bluuebunny/crossref_metadata_2025_split huggingface dataset:
Protein-Based Hydrogels for Cell Transplantation under Constant Physiological Conditions
Authors: Foo Cheryl T Wong Po , Heilshorn Sarah 
Published: April 2011

ABSTRACTA promising treatment for multiple neurological disorders including stroke, Huntington's, and Parkinson's is the transplantation of stem cells into the diseased site to promote regeneration of the neural tissue. However, viability of transplanted cells is often low (15-35%) and unpredictable. Cell viability has been directly correlated with functional outcome of the treatment, motivating the development of more reliable cell transplantation procedures. To protect transplanted cells from shear stress during injection and from the hostile, inflammatory environment of the diseased brain tissue, many research groups are exploring physical hydrogels as a protective, growth-permissive matrix to enhance cell viability. However, physical hydrogels require an environmental trigger to induce gelation. These environmental triggers include sudden changes in temperature, pH, or salt concentration - all of which are detrimental to encapsulated cells and proteins and complicate their use in a clinical environment. To address this need, we have designed a two-component, protein-based hydrogel system that can self-assemble under constant physiological conditions.Both components of the hydrogel system are created using recombinant protein technology, which allows synthesis of exact monomer sequences within monodisperse polymers. The first hydrogel component is a block copolymer made of several repeats of a peptide sequence encoding the WW domain-fold, a short triple-stranded, anti-parallel, beta-sheet. The WW domains are interspersed with a random-coil, hydrophilic spacer to enhance polymer flexibility and solubility. The second hydrogel component is made of several repeats of a polyproline rich peptide sequence interspersed with a random-coil, hydrophilic spacer. Upon mixing the two hydrogel components together, the WW-domains in component 1 and the polyproline rich peptides in component 2 bind together with 1:1 stoichiometry. This binding has an apparent association constant of 2.2×105 M, as measured by isothermal titration calorimetry. This peptide-binding event serves as the physical crosslinks to form a polymeric network composed of the two components. Because gelation is initiated by simply mixing the two components together at physiological pH, temperature, and ionic strength, this system is highly biocompatible and easy to use. Furthermore, the precision of protein engineering allows both components to be easily modified. For example, increasing the length of the hydrophilic spacers will increase the resulting network pore size. Additionally, bioactive peptide sequences, such as the RGD cell-binding domain, have been introduced into the hydrophilic spacers to modify cell-scaffold interactions. Our long-term objective is to design a self-assembling hydrogel system for cell delivery that will both improve cell viability and mimic many of the essential cues in the developmental niche to encourage cell differentiation and outgrowth.
Live-cell Imaging at Low Interaction Forces
Authors: Campbell Paul 
Published: April 2011

ABSTRACTImaging live cells using atomic force microscopy (AFM) is perhaps the most challenging role within which the tool can be deployed. The procedure requires that the target cells be maintained under thermostated physiological fluids in order that viability is retained. Furthermore, once the imaging probe has engaged with the target cells, the use of appropriate imaging forces that guarantee reasonable spatial resolution must be weighed against the need to maintain a ‘light touch’ so that the integrity of this most delicate structure is not compromised. The purpose of the present study was ostensibly to image live cells (PtK2 epithelial cells)in-vitroand to examine those force regimes and tip properties that lead to best imaging. Interestingly, by employing ultra low imaging forces (FL< 100pN) whilst operating in contact mode, as opposed to ‘tapping’ mode, it was possible to achieve spatial resolutions in the range of about 25nm, which was sufficient to resolve the constituent fibres of the cytoskeletal network and other subcellular detail. Emipircally, certain tips were found to generate better resolution images than others, and we characterized those tips by imaging a commercial ion-beam etched spike array to determine not only the radius of curvature at the active imaging tip, but also the general morphology of the apex region. Force distance curves could be obtained which allowed a Hertzian analysis of the cellular elasticity. In this instance a value for the Young's modulus, EC, was determined to be 75kPa. Time-lapse imaging in this low force regime allowed the non-intrusive observation of cytoskeletal reorganisation during motility over extended periods of up to 7 hours.
Spontaneous Self-Assembly, Functionalization, and Meso-Scale Host-Guest Science of Organic Nanotubes
Authors: Kameta Naohiro , Masuda Mitsutoshi , Shimizu Toshimi 
Published: April 2011

