Tensile behaviour of individual fibre bundles in the human lumbar anulus fibrosus.

Disc degeneration is a common medical affliction whose origins are not fully understood. An improved understanding of its underlying mechanisms could lead to the development of more effective treatments. The aim of this paper was to investigate the effect of (1) degeneration, (2) circumferential region and (3) strain rate on the microscale mechanical properties (toe region modulus, linear modulus, extensibility, phase angle) of individual fibre bundles in the anulus fibrosus lamellae of the human intervertebral disc. Healthy and degenerate fibre bundles excised from different circumferential regions in the outer anulus (posterolateral, lateral, anterolateral, anterior) were tensile tested at slow (0.1%/s), medium (1%/s) and fast (10%/s) strain rates using a micromechanical testing system. Our preliminary results showed that neither degeneration nor circumferential region significantly affected the fibre bundles' mechanical behaviour. However, when the fibre bundles were tested at higher strain rates, this resulted in significantly higher linear moduli and lower phase angles. These findings, compared with data from other studies investigating single and multiple lamellae sections, suggest that degeneration has minimal effect on outer anulus mechanics irrespective of structural level, and the inter- and intra-lamellar arrangement and continuity of the fibre bundles may influence the lamellae's regional behaviour and viscoelasticity.

Planar silver nanowire, carbon nanotube and PEDOT:PSS nanocomposite transparent electrodes.

Highly conductive, transparent and flexible planar electrodes were fabricated using interwoven silver nanowires and single-walled carbon nanotubes (AgNW:SWCNT) in a PEDOT:PSS matrix via an epoxy transfer method from a silicon template. The planar electrodes achieved a sheet resistance of 6.6 ± 0.0 Ω/□ and an average transmission of 86% between 400 and 800 nm. A high figure of merit of 367 Ω-1 is reported for the electrodes, which is much higher than that measured for indium tin oxide and reported for other AgNW composites. The AgNW:SWCNT:PEDOT:PSS electrode was used to fabricate low temperature (annealing free) devices demonstrating their potential to function with a range of organic semiconducting polymer:fullerene bulk heterojunction blend systems.

The influence of nanopore dimensions on the electrochemical properties of nanopore arrays studied by impedance spectroscopy.

The understanding of the electrochemical properties of nanopores is the key factor for better understanding their performance and applications for nanopore-based sensing devices. In this study, the influence of pore dimensions of nanoporous alumina (NPA) membranes prepared by an anodization process and their electrochemical properties as a sensing platform using impedance spectroscopy was explored. NPA with four different pore diameters (25 nm, 45 nm and 65 nm) and lengths (5 µm to 20 µm) was used and their electrochemical properties were explored using different concentration of electrolyte solution (NaCl) ranging from 1 to 100 µM. Our results show that the impedance and resistance of nanopores are influenced by the concentration and ion species of electrolytes, while the capacitance is independent of them. It was found that nanopore diameters also have a significant influence on impedance due to changes in the thickness of the double layer inside the pores.

Unraveling the interplay of backbone rigidity and electron rich side-chains on electron transfer in peptides: the realization of tunable molecular wires.

Electrochemical studies are reported on a series of peptides constrained into either a 310-helix (1-6) or ß-strand (7-9) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (1 and 2) and (7 and 8) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides 1, 4 and 5, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides 3-6 confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (1 and 7) and saturated tethered peptides (2 and 8) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on ß-strand models analogous to 7, 8 and 9 provide further insights into the relative roles of backbone rigidity and electron rich side-chains on intramolecular electron transfer. Furthermore, electron population analysis confirms the role of the alkene as a "stepping stone" for electron transfer. These findings provide a new approach for fine-tuning the electronic properties of peptides by controlling backbone rigidity, and through the inclusion of electron rich side-chains. This allows for manipulation of energy barriers and hence conductance in peptides, a crucial step in the design and fabrication of molecular-based electronic devices.

Separation of double-walled carbon nanotubes by size exclusion column chromatography.

