Yuhai Zhang

Surface Modification of Fluoropolymers via Molecular Design

Fluoropolymer surfaces with new and specific functionalities, such as metal-free conductivity, biocompatability, and bondability to metals, can be obtained through the intelligent choice of functional monomers for graft copolymerization on pre-activated fluoropolymer surfaces, as highlighted in this review. The Figure shows a gold/fluoropolymer laminate held together by crosslinked glycidyl methacrylate polymer grafted on both surfaces.

Fabrication of porous electrospun nanofibres

Immiscible biopolymers of gelatin (Gt) and polycaprolactone (PCL) were first electrospun into a biomimicking composite fibre of Gt/PCL. Based on a phase separation study of the electrospun fibres, a leaching method was employed to generate 3D porous nanofibres by selectively removing the water soluble component of gelatin in a 37 °C aqueous solution of phosphate buffered saline. It was found that leaching treatment gave rise to a unique nanotopography containing grooves, ridges and elliptical pores on the surface as well as inside of the resultant individual nanofibres. Brunauer–Emmett–Teller (BET) area measurement indicated that the formed 3D porous fibres also brought in a pronounced increase of the surface area of fibres. The BET surface area of the porous fibres was observed to be about 2.4 times that of the precursor fibres, up to 15.84 m2 g−1 at its relatively large size of 800 nm diameter. The 3D porous fibres herein prepared could have considerable value for uses in developing highly integrated cell–scaffold tissue complexes and other industrial applications.

Fabrication of modified and functionalized polycaprolactone nanofibre scaffolds for vascular tissue engineering

Electrospun polymer nanofibres were originally developed for their durability and resistance to all forms of degradation and biodegradation. Some polymer nanofibres are biocompatible and biodegradable and therefore suitable for replacement of structurally or physiologically deficient tissues and organs in humans. Here, biocompatible polycaprolactone (PCL) nanofibre scaffolds modified with collagen types I and III were used for vascular tissue engineering. Coronary artery smooth muscle cells (SMCs) were grown on PCL nanofibres, modified PCL/collagen biocomposite nanofibres and collagen nanofibres. The results show that the modified PCL/collagen biocomposite nanofibre scaffolds provide required mechanical properties for regulation of normal cell function in vascular tissue engineering.

Nanotechnology for Nanomedicine and Delivery of Drugs

Nanotechnology is an emerging technology seeking to exploit distinct technological advances controlling the structure of materials at a reduced dimensional scale approaching individual molecules and their aggregates or supramolecular structures. The manipulation and utilization of materials at nanoscale are expected to be critical drivers of economic growth and development in this century. In recent years, nanoscale sciences and engineering have provided new avenues for engineering materials down to molecular scale precision. The resultant materials have been demonstrated to have enhanced properties and applicability; and these materials are expected to be enabling technologies in the successful development and application of nanomedicine. Nanomedicine is defined as the monitoring, repair, construction, and control of human biological systems at the molecular level using engineered nanodevices and nanostructures. Electrospinning is a simple and cost-effective technique, capable of producing continuous fibers of various materials from polymers to ceramics. The electrospinning technique is used for the preparation of nanofibers and macroporous scaffolds intended for drug delivery and tissue engineering. These have special characteristics in terms of fabrication, porosity, variable diameters, topology and mechanical properties. This review summarizes the recent developments in utilizing nanofibers for drug delivery and tissue engineering applications.

Thermal Scanning at the Cellular Level by an Optically Trapped Upconverting Fluorescent Particle.

3D optical manipulation of a thermal-sensing upconverting particle allows for the determination of the extension of the thermal gradient created in the surroundings of a plasmonic-mediated photothermal-treated HeLa cancer cell.

Surface modification of polyimide films via plasma polymerization and deposition of allylpentafluorobenzene

Plasma polymerization of allylpentafluorobenzene (APFB) on the plasma-pretreated polyimide (PI) films was carried out. The fluorinated aromatic groups of the plasma-polymerized APFB (pp-APFB) could be preserved, to a large extent, by controlling the glow discharge parameters. The effect of the glow discharge parameters, including the type of the carrier gas and the input RF power, on the surface composition and chemical structure of the pp-APFB films were studied by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and time-of-flight secondary ion mass spectrometry. The surface topography of the APFB plasma-polymerized PI (pp-APFB-PI) films was studied by atomic force microscopy. For plasma polymerization carried out at a high RF power and using argon as the carrier gas, an ultra-hydrophobic pp-APFB-PI surface was also obtained. The ultra-hydrophobic surface exhibited advancing/receding water contact angles (θA/θR) of 174°/135°. The effectiveness of the carrier gas in defluorinating the pp-APFB films followed the order of O2>N2>H2>Ar. Thus, the role of the carrier gas in improving the surface hydrophobicity of the resulting pp-APFB-PI films followed the order of O2

Unraveling Epitaxial Habits in the NaLnF4 System for Color Multiplexing at the Single-Particle Level.

We report an epitaxial growth technique for scalable production of hybrid sodium rare-earth fluoride (NaLnF4 ) microcrystals, including NaYF4 , NaYbF4 , and NaLuF4 material systems. The single crystalline nature of the as-synthesized products makes them strong upconversion emission. The freedom of combining a lanthanide activator (Er(3+) or Tm(3+) ) with a sensitizer (Yb(3+) ) at various doping concentrations readily gives access to color multiplexing at the single-particle level. Our kinetic and thermodynamic investigations on the epitaxial growth of core-shell microcrystals using NaLnF4 particle seeds suggest that within a certain size regime it is plausible to exert precise control over shell thickness and growth orientation under hydrothermal conditions.

Subwavelength imaging through ion-beam-induced upconversion

The combination of an optical microscope and a luminescent probe plays a pivotal role in biological imaging because it allows for probing subcellular structures. However, the optical resolutions are largely constrained by Abbes diffraction limit, and the common dye probes often suffer from photobleaching. Here we present a new method for subwavelength imaging by combining lanthanide-doped upconversion nanocrystals with the ionoluminescence imaging technique. We experimentally observed that the ion beam can be used as a new form of excitation source to induce photon upconversion in lanthanide-doped nanocrystals. This approach enables luminescence imaging and simultaneous mapping of cellular structures with a spatial resolution of sub-30 nm.

Microrheometric upconversion-based techniques for intracellular viscosity measurements

Rheological parameters (viscosity, creep compliance and elasticity) play an important role in cell function and viability. For this reason different strategies have been developed for their study. In this work, two new microrheometric techniques are presented. Both methods take advantage of the analysis of the polarized emission of an upconverting particle to determine its orientation inside the optical trap. Upconverting particles are optical materials that are able to convert infrared radiation into visible light. Their usefulness has been further boosted by the recent demonstration of their three-dimensional control and tracking by single beam infrared optical traps. In this work it is demonstrated that optical torques are responsible of the stable orientation of the upconverting particle inside the trap. Moreover, numerical calculations and experimental data allowed to use the rotation dynamics of the optically trapped upconverting particle for environmental sensing. In particular, the cytoplasm viscosity could be measured by using the rotation time and thermal fluctuations of an intracellular optically trapped upconverting particle, by means of the two previously mentioned microrheometric techniques.