How useful is SBF in predicting in vivo bone bioactivity

Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, may be bioinert (alumina, zirconia), resorbable (tricalcium phosphate), bioactive (hydroxyapatite, bioactive glasses, and glass-ceramics), or porous for tissue ingrowth (hydroxyapatite-coated metals, alumina). Applications include replacements for hips, knees, teeth, tendons, and ligaments and repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jaw bone, spinal fusion, and bone fillers after tumor surgery. Carbon coatings are thromboresistant and are used for prosthetic heart valves. The mechanisms of tissue bonding to bioactive ceramics are beginning to be understood, which can result in the molecular design of bioceramics for interfacial bonding with hard and soft tissues. Composites are being developed with high toughness and elastic modulus match with bone. Therapeutic treatment of cancer has been achieved by localized delivery of radioactive isotopes via glass beads. Development of standard test methods for prediction of long-term (20-year) mechanical reliability under load is still needed.

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Bioceramics: From Concept to Clinic

Bioceramics : from concept to clinic

High-strength bioactive glass-ceramic A-W was soaked in various acellular aqueous solutions different in ion concentrations and pH. After soaking for 7 and 30 days, surface structural changes of the glass-ceramic were investigated by means of Fourier transform infrared reflection spectroscopy, thin-film x-ray diffraction, and scanning electronmicroscopic observations, in comparison with in vivo surface structural changes. So-called Tris buffer solution, pure water buffered with trishydroxymethyl-aminomethane, which had been used by various workers as a "simulated body fluid," did not reproduce the in vivo surface structural changes, i.e., apatite formation on the surface. A solution, ion concentrations and pH of which are almost equal to those of the human blood plasma--i.e., Na+ 142.0, K+ 5.0, Mg2+ 1.5, Ca2+ 2.5, Cl- 148.8, HCO3- 4.2 and PO4(2-) 1.0 mM and buffered at pH 7.25 with the trishydroxymethyl-aminomethane--most precisely reproduced in vivo surface structure change. This shows that careful selection of simulated body fluid is required for in vitro experiments. The results also support the concept that the apatite phase on the surface of glass-ceramic A-W is formed by a chemical reaction of the glass-ceramic with the Ca2+, HPO4(2-), and OH- ions in the body fluid.

Solutions able to reproduce in vivo surface-structure changes in bioactive glass-ceramic A-W.

Titanium and titanium alloys are widely used in biomedical devices and components, especially as hard tissue replacements as well as in cardiac and cardiovascular applications, because of their desirable properties, such as relatively low modulus, good fatigue strength, formability, machinability, corrosion resistance, and biocompatibility. However, titanium and its alloys cannot meet all of the clinical requirements. Therefore, in order to improve the biological, chemical, and mechanical properties, surface modification is often performed. This article reviews the various surface modification technologies pertaining to titanium and titanium alloys including mechanical treatment, thermal spraying, sol–gel, chemical and electrochemical treatment, and ion implantation from the perspective of biomedical engineering. Recent work has shown that the wear resistance, corrosion resistance, and biological properties of titanium and titanium alloys can be improved selectively using the appropriate surface treatment techniques while the desirable bulk attributes of the materials are retained. The proper surface treatment expands the use of titanium and titanium alloys in the biomedical fields. Some of the recent applications are also discussed in this paper.

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Surface modification of titanium, titanium alloys, and related materials for biomedical applications

Formation of particulate opaque silica gels from highly acidic solutions of tetramethoxysilane

The third order nonlinear optical susceptibilities χ(3) of PbO-SiO2 and PbO-B2O3 glasses have been measured by the third harmonic generation (THG) method using silica glass as reference. It is found that the third order nonlinear susceptibilities χ(3) of each series of glasses increase with increasing lead content, corresponding to the increase in the polarizability per unit volume and the decrease in the energy gap of the glasses. The largest χ(3) values obtained are 31.1×10-14esu for a 66PbO⋅34SiO2 glass and 31.2×10-14esu for a 70PbO⋅30B2O3 glass, about 11 times larger than that of pure silica glass.

Third Harmonic Generation in PbO-SiO2 and PbO-B2O3 Glasses

Gallate glasses containing no conventional glass formers were obtained in the systems (Na 2 O, K 2 O or Cs 2 O)-Ta 2 O 5 Ga 2 O 3 and (Sr or BaO)-Ta 2 O 5 Ga 2 O 3 by an ordinary crucible-melting technique. The glasses showed high optical transmission in the infrared as well as in the visible region. Infrared spectroscopic analysis suggested that the Ga 3+ ions are tetrahedrally coordinated in the glasses. The glass-forming tendency of the melt and the infrared transmission of the glasses are discussed in terms of the glass structure.

Glass formation and optical properties of glasses in the systems (R2O or R'O)-Ta2O5Ga2O3

Ab initio molecular orbital calculation was applied to the model molecule which was quarried out from the framework structure of silicon oxynitride glass to determine chemical bonding parameters with special attention to the nitrogen atom. The dependence of the potential energy on the bridging bond length and the bond angle was calculated for the model molecule in the range of the geometry close to those for the minimum energy configuration. The bending force constant Kθ was 97.3 N/m, while Kr = 507 N/m was obtained as the stretching force constant. The Kθ value for the N[Si(OH)3]3 was much greater than the SiOSi bending force constant for the (HO)3SiOSi(OH)3 model molecule. This can be interpreted as showing why an oxynitride glass which is produced by substituting nitrogens for some of the oxygens in an oxide glass shows a much higher elastic modulus. The frequencies of the normal vibration calculated from these force constants were in accord with that corresponding to the same vibrational mode observed in the infrared spectra of the silicon oxynitride.

Ab initio molecular orbital calculation of the interatomic potential and force constants in silicon oxynitride glass

71Ga NMR spectra of GaAs and β-LiGaO2 crystals consisting of four-coordinated Ga3+ ions, GaNbO4 and α-Ga2O3 crystals consisting of six-coordinated Ga3+ ions, and PbO-Ga2O3 glasses were measured. About 240 ppm difference in chemical shift was observed between the spectra of β-LiGaO2 crystal and GaNbO4 crystal. It has been found that Ga3+ ions are mainly tetrahedrally coordinated by four oxygen ions in the glasses by comparison of spectra of the glasses with those of the crystals.

Sumio Sakka

Papers

Formation of particulate opaque silica gels from highly acidic solutions of tetramethoxysilane

Third Harmonic Generation in PbO-SiO2 and PbO-B2O3 Glasses

Glass formation and optical properties of glasses in the systems (R2O or R'O)-Ta2O5Ga2O3

Ab initio molecular orbital calculation of the interatomic potential and force constants in silicon oxynitride glass

Coordination of Ga3+ ions in PbO-Ga2O3 glasses as determined by 71Ga NMR