bluuebunny/crossref_metadata_2025 huggingface dataset:
Dielectrically Confined Excitons and Polaritons in Natural Superlattices -Perovskite Lead Iodide Semiconductors
Authors: Gippius N. A. , Muljarov E. A. , Tikhodeev S. G. , Ishihara T. , KELDYSH L. V.
Published: March 2011

A large class of new layered semiconductors — lead iodide compounds — is of great interest because of possible optoelectronic applications due to pronounced excitonic effects. These compounds may be regarded as naturally grown semiconductor/insulator superlat-tices, with perovskite lead iodide (semiconductor) layers sandwiched by alkylammonium (insulator) layers. Exciton binding energies and oscillator strength in these structures are enhanced due to the so-called “dielectric confinement” caused by large difference between dielectric constants of adjoining layers. The binding energies, wave functions,& diamagnetic coefficient of excitons in these naturally grown superlattices are calculated with allowance for the image potential and the superlattice structure of the compounds. The localization of excitons in lead iodide layers causes also a strong dependence of a polariton spike in reflection spectra on the polarization of electromagnetic wave. The results obtained are in agreement with the experimental data.
Negative Magnetoresistance in Activated Carbon Fibers Heat-Treated Above 2000°C
Authors: Fung A. W. P. , Wang Z. H. , Dresselhaus M. S. , Dresselhaus G. , Endo M.
Published: March 2011

Activated carbon fibers (ACFs) were heat-treated at temperatures above 2000°C to study both the effect of heat treatment on the order development in ACFs and the effect of granularity on the transport properties of granular materials in general. The electrical conductivity σ(T) and Magnetoresistance (MR) were measured as a function of temperature for ACFs Made of two different precursors and heat-treated at different temperatures. While the field dependence of the observed negative MR could be fit to the two-dimensional weak localization (2D WL) theory at each measurement temperature, σ(T) showed only a weak temperature dependence, inconsistent with the ln (T) dependence predicted by the same theory. Even More interesting is the observation of a negative MR, which is a quantum-Mechanical phenomenon, near room temperature. It is thought that the grain boundaries might be responsible for such deviations from the standard 2D WL theory.
Optimization of Conducting Polymer Synthesis for Battery Applications
Authors: Otero T. F. , Santamaria C. , Rodriguez J.
Published: March 2011

The evolution of the capacity to store electrical charges of electrogenerated polypyrrole and polythiophene films, as a function of the parameters of synthesis (electrical potential, solvent, Monomer concentration and temperature) was analyzed. The polymer production was followed by “ex situ” ultramicrogravimetry. The stored charge in each film was controlled by voltammetry and chronoamperometry, in the background electrolyte (in absence of Monomer). The charge storage ability was calculated from the ratio between stored charge and polymer mass adhered to the electrode. The charge storage ability of an electrogenerated film decreases several times when one of the parameters of synthesis: potential of polymerization, temperature, concentration of monomer or donor number of the solvent, increase. The change on the polymer property when the conditions of synthesis shift, points to a mixed polymerization-degradation process during polymer growth. The knowledge of those variations allows to optimize the conditions of synthesis to generate conducting polymers for specific batteries applications.
Electronic Deep Levels in Laser – Crystallized Silicon Thin-Film MOS Capacitors on Fused Silica
Authors: Johnson N. M. , Moyer M. D.
Published: March 2011

Residual electronic deep levels in fully – processed, cw laser – crystallized silicon thin films on fused silica were measured by transient capacitance spectroscopy, supplemented with capacitance – voltage techniques. The test devices were metal – oxide – silicon thin – film capacitors with p – type conductivity. The hole emission spectra are dominated by a continuous distribution of deep levels in the lower half of the silicon band gap which are associated with the Si – SiO2 interface; the spectra also display the effects of surface generation. The interface – state density near midgap is estimated to be 6×1010 eV−1 cm−2, and there are no detectable bulk deep levels with densities > 1×1014 cm−3.
Offset-Gate Structures for Increased Breakdown Voltages in Silicon-On-Insulator Transistors
Authors: Drowley C. I. , Kamins T. I.
Published: March 2011

An offset-gate structure was used to fabricate p-channel MOS transistors in laser-recrystallized silicon-on-insulator (SOI) films. The breakdown voltage increased from about -18 V with a conventional gate structure to about -38 V with the offset gate and was then limited by bulk breakdown in the film, rather than by the high fields near the gate drain overlap region. Simulations indicate that breakdown voltages of about -60 V can be achieved in the structure used, provided that the back-surface fixed-charge density is limited to 1×10″ cm−2.
A 3-D Integration Strategy in VLSI
Authors: Malhi Satwinder D. S.
Published: March 2011

Nearly two decades of work in fabricating active devices in small grain LPCVD polysilicon by various workers has shown that the material is generally suitable for junction diodes and MOSFETs [1–10]. Recently, there has been a considerable activity in the domain of beam recrystallization of polysilicon. One of the goals of this effort is 3-D integration for VLSI. These recrystallization techniques require several years of industrywide effort before they become acceptable tools in IC manufacturing. However, there exists a great demand today, especially in large memories, for an SOI MOSFET that can be integrated in existing bulk silicon based technologies.

