Wenjian Weng

SOL-GEL DERIVED POROUS HYDROXYAPATITE COATINGS

The preparation of hydroxyapatite coatings on alumina substrates by a sol–gel method was investigated. A mixed ethanol solution of Ca(NO3)2·4H2O and P2O5 was used as a dipping source. The samples were characterized by solid-state 31P nuclear magnetic resonance spectroscopy, differential thermal analysis, thermogravimetry, X-ray diffraction, scanning electron microscopy and infrared reflection spectroscopy. The coating obtained at 500°C had good hydroxyapatite crystallinity, adhesive strength of about 10 MPa and dense morphology. The coating obtained at 750°C also had good crystallinity and adhesive strength but porous morphology.

Percolative conductor/polymer composite films with significant dielectric properties

A percolative film with conductive acetylene black introduced into β-polyvinylidene fluoride was prepared by dip-coating method. Percolation theory was employed to explain the dielectric behavior of polymer/conductor composite films. Experimental results showed that the dielectric constant of polymer/conductor composite films can reach 56 and the dielectric loss is below 0.15 when acetylene black concentration is in the neighborhood of percolation threshold (fc). The experimental results are in good agreement with classic percolation power law, with fc≈1.3% and exponent q≈0.53. Such composite films have a potential to become capacitors and can be easily fabricated due to its flexibility.

Sol-gel preparation of bioactive apatite films

The surface of biomedical metallic implants covered by a bioactive apatite film can create bioactivity of the implant and shorten healing time. In this work, apatite films on Ti6Al4V were prepared by sol–gel route using Ca(NO ) , P O and HPF as 32 2 5 6 the precursors, in vitro evaluations of the resulting hydroxyapatite (HA) and fluorapatiteyhydroxyapatite solid solution (FHA) films were done in Kokubo’s simulated body fluid and citric acid modified phosphate buffer solution (CPBS). HPF showed a 6 good reagent for the incorporation of fluorine into apatite films. The FHA film demonstrated to have good bioactivity, and to have better stability in CPBS and higher adhesion strength than the HA film. When fluorine is incorporated into the film, an increase in crystallinity of the apatite film and a decrease in intrinsic solubility of the FHA film could make significant contributions to the improvement in the stability; the thermal expansion coefficient of the FHA film getting closer to that of Ti6Al4V could be responsible for the increase in adhesion strength. 2002 Elsevier Science B.V. All rights reserved.

Light-induced cell detachment for cell sheet technology.

The phenomenon of light-induced cell detachment is reported. Mouse calvaria-derived, pre-osteoblastic (MC3T3-E1) cells were cultured on a TiO(2) nanodot-coated quartz substrate. After 20 min of UV365 illumination, over 90% of the cells would detach from the surface. Moreover, intact cell sheets could be obtained in the same way. It was found that the as-obtained cells showed good viability, and could be used for further culture processes and other applications. Also, biocompatibility and safety characterizations indicated that the use of TiO(2) nanodots and UV365 illumination was safe for such cell detachment. It is suggested that adsorbed extracellular matrix proteins play key roles in developing cell sheets and ensuring biocompatibility. The present light-induced cell detachment method demonstrates a promising way for rapid cell/cell sheet harvesting.

PbTiO3 nanofibers with edge-shared TiO6 octahedra.

A new tetragonal phase of PbTiO(3) was discovered, in which each TiO(6) octahedron pair shares an edge and stacks over following pairs in an interlaced manner to form a one-dimensional (1D) columned structure along the c-axis. This new tetragonal phase of PbTiO(3) transforms into a normal perovskite phase in air at elevated temperature.

