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 vibrational spectra related to the SiO 4 units have been non-empirically calculated, in order to simulate the effect of incorporation of non-bridging oxygens into silica network. Harmonic frequencies and force constants have been calculated for the silicate anion model clusters in silica, disilicate, metasilicate, pyrosilicate and orthosilicate composition by ab initio molecular orbital method using STO-3G basis set at Hartree-Fock SCF level. The calculation showed that the totally symmetric Si-O stretching vibrations of SiO 4 tetrahedra shifted to lower wavenumbers with increasing number of nonbridging oxygens.

AB initio molecular orbital study on the vibrational spectra of silicate glasses

The SiKβ fluorescence X-ray and infra-red absorption spectra of Na2O-TiO2-SiO2 and K2O-TiO2-SiO2 glasses have been measured in order to study the Si-O bonding as a function of the composition of glass. The chemical shifts of the SiKβ peak relative to that of silica glass [Δλ=λ(SiO2)-λ(specimen)>0] and the wavenumbers of the infra-red absorption peaks around 950cm−1 and 1100 cm−1 have been determined from the spectra. The SiKβ chemical shift in both series of glasses increased with increasing total content of R2O and TiO2 and with decreasing ratio of TiO2/(K2O+TiO2), where R2O represents Na2O or K2O. The infra-red peaks around 950 cm−1 and 1100 cm−1 shifted towards lower wavenumbers with increasing total content of R2O and TiO2 and with decreasing ratio of TiO2/(R2O+TiO2). These experimental facts were interpreted as showing that the Si-O bond in glass was weakened as the total content of R2O and TiO2 increased and that the Si-O bond was weakened by R2O more than by TiO2.

The Si-O bonding in Na2O-TiO-SiO2 and K2O-TiO2-SiO2 glasses as studied by SiKβ X-ray fluorescence and infra-red absorption spectroscopy

The structure and distribution of chemical species of hydrolysis and polycondensation products of methyltriethoxysilane in aqueous solutions containing sodium ions have been studied with the trimethylsilylation technique and by 29 Si n.m.r. spectroscopy. 11 trimethylsilylated derivatives of the products were obtained from the solutions. The recovery of methyltrisilanol (CH 3 Si(OH) 3 was much higher than that of the monosilicic acid in an aqueous sodium silicate solution at the same Si concentration and the same sodium ion-to-silicon molar ratio, suggesting that the polymerization of silicate anions is easier than that of hydrolysis products of methyltriethoxysilane in aqueous solutions. On the basis of the distribution, assignment of 29 Si n.m.r. peaks corresponding to low-molecular weight species formed from methyltriethoxysilane has been discussed

Polymerization of hydrolysis products of methyltriethoxysilane in aqueous solutions

The occurrence of the spinnability in the sols prepared by the hydrolysis and polycondensation of tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane and tetranormalbutoxysilane has been investigated. It has been found that the spinnability appears at high viscosities in all of these solutions when the H2O/Si(OR)4 mole ratio of the starting solution is 2 and an acid is used in the hydrolysis reaction. It has also been shown that the spinnable solutions show the Newtonian behavior at high viscosities.

Fiber Drawing from Silicon Alkoxide Solutions in the Sol–Gel Process

Ferroelectric Pb(Fe0.5Nb0.5)O3(PFN)-PbTiO3(PT) thin films have been prepared on silica glass and silicon single crystal substrates by the sol-gel method using lead acetate, iron nitrate, niobium ethoxide and titanium tetraisopropoxide as precursors. It has been found that 38 mol% excess lead must be added to a starting solution to obtain single phase perovskite PFN coating films, while single phase perovskite 0.2PFN·0.8PT coating films can be prepared from the corresponding stoichiometric starting solution. The coating film shows a dielectric constant of about 500-1100 and dielectric loss of about 0.06-0.18 at 1000 Hz.

Sumio Sakka

Papers

AB initio molecular orbital study on the vibrational spectra of silicate glasses

The Si-O bonding in Na2O-TiO-SiO2 and K2O-TiO2-SiO2 glasses as studied by SiKβ X-ray fluorescence and infra-red absorption spectroscopy

Polymerization of hydrolysis products of methyltriethoxysilane in aqueous solutions

Fiber Drawing from Silicon Alkoxide Solutions in the Sol–Gel Process

Preparation of Lead-Based Perovskite Films by Sol-Gel Method and Their Properties : Thin Films