Fortunately, acceptable MOSFETs can be manufactured in small grain poly-silicon without resorting to beam recrystallization [11–13]. One consistent problem with small grain polysilicon MOSFETs has been a high threshold voltage, which makes these devices unacceptable for standard IC applications that require 5V operation. It has been shown that this characteristic can be remedied by proper device design [11–13]. In particular, thin gate insulator, accumulation mode behaviour, and some form of grain boundary passivation, used alone or in a combination, are effective means of reducing threshold voltage.

The other problem of the polysilicon devices has been high leakage current. This is a result of defects in polysilicon. It has been shown that grain boundary hydrogenation drastically reduces the leakage current by passivating these defects [11–13]. As a result, it is possible to manufacture MOSFETs, in small grain LPCVD polysilicon, with on to off current ratio of seven orders of magnitude.

With improved device design, it has been possible to build short channel p-channel and n-channel MOSFETs with arbitrary threshold voltage and leakage current of the order of 1 pA/μm channel width. The channel mobility is about 10 cm2/V sec. The on to off current ratio is about seven orders of magnitude. Despite the low mobility, these devices are useful for a variety of high density memory applications.

Since no nonstandard materials, tools and processes are required in the fabrication of these devices, manufacturable 3-D integration processes are presently possible with such devices. Besides permitting useful products today, this strategy allows construction of a design and manu-facturing infrastructure that will facilitate infusion of future 3-D concepts in bulk silicon technologies.

We have used p-channel devices built in small grain LPCVD polysilicon to develop a 2 μm stacked CMOS process. We have fabricated 64K static RAMs with this process. The cell size is 307 sq.μm and chip size is 55000 sq. mils. The access time is 120 ns. This provides a demonstration of our strategy.
Amorpiious Silicon Thin Film Transistor and its Applications to Large-Area Electironics
Authors: Tuan H. C.
Published: March 2011

In this paper, the amorphous silicon thin film transistor (a-Si:HTFT) technology is reviewed. Its applications to both one- and two-dimensional large-area devices are described. The issues related to the fabrication of TFT arrays on large-area substrates are also discussed.
Vertical-Type a-Si:H Field-Effect Transistors
Authors: Uchida Yasutaka , Matsumura Masakiyo
Published: March 2011

Vertical-type a-Si:H Field Effect Transistors with 1 μm channel length have been investigated. A simple analysis of the FET characteristics indicates that the reduction of the channel length is an effective method to improve the FET characteristics at least up to the channel length of 1 μm. Experimental results showed that the on-resistance is approximately propotional to the channel length and that on off current ratio of the vertical-type FET with 1 μm channel length was more than 104.
Characteristics of Amorphous Silicon Based Alloy Field Effect Transistors
Authors: Shur M. , Hack M. , Hyun C.
Published: March 2011

We have developed a new theory to describe the current-voltage characteristics of amorphous silicon based alloy field effect transistors. We show that the transition from below to above threshold operation occurs when the Fermi level in the accumulation region moves from the deep to tail localized states in the energy gap and that the field effect mobility is dependent on gate voltage. We also propose a new technique to determine the flat-band voltage from the I-V characteristics in the below threshold regime.
Biologically Derived Nanometer-Scale Patterning on Chemically Modified Silicon Surfaces
Authors: Holland Bradford W. , Douglas Kenneth , Clark Noel A.
Published: March 2011

In recent experiments we have patterned smooth HOPG surfaces with periodic arrays of nanometer dimension holes on a 20nm lattice using two-dimensional (2-D) protein crystals as templates. The bacterial cell wall crystals were deposited on HOPG substrate and overcoated at oblique incidence with an ultrathin (3.5 nmn) TiO2 film. Fast atom beam (FAB) milling patterns the TiO2 film into a screen having the protein lattice periodicity and the screen then acts as a mask for the pattern transfer to the HOPG substrate. This method provides an inexpensive, “benchtop,” intrinsically parallel technique for the periodic nanostructuring of surfaces. Here we extend it to the patterning of silicon single crystal surfaces. We will describe the use of silane coupling agents to enable protein adhesion with the cytoplasmic side up, as is preferable for the patterning. We will show AFM images of the T1O2 -protein-silicon composite surface at various stages of the fabrication process.
Bioactive Silk-Like Protein Polymer Films on Silicon Devices
Authors: Anderson J. Philip , Nilsson Susanne C. , Rajachar Rupak M. , Logan Randy , Weissman Neil A. , Martin David C.
Published: March 2011

Coatings of genetically engineered protein polymers based on the crystalline segment of B. Mori silk fibroinand cell binding domains from extracellular matrix proteins (ProNectin™ by Protein Polymer Technologies, Inc.) were applied to bare silicon wafers used to mimic microcircuit devices. These silicon devices have applications in the stimulation and monitoring of central nervous system activity but need bioactive coatings for integration into nervous tissue. Gel point coating technology was developed by preparing solutions at the onset of phase separation in protein polymer/formic acid/ ethanol systems. Dipping silicon wafer substrates into such solutions produced homogeneous thin protein polymer coatings. Quench coating techniques that create rough surfaces in a controlled manner were explored by driving protein polymer solutions through different regions of the protein polymer/formic acid/methanol system before drying. Atomic force microscopy was used to characterize the protein films.
Biotinylated Thiophene Copolymer – A Novel Biomaterial for LB Film Assembly
Authors: Chittibabu K. G. , Kamath Manjunath , Lim Jeong-Ok , Marx Kenneth A. , Kumar Jayant , Tripathy Sukant K. , Samuelson Lynne A. , Kaplan David L.
Published: March 2011