ABSTRACTSelf-assembly in water at pH 6 and 10 of a wedge-shaped bolaamphiphile (1), bearing amino and glucose hydrophilic headgroups, was found to give two types of nanotubes with different inner diameters of 20 and 80 nm, respectively. X-ray diffraction and IR measurement revealed that the nanotubes have distinct inner and outer surfaces covered with amino and glucose headgroups, respectively. The nanotubes were able to effectively encapsulate an anionic spherical protein, ferritin, and DNA into the hollow cylinder under neutral pH conditions. Positively charged amino groups in the nanotube hollow cylinder proved to accelerate the encapsulation of the anionic biomacromolecules via electrostatic interaction. Covalent modification of the amino groups with a fluorescent donor dye on the inner surface of the nanotube allowed us to achieve the construction of an optical recognition system for encapsulation of guest molecules. Fluorescence resonance energy transfer (FRET) from the fluorescent donor located on the inner surface to the ferritin labeled with fluorescent acceptor enabled us to visualize the encapsulation and transportation features of the ferritin in the nanochannel shaped by the hollow cylinder structure.
Sol-gel Encapsulated Gold-Silica Nanoshell-based SERS Sensors
Authors: Lin Yu-Jen , Gala Pankti , Bishnoi Sandra Whaley 
Published: April 2011

ABSTRACTWe have used sol-gel methods to immobilize gold-silica nanoshells to create robust SERS based sensors. Using a protocol commonly used to immobilize proteins, biologically friendly SERS sensors for the study of gold binding peptides and proteins have been created. Specifically, by combining tetramethyl orthosilicate (TMOS), methyltrimethoxysilicate (MTMS), phosphate buffer, and gold nanoparticles we have created sol-gels with reduced fluorescence and Raman backgrounds. The resulting substrates have been tested using the Raman scattering response of 4-mercaptonbenzoic acid (4-MBA) to determine porosity and long-term stability of this SERS substrate. Multiple rinse cycles using phosphate buffer showed no significant decline in the SERS response of the substrate up to ten rinse cycles. Future studies will test the feasibility of using such substrates for the detection of biomolecules on the surface of gold.
Functionalized Porous Silicon in a Simulated Gastrointestinal Tract: Modeling the Biocompatibility of a Monolayer Protected Nanostructured Material
Authors: Albrecht Daniel S. , Lee Jacob T. , Molby Nick , Rhodes Steven D. , Dam Hieu Minh , Siegel Jason L. , Porter Lon A. 
Published: April 2011

ABSTRACTOwing to its photoluminescent properties and high surface area, porous silicon (por-Si) has shown great potential toward a myriad of applications including optoelectronics, chemical sensors, biocomposite materials, and medical implants. However, the native hydride-termination is only metastable with respect to surface oxidation under ambient conditions. Por-Si samples oxidize and degrade even more quickly when exposed to saline aqueous environments. Borrowing from solution phase synthetic methods, a selection of hydrosilylation reactions has been recently reported for functionalizing organic groups onto oxide-free, hydride-terminated porous silicon surfaces. Monolayers, bound through direct silicon-carbon bonds, are produced via thermal, microwave, Lewis acid, and carbocation mediated pathways. All of these wet, benchtop methods result in the formation of stable monolayers which protect the underlying silicon surface from ambient oxidation and chemical attack. However, no direct comparison of monolayer stability resulting from these diverse mechanisms has been reported. A variety of alkyl monolayers were prepared on porous silicon using the diverse hydrosilylation routes describe above and then immersed into a sequence of simulated gastric and intestinal fluids to replicate the conditions of potential por-Si biosensors or medicinal delivery systems in the human gastrointestinal tract. Degradation of the organic monolayers and oxidation of the underlying por-Si surfaces were monitored using both qualitative and semiquantitative transmission mode Fourier transform infrared spectroscopy (FTIR). Our initial results indicate that methods employing chemical catalysts often incorporate these species within the monolayer as defects, producing less robust surfaces compared to catalyst-free reactions. Regardless, monolayer protected por-Si samples demonstrated superior durability as opposed to the unfunctionalized controls.
Light Emission Properties and Biological Applications of Lanthanide Doped Oxide Nanoparticles
Authors: Mialon Genevieve , Giaume Domitille , Moreau Melanie , Casanova Didier , Nguyen Thanh-Liem , Popoff Michel-Robert , Alexandrou Antigoni , Gacoin Thierry , Boilot Jean-Pierre 
Published: April 2011

