Key Engineering Materials Vols. 309-311

Abstract: A novel synthesis of nano-fluoride-substituted hydroxyapatite (nano-F-HAP) was successfully realized through dialysis process within 4 h, which required much shorter time than the methods reported so far. In new preparation, a dialysis was employed to purify unwanted ions. The removal efficiency of impurity ions in dialysis was evaluated by calculating the concentration of the representative irons NH4 + between the inner slurry and outer distilled water. Results showed that total dialysis efficiency came to 94.5%. The final products were characterized by XRD, HR-TEM, and FT-IR. The XRD and FT-IR results strongly supported substitution of F- for OH-, and the TEM pictures further indicated that the final crystals are about 100nm in length and about 20 nm in diameter without obvious aggregation. Therefore, comparing with traditional purifying processing, such a new synthesis provides a promising application for scale preparation of fine nano-F-HAP crystals.

Abstract: A novel porous beta-tricalcium phosphate /collagen fibers (β-TCP/CF) composite, having a well-dispersed nano-sized β-TCP in collagen matrix, was developed by a wet-chemical method. The nano-composite was compared to conventional β-TCP on cytocompatibility by cell attachment, proliferation, alkaline phosphotatse (AKP) activity and scanning electron microscopy (SEM) analysis. These in vitro assays showed that the β-TCP/CF composite elicited cell adhesion and proliferation better then controls. Moreover experiments on osteoblast-like cells showed improved cell growth with the highly characterized nanophase structure. SEM micrographs also showed that the nano-sized composite exhibited much more viable cells in attachment on the surface compared with the controls. At 1, 3 and 5 days, AKP activity was not significant different for the tested and control samples, while at 7 day after culture, significantly increased AKP activity was observed for β-TCP/CF than for the control. The in vitro results obtained confirmed the remarkable improvement of cell adhesion and proliferation of the nano-sized β-TCP/CF composite, which may be a new promising candidate for tissue engineered bone substitute.

Abstract: β-tricalcium phosphate (β-TCP)/collagen composites are in the limelight for their biomedical applications. It is believed that joint status of β-TCP particles with collagen fibrils plays key roles in both osteoconductivity and biodegradability of composites. In this work, the influence of acidity during synthesis on the joint status between nano-sized β-TCP particles and collagen fibrils is investigated. The composites are characterized by X-ray diffractometer and Field Emission Scanning Electron Microscope. The results show that the joint status of nano-sized β-TCP particles with collagen fibrils in the composites depends on the acidity in collagen suspensions. A desired joint status with obvious disassembled collagen fibril, good particle dispersion and strong boding between the particles and the fibrils could be obtained when acidity of the collagen suspension is pH 2.

Abstract: To produce ceramics with high mechanical strength and bioactivity, we developed the little amount of nano-sized hydroxyapatite (HA)-doped zirconia composite ceramics (nanoHA-Z). The bioactivity of the nanoHA-Z was studied by in vitro estimation with simulated body fluid (SBF). Scanning electron microscopy observation showed deposited bone-like apatite layer entire covering the surface of nanoHA-Z ceramics in SBF. The enhanced apatite formability was attributed to higher Ca and PO4 concentrations in the vicinities of the nanoHA-Z surfaces due to the dissolution of the β-tricalcium phosphate decomposed from the added HA. Utilization of Chemicovector effect was proved to be one of the powerful approaches for improvement method of biomaterials.

Abstract: Biomimetic actuators that can produce soft-actuation but large force generation capability are of interest. NafionTM, an effective ionomeric material from DuPont, has been shown to produce large deformation under low electric fields (<10V/mm). In this effort, multi-walled carbon nanotube (M-CNT)/NafionTM nanocomposites were prepared by casting in order to investigate the effect of M-CNT loading in the range of 0 to 7 wt% on electromechanical properties of the MCNT/ NafionTM nanocomposites. The measured elastic modulus and actuation force of the MCNT/ NafionTM nanocomposites are drastically different, showing larger elastic modulus and improved electromechanical coupling, from the one without M-CNT. In this work, we attempted to incorporate an equivalent circuit analysis to address the effect of capacitance and resistance of such M-CNT/NafionTM nanocomposites that would differ from conventional IPMCs.

