Electrospinning is an inexpensive and simple method of producing non-woven fiber mats. Electrostatic forces are employed to produce the mats, which intrinsically have larger specific surface to volume ratio and smaller pores than traditional fibers. Fibrous mats are typically used in a wide variety of industries such as filter media, tissue engineering, and sensors. Chitosan, the N-deacetylated derivative of chitin, is environmentally friendly, non-toxic, biodegradable, and anti-bacterial. However, due to chitosan’s solubility in aqueous acids, it is electrospun using trifluoroacetic acid (TFA). Modified chitosans, such as carboxymethylchitosan, are currently under investigation as a means of creating designed nanofibrous mats with specific chemistries. However, typically an entirely new set of electrospinning conditions has to be developed for each novel chemistry due to differences in solubility and viscosity. In the present study, we have electrospun chitosan mats and post-processed the fibers. Two different post-processing conditions were employed. One post-production procedure, featuring vapor-phase glutaraldehyde, effectively crosslinks the fiber mats utilizing a Schiff base imine functionality. In another post-processing procedure, the as-spun mats are solution-phase post-processed by chemically functionalizing the mats with cyano, carboxylic acids and thiol groups. While both methods maintained fiber shape and characteristics, there is a definite increase in fiber diameters due to processing. FTIR, NMR, SEM and tensile testing have been performed on the pre- or post-processed fiber mats. Investigations into the percent modification are currently underway.

A recent approach in disease diagnosis and viral epidemics is aimed at point-of-care tests that could be administered near the patient rather than time-consuming processes involving centralized laboratories. Point-of-care devices provide rapid results in simple and low-cost manner requiring only small sample volumes. These devices will strongly benefit from advanced materials and fabrication methods to improve their efficiency and sensitivity. We report a functionalized carbon nanotube label for an immunosensor application. Carbon nanotube label was prepared by modifying the carbon nanotube surface to anchor biomolecules. First, the carboxylic acid treated multi-walled carbon nanotubes (MWCNTs) were uniformly dispersed with polyvinylpyrrolidone (PVP) by sonication in aqueous solution. PVP partially wraps around the carbon nanotubes and exposes the surface of the nanotubes for further functionalization. The MWCNTs were then conjugated with human immunoglobulin G (IgG) using EDC/Sulfo-NHS coupling chemistry, where the antibodies occupied sites not covered by PVP. The dispersion, surfactant modification, and antibody conjugation of the MWCNTs were also confirmed using SEM and TEM images. The successful functionalization of the MWCNTs and reactivity of the covalent attached antibodies were demonstrated for specific antigen binding on the microelectrode device. The carbon nanotube-based detection mechanism could be tailored for screening various analyte specific molecules. Furthermore, the reported technique could easily be integrated in various microfluidic and lab-on-a-chip devices for the development of functional electronic sensors providing quantitative, sensitive, and low-cost detection in pointof- care setup.

We describe two techniques to create sharp tips. The first involves the buckling of thin metal films deposited on soft, stretchable substrates. The second involves the formation of narrow necked capillary bridges.

Crystal structure, pressure response, and polymorph transformation were investigated for crystalline indole through dispersion-corrected density functional theory (DFT-D) method. An accurate, nonempirical method (as in the latest implementations of CASTEP) is used to correct for the general DFT scheme to include van der Waals interactions important in molecular crystals. Ambient structural details, including space group symmetry, density, and fine structural details, such as bicyclic angles, have been reproduced to within experimental accuracy. Pressure response of the structure was obtained to isostatic pressure up to 25 GPa, in increments of 1 GPa. Evolution of space group symmetry and the bicyclic angle were mapped as a function of pressure. A previously unknown phase transformation has been identified around 14 GPa of isostatic pressure. Total energies of the phases before and after phase transformation are nearly identical, with a phase transformation barrier of 0.9 eV. The study opens up the door to reliable DFT investigations of chemical reactions of crystalline aromatic systems under high pressure (e.g. formation of amorphous sp3 hybridized phases).

