Anup Kumar Keshri

Boron nitride nanotube reinforced polylactide-polycaprolactone copolymer composite: mechanical properties and cytocompatibility with osteoblasts and macrophages in vitro.

Biodegradable polylactide-polycaprolactone copolymer (PLC) has been reinforced with 0, 2 and 5wt.% boron nitride nanotubes (BNNTs) for orthopedic scaffold application. Elastic modulus of the PLC-5wt.% BNNT composite, evaluated through nanoindentation technique, shows a 1370% increase. The same amount of BNNT addition to PLC enhances the tensile strength by 109%, without any adverse effect on the ductility up to 240% elongation. Interactions of the osteoblasts and macrophages with bare BNNTs prove them to be non-cytotoxic. PLC-BNNT composites displayed increased osteoblast cell viability as compared to the PLC matrix. The addition of BNNTs also resulted in an increase in the expression levels of the Runx2 gene, the main regulator of osteoblast differentiation. These results indicate that BNNT is a potential reinforcement for composites for orthopedic applications.

Carbon Nanotube Reinforced Polylactide−Caprolactone Copolymer: Mechanical Strengthening and Interaction with Human Osteoblasts in Vitro

This study proposes the use of carbon nanotubes (CNTs) as reinforcement to enhance the mechanical properties of a polylactide-caprolactone copolymer (PLC) matrix. Biological interaction of PLC-CNT composites with human osteoblast cells is also investigated. Addition of 2 wt % CNT shows very uniform dispersion in the copolymer matrix, whereas 5 wt % CNT shows severe agglomeration and high porosity. PLC-2 wt % CNT composite shows an improvement in the mechanical properties with an increase in the elastic modulus by 100% and tensile strength by 160%, without any adverse effect on the ductility up to 240% elongation. An in vitro biocompatibility study on the composites shows an increase in the viability of human osteoblast cells compared to the PLC matrix, which is attributed to the combined effect of CNT content and surface roughness of the composite films.

Wear behavior and in vitro cytotoxicity of wear debris generated from hydroxyapatite-carbon nanotube composite coating.

This work evaluates the effect of carbon nanotube (CNT) addition to plasma-sprayed hydroxyapatite (HA) coating on its tribological behavior, biocompatibility of the coating, and cytotoxicity of CNT-containing wear debris. Biological response of the CNT-containing wear debris is critical for osteoblasts, the bone-forming cells, and macrophages, the cells that clear up wear debris from blood stream. The addition of 4 wt % CNTs to HA coating reduces the volume of wear debris generation by 80% because of the improved elastic modulus and fracture toughness. CNT reinforcement has a pronounced effect on the particle size in the wear debris and subsequent biological response. There was a slight increase in the numbers and viability of osteoblasts grown on HA-CNT compared with HA alone. The cytotoxic effect of HA and HA-CNT debris to macrophages and osteoblasts was similar, demonstrating that loose CNT does not pose a problem to these cells.

Multi-scale hierarchy of Chelydra serpentina: microstructure and mechanical properties of turtle shell.

Carapace, the protective shell of a freshwater snapping turtle, Chelydra serpentina, shields them from ferocious attacks of their predators while maintaining light-weight and agility for a swim. The microstructure and mechanical properties of the turtle shell are very appealing to materials scientists and engineers for bio-mimicking, to obtain a multi-functional surface. In this study, we have elucidated the complex microstructure of a dry Chelydra serpentinas shell which is very similar to a multi-layered composite structure. The microstructure of a turtle shells carapace elicits a sandwich structure of waxy top surface with a harder sub-surface layer serving as a shielding structure, followed by a lamellar carbonaceous layer serving as shock absorber, and the inner porous matrix serves as a load-bearing scaffold while acting as reservoir of retaining water and nutrients. The mechanical properties (elastic modulus and hardness) of various layers obtained via nanoindentation corroborate well with the functionality of each layer. Elastic modulus ranged between 0.47 and 22.15 GPa whereas hardness varied between 53.7 and 522.2 MPa depending on the microstructure of the carapace layer. Consequently, the modulus of each layer was represented into object oriented finite element (OOF2) modeling towards extracting the overall effective modulus of elasticity (~4.75 GPa) of a turtles carapace. Stress distribution of complex layered structure was elicited with an applied strain of 1% in order to understand the load sharing of various composite layers in the turtles carapace.

Apatite formability of boron nitride nanotubes

This study investigates the ability of boron nitride nanotubes (BNNTs) to induce apatite formation in a simulated body fluid environment for a period of 7, 14 and 28 days. BNNTs, when soaked in the simulated body fluid, are found to induce hydroxyapatite (HA) precipitation on their surface. The precipitation process has an initial incubation period of ∼ 4.6 days. The amount of HA precipitate increases gradually with the soaking time. High resolution TEM results indicated a hexagonal crystal structure of HA needles. No specific crystallographic orientation relationship is observed between BNNT and HA, which is due to the presence of a thin amorphous HA layer on the BNNT surface that disturbs a definite orientation relationship.

