THERMORESPONSIVE PROPERTIES OF GOLD HYBRID NANOPARTICLES OF POLY(DI(ETHYLENE GLYCOL) METHYL ETHER METHACRYLATE) (PDEGMA) AND ITS BLOCK COPOLYMERS WITH DIFFERENT ANCHORING REGIMES

Thermo-responsive materials have been of interest for many years, and have been studied mostly as thermally stimulated drug delivery vehicles. Recently acrylate and methacrylates with pendant ethylene glycol methyl ethers been studied as thermo responsive materials. This work explores thermo response properties of hybrid nanoparticles of one of these methacrylates (DEGMA) and a block copolymer with one of the acrylates (OEGA), with gold nanoparticle cores of different sizes. We were interested in the effects of gold core size, number and type of end groups that anchored the chains to the gold cores, and location of bonding sites on the thermo-response of the polymer. To control the number and location of anchoring groups we using a type of controlled radical polymerization called Reversible Addition Fragmentation Transfer (RAFT) Polymerization. Smaller gold cores did not show the thermo responsive behavior of the polymer but the gold cores did seem to self-assemble. Polymer anchored to larger gold cores did show thermo responsivity. The anchoring end group did not alter the thermoresponsivity but thiol-modified polymers stabilized gold cores less well than chains anchored by dithioester groups, allowing gold cores to grow larger. Use of multiple bonding groups stabilized the gold core. Using block copolymers we tested the effects of number of thiol groups and the distance between them. We observed that the use of multiple anchoring groups on the block copolymer with a sufficiently large gold core did not prevent thermo responsive behavior of the polymer to be detected which allows a new type of thermo-responsive hybrid nanoparticle to be used and studied for new applications.

Investigation into the enhancement of polycarbonate with conductive nanomaterials

Polymers are typically electrically and thermally insulating materials. The electrical and thermal conductivities of polymers can be increased by the addition conductive fillers such as carbons. Once the polymer composites have been made electrically and thermally conductive, they can be used in applications where these conductivities are desired such as electromagnetic shielding and static dissipation. In this project, three carbon nanomaterials are added to polycarbonate to enhance the electrical and thermal conductivity of the resulting composite. Hyperion Catalysis FIBRILs carbon nanotubes were added to a maximum loading of 8 wt%. Ketjenblack EC-600 JD carbon black was added to a maximum loading of 10 wt%. XG Sciences xGnP™ graphene nanoplatelets were added to a maximum loading of 15 wt%. These three materials have drastically different morphologies and will have varying effects on the various properties of polycarbonate composites. It was determined that carbon nanotubes have the largest effect on electrical conductivity with an 8 wt% carbon nanotube in polycarbonate composite having an electrical conductivity of 0.128 S/cm (from a pure polycarbonate value of 10-17 S/cm). Carbon black has the next largest effect with an 8 wt% carbon black in polycarbonate composite having an electrical conductivity of 0.008 S/cm. Graphene nanoplatelets have the least effect with an 8 wt% graphene nanoplatelet in polycarbonate having an electrical conductivity of 2.53 x 10-8 S/cm. Graphene nanoplatelets show a significantly higher effect on increasing thermal conductivity than either carbon nanotubes or carbon black. Mechanically, all three materials have similar effects with graphene nanoplatelets being somewhat more effective at increasing the tensile modulus of the composite than the other fillers. Carbon black and graphene nanoplatelets show standard carbon-filler rheology where the addition of filler increases the viscosity of the resulting composite. Carbon nanotubes, on the other hand, show an unexpected rheology. As carbon nanotubes are added to polycarbonate the viscosity of the composite is reduced below that of the original polycarbonate. It was seen that the addition of carbon nanotubes offsets the increased viscosity from a second filler, such as carbon black or graphene nanoplatelets.

