| Biomimetic apatites are calcium phosphate minerals which self-assemble to form crystalline structures under near-physiological conditions. Recent evidence suggests that the self-assembly process may be controlled to produce apatites with distinctive crystalline structures and concomitant biological properties. These biomimetic apatites have been shown to mediate and promote bone regeneration around wounds. However, the conventional apatite coating technique requires long immersion time (7-14 days) in simulated body fluid in vitro. The need to accelerate the apatite coating process and retain similar osteoconductivity is desired. Despite the large number of reports in the apatite field, relatively little is known about accelerated apatite coating technique, and even less is known about this precise formation mechanism and biological interactions. The objective of this thesis is to characterize the accelerated apatites and evaluate their biological effect. It was found that the accelerated apatites with plate-like morphology were calcium-deficient, carbonated and single crystalline structure in nature. These apatites supported osteoblastic attachment, spreading, viability, proliferation and promoted osteopontin (OPN), osteocalcin (OCN) and bone sialoprotein (BSP) gene expressions on two-dimensional apatite-coated polystyrene dishes and within three-dimensional apatite-coated porous bioresorbable synthetic scaffolds in vitro. The cross-sectional TEM micrographs demonstrated that MC3T3-E1 cells could remodel the apatite microenvironments during in vitro culture. In vivo, the accelerated apatites provided the microenvironment for primary osteoblasts, bone marrow-derived and adipose-derived stromal cells to heal critical sized mouse calvarial defects. Furthermore, the results indicated increased ERK1/2 phosphorylation occurred on apatite-coated surfaces and confirmed the protein layer was critical to mediate cell-apatite interactions. The apatite-promoted OPN expression was partially regulated by ERK1/2 phosphorylation and PKC pathways, but not Na-dependent phosphate transporters. Collectively, this thesis provides the initial understandings toward the formation and biological interaction of accelerated apatites. |
