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Record 2921 to 2940

Multimillimetre-large superlattices of air-stable iron-cobalt nanoparticles
Desvaux, C., C. Amiens, et al. (2005), Nat Mater 4(10): 750-3.
Abstract: Self-organization of nanoparticles into two- and three-dimensional superlattices on a large scale is required for their implementation into nano- or microelectronic devices. This is achieved, generally after a size-selection process, through spontaneous self-organization on a surface, layer-by-layer deposition or the three-layer technique of oversaturation, but these techniques consider superlattices of limited size. An alternative method developed in our group involves the direct formation in solution of crystalline superlattices, for example of tin nanospheres, iron nanocubes or cobalt nanorods, but these are also of limited size. Here, we report the first direct preparation in solution of multimillimetre-sized three-dimensional compact superlattices of nanoparticles. The 15-nm monodisperse FeCo particles adopt an unusual short-range atomic order that transforms into body-centred-cubic on annealing at 500 degrees C. The latter process produces an air-stable material with magnetic properties suitable for radiofrequency applications.

Multiphase nature and structure of biomaterials studied by ultrasounds
Kaczmarek, M., M. Pakula, et al. (2000), Ultrasonics 38(1-8): 703-7.
Abstract: The paper discusses the applicability of a two-phase model of saturated porous materials for a description of the results of broadband ultrasonic studies of wave parameters in bovine trabecular bone. The analysis is focused on the role of the internal structure of the materials in the propagation of dilatational waves within the frequency range with a significant attenuation of wave energy due to absorption and scattering. The applicability of ultrasonic studies for the determination of characteristic macro- and micro-structural parameters of biomaterials using a model-based approach is considered.

Multiple overlapping drug-eluting stents to treat diffuse disease of the left anterior descending coronary artery
Tsagalou, E., A. Chieffo, et al. (2005), J Am Coll Cardiol 45(10): 1570-3.
Abstract: OBJECTIVES: We sought to determine the safety and efficacy of using multiple overlapping drug-eluting stents (DES) in patients with diffuse left anterior descending coronary artery (LAD) disease. BACKGROUND: Diffuse LAD disease represents a therapeutic challenge. Results after coronary artery bypass surgery are suboptimal, whereas the use of bare metal stents is limited by high rates of restenosis. The introduction of DES prompted treatment of long diffuse disease with multiple overlapping stents. METHODS: All consecutive patients with de novo diffuse LAD disease treated with more than 60-mm long DES from April 2002 to March 2004 were analyzed. RESULTS: The study population consisted of 66 patients. Thirty-nine patients were treated with sirolimus-eluting stents (SES), average length 84 +/- 22 mm, and 27 patients with paclitaxel-eluting stents (PES), average length 74 +/- 14 mm. The number of stents implanted per patient was 2.8 +/- 0.7, whereas the mean total stent length for the LAD treatment was 80 +/- 20 mm. Angiographic as well as procedural success was achieved in 95% of cases. Eleven (16.6%) patients had in-hospital non-Q-wave myocardial infarction (five SES and six PES), and one patient developed intraprocedural stent thrombosis. All patients had clinical follow-up, and 52 patients (79%) had an angiographic follow-up at six months. Hierarchical major adverse cardiac event rate was 15% (7.5% for SES and 7.5% for PES). No patients died, one patient had non-Q-wave myocardial infarction (non-index vessel), and 10 patients (15%) underwent target vessel revascularization. CONCLUSIONS: The implantation of multiple overlapping DES in patients with a diffusely diseased LAD is relatively safe and associated with good midterm clinical outcomes.

Multiscale structure of sheet nacre
Rousseau, M., E. Lopez, et al. (2005), Biomaterials 26(31): 6254-62.
Abstract: This work was conducted on Pinctada maxima nacre (mother of pearl) in order to understand its multiscale ordering and the role of the organic matrix in its structure. Intermittent-contact atomic force microscopy with phase detection imaging reveals a nanostructure within the tablet. A continuous organic framework divides each tablet into nanograins. Their shape is supposed to be flat with a mean extension of 45nm. TEM performed in the darkfield mode evidences that at least part of the intracrystalline matrix is crystallized and responds like a 'single crystal'. The tablet is a 'hybrid composite'. The organic matrix is continuous. The mineral phase is thus finely divided still behaving as a single crystal. It is proposed that each tablet results from the coherent aggregation of nanograins keeping strictly the same crystallographic orientation thanks to a hetero-epitaxy mechanism. Finally, high-resolution TEM performed on bridges from one tablet to the next, in the overlying row, did not permit to evidence a mineral lattice but crystallized organic bridges. The same organic bridges were evidenced by SEM in the interlaminar sequence.

