Cell entry of one-dimensional nanomaterials occurs by tip recognition and rotation

Materials with high aspect ratio, such as carbon nanotubes and asbestos fibres, have been shown to cause length-dependent toxicity in certain cells because these long materials prevent complete ingestion and this frustrates the cell. Biophysical models have been proposed to explain how spheres and elliptical nanostructures enter cells, but one-dimensional nanomaterials have not been examined. Here, we show experimentally and theoretically that cylindrical one-dimensional nanomaterials such as carbon nanotubes enter cells through the tip first. For nanotubes with end caps or carbon shells at their tips, uptake involves tip recognition through receptor binding, rotation that is driven by asymmetric elastic strain at the tube-bilayer interface, and near-vertical entry. The precise angle of entry is governed by the relative timescales for tube rotation and receptor diffusion. Nanotubes without caps or shells on their tips show a different mode of membrane interaction, posing an interesting question as to whether modifying the tips of tubes may help avoid frustrated uptake by cells.     

Bythotrephes longimanus in shallow,nearshore waters: Interactions with Leptodora kindtii, impacts on zooplankton,and implications for secondary dispersal from southern Green Bay,Lake Michigan

The spiny water flea Bythotrephes longimanus is a predatory cladoceran that invaded Green Bay, Lake Michigan by 1988 and has been shown to negatively affect zooplankton prey. Bythotrephes is thought to occur where a deep-water daytime refuge from fish predation is available. Information from shallow, nearshore environments is relatively sparse, yet risk of secondary dispersal from these areas to inland waters is high. The production of desiccation-tolerant resting eggs, coupled with recreational boating activities, can facilitate spread inland. We determined Bythotrephes population demographics and dynamics at two sites in southern Green Bay during 2015 and 2016 to examine interactions with zooplankton and timing of resting egg production. Estimates of prey consumption rates by Bythotrephes were compared to those for a native predatory zooplankter, Leptodora kindtii, and against productivity estimates for potential crustacean prey. Bythotrephes population dynamics were similar at both sites in each year, with biomass peaks in September 2015 and July 2016. Earliest resting egg production occurred by 8 July 2015 and 17 June 2016; resting eggs occurred until at least October each year, when sampling ceased. Consumption by Bythotrephes generally exceeded that by Leptodora. Zooplankton productivity rates were lower than consumption rates on all dates in 2015 but approximated or exceeded consumption rates in 2016. Bythotrephes has become a major predator in the Green Bay lower food web, changing energy transfer through this major Great Lakes ecosystem. Its success has increased potential dispersal to inland lakes, especially from shallow, nearshore habitats such as occur in southern Green Bay.     

Nonlinear absorption of laser light in Bi12GeO20 single crystals

Two-photon absorption (TPA) at 532 nm was investigated in BGO (Bi₁₂GeO₂₀) single crystals using a 16 ps pulse width Nd: YAG laser. The TPA coefficient was measured to be 2.2–2.6 cm/GW for undoped BGO. This suggests that nonlinear absorption plays a significant role in the carrier generation processes induced by short laser pulses. The TPA coefficient for heavily Al-doped BGO is only slightly smaller (1.9–2.3 cm/GW) than that of the undoped BGO. This result has specific importance since linear absorption in the visible wavelength region is strongly suppressed by Al doping.     

Antioxidant deactivation on graphenic nanocarbon surfaces

This article reports a direct chemical pathway for antioxidant deactivation on the surfaces of carbon nanomaterials. In the absence of cells, carbon nanotubes are shown to deplete the key physiological antioxidant glutathione (GSH) in a reaction involving dissolved dioxygen that yields the oxidized dimer, GSSG, as the primary product. In both chemical and electrochemical experiments, oxygen is only consumed at a significant steady-state rate in the presence of both nanotubes and GSH. GSH deactivation occurs for single- and multi-walled nanotubes, graphene oxide, nanohorns, and carbon black at varying rates that are characteristic of the material. The GSH depletion rates can be partially unified by surface area normalization, are accelerated by nitrogen doping, and suppressed by defect annealing or addition of proteins or surfactants. It is proposed that dioxygen reacts with active sites on graphenic carbon surfaces to produce surface-bound oxygen intermediates that react heterogeneously with glutathione to restore the carbon surface and complete a catalytic cycle. The direct catalytic reaction between nanomaterial surfaces and antioxidants may contribute to oxidative stress pathways in nanotoxicity, and the dependence on surface area and structural defects suggest strategies for safe material design.     

Ferulic acid‐loaded collagen hydrolysate and polycaprolactone nanofibres for tissue engineering applications

There is a great need for the progress of composite biomaterials, which are effective for tissue engineering applications. In this work, the development of composite electrospun nanofibres based on polycaprolactone (PCL) and collagen hydrolysate (CH) loaded with ferulic acid (FA) for the treatment of chronic wounds. Response Surface Methodology (RSM) has been applied to nanofibres factor manufacturing assisted by electrospinning. For wound healing applications, the authors have created the efficacy of CH, and PCL membranes can act as a stable, protective cover for wound, enabling continuous FA release. The findings of the RSM showed a reasonably good fit with a polynomial equation of the second order which was statistically acceptable at P  < 0.05. The optimised parameters include the quantity of hydrolysate collagen, the voltage applied and the distance from tip‐to‐collector. Based on the Box–Behnken design, the RSM was used to create a mathematical model and optimise nanofibres with minimum diameter production conditions. Using FTIR, TGA and SEM, optimised nanofibres were defined. In vitro, cytocompatibility trials showed that there was an important cytocompatibility of the optimised nanofibres, which was proved by cell proliferation and cell morphology. In this research, the mixed nanofibres of PCL and CH with ferulic could be a potential biomaterial for wound healing.Inspec keywords: tissue engineering, polymer fibres, wounds, electrospinning, nanofibres, response surface methodology, cellular biophysics, proteins, molecular biophysics, scanning electron microscopy, biomedical materials, nanomedicine, nanocomposites, nanofabrication, Fourier transform infrared spectraOther keywords: wound healing applications, PCL membranes, stable cover, protective cover, continuous FA release, RSM, optimised parameters, hydrolysate collagen, mathematical model, optimised nanofibres, polycaprolactone nanofibres, tissue engineering applications, composite biomaterials, composite electrospun nanofibres, collagen hydrolysate, ferulic acid, chronic wounds, Response Surface Methodology, nanofibres factor     

Theoretical analysis of a carbon-carbon dimer placement tool for diamond mechanosynthesis

Density functional theory is used with Gaussian 98 to analyze a new family of proposed mechanosynthetic tools that could be employed for the placement of two carbon atoms--a carbon-carbon (CC) dimer--on a growing diamond surface at a specific site. The analysis focuses on specific group IV-substituted biadamantane tool tip structures and evaluates their stability and the strength of the bond they make with the CC dimer. These tools should be stable in a vacuum and should be able to hold and position a CC dimer in a manner suitable for positionally controlled diamond mechanosynthesis at room temperature.