Atomic force microscopy (AFM) allows for high-resolution topography studies of biological cells, measurement of their mechanical properties, and quantification of protein-protein interactions in physiological conditions. In this work, AFM was employed to investigate morphological, material, and chemomechanical properties of red blood cells from human subjects with sickle cell trait. We measured the stiffness of the cells and demonstrated that the Young’s modulus of pathological erythrocytes was three times greater than in normal cells. A single molecule AFM method was employed to report that erythrocytes from human subjects with the sickle cell trait express a greater number of the laminin receptors BCAM/Lu (p < 0.05) than erythrocytes from normal human subjects. Observed differences indicate the effect of sickle hemoglobin in the erythrocyte and possible changes in the organization of the cell cytoskeleton and membrane proteins associated with the sickle cell trait.

Photosynthetic membrane proteins convert solar light into chemical energy in a significantly high efficiency. Up-to-date reports of the photosynthetic bacterium suggest that such effective light conversion is due to the energy transfer between two light-harvesting (LH) protein complexes that are patterned in two dimensions. In this report, LH complex isolated from Rb. sphaeroides was immobilized onto a patterned gold surface with self-assembled monolayers (SAMs) and lipid bilayers at two main objectives: (1) micron-scale patterning of LH complex, and (2) prevention of quenching for pattern observation.

Mineralized biological materials such as nacre and bone achieve remarkable combinations of stiffness and toughness through staggered arrangements of stiff components bonded by softer materials. These natural composites are therefore substantial source of inspiration for emerging synthetic materials. In order to gain new insights into structureperformance relationships of these staggered structures, nacres from four species were compared in terms of fracture toughness and damage propagation pattern. Fracture tests revealed that all nacres display rising crack resistance curves, but to different extents. Using in-situ optical and atomic force microscopy, two distinct patterns of damage propagation were identified in columnar and sheet nacre respectively. These two different patterns were further confirmed by means of large scale numerical models of staggered structures. Similar mechanisms possibly operate at the smallest scales of the microstructure of bone.

The immobilization of DNA on passivated n-type InAs (100) surfaces has been studied using X-ray and ultraviolet photoelectron spectroscopy. The benefits of sulfur passivation using ammonium sulfide solution ((NH4)2S) for DNA immobilization were examined. The XPS/UPS data carried out on non-functionalized and functionalized surfaces demonstrate that the DNA probes reacted with the sulfur-passivated InAs surface. The XPS data in combination with fluorescently-tagged DNA indicate that the sulfur passivation process leads to a higher and more uniform attachment of DNA over the surface compared to non-sulfur-passivated InAs surfaces. The XPS data obtained immediately after sulfur passivation clearly observes In-S bonding, with little or no As-S. In addition, the XPS spectra of As 3d core-levels immediately after sulfur passivation shows that there is a negligible amount of As-Ox, but the peak become considerable after exposure to the aqueous DNA probe solution. The increase in As-Ox is likely due to the presence of non-sulfur bonded As atoms present on the surface. The presence of sulfur on the surface does lead to the high areal density of attached ssDNA. This system forms the basis of a DNA sensing system. While chemically passivating the surface against oxidation and facilitating probe attachment, the changes in Fermi level position were also monitored by UPS. UPS spectra show that the Fermi level of a clean InAs surface is located ~0.6 eV above the valence band maximum. The changes in electronic states induced by sulfur passivation and the pinning of EF are discussed.

Novel strategies of transduction may help to improve the biosensor performance by enhancing its sensitivity or linearity or by allowing a better integration with the electronics, which in turn favors the miniaturization of the sensing devices. In this work, a combination of a conductometric element containing the bioreceptor with a MOSFET is proposed as a transduction strategy. Simulations of the gate voltage and drain current versus conductance curves are used to confirm the feasibility of the proposed strategy. One of the advantages of the presented device is that the sensing element can be deposited by back-end processes compatible with current IC technology.

