bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bacterial Macrofibers and Bionites: Materials of Natural and Synthetic Design
Authors: Mendelson Neil H. 
Published: March 2011

ABSTRACTTwo fiber forms can be obtained from cells of the rod-shaped bacterium,Bacillus subtilis, one called macrofibers, the other bacterial thread. Macrofibers are highly organized, multicellular structures, millimeters in length that selfassemble in a unique way. Each fiber is essentially a single chain of cells linked end-to-end that has repeatedly folded upon itself and twisted into helical form. The growth of individual cells yields both the material of the macrofiber and the forces required for its assembly. The forces involved stem from twisting motions caused by cell growth geometry. The folding process is akin to negative supercoiling. New approaches have been used to estimate the magnitude of forces. Torque generated by single filaments has been estimated from snapopening motions resulting from aborted attempts at folding to be in the range of 10−10to10−8dyne-cm. In contrast, multifilament fibers carrying small wires in their loops must have generated a torque of at least 10−5dyne-cm and a supercoiling force of at least 10−5dyne in order to have moved the wires in viscous solutions at the rates observed. The second bacterial fiber form, bacterial thread, and its mineralized derivatives, called bionites, are man-made materials. They are produced by the drawing and drying of bacterial cell filaments from cultures grown in the form of a textile-like web. The material properties of bacterial thread reflect primarily those of the strength-bearing cell wall polymer, peptidoglycan. A variety of new fiber-like materials have been produced by mineralizing the cell walls in situ in web cultures and drawing the products. Iron, copper, calcium, and potassium phosphate-containing bionites have been obtained in this manner. We are currently searching for order in the bionite crystal forms that may reflect the electrostatic nature of the wall polymer structural templates.
Synthesis, Surface and Cell-Adhesion Properties of Polyurethanes Containing Covalently Grafted RGD-Peptides
Authors: Lin Horng-Ban , Cooper Stuart L. 
Published: March 2011

AbstractIn an attempt to improve endothelial cell adhesion and growth on a polyurethane copolymer, cell adhesive RGD-containing peptides were grafted to the polymer backbone. Two peptide grafting reaction schemes, including one-step and two-step approaches, were developed. Amino acid analysis confirmed that the two-step approach had a higher peptide coupling efficiency. The two-step reaction scheme was utilized to prepare GRGDSY, GRGDVY and GRGESY (inactive control) peptide grafted polyurethanes with two different peptide densities (100 and 250 μmol/g polymer). Dynamic contact angle measurements indicated that the surfaces of the peptide grafted polyurethanes were more hydrophilic than the starting and carboxylated versions of the precursor polyurethane. In-vitro endothelial cell adhesion experiments showed that, without the presence of serum in culture medium, the GRGDSY- and GRGDVY-grafted polyurethanes dramatically enhanced cell attachment and spreading. Increasing the peptide density from 100 to 250 μmol/g polymer for the GRGDSYand GRGDVY-grafted polyurethanes resulted in an increase in cell attachment. With approximately the same peptide density (100 or 250 μmol/g polymer), the GRGDVY-grafted polymers supported more adherent cells than the GRGDSY-grafted polymers. Similar trends were observed in the in-vitro endothelial cell growth studies using culture medium containing serum and endothelial cell growth supplement. These RGD-peptide grafted polyurethanes may be useful in providing an easily prepared cell-adhesive substrate for various implantable devices and hybrid organs.
Integrin-Mediated Fibroblast Adhesion Strength: Role of the β1 Subunit
Authors: Ward Kelly A. , Guan Jun-Lin , Hammer Daniel A. 
Published: March 2011

AbstractCell-substratum adhesion is important in wound healing [4], embryogenic development [11], tissue architecture [6], and metastasis [7]. Integrins constitute a major class of heterodimeric cell-surface glycoproteins involved in receptor-mediated adhesion to the extracellular matrix (ECM). Focal contacts are regions of the cell-substratum adhesion in which clusters of integrin receptors connect the cytoskeleton to extracellular matrix molecules such as fibronectin. Focal contacts strengthen cell-substrate adhesion, and are sites of biochemical activity. Since cell adhesion strength in part depends on the cell's ability to cluster receptors and cytoskeleton into focal contacts, the integrity of the focal contact, and hence a cell's adhesive strength, will depend both on integrin-cytoskeletal binding as well as integrin-ligand binding.Using a centrifugation assay, we have quantified cell-substratum adhesion strength of mouse 3T3 cells transfected with the avian β1 integrin receptor (wild type), including various deletion mutants of its cytoplasmic domain, to surfaces containing varying concentrations of CSAT, a monoclonal antibody against the extracellular domain of the avian β1 subunit. For all the transfectants, adhesion strength decreases with decreasing CSAT concentration and increasing centrifugal strength. Different truncations of the cytoplasmic domain lead to different levels of adhesion. There is no simple correlation between the length of the cytoplasmic domain and the strength of adhesion.
Ionotropically Gelled Bicontinuous Cubic Phase as a Matrix for Controlled Release
Authors: Puvvada S. , Naciri J. , Ratna B. R. 
Published: March 2011