The coupling of a photodynamic protein to an electroactive polymer may be employed in opto-electronic signal transduction for optical displays, color mimicking and biosensor applications. We have synthesized a novel biomaterial, biotin-LC-hydrazide substituted poly(3-undecylthiophene-co-3-thienylcarboxaldehyde) [B-PUAT], which is capable of incorporating any biotinylated molecule through a bridging streptavidin protein. A long spacer group between the conjugated polymer backbone and the biotin side group improves monolayer formation at the airwater interface and enhances the material's ability to bind protein. The LB technique has been employed to couple this biomaterial and streptavidin through the well known biotin-streptavidin complexation. Biotinylated phycoerythrin [B-PE] is incorporated into the above monolayer by binding the unoccupied biotin binding sites on the bound streptavidin.
Composite Microstructure of Spider (Nephila Clavipes) Dragline
Authors: Thiel Brad , Kunkel Dennis , Guess Keith , Viney Christopher
Published: March 2011

Dragline fibers collected at a controlled silking rate from Nephila clavipes spiders were studied by analytical transmission electron microscopy (TEM). The physical microstructure consists of irregularly-shaped ß-sheet crystallites (approx. 70–100 nm in diameter, and comprising approx. 50 volume per cent) in an amorphous matrix. Electron diffraction from single crystallites indicates an orthogonal unit cell with space group P21; the lattice parameters area= 13.31 Å (inter-sheet repeat),b= 9.44 Å (inter-chain repeat within ß-sheets) andc= 20.88 Å (intra-chain repeat). The crystallites are not truly periodic structures having long range positional order, but are better described as non-periodic layered structures, similar to the ordered structures formed when liquid crystalline random copolymers solidify. Electron energy loss spectroscopy (EELS) reveals chemical microstructure in the fibers. The matrix contains bands (approx. 200 nm wide) of alternately higher and lower nitrogen content. This variation cannot be explained in terms of known protein domains alone, and may reflect the presence of retained small-molecule species from secretory granules. Calcium is localized uniquely to the crystallites (at a concentration of approx. one calcium atom per 120 amino acid residues, as measured by inductively coupled plasma spectroscopy). Varying the calcium content may be one mechanism by which the spider can tailor the evolution of the microstructure, and hence the physical properties of the silk fiber.
Genetically Engineered Pores as Metal Ion Biosensors
Authors: Kasianowicz John , Walker Barbara , Krishnasastry Musti , Bayley Hagan
Published: March 2011

We are adapting proteins that form pores in lipid bilayers for use as components of biosensors. Specifically, we have produced genetically engineered variants of the α hemolysin (αHL) fromStaphylococcusaureus with properties that are sensitive to low concentrations of divalent cations. For example, the pore-forming activity of one mutant (αHL-H5: residues 130–134 inclusive replaced with histidine) is inhibited by Zn2+at concentrations as low as 1 μM, as judged by the reduction in its ability to lyse rabbit red blood cells and to increase the conductance of planar lipid bilayer membranes. When αHL-H5 is added to the aqueous phase bathing one side of a planar membrane, the subsequent addition of 100 μM Zn2+to either side blocks the pores that form. This result suggests that at least part of the mutated region lines the channel lumen. Ca2+and Mg2+do not block the channel and therefore the H5 mutation confers a degree of analyte specificity to the αHL pore. The results suggest that genetically engineered pores have great promise for the rapid and sensitive detection of metal cations and we discuss the merits and potential limitations for their use in this application. Specifically, we examine the issues of selectivity, sensitivity, response time, dynamic range and longevity. Some of these properties are interdependent. For example, the goals of high sensitivity and rapid response time can be in conflict.
Synthesis and Characterization of Polymer Substrates for Rat H Epatocyte Culture
Authors: Gutsche Annie Tang , Zurlo Joanne , Lo Hungnan , Leong Kam W.
Published: March 2011

Lactose and heparin were covalently coupled to poly(chloromethyl styrene) and the modified polymer was used as a substrate for rat hepatocyte culture. Lactose and heparin are recognized by rat hepatocytes and can be used to mediate cell attachment to the substrate. Rat hepatocytes cultured in serum-free media on these substrates were able to maintain enzymes and peptides important in the detoxification functions of hepatocytes, without the addition of hormones such as dexamethasone, media additives such as DMSO, or complex biological extracellular factors.

The growing interest in large-scale cell culture and in tissue engineering requires substrates of different geometries. Therefore, we have fabricated the derivatized polymers into microcarriers and, most recently, foams. These three-dimensional structures, combined with the chemistries of the polymers, provided the hepatocytes with more cell-cell interactions and in vivo-like geometries than conventional flat-dish culture.
Observation and Analysis of Self-Diffraction in Bacteriorhodopsin Films
Authors: Gross Richard B. , Chen Zhongping , Birge Robert R.
Published: March 2011

High order self-diffraction is observed from a 5.2 OD570 thin film containing chemically enhanced bacteriorhodopsin. Up to fourteen diffracted orders (±7) could be discerned by eye at a laser intensity of 23 mW/cm2. The results for the first and second order diffracted beams are analyzed in terms of a modified form of the recent self-diffraction model proposed by Fragnito et al.[1].
Genetically Modified Bacteriorhodopsin as a Bioelectronic Material
Authors: Hong Filbert H. , Chang Man , Ni Baofu , Needleman Richard B. , Hong Felix T.
Published: March 2011

