Characterization and human gingival fibroblasts biocompatibility of hydroxyapatite/PMMA nanocomposites for provisional dental implant restoration

The aim of this study was to determine nHA/PMMA composites (H/P) in an optimal ratio with improved cytocompatibility as well as valid physical properties for provisional dental implant restoration. 20 wt.%, 30 wt.%, 40 wt.% and 50 wt.% H/P were developed and characterized using XPS, bending strength test and SEM. Human gingival fibroblasts cultured in extracts or directly on sample discs were investigated by fluorescent staining and MTT assay. Chemical integration in nHA/PMMA interface was indicated by XPS. Typical fusiform cells with adhesion spots were detected on H/P discs. MTT results also indicated higher cell viability in 30 wt.% and 40 wt.% H/P discs (P < 0.05). We conclude that nHA addition to PMMA enhances cytocompatibility and the optimal nHA/PMMA ratio for provisional fixed crowns (PFC) is 0.4:1.     

Tunable cell membrane mimetic surfaces prepared with a novel phospholipid polymer

A novel method to fabricate and tune cell membrane mimetic surfaces was developed based on the use of an amphiphilic random copolymer bearing phosphorylcholine (PC), stearyl and crosslinkable trimethoxysilylpropyl groups synthesized by free radical copolymerization. The polymer was coated on glass coverslips by dip-coating. The coated films were treated in water allowing reorganization of the surface groups to mimic the structure of cell outer membranes. This structure was fixed by crosslinking of the trimethoxysilylpropyl groups linked to the copolymer chains, as ascertained by dynamic contact angle (DCA) and attenuated total reflectance infrared spectroscopy (ATR-FTIR) measurements. Our results indicate that the surface structure can be tuned to a great extent to obtain a stable outer membrane mimetic surface/interface.     

Interaction of endothelial cells with biodegradable strontium-doped calcium polyphosphate for bone tissue engineering

Angiogenesis is of great importance in bone tissue engineering, and has gained large attention in the recent 10 years. However, little research has been done on the effect of biodegradable materials, especially their degradation products on the angiogenesis process. Strontium-doped calcium polyphosphate (SCPP) has been proved to be able to promote osteoblasts growth in vitro before. In the present work, the interaction of endothelial cells (ECs) with the scaffold of SCPP was investigated to evaluate its potential influences on angiogenesis. The cell adhesion on SCPP scaffold as well as the angiogenic behaviors including proliferation, migration and tube-like structure (TLS) formation of ECs treated by its degradation products was tested. The results were compared with those of CPP group and physiological saline (negative control). As the results showed, the surface of SCPP could promote the adhesion and spreading of ECs. Ca²⁺ and Pi as well as Sr²⁺ were the main degradation products of SCPP. They did not inhibit but could promote the proliferation of ECs within 90 days. Moreover, they could induce the migration and TLS formation of ECs. Since SCPP bears the ability to improve the adhesion and angiogenic behaviors of endothelial cells, it might benefit angiogenesis and serve as a more promising scaffold for bone tissue engineering application. Besides, this work may provide a new method for in vitro evaluation of biodegradable materials’ potential effects on angiogenesis.     

Infiltration of colloidal crystal with nanoparticles using capillary forces: a simple technique for the fabrication of films with an ordered porous structure

A dipping method has been developed for the infiltration of nanoparticles into an opal template to fabricate high quality inverse opal. Titania and silica inverse opal films, with a uniform color over centimeter dimensions were derived. As there is no need for special substrates or equipment, a widespread application of this method is anticipated. Received: 23 August 2001 / Accepted: 27 August 2001 / Published online: 30 October 2001     

Hydrogenase-based nanomaterials as anode electrode catalyst in polymer electrolyte fuel cells

We consider hydrogenase-based nanomaterials for possible use as anode electrode catalysts in polymer electrolyte fuel cells (PEFCs). We choose Fe-only hydrogenase component of Desulfovibrio desulfuricans (DdHase) as a hydrogenase complex, and investigate its catalytic activity for H₂ dissociation using ab initio calculations based on density functional theory (DFT). We found two possible H-H bond cleavage pathways, which are heterolytic and possess low activation barriers. Moreover, the H₂ dissociation can be promoted by inducing spin polarization of the H₂ adduct. We report that hydrogenase or hydrogenase-based nanomaterials can manipulate to exhibit the catalytic activity equivalent to the well-known platinum catalyst.     