Structural and surface property characterization of titanium dioxide nanotubes for orthopedic implants

This research focused on the to modification of the surface structure of titanium implants with nanostructured morphology of TiO2 nanotubes and studied the interaction of nanotubes with osteoblast cells to understand the parameters that affect the cell growth. The electrical, mechanical, and structural properties of TiO2 nanotubes were characterized to establish a better understanding on the properties of such nanoscale morphological structures. To achieve the objectives of this research work I transformed the titanium and its alloys, either in bulk sheet form, bulk machined form, or thin film deposited on another substrate into a surface of titania nanotubes using a low cost and environmentally friendly process. The process requires only a simple electrolyte, low cost electrode, and a DC power supply. With this simple approach of scalable nanofabrication, a typical result is nanotubes that are each approximately 100nm in diameter and have a wall thickness of about 20nm. By changing the fabrication parameters, independent nanotubes can be fabricated with open volume between them. Titanium in this form is termed onedimensional since electron transport is narrowly confined along the length of the nanotube. My Ph.D. accomplishments have successfully shown that osteoblast cells, the cells that are the precursors to bone, have a strong tendency to attach to the inside and outside of the titanium nanotubes onto which they are grown using their filopodia – cell’s foot used for locomotion – anchored to titanium nanotubes. In fact it was shown that the cell prefers to find many anchoring sites. These sites are critical for cell locomotion during the first several weeks of maturity and upon calcification as a strongly anchored bone cell. In addition I have shown that such a surface has a greater cell density than a smooth titanium surface. My work also developed a process that uses a focused and controllably rastered ion beam as a nano-scalpel to cut away sections of the osteoblast cells to probe the attachment beneath the main cell body. Ultimately the more rapid growth of osteoblasts, coupled with a stronger cell-surface interface, could provide cost reduction, shorter rehabilitation, and fewer follow-on surgeries due to implant loosening.

Biomechanics of meniscal horn attachments

Menisci are anchored to the tibia by means of ligament-like structures called meniscal attachments. Failure material properties of bovine meniscal attachments were obtained. There were no significant differences in the structural properties or ultimate stress between the meniscal attachments (p>0.05). Furthermore, Glycosaminoglycan (GAG) fraction and crimping frequency was obtained for each attachment using histology and differential interference contrast (DIC) respectively. Results showed that the anterior attachment’s insertion had the greatest GAG fraction when compared to the posterior attachment’s insertion. Crimp frequency of the collagen fibrils was homogeneous along the length. Moreover, Scanning Electron Microscopy (SEM) technique was used to reveal the morphology of collagen in human meniscal attachments. Its midsubstance was composed of collagen fascicles running parallel to the longitudinal axis, with a few fibrils running obliquely, and others transversely. There were no differences between attachments for crimping angle or length. Since ligamentous-type tissues are comprised mainly of water, the fluid pressure within meniscal horn attachments was measured using a Fiber Optic Microsensor (FOM). Four cadaveric human joints were subjected to 2BW compressive load (ramp) at 0-, 15-, and 30-degrees of flexion for a minute and then the load was hold for 20 minutes (equilibrium). There were significant differences between 0- and 15- (p1– c5) were obtained. Significant differences were found on the straightened collagen fibers coefficient (c5) between MP and LA attachments (p

DESIGN, SYNTHESIS AND APPLICATIONS OF FLUORESCENT AND ELECTROCHEMICAL PROBES

“Seeing is believing” the proverb well suits for fluorescent imaging probes. Since we can selectively and sensitively visualize small biomolecules, organelles such as lysosomes, neutral molecules, metal ions, anions through cellular imaging, fluorescent probes can help shed light on the physiological and pathophysiological path ways. Since these biomolecules are produced in low concentrations in the biochemical pathways, general analytical techniques either fail to detect or are not sensitive enough to differentiate the relative concentrations. During my Ph.D. study, I exploited synthetic organic techniques to design and synthesize fluorescent probes with desirable properties such as high water solubility, high sensitivity and with varying fluorescent quantum yields. I synthesized a highly water soluble BOIDPY-based turn-on fluorescent probe for endogenous nitric oxide. I also synthesized a series of cell membrane permeable near infrared (NIR) pH activatable fluorescent probes for lysosomal pH sensing. Fluorescent dyes are molecular tools for designing fluorescent bio imaging probes. This prompted me to design and synthesize a hybrid fluorescent dye with a functionalizable chlorine atom and tested the chlorine re-activity for fluorescent probe design. Carbohydrate and protein interactions are key for many biological processes, such as viral and bacterial infections, cell recognition and adhesion, and immune response. Among several analytical techniques aimed to study these interactions, electrochemical bio sensing is more efficient due to its low cost, ease of operation, and possibility for miniaturization. During my Ph.D., I synthesized mannose bearing aniline molecule which is successfully tested as electrochemical bio sensor. A Ferrocene-mannose conjugate with an anchoring group is synthesized, which can be used as a potential electrochemical biosensor.