This article shows the effect of point mutations on the photoelectric behavior of membranes reconstituted from mutant bacteriorhodopsins.
BLM-Based Electrochemical Sensors
Authors: Leitmannova-Ottova A. , Liu W. , Zhou T.-A. , Tien H. T.
Published: March 2011

Bilayer lipid membranes (BLMs), especially self-assembled bilayer lipid membranes on solid supports (s-BLMs), have been used in the last three years as lipid bilayer-based biosensors. In this paper, we will describe as well as review briefly our work on s-BLMs and closely related systems including the preparation and characterization of s-BLMs, hydrogen peroxide-sensitive electrodes based on s-BLMs, alkaline-pretreated aluminum electrodes as pH sensors, immobilization of ferrocene on a s-BLM as anamperometric sensor of Fe(CN)63-/4- ions, cyclic voltanmmetry studies of s-BLMs modified with electron mediators, TCPBQ/TCOBQ modified s-BLMs for pH measurements, TCNQ-modified s-BLMs for glucose detection, and s-BLMs on interdigital electrodes prepared by microelectronic techniques.
Heme Proteins Encapsulated in Sol-Gel Derived Silica Glasses and their Reaction with Ligands
Authors: Lan E. H. , Davidson M. S. , Ellerby L. M. , Dunn B. , Valentine J. Selverstone , Zink J. I.
Published: March 2011

Hemoglobin (Hb) and myoglobin (Mb) were encapsulated in transparent silica glasses prepared by the sol-gel method. The preparation of the silica glasses was tailored so that when proteins were entrapped in the pores of the inorganic matrix, they retained their biochemical activity, i.e. they could bind ligands reversibly. Using optical spectroscopy to monitor ligand binding, we studied the binding of O2, CO, and NO with these two heme proteins encapsulated in silica glasses and compared them to heme proteins in aqueous buffer. Both Hb and Mb in the sol-gel glass bound O2, CO, and NO, producing the same spectroscopic properties as those in aqueous buffer. In addition, silica encapsulated Mb was used to evaluate the rate of ligand (O2) transport through the pores of the glass. When varying oxygen concentration and measuring the time required for full conversion of deoxyMb to MbO2in the silica gel, the time vs. concentration data followed an exponential trend, as expected for diffusion controlled processes.
Peptide Nucleic Acid (PNA). a Structural DNA Mimic
Authors: Nielsen Peter E.
Published: March 2011

Deoxyribonucleic acid (DNA) may be regarded as the central molecule of life since it is the carrier of genetic information; it is the chemical constituent of the genes. DNA is a biopolymer composed of deoxyribonucleoside units connected via phosphodiester bridges (Figure 1a). It is the linear order of the nucleobases (A, C, G & T) that contain the genetic information, whereas the deoxyribose phosphate backbone primarily fulfils a structural role.
Interfacing Conducting Polymers and Biological Macromolecules: A Case Study of Insecticide Biosensor Development
Authors: Marx Kenneth , Ayyagari Madhu , Kamtekar Sanjay , Pande Rajiv , Lim Jeong Ok , Kamath Manjunath , Chittibabu K. G. , Tripathy Sukant , Kumar Jayant , Samuelson Lynne , Akkara Joseph , Kaplan David
Published: March 2011

The creation of smart materials is a current goal of many laboratories including our own. We are involved in studying a number of thin film and monolayer systems which share the common features of involving highly conjugated conducting organic polymers and the evolved properties of specific biological macromolecules. In this report we describe a generic ‘cassette’ methodology for immobilizing biotinylated biological macromolecules to hydrophobic surfaces using a novel class of conducting copolymers of polythiophene. These copolymers are derivatized with long alkyl chains and biotin moieties to bind, respectively, to the hydrophobic surface and the biotinylated species, through the biotin - streptavidin interaction. We utilize the monolayer ‘cassette’ approach to attach a signal transducing biomolecule alkaline phosphatase to the surface of a glass capillary. This produces a flexible system in which chemiluminescence provides the basis for a useful measurement strategy. A novel technique involving the generation of chemiluminescence signal from alkaline phosphatase catalyzed dephosphorylation of a macrocyclic phosphate compound is described. Detection of paraoxon and methyl parathion, both enzyme inhibitors, has been achieved at ppb levels. The technique is rapid, sensitive, and is applicable to the detection of all organophosphorus based insecticides. The technique will be used in developing a fiber;optic biosensor for remote detection of insecticides.
Biophysics of Energy Converting Model Proteins
Authors: Urry D. W.
Published: March 2011

The biophysics of energy converting model proteins is presented as a general set of three postulates with fifteen corollaries for fifteen subtypes of molecular machines. All of the molecular machines utilize a common structural transition, an inverse temperature transition characterized by increased hydrophobic folding and/or assembly as the temperature is increased through a transition temperature range identified by Tt. These molecular machines, which can be polymers (e.g., proteins or protein-based polymers), are capable of interconverting the free energies involving the six intensive variables of mechanical force, temperature, pressure, chemical potential, electrochemical potential, and electromagnetic radiation.

