TEM studies of calcium phosphates for the understanding of biomineralization.

摘要

Calcium phosphate (Ca-P) formation and bone minerals have been the focus of research for several decades because achievements in these areas could provide valuable insights into the understanding of biomineralization. In this thesis work, Ca-P formation, octacalcium phosphate (OCP) to hydroxyapatite (HA) transformation and bone minerals were systematically studied by transmission electron microscopy (TEM) techniques.; Ca-P formations on various bioceramics in simulated body fluid and in rabbit muscle sites were investigated. The bioceramics included sintered bioglass RTM, A-W glass-ceramics, HA, alpha-tricalcium phosphate (TCP), beta-TCP and HA-TCP. The comparative studies showed that OCP formation occurred on all types of bioceramic surfaces in vitro and in vivo, except on beta-TCP; however HA formation did not occur on every type of bioceramics; it less likely occurred on the surfaces of HA and alpha-TCP. These findings were contradicted to the common statements in literatures.; OCP to HA transformations in vitro and in vivo were observed by high-resolution TEM (HRTEM). The in vitro transformation was induced by electron beam irradiations of in situ TEM on synthetic OCP crystals. The in vivo transformation was revealed on rod-like HA precipitates formed in dog muscle sites. Based on HRTEM examinations and image simulations, OCP/HA crystallographic orientations were determined to be OCP (010) // HA (01¯0) and OCP (001) // HA (001¯), which differed from a well known model proposed by Brown et al.; The minerals of cortical bone were extracted from human tibiae and rat femurs using 10% neutral ethylenediamine tetraacetic acid (EDTA) solution. TEM examinations showed that the dominance of bone minerals was plate-like and a few were needle-like. The length of most plate-like minerals ranged from 50 to 150 nm but could be up to 200 nm. To the author's knowledge, OCP structure was for the first time, identified in a number of plate-like bone minerals by selected area electron diffraction (SAED) and HRTEM.