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In this study, nucleation and growth of bone-like hydroxyapatite (HAp) mineral in modified simulated body fluids (m-SBF) were induced on chitosan (CS) substrates, which were prepared by spin coating of chitosan on Ti substrate. The m-SBF showed a two fold increase in the concentrations of calcium and phosphate ions compared to SBF, and the post- NaOH treatment provided stabilization of the coatings. The calcium phosphate/chitosan composite prepared in m-SBF showed homogeneous distribution of approximately 350 nm-sized spherical clusters composed of octacalcium phosphate (OCP; Ca8H2(PO4)6·5H2O) crystalline structure. Chitosan provided a control over the size of calcium phosphate prepared by immersion in m-SBF, and post-NaOH treatment supported the binding of calcium phosphate compound on the Ti surface. Post-NaOH treatment increased hydrophilicity and crystallinity of carbonate apatite, which increased its potential for bio- medical application.

The aim of this study was to investigate the role of the passive layers in galvanic corrosion of Ti–Nb alloys and commercially pure titanium (cp-Ti). Ti–Nb alloys with 5, 10, 15, and 20 wt% niobium (Nb) content were prepared using an arc-melting technique under high purity Ar gas. The cp-Ti was used as a control. The electrochemical corrosion behaviors were investigated by A.C. impedance, potentiodynamic polarization, and galvanic corrosion tests. According to the results of impedance analysis, the passivation layer on Ti–Nb alloys consisted of outer, intermediate, inner, and metal defect layers, while the passivation layer on cp-Ti consisted of outer, intermediate, and inner layers. According to the results of anodic polarization tests, Ti–Nb alloys exhibited better zero potentials and reduced zero current densities. The outer layer and the inner layer of Ti–Nb alloys and cp-Ti had an effect mainly on the values of the initial galvanic current density and the sign of galvanic current density, respectively. Ti–10Nb alloy exhibited a relatively high initial galvanic current density compared to the other Ti–Nb alloys. Unlike Ti–5Nb, Ti–10Nb, and Ti–15Nb, which exhibited galvanic current densities with a minus sign, Ti–20Nb exhibited a galvanic current density with a plus sign due to its weaker inner layer than that of Ti.

Recently, a quantum mechanical Class II force field (QMFF) was derived from a fit of HF/6–31G* ab initio energy and energy derivative data for alkanes, and a comparison of this quantum force field and the ab initio energy and energy derivatives was presented. In this work, the quantum force field is further evaluated with regard to its accuracy, and, more importantly, transferability. A detailed comparison between structures, frequencies, and energies calculated from quantum mechanics and from the classical analytical form is given for a set of molecules selected from both those used in the original training set and molecules selected from outside the training set. None of these properties were used directly in the original derivation of the force field. In order to assess the importance of anharmonic and coupling interactions that occur in and contribute to molecular energy surfaces, the results are compared to a diagonal quadratic force field. It is demonstrated that the QMFF functional form is capable of calculating the ab initio bond lengths, bond angles, torsion angles, and conformational energy differences to an rms accuracy of 0.003 A, 0.4°, 1.2°, and 1.0 kcal/mol, respectively. This compares quite well to corresponding deviations of 0.006 A, 0.8 A, 2.3°, and 3.3 kcal/mol for a harmonic diagonal force field. Excluding three- or four-membered rings, the QMFF rms frequency deviations were 24 cm−1, which again is much better than the ˜100 cm−1 deviations for the harmonic diagonal force field. Larger average rms frequency deviations of 36 and 71 cm−1 were found with QMFF for molecules with three- and four-membered rings. An in-depth analysis of C-H and C-C bond length, H-C-H, H-C-C, and C-C-C bond angle, and C-C-C-C torsion angle deviations is also presented, along with a similar characterization of frequency deviations in C-H stretching, C-C stretching, C-C-C bending, and torsion modes. It is concluded from these results that the use of quantum energy surfaces allows us to derive a (Class II) functional form which is not only more accurate, but also more transferable than previous generation force fields.