First-order molecular machines of the Tt-type are molecular engines which, with the appropriate energy input, can result in the production of useful mechanical motion. Postulate I is for the thermally-driven molecular engine. Postulate II with four corollaries is for the four cases where the energy inputs drive hydrophobic folding by lowering the temperature, Tt, at which the inverse temperature transition occurs. This is called the ΔTt-mechanism. The four energy inputs that have been shown to change the value of Ttare due to changes (1) in concentrations of chemicals, (2) in oxidative state of attached prosthetic groups, (3) in pressure, and (4) resulting from the absorption of light by attached chromophores. Postulate III with ten corollaries are for the ten pairwise energy conversions involving the intensive variables listed above exclusive of mechanical force. These energy conversions utilize the hydrophobic association transition but do not result in the motion implicit in the folding or assembly process. These are second-order molecular machines of the Tt-type.

The physical basis for the ΔTt-mechanism of energy conversion of Postulates II and III is proposed to arise due to competition for hydration between apolar (hydrophobic) and polar moieties. This competition is capable of effecting large changes in pKa values of Glu, Asp, Lys and His residues. This mechanism is proposed to be a dominant process in protein folding, assembly, and function.
Chemical Synthesis of Nanostructures
Authors: Seeman Nadrian C. , Zhang Yuwen , Fu Tsu-Ju , Zhang Siwei , Wang Yinli , Chen Junghuei
Published: March 2011

The control of structure on the nanoscale relies on intermolecular interactions whose specificity and geometry can be treated on a predictive basis. With this criterion in mind, DNA is an extremely favorable construction medium: The sticky-ended association of DNA molecules occurs with high specificity, and it results in the formation of double helical DNA, whose structure is well known. The use of stable branched DNA molecules permits one to make stick-figures. We have used this strategy to construct a covalently closed DNA molecule whose helix axes have the connectivity of a cube. The molecule has twelve double helical edges; each edge is two helical turns in length, resulting in a hexacatenane, each of whose strands corresponds to a face of the object. The cube has been fabricated in solution, which is inefficient. We have developed a solid-support-based synthetic methodology that is much more effective. The key features of the technique are control over the formation of each edge of the object, and the topological closure of each intermediate. Each edge results from the restriction of two hairpins, which are then ligated together. The isolation of individual objects on the surface of the support permits one to use both symmetric and asymmetric sites in the formation of edges that close polygons. We have used solid-support-based methodology to construct a molecule whose helix axes have the connectivity of a truncated octahedron. This figure has 14 faces, of which six are ideally square and eight are hexagonal; this Archimedean polyhedron contains 24 vertices and 36 edges. Control of topology is strong in this system, but control of 3-D structure remains elusive. Topological control is enhanced by the use of topological protection techniques. Our key aim is the formation of prespecified 2-D and 3-D periodic structures with defined topologies. Applications envisioned include nanomanipulators and scaffolding for molecular electronic devices.
The Tissue Engineering Approach to Ligament Reconstruction
Authors: Dunn Michael G. , Liesch J. B. , Tiku M. L. , Maxian S. H. , Zawadsky J. P.
Published: March 2011

Previous studies in our laboratory showed that acellular collagen scaffold implants induce tissue ingrowth and perform similar to autografts following reconstruction of rabbit Achilles tendon or anterior cruciate ligament (ACL). We chronologically review these and related studies, and report preliminary development of fibroblast-seeded collagen scaffolds potentially useful for ACL reconstruction. The ‘healing potential’ of fibroblasts was measured within collagen scaffolds in vitro, as a function of fibroblast source. Aligned collagen scaffolds were seeded with fibroblasts from rabbit ACL, synovium, patellar tendon, or skin. Fibroblast viability, adherence, spreading, proliferation, and protein and collagen deposition were measured on collagen scaffolds. The fibroblasts attached to the scaffolds, and spread along the long axis of the collagen fibers. ACL fibroblasts adhered better than other fibroblast types; however, the ACL fibroblasts proliferated at the slowest rate. Patellar tendon fibroblasts proliferated at the most rapid rate. All four of the fibroblast types secreted protein and collagen within the collagen scaffolds.

Preliminary in vivo studies suggest that fibroblasts seeded onto collagen scaffolds can remain viable following reimplantation into the donor rabbit. Ongoing studies will elucidate the role of autogenous seeded fibroblasts in neoligament formation/remodeling. These ‘ligament analogs’ are potentially useful for clinical ACL reconstruction: fibroblasts would be obtained from biopsy, cultured, seeded onto a collagen scaffold, and implanted as an ACL substitute into the same patient.
Cell Interactions With Fibronectin-Coated Electrically Conducting Polypyrrole Thin Films
Authors: Wong Joyce Y. , Langer Robert , Ingber Donald E.
Published: March 2011

Surface properties of electrically conducting polymers, including charge-density and wettability, can be altered reversibly by oxidation or reduction. Thus, these materials are interesting systems on which to study the interactions of proteins and cells with surfaces. The properties of polypyrrole were studied in environments suitable for protein adsorption and cell culture. Optically transparent films of polypyrrole were synthesized, and the stability of the oxidized and reduced states in aqueous media were studied. UV/VIS spectroscopy, cyclic voltammetry, and spectroelectrochemistry measurements confirmed the oxidation state of the polymer films. The positively-charged form of polypyrrole could be changed to its neutral form by applying a constant potential (-0.5 V vs. Ag/AgCl reference). It was found that the shape of bovine aortic endothelial cells on fibronectin-coated polypyrrole films can be controlled by varying the oxidation state of the polypyrrole.
Macromolecular Nutriend Limitations of Encapsulated Cells
Authors: Hancock Erik Einar , Cima Linda Griffith
Published: March 2011

