In this work the potential of graphene-like particles for mechanical reinforcement is investigated. Different polymer processing methods are studied from traditional ones to more advanced techniques. The potential of graphene as a reinforcement for polymer composites is addressed as a result of polymer modifications and the morphology of the graphene like particles. First, a composites of polycarbonate (PC) and graphite nanoplatelets (GNP) are produced by a traditional melt-mixing method. The GNP composites present a low mechanical reinforcing efficiency which is believed to be due to a poor dispersion of the GNP and a weak interaction between the GNP and the matrix. Secondly, solution cast composites of polyvinyl alcohol (PVA) with very low loadings of graphene oxide (GO) are produced. The polymer morphology undergoes some modifications after the addition of GO. A strong increase of the Tg is observed after the addition of GO which is the result of a reduction in polymer mobility, while a dramatic increase of the mechanical properties is seen as well. Uni-axial drawing is applied in order to align the particles. No polymer modifications are observed between the drawn PVA and the drawn nanocomposites due to the strong alignment of the polymer chains during the drawing. Mechanical reinforcement is observed after addition of the GO showing real reinforcement. Finally, a more advanced processing method is investigated using spraying. The condition of spraying a layer of polymer and GO is studied. Finally a hierarchical composite of PVA - GO is produced by this spraying method. 150 bi-layers are deposited to create a film with improved mechanical properties at a loading of 5.4 wt.% GO. The Young’s modulus and strength of these films doubled or nearly doubled which is believed to be due to the high level of structural organization of the layered nanocomposite incorporating the 2D GO nanofiller, together with hydrogen bonding between the PVA and the GO sheets.

Graphene Nanoplatelets (GNP) was incorporated into polyamide 6 (PA6) matrix by melt compounding method and the enhancements in the properties of the nanocomposites were studied. Response Surface Methodology (RSM) was employed to assist in the study of processing conditions in melt compounding. RSM analysis revealed that the GNP concentrations to be the most significant term to affect the tensile modulus and crystallinity followed by the screw speed whereas the residence time was found to be non-significant. GNP with 5 Î1⁄4m (G5) and 25 Î1⁄4m (G25) were used in the GNP aspect ratio study. The average flake size of G5 and G25 to was measured to be 5.07 Î1⁄4m and 22.0 Î1⁄4m, respectively with the G5 distributed narrowly whereas the G25 exhibit broad distribution. TGA analysis shown that HT25 is more thermally stable compared to G25 due to some remnants lost during thermal treatment and this was confirmed by EDX and CHNS analysis. XRD profiles of the PA6-G-NC illustrate typical peaks of PA6 crystals phase as well as pure graphite characteristic peak. PA6-G25-NC observed to exhibit slightly higher peak intensity compared to PA6-G5-NC suggesting more formation of PA6 crystals. Similar improvement was observed on PA6-HT25-NC compared to PA6-G25-NC indicating more formation of PA6 crystals due improved dispersion of HT25. DSC on PA6-G25-NC showed higher cooling temperature and crystallinity compared to PA6-G5-NC due to larger surface area of the G25. Similarly, PA6-HT25 showed better improvement in crystallinity over PA6-G25-NC due to increase nucleation sites by the HT25. The thermal conductivity of PA6-G25-NC is slightly higher than the thermal conductivity of PA6-G5-NC but not significant considering the G25 is 5 times larger than G5. Instead, no significant difference was observed between PA6-HT25-NC and PA6-G25-NC. Addition of GNP increased the thermal stability of the PA6-G-NC systems under both nitrogen and air atmospheres regardless of the GNP aspect ratio. The viscoelastic properties showed insignificant difference between PA6-G5-NC and PA6-G25-NC. The inefficient improvement by G25 might be due to agglomeration formed during processing. The storage modulus and tan Î ́ of PA6-HT25-NC decreased but the Tg significantly improved compared to PA6-G25-NC. This was assumed to be because of improved dispersion of HT25 but reduced interfacial interaction after the heat treatment. The shear storage modulus, G’ and complex viscosity, |η*| were observed to increase with increasing GNP content with more pronounced improvement seen on PA6-G25-NC compared to PA6-G5-NC. However, no network percolation threshold was observed until 20 wt.% of GNP. The poor interfacial interaction of HT25 resulted in lower G’ and |η*| compared to G25. Tensile test results showed typical improvement with PA6-G25-NC having higher tensile modulus compared to PA6-G5-NC. Further enhancement was obtained with PA6-HT25-NC suggesting improved dispersion and volume of constrained chains mobility despite the poor surface interaction. Comparison with Halphin-Tsai modulus revealed that the effective modulus to be 150 GPa for G5 and 200 GPa for G25. The water uptake measurement results showed that GNP reduced the water uptake percentage and diffusion coefficient especially with G25. The test conducted on saturated PA6-G-NC results in improved thermal conductivity due to the high thermal conductivity of water but the viscoelastic and tensile properties severely reduced due to plasticisation effect.