AbstractRelease studies from a lipid-based matrix, known as the bicontinuous cubic phase, are presented. This matrix consists of nano-sized pores within which various proteins and drugs can be dispersed and subsequently released to the exterior. To control the release rate, the aqueous pores of the cubic phase were gelled using sodium alginate, a water soluble polysaccharide. Studies show that the release rate is significantly lowered upon gelation and the first order release profile exhibited by the ungelled cubic phase is converted to a zeroorder linear profile. Further, it has been shown that the release trends can be reversed by degelation. This opens up the possibility of releasing large quantities of the protein when required (drugs on demand concept) by degelling the gelled samples.
Preliminary XPS Spectroscopic Characterization of Autoclaved TiNi Shape Memory Alloys for Implants
Authors: Shabalovskaya Svetlana A. , Anderegg J. W. , Sachdeva R. L. C. , Harmon B. N. 
Published: March 2011

AbstractThis paper reports a preliminary spectroscopic characterization of the surface elemental and phase compositions of Ti49Ni51 alloy treated using various sterilization procedures (autoclaving in water, steam, sealed envelopes; boiling in water and chemical etching). The surface of TiNi is found to consist of a thin oxide covered by a carbon-dominated contamination layer. The surface oxide of autoclaved samples is (TiO2)xNiy where y varies in the range 0-6 at.% depending on the surface preparation procedure. Minor amounts of suboxides as well as metallic Ni are also detected. Preliminary estimations of the oxide film thickness showed that it varies in the range 7- 26 nm depending on the employed method of sterilization. Mechanisms of surface state formation are briefly discussed.
Synthesis and Characterization of Tetraethylene Glycolpoly(Ethylene Oxide) Hydrogels for Tissue Engineering Applications
Authors: Royappa A. T. , Lopina S. T. , Cima L. G. 
Published: March 2011

AbstractA new poly(ethylene oxide) based biomaterial has been synthesized by co-crosslinking linear poly(ethylene oxide) (PEO) with tetraethylene glycol (TEG) in aqueous solution using electron beam radiation. This process results in hydrogels with variable concentrations of hydroxyl groups, tunable by adjusting the concentration of TEG in solution. FTIR analysis of these gels shows no changes in chemical composition on crosslinking.
High Porosity Polymeric Carbon Ware for Controlled Release of Drugs
Authors: Ila D. , Jenkins G. M. , Zimmerman R. L. , Evelyn A. L. 
Published: March 2011

AbstractPolymeric carbon ware prepared at various temperatures with variable accessible pore volume was filled with lithium by submerging in molten LiCl at 700°C. Using Li(p,α) nuclear reaction analysis the concentration profile and the volume density of Li were measured. It was found that they were highest for polymeric carbon samples prepared at 650°C.
A Novel Biodegradable Poly(Lactic-Co-Glycolic Acid) Foam for Bone Regeneration
Authors: Thomson Robert C. , Yaszemski Michael J. , Powers John M. , Mikos Antonios G. 
Published: March 2011