Encapsulated cells are likely to encounter transport limitations of trace nutrients carried by macromolecules due to a high diffusion resistance in the encapsulating membrane. We modeled the transport of transferrin to encapsulated cells and found that the transport limitation of transferrin is potentially significant in comparison to oxygen, which is limiting in unencapsulated tissue. Since transferrin is the primary biological iron carrier, deprivation of transferrin to encapsulated cells may limit long term function and viability in vivo.
A Photopaiterned Glucose Responsive Hydrogel for Use in a Conductimetric Sensor
Authors: Lesho Matthew J. , Sheppard Norman F.
Published: March 2011

The glucose responsive hydrogels developed by Horbett et al. [1, 2] are potentially useful as materials for constructing glucose sensors. The construction of microsensors presents challenges in developing processes for preparing these gels that are compatible with semiconductor fabrication technology.

We have lithographically patterned a pH-sensitive copolymer (poly-(2-hydroxyethyl methacrylate-co-dimethyl aminoethyl methacrylate) 90:10 (mole ratio) (HEMA/DMA) from a prepolymer solution of monomers, crosslinker, solvent, and a viscosity agent (p(HEMA)). Varying the spin speed and p(HEMA) concentration resulted in reproducible thicknesses between 5 and 25 μm. pH sensors produced by this method showed sensitivity ranging from 20 to 50%/pH and a response time (10%–90%) of 6.8 minutes. Sensitivity dropped by a factor of two over a 24 day testing period. The limited lifetime is thought to be due to loss of adhesion of the polymer to the substrate.

Derivatizing glucose oxidase with a photoactivatible crosslinker allowed it to be covalently immobilized onto the surface of the gel layer in a spatially specific manner. After immobilization, GOX specific staining showed that enzyme activity was preserved, however the amount of enzyme immobilized was insufficient to create a working glucose sensor.
Poly(Methacrylic Acid-g-Ethylene Glycol) Hydrogels as pH Responsive Biomedical Materials
Authors: Bell Cristi L. , Peppas Nicholas A.
Published: March 2011

Novel graft copolymeric, pH responsive hydrogels have been synthesized by solution polymerization. Poly(methacrylic acid-g-ethylene glycol) hydrogels exhibit reversible complexation as a function of pH because of hydrogen bonding between the PEG grafts and the PMAA main chains. These gels are being developed as pH responsive membranes for use in biomedical applications. ATR-FTIR results indicate that there is hydrogen bonding occurring in membranes swollen under conditions favorable for complexation. Equilibrium swelling studies have shown that the pH of the surrounding environment has a significant effect on the swelling behavior of these membranes. The swelling behavior has also been shown to respond rapidly to changing pH conditions. P(MAA-g-EG) membranes also show pH sensitive permeability toward solutes as a result of this environmentally sensitive swelling.
Effects of Temperature on Bulk Properties of Hydrogels Made from Hydrophobically Modified Hydroxyethyl Cellulose in Surfactant Solutions
Authors: Wu Shun-Yuan , Steiner Carol A.
Published: March 2011

The temperature response of hydrogels made from hydrophobically modified water soluble polymers is complicated by the fact that while the hydrophobilic backbone becomes dehydrated and thus less compatible with aqueous solvents as the temperature is increased, the hydrophobic side chains become more compatible. These opposing effects taken together will govern gel properties such as volume, storage modulus, etc. We will discuss the effects of temperature on the composition, volume and reheological properties of hydrogels made from hydrophobically modified hydroxyethyl cellulose (HMHEC) in aqueous solutions containing the surfactant sodium dodecyl sulfate (SDS).
Collagen as a Biomaterial: An Application in Knee Meniscal Fibrocartilage Regeneration
Authors: Li Shu-Tung , Yuen Debbie , Li Peggy C. , Rodkey William G. , Stone Kevin R.
Published: March 2011

Fibrous typeIcollagen possesses unique physicochemical, mechanical and biological properties which are useful for biomedical applications. Our research in applying collagen materials for various tissue repair has led to the development of a resorbable collagen based implant for meniscal tissue regeneration applications. We discuss here the design and development of this resorbable collagen based implant. The results of safety and efficacy studies indicate that the collagen based implant, if designed properly, can be a safe and effective template to support meniscal tissue regeneration in the knee joint.
Biodegradable Polymer Composites for Temporary Replacement of Trabecular Bone: The Effect of Polymer Molecular Weight on Composite Strength and Modulus
Authors: Yaszemski Michael J. , Mikos Antonios G. , Payne Richard G. , Hayes Wilson C.
Published: March 2011

Our laboratory has been developing a particulate composite material as a temporary replacement for trabecular bone. The material is degradable in physiologic fluids, and uses starting materials that the body can metabolize and excrete. This study investigates the influence of the molecular weight of one component, a linear polyester, on the mechanical strength of the composite material. The compressive strength and modulus increase from “low” to “medium” molecular weight, but do not increase further from “medium” to “high” molecular weight. Low, medium, and high are relative to the highest molecular weight attainable with the current reaction scheme, which is a number average molecular weight (Mn) of 2,038 and a weight average molecular weight (Mw) of 11,916.
Immobilization of Protein on Silanized Orthopedic Biomaterials
Authors: Puleo D. A.
Published: March 2011

