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京都大学 / 新制・課程博士 / 博士(工学) / 甲第24105号 / 工博第5027号 / 新制||工||1784(附属図書館) / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 安部 武志, 教授 阿部 竜 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

Articular cartilage has limited intrinsic healing capacity due to its dense and avascular structure. Clinical approaches have been developed to address the limitations associated with the poor ability of articular cartilage to regenerate. Current clinically approved techniques, however, can result in repair tissue that lacks appropriate hyaline cartilage biochemical and biomechanical properties, which lead to uncertain long-term clinical outcomes. Using tissue engineering strategies and a range of scaffolding materials, cell types, growth factors, culture conditions, and culture times, engineered tissues have been produced with compositional and biomechanical properties that approximate that of native tissue. In these studies, a considerable number of samples are typically sacrificed to evaluate compositional and mechanical properties, such as the amount of deposited collagen and sulfated glycosaminoglycan (sGAG) in the constructs. The number of sacrificed samples, as well as the amount of time and resources spent to evaluate the sacrificed samples using current gold standards, motivates an alternative method for evaluation of compositional properties. Vibrational spectroscopy, including infrared, has been considered as an alternative technique for assessment of tissues over the last 15-20 years. Infrared spectroscopy is based on absorbance of infrared light by tissue functional groups at specific vibrational frequencies, and thus, no external contrast is required. Vibrational spectroscopy is typically performed in two frequency regions, the mid infrared region (750-4000 cm-1), where penetration depth is limited to approximately 10 microns, and the near infrared (NIR) region (4000-12000 cm-1). In the NIR region, penetration of light is on the order of millimeters or centimeters, which makes it ideal for obtaining data through the full depth of engineered constructs. Here we employ NIR spectroscopy to nondestructively monitor the development of tissue-engineered constructs over culture period. / Bioengineering

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Infrared reflectivity and transmittance measurements (200-5000 cm⁻¹) were carried out on heavily-doped GaAs:C films grown by molecular beam epitaxy. With increasing carbon concentration, a broad reflectivity minimum develops in the 1000-3000 cm⁻¹ region and the one-phonon band near 270 cm⁻¹ rides on a progressively increasing high-reflectivity background. An effective-plasmon/one-phonon dielectric function with only two free parameters (plasma frequency ω_p and damping constant γ_p) gives a good description of the main features of the reflectivity spectra. The dependence of effective plasma frequency on hole concentration p is linear. At each doping, the effective-plasmon damping constant γ_p is large and corresponds to an optical hole mobility that is about half the Hall mobility at that p. Secondary-ion mass spectroscopy and localized-vibrational-mode measurements indicate that the Hall-effect-derived hole concentration is close to the carbon concentration and that the Hall factor is close to unity, so that the Hall mobility provides a good estimate of the actual dc mobility. Also, analysis shows that, for our highly-doped samples, the observed dichotomy between the dc and infrared mobilities is not a statistical-averaging artifact of the approximations involved in the model. The explanation of the small infrared mobility resides in the influence of intervalence band absorption on the effective-plasmon fit, which operationally defines that mobility via the effective-plasmon damping. The optical properties obtained with the use of the effective-plasmon model for GaAs:C yield a phenomenological, approximate, overall picture of the infrared spectra. But the neglect of intervalenceband transitions, for this p-type semiconductor, is shown (in this dissertation) to be a serious drawback of this simple model. In order to obtain the optical properties of GaAs:C in a model-independent way, and to attempt to resolve the apparent dc/infrared mobility dichotomy, we made use of a recently-developed spectroscopic-analysis procedure. Using direct numerical-solution techniques for the reflectance (R) and transmittance (T) equations of a multilayer structure, we analyzed our infrared R and T results for highly-doped films having hole concentrations from 2 × 10¹⁹ up to 1.4 × 10²⁰ cm⁻³. The optical properties were determined for photon energies from 0.07 to 0.6 eV, in which region plasmon (intraband) and intervalenceband contributions are in competition. Our results for the optical absorption coefficient resolve two separate peaks located (at high doping) at about 0.1 and 0.2 eV. (The effective-plasmon model necessarily missed the two-peak character of the actual absorption spectrum.) By carrying out theoretical calculations of the intervalenceband (IVB) absorption processes for our dopings, we identify the peak near 0.2 eV with light-hole to heavy-hole IVB transitions, and we attribute the lower-energy peak to the hole plasmon. Our experimental absorption spectra are very well described by a model combining the intervalenceband contribution to the dielectric function with a plasmon contribution. The hole-plasmon parameters ω_plasmon and γ_plasmon that we obtain for highly-doped p-GaAs yield an infrared mobility which (unlike the too-small IVB-entangled infrared mobility implied by the use of the usual effective-plasmon model) is in substantial agreement with the dc mobility. Therefore, in actuality, there is no dc/infrared mobility discrepancy. The discrepancy implied by the use of the usual, standard-operating-procedure, effective-plasmon model is a consequence of the inadequacy of that model for p-type semiconductors exhibiting intervalenceband infrared absorption. Raman-scattering measurements were carried out on the GaAs:C films. Only the phononlike coupled plasmon-phonon mode is observed. The non-occurrence of the plasmonlike mode is due to the large damping of the hole plasmon and the competition with strong Raman scattering by intervalenceband transitions among the heavy-hole, light-hole, and split-off bands. Analysis of the phononlike coupled mode, within the framework of the wavevector-dependent Lindhard-Mermin dielectric function, supports the hole properties that we determined by Hall and infrared studies. Photoluminescence measurements showed that the split-off band also participates in the photoluminescence of GaAs:C, giving rise to an above-bandgap emission band corresponding to transitions from the conduction band to the split-off valence band. / Ph. D.