ABSTRACTRare-earth doped oxides as bulk materials are well known for their numerous applications in light emitting devices. Emission properties of nanoparticles, in association with their small size, open the way to new applications such as the elaboration of transparent luminescent devices or new biological labels. The key issue for such applications is the control of the surface state of the particles in order to preserve their dispersion state, to guarantee a strong emission and/or ensure strong interactions with specific target sites. Our work in this field mainly concerns yttrium vanadate particles (YVO4:Ln with Ln=Eu, Dy and Yb/Er) that are obtained as aqueous suspensions through a simple reaction of coprecipitation [1]. As compared to the bulk material, these particles (10-40 nm in diameter) exhibit the characteristic emission from the lanthanide dopant but with a lower efficiency (quantum yield of 15% and emission lifetime of 0.7 ms). The first part of our work is devoted to the improvement of the emission properties of particles. Our results show that the emission process is altered either by surface hydroxyl groups or by the poor cristallinity of the particles. We show that large improvement can be obtained following an original process which allows recovering the particles as colloidal dispersions after their thermal treatment at 1000°C. In the case of Eu3+ doped particles, quantum yield and emission lifetime were increased up to 40% and 0.8 ms respectively without notable increase of particle size. Moreover, the emission spectrum, either from colloidal suspensions or from single particles fits almost perfectly to the one from the bulk material. The second part of our work is devoted to the surface derivatization of the particles for applications as biological probes [2]. We chose a general scheme involving the coating of the nanoparticles with a thin layer of amino-silane. This process was chosen in order to allow further versatile grafting reactions trough the surface amino groups. This strategy will be detailed in the case of the coupling between our particles and a protein through the use of a homo-bifunctional cross-linker. The quantification of the number of attached proteins was achieved using dual-color microscopy and fluorescently-tagged proteins, by observing the step-like photobleaching of the organic fluorescent tag. The observation of labelled toxins interacting with living cells shows the high potentiality of rare-earth-doped oxide particles as new biological probes.
Fluorescent Hydrogel Sensor Particles for Detection of Protease Activity
Authors: Patrick Alison , Ulijn Rein V 
Published: April 2011

ABSTRACTWe demonstrate the design of novel sensor particles that display fluorescence in the presence of elastase, an enzyme that is present at elevated levels in chronic (non-healing) wounds. Poly(ethyleneglycol acrylamide) hydrogel particles, approximately 200μm in diameter are used as a polymeric matrix, to which a peptide based sensing element is attached. This sensing element consists of a Förster resonance energy transfer (FRET) pair separated by an enzyme cleavable linker. In addition, negatively charged Glutamic acid (Glu) residues are incorporated into the hydrogel structure to facilitate diffusion of the positively charged enzyme into the hydrogel matrix. Enzymatic hydrolysis of the enzyme cleavable linker results in fluorescence of the donor molecule being switched on. We have shown that these particles can detect elastase to a concentration of 100ng/ml, a concentration found in chronic wound fluids. These particles simultaneously detect and address balances in elastase levels and may therefore find applications as smart wound dressings.
Biocatalysis for Material Science and Drug Discoveries
Authors: Bruno Ferdinando Francesco , Samuelson Lynne A , Nagarajan Subhalakshmi , Nagarajan Ramaswamy , Kumar Jayant 
Published: April 2011

