Fibers in biological scaffolds like fibronectin stiffen when they experience forces between cells. It will expose binding sites under contractile forces and then form disulfide bonds. This on-demand strain-stiffening is a desirable property in synthetic materials. Tran et.al. (2017) mimicked the “cryptic” design of fibronectin by copolymerizing thiol crosslinking sites with monomers containing poly (ethylene glycol) chains. When the PEG chain increased from 350 to 950 g/mol, the strains-stiffening became on-demand while the curing process extended from 3 hours to 15 hours. Extra steric hindrance brought by longer PEG chains caused decreasing mass transfer rates of cryptic sites while the same level of strain rate was introduced. I proposed to use stronger ultrasound mechanical perturbation so that higher strain rate can be induced, and the shielding effect brought by the PEG chain can be overcome more easily. Utilizing ultrasound as a stimuli has the potential to improve the gelation speed or achieve high mechanical performance while retain the long shelf life of the “cryptic” materials. To test this hypothesis, I synthesized “cryptic” polymer with aceto-acetoxy and primary amine as crosslinking sites such that, the only time limiting step is brought by the long PEG chain. This is because the bond formation reaction between these two reactive groups is rapid and spontaneous. When switching from weak to strong mechanical perturbation, the change in gelation speed owing to accelerated mass transfer between crosslinking sites can be easily compared. When the PEG chain is 300 Mw and 30 mol % crosslinking sites density, this “cryptic” polymer only showed strain-stiffening under ultrasound while strain under a rheometer was not able to overcome steric hindrance. Signs of chain scission appeared when the ultrasound amplitude was set at 75 %, but was counteracted by reducing amplitude mode over the time. The crosslinking was optimized by varying the ultrasound amplitude and intensity and a final mode of 1 hour 75 % amplitude, 0.5 hour 50 % amplitude and 3.5 hours 25% amplitude provided greatly improved on demand crosslinking. The estimated kinetic constant using this mode was two times higher than that of under simple shear strain. Through this study, I found that ultrasound can improve the curing time of this “cryptic” polymer system since it induces higher strain rate and expedite the mass transfer rate between crosslinking sites and optimizing the ultrasonic amplitude profile to limit chain scission provides improved crosslinking performance.

The purpose of this study was to examine the relationship between urban teachers’ perceptions and their implementation of culturally responsive materials into the classroom. Specifically, this study examined the influences of age, years of teaching experience, level of education, professional development, and prior knowledge with culturally diverse populations on perceptions of implementing culturally responsive materials into urban elementary classrooms. Based on the results of this research, the variables of age, teaching experience, and professional development were found to affect how teachers value culturally responsive materials. This suggests that variables can have important ramifications for educators and administrators in urban and culturally diverse schools.

