Abstract
In the recent years, devices of micro-electro-mechanical systems (MEMS) or biochips for diagnosis to be implanted into human body require a biocompatible and protective coating to avoid inflammatory effects. Besides, photo-luminescent agents are playing important roles in gene transfection, diagnoses and bio-optoelectronics. In the first part of this dissertation, I had developed a method to deposit a bioactive hydroxyapatite (HAp) layer onto pretreated hydrophilic Si (111) and Si (100) from supersaturated solutions of Ca2+ and PO43- ions with a pH value 7.4 at 298K. The deposition started with an initial uniform deposit at a low rate around 25 nm/h. Growth then took place predominantly along the direction normal to the substrate through in-plane nucleation of multiple embryos at a high rate around 325 nm/h. The deposition rate increased with increasing time duration, attaining a maximum at a thickness around 8 μm, and then decreased. Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS) indicated the presence of HAp with typical chemical states. X-ray diffraction pattern of a 4-day deposit showed the direct formation of crystalline HAp corroborating with the XPS results. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) observations showed the wavy coating on Si (100). In the second part, three polymers including collagen, diblock PEG-PLGA copolymer and triblock PEG-PLGA-PEG copolymer were utilized for biomimetic hydroxyapatite preparation. Average crystallite sizes of precipitated HAp from polymer solutions were estimated from XRD patterns to be ca. 23 nm for those in collagen-HAp hybrids and 30 nm for those without polymer addition. Transmission electron microscopy (TEM) and SEM micrographs showed the organic macromolecules induced HAp has regular plate-like shapes and nano-sized structure. Solid state NMR revealed polymer incorporation in HAp crystal. The hybrids containing these biodegradable polymers can be processed to various morphologies for tissue engineering applications. In the third part, photo-luminescent (PL) properties of prepared HAp coatings and composite powders were studied. Color-center-doped HAps were prevalently used as fluorescent materials. HAp based PL material might be an ideal agent for bio-imaging. The PL spectra using a 325 nm He-Cd laser source showed that the as-prepared HAp coatings on silicon substrate emitted phosphorescent light peaking at 463 nm and 513 nm. Intensity of emission was greater with increasing coating thickness. Collagen alone emitted brighter fluorescence peaked around 410 nm but was quickly quenched, while collagen-HAp composite powders (col-HAp) emitted sustaining PL light peaking around 415 nm. In vitro transfection results of HEK-293 cell showed that col-HAp is an efficient gene delivery agent for GFP-containing plasmid without cyto-toxicity, and could be easily differentiated under an optical microscope. The developed photo-luminescent bioceramics are of great potential in bio-optoelectronics.