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

A method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth. The theoretical analysis showed that the term ln[C
pd(δT)/dt+KδT] should be a linear function of l/T, whereC
p is the heat capacity of sample and sample holder,K is the heat transfer coefficient,δT is the temperature difference between the sample and reference substance andt is the time. The energy term,E
D, obtained by multiplying the slope of the resulting straight line byR is indicative of the activation energy for crystal growth. It was shown thatE
D should be three times the activation energy for crystal growth when bulk nucleation is dominant, and equal to that for crystal growth only when surface nucleation predominates. The result of the analysis was tested by comparing the experimentally determinedE
D's with the activation energy for viscous flow, which was known to represent that for crystal growth. TheE
D for Li2O·2SiO2 glass with dominant bulk nucleation, approached three times the activation energy for viscous flow, as the heating rate in DTA decreased. TheE
D for 33.3Li2O·66.7SiO2·3TiO2 glass with dominant surface nucleation approached the activation energy for viscous flow as the heating rate increased, suggesting the validity of the analysis.

Determination of the activation energy for crystal growth by differential thermal analysis

ZnO films were prepared on silica glass substrates by the sol-gel method from Zn(CH3COO)2⋅2H2O-2-methoxyethanol solutions containing monoethanolamine (MEA) or diethanolamine (DEA). Smooth and transparent ZnO films were obtained by heating at temperatures from 200 to 500°C for 10min after each coating and finally at the same temperatures for 1h. The films prepared from coating solutions containing MEA were strongly oriented along the (002) plane. The effects of heating temperature and ethanolamines on the film morphology, grain size distribution and crystallographic orientation are discussed based on X-ray diffraction and scanning electron microscopy.

Preparation of ZnO Films with Preferential Orientation by Sol-Gel Method

Raman spectra of K2O-Nb2O5-SiO2 glasses are measured in order to compare the coordination state of Nb5+ ions in gallate glasses with that in silicate glasses. It is found that less-distorted NbO6 octahedra with no non-bridging oxygens as well as NbO6 octahedra with non-bridging oxygens and/or with much distortion are present in the K2O-Nb2O5-SiO2 glasses. The Raman band in the 800 to 900 cm−1 region is attributed to the NbO6 octahedra with non-bridging oxygens and/or with much distortion. The broad bands in the 600 to 800 cm−1 region are attributed to less-distorted NbO6 octahedra with no non-bridging oxygens. An increase in the molar ratio Nb2O5/K2O leads to an increase in the oxygens shared by more than two polyhedra and/or a decrease in non-bridging oxygens for the NbO6 octahedra which possess non-bridging oxygens, or to an increase of distortion for much-distorted NbO6 octahedra. At the same time, an increase in the molar ratio Nb2O5/K2O increases the less-distorted NbO6 octahedra with no non-bridging oxygens. In short, GaO4 tetrahedra and NbO6 octahedra compete to attract alkali ions in gallate glasses but such competition is not found in silicate glasses.

Coordination state of Nb5+ ions in silicate and gallate glasses as studied by Raman spectroscopy

The effect of preparation condition on the melting behavior and the effect of nitrogen content on the properties were investigated for CaAlSiON OXYNITRIDE GLASSES. It was found that melting at lower temperatures produces more homogeneous and clearer glasses than melting at higher temperatures when the glass is melted at temperatures between 1530°C and 1750°C. The density, glass transition and softening temperatures, Vickers hardness and Young's modulus increased markedly with increasing nitrogen content. The observed values of densities of nitrogen-containing glasses was found to agree well with the additivity calculation based on the assumption that each nitrogen atom in the glass structure is connected with three silicon atoms.

Preparation and properties of CaAlSiON oxynitride glasses

Sol-gel-derived TiO2 film semiconductor electrode for photocleavage of water : preparation and effects of postheating treatment on the photoelectrochemical behavior

Sumio Sakka

Papers

Determination of the activation energy for crystal growth by differential thermal analysis

Preparation of ZnO Films with Preferential Orientation by Sol-Gel Method

Coordination state of Nb5+ ions in silicate and gallate glasses as studied by Raman spectroscopy

Preparation and properties of CaAlSiON oxynitride glasses

Sol-gel-derived TiO2 film semiconductor electrode for photocleavage of water : preparation and effects of postheating treatment on the photoelectrochemical behavior