separation in the neat melt phase. After an initial study optimizing the synthesis and verifying the block architecture, a series of 16 poly(RTIL)-based BCP samples were synthesized with varying compositions of 0.42-0.96 vol% poly(norbornene dodecyl ester). A phase diagram was developed through a combination of small-angle X-ray scattering and dynamic rheology. Morphologies identified and assigned within the phase space studied include lamellae (Lam), hexagonally packed cylinders (Hex), a coexistence of Hex and Lam domains in place of the gyroid region, spheres on a body-centered cubic lattice (SBCC), and a "liquid like" packing of spheres (LLP). Annealing samples containing a coexistence of Lam and Hex domains suggest extremely slow ordering kinetics disposing one of the morphologies. The studied poly(RTIL)-based BCPs containing highly charges species are very strongly segregated (large Chi parameter), resulting in limited if any access to the disordered and gyroid regime. Finally, in Appendix I a supramolecular polymer system comprised of benzene-1,3,5-tricarboxamide (BTA) and 2-ureido-4[1H]-pyrimidinone (UPy) functional hydrogenated polybutadiene was developed that forms two unique and independent nanorods motif assemblies. When the two supramolecular motifs are end-capped to different homopolymers, the motifs self-assemble independent of each other into separate nanorod stacked structures. However, when a telechelic polymer is introduced into the system containing both supramolecular motifs (one on each end), a network is formed between the nanorod assemblies. Without the telechelic polymer, the supramolecular material is a viscous liquid with little mechanical integrity. In contrast, addition of the telechelic polymer acts as a cross-linker and results in a networked material that is highly elastic with excellent mechanical properties.Item Open Access Phototunable block copolymer hydrogels(Colorado State University. Libraries, 2017) Huq, Nabila A., author; Bailey, Travis S., advisor; Kipper, Matthew J., committee member; Reynolds, Melissa M., committee member; Snow, Christopher D., committee memberThermoplastic elastomer (TPE) hydrogel networks, based on swelling of nanostructured blends of amphiphilic, sphere-forming AB diblock and ABA triblock copolymers, provide direct access to thermally processable plastics that exhibit exceptional elastic recovery and fatigue resistance even after hydration. In such two-component systems, the ratio of ABA to AB block copolymer (BCP) is used to control the resultant swelling ratio, system modulus, and overall mechanical response. This dissertation focuses on developing material strategies through which adjustment of such AB/ABA ratios, and thus the resultant properties, can be accomplished using light. The chapters within capture the manipulation of a photoreactive AB diblock copolymer micelle-like spheres to controllably generate ABA triblock copolymer and the network nanostructure in situ, both in the melt state and after dispersal in solution. This was accomplished using efficient photoinduced [4 + 4]cycloaddition (λ = 365 nm) between terminal anthracene units on a ω-anthracenylpolystyrene-b-poly(ethylene oxide) diblock copolymer precursor to produce the desired amount of polystyrene-b-poly(ethylene oxide)-b-polystyrene triblock copolymer. This direct, UV-mediated handle on tethering between adjacent micelles in the BCP matrix was found to be capable of controllably manipulating hydrogel material properties using (1) duration of irradiation, (2) hydration level and consequent micelle spacing upon exposure, and (3) photopatterning strategies to spatially direct swelling and mechanics. This level of control yielded an array of hydrogels, ranging from those irradiated in the dry melt to produce high-modulus, elastic materials suited for fibrocartilage repair and replacement, to moldable or injectable precursor solutions irradiated into soft, conformally shaped TPE hydrogels ideal for use in high contact applications such as wound healing. The development and scope of this versatile new photoactive BCP system is enclosed.