Systematic considerations for the patterning of photonic crystal devices by electron beam lithography

Photonic crystal devices with feature sizes of a few hundred nanometers are often fabricated by electron beam lithography. The proximity effect, stitching error and resist profiles have significant influence on the pattern quality, and therefore determine the optical properties of the devices. In this paper, detailed analyses and simple solutions to these problems are presented. The proximity effect is corrected by the introduction of a compensating dose. The influence of the stitching error is alleviated by replacing the original access waveguides with taper-added waveguides, and the taper parameters are also discussed to get the optimal choice. It is demonstrated experimentally that patterns exposed with different doses have almost the same edge-profiles in the resist for the same development time, and that optimized etching conditions can improve the wall angle of the holes in the substrate remarkably.     

Surface morphology of laser tracks used for forming the non-smooth biomimetic unit of 3Cr2W8V steel under different processing parameters

Aiming to form the high quality of non-smooth biomimetic unit, the influence of laser processing parameters (pulse energy, pulse duration, frequency and scanning speed in the present work) on the surface morphology of scanned tracks was studied based on the 3Cr2W8V die steel. The evolution of the surface morphology was explained according to the degree of melting and vaporization of surface material, and the trend of mean surface roughness and maximum peak-to-valley height. Cross-section morphology revealed the significant microstructural characteristic of the laser-treated zone used for forming the functional zone on the biomimetic surface. Results showed that the combination of pulse energy and pulse duration plays a major role in determining the local height difference on the irradiated surface and the occurrence of melting or vaporization. While frequency and scanning speed have a minor effect on the change of the surface morphology, acting mainly by the different overlapping amount and overlapping mode. The mechanisms behind these influences were discussed, and schematic drawings were introduced to describe the mechanisms.     

The application with tetramethyl pyrazine for antithrombogenicity improvement on silk fibroin surface

Chuanxiongqin (tetramethyl pyrazine, TMPZ) is an active ingredient of the Chinese herb and was used to improve the anticoagulant activity of silk fibroin (SF). The side methyl of TMPZ was oxidized, and then linked to polyacrylic acid (PAA) via an ester bond. The prepared conjugate was further mixed with SF solutions at different ratios to make blend films. The resulting products were characterized by FTIR, UV spectrometer and X-ray photoelectron spectroscopy (XPS). The in vitro antithrombogenicity were evaluated by the activated partial thromboplastin time (APTT) and the prothrombin time (PT). It was shown that blend films had longer coagulation time than the pure SF film.     

Radiation Acoustic Field of a Linear Phased Array on a Cylindrical Surface

A new linear ultrasonic phased array fixed on a cylindrical surface is designed. This kind of the cylindrical phased array can meet the specific requirements of the application in testing pipe quality inside pipes. Using the transducer, we can not only avoid mechanical rotating but also test the quality of any point in a pipe by ultrasonic phase array technology. The focused acoustic field distributions in the axial, radial and tangential directions of the transducer are investigated theoretically by numerical simulation. The energy flux density, the width of the main lobe, the imaging resolution, the grating lobe elimination and other characteristics are analysed. The effect of the focal distance, effective aperture, transducer radius, number of total element, and steering angle on the acoustic field distribution is also studied.thoroughly. Many important results are obtained.     