Mutual relationships between soils and biological carrier systems
Zohar-Perez, C., I. Chet, et al. (2005), Biotechnol Bioeng 92(1): 54-60.
Abstract: Improved viability and antagonistic activity of biocontrol agents during soil inoculation is of crucial importance to their effective application. The chitinolytic bacterium Serratia marcescens was used as a model organism to study the efficacy of freeze-dried alginate beads (in comparison to their non-dried counterparts) as possible carriers for immobilized biocontrol agents. The release of bacteria and chitinolytic enzyme from alginate beads, before and during their application in soil, was examined, and the beads' physical properties characterized. Dispersal of the alginate bead-entrapped S. marcescens in the soil resulted in high soil cell densities throughout the 35 days of the experiment. Chitin inclusion in the beads resulted in significantly higher chitinolytic activity of S. marcescens, increased dry-bead porosity and decreased stiffness. Rehydration of the dried beads (after immersion in soil) resulted in a sixfold increase in weight due to water absorption. No significant differences were found in bacterial count inside the non-dried (gel) versus dried beads. However, higher cell densities and chitinase activity were detected in soil containing dried beads with chitin than in that containing their non-dried counterparts. The biological performance of S. marcescens was examined in the greenhouse: a free cell suspension reduced bean (Phaseolus vulgaris L.) disease by 10%, while immobilized bacteria found in the dried, chitin-containing beads reduced disease by 60%.

Mylar and Teflon-AF as cell culture substrates for studying endothelial cell adhesion
Anamelechi, C. C., G. A. Truskey, et al. (2005), Biomaterials 26(34): 6887-96.
Abstract: The textured and opaque nature of Dacron and ePTFE has prevented the use of these fabrics in conventional cell culture techniques normally employed to optimize cell attachment and retention. This lack of optimization has led, in part, to the poor performance of endothelialization strategies for improving vascular graft patency. Here we show that thin, transparent films of Mylar and Teflon-AF are viable in vitro cell culture mimics of Dacron and ePTFE vascular graft materials, particularly for the study of protein mediated endothelial cell (EC) attachment, spreading and adhesion. Glass substrates were used as controls. X-ray photoelectron spectroscopy (XPS) and contact angle analysis showed that Mylar and Teflon-AF have surface chemistries that closely match Dacron and ePTFE. (125)I radiolabeling was used to quantify fibronectin (FN) adsorption, and FN and biotinylated-BSA "dual ligand" co-adsorption onto glass, Mylar and Teflon-AF substrates. Native human umbilical vein endothelial cells (HUVEC) and streptavidin-incubated biotinylated-HUVEC (SA-b-HUVEC) spreading was measured using phase contrast microscopy. Cell retention and adhesion was determined using phase contrast microscopy under laminar flow. All surfaces lacking protein pre-treatment, regardless of surface type, showed the lowest degree of cell spreading and retention. Dual ligand treated Mylar films showed significantly greater SA-b-HUVEC spreading up to 2 h, but were similar to HUVEC on FN treated Mylar at longer times; whereas SA-b-HUVEC spreading on dual ligand treated Teflon-AF was never significantly different from HUVEC on FN treated Teflon-AF at any time point. SA-b-HUVEC retention was significantly greater on dual ligand treated Mylar compared to HUVEC on FN treated Mylar over the entire range of shear stresses tested (3.54-28.3 dynes/cm(2)); whereas SA-b-HUVEC retention to dual ligand and HUVEC retention to FN treated Teflon-AF gave similar results at each shear stress, with only the mid-range of stresses showing significant difference in cell retention to Teflon-AF.