Substrate Rotation Chemical Bath Deposition of Cadmium Sulfide Buffer Layers for Thin Film Solar Cell Application

A method for deposition of cadmium sulfide (CdS) buffer layer thin films on fluorine-doped tin oxide (FTO) glass, by chemical bath deposition (CBD), has been modified. For achieving relatively uniform and pin-hole-free CdS films, substrate rotation, concentration of CdS salts, and deposition time were optimized. The deposited films were characterized by UV-Vis-NIR spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and atomic force microscopy (AFM). Band gap of ~2.4 eV was measured by UV-Vis-NIR spectroscopy, CdS phase was confirmed by XRD, and film uniformity and roughness (~15–20 nm) were measured by SEM and AFM, respectively.

Microwave synthesis of copper indium gallium (di)selenide nanopowders for thin film solar applications

This work reports on the synthesis of nanopowder and nanoink of Copper-Indium-Gallium-(di)Selenide (CIGS) (CuIn0.7Ga0.3Se2) of 20–80 nm with a band gap of 1.1 eV by a facile microwave technique. For CIGS synthesis, precursor mixtures consisting of metal acetylacetonates and selenium powder in oleylamine were heated in a microwave at 180–210 °C for 20–60 min. The resultant nanopowder was characterized and optimized for particle size by dynamic light scattering, phase by X-ray diffraction, morphology, and elemental distribution by scanning electron microscopy and band-gap by UV-Vis-near-infrared spectroscopy. CIGS ink, suitable for spin coating and ink-jet printing, was prepared and thin film was deposited and characterized.

Enhanced Tribological and Bacterial Resistance of Carbon Nanotube with Ceria- and Silver-Incorporated Hydroxyapatite Biocoating

Pertaining to real-life applications (by scaling up) of hydroxyapatite (HA)-based materials, herein is a study illustrating the role of carbon nanotube (CNT) reinforcement with ceria (CeO2) and silver (Ag) in HA on titanium alloy (TiAl6V4) substrate, utilizing the plasma-spraying processing technique, is presented. When compared with pure HA coating enhanced hardness (from 2.5 to 5.8 GPa), elastic modulus (from 110 to 171 GPa), and fracture toughness (from 0.7 to 2.2 MPa·m1/2) elicited a reduced wear rate from 55.3 × 10−5 mm3·N−1·m−1 to 2.1 × 10−5 mm3·N−1·m−1 in HA-CNT-CeO2-Ag. Besides, an order of magnitude lower Archard’s wear constant and a 41% decreased shear stress by for HA-CNT-CeO2-Ag coating depicted the effect of higher hardness and modulus of a material to control its wear phenomenon. Antibacterial property of 46% (bactericidal) is ascribed to Ag in addition to CNT-CeO2 in HA. Nonetheless, the composite coating also portrayed exaggerated L929 fibroblast cell growth (4.8 times more than HA), which was visualized as flat and elongated cells with multiple filopodial protrusions. Hence, synthesis of a material with enhanced mechanical integrity resulting in tribological resistance and cytocompatible efficacy was achieved, thereupon making HA-CNT-CeO2-Ag a scalable potent material for real-life load-bearing implantable bio-coating.

Strontium mediated modification of structure and ionic conductivity in samarium doped ceria/sodium carbonate nanocomposites as electrolytes for LTSOFC

The structural changes on the addition of strontium in samarium doped ceria/Na2CO3 nanocomposites were investigated with respect to sintering temperature. The nanocomposites prepared by a co-precipitation method in the presence (SrSDS) and absence (SDS) of strontium were sintered at 500, 600 and 700 °C. XRD results indicated an increase in crystallite size and lattice parameter with respect to sintering temperature in the presence of strontium. Raman, SEM and FT-IR studies confirmed the presence of Na2CO3 and CeO2 phases. The observed changes in crystallinity and oxygen vacancy concentrations indicate the beneficial role of strontium upon sintering up to 600 °C. The impedance spectral analysis clearly shows the beneficial effect of adding strontium to the composite. The lowest activation energy (0.61 eV) with the highest conductivity (3.8 × 10−3 S cm−1) for SrSDS sintered at 600 °C arises due to the strong interaction between the Na2CO3 and CeO2 phase. However, sintering the composites at 700 °C indicated a negligible effect of strontium due to the decomposition of Na2CO3, thereby limiting the operational temperature of the nanocomposites for potential fuel cell applications.

Coatings for Energy Applications

This chapter aims at providing an understanding about the potential applications of various types of coatings in energy sector. As the energy demands are growing day by day, there is need of enhancing the efficiency of energy systems, which can be enhanced using the advanced coatings. This chapter summarizes about the application of thin films and thick coatings of conventional/nanomaterials in both renewable and non-renewable energy sectors. A comparison between the efficiencies of systems with and without coatings has also been addressed. The importance and challenges associated with adding nanomaterials like carbon nanotubes (CNT), graphene, and various nanostructures with conventional coating material have also been discussed. This chapter can lead to better fundamental understanding about the coatings, which ensures new designs, high efficiency, and large application of coatings in energy sector.