In this report we demonstrate the separation of raw carbon nanotube material into fractions of double-walled (DWCNTs) and single-walled carbon nanotubes (SWCNTs). Our method utilizes size exclusion chromatography with Sephacryl gel S-200 and yielded two distinct fractions of single- and double-walled nanotubes with average diameters of 0.93 ± 0.03 and 1.64 ± 0.15 nm, respectively. The presented technique is easily scalable and offers an alternative to traditional density gradient ultracentrifugation methods. CNT fractions were characterized by atomic force microscopy and Raman and absorption spectroscopy as well as transmission electron microscopy.

Surfactant concentration dependent spectral effects of oxygen and depletion interactions in sodium dodecyl sulfate dispersions of carbon nanotubes.

Quenching of optical absorbance spectra for carbon nanotubes (CNTs) dispersed in sodium dodecyl sulfate (SDS) has been observed to be more pronounced at higher concentrations of the surfactant. The protonation-based quenching behavior displays wavelength dependence, affecting larger diameter nanotube species preferentially. Although absorbance may be recovered by hydroxide addition, pH measurements suggest that hydrolysis of SDS does not play a major role in the short term quenching behavior at high SDS concentrations. The degree of quenching is observed to correlate well with an increase in attractive depletion as SDS concentration is increased, while the extent of depletion is found to depend heavily on the concentration of preparation in comparison to the final SDS concentration. Attractive depletion in SDS is also found to be preferential for CNTs of larger diameter. It is proposed that depletion enhances the quenching effect due to close association of CNT-SDS complexes providing higher SDS densities on the CNT surface, leading to further oxidation. In addition, the quenching behavior in SDS is found to strongly suppress the optical and Raman signal from metallic nanotube species even at high pH. Displacement of SDS by sodium deoxycholate as a secondary surfactant is able to reverse the effects of protonation of metallic species, whereas hydroxide addition is only partially effective.

The effect of a macrocyclic constraint on electron transfer in helical peptides: a step towards tunable molecular wires.

Two helical peptides, one constrained by a covalent side-chain staple, exhibit vastly different electronic properties despite adopting essentially the same backbone conformation. High level calculations confirm that these differences are due to the additional backbone rigidity imparted by the macrocyclic constraint.

Impedance nanopore biosensor: influence of pore dimensions on biosensing performance.

Knowledge about electrochemical and electrical properties of nanopore structures and the influence of pore dimensions on these properties is important for the development of nanopore biosensing devices. The aim of this study was to explore the influence of nanopore dimensions (diameter and length) on biosensing performance using non-faradic electrochemical impedance spectroscopy (EIS). Nanoporous alumina membranes (NPAMs) prepared by self-ordered electrochemical anodization of aluminium were used as model nanopore sensing platforms. NPAMs with different pore diameters (25-65 nm) and lengths (4-18 µm) were prepared and the internal pore surface chemistry was modified by covalently attaching streptavidin and biotin. The performance of this antibody nanopore biosensing platform was evaluated using various concentrations of biotin as a model analyte. EIS measurements of pore resistivity and conductivity were carried out for pores with different diameters and lengths. The results showed that smaller pore dimensions of 25 nm and pore lengths up to 10 µm provide better biosensing performance.

Grafting of poly(ethylene glycol) on click chemistry modified Si(100) surfaces.

Poly(ethylene glycol) (PEG) is one of the most extensively studied antifouling coatings due to its ability to reduce protein adsorption and improve biocompatibility. Although the use of PEG for antifouling coatings is well established, the stability and density of PEG layers are often inadequate to provide optimum antifouling properties. To improve on these shortcomings, we employed the stepwise construction of PEG layers onto a silicon surface. Acetylene-terminated alkyl monolayers were attached to nonoxidized crystalline silicon surfaces via a one-step hydrosilylation procedure with 1,8-nonadiyne. The acetylene-terminated surfaces were functionalized via a copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction of the surface-bound alkynes with an azide to produce an amine terminated layer. The amine terminated layer was then further conjugated with PEG to produce an antifouling surface. The antifouling surface properties were investigated by testing adsorption of human serum albumin (HSA) and lysozyme (Lys) onto PEG layers from phosphate buffer solutions. Detailed characterization of protein fouling was carried out with X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) combined with principal component analysis (PCA). The results revealed no fouling of albumin onto PEG coatings whereas the smaller protein lysozyme adsorbed to a very low extent.

Highly conductive interwoven carbon nanotube and silver nanowire transparent electrodes.