L’environnement réactif du plasma constitue un outil puissant dans la science des matériaux, permettant la création de matériaux innovatifs et l'amélioration de matériaux existants qui ne serait autrement pas possible.Le plasma fournit simultanément des fluxes de particules chargées, des molécules chimiquement actives, des radicaux, de la chaleur, des photons, qui peuvent fortement influencer les voies d'assemblage à différentes échelles temporelles et spatiales, y compris à l’échelle atomique.Dans cette thèse de doctorat, des méthodes tenant pour base des plasmas micro-ondes ont été utilisées pour la synthèse de nanomatériaux de carbone, y compris graphène, graphène dopé à l'azote (N-graphène) et structures de type diamant.À cette fin, ce travail est lié à optimisation de la synthèse de nanostructures 2D du carbone, comme graphène et N-graphène par la poursuite de l'élaboration et du raffinement de la méthode développée en Plasma Engineering Laboratory (PEL). La synthèse de graphène de haute qualité et en grandes quantités a été accomplie avec succès en utilisant des plasmas d'Ar-éthanol à ondes de surface dans des conditions de pression ambiante. De plus, le N-graphène a été synthétisé par un procédé en une seule étape, de l'azote a été ajouté au mélange d’Ar-éthanol, et par un procédé en deux étapes, en soumettant des feuilles de graphène préalablement synthétisées ont été exposées à un traitement plasma argon-azote à basse pression. Les atomes d'azote ont été incorporés avec succès dans le réseau de graphène hexagonal, formant principalement liaisons pyrroliques, pyridiniques et quaternaires. Un niveau de dopage de 25 at.% a été atteint.Différents types de nanostructures de carbone, y compris du graphène et des structures de type diamant, ont été synthétisées au moyen d'un plasma d’argon en utilisant du méthane et du dioxyde de carbone comme précurseurs du carbone.De plus, des plasmas à couplage capacitif ont également été utilisés pour la fonctionnalisation du graphène et pour la synthèse de nanocomposites, tels que les composites de Polyaniline (PANI)-graphène. Les utilisations potentielles de ces matériaux ont été étudiées et les deux structures ont démontré avoir des attributs remarquables pour leur application aux biocapteurs. / Plasma environments constitute powerful tools in materials science by allowing the creation of innovative materials and the enhancement of long existing materials that would not otherwise be achievable. The remarkable plasma potential derives from its ability to simultaneously provide dense fluxes of charged particles, chemically active molecules, radicals, heat and photons which may strongly influence the assembly pathways across different temporal and space scales, including the atomic one.In this thesis, microwave plasma-based methods have been applied to the synthesis of advanced carbon nanomaterials including graphene, nitrogen-doped graphene (N-graphene) and diamond-like structures. To this end, the focus was placed on the optimization of the production processes of two-dimensional (2D) carbon nanostructures, such as graphene and N-graphene, by further elaboration and refinement of the microwave plasma-based method developed at the Plasma Engineering Laboratory (PEL). The scaling up of the synthesis process for high-quality graphene using surface-wave plasmas operating at atmospheric pressure and argon-ethanol mixtures was successfully achieved. Moreover, N-graphene was synthetized via a single-step process, by adding nitrogen to the argon-ethanol mixture, and via two-step process, by submitting previously synthetized graphene to the remote region of a low-pressure argon-nitrogen plasma. Nitrogen atoms were usefully incorporated into the hexagonal graphene lattice, mainly as pyrrolic, pyridinic and quaternary bonds. A doping level of 25% was attained.Different types of carbon nanostructures, including graphene and diamond-like nanostructures, were also produced by using methane and carbon dioxide as carbon precursors in an argon plasma.Additionally, capacitively-coupled radio-frequency plasmas have been employed in the functionalization of graphene and in the synthesis of Polyaniline (PANI)-graphene composites. The potential uses of these materials were studied, with both showing favourable characteristics for their applicability in biosensing applications.