Bridging of lateral nanoelectrodes with a metal particle chain

Received: 4 September 1998/Accepted: 9 September 1998     

Force-feedback joystick as a low-cost haptic interface for an atomic-force-microscopy nanomanipulator

In order to manipulate materials at the nanometer scale, new methods and devices have to be developed. A nanomanipulator interface was designed and implemented in a commercial atomic-force-microscope (AFM) system. With the aid of a positioning joystick, direct positioning of the AFM probe with nanometer precision was possible. A commercial force-feedback joystick served as a haptic interface and provided the user with real-time feeling of the tip–sample interactions. Due to the open design, the manipulator interface could be used with other microscopes of the SPM family. In addition, the nanomanipulator and an UV-laser microbeam for photoablation were combined on an inverted optical microscope. To test the nanomanipulator, human metaphase chromosomes were dissected using both photoablation and mechanical AFM manipulation. The experimental results show that by combining both methods, biological material can be manipulated on different size scales in one integrated instrument. The effects of manipulation on the chromosome were studied in detail by AFM. Sub-400 nm cuts were achieved by photonic ablation. Chromosomal fragments of a size less than of 500 nm could be isolated. By means of mechanical microdissection, different cut sizes ranging from 80 nm to 500 nm could be easily obtained by applying different load forces. Received: 2 September 2002 / Accepted: 2 September 2002 / Published online: 5 March 2003 RID="*" ID="*"Current affiliation: Nanotechnology Group, ETH Zurich, Switzerland RID="**" ID="**"Corresponding author. Fax: +49-89/2180-4331, E-mail: heckl@lmu.de     

Magnetic molecular nanostructures: Design of magnetic molecular materials as monolayers, multilayers and thin films

In this paper we summarize the importance and versatility of the molecular approach in the design and development of novel magnetic molecular materials. These materials processing, in order to obtain controlled molecular structures at the nanoscale, will also be remarked.     

Design and application of a femtosecond optical parametric oscillator for time-resolved spectroscopy of semiconductor heterostructures

Femtosecond pulses of a collinearly pumped Optical Parametric Oscillator (OPO) are applied for investigations of the carrier dynamics in ternary and quaternary semiconductor quantum wells. The design and the specifications of the OPO are given in detail. We show that no measurable jitter exists between the pump pulses and the output pulses of the OPO. Therefore, it is possible to use the OPO and its pump laser for two-color experiments with a time resolution limited by the pulse lengths. We present and discuss results of transient four-wave mixing experiments on (InGa) As/InP quantum wells, and find a new kind of polarization-dependent quantum beat phenomenon. In addition, non-degenerate experiments on quantum wells from the quaternary (InGaAl) As material system, using two pulses at different wavelengths (one from the OPO and one from the pump laser), are discussed as a novel experimental technique to study carrier trapping into quantum wells.     

Electrochemical fabrication of a novel conducting polythiophene film junction

A compact conductive polythiophene (PT) film junction was prepared by potential controlled electrochemical doping after electropolymerization of thiophene. The polythiophene film was cation-doped on one side, while its other side was anion-doped, which resulted in a polythiophene p-n junction film diode. The free-standing polythiophene film junction diode was flexible and was 1.5 times stronger than aluminum metal. After treatment by a strong electric field, the polythiophene p-n junction exhibits a novel electric property like an intelligent electric switch.     

Structure-property relationships in major ampullate spider silk as deduced from polarized FTIR spectroscopy

Polarized Fourier Transform Infrared (FTIR) spectroscopy is employed to study structure-property relationships in major ampullate spider silk being exposed to an external mechanical strain. From the measured infrared dichroism of aminoacid-residue - specific bands the molecular order parameter, the frequency width at half-maximum (FWHM) and the spectral position of the absorption maximum are determined in dependence on the external strain. For the highly ordered alanine-rich β sheets a change in the vibrational potential is found for macroscopic strains as low as a few percent. It can be quantitatively described by a quantum-mechanical approach in which the mechanical strain is treated as a weak external perturbation. The immediate microscopic response to the external field proves that β -sheeted crystals are tightly interconnected by pre-stretched chains as suggested recently (Y. Liu et al., Nat. Mater. 4, 901 (2005)).     

