bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTThe 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

ABSTRACTDragline 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

ABSTRACTWe 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

ABSTRACTLactose 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

ABSTRACTHigh 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].
BLM-Based Electrochemical Sensors
Authors: Leitmannova-Ottova A. , Liu W. , Zhou T.-A. , Tien H. T. 
Published: March 2011

ABSTRACTBilayer 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

ABSTRACTHemoglobin (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.
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

ABSTRACTThe 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

ABSTRACTThe 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

ABSTRACTThe 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

AbstractPrevious 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

AbstractSurface 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

AbstractEncapsulated 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

AbstractThe 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

AbstractNovel 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

AbstractThe 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

AbstractFibrous 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

AbstractOur 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.