The growing incidences of orthopedic problems globally have created a huge demand for strong bioactive materials for bone tissue engineering. Over the years, studies have shown chemical, physical, and mechanical properties of biomaterials influence the cellular interactions at the material-tissue interface, which subsequently controls biological response to materials. Strong biomaterials with surface properties that actively direct cellular response hold the key for engineering the next generation orthopedic implants. With its unique properties graphene can be used to reinforce poly (ε-caprolactone) (PCL) to prepare strong and bioactive polymer nanocomposites for bone tissue regeneration. The thesis entitled ―Engineering bioactive and multifunctional graphene polymer composites for bone tissue regeneration” systematically studies the effect of different chemically functionalized and metal-graphene hybrid nanoparticles in PCL composites for bone tissue engineering. The thesis comprises of seven chapters. Chapter 1 is an outline review on the impact of graphene and graphene derived particles to prepare supporting substrates for tissue regeneration and the associated cell response to multifunctional graphene substrate. This chapter discusses how cells interact with different graphene based particles and the interplay between cells performance and multifunctional properties of graphene based substrates. Chapter 2 describes the role, if any, of the functionalization of graphene on mechanical properties, stem cell response and bacterial biofilm formation. PCL composites of graphene oxide (GO), reduced GO (RGO) and amine-functionalized GO (AGO) were prepared at different filler contents (1%, 3% and 5%). Although the addition of the nanoparticles to PCL markedly increased the storage modulus, this increase was higher for GO and AGO than with RGO. In vitro cell studies revealed that the AGO and GO particles significantly increased human mesenchymal stem cell (hMSC) proliferation. AGO was most effective in augmenting stem cell osteogenesis leading to mineralization. Bacterial studies revealed that interaction with functionalized GO induced bacterial cell death due to membrane damage which was further accentuated by amine groups in AGO. The synergistic effect of oxygen containing functional groups and amine groups on AGO-reinforced composites renders the optimal combination of improved modulus, favorable stem cell response and biofilm inhibition desired for orthopaedic applications. In Chapter 3, toward preparing strong multi-biofunctional materials, poly(ethylenimine) (PEI) conjugated graphene oxide (GO_PEI) was synthesized using poly(acrylic acid) (PAA) as spacer and incorporated in PCL at different fractions. GO_PEI significantly promoted proliferation and formation of focal adhesions in hMSCs on PCL. GO_PEI was highly potent in inducing stem cell osteogenesis leading to 90% increase in alkaline phosphatase activity and mineralization over neat PCL with 5% filler content and was 50% better than GO. Remarkably, 5% GO_PEI was as potent as soluble osteo-inductive factors. Increased adsorption of osteogenic factors due to the amine and oxygen containing functional groups on GO_PEI augment stem cell differentiation. GO_PEI was also highly efficient in imparting bactericidal activity with 85% reduction in counts of E. coli colonies compared to neat PCL at 5% filler content and was more than twice as efficient as GO. This may be attributed to the synergistic effect of the sharp edges of the particles along with the presence of the different chemical moieties. Thus, in contrast to using labile biomolecules, GO_PEI based polymer composites can be utilized to prepare bioactive resorbable biomaterials for fabricating orthopedic devices for fracture fixation and tissue engineering. Chapter 4 describes the preparation of hybrid nanoparticles of graphene sheets decorated with strontium metallic nanoparticles and its advantages in bone tissue engineering. Strontium-decorated reduced graphene oxide (RGO_Sr) nanoparticles were synthesized by facile reduction of graphene oxide and strontium nitrate. X-ray diffraction, transmission electron microscopy, and atomic force microscopy revealed that the hybrid particles were composed of RGO sheets decorated with 200 – 300 nm metallic strontium particles. Thermal gravimetric analysis further confirmed the composition of the hybrid particles as 22 wt% of strontium. Macroporous tissue scaffolds were prepared incorporating RGO_Sr particles in PCL. The PCL/RGO_Sr scaffolds were found to elute strontium ions in aqueous medium. Osteoblast proliferation and differentiation was significantly higher in the PCL scaffolds containing the RGO_Sr particles in contrast to neat PCL and PCL/RGO scaffolds. The increased biological activity can be attributed to the release of strontium ions from the hybrid nanoparticles. This study demonstrates that composites prepared using hybrid nanoparticles that elute strontium ions can be used to prepare scaffolds with osteoinductive property. These findings have important implications for designing the next generation of biomaterials for use in tissue regeneration. Chapter 5 discusses the use of hybrid graphene-silver particles (RGO_Ag) to reinforce PCL and compared with PCL/RGO and PCL/Ag composites containing RGO and silver nanoparticles (AgNPs), respectively. RGO_Ag hybrid particles were well dispersed in the PCL matrix unlike the RGO and AgNPs due to enhanced exfoliation. RGO_Ag led to 77 % increase in the modulus of PCL and provided a conductive network for electron transfer. Electrical conductivity increased four orders of magnitude from 10-11 S/cm to 10-7 S/cm at 5 wt % filler that greatly exceeded