From the material point of view, the extracellular matrix (ECM) of bone is a natural nanocomposite consisting of an organic matrix (mainly collagen) and inorganic nanofillers (bone apatite) which are inserted in a parallel way into the collagen fibrils. For human bone tissue repair or regeneration, nanocomposites consisting of a biodegradable polymer matrix and nano-sized fillers such as bioactive ceramics or glasses, which mimic the hierarchical structure of bone, are considered a promising strategy. Combining living cells with biodegradable materials and/or bioactive component(s), the concept of tissue engineering first elucidated in the early 1990s represented a paradigm shift from tissue grafting, with autografts being the gold standard, or even completely from prosthesis implantation. In scaffold-based tissue engineering, scaffolds play an important role for tissue regeneration. Currently, acellular scaffolds with or without biomolecules such as growth factors are considered as an effective strategy for certain tissue repair due to their relatively low costs and easier process to gain surgeons’ acceptance and regulatory approval. In the current study, integrating an advanced manufacturing technique, nanocomposite material and controlled delivery of growth factor to form multifunctional tissue engineering scaffolds was investigated. Three-dimensional, osteoconductive and totally biodegradable calcium phosphate (Ca-P)/poly(hydroxybutyrate-co-hydroxyvalerate) (PHBV) nanocomposite scaffolds with customized architecture, controlled porosity and interconnecting pores were designed and fabricated using selective laser sintering (SLS). The surface of nanocomposite scaffolds was modified with gelatin and then heparin, which facilitated the incorporation of a growth factor, recombinant human bone morphogenetic protein-2 (rhBMP-2). Experimental results demonstrated the effectiveness of this strategy in guiding the osteogenic differentiation of mesenchymal stem cells. Together with osteoconductive nanocomposite material and controlled growth factor delivery, the use of SLS technique to form complex scaffolds provides a promising route towards individualized bone tissue regeneration.

Different types of biological adhesion can be categorized according to the length scales, structures, and materials involved. The setal adhesion system of the gekkonid lizards occupies a hierarchy of scales from the toes (~ 1 cm) to the terminal spatular pads on the setal branches (~ 100 nm). This unique combination of scale and foot-hair morphology allow the animal robust, controllable, and near-universal adhesion via van der Waals attraction, but it is also apparent that the mechanical behavior of the β-keratin plays an important role in an animal’s climbing ability. Experimental results show a four-fold increase in the viscoelastic loss tangent of β-keratin, alongside a substantial increase in adhesion of setal arrays, over a range of relative humidity from 10 to 80%. A model of single-spatular deformation predicts that the elastic energy stored in the setal branches, energy which is not completely recovered on detachment, is strongly influenced by these properties changes. The enhanced dissipation characteristics of the system explain the effects of environmental humidity on the clinging ability of geckos.

Many systems, including peptide systems, have been identified that self-assemble into nanometer sized structures. However, continued self-assembly to the macroscopic scale has remained elusive even though nature routinely does it. Here, a unique hierarchical peptide self-assembly process is described from the nanometer to the micrometer scale.

Electroless synthesis and hierarchical organization of 1.4 nm Pd and Pt nanoparticles (NPs) on self-assembled Rosette Nanotubes (RNTs) is described. The nucleated NPs are nearly monodisperse and reveal supramolecular organizations guided by RNT templates. Interestingly, the narrow size distribution is attributable to unique templating behavior of RNTs. The resulting metal NP-RNT composites were characterized by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). X-ray Photoelectron Spectroscopy (XPS) was also performed to confirm the nature and composition of RNT-templated NPs.

Biomolecules rich in aspartic acid (Asp) are known to play a role in biomineral morphology and polymorph selection, and have been shown to greatly enhance the growth kinetics of calcite. The mechanism by which these compounds favor calcification may be related to their effects upon cation solvation. Using molecular dynamics, we investigated the influence of small carboxylated molecules on the hydration states and water exchange rates of divalent cations. We show that the carboxylate moieties of Asp promote dehydration of Ca2+ and Sr2+ and that contact ion pair (CIP) formation is not required to disrupt the hydration of these cations. Ca2+- Asp and Sr2+ - Asp CIP formation decreases the total inner sphere coordination from an average of 8.0 and 8.4 in bulk water to 7.5 and 8.0, respectively. Water residence times estimated for Mg2+, Ca2+and Sr2+ follow the expected trend of decreasing residence time with increasing ionic radius. In the presence of Asp, both solvent-separated ion pair (SSIP) and CIP formation decrease the residence times of Ca2+and Sr2+ inner sphere water molecules. Comparable impacts on Mg2+ hydration are not observed. Mg2+ - Asp CIP formation is energetically unfavorable and Asp does not affect Mg2+ inner sphere water residence times.