Electrodes fabricated using commercially available silver nanowires (AgNWs) and single walled carbon nanotubes (SWCNTs) produced sheet resistances in the range 4-24 Ω â–¡-1 with specular transparencies up to 82 %. Increasing the aqueous dispersibility of SWCNTs decreased the bundle size present in the film resulting in improved SWCNT surface dispersion in the films without compromising transparency or sheet resistance. In addition to providing conduction pathways between the AgNW network, the SWCNTs also provide structural support, creating stable self-supporting films. Entanglement of the AgNWs and SWCNTs was demonstrated to occur in solution prior to deposition by monitoring the transverse plasmon resonance mode of the AgNWs during processing. The interwoven AgNW/SWCNT structures show potential for use in optoelectronic applications as transparent electrodes and as an ITO replacement.

Electron transfer through α-peptides attached to vertically aligned carbon nanotube arrays: a mechanistic transition.

The mechanism of electron transfer in α-aminoisobutyric (Aib) homoligomers is defined by the extent of secondary structure, rather than just chain length. Helical structures (Aib units ≥3) undergo an electron hopping mechanism, while shorter disordered sequences (Aib units <3) undergo an electron superexchange mechanism.

Nanoporous anodic aluminium oxide membranes with layered surface chemistry.

A new and facile method is described to prepare Janus-like nanoporous anodic aluminium oxide (AAO) membranes with distinctly different internal and external surface chemistry.

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays--a step toward light harvesting antenna and multibit information storage.

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.

Micromechanical properties of human trabecular bone: a hierarchical investigation using nanoindentation.

The ability to assess the risk of fracture, evaluate new therapies, predict implant success and assess the influence of bone remodeling disorders requires specific measurement of local bone micromechanical properties. Nanoindentation is an established tool for assessing the micromechanical properties of hard biological tissues. In this study, elastic modulus and hardness were quantified using nanoindentation for human trabecular bone from the intertrochanteric region of the proximal femur. These properties were demonstrated to be heterogeneous and highly correlated at the intraspicule, interspicule, and interspecimen levels. The results of this study have important implications for current understanding of structure-function relationships throughout the trabecular bone structural hierarchy.

Carbon nanotube systems to communicate with enzymes.

The efficient transfer of electrons between enzymes and electrodes is important for understanding the intrinsic redox properties as well as for developing protein-based biosensors and bioelectronic devices. One strategy to achieve efficient electron transfer to proteins is to build up the electrode inside the protein so that it is close to the redox-active center of the protein. To achieve this requires exceedingly small electrodes. Carbon nanotubes, which are as small as 1 nm in diameter, have the potential to be such electrodes. This chapter outlines recent research toward this goal via the self-assembly of vertically aligned single-walled carbon nanotubes on electrode surfaces followed by the subsequent attachment of proteins to the free ends of the tubes.

Fabrication of gold nanorod arrays by templating from porous alumina.

A simple procedure for fabrication of gold films with nanorod arrays is described. The method is based on thermal evaporation of gold onto a porous alumina (PA) membrane used as a template. The gold films were obtained after removing the template and characterized using scanning electron microscopy, atomic force microscopy and ultraviolet-visible spectrophotometry. The prepared gold films are composed of arrays of sharp (<20 nm at apex) rod-shaped gold nanostructures. These structures closely follow the organization and distribution of pores of the PA template. The length of the gold nanostructures is estimated to range from 300 nm to more than 1000 nm. It was found that their length is influenced by the size of the pores in the PA and the temperature of the PA during gold evaporation. Spectrophotometric characterization shows that the prepared gold films exhibit a surface plasmon resonance absorption peak located between 525 and 540 nm.

Protein electrochemistry using aligned carbon nanotube arrays.

The remarkable electrocatalytic properties and small size of carbon nanotubes make them ideal for achieving direct electron transfer to proteins, important in understanding their redox properties and in the development of biosensors. Here, we report shortened SWNTs can be aligned normal to an electrode by self-assembly and act as molecular wires to allow electrical communication between the underlying electrode and redox proteins covalently attached to the ends of the SWNTs, in this case, microperoxidase MP-11. The efficiency of the electron transfer through the SWNTs is demonstrated by electrodes modified with tubes cut to different lengths having the same electron-transfer rate constant.