AbstractWe present a novel method for manufacturing three-dimensional, biodegradable poly(DL-lactic-co-glycolic acid) (PLGA) foam scaffolds for use in bone regeneration. The technique involves the formation of a composite material consisting of gelatin microspheres surrounded by a PLGA matrix. The gelatin microspheres are leached out leaving an open-cell foam with a pore size and morphology defined by the gelatin microspheres. The foam porosity can be controlled by altering the volume fraction of gelatin used to make the composite material. PLGA 50:50 was used as a model degradable polymer to establish the effect of porosity, pore size, and degradation on foam mechanical properties. The compressive strengths and moduli of PLGA 50:50 foams were found to decrease with increasing porosity but were largely unaffected by pore size. Foams with compressive strengths up to 2.5 MPa were manufactured. From in vitro degradation studies we established that for PLGA 50:50 foams the mechanical properties declined in parallel with the decrease in molecular weight. Below a weight average molecular weight of 10,000 the foam had very little mechanical strength (0.02 MPa). These results indicate that PLGA 50:50 would not be suitable as a scaffold material for bone regeneration. However, the dependence of mechanical properties on porosity, pore size, and degree of degradation which we have determined will aid us in designing a PLGA foam (with a comonomer ratio other than 50:50) suitable for bone regeneration.
Biodegradable Foams for Cell Transplantation
Authors: Lo H. , Kadiyala S. , Guggino S. E. , Leong K. W. 
Published: March 2011

AbstractA processing technique based on the principle of phase separation was developed to fabricate three-dimensional microcellular foams to act as templates for cell transplantation. The polymers used to make the foams were polylactic acid (PLLA) and a polyphosphoester (BPA/PP). The resulting foams had relatively uniform, open cells throughout the matrix. The foams could also be fabricated into complex shapes to meet specific design requirements. The foam morphology and microstructure were characterized by mercury porosimetry and scanning electron microscopy. Osteoblast like cells ROS17/2.8 were successfully cultured in the foams. Cell attachment to the foam interior was verified by confocal microscopy. The fabrication technique allows incorporation of drugs or nutrients into the highly porous structure as demonstrated by the intimate dispersion of fluorescein isothiocyanate (FITC) in the matrix.
Attachment of Mucin Specific Lectins to Alginate for Use as Bioadhesives
Authors: Chickering Donald E. , Jacob Jules S. , Keung Annie , Desai Tejal A. , Mathiowitz Edith 
Published: March 2011

AbstractThe use of bioadhesive materials for orally-delivered, controlled release systems could increase GI transit time and improve bioavailability. Through the covalent attachment of various ligands to drug delivery systems it is possible to engineer materials to adhere to specific moieties endogenous to the alimentary mucosal layer. The entire GI tract is covered by a continuous, protective, mucous coating made of 95% water and 5% electrolytes, lipids, proteins, and glycoproteins. The GI glycoproteins consist of a protein core with covalently attached carbohydrate side chains terminating in either L-fucose or sialic acid residues. There exist several plant and animal lectins which display high affinity binding to either of these sugars.We have studied the effect on bioadhesion of attaching biotinylated Ulex Europaeus I (UEA-I), an L-fucose specific lectin derived from the gorse seed, to barium-loaded alginate microspheres. Two carbodiimidazole (CDI) coupling procedures were investigated: premicrosphere-fabrication coupling and post-microsphere-fabrication coupling. The attachment of lectin was confirmed using an ABC reaction with HRP staining. The pre-modified microspheres clearly showed better labeling than the post-modified. For in vivo assessment of bioadhesion, 3 cohorts of 4 rats were force fed slurries of control, pre- and post-modified microspheres in saline. The animals were X-rayed 1 hour after feeding and sacrificed 19 hours later. Their entire GI tracts were excised, X-rayed and the microsphere distribution was assessed. The premodified microspheres showed greater retention in all areas of the alimentary canal. The total percentage of microspheres remaining in the GI tract after 19 hours was: 18.6% post-modified and 37.1% pre-modified. These results correlate well with the intensity of the reaction seen with the HRP staining, and suggest that attachment of mucin specific ligands to polymer microspheres may improve bioadhesion.
Reaction Kinetics on Diamond: Measurement of HI Atom Destruction Rates
Authors: Harris Stephen J. , Weiner Anita M. 
Published: March 2011

AbstractWe describe the first measurements of reaction kinetics between diamond and a gas phase species—H atoms—involved in its formation. We develop a remarkably simple method to measure H atom concentrations and use the method to measure γd, the destruction probability of H atoms on diamond at 20 torr and 1200 K. We find γd = 0.12. This value is close to that estimated from gas phase alkane rate constants.
A Novel Molecular Beam Reactor for The Study of Diamond Surface Chemistry
Authors: Wolden C. A. , Zau G. , Conner W. T. , Sawin H. H. , Gleason K. K. 
Published: March 2011