Wide Angle X-ray scattering (WAXS) and indentation hardness have been used to study the development of crystallinity at room temperature of biodegradable poly(hydroxybutyrate) (PHB) and its copolymer with hydroxyvalerate (PHB/HV) containing 12% of valerate. Measurements were carried out immediately after quenching the samples from the molten state (200 ºC) in ice water and over two weeks of storage at room temperature. WAXS showed that the crystallization of the PHB-based polymers initiated within the first minutes of storage at room temperature, the copolymer displaying a higher rate of crystallization than the homopolymer. For all samples, the degree of crystallinity, α, nearly reached a plateau value within the first hour of crystallization. Concurrently to the development of crystallinity, microhardness values, H, clearly rose as crystallization occurred. Monitoring the crystallization for over two weeks showed that after the rapid increase of α and H, there was a slow monotonic growth of these properties. A correlation between nanostructure and microhardness is found at all stages of the crystallization process.

In this paper we present a novel approach for interface bilayer formation in which the uptake of an aqueous lipid vesicle solution by two polymeric hydrogels contained in a substrate causes the gels to swell so as to come into contact within an internal oil-filled region of the device. An interface bilayer, similar to those formed using the droplet interface bilayer (DIB) method, forms upon contact in oil between the lipid-encased ends of the two gels. Experimental measurements provide initial evidence that gel swelling enables automatic bilayer formation within a few minutes after the addition of lipid solution. The approach presented herein works toward the development of a new portable, easy-to-use screening platform that features tailored interface bilayers for a wide variety of screening applications.

We demonstrate a dual-mode sensing platform based on porous silicon (PSi) substrates coated with colloidal gold (Au) nanoparticles (NPs). This Au-PSi composite structure supports both molecular fingerprinting via surface enhanced Raman scattering (SERS) and quantification of molecular binding via reflectance measurements. Reflectance shifts of 7-10 nm in the infrared region were observed in the case of adsorbing benzenethiol or antioxidant glutathione molecules on the surface of Au NPs. Subsequent SERS measurements showed unique identification for both molecules and provided a < 1 μM and < 1 mM detection resolution for benzenethiol and glutathione, respectively.

Wood strength is highly anisotropic, due to the inherent structural hierarchy of the material. In the framework of a combined random-periodic multiscale poro-micromechanics model, we here translate compositional information throughout this hierarchy into the resulting anisotropic strength at the softwood level, based on “universal” elastic properties of cellulose, hemicelluloses, and lignin, and on the shear strength of the latter elementary constituent. Therefore, derivation of the elastic energy in a piece (representative volume element – RVE) of softwood, stemming from homogeneous macroscopic strains prescribed in terms of displacements at the boundary of the RVE and from pressure exerted by water filling the nanoporous space between the hemicelluloses-lignin network within the cell walls, with respect to the shear stiffness of lignin, yields higher order strains in the lignin phase, approximating micro-stress peaks leading to local lignin failure. Relating this (quasi-brittle) failure to overall softwood failure (or strictly speaking, elastic limit of softwood) results in a macroscopic microstructure-dependent failure criterion for softwood. The latter satisfactorily predicts the biaxial strength of spruce at various loading angles with respect to the grain direction. The model also predicts the experimentally well-established fact that uniaxial tensile and compressive strengths, as well as the shear strength of wood, depend quasi-linearly on the cell water content, but highly nonlinearly on the lumen porosity.

Molecular dynamics simulations were performed to estimate sequence dependent force required to stretch single stranded DNA (ssDNA) homo oligonucleotides. Simulations suggest that polyA and polyC oligonucleotides exhibit similar force profiles and corresponding elongation. Among single stranded DNA strands polyT is the most flexible and needs the most force to unwind from an equilibrium folded structure. In contrast, polyG had a very small recoverable deformation prior to a non-linear stretching. Our results indicate that mechanical properties of ssDNA chains are directly related to their sequence.

In this study we have established a new approach to more accurately map acoustic wave speed (which is a measure of stiffness) within soft biological tissues at micrometer length scales using scanning acoustic microscopy. By using thin (5 μm thick) histological sections of human skin and porcine cartilage, this method exploits the phase information preserved in the interference between acoustic waves reflected from the substrate surface as well as internal reflections from the acoustic lens. A stack of images were taken with the focus point of acoustic lens positioned at or above the substrate surface, and processed pixel by pixel using custom software developed with LABVIEW and IMAQ (National Instruments) to extract phase information. Scanning parameters, such as acoustic wave frequency and gate position were optimized to get reasonable phase and lateral resolution. The contribution from substrate inclination or uneven scanning surface was removed prior to further processing. The wave attenuation was also obtained from these images.