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

The electrical conductivities of (1− x ) Li 2 O · x BaO · 2 SiO 2 , (1− x ) Na 2 O · x MgO ·2 SiO 2 , (1− x ) Na 2 O · x CaO · SiO 2 and (1− x ) Na 2 O · x BaO · 2SiO 2 glasses were measured at temperature ranging from room temperature to 450°C. The transport numbers for Na + ion in (1− x ) Na 2 O · x BaO · 2 SiO 2 glasses were measured. It was found that the alkali ion carried a significant part of the current in these glasses except one that had no alkali ions, and the conductivity decreased markedly as the alkali oxide was substituted by an alkaline earth oxide. The results of conductivity measurements combined with the data hitherto reported on mixed alkali glasses led to the proposal that the so-called mixed alkali effect could be explained on the basis of the independent path model in which it is assumed that cations can move only through vacant sites left by those of the same type.

Electrical conductivities of mixed cation glasses

Kinetic Study on Non-Isothermal Crystallization of Glass by Thermal Analysis (Commemoration Issue Dedicated to Professor Megumi Tashiro on the Occation of his Retirement) Author(s) Matsushita, Kazumasa; Sakka, Sumio Citation Bulletin of the Institute for Chemical Research, Kyoto University (1981), 59(3): 159-171 Issue Date 1981-09-01 URL http://hdl.handle.net/2433/76947 Right Type Departmental Bulletin Paper Textversion publisher

https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/76947/1/chd059_3_159.pdf

Kinetic Study on Non-Isothermal Crystallization of Glass by Thermal Analysis (Commemoration Issue Dedicated to Professor Megumi Tashiro on the Occation of his Retirement)

X-ray radial distribution analysis and Raman spectroscopic measurement were carried out on Na2O-2TiO2 glass prepared by twin-roller quenching method. It is found that four-coordinated Ti4+ ions may be predominant over six-coordinated ones in the present glass. It is also found that the fraction of six-coordinated Ti4+ ions is larger in the present glass than in K2O·2TiO2 and Cs2O·2TiO2 glasses. Poorer glass-forming ability of the Na2O-TiO2 system compared with the K2O-TiO2 and Cs2O-TiO2 systems is ascribed to a larger fraction of TiO6 octahedron for the former system.

Structure of na2o.2tio2 glass

The surface of a TiO2 film electrode, about 1 μm thick, prepared by the sol-gel method, was modified by being additionally coated with about 0.1 μm thick TiO2SiO2, TiO2ZrO2 or TiO2Al2O3 films. The effect of the additional coating on the photoelectrochemical properties of a TiO2 film electrode was investigated in detail. On addition of the second additive to TiO2, the flat band potential was shifted toward negative potential for SiO2 and positive potential for ZrO2 and Al2O3, which is attributed to the change in the point of zero zeta potential (pzzp), not in the electron affinity (EA). However, enhancement in photocurrent was not observed for all the cases.

Surface modification of a TiO2 film electrode prepared by the sol-gel method and its effect on photoelectrochemical behavior☆

The SiKα and Kβ X-ray emission spectra of binary silicate glasses of the Li 2 O–SiO 2 , Na 2 O–SiO 2 , K 2 O–SiO 2 , Cs 2 O–SiO 2 , B 2 O 3 –SiO 2 , and GeO 2 –SiO 2 systems were measured with an X-ray fluorescence spectrometer to examine the chemical effects on the spectra. The SiKα peak wavelengths for all the glasses agreed with that for SiO 2 glass, which corresponded to the concept that the coordination number of Si shouldbe four in all the glasses examined in this study. The SiKβ peak wavelength decreased with increasing alkali content in the alkali silicate glasses, indicating that the Si–O bond weakend in average as the alkali oxide was added to SiO 2 glass. On the other hand, no drastic shift in the SiKβ peak wavelength was observed in the B 2 O 3 –SiO 2 and GeO 2 –SiO 2 systems, and this was interpreted as showing the constancy of Si–O bond strength in these glasses.

Sumio Sakka

Papers

Electrical conductivities of mixed cation glasses

Kinetic Study on Non-Isothermal Crystallization of Glass by Thermal Analysis (Commemoration Issue Dedicated to Professor Megumi Tashiro on the Occation of his Retirement)

Structure of na2o.2tio2 glass

Surface modification of a TiO2 film electrode prepared by the sol-gel method and its effect on photoelectrochemical behavior☆

Studies on binary silicate glasses based on the SiKα and SiKß emission X-rays