The orientation and structure of pyridine adsorbed on a highly ordered Au(111) surface from 0.1 M
NaClO4 + x M (10-6 ≤ x ≤ 10-3) pyridine aqueous solutions have been investigated as a function of applied
potential by in situ surface-enhanced infrared absorption spectroscopy (SEIRAS) and scanning tunneling
microscopy (STM). Symmetric in-plane pyridine ring vibrations (A1 modes) were observed in the SEIRA
spectra at potentials positive of about −0.3 V versus SCE, while asymmetric in-plane ring vibrations (B1
modes) were hardly detected. The symmetric ring-breathing mode showed a blue shift upon adsorption,
indicating the adsorption via the N atom. The band intensities were found not to be proportional to the
surface concentration (the relative Gibbs surface excess) reported in the literature. On the basis of the
surface selection rule in SEIRAS, the results are explained in terms of the potential-dependent reorientation
of pyridine. The molecule is flatly adsorbed on the surface at negative potentials, and its molecular plane
rises up as the applied potential increases and the surface concentration increases. Flat-lying, tilted, and
vertically standing pyridine molecules were observed at different potentials also by STM for the first time.
Bone marrow has been shown to contain a population of rare cells capable of differentiating to the cells that form various tissues. These cells, referred to as mesenchymal stem cells (MSCs), are capable of forming bone when implanted ectopically in an appropriate scaffold. The aim of this study was to investigate the potential of a new beta-tricalcium phosphate (beta-TCP) as a scaffold and to compare the osteogenic potential between beta-TCP and hydroxyapatite (HA). The beta-TCP and HA loaded with MSCs were implanted in subcutaneous sites and harvested at 1, 2, 4, and 8 weeks after implantation for biochemical and histological analysis. Biochemically, in both beta-TCP and HA composites, the alkaline phosphatase activity in the composites could be detected and was maintained at a high level for 8 weeks. In the histological analysis, active bone formation could be found in both the beta-TCP and HA composites. These findings suggest that beta-TCP could play a role as a scaffold as well as HA. The fabricated synthetic bone using biodegradable beta-TCP as a scaffold in vivo is useful for reconstructing bone, because the scaffold material is absorbed several months after implantation.
Poly(lactic acid) composites containing a mixture of calcium carbonates (vaterite, aragonite, and calcite) were prepared by a carbonation process in methanol. Soaking of the composites for 3 h in simulated body fluid (SBF) at 37°C resulted in the deposition of bonelike apatite particles on the composite surface. After soaking the composites, vaterite phase in the composites was forward to dissolve rapidly, resulting in increase the supersaturation of the apatite in SBF. 13 C cross-polarization magic angle spinning nuclear magnetic resonance ( 13 C CP/MAS-NMR) spectra of the composites suggested the formation of a bond between Ca 2+ ion and the COO − group, which induces the apatite nucleation. These results may elucidate the mechanism of means to reduce the induction period for apatite formation.Artificial materials are generally encapsulated by a fibrous tissue to be isolated from the surrounding bones when implanted into the bone defects. However, a kind of ceramics and glasses such as hydroxyapatite ceramics or Bioglass bond directly to living bone without forming the fibrous tissue and they are often called bioactive materials. They form a carbonate-containing hydroxyapatite layer on their surface in the living body and bond to living bone through apatite layers. 1,3 This layer is very similar to the apatite in the bone in its composition and structure (bonelike apatite). 4 The apatite can be formed biomimetically on bioactive materials even in simulated body fluid (SBF), which is a buffer solution with inorganic ion concentrations nearly equal to those of human blood plasma. 5 Two indispensable conditions needed for the formation of bonelike apatite on materials are (i) the existence of the surface functional groups that induce nucleation of the apatite and (ii) the supersaturation of the apatite in body fluid or SBF should be increased. [5][6][7] Materials having a high bioactivity or biodegradability play an important role in the recovery of the part of bone defects. In this work, highly bioactive bone-filler materials were prepared for bone substitution at an early stage after clinical operation. Biodegradable poly(lactic acid) (PLA), because of many carboxy groups, is one of the promising candidates for supplying inducers for the bonelike apatite nucleation. A carboxy group is known to induce apatite nucleation 6 and can be formed by hydrolyzation of PLA. To increase the supersaturation of apatite in body fluid or SBF, a large amount of Ca 2+ ions should be dissolved from the materials. Formation of apatite having lattice constant and Ca/P atomic ratio close to those of natural bone has been reported to influence carbonate ions in the solution. 8 From this point of view, calcium carbonate is expected to supply both Ca 2+ and carbonate ions simultaneously into body fluid or SBF resulting in increase in the supersaturation of the apatite.It is well-known that calcium carbonate has three polymorphs, viz., calcite, aragonite, and vaterite. Solubility of vaterite is higher than that of calcite or aragonite. 9...
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