Because of the latest developments in nanotechnology and the need to have new functions, a high demand for innovative materials is created. The technological requirements for new applications cannot be fulfilled by most of the well-developed materials like metals, plastics, or ceramics. Therefore, composite materials that can exhibit better properties in contrast to their single counterpart represents a valuable and interesting alternative for the development of new and more performing functional materials. In the past few years, one of the most rapidly developing fields in materials chemistry is research and development of innovative hybrid materials and nanocomposites having exceptional properties. A significant reason for this is that this group of materials closes the gaps between different scientific fields and brings together the ideal properties of the different disciplines into a single system. Conventional materials like polymers or minerals can be mixed with substances of a different kind, like biological molecules and different chemical functional groups to create unique functional materials with the help of a building block method. Inorganic and organic chemistry, physical and biological sciences are integrated in the search for new recipes in a purely interdisciplinary way to generate unique materials. Compounds that are created frequently have interesting new properties for forthcoming functional materials and technological applications. Natural materials frequently function as a model for these systems and various examples of biomimetic methods can be obtained while generating these hybrid materials. The research and development of these materials is driven by the needs of future technologies. The research carried out in this thesis is entirely based on hybrid organic-inorganic materials; hence, it consists of soft organic/bioorganic section that makes it possible to generate multifunctional materials, whereas the hard inorganic section functions as a rigid and stable platform for developing nanocarriers and imaging agents. A key domain in materials chemistry is the creation of smart materials that have the ability to respond to environmental changes or be triggered on demand. These materials have led to the creation of new technologies, like electroactive materials, electrochromic materials, biohybrid materials, sensors and membranes, etc. The required functionality can be provided by the organic or inorganic components, or from both. In this dissertation, the synthesis, methodology, and creation of three unique organic-inorganic hybrid stimuli responsive systems having targeted features for specific applications are examined. The first example is represented by supramolecular microtoroids created by spontaneous self-assembly of amphiphilic molecules and a hydrophilic polymer (chitosan), in the presence of iron (III) chloride. Light irradiation is the stimulus responsible for assembly/disassembly of this new supramolecular entities. The basis of the photo-response of the microtoroids is the photoreaction of the anthracene derivatives. In order to make these materials bio applicable, the microtoroid size was controlled and narrowed down to nanometers, which has led to our second system called metal organic complexes (MOCs). In this system, chitosan was replaced by PNIPAM polymer at optimized concentrations. The reversible thermo-response of MOCs comes from the phase transition ability of PNIPAM. The third hybrid material is the core-shell system consisting of mesoporous organosilica coated with iron oxide nanoparticles, used for cargo delivery and cell imaging. The magnetic-response of the core-shell system results from the strong magnetic properties of iron oxide nanoparticles, while the presence of PMOs increased its biocompatibility. Our research on such organic-inorganic hybrid materials represents a promising development in the field of materials chemistry. Due to the possibility of mixing various properties in a single material, a variety of combinations regarding possible materials and applications have emerged.

The corrosion of infrastructure imposes a significant monetary cost, and at times human cost, upon society. Methods to improve corrosion resistance of materials are described herein which utilize the reversibility of the Diels-Alder reaction to impart thermal responsiveness upon materials. Such stimuli responsiveness can potentially play a role in self healing properties which lead to reduced cracking and thus increased corrosion protection. Reversible Diels-Alder chemistry was utilized to manipulate the surface energy of glass substrates. Hydrophobic dieneophiles were prepared and attached to glass slides and capillaries to yield a nonwetting surface. Thermal treatment of the surfaces cleaved the Diels-Alder linkage, and resulted in the fabrication of a hydrophilic surface. Preliminary analysis utilized contact angle (CA) measurements to monitor the change in surface energy, and observed a hydrophilic state (CA - 70±3°) before attachment of the dieneophile to a hydrophobic state (CA - 101±9°) followed by regeneration of the hydrophilic state (CA - 70±6°) upon cleavage of the Diels-Alder linkage. The treatments were then applied to glass capillaries, with effective treatment confirmed by fluid column measurements. Patterned treatments were also demonstrated to provide effective fluid flow gating. Reversible Diels-Alder linkages were incorporated into polymer thermoset binding resins in order to provide a means by which a crosslinked thermoset could undergo stimuli responsive reversible crosslinking. The binder systems which were utilized included two types of amine curing agents, polydimethylsiloxane (PDMS) and Jeffamine® polyetheramines (PEA), and two types of epoxy resins, EPON resin based on diglycidyl ether of Bisphenol-A and epoxidized soybean oil. Various dienes and dienophiles were employed to functionalize the selected binder systems and were met with various degrees of success. The synthetic technique which proved to be the most promising was the Diels-Alder modification of the epoxidized soybean oil.

No description available.

