You-Xiong Wang

Effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility.

Polymeric biomaterials have extensively been used in medicinal applications. However, factors that determine their biocompatibility are still not very clear. This article reviews various effects of the chemical structure and the surface properties of polymeric biomaterials on their biocompatibility, including protein adsorption, cell adhesion, cytotoxicity, blood compatibility, and tissue compatibility. Understanding these aspects of biocompatibility is important to the improvement of the biocompatibility of existing polymers and the design of new biocompatible polymers.

Layer-by-layer ionic self-assembly of Au colloids into multilayer thin-films with bulk metal conductivity

Abstract Colloidal Au nanoparticles, each encapsulated by polyelectrolytes, have been self-assembled into multilayer films in a layer-by-layer fashion. Atomic force microscopy (AFM) demonstrates that close-packed, three-dimensional arrays with uniform roughness have been achieved. Organic interconnects (alternating cationic and anionic monolayers) covalently and electrostatically linked adjacent metal nanoparticles and formed uniform tunnel junctions. Electrical conductance measurements reveal that a resistivity of 5×10−6 Ω cm for 15 layers of 5 nm Au colloid films, the same order of magnitude of that of bulk gold metals, has been achieved for the first time.

Nanostructured optical fibre sensors for breathing airflow monitoring

A nanostructured optical fibre-based thin film sensor was designed for non-invasive, fast and reliable monitoring of respiratory airflow. Molecular-level self-assembly processing method was used to form multi-layered inorganic nanocluster and polymer thin films on the distal ends of optical fibres to form such sensors. In order to optimize the sensing performance, an analytical model based on the condensation of exhaled water vapour on the coating surface was established for the breathing analysis. By varying thin film chemistry the physically small sensors offer high sensitivity to breathing air in terms of variations in the reflected optical power. Moreover, the sensor performances in comparison with a medical nasal thermistor suggest such a thin film sensor is an excellent device for advanced breathing airflow monitoring.

Self-assembled flexible electrodes on electroactive polymer actuators

Thin film metal/polymer composite electrodes with electrical conductivities on the order of those of bulk metals have been formed on electroactive polymer actuator elements using a novel self-assembly technique. The electrodes exhibit good flexibility and mechanical performance.

Giant magnetoelectric effect in nonlinear Metglas/PIN-PMN-PT multiferroic heterostructure

In this paper, we demonstrate high converse magnetoelectric (ME) coupling in a Metglas/Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) laminated ME composite by exploiting stress and field induced reversible ferroelectric-ferroelectric phase transitions in a relaxor ferroelectric single crystal. The approach exploits large transformational strain induced by low applied electric field in a PIN-PMN-PT crystal that was mechanically stressed close to a rhombohedral to orthorhombic phase transformation. The ME coefficient was enhanced by an order of magnitude as compared to the linear piezoelectric regime, with a maximum value of 1.3 × 10−7 s m−1 in non-resonant mode. This phenomenon can thus be exploited to provide improvements in the development of ME devices and magnetic sensors.

Characterization of electrostatically self-assembled nanocomposite thin films

Multilayer thin films of metallic nanoclusters, polymers and other molecules have been formed using a novel electrostatic self-assembly method and analysed by multiple characterization techniques. Nanocluster size measurements, ellipsometry and UV-visible absorption spectroscopy have been used to confirm the linear build-up of the thin film thickness with the number of deposited nanocluster, polymer and other molecular layers. Auger electron spectroscopy allowed verification of the distribution of molecular species through thick films with multilayer segments containing different elements. Field emission scanning electron microscopy and atomic force microscopy permitted visualization of the morphologies of the outermost layers of the deposited films. Together, such characterization allows improved understanding and the basis for the design of multilayer thin film materials engineered to have specific molecular level structures and macroscopic functionalities.

AC magnetic dipole localization by a magnetoelectric sensor

We report progress towards achievement of a triple-axis magnetoelectric (ME) sensor technology that is capable of localizing an AC magnetic dipole at quasi-static frequencies. Estimation of the location of the AC dipole was realized with the help of a grid search (GS) algorithm. The results show good convergence and accuracy of object location along three orthogonal directions. Through simulation analysis, the major localization errors were found to arise from sensor calibration.

Biocompatible thin film coatings fabricated using the electrostatic self-assembly process

Biomaterials are substances that are produced synthetically or biologically for use in the medical and the other fields. The use of biomaterials to interface with living systems, such as fluids, cells, and tissues of the body, has played an increasingly important role in medicine and pharmaceutics. In particular, the design of biocompatible synthetic surfaces to control the interaction between a living system and an implanted material remains the major theme for biomaterial applications in medicine. The novel and low-cost electrostatic self-assembly (ESA) technique provides an effective approach to incorporate various biomaterials on substrate surfaces, and gives greater opportunity to develop unique biocompatible materials with well-controlled interfaces between the living system and the implanted materia. This paper presents the design, synthesis, and characterization of multilayer thin films fabricated layer-by-layer by the ESA process using ceramics, polymers and functionalized fullerenes as candidate biomaterials.

Observation of whispering-gallery and directional resonant laser emission in ellipsoidal microcavities

Whispering-gallery resonant laser emission is reported in CdSe-tagged polystyrene microcavities. A clear intensity threshold for laser emission is observed. Using a recently developed asymptotic expansion derived from Mie theory, we have theoretically identified the experimentally observed discrete resonant peaks and assigned them to different quantum states. In fluorescent carboxylate-modified ellipsoidal polystyrene microcavities, we have observed that whispering-gallery mode and directional laser emission can be excited simultaneously. To understand our experimental results, we extend the asymptotic expansion from spherical to ellipsoidal microcavities to explain the whispering-gallery mode behavior and develop a simple ray-optics model to interpret the directional emission. The obtained numerical data agree well with experimental observation.

Electrostatic self-assembly processes for noncentrosymmetric thin films and devices

The electrostatic self-assembly (ESA) method of creating multifunctional, multi-component thin films layer by layer has proven to yield noncentrosymmetric structures that possess large second order nonlinear responses. The nature of the deposition process results in an alignment of the NLO chromophores that is stable over time, in contrast to poled polymers. ESA nonlinear optical thin films offer the additional major advantages of excellent homogeneity for low scattering loss, high thermal and chemical stability, simplicity of fabrication and low cost. The polar ordering of molecules that occurs due to the inherent nature of the ESA process suggests that a number of NLO thin films may be synthesized using both standard chromophore dyes and molecules specifically designed to yield an enhanced macro- scale net dipole moment. Consequently, we have designed and synthesized several new NLO polymers and fabricated noncentrosymmetric thin-films using the ESA process. These novel polymer films exhibit substantial (chi) (2) values as well as uniform growth and exceptional film ordering.