ABSTRACTA novel biomimetic route for the synthesis of conducting homopolymers and copolymers from aniline, phenol, pyrrole and 3,4-ethylenedioxy-thiophene in the presence of a polyelectrolyte, such as polystyrene sulfonate (SPS) is presented. A poly(ethylene glycol) modified hematin (PEG-Hematin) and the enzyme horseradish peroxidase (HRP) were used to catalyze the copolymerization of different monomers. UV-vis, FTIR, XPS, TGA and electrical conductivity studies for all complexes indicated the presence of a stable and electrically conductive form of these polymers. Furthermore, the presence of a polyelectrolyte, such as SPS, in this complex provides a unique combination of properties such as processability and water-solubility. Additionally catechins, the active compounds found in green tea, were polymerized and found to exhibit very interesting anti-carcinogenic properties. Here we report a unique enzymatic approach for the synthesis of water-soluble poly(catechins) with enhanced stability and potent anti-proliferative effects on human cancer cells in vitro. Various stereoisomers of catechin [(+), (-), (±)] and (-)-epicatechin have been biocatalytically polymerized using HRP in ethanol/buffer mixtures. This one-pot biocatalytic polymerization is carried out in ambient conditions yielding water-soluble poly(catechins). These synthesized poly(catechins) were tested for their growth inhibitory properties using a variety of normal and cancerous human epithelial cell lines. The poly(catechins) exhibit statistically significant greater growth inhibitory effects when compared to the monomers and exhibited specificity, inhibiting the growth of breast, colorectal and esophageal cancer cells while having little effect on normal epithelial cell growththus achieving a high therapeutic ratio. The synthesis, characterization and the growth inhibitory effects of these novel water-soluble poly(catechins) will also be presented.
Optical Properties of Carbon Nanotubes: Near-Infrared Induced Hyperthermia as Therapy for Brain Tumors
Authors: Gomez-De Arco Lewis , Chen Meng-Tse , Wang Weijun , Vernier Thomas , Pagnini Paul , Chen Thomas , Gundersen Martin , Zhou Chongwu 
Published: April 2011

ABSTRACTIn this work chemical functionalization of carbon nanotubes was conducted with the aim of improving their ability to be integrated into biological systems. Functionalized SWNT demonstrated to be an excellent vehicle to translocate a highly conjugated organic fluorophore across the cell membrane while causing little toxicity to the cells. Functionalized SWNT were introduced into different lines of the primary brain tumor cells Glioblastoma Multiforme (GBM). Once within the cell interior, the optical properties of the SWNT were used for both fluorescent imaging characterization and selective killing of tumor cells that had exhibited high SWNT uptake levels upon exposure to NIR radiation. Propidium iodide (PI) was employed as an indicator to determine the number of cells with compromised plasma membrane. Cell surviving ratio of as little as 10-20 percent were found in samples with intracellular nanotubes exposed to NIR radiation while a cell surviving ratio of about 95 percent was typical in irradiated samples without intracellular nanotubes. Control samples showed cell surviving ratios comparable to exposed samples without intracellular nanotubes. This study reveals new insights upon the influence of SWNT optical properties in the physicochemical processes within cells and how they can be used to develope therapy for cancerous brain tumors.
Understanding of Passivation Mechanism in Heterojunction c-Si Solar Cells
Authors: Kondo Michio , De Wolf Stefaan , Fujiwara Hiroyuki 
Published: April 2011

ABSTRACTIntrinsic hydrogenated amorphous silicon (a-Si:H) films can yield in outstanding electronic surface passivation of crystalline silicon (c-Si) wafers as utilized in the HIT (heterojunction with intrinsic thin layer) solar cells. We have studied the correlation between the passivation quality and the interface nature between thin amorphous layers and an underlying c-Si substrate for understanding the passivation mechanism. We found that a thin (∼5nm) intrinsic layer is inhomogeneous along the growth direction with the presence of a hydrogen rich layer at the interface and that completely amorphous films result in better passivation quality and device performance than an epitaxial layer. Post annealing improves carrier lifetime for the amorphous layer, whereas the annealing is detrimental for the epitaxial layer. We have also found that the passivation quality of intrinsic a Si:H(i) film deteriorates severely by the presence of a boron-doped a-Si:H(p+) overlayer due to Si-H rupture in the a-Si:H(i) film. Finally, for a passivation layer in the hetero-junction structure, a-Si1−xOx will be demonstrated in comparison with a-Si:H.
MW plasma enhanced CVD of intrinsic Si for thin film solar cells
Authors: Van Aken Bas B. , Leegwater Hans , Dorenkamper Maarten , Devilee Camile , Loffler Jochen , Heijna Maurits C.R. , Soppe Wim J. 
Published: April 2011

ABSTRACTOur aim is the development of high-throughput production technology for high efficiency, amorphous and microcrystalline thin film silicon photovoltaics (PV) on flexible substrates. A roll-to-roll system is developed, with three deposition chambers for the continuous deposition of n-type, intrinsic and p-type Si. Novel MW sources for plasma enhanced chemical vapour deposition (PECVD) are introduced in the roll-to-roll coater as MW-PECVD combines good quality with large area, high rate deposition of intrinsic Si. A comparison is made between Raman and UV-reflection spectroscopy.
Low Temperature Synthesis of Nanocrystalline Silicon and Silicon Oxide Films by Plasma Chemical Vapor Deposition
Authors: Tomyo Atsushi , Kaki Hirokazu , Takahashi Eiji , Hayashi Tsukasa , Ogata Kiyoshi , Uraoka Yukiharu 
Published: April 2011