In this article, a multiple-responsive polymer micelles system was constructed by using ionic bond to link the hydrophobic tetraphenylthiophene (TP) fluorophores, which possess the property of aggregation-induced emission enhancement (AIEE), with the hydrophilic poly(N-isopropyl acrylamide) (PNIPAM). The susceptibility of the ionic ammonium-sulfonate (Am-Sul) bonds towards metal ions, acid and base triggered the AIEE-operative fluorescence (FL) response. To exercise the idea, PNIPAM with sulfonate terminal was primarily prepared to react with TP-derivatives functionalized with ammonium groups to generate polymer complex of TP-PNIPAM. When in water, the polymer complex TP-PNIPAM formed micelles with the aggregated TP core interconnecting the hydrophilic PNIPAM shell by the ionic Am-Sul bonds. With the operative AIEE effect, the aggregated TP core of the micelles fluoresced but upon the additions of metal ions, acid and base, the ionic bonds dissociated to result in the collapse of the micelles and the FL quenching. A novel fluorogenic sensor capable to respond to multi-stimuli was therefore constructed. Amphiphilic micelle systems with the hydrophilic poly(N-isopropyl amide) (PNIPAM) shell and the hydrophobic tetraphenylthiophene (TP), which has the novel aggregation-induced emission enhancement (AIEE) feature, core inter-connected by ionic bonds were prepared in this study to explore the AIEE-operative emission response towards critical micelle concentration (CMC) and lower critical solution temperature (LCST). To exercise the idea, TP functionalized ammonium cations and PNIPAM with terminal sulfonate group were individually prepared and mixed together to yield three amphiphilic TP-PNIPAM complexes with different hydrophobic TP to the hydrophilic PNIPAM (x/y) ratios. When in aqueous solution, TP-PNIPAMs form micelles with the aggregated TP core, which emits strongly due to the operative AIEE effect, encompassed by the PNIPAM shell. The resultant CMC and LCST of the TP-PNIPAM micelles can be varied by changing the hydrophobic to the hydrophilic x/y ratio and can be monitored by the AIEE-dominant fluorescence responses towards concentration and temperature variables.

Le travail de recherche de cette thèse se concentre sur le développement de nanoparticules de silice organo-hybrides pour des applications en nanomédecine et agroalimentaire. Ces nanoconteneurs de silice, comportant des liens disulfures, sont capables de se briser en petits fragments en présence du milieu réductif intracellulaire. Des nanoparticules présentant de larges pores ont été synthétisées pour la livraison d’un siRNA PLK1 pour le traitement du carcinome hépatocellulaire et ont démontré des résultats prometteurs in vitro et in vivo. Ces particules ont été également utilisées pour charger un peptide cytotoxique, souvent utilisé comme pesticide dans l’industrie agroalimentaire. Les nanoparticules cassables ont ensuite été miniaturisées pour le relargage d’agents thérapeutiques dans des glioblastomes humains. Le système présentait un relargage plus rapide comparé à la forme liposomale actuellement sur le marché. Enfin, des nanoparticules contenant des liens répondant aux réactifs dérivés de l’oxygène ont été développées et ont démontré une fragmentation importante en présence d’oxygène singulet. / The research work presented throughout this thesis focuses on the development of organo-hybrid mesoporous silica nanoparticles for their applications in nanomedicine and crop industry. Disulfide doped silica nanocarriers, able to break down in small pieces in presence of the intracellular reductive environment have been tailored. A large pore stimuli-responsive system was developed to deliver a PLK1 siRNA within hepatocellular carcinoma cells demonstrating promising results both in vitro and in vivo. The particles were further used to deliver a venom peptide, often utilized as esticide in the crop industry. The breakable nanocarriers were further miniaturized for the delivery of chemotherapeutic agents within human glioblastoma cells. The system presented a faster delivery compared to the commercially available liposomal form. Finally, Reactive-Oxygen-Species-responsive mesoporous silica nanoparticles were developed and demonstrated fast breakability upon incubation with singlet oxygen.

No description available.

