This paper reviews the past, present, and future of the hydroxyapatite (HAp)-based biomaterials from the point of view of preparation of hard tissue replacement implants. Properties of the hard tissues are also described. The mechanical reliability of the pure HAp ceramics is low, therefore it cannot be used as artificial teeth or bones. For these reasons, various HAp-based composites have been fabricated, but only the HAp-coated titanium alloys have found wide application. Among the others, the microstructurally controlled HAp ceramics such as fibers/whiskers-reinforced HAp, fibrous HAp-reinforced polymers, or biomimetically fabricated HAp/collagen composites seem to be the most suitable ceramic materials for the future hard tissue replacement implants.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400042527

Processing and properties of hydroxyapatite-based biomaterials for use as hard tissue replacement implants

Structural engineering of polyurethane coatings for high performance applications

For the synthesis of hydroxyapatite crystals from aqueous solutions three preparation methods were employed. From the experimental processes and the characterization of the crystals it was concluded that aging and precipitation kinetics are critical for the purity of the product and its crystallographic characteristics. The authentication details are presented along with the results from infrared spectroscopy, X-ray powder diffraction, Raman spectroscopy, transmission and scanning electron photographs, and chemical analysis. Analytical data for several calcium phosphates were collected from the literature, extensively reviewed, and the results were grouped and presented in tables to provide comparison with the data obtained here.

Synthesis and characterization of hydroxyapatite crystals: A review study on the analytical methods

Using tabulated thermodynamic data, a comprehensive investigation of the thermo-dynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient data exist to conclude that all binary oxides except the following are thermodynamically unstable in contact with silicon at 1000 K: Li2O, most of the alkaline earth oxides (BeO, MgO, CaO, and SrO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3, where Re is a rare earth), ThO2, UO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient data exist to conclude that BeO, MgO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K. Our results are consistent with reported investigations of silicon/binary oxide interfaces and identify candidate materials for future investigations.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0884291400010384

Thermodynamic stability of binary oxides in contact With silicon

This review is concerned with quantum confinement effects in low-dimensional semiconductor systems. The emphasis is on the optical properties, including luminescence, of nanometre-sized microcrysta...

Low-dimensional systems: quantum size effects and electronic properties of semiconductor microcrystallites (zero-dimensional systems) and some quasi-two-dimensional systems

The structure of alkoxysilane-derived SiO 2 gels which were prepared under the partial hydrolysis condition and contained a considerable amount of unhydrolyzed alkoxy groups, and the structure change of the gels in the early stage of gel to glass conversion were investigated as a function of the behavior of a small IR band peaking at 550–600 cm −1 . The 550–600 cm −1 peak was assigned to the skeletal vibration of the 4-fold siloxane rings by reference to various cyclic siloxanes and silicate minerals. The presence of unhydrolyzed alkoxy groups was important for the formation or retention of 4-fold rings in the gels. On heating the gels in air, it was found that the 4-fold siloxane rings were broken to form SiOH bonds with release of alkoxy groups around 200°C, at which temperature the siloxane network was degraded, followed by healing through the condensation of SiOH at a higher temperature.

IR study on the structural evolution of sol-gel derived SiO2 gels in the early stage of conversion to glasses

Third harmonic generation from high refractive index Li 2 OTiO 2 TeO 2 glasses was investigated. The maximum content of TiO 2 in the glass forming region was 10 mol% by conventional melt-quenching technique, and gc (3) was dependent on TiO 2 /(Li 2 O+TiO 2 ). The highest χ (3) , 8.0 × 10 −13 esu, was observed in 10Li 2 O·10TiO 2 ·80TeO 2 (mol%). In these glasses, χ (3) is 40 times larger than that of SiO 2 glass.

Third harmonic generation from Li2OTiO2TeO2 glasses

Third-order optical nonlinear susceptibilities (χ(3)) of some high-refractive-index chalcogenide glasses were evaluated from third-harmonic generation. Compared with oxide glasses whose χ(3) has been known, χ(3) of the present glasses was higher by an order of magnitude. The addition of selenium drastically increased χ(3). The highest χ(3) was 1.4 × 10–11 esu, being comparable with those of high-χ(3)-organic compounds. Further, χ(3) generally increased with increasing density in the present glasses.

Third-Harmonic Generation from Some Chalcogenide Glasses

Optical third-harmonic generation from some high-index glasses was investigated. The highest χ(3) was obtained from As2S3 glass 2.2 × 10−12 esu/ This value was 100 times higher than that of pure SiO2 glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ(3). From the relationship between χ(3) and composition, sulfide glasses were found to have higher χ(3) than oxide or semiconductor-doped oxide glasses with similar refractive indices.

Optical third-harmonic generation from some high-index glasses

Optical second harmonic generation has been observed in electrically poled Li 2 ONb 2 O 5 TeO 2 glasses. Electrical poling was performed at 250°C for 30 min under an applied dc potential of 3–4 kV. Second harmonic generation takes place in binary Li 2 OTeO 2 and Nb 2 O 5 TeO 2 glasses as well as ternary 10Li 2 O · 10Nb 2 O 5 · 80TeO 2 and 15Li 2 O · 15Nb 2 O 5 · 70TeO 2 glasses as previously reported. The observation of second harmonic generation in tellurite glasses which do not contain Li + ions leads to speculation that the second harmonic generation is not attributed to the Li + ion migration but is presumably ascribed to a long-range orientation of electric dipoles due to asymmetrical structural units, i.e., TeO 4 trigonal bipyramids and TeO 3 trigonal pyramids.

Hiroyuki Nasu

Papers

IR study on the structural evolution of sol-gel derived SiO2 gels in the early stage of conversion to glasses

Third harmonic generation from Li2OTiO2TeO2 glasses

Third-Harmonic Generation from Some Chalcogenide Glasses

Optical third-harmonic generation from some high-index glasses

Second harmonic generation in electrically poled Li2ONb2O5TeO2 glasses