ABSTRACTNanocrystalline silicon (nc-Si) and SiO2 films have been synthesized at a low substrate temperature using inductively coupled plasma chemical vapor deposition (ICP-CVD) methods with internal low-inductance antenna (LIA) units. The synthesis of these materials was performed in the separate vacuum containers where LIA units were installed so that the induced electric field from an antenna could be used effectively. Radio frequency (13.56 MHz) power was supplied through the matching circuit units. H2 and SiH4 gases were used for nc-Si synthesis, and O2 and SiH4 gases were used for SiO2 deposition. The gas flow ratios were 15 for H2/SiH4 and 4.0 for O2/SiH4. A substrate temperature, gas pressure, RF power and process time were varied in order to investigate optimum conditions for nc-Si synthesis. Silicon oxide films were deposited under conditions of 300°C, 0.2 Pa and 24 mW/cm3. A sample was prepared by SiO2 deposition and subsequent nc-Si synthesis after removing the natural oxide on silicon substrate by buffered 1%-HF (BHF) solution. In some cases, plasma treatments were inserted before or after nc-Si synthesis. The diameter and number density of nc-Si were determined by a high-resolution transmission electron microscopy (HR-TEM). Plan-view TEM images of nc-Si showed that spatially isolated nc-Si was synthesized and that the diameter and the standard deviation of nc-Si could be controlled not only with a substrate temperature, gas pressure, RF power and process time but also with pre/post plasma treatments. The resultant trend suggests that radical precursors and reactive nucleation sites on the SiO2 surface have an important role in the synthesis of nc-Si. The diameter of almost all nc-Si under the present conditions was less than 10 nm. In particular, under conditions of the substrate temperature of 200°C and 4.0 Pa with oxygen plasma pretreatment and hydrogen plasma posttreatment, the mean diameter and number density of nc-Si were 2.7 ± 0.5 nm and 6.5 × 1011 cm−2, respectively. This result is suitable for quantum effect device applications. In addition, electronic properties of a single SiO2 film were examined with the fabricated metal oxide semiconductor (MOS) capacitor. Breakdown voltage was 7.5 MV/cm at 1.0 × 10−6 A/cm2 and leakage current was 1.0 × 10−9 A/cm2 at 2.0 MV/cm for a SiO2 film with a thickness of 12 nm. This result clearly supports the present SiO2 film is capable of the thin dielectric layer of nc-Si devices.
Cyclically Varying Hydrogen Dilution for the Growth of Very Thin and Doped Nanocrystalline Silicon Films by Hot-Wire CVD
Authors: Lopez Fernando Villar , Antony Aldrin , Muñoz Delfina , Rojas Fredy , Escarré Jordi , Stella Marco , Asensi José Miguel , Bertomeu Joan , Andreu Jordi 
Published: April 2011

ABSTRACTAn important issue for the massive implementation of thin silicon technology in photovoltaic is the use of plastic substrates, which allow the use of roll-to-roll deposition systems and planar monolithic interconnection between the cells. However, the use of plastic substrates require a fully low temperature process; especially critical in the deposition of the thin amorphous (a-Si:H) or nanocrystalline (nc-Si:H) layers. Hot-Wire Chemical Vapour Deposition (HW-CVD) technique has demonstrated to be a good alternative to deposit quality thin films at low temperature. In this paper we focus our study on very thin (50 nm) n- and p-doped nc-Si:H films deposited at low substrate temperature around 100°C. We have observed that, in this low temperature deposition conditions, the promotion of an a Si:H incubation layer leads to a poor doping efficiency and poor electrical properties of the films. Hence, in addition to the optimization of the deposition conditions, we deposited doped layers by cyclically varying the hydrogen dilution (CVH) during deposition process. This CVH method promotes a layer-by-layer growth and inhibits the formation of the incubation layer. Several doped nc-Si:H layers have been deposited with and without this CVH method. The structural, electrical and optical properties of these films and advantage of CVH in improving the device quality of the thin doped layers are reported.