Chopped CW laser-induced optogalvanic effect in a neon hollow cathode discharge

A detailed model for the optogalvanic effect in a neon hollow cathode discharge irradiated by a chopped CW dye laser is presented. A rate equation formalism is used to calculate the evolution of the first and second electronic configuration populations coupled by the laser and of the electric charges number density. Processes as ambipolar-like electrons loss, electronic collisional coupling of level populations and electron emission by the cathode due to VUV radiation from the 1s ₂ resonant level are taken into account and further discussed.The transients and steady-state magnitude of the optogalvanic signal are calculated, compared with experimental data and related to population changes. We predict sign changes of the optogalvanic signal when the laser is tuned over transitions originating from the resonant level with respect to transitions involving the metastables states. The optogalvanic signal is shown to be basically determined by the laser-induced variations of the excited-state populations while changes in the electron temperature, due to laser energy transfer by collisions between electrons and excited atoms, play a negligible role.     

Analysis of the airport network of India as a complex weighted network

Transportation infrastructure of a country is one of the most important indicators of its economic growth. Here we study the Airport Network of India (ANI) which represents India’s domestic civil aviation infrastructure as a complex network. We find that ANI, a network of domestic airports connected by air links, is a small-world network characterized by a truncated power-law degree distribution and has a signature of hierarchy. We investigate ANI as a weighted network to explore its various properties and compare them with their topological counterparts. The traffic in ANI, as in the World-wide Airport Network (WAN), is found to be accumulated on interconnected groups of airports and is concentrated between large airports. In contrast to WAN, ANI is found to be having disassortative mixing which is offset by the traffic dynamics. The analysis indicates possible mechanism of formation of a national transportation network, which is different from that on a global scale.     

Preparation and study of complex self-assembled film as a super-thin barrier on silver

A self-assembled monolayers (SAMs) of (3-mercaptopropy) trimethoxysilane (3-MPT) chemisorbed on silver surface was chemically modified by 1-octadecanethiol (C₁₈H₃₇SH) (to form self-assembled mixed-monolayer (SAMM)) and the co-polymer of N-vinylcarbazole and methyl methacrylate ester to form complex self-assemblied film (CSAF). The combinative state of interface between SAMs (or SAMM) and co-polymer were characterized by dynamic mechanical thermal analysis (DMTA). The thickness of film on Ag was characterized by X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry (CV) measurements in 10% NaOH aqueous solution with the silver surface and covered with film indicated that 3-MPT SAMs modified with C₁₈H₃₇SH and then with co-polymer have higher capability against oxidation.     

Transport and crystallization of colloidal particles in a thin nematic cell

In a thin planar nematic cell, the application of an AC electric field induces a macroscopic transport of micrometer-sized colloidal particles along the nematic director. We have analyzed the dependence of particle velocities on the electric-field amplitude and frequency and found that it decreases exponentially with increasing frequency. Using specially designed electrodes we have observed that colloidal particles could be pumped and accelerated across the field-no-field interface, and measured the structural force and the corresponding potential, which is of the order of 10000 k_BT for 4μm particles. We demonstrate that spatially periodic close-packed crystalline colloidal structures can be obtained, which are thermodinamically metastable for many days after turning off the electric field and slowly decay into linear chains. Above the nematic-isotropic phase transition, such crystalline structures are non-stable and decay in few minutes.     

Analysis of chemical dissolution of the barrier layer of porous oxide on aluminum thin films using a re-anodizing technique

Chemical dissolution of the barrier layer of porous oxide formed on thin aluminum films (99.9% purity) in the 4% oxalic acid after immersion in 2 mol dm⁻³ sulphuric acid at 50 °C has been studied. The barrier layer thickness before and after dissolution was calculated using a re-anodizing technique. It has been shown that above 57 V the change in the growth mechanism of porous alumina films takes place. As a result, the change in the amount of regions in the barrier oxide with different dissolution rates is observed. The barrier oxide contains two layers at 50 V: the outer layer with the highest dissolution rate and the inner layer with a low dissolution rate. Above 60 V the barrier oxide contains three layers: the outer layer with a high dissolution rate, the middle layer with the highest dissolution rate and the inner layer with a low dissolution rate. We suggest that the formation of the outer layer of barrier oxide with a high dissolution rate is linked with the injection of protons or H₃O⁺ ions from the electrolyte into the oxide film at the anodizing voltages above 57 V.