the improvements with the use of RGO and AgNP in PCL. RGO_Ag particles reinforced in PCL showed sustained release of silver ions from the PCL matrix unlike the burst release from PCL/Ag. PCL/RGO_Ag and PCL/RGO composites were non-toxic to hMSCs and supported osteogenic differentiation unlike the PCL/Ag composites which were highly toxic at ≥3% filler content. The PCL/RGO_Ag composites exhibited good antibacterial effect due to a combination of silver ion release from the AgNPs and the mechanical rupture induced by the RGO in the hybrid nanoparticles. Thus, the synergistic effect of Ag and RGO in the PCL matrix uniquely yielded a multifunctional material for use in implantable biomedical devices and tissue engineering. Chapter 6 presents investigation of potential differences in the biological response to graphene in polymer composites in the form of 2D substrates and 3D scaffolds. Results showed that osteoblast response to graphene in polymer nanocomposites is markedly altered between 2D substrates and 3D scaffold due to the roughness induced by the sharp edges of graphene at the surface in 3D but not in 2D. Osteoblast organized into aggregates in 3D scaffolds in contrast to more well spread and randomly distributed cells on 2D discs due to the macro-porous architecture of the scaffolds. Increased cell-cell contact and altered cellular morphology led to significantly higher mineralization in 3D scaffolds compared to 2D. This study demonstrates that the cellular response to nanoparticles in composites can change markedly by varying the processing route. Chapter 7 summarizes the important results and future directions of the work. This chapter provides general conclusions arising from this study, and makes suggestions for future work designed to provide a greater understanding of the in vivo response in terms of bio-distribution of the released functionalized graphene from the scaffold or substrate must be assessed with special attention on their accumulation or excretion.

The biggest hurdle in success of gene and drug therapy is designing and preparation of suitable bio-nanomaterials to carry the desired nucleic acid and drug to the targeted site. The work described in the present thesis encompasses two different approaches for the delivery of bioactive oligo/polynucleotides and drugs in vitro and in vivo using either cationic lipids or their nanocomposites with different carbon nanomaterials. The idea of using carriers for oligo/polynucleotides and drugs came into existence because of numerous physiological barriers in pathway of delivery of naked oligo/polynucleotides or drugs which reduces the overall activity of these bioactives in biological systems. These barriers trigger scientific research toward the preparation of appropriate biomaterials which can overcome the physiological barriers and improve the activity of bioactive oligo/polynucleotides and drugs in cellular systems. Toward this end, the design and synthesis of different cationic lipids and carbon nanomaterials were undertaken as described in seven chapters of the thesis. A series of novel cationic lipids with structural variability was prepared and used for gene delivery in vitro. They were further tuned chemically to sustain delivery efficiency in high serum percentage during in vitro transfection. These serum compatible lipids were used to perform transfection of reporter gene plasmid and found to be more efficient compared to the some well known commercial products for the same purpose. Another series of novel lipids were synthesized for the targeted gene delivery in vitro. These tryptophan based cholesteryl lipids were used to prepare mixed liposomes. These mixed liposomes were highly efficient in targeting sigma receptor rich HEK293T over sigma receptor negative HeLa cells. Mixed liposomes were also prepared for selective targeting of αvβ3 and αvβ5 integrins in gene transfection protocol using a palmitoyl-RAFT-RGD4 template. A mixed liposomal formulation was developed to carry out anti-sense siRNA mediated knockdown of Smad-2 protein with better efficiency compared to some of the best known commercial products for the same purpose. These mixed liposomes were also highly efficient for regression via induction of p53 mediated apoptosis in xenograft tumors developed in nude mice. Carbon nanomaterials have been extensively explored as nanoscale gene/drug carriers for potential applications. But the challenge is to solubilize these highly hydrophobic materials in aqueous medium for use in biological systems. Although there are reports for covalent modifications of such nanomaterials but it could be done only with the loss of some beneficial features of these materials. Herein a non-covalent technique has been efficiently used to suspend single walled carbon nanotubes in water using biocompatible cationic lipids. These nanosuspensions were used to complex plasmid DNA and transfect them in vitro. They proved to be highly serum compatible DNA carriers which did not drop the efficiency even in very high percentage of serum. Similarly exfoliated graphene was modified with cationic lipid and serum components to improve IC50 of Tamoxifen citrate and Methotrexate to a considerable extent in vitro. The improved Methotrexate formulations were highly efficient for regression in size of xenograft tumors developed in nude mice. Thus, the present thesis entails generation of cationic lipids and carbon nanomaterials based nanocomposites which were not only highly biocompatible themselves but their efficiency was found many fold better compare to some of the best commercial delivery agents. These were useful for the delivery of various bioactive oligo/polynucleotides and drugs in vitro and in vivo.