The effect of citric acid addition on the formation of sol-gel derived hydroxyapatite

In order to improve the gelation in sol–gel preparation of hydroxyapatite by using Ca(NO3)2 and PO(OH)3−x (OEt)x precursors, citric acid was selected as an enhancing gelation additive. Hydroxyapatite derived from the mixed precursor solutions (Ca/P molar ratio of 1.67) with citric acid showed a different reaction path from that without citric acid. The addition of citric acid led to formation of amorphous as-prepared powder, the powders calcined at 650 ◦ C contained three phases: hydroxyapatite, carbonated hydroxyapatite and a small amount of -tricalcium phosphate. The powders calcined at 800 ◦ C contained only a single phase of oxy-hydroxyapatite. It is suggested that citric acid plays a role in enhancing gelation through a strong coordination ability of Ca ions with citrate groups.

Synthesis of hydroxyapatite/fluoroapatite solid solution by a sol–gel method

Abstract A sol–gel method is developed to synthesize hydroxyapatite (HA)/fluoroapatite (FA) solid solution for providing a basis of preparation of the solid solution film or coating. Calcium nitrate-4 hydrate, phosphoric pentoxide and trifluoroacetic acid (TFA) were used as the precursors. Triethanolamine (TEA) was used as a promoter for incorporating fluorine into Ca phosphates. Mixed ethanol solutions of the Ca and P precursors in Ca/P ratio of 1.67 with different amounts of TFA and TEA were prepared; the mixed solutions were dried on a hot plate to convert them to the as-prepared powders. After the powders were calcined at temperatures up to 900°C, HA/FA solid solutions were obtained. It was found that the fluorine contents in the apatite were dependent on the amounts of TFA and TEA in the mixed solutions.

Preparation and characterization of novel biphasic calcium phosphate powders (α‐TCP/HA) derived from carbonated amorphous calcium phosphates

Novel biphasic calcium phosphate (BCP) powders composed of alpha-tricalcium phosphate (alpha-TCP) and hydroxyapatite (HA) were prepared by thermal decomposition of carbonated amorphous calcium phosphates (CACP). At first, the CACP precipitates were synthesized by adding ammonium carbonate in the presence of poly(ethylene glycol) at pH 10 with an initial Ca/P molar ratio of 1.60 at 5 degrees C. The Ca/P molar ratios of the CACP precursors are between 1.50 and 1.67 investigated by ICP. Then BCP (alpha-TCP/HA) powders were obtained after heating the CACP precursors at relatively low temperature (800 degrees C) for 3 h. alpha-TCP/HA powders were characterized by X-ray diffractometry, Fourier transform infrared spectra, transmission electron microscopy/scanning electron microscopy, and sedimentation experiment. The results show that alpha-TCP and HA phases form in one powder, alpha-TCP/HA powders are sphere with the diameter of 300 nm to less than 100 nm varied with their chemical compositions and the ratio of alpha-TCP and HA in the powders can be adjusted by the adding amount of carbonates. The possible formation process of biphasic alpha-TCP/HA powders was proposed.

Ag nanoparticle dispersed PbTiO3 percolative composite thin film with high permittivity

Ag nanoparticle dispersed PbTiO3 percolative composite thin films were prepared in situ by sol-gel method using Pb(NO3)2, Ti(C4H9O)4, and AgNO3 as raw materials and lactic acid along with citric acid as complexing agent. The size of the Ag nanoparticles measured by ultraviolet-visible spectra is about 3nm. The percolation effect occurs in composite thin films. The composite exhibits relatively high dielectric constant which is about five times higher than that of PbTiO3 thin film and comparatively low dielectric loss comparable to pure PbTiO3 system. It is highly attractive in application of high quality dielectric devices and miniaturization.

Enhanced Luminescence of Eu-Doped TiO2Nanodots

Monodisperse and spherical Eu-doped TiO2nanodots were prepared on substrate by phase-separation-induced self-assembly. The average diameters of the nanodots can be 50 and 70 nm by changing the preparation condition. The calcined nanodots consist of an amorphous TiO2matrix with Eu3+ions highly dispersed in it. The Eu-doped TiO2nanodots exhibit intense luminescence due to effective energy transfer from amorphous TiO2matrix to Eu3+ions. The luminescence intensity is about 12.5 times of that of Eu-doped TiO2film and the luminescence lifetime can be as long as 960 μs.