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Heteroatomic nanotubes consisting of graphitic carbon (g-C) and hexagonal boron nitride (h-BN) were first synthesised over two decades ago, representing the earliest example of a carbon nanotube (CNT) covalently doped with h-BN. This opened up a exiting new field of study into BxCyNz heteronanotubes that exhibit tunable electronic properties based on stoichiometry. Increased research focus on such heteronanotubes has also led to the development of novel configurations of g-C and h-BN in van der Waals type hybrids. In particular, heteronanotubes consisting of a core CNT sheathed with h-BN, coaxial shell layers (CNT@BN), have recently witnessed advances in their synthesis and exploitation. CNT@BNs exhibit superior thermal stability, chemical inertness and mechanical robustness in comparison to CNTs, whilst the h-BN also adds the rare duo of thermal conduction pathways and electrical insulation. The various synthesis methods yield a range of different structure, crystallinity and composition profiles in CNT@BN. Here, we review the current methods of CNT@BN production and characterisation and highlight the prospect for application of these heteronanotubes in high temperature composites, nano-mechanical components, nano-electronics, field emitters and thermal management materials, and propose future avenues of research.

Many bacteria become progressively more resistant to antibiotics and it remains a challenging task to control their overall levels. Polymers combined with active biomolecules come to the forefront for the design of antibacterial materials that can address this encounter. In this work, we investigated the photo-crosslinking approach of UV-sensitive benzophenone molecule (BP) with polyvinylpyrrolidone (PVP) polymer within electrospun fibres. The BP and PVP solutions allowed fabricating polymer mats that were subsequently functionalised with antibacterial lysozyme. The physical properties of the crosslinked electrospun fibres were investigated by scanning electron microscopy and atomic force microscopy. The average diameter of the obtained fibres decreased from 290 ± 50 nm to 270 ± 70 nm upon the addition of the crosslinking molecules and then to 240 ± 80 nm and 180 ± 90 nm after subsequent crosslinking reaction at an increasing time: 3 and 5 h, respectively. The peak force quantitative nanomechanical mapping (PF-QNM) indicated the increase of DMT modulus of obtained cross-linked fibres from 4.1 ± 0.8 GPa to 7.2 ± 0.5 GPa. Furthermore, the successful crosslinking reaction of PVP and BP solution into hydrogels was investigated in terms of examining photo-crosslinking mechanism and was confirmed by rheology, Raman, Fourier transform infrared and nuclear magnetic resonance. Finally, lysozyme was successfully encapsulated within cross-linked PVP-BP hydrogels and these were successfully electrospun into mats which were found to be as effective antibacterial agents as pure lysozyme molecules. The dissolution rate of photo cross-linked PVP mats was observed to increase in comparison to pure PVP electrospun mats which opened a potential route for their use as antibacterial, on-demand, dissolvable coatings for various biomedical applications., Graphical Abstract

This study examines the use of oxidized multi-walled carbon nanotube/iron (O-MWCNT/Fe) nanohybrids modified with polyethylene glycol (PEG) as multifunctional cellular imaging agents for magnetic resonance imaging (MRI) and fluorescence microscopy. The PEGylated MWCNTs with embedded iron particles were investigated as T2-weighted contrast agents for MRI. The number of PEG molecules attached to the MWCNT surface was calculated. The PEG–MWCNT/Fe complex was characterized by transmission electron microscopy, scanning electron microscopy, Fourier transform infrared and Raman spectroscopies. Covalent surface modification of the MWCNTs improves their solubility and enables the attachment of further biomolecules to their surface. The PEGylated nanostructures were labeled with the MDC organic dye and internalized inside HeLa cells for cellular imaging. Additionally, the minimal cytotoxic effect of PEGylated complexes in comparison to non-PEGylated samples was measured using the WST-1 test and an In Cell Analyzer. A confocal microscopy study of the organelle morphology also confirmed that the HeLa cell morphology was unchanged after treatment with PEGylated MWCNTs.

Composite coatings provide a promising way of in vitro cell behavior screening. Previous efforts included fabrication of single-walled carbon nanotubes (SWCNTs)-polymer materials, however in this work, for the first time we combined two polymers of different hydrophobic character: poly(maleic-alt-1-octadecene) and polyvinylpyrrolidone with multi-walled carbon nanotubes (MWCNTs) to produce composite coatings with varied hydrophobicity. Prior to their incorporation, MWCNTs were characterized using Raman spectroscopy during ball-milling procedure at different times to establish ideal fabrication conditions for their best quality. Electrostatic force microscopy was then used to look at the distribution and MWCNTs networks formation in the composite coatings. Atomic force and scanning electron microscopies were used to establish the topographical features and thicknesses of produced coatings, which varied with the content of MWCNTs. All composites as well as control pure polymer coatings proved to be biocompatible and exhibited a viability of >80% on two human cell lines: cancerous osteosarcoma (U2OS) and fibroblast (MSU-1.1) that varied by their tumorigenicity, irrespectively of the hydrophobicity of the coating. Both cell lines were further shown by scanning electron microscopy to remain in the typical morphological state with high proliferation and attachment to all formed composites. These results show the potential of formation of MWCNTs-polymer composites by facile preparation way (spin-coating) and their potential as coatings for 2D in vitro cell culture platforms.

Purpose The study discusses the value of electrospun cilostazol-loaded (CIL) polymer structures for potential vascular implant applications. Methods Biodegradable polycaprolactone (PCL) fibers were produced by electrospinning on a rotating drum collector. Three different concentrations of CIL: 6.25%, 12.50% and 18.75% based on the amount of polymer, were incorporated into the fibers. The fibers were characterized by their size, shape and orientation. Materials characterization was carried out by Fourier Transformed Infrared spectroscopy (FTIR), Raman spectroscopy, differential scanning calorimetry (DSC) and X-ray diffraction (XRD). In vitro drug release study was conducted using flow-through cell apparatus (USP 4). Results Three-dimensional structures characterized by fibers diameter ranging from 0.81 to 2.48 μm were in the range required for cardiovascular application. DSC and XRD confirmed the presence of CIL in the electrospun fibers. FTIR and Raman spectra confirmed CIL polymorphic form. Elastic modulus values for PCL and the CIL-loaded PCL fibers were in the range from 0.6 to 1.1 GPa. The in vitro release studies were conducted and revealed drug dissolution in combination with diffusion and polymer relaxation as mechanisms for CIL release from the polymer matrix. Conclusions The release profile of CIL and nanomechanical properties of all formulations of PCL fibers demonstrate that the cilostazol loaded PCL fibers are an efficient delivery system for vascular implant application. Electronic supplementary material The online version of this article (10.1007/s11095-017-2314-0) contains supplementary material, which is available to authorized users.