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

Na+ ⇌ Li+ Ion Exchange in Fluoride Glasses

Two types of silver chloride photochromic glasses, one based on the Na2O-B2O3-Al2O3-SiO2 system (Glass I) and the other on the Li2O-Na2O-B2O3-Al2O3-SiO2 system (Glass II), which were prepared by precipitating AgCl crystals at high temperatures of 560°-580°C, have been reheated at low elevated temperatures ranging from 200° to 520°C, and ultraviolet induced darkening has been measured. It was found that the reheating markedly affected the darkening characteristics of the photochromic glasses and the effect varied with their base composition and thermal history of the glass. Generally, the degree of darkening of Glass I lowered as a result of reheating, regardless of the reheating temperature. Especially, it lowered to the value as low as 50% of that before reheating when the glass was reheated around 520°C. On the other hand, a pronounced increase in the degree of darkening, reaching 100-200% sometimes, occurred when some samples of Glass II were reheated at the temperatures in the range 300°-420°C. No increase in the degree of darkening was seen in Glass II, however, when the condition of heating for precipitation of AgCl crystals was different and the degree of darkening before the reheating was already high. The rate of fading of U. V. -darkened photochromic glasses was also affected by the lower temperature reheating.The occurrence of these variations of photochromic characteristics resulting from the heating at low elevated temperatures seems to indicate that the “AgCl” particles precipitated in glasses are actually mixtures or solid solutions of AgCl and NaCl (or LiCl) and that the reheating alters the state of solid solution within the particles.

http://www.jstage.jst.go.jp/article/jcersj1950/82/943/82_943_165/_pdf

Effect of Heat Treatment on Darkening and Fading of Photochromic Glasses

L'INVENTION CONCERNE UN PROCEDE DE PRODUCTION D'UNE PELLICULE DE VERRE. SELON L'INVENTION, IL CONSISTE A PREPARER UNE SOLUTION D'ALCOOLATE CONTENANT UN ALCOOLATE DE SILICIUM, DE L'EAU ET UN SOLVANT ORGANIQUE HYDROPHILE; A LAISSER L'ALCOOLATE DE SILICIUM DANS LA SOLUTION S'HYDROLYSER JUSQU'A CE QUE CETTE SOLUTION DEVIENNE UNE SOLUTION VISQUEUSE DE FACON APPROPRIEE; A FORMER UNE PELLICULE DE LA SOLUTION VISQUEUSE DANS UN ESPACE LIBRE; ET A CHAUFFER LA PELLICULE JUSQU'A UNE TEMPERATURE SUFFISANTE POUR LA CONVERTIR EN UNE PELLICULE DE VERRE. L'INVENTION S'APPLIQUE NOTAMMENT A LA FORMATION DE PELLICULES DE PROTECTION POUR AUTRES VERRES, MATIERES PLASTIQUES ET AUTRES.

Procede de production d'une pellicule de verre en utilisant une solution contenant de l'alcoolate de silicium

S showed that, during its heat treatment, ,8-eucryptite was first precipitated at about 850°C and then ,8-spodLlmene at about 1000uC. Microscopic examination showed that ,8-spodumene, after its precipitation, decreased its grain size by fission, by still unknown reason, with increasing temperature. Above 1000°C the marked increase in specific density of the specimen with increasing temperature was also observed. ( il) Effects of heat treatments on streng-tho The conditions of heat treatment such as the heating rate and the maximum holding temperature were varied and their effects on the modulus of rupture of the resultant polyerystalline materials were determined. The slow heating with the rate at least below 5\"Cj min. in the temperature interval of 800 to 900°C, in which ,8-eucryptite was first precipitated in the specimen, was found to be necessary increasing the strength. The specimen which missed this heat treatment had poor strength. The strength was also found to increase with incresing the maximum holding temperature. This change was attributed to the decrease in grain size of ,8-spodumene and also to the compacting of microstructure. Studies on the Dielectric Loss of PolycrystalIine Material Produced from the Glass of the System LizO-MgO-AhOa-SiOe Sumio SAKKA and Megumi TASHIRO Yogyo Kyolwishi (Journal of the Ceramic Association, japan), 69, 393 (1961) In the previous paper (J. Ceram. Assoc. japan, 60 [10J 223 (1960» the authors have given the method of converting the glasses of the system LLO-MgO-ALO,,SiOz into a polycrystalline material with or without the addition of platinum nucleus, the amount of which was limited to a very small value. The results of the measurement of the mechanical and thermal properties of the material produced were also published (J. Ceram. Assoc., japan, 69 [2J 35 (1961». The present paper concerns the dielectric loss of the same material which was expected to show the effect of chemical composition and heat treatment. ( 1) Effect of heat treatment. The glass of the composition, MgO 15, AleO\" 23, Si02 62, Li20 x, I\",here x 4, 6, 8, 12 by weight ratio, were melted, and reheated with the constant rate of 5°Cjmin. to a temperature from 750°C to 1200°C. The tan 0 at 1 Me of the crystallized specimens showed that, in general, it became higher than the base glass by the heat treatment at a temperature between 750°C and 950°C, whereas the heating at a temperature higher than 1000°C brought about a great deCl-ese in tan o. The increase of tan 0 may be attributed to the formation of ,8-eucriptite which usually occurs in the low temperature range, while the sudden decrease in tan 0 may be attributed to the formation of ,8-spodumen which appears with the cost of vanishing ,8-eucryptite. ( 2) Effect of the chemical composition of the base glass. It is likely that

/pdf/studies-on-the-dielectric-loss-of-polycrystalline-material-3ozg0rx3cb.pdf

Sumio Sakka

Papers

Na+ ⇌ Li+ Ion Exchange in Fluoride Glasses

Effect of Heat Treatment on Darkening and Fading of Photochromic Glasses

Procede de production d'une pellicule de verre en utilisant une solution contenant de l'alcoolate de silicium

Studies on the Dielectric Loss of Polycrystalline Material Produced from the Glass of the System Li₂O-MgO-Al₂O₃-SiO₂

Effects of Vanadium Oxide on the Strength of Adherence of Heat Resisting Enamel Applied on Nickel-Chrome Stainless Steel