Kui Cheng

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.

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.

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.

Highly sensitive hydrogen peroxide biosensors based on TiO2 nanodots/ITO electrodes

Uniformly dispersed and size-controllable TiO2 nanodots (TN) were directly synthesized on indium-tin-oxide (ITO) electrodes and were further utilized to immobilize horseradish peroxidase (HRP) enzyme and facilitate direct electron transfer for construction of a hydrogen peroxide (H2O2) biosensor. The enzyme adsorption ability of TN/ITO electrodes were investigated using a UV–vis spectrometer, and the results indicated that TiO2 nanodots possess better enzyme adsorption ability than TiO2 film, and this ability could be further improved by varying the mean diameter of the nanodots from 30 nm to 79 nm. The sensitivity of the H2O2 biosensors based on Nafion/HRP/TN/ITO electrodes was significantly increased by adjusting the dimension of TiO2 nanodots on the modified electrode and the sensitivity differences among these electrodes are in accord with their enzyme adsorption ability. TiO2 nanodots with the largest diameter (79 nm) on a ITO electrode had the best enzyme adsorption ability and biosensor performance with a high sensitivity of 1176 μA mM−1 cm−2 as well as a wide linear range of 1–780 μM. These results show that well-dispersed, high surface area and high curvature TiO2 nanodots could be a promising material for protein adsorption and fabrication of electrochemical biosensors.

Shape-controlled growth of SrTiO3 polyhedral submicro/nanocrystals

A series of SrTiO3 polyhedral submicro/nanocrystals with systematic morphology evolution from cubic to edge-truncated cubic and truncated rhombic dodecahedra have been synthesized by using a series of alcohol molecules with different acidities as surfactants. The concentration and pKa value of the alcohols both play important roles in determining the size and shape of the SrTiO3 polyhedral submicro/nanocrystals. The adsorption energy of alcohol molecules on SrTiO3 {110} facets depends on their pKa values, which are therefore critical for morphology control. Using the same strategy, a series of BaTiO3 polyhedral submicro/nanocrystals with systematic morphology evolution have also been successfully prepared.

Immobilization of RGD peptide on HA coating through a chemical bonding approach.

In this work, Arg-Gly-Asp (RGD) sequence containing peptide was immobilized on hydroxyapatite (HA) coatings through a chemical bonding approach in two steps, surface modification with 3-aminopropyltriethoxysilane (APTES) and RGD immobilization. The results indicate that RGD has been successfully immobilized on HA coatings. Comparing with physical adsorption coatings, the chemically bonded RGD on the coatings shows much better anti-wash-out ability. Since RGD is able to recognize cell-membrane integrins on biointerfaces, the present method will be an effective way to favor interaction of cells with HA coatings.

Preparation and antibiotic drug release of mineralized collagen coatings on titanium

In this study, a mineralized collagen coating was electrolytically deposited onto titanium. The results showed that the mineralized collagen coatings with dense or porous morphology could be obtained. The mineral phase was mainly hydroxyapatite. In vitro evaluation showed the mineralized collagen coatings were stable in Kokubo’s simulated body fluid, and displayed a good cytocompatibility in the cell multiplication test. The mineralized collagen coatings loaded with vancomycin hydrochloride showed an inhibitory effect on the growth of S.aureus. The present mineralized collagen coating demonstrates good suitability for surface modification of orthopedic metal implants.

The effect of triethanolamine on the formation of sol–gel derived fluoroapatite/hydroxyapatite solid solution

Fluoroapatite/hydroxyapatite (FA/HA) solid solution shows good bioactivity and stability, and is one of promising biomaterials. In this work, 1.67Ca(NO3)2–PO(OEt)x(OH)3−x ethanol solutions with different concentrations of trifluoroacetic acid and triethanolamine were mixed. The mixed solutions were transformed into the as-prepared powder on a hot plate. After the as-prepared powder was calcined at 500 or 900 ◦ C, a pure FA/HA phase could be obtained. The fluorine contents in the FA/HA strongly depended on the ratios of triethanolamine/trifluoroacetic acid. The presence of triethanolamine in the mixed solutions enhances the dissociation of trifluoroacetic acid and accelerates the formation of unevaporable Ca(OOCF3C)x(NO3)2−x complex species, as a result, more fluorine could be incorporated into the apatite to form the solid solution.

Size- and density-controlled synthesis of TiO2 nanodots on a substrate by phase-separation-induced self-assembly

This work presents a facile way, i.e. phase-separation-induced self-assembly, to prepare TiO(2) nanodots on a substrate. This method induces convective flow in a spin-coated titanium tetrabutoxide (TBOT)/polyvinyl pyrrolidone (PVP)/ethanol liquid film through the Marangoni effect and turns TBOT into crystalline TiO(2) nanodots on a substrate after calcination. The size and density of the TiO(2) nanodots can be finely tailored by controlling the concentrations of TBOT and PVP in the precursor sol. The TiO(2) nanodot-deposited surface showed a hydrophilic characteristic and the wettability was obviously improved by increasing nanodot size.