We have begun to examine methods for biochemically modifying orthopedic biomaterials by covalently immobilizing peptides, proteins, and enzymes. The surfaces of Co-Cr-Mo samples were first silanized using γ-aminopropyltriethoxysilane (APS), which interacts with surface hydroxyl moieties. Derivatization of biomaterial samples with solutions of APS in acetone produced a concentration-dependent number of reactive NH2 groups. The silane layers became unstable and were easily disrupted at concentrations above 2% APS. The enzyme, trypsin, was then coupled to the alkylamine-derivatized samples by formation of Schiff's base linkages via glutaraldehyde. Enzymatic activity of trypsin-conjugated Co-Cr-Mo samples was quantified by determining cleavage of the substrate BAEE. Both alkoxysilane-treated and untreated samples bound trypsin in an active state. When treated with 5 M guanidine hydrochloride to elute noncovalently bound protein, however, nearly all of the trypsin was removed from or rendered inactive on samples either not treated with APS or derivatized with low (<0.5%) concentrations. On the contrary, 1 and 2% APS-treated samples retained appreciable enzyme activity. Approximately 27 and 35% residual trypsin activity was measured on the 1 and 2% APSderivatized Co-Cr-Mo samples, respectively. Active trypsin remained immobilized on the APS-derivatized substrates when at least 35 free amino groups per nm2 of nominal surface area were available for protein coupling.
Hydroxyapatite Coatings of Varying Crystallinity
Authors: Maxian Suzanne H. , Liesch Janice B. , Tiku Moti L. , Zawadsky Joseph P. , Dunn Michael G.
Published: March 2011

Questions remain as to the integrity of hydroxyapatite (HA) coatings on orthopaedic implants and the possibility of failure at the coating/implant interface in vivo. Previous investigations of resorbable HA coated implants showed bone bonding strengths equal to non-resorbable HA coated surfaces in interference fit surgical model. If the concept of a resorbing coating will alleviate concerns of interface failure, further investigation as to the mode of coating resorption and the cellular events at the interface are required. The effect of coating these implants with Matrigel, as a means to enhance bone cell attachment and growth was studied. Fibroblast cell behavior on resorbable, non-resorbable HA coated and uncoated rough titanium implants were studied at 4 and 24 hours for attachment and spreading. Postnatal rat calvarial cell attachment, growth and morphology studies were also performed on these three implants and on tissue culture plates with and without Matrigel at 2, 7, and 10 days. Resorbable HA coatings showed greater surface activity and cell spreading, but not greater cell attachment at 4 and 24 hours. Greater alkaline phosphatase production per cell was seen on Matrigel coated tissue culture plates than uncoated wells. Cytoplasmic processes similar to osteocytic canalicular networks were seen. Matrigel coating on the three types of implants showed slightly greater alkaline phosphatase production of cells than without Matrigel coating.
Control of Pore Size and Morphology in Collagen Microspheres
Authors: Maffia Gennaro J.
Published: March 2011

Collagen microspheres are used to immobilize mammalian and hybridoma cells in commercial cell culture in a continuous fluidized bed bioreactor. One advantage of this technology is the high cell densities and the resulting high reactor volume productivity. Cell densities have exceeded 108 cells per milliliter of reactor volume in steady state culture of CHO cells. The microsphere is manufactured in a multi-stage batch process that initially involves pretreating insoluble, Type I bovine hide collagen to remove fats, triglycerides and any soluble compounds. The collagen fibers are then milled and dispersed in an acid solution. Water to collagen ratios of 500/1, mass basis, have been achieved. Stainless steel weighting material is blended in the collagen dispersion in order to control the specific gravity. The dispersion is cast into droplets which are in turn frozen, thermally soaked, lyophilized, fractionated by terminal velocity, crosslinked and finally sterilized. The morphology and pore size are created during the soaking phase, wherein the completely frozen collagen dispersion is partially melted to provide a mobile phase for the collagen fibrils to rearrange. In their dispersed form, collagen fibrils have additional uses in separation and purification due to the ability to precisely control the swelling and collapsing by pH, surface area and concentration.
Design of Bioerodible Devices with Optimal Release Characteristics
Authors: Zygourakis Kyriacos
Published: March 2011

The development of a computational tool to design bioerodible devices with optimal release characteristics is presented. This computational tool uses cellular automata and discrete iterations to model and simulate the release of bioactive agents (drugs) from bioerodible matrices. The simulations can accurately model surface erosion processes in multicomponent systems of arbitrary geometry and with different dissolution rates for each component. Simulation results are analyzed to show how the overall release rates are affected by the intrinsic dissolution rates, drug loading and the dispersion of the drug in the bioerodible matrix. Heterogeneities in the structure of the bioerodible matrix that can lead to local variations of erosion rates are also considered. A strongly nonlinear dependence of release rates on drug loading and dispersion is obtained and the effects of matrix heterogeneities are elucidated. Finally, guidelines are presented for screening of alternatives to minimize the development effort and experimentation required for designing devices with desired release characteristics.
Using Molecular-Beam Mass Spectrometry to Study the Pecvd of Diamondlike Carbon Films
Authors: Graff I.B. , Pugliese R.A. , Westmoreland P.R.
Published: March 2011

