Study On Controllable Preparation, Characterization And Stabilization Of Apatite Nanoparticles For Biomedical Applications

The dimensions of nanoparticles range from 1 to 100 nanometers in diameter. Nanoparticles are capable of many properties that are different from both macroscopic materials and microscopic single atoms due to nanoeffects. This dissertation studies on preparation and characterization of nano apatite sol for biomedical applications, controllable growth of nanoparticles and stability mechanism of nano apatite sol. The goals of these studies are to obtain apatite nanoparticles whose dimensions fall into a narrow scope, to realize the controllable synthesis of apatite particles and to search suitable stabilizer of the sol. The dispersion characteristics of apatite nanoparticles and stability mechanism are studied in the dissertation. Some biomedical nanoeffects of apatite nanoparticles are discussed as well.Hydroxyapatite, strontium-containing apatite and strontium apatite are prepared through homogeneous co-precipitation method, hydrothermal method and acid-base neutralization titration method. The size and size distribution are controllable in the preparation process. Apatite nanoparticles with given size could be obtained when the desired mean diameter of particles is between 20 nanometers and 100 nanometers. Furthermore, the size distribution scope could be very narrow. For instance, among those particles with 75.7 nanometers as mean diameter, the dimension difference between the smallest particle and the biggest one is less than 16 nanometers. The diameter deviation among particles is 10% only.It is realized to controllably synthesize apatite nanoparticles in given morphology. Transmission electron microscope and atomic force microscope are applied to study the particles. The hydroxyapatite particles are spherical grains. All particles are nearly the same in morphology and size.The c axis of the gained hydroxyapatite is elongated while a, b axis are shortened. The growth priority along c orientation is restrained by these changes of crystal lattice parameters. The grains do not grow in needle-like shape. For apatite, the elongation of c axis means the distance between Ca²+ and O²- in tetrahedral [PO₄]becomes longer. Thus the Ca2+ ions are more active in reaction. The reaction activity is the structure base of bioeffects of nano apatite. It enables apatite higher activity. The crystal lattice parameters of strontium-containing apatite and strontium apatite are also distinctively altered.With increasing of strontium ions substitution for calcium ions in apatite, the absorption band of hydroxyl group shifts towards high wave numbers. There is regularity between the shift and cation substitution. The wave number of OH' band increases with an increase in the radii of cations of hydroxyapatite owing to the increase in hydrogen bond distance OH--O. The doping of strontium cation in apatite also has effects on P-0 bond in [PO4] tetrahedron. The wave number of PO43" band decreases with an increase of substitution of strontium cations for calcium cations in hydroxyapatite crystals. The shift direction of phosphate anion bang is opposite to that of hydroxyl group band. The array and orientation of [PO4] tetrahedron are affected by the doping of strontium cations; and the length of P-0 bond is changed by them too. These effects result in diversity of physicochemical and biological characteristics of three kinds of apatite.The surface elements and their distribution of nano apatite are studied by Auger electron spectrum and energy dispersive spectrum. The qualitative analysis of Auger electron spectrum about surface elements reveals that no special elements are accumulated or segregated. The energy dispersion spectrum indicates that there are calcium vacancies in the crystal structure of nanoparticles. The hexagonal symmetric lattice is modified so spherical grains form. The deficiency of calcium on surface lowers the stability of the crystal surface which results in high reaction activity.Specific surface of nanoparticles are measured by nitrogen adsorption method. The BET specific surface area of nano apatite is more than 150 square meters per gram while Langmuir specific surface area is higher than 250 square meters per gram. That means there are nearly 20% of all atoms on the apatite nanoparticles' surface. Apatite nanoparticles thus possess high surface effect.Solubility study on nano hydroxyapatite reveals that there is big difference between nano hydroxyapatite and normal block hydroxyapatite in solubility. The pKsp value of nano hydroxyapatite is about 75. That is quite different from the knownvalue-117 of hydroxyapatite. It is even slightly lower than that of amorphous calcium phosphate. It shows great difference between dissolution properties of nano hydroxyapatite and that of block hydroxyapatite. The solubility and dissociation degree of nano hydroxyapatite are much higher than those of block hydroxyapatite.The aquatic dispersion specialties of apatite nanoparticles are also discussed in the dissertation. The Zeta potential of the sol system is a token of the stability. The effects of stabilizer and its concentration on surface potential are studied. The dissertation gives deep discuss about variation trend of enthalpy-entropy when stabilizer exists. The adsorption model of stabilizer A on apatite surface is established capitalizing on surface Auger electron spectrum. Stabilizer's existence creates interspace steric effects and osmotic pressure effects. These effects make the sol system stable. The discussed stability mechanism is used as theory to select other kinds of stabilizer.Some bioeffects of three kinds of nano apatite are studied. Human liver cancer cells and normal hepatic cells are treated by three kinds of apatite nanoparticles. Synchrotron radiation X-ray fluorescence analysis is used to detect the content variation of calcium and phosphor elements in cancer cells when the cells are treated by hydroxyapatite nanoparticles. Experiments verify that the contents of calcium and phosphor elements in hepatocellular carcinoma have obvious increases after the cells are treated by hydroxyapatite nanoparticles. And the contents increase with hydroxyapatite concentration and treatment time increasing. The Ca/P molar ratio in treated cell is different from both that in hydroxyapatite and that in untreated cancer cell. Apatite nanoparticles evidently alter the calcium and phosphor environments in treated hepatocellular carcinoma cells. That finally halts the proliferation of carcinoma cells.