"Multi-functionalized Side-chain Supramolecular Polymers:A Methodology Towards Tunable Functional Materials". Even as we see a significant growth in the field of side-chain supramolecular polymers in the last ten years, systems employing multiple non-covalent interactions have been scarcely studied. Non-covalent multi-functionalization provides unique advantages such as rapid optimization via reversible functionalization as well as for the tuning of materials properties by exploiting the differences in the nature of these reversible interactions. This thesis involves the design principles, synthesis & methodology of side-chain multi-functionalized polymers. The combination of the principles of a functionally tolerant & a controlled polymerization technique such as ROMP with multiple noncovalent interactions such as hydrogen bonding, metal coordination & Coulombic self-assembly has been used to synthesize multi-functionalized polymers. Furthermore, the orthogonality between hydrogen bonding, metal coordination & ionic self-assembly in random/block copolymers has been studied in detail. In order to validate the viability of this multi-functionalization methodology towards materials design non-covalent crosslinking of polymers was used as a potential application. Three classes of crosslinked networks have been studied: complementary multiple-hydrogen bonded networks, multiple-metal crosslinked networks, & multi-functionalized hydrogen bonded & metal coordinated networks. By using non-covalent multi-functionalization, important materials properties & its responsiveness towards chemical agents have been tuned & controlled to yield novel materials which would be difficult to be obtained via traditional covalent techniques or by using single non-covalent interactions.

Ce travail avait pour but de développer un nouveau type de matériaux basés sur des complexes polyelectrolytes. Ces matériaux ont été obtenus par l’ultracentrifugation des complexes soit d’origine naturelle ou soit d’origine synthétique. Le système de polyélectrolytes ainsi que les conditions dans lesquelles ces matériaux peuvent être obtenus, suivi par le choix du système optimal pour des études complémentaires ont été décrits. PAA / PAH CoPECs a été choisi comme systèmes modèles de synthèse et ses propriétés physico chimiques (composition, structure et les propriétés mécaniques) ont été décrits ici en détails. Nous avons montré que les propriétés de la composition, la structure et mécanique de le PAA/PAH CoPECs peut être contrôlée en modifiant les conditions d’assemblage (pH, concentration des polyélectrolytes, [NaCl], la vitesse et la commande de l’addition). Également, les conditions environnementales ([NaCl] et pH) ont également été utilisés pour contrôler la taille des pores et porosité des PAA/PAH CoPECs . Enfin, leur capacité à servir de support pour l’immobilisation d’enzymes a également été étudiée. Nous avons optimise les conditions d’assemblage afin de maintenir le maximum quantité de l’enzyme dans le complexe. Nous avons également démontré que CoPECs fournit la stabilisation à long terme, ainsi que la protection de l’enzyme à des températures élevées. Ainsi, PAA / PAH CoPECs sont des candidats potentiels pour être utilisé comme des supports pour l’ingénierie tissulaire et pour l’immobilisation d’enzymes. / This work was aimed to the develop of a new kind of materials of polyelectrolytes complexes. These materials were obtained by the ultracentrifugation of complexes either of natural or synthetic origin. The polyelectrolytes systems as well as the conditions under which these materials could be obtained, followed by the selection of the optimal system to further studies was described. PAA/PAH CoPECs was chosen as synthetic model systems and its physiochemical properties (composition, structure and mechanical properties) were here deeply described. We demonstrated that the composition, structure and mechanical properties can be controlled by changing the assembly conditions (pH, concentration of the polyelectrolytes, [NaCl], speed and order of addition). Moreover, the environmental conditions ([NaCl] and pH) were also used to control the porosity and pores size of the PAA/PAH CoPECs. Finally their ability to serve as scaffold for enzyme immobilization was also studied. We optimized the assembly conditions to keep the maximum of the activity. We also demonstrated that the CoPECs structure provides the stabilization in long term as well as the protection of the enzyme from high temperature. Thus, PAA/PAH CoPECs is a potential and suitable candidates as scaffold for tissue engineering and for the immobilization of enzymes.