Myocardial tolerance to mechanical actuation is affected by biomaterial characteristics
Anstadt, M. P., R. A. Perez-Tamayo, et al. (1994), Asaio J 40(3): M329-34.
Abstract: Direct mechanical ventricular actuation (DMVA) uses a pressure regulated heart cup, fabricated from silicone rubber (SR) for mechanical massage of the heart. Because DMVA has demonstrated potential for long-term circulatory support, investigations are currently exploring the use of more durable materials for fabricating DMVA heart cups. This study assessed the acute effects of heart cups fabricated from SR versus polyurethane (PU) on the myocardium. Dogs (n - 18) received DMVA for 4 hr of ventricular fibrillation (VF) using either SR (n = 10) or PU (n = 8) cups. Microspheres were used to determine perfusion during sinus rhythm (control) and at 2 and 4 hr of support. After support, myocardial biopsies were assayed for high energy phosphate content. Results demonstrated that PU cups required relatively frequent adjustments in drive line parameters that were likely due to material softening during PU cup support. Both PU and SR cups achieved similar hemodynamics during 4 hr of support. Myocardial perfusion, however, demonstrated a marked hyperemia at 4 hr of PU versus SR cup support. Regional high energy phosphate content was significantly decreased in hearts supported by PU versus SR cups. These results suggest that the relatively compliant characteristics of SR materials are important for achieving effective DMVA support without injuring the myocardium.

Nano- and micro-fiber combined scaffolds: A new architecture for bone tissue engineering
Tuzlakoglu, K., N. Bolgen, et al. (2005), J Mater Sci Mater Med 16(12): 1099-104.
Abstract: One possible interesting way of designing a scaffold for bone tissue engineering is to base it on trying to mimic the biophysical structure of natural extracellular matrix (ECM). This work was developed in order to produce scaffolds for supporting bone cells. Nano and micro fiber combined scaffolds were originally produced from starch based biomaterials by means of a fiber bonding and a electrospinning, two step methodology. The cell culture studies with SaOs-2 human osteoblast-like cell line and rat bone marrow stromal cells demonstrated that presence of nanofibers influenced cell shape and cytoskeletal organization of the cells on the nano/micro combined scaffolds. Moreover, cell viability and Alkaline Phosphatase (ALP) activity for both cell types was found to be higher in nano/micro combined scaffolds than in control scaffolds based on fiber meshes without nanofibers.Consequently, the developed structures are believed have a great potential on the 3D organization and guidance of cells that is provided for engineering of 3-dimensional bone tissues.

Nanobiotechnology: implications for the future of nanotechnology in orthopedic applications
Sato, M. and T. J. Webster (2004), Expert Rev Med Devices 1(1): 105-14.
Abstract: Nanotechnology involves the use of materials with components, such as fibers, grains and particles, that have dimensions of less than 100 nm. While numerous advantages of nanomaterials have been elucidated for catalytic, processing, mechanical, electrical, and optical applications, few have been described for orthopedic applications. Better orthopedic biomaterials are needed since the average lifetime of a bone biomaterial is less than 15 years. This review discusses recent studies that have been conducted to determine the efficacy of nanophase materials as bone implants. In doing so, it is suggested that nanophase materials can be synthesized to possess similar nanometer dimensions to components of bone tissue to promote new bone formation, compared with conventional orthopedic implant materials.

Nano-C60 cytotoxicity is due to lipid peroxidation
Sayes, C. M., A. M. Gobin, et al. (2005), Biomaterials 26(36): 7587-95.
Abstract: This study examines the biological effects of water-soluble fullerene aggregates in an effort to evaluate the fundamental mechanisms that contribute to the cytotoxicity of a classic engineered nanomaterial. For this work we used a water-soluble fullerene species, nano-C60, a fullerene aggregate that readily forms when pristine C60 is added to water. Nano-C60 was cytotoxic to human dermal fibroblasts, human liver carcinoma cells (HepG2), and neuronal human astrocytes at doses>or= 50 ppb (LC50=2-50 ppb, depending on cell type) after 48 h exposure. This water-soluble nano-C60 colloidal suspension disrupts normal cellular function through lipid peroxidation; reactive oxygen species are responsible for the membrane damage. Cellular viability was determined through live/dead staining and LDH release. DNA concentration and mitochondrial activity were not affected by the nano-C60 inoculations to cells in culture. The integrity of cellular membrane was examined by monitoring the peroxy-radicals on the lipid bilayer. Subsequently, glutathione production was measured to assess the cell's reaction to membrane oxidation. The damage to cell membranes was observed both with chemical assays, and confirmed physically by visualizing membrane permeability with high molecular weight dyes. With the addition of an antioxidant, L-ascorbic acid, the oxidative damage and resultant toxicity of nano-C60 was completely prevented.