AbstractA novel reactor has been constructed to investigate the fundamental surface kinetics of diamond chemical vapor deposition(CVD). The molecular beam reactor permits independent control of the atomic hydrogen flux, the methyl radical flux and the substrate temperature. The low pressure in the growth chamber (≈ 1 mTorr) minimizes the impact of gas-phase chemistry. The reactive mixture impinging the substrate is sampled through an orifice and analyzed by mass spectroscopy. Differential pumping in the two adjacent chambers quenches the beam, allowing quantitative analysis of radical species such as H and CH3. In preliminary experiments deposition was achieved onto seeded molybdenum substrates.
The Role of Unprecracked Hydride Species Adsorbed on The GaAs(100) in The Growth of GaAs by Ultrahigh Vacuum Chemical Vapor Deposition Using Trimethylgallium and Triethylgallium
Authors: Park Seong-Ju , Ro Jeong-Rae , Sim Jae-Ki , Ha Jeong Sook , Lee El-Hang 
Published: March 2011

AbstractsWe have grown GaAs epilayers by ultrahigh vacuum chemical vapor deposition(UHVCVD) using adsorbed hydrides and metalorganic compounds via a surface decomposition process. This result indicates that unprecracked arsine(AsH3) can be used in chemical beam epitaxy(CBE) and that a new hydride source with a low decomposition temperature, monoethylarsine(MEAs) can replace the precracked AsH3 source in CBE. The impurity concentrations in GaAs grown with trimethylgallium(TMG) and triethylgallium(TEG) were found to be very sensitve to growth temperature. It was also found that the uptake of carbon impurity is significantly reduced when TMG is replaced with TEG. The carbon concentrations in epilayers grown using TMG and TEG with unprecracked AsH3 and MEAs were reduced by 2-3 orders of magnitude compared to those by CBE process employing TMG and arsenics from precracked hydrides. We have also found that the hydrogen atoms play an important role in the reduction of carbon content in GaAs epilayer. Intermediates like dihydrides from MEAs decomposed on the surface are considered to supply hydrogen atoms and hydrides during growth, which may remove other carbon containing species.
Controlled Impurity Introduction In CVD: Chemical, Electrical, and Morphological Influences
Authors: Kuech T. F. , Redwing J. M. , Huang J.-W. , Nayak S. 
Published: March 2011

AbstractWe present here an overview of recent studies of the influence of oxygen doping on the electrical and structural properties of semiconductors grown through the metal organic vapor phase epitaxy (MOVPE) technique. In particular, we have measured the impact of oxygen introduction on several of the principal aspects of the growth process: incorporation, activation, and influence on the growing surface structure. The gas phase chemistry and dopant incorporation was investigated for two different precursors: dimethyl aluminum methoxide and diethyl aluminum ethoxide. The simple change in the structure of the oxygen source leads to significant changes in the oxygen incorporation behavior. Complementary studies of the gas phase decomposition of these oxygen sources have indicated that the decomposition mechanism is substantially different for these two sources leading to the change in incorporation behavior. The impact of the selective incorporation of oxygen at heterointerfaces has been studied here through the growth of superlattice structures. Glancing angle X-ray diffraction and atomic force microscopy measurements have shown that the incorporation of oxygen at the GaAs-to-AlxGaI-x As interface leads to modest increases in the average roughness of the heterointerface with more significant changes in the interfacial structure. The structure of this interfacial roughness was also studied through measurements of the diffuse X-ray scattering about a Bragg peak. Measurements of the component of the roughness which is correlated between the superlattice layers show significant changes with oxygen addition.
Probing Selective Deposition of Aluminum Using in Situ Infrared Spectroscopy
Authors: Gladfelter Wayne L. , Simmonds Michael G. , Zazzera Larry A. , Evans John F. 
Published: March 2011

AbstractDimethylethylamine alane (DMEAA) has been used to deposit thin films of aluminum selectively on gold in the presence of silicon oxide. This paper presents studies of the effect of temperature, pressure, and substrate pattern on the selectivity. A specially designed reactor allowed us to probe the structure of the species on the silica surface using infraed spectroscopy. At room temperature two absorptions in the Al-H stretching region were assigned to two species; weakly bound molecules of the intact precursor and a strongly bound dihydride formed from the reaction of DMEAA with surface bound (and H-bonded) hydroxyls (from H2O or silanol groups). At higher temperatures the CH vibrations of the amine disappeared, and the Al-H stretch shifted to higher energy. A weak absorption at 2250 cm−1 attributable to a Si-H also appeared. The impact of these observations on the loss of selectivity is discussed.
Influence of Flow Dynamics on The Morphology of CVD Aluminum Thin Films
Authors: Speckman Donna M. , Leung Denise L. , Wendt Jerry P. 
Published: March 2011