Molecular-beam mass spectrometry has been used to study plasma-enhanced chemical vapor deposition (PECVD) of diamondlike carbon films. A threshold-ionization technique was used to identify and quantify species in the plasma. Mole fractions of H, H2, CH4, C2H2, C2H6 and Ar were measured in an 83.3% CH4/Ar mixture at a pressure of 0.1 torr and a total flow of 30 sccm. Comparisons were made between mole fractions measured at plasma powers of 25W and 50W. These results were compared to measured concentration profiles and to film growth rates.
Mass Spectrometric Analysis of a High Pressure, Inductively Coupled Plasma During Diamond Film Growth
Authors: Greuel Peter G. , Yoon Hyun J. , Ernie Douglas W. , Roberts Jeffrey T.
Published: March 2011

Determination of the gas phase composition at or near a substrate surface during plasma assisted chemical vapor deposition presents a challenging problem. The species located at a growing surface include highly reactive radicals which are difficult to detect in atmospheric plasma conditions. A system has been designed which consists of an inductively coupled rf plasma reactor linked to a quadrupole mass spectrometer (QMS) via a supersonic convergent-divergent nozzle. Differential pumping in the transient stages allows the plasma chamber to be operated at or near atmospheric pressures, while facilitating the detection of reactant species present in the growth boundary layer with the QMS.
Gas-Phase and Surface Decomposition of Tris-Dimethylamino Arsenic
Authors: Xi Ming , Salim Sateria , Jensen Klavs F. , Bohling David A.
Published: March 2011

Gas phase and surface decomposition reactions of a novel arsenic precursor tris- (dimethylamino) arsenic (DMAAs) have been studied. Optical fiber-based Fourier transform infrared spectroscopy was used to monitor, in situ, the gas-phase pyrolysis of DMAAs. Homolysis of the arsenic-nitrogen bond with formation of dimethylamine radicals was identified as the key gas-phase reaction pathway. Formation of methylmethyleneimine from reactions with the decomposition products was directly observed. Surface decomposition of DMAAs on GaAs(100) was investigated by low energy electron diffraction and temperature-programmed reaction under ultra-high vacuum conditions. DMAAs adsorbed onto GaAs(100)-(4x6) was found to decompose with 100% efficiency and two surface reaction pathways were identified. The first reaction channel was homolysis of the arsenic-nitrogen bond with formation of dimethylamine radicals, whereas the second pathway involved a β-hydrogen transfer.
Study of Silicon Incorporation in GaAs Movpe Layers Grown With Tertiarybutylarsine
Authors: Redwing J.M. , Kuech T.F. , Simka H. , Jensen K.F.
Published: March 2011

MOVPE growth experiments have been used to evaluate the role of gas phase and surface chemistry in the silicon doping of GaAs films grown using SiH4 and Si2H6 dopant sources and tertiarybutylarsine (t-C4H9AsH2 or TBAs) as the Group V source. The use of TBAs with SiH4 results in a greater Si doping efficiency and weaker dependence on growth temperature than is typically observed with AsH3. Gas phase pyrolysis studies combined with reactor residence time experiments indicate that heterogeneous chemistry is responsible for this enhanced Si doping process. TBAs has much less of an effect on Si incorporation from Si2H6, a doping process controlled by homogeneous Si2H6 chemistry. Increased Si doping from Si2H6 with TBAs can be attributed to contributions from the enhanced doping efficiency of SiH4, a product of Si2H6 decomposition. The influence of TBAs on SiH4 doping chemistry was found to improve the doping uniformity of GaAs films grown in our reactor, from +/-12% for films grown with AsH3to +/-5% for TBAs-based material.
Preparation and Evaluation of Erbium Tris(Amide) Source Compounds for Erbium Doping of Semiconducting Materials
Authors: Rees William S. , Lay Uwe W. , Greenwald Anton C.
Published: March 2011

Rare earth elements are important as dopants in the preparation of semiconductors, particularly for temperature-independent optical devices. The compound Er{N\Si(CH3)3]2}3 has been demonstrated to be a suitable source compound for erbium doping of semiconducting materials. Further investigations of this and related compounds have been carried out. New compounds have been characterized by 1H NMR, FTIR, TGA and elemental analysis techniques. Vapor pressures and decomposition profiles have been examined for these compounds.
Growth of InAs and (InAs)1(GaAs)l Superlattice Quantum Well Structures on GaAs by Atomic Layer Epitaxy Using Trimethylindium-Dimethylethylamine Adduct
Authors: Ohtsuka Nobuyuki , Ueda Osamu
Published: March 2011

Atomic layer epitaxy (ALE) of InAs has been developed using trimethylindium-dimethylethylamine adduct (TMIDMEA) as a novel In source. Distinct self-limiting growth of InAs was successfully carried out over a wide temperature range from 350°C to 500°C because of the high thermal stability of TMIDMEA. The possible growth temperature range for ALE-InAs was extended by using TM1DMEA. These results lead us to conclude that the use of TMIDMEA enables us to grow InAs/GaAs heterostructures at a single growth temperature. Using this technique, (InAs)1(GaAs)l short period superlattice (12 periods) quantum-well structures were grown on a GaAs(100) substrate at 460°C. A photoluminescence peak at 1.3 µm was observed in these structures at room temperature.
The Surface Chemistry of CdTe Mocvd
Authors: Liu Wen-Shryang , Aupp Gregory B.
Published: March 2011

Temperature programmed desorption (TPD) studies in ultra high vacuum revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe. Dimethylcadmium partially decomposes to produce Cd adatoms; a large fraction of the excess Cd atoms desorb upon heating. In contrast, DETe desorbs without decomposing, suggesting that the rate limiting step in CdTe MOCVD on CdTe(111)A is surface decomposition of the tellurium alkyl.