Abstract: This paper reports development of a production method to produce a composite material that is biocompatible, with high mechanical strength and resilience. The chemical precipitation conditions necessary for the production of synthetic hydroxyapatite (HAp) were determined and include pH, temperature and rate of reaction. A gas phase purification method was optimised to remove the soot impurity from the nanotubes, with transmission electron microscopy showing the preservation of the carbon nanotubes. Subsequent development of chemical and physical reinforcement techniques to produce a HAp + carbon nanotube composite material have been trialled. Hot isostatically pressed samples showed excellent densification and strength.

Abstract: TiO2 and HA thin film double coating has been proposed. The TiO2/HA thin film was coated on the glass by a Radio Frequency magnetron sputtering, and the characteristic of the thin film has been studied. The absorption of Formaldehyde (HCHO) gas in the TiO2/HA thin film was detected by gas chromatography, and the sterilization of Escherichia coli (E. coli) was evaluated in the antibacterial test. In the deodorization test, HCHO gas remained 0[%], 11[%] and 85[%] for TiO2/HA thin film, TIO2 thin film and thin film respectively. The sterilization result shows that E. coli for TiO2/HA thin film and HA thin film decreased 89[%] and 75[%] respectively.

Abstract: The dissolution and precipitation behavior of various porous, ESD-derived calcium phosphate coatings was investigated a) in vitro after soaking in Simulated Body Fluid (SBF) for several time periods (2, 4, 8, and 12 weeks), and b) in vivo after subcutaneous implantation in the back of goats for identical time periods. At the end of these studies, the physicochemical properties of the coated substrates were characterized by means of Scanning Electron Microscopy (SEM), XRay Diffraction (XRD), Fourier-Transform InfraRed spectroscopy (FTIR) and Energy Dispersive Spectroscopy (EDS). Moreover, part of the implants was prepared for light microscopical evaluation of the tissue response. In vitro, a highly bioactive behavior was observed for all ESD-coatings, characterized by the deposition of a thick and homogeneous carbonate hydroxyapatite precipitation layer on top of the porous coatings. Regarding the in vivo study, no adverse tissue reactions (toxic effects/inflammatory cells) were observed using light microscopy, and all coatings became surrounded by a thin, dense fibrous tissue capsule after implantation. The ESD-coatings degraded gradually at a dissolution rate depending on the specific chemical phase, thereby enabling synthesis of CaP coatings with a tailored degradation rate.

Abstract: In situ measurements of electrospray droplet sizes and velocities were performed by Phase Doppler Anemometry during Electrostatic Spray Deposition (ESD) of calcium phosphate (CaP) coatings. Numerous processing parameters were varied (nozzle-to-substrate distance, deposition temperature, nozzle geometry, and composition of the precursor solution), whereafter the morphological characteristics of these ESD-derived CaP coatings were correlated with measured droplet characteristics. Equal droplet sizes and velocities were measured for nozzle-to-substrate distances up to 40 mm and deposition temperatures up to 400 °C, indicating that electrospray droplets did not shrink at all during droplet flight using an involatile solvent butyl carbitol with a high boiling point (Tb = 231 °C). Nevertheless, coatings with considerably different surface morphologies were obtained under these conditions, varying from microporous structures with coalesced pore walls to morphologies revealing isolated rings on top of dense or grainy underlayers. The chemical composition of the precursor solutions and the mixing characteristics of the calcium and phosphate precursor components strongly influenced the initial droplet sizes, precipitation kinetics of the CaP solute, and subsequent coating morphology. Unique, reticular coating morphologies were deposited at a deposition rate of 3.2 µm/hour, which have a graded structure consisting of a dense underlayer, a submicron-porous intermediate layer, and a roughened toplayer revealing droplet-derived features such as isolated rings or coalesced, hollow surface pits.

Abstract: Highly oriented hydroxyapatite (HA) coatings were prepared on titanium (Ti) substrates through a radio-frequency thermal plasma spraying method. XRD patterns showed that the HA coating layer had an structure with (00l) preferred crystal orientation. TEM observation showed that 200-800 nm-width prismatic crystals were formed in HA splats and the longitudinal axis of such prismatic crystals oriented vertical to the coating's surface. TEM images also indicate that the interface between prismatic crystals became compacted. SAD pattern show that the longitudinal axis of prismatic crystals corresponds to the <001> axis of HA.