Nano-composite of poly(L-lactide) and surface grafted hydroxyapatite: mechanical properties and biocompatibility
Hong, Z., P. Zhang, et al. (2005), Biomaterials 26(32): 6296-304.
Abstract: In order to improve the bonding between hydroxyapatite (HAP) particles and poly(L-lactide) (PLLA), and hence to increase mechanical properties of the PLLA/HAP composite as potential bone substitute material, the HAP nano-particles were surface-grafted with PLLA and further blended with PLLA. The structure and properties of the composites were subsequently investigated by the mechanical property testing, the differential scanning calorimeter measurements (DSC), the scanning electron microscopy (SEM), the polarized optical microscopy (POM), and the cell culture. The PLLA molecules grafted on the HAP surfaces, as inter-tying molecules, played an important role in improving the adhesive strength between the particles and the polymer matrix. At a low content (approximately 4 wt%) of surface grafted-HAP (g-HAP), the PLLA/g-HAP nano-composites exhibited higher bending strength and impact energy than the pristine PLLA, and at a higher g-HAP content (e.g., 20 wt%), the modulus was remarkably increased. It implied that PLLA could be strengthened as well as toughened by g-HAP nano-particles. The results of biocompatibility test showed that the g-HAP existing in the PLLA composite facilitated both adhesion and proliferation of chondrocytes on the PLLA/g-HAP composite film.

Nanoconstructions based on double-stranded nucleic acids
Yevdokimov, Y. M., S. G. Skuridin, et al. (2005), Int J Biol Macromol 36(1-2): 103-15.
Abstract: We describe the formation and properties of nanoconstruction that consists of the double-stranded DNA molecules located at distance of 35-50 A in the spatial structure of particles of their cholesteric liquid-crystalline dispersions and cross-linked by artificial nanobridges. The resulting nanostructures possess the peculiar spatial and optical properties.

Nano-devitrification of glassy alloys
Louzguine-Luzgin, D. V. and A. Inoue (2005), J Nanosci Nanotechnol 5(7): 999-1014.
Abstract: This overview paper summarizes a large number of data connected with nano-devitrification of metallic glassy and amorphous alloys on heating which form nanoscale crystalline or quasicrystalline particles. In some alloys this effect leads to formation of the nanocomposites with enhanced mechanical properties compared to fully glassy and crystalline alloys.

Nanofiber generation of hydroxyapatite and fluor-hydroxyapatite bioceramics
Kim, H. W. and H. E. Kim (2005), J Biomed Mater Res B Appl Biomater
Abstract: In this study, we produced hydroxyapatite (HA) and fluor-hydroxyapatite (FHA) bioceramics as a novel geometrical form, the nanoscale fiber, for the biomedical applications. Based on the sol-gel precursors of the apatites, an electrospinning technique was introduced to generate nanoscale fibers. The diameter of the fibers was exploited in the range of a few micrometers to hundreds of nanometers (1.55 mum-240 nm) by means of adjusting the concentration of the sols. Through the fluoridation of apatite, the solubility of the fiber was tailored and the fluorine ions were well released from the FHA. The HA and FHA nanofibers produced in this study are considered to find potential applications in the biomaterials and tissue engineering fields. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2005.

Nanogold particle-enhanced oriented adsorption of antibody fragments for immunosensing platforms
Wang, H., J. Wu, et al. (2005), Biosens Bioelectron 20(11): 2210-7.
Abstract: A general design strategy for immunosensing platforms has been proposed on the basis of Nanogold particle-enhanced oriented adsorption of antibody fragments. Quartz crystal microbalance (QCM) as a model transducer was fabricated with plasma-polymerized film (PPF) of n-butyl amine and then with nanogold particles resulting in a PPF-nanogold adsorption procedure for half-IgG fragments obtained by reduction of intact immunoglobulin (IgG). Thermodynamic studies reveal that the proposed procedure is superior to the traditional oriented ones in that it created immunosurface of increased antibody surface density (amount) and antigen binding constants. Sensors produced according to the new immobilization procedure exhibit better immunosensing performances including high sensitivity, fast response rate, and favorable operational stability etc. This Nanogold particle-enhanced immobilization technique may be tailored as a promising alternative for various immunosensing platforms in solid-phase immunoassay and affinity chromatography.

