Collagen/hydroxyapatite (HA) nanocomposite thin films containing 10, 20, and 30 wt.% HA were prepared on commercially pure titanium substrates by the spin coating of their homogeneous sols. All of the nanocomposite coatings having a thickness of *7.5 lm exhibited a uniform and dense surface, without any obvious aggregation of the HA particles. A minimum contact angle of 36.5°w as obtained at 20 wt.% HA, suggesting that these coatings would exhibit the best hydrophilicity. The in vitro cellular assays revealed that the coating treatment of the Ti substrates favored the adhesion of osteoblast-like cells and significantly enhanced the cell proliferation rate. The cells on the nanocomposite coatings expressed much higher alkaline phosphatase (ALP) levels than those on the uncoated Ti substrates. Increasing the amount of HA resulted in a gradual improvement in the ALP activity. The nanocomposite coatings on Ti substrates also exhibited much better cell proliferation behaviors and osteogenic potentials than the conventional composite coatings with equivalent compositions, demonstrating the greater potential of the former as implant materials for hard tissue engineering.
The effects of the residual stress (either compressive or tensile) induced during the heat-treatment process on the electrical properties of Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) films were investigated. The PZT films were deposited on platinized silicon substrates by the rf-magnetron sputtering method using a single oxide target. After their deposition, the films were bent elastically by means of a specially designed fixture during the annealing process. Residual stress was induced in the film by removing the substrate from the fixture after annealing. The ferroelectric and piezoelectric properties of the films were markedly changed by the residual stresses; the remnant polarization (P r ) and saturation polarization (P sat ) increased when a compressive stress was induced. On the other hand, the piezoelectric properties increased when a tensile stress was induced in the film.
Highly (100)- and (111)-oriented lead zirconate titanate (PZT) films with a thickness of 350 nm were deposited on platinized Si substrates through a single spinning of a PZT sol containing polyvinylpyrrolidone (PVP) as an additive. The crystallographic orientation of the film was strongly influenced by pyrolysis conditions after spin coating. When the spin-coated sol was pyrolyzed at temperatures above 320 °C for relatively long periods of time (>5 min), (111)-oriented film was formed after annealing at 700 °C for 10 min. On the other hand, when the same sol was pyrolyzed at 320 °C for short periods of time (<5 min), the film was strongly oriented to the (100) direction after annealing. Organic residues derived from PVP decomposition acted as nucleation sites for the (100) oriented grains during annealing after the pyrolysis. The effective d33 of the (100)-oriented PZT film (100 pC/N) was much higher than that of the (111)-oriented film (62 pC/N) with the same thickness.
Highly oriented lead zirconate titanate (PZT) films were fabricated on a platinized silicon substrate using a combination of sol-gel and radio frequency (RF) magnetron sputtering deposition methods. A sol-gel derived PZT layer highly oriented to the (100) plane was deposited as a seed layer, and PZT with the same composition then was deposited on the seed layer by RF-magnetron sputtering. The film deposited on the seed layer showed a strong (100) preferred orientation, while the film deposited without the seed layer showed a (111) preferred orientation. Furthermore, a thick PZT film of up to 4 μm was able to be deposited without cracks by using the seed layer. The piezoelectric property of the (100) oriented film was much better than that of the (111) oriented film.
Highly oriented Pb(Zr,Ti)O3 (PZT) films were deposited on Pt/Ti/SiO2/Si substrates by the sol-gel method using lanthanum nitrate as a buffer layer. When the lanthanum nitrate buffer layer was heat treated at temperatures between 450 and 550 °C, the PZT layer coated onto this buffer layer showed a strong (100) preferred orientation. Regardless of the other deposition conditions, such as the pyrolysis temperature, pyrolysis time, annealing temperature and heating rate, the film deposited on the buffer layer had this orientation. Thick films were also fabricated using the sol-gel multi-coating method, and the (100) texture was found to be maintained up to a thickness of 10 μm. The ferroelectric hysteresis and piezoelectric coefficient (d33) of highly oriented PZT thick films were characterized, and the (100) oriented PZT film showed higher piezoelectric property than the (111) oriented film.
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