AbstractAluminum thin films were deposited by chemical vapor deposition on SiO2 substrates using trimethylamine alane (TMAA) in a low pressure CVD reactor system. A high TMAA flow rate during deposition, combined with an initial burst of added argon during the nucleation of the substrate surface resulted in the growth of aluminum thin films with excellent purity and surface morphologies. Film resistivities averaged 3.4 μΩ-cm, and the average surface peak-to-valley height for each film was found to be <4% of the film thickness. The surfaces of films with thicknesses of ≤ 1 μm were extremely smooth and reflective. In contrast, the use of a high alane flow rate in the absence of any added argon resulted in the growth of films with extremely textured surface morphologies. Furthermore, films grown using an argon carrier gas, but with a slow alane flow rate, exhibited both textured surface morphologies and whisker growth.
Deposition of Tungsten Films by Pulsed Excimer Laser Ablation Technique
Authors: Dhote A.M. , Ogale S.B. 
Published: March 2011

AbstractLow temperature deposition of W on Semiconductor substrates is vital for microelectronics technology. Laser ablation technique using KrF (248 nm) excimer laser has been employed to deposit W films from W(CO)6. The substrates used are Si(100) and SiO2. The influence of substrate temperature on the film growth rate was investigated in a broad temperature range (20 - 500 °C), keeping the laser fluence fixed at 0.4 Jcm−2. The substrate temperature is found to have a strong influence on the resistivity of the deposited films. Film resistivities within a factor of 3 of the value for pure bulk W have been observed in the substrate temperature range of 300 - 500 °C. X-ray diffraction data were also obtained. These revealed that the crystal structure of the film deposited in this temperature range corresponds specifically to the m-phase. Optical emissions from the plasma generated during the pulsed excimer laser ablation of W(CO)6 are also examined by an optical Multichannel Analyser (OMA).
Gaas Etching by C12 and HCI: Ga- vs. As- Limited Etching
Authors: Su Chaochin , Dai Zi-Guo , Hou Hui-Qi , Xi Ming , Vernon Matthew F. , Bent Brian E. 
Published: March 2011

AbstractResults in the literature indicate that C12 etches GaAs at room temperature but HCl etches GaAs at a measurable rate only at temperatures above ∼670 K. In this work, molecular beam scattering and surface analysis techniques have been applied to address the fundamental kinetic differences between these two systems. The results indicate that the onset of GaAs etching by C12 is determined by the kinetics of Ga-removal as GaC13 while etching by HCl is limited by As evaporation as As2. The results also suggest that HCl selectively etches gallium from GaAs at temperatures between 600 and 650 K.
Chemical Topography of Si Etching in a Cl2 Plasma, Studied by X-RAY Photoelectron Spectroscopy and Laser-Induced Thermal Desorption
Authors: Donnelly V. M. , Guinn K. V. , Cheng C. C. , Herman I. P. 
Published: March 2011

AbstractThis paper describes x-ray photoelectron spectroscopy (XPS) studies of etching of Si in high-density Cl2 plasmas. Polycrystalline Si films, masked with photoresist stripes, are etched and then transferred in vacuum to the XPS analysis chamber. Shadowing of photoelectrons by adjacent stripes and differential charging of the photoresist and poly-Si were used to separate contributions from the top of the mask, the side of the mask, the etched poly-Si sidewall, and the bottom of the etched trench. In pure Cl2 plasmas, surfaces are covered with about one monolayer of Cl. If oxygen is introduced into the plasma, either by addition of O2 or by erosion of the glass discharge tube, then a thin Si-oxide layer forms on the sides of both the poly-Si and the photoresist. Laser-induced thermal desorption (LITD) was used to study etching in real time. LITD of SiCI was detected by laser-induced fluorescence. These studies show that the Si-chloride layer formed during plasma etching is stable after the plasma is extinguished, so the XPS measurements are representative of the surface during etching. LITD measurements as a function of pressure and discharge power show that the etching rate is limited by the positive ion flux to the surface, and not by the supply of Cl2, at pressures above 0.5 mTorr and for ion fluxes of σ4× 1016cm−2 s−1.