Nanoindentation of injection molded PLA and self-reinforced composite PLA after in vitro conditioning for three months
Wright-Charlesworth, D. D., D. M. Miller, et al. (2005), J Biomed Mater Res A 74(3): 388-96.
Abstract: Poly(lactic acid) (PLA) is used for medical devices such as sutures or orthopedic screws. A standard way to determine the loss of mechanical properties of a degradable polymer would be to soak the polymer in phosphate buffered saline (PBS) and test the desired property as a function of immersion time. This method is not sensitive enough to discern changes in mechanical properties through the cross-section of the polymer and neglects the degradation that is occurring at the molecular level. This article presents results of a nanoindentation study carried out with PLA. The modulus and hardness of PLA is characterized as a function of processing method, immersion time in PBS, and location of the indent. Measuring local properties with the nanoindenter allowed detection of differences in material properties as a function of all three of these variables. The mechanical properties on the edge were lower than the interior of the sample after in vitro degradation, and changes were seen earlier for nanoindentation than for traditional flexural or tensile tests. The nanoindenter is a valuable tool for quantifying changes in material properties and may have applicability for accelerated tests to screen biomaterials.

Nanolayer characterization through wavelength multiplexing of a microsphere resonator
Noto, M., F. Vollmer, et al. (2005), Opt Lett 30(5): 510-2.
Abstract: We optically characterize nanolayer (<150 nm) formation in situ on a silica microsphere in an aqueous environment by simultaneously following the shifts of whispering-gallery modes at two wavelengths. This approach was inspired by layer perturbation theory, which indicates that these two measurements can be used to determine independently both the thickness and the optical dielectric constant. The theory is verified for extreme cases and used to characterize a biophysically relevant hydrogel nanolayer with an extremely small excess refractive index of 0.0012.

Nanoliter-scale synthesis of arrayed biomaterials and application to human embryonic stem cells
Anderson, D. G., S. Levenberg, et al. (2004), Nat Biotechnol 22(7): 863-6.
Abstract: Identification of biomaterials that support appropriate cellular attachment, proliferation and gene expression patterns is critical for tissue engineering and cell therapy. Here we describe an approach for rapid, nanoliter-scale synthesis of biomaterials and characterization of their interactions with cells. We simultaneously characterize over 1,700 human embryonic stem cell-material interactions and identify a host of unexpected materials effects that offer new levels of control over human embryonic stem cell behavior.

Nanoparticle targeting of anticancer drug improves therapeutic response in animal model of human epithelial cancer
Kukowska-Latallo, J. F., K. A. Candido, et al. (2005), Cancer Res 65(12): 5317-24.
Abstract: Prior studies suggested that nanoparticle drug delivery might improve the therapeutic response to anticancer drugs and allow the simultaneous monitoring of drug uptake by tumors. We employed modified PAMAM dendritic polymers <5 nm in diameter as carriers. Acetylated dendrimers were conjugated to folic acid as a targeting agent and then coupled to either methotrexate or tritium and either fluorescein or 6-carboxytetramethylrhodamine. These conjugates were injected i.v. into immunodeficient mice bearing human KB tumors that overexpress the folic acid receptor. In contrast to nontargeted polymer, folate-conjugated nanoparticles concentrated in the tumor and liver tissue over 4 days after administration. The tumor tissue localization of the folate-targeted polymer could be attenuated by prior i.v. injection of free folic acid. Confocal microscopy confirmed the internalization of the drug conjugates into the tumor cells. Targeting methotrexate increased its antitumor activity and markedly decreased its toxicity, allowing therapeutic responses not possible with a free drug.

Nanoparticle-free single molecule anti-stokes Raman spectroscopy
Peyser-Capadona, L., J. Zheng, et al. (2005), Phys Rev Lett 94(5): 058301.
Abstract: In the absence of large, plasmon-supporting nanoparticles, biocompatible dendrimer- and peptide-encapsulated few-atom Ag nanoclusters produce scaffold-specific single molecule (SM) Stokes and anti-Stokes Raman scattering. The strong SM vibrational signatures are enhanced by the Agn transitions in nanoparticle-free samples and cannot arise from plasmon enhancement. Characteristic SM-Raman intermittency is observed, with antibunching of the underlying Agn emission directly confirming the SM nature of the emissive species.

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