PART I: FABRICATION AND SURFACE MODIFICATION OF COMPOSITE BIOMATERIALS BASED ON SILICON AND CALCIUM DISILICIDE; PART II: SYNTHESIS AND CHARACTERIZATION OF ERBIUM DOPED SILICON NANOCRYSTALS ENCAPSULATED BY ALUMINUM AND ZINC OXIDES

• Main Author: Seregin, Vladimir Victor
• Other Authors: Jeffery L Coffer
• Format: Others
• Language: en
• Published: Texas Christian University 2006
• Subjects: College of Science and Engineering
• Online Access: http://etd.tcu.edu/etdfiles/available/etd-04252006-145309/

A dry-etch spark ablation method was used to produce porous silica (SiO2/Si) and calcium disilicide (CaSi2/Si) layers on silicon (Si) surfaces for the electrochemical growth of apatitic phosphates (CaP). Both SiO2/Si and CaSi2/Si composite electrodes readily calcify in vitro under the application of a small electric potential, and with proper treatment the electrodeposition of CaP is localized to the sparked areas. In addition to increasing the local concentration of Ca2+, interfacial layers of CaSi2 on Si exhibit exceptional site-selectivity towards CaP formation under bias due to the difference in conductivity between Si and CaSi2. This work also describes routes to surface modification of calcified composite electrodes with medicinally relevant compounds. To assess the suitability of this material as an antibiotic delivery platform, release of norfloxacin was also monitored as a function of time. Mechanistic insights regarding biomineralization of CaSi2/Si layers on Si surfaces under zero bias were derived from an analysis of film growth morphology and chemical composition after various soaking periods in standard SBF. Changes in CaSi2 calcification behavior as a function of reaction temperature and pH, SBF concentration, and various surface modification processes were also employed for this purpose. The incorporation of CaSi2 grains within a polycaprolactone (PCL) framework results in bioactive and biodegradable scaffolds which may be used in bone tissue regeneration. Porous PCL scaffolds were prepared via a combination of salt-leaching/microemulsion methods. To provide markedly different structural environments for the inorganic phase, calcium disilicide powder was either added to a mixed-composition porogen during a given scaffolds preparation, or alternatively added to pre-formed scaffolds. Selective fluorescent labeling, SEM, and EDX were employed to assess scaffold calcification in vitro. A separate part of this work deals with rare earth-doped Si nanocrystals. Several selective surface modification reactions with inorganic capping layers comprised of either aluminum or zinc oxide were analyzed in an attempt to improve the photoluminescence (PL) efficiency of these nanocrystals by reducing interfacial defect density. It is shown that coating Er/Si-NCs with aluminum oxide via kinetically controlled chemical reaction doubles the PL efficiency. Zinc oxide, deposited under thermodynamic control, improves the PL by a factor of four.