Synthesis And Application Of Bone-like Hydroxyapatite

Since calcium phosphate (CaP) are the main inorganic constituents of bone and teeth in living organisms, the synthesis of CaP has become the focused issue in the fields of chemistry, materials and biomedicine engineering et.al. With the outstanding biocompatibility and biodegradability, CaP materials has been widely used in many area such as drug delivery, bioimaging and medicine tissue engineering et.al. Mimicking the formation of bone tissues enormously contributes to the understanding of biomineralization and biological hard tissues, and also contributes to the determination of the biological functions of ultrathin HAP platelets in bone. Moreover, the special properties of biomaterials may regulate the efficiency in medical diagnosis and medicine treatment. However, the synthesis of platy HAP with a large (100) surface have yet been reported. We synthesized platy HAP (p-HAP). The ultrathin characteristic and crystal orientation of p-HAP are similar to the biological HAP in bone. And our study also implies the great potential of bone-like HAP plates in biomedical applications for bone engineering. The thesis is composed of five parts, and the main investigate contents are described as follows:In chapter 1, we provide an overview about biomineralization, cells and extracellular matrix. Then, the preparation method and the bioactive effects of nano CaP materials are also described. Finally, we review the application of nano CaP in biomedicine.In chapter 2, hydroxyapatite (HAP) nanocrystallites in all kinds of bones are characterized by their ultrathin characteristics, which are uniaxially oriented with the fibrillar collagen to uniquely expose the (100) faces. Here, a new kind of HAP nanoparticles (p-HAP) were synthesized by using ethylene glycol (EG) as the solvent. The thickness of p-HAP was only 2-4 nm, and this dimension was similar to that of HAP in bone. And the high resolution transmission electron microscopy (HRTEM) image of p-HAP shows that the exposed crystal face of p-HAP was a (100) plane, indicating that the exposed crystal face of p-HAP is identical to the exposed crystal face of HAP platelets in bone. The ultrathin characteristic and crystal orientation of the p-HAP are analogous to the biological HAP in bone. Additionally, two kinds of rod-like HAP were also synthesized. The cytotoxicity of mesenchymal stem cells (MSCs) upon treatment with t-HAP, n-HAP and p-HAP confirmed that none of the HAP particles are biosecurity.In chapter 3, bone-like platy HAP (p-HAP) and two different rod-like HAPs (t-HAP and n-HAP) were used to prepare different HAP films to be the substrates for the in vitro experiments. The three kinds of HAP films used to estimate the ultrathin mineral modulating effect on cell bioactivity and osteoinductions. We found that the bone-like p-HAP film increased the adhesion and proliferation of MSCs, and showed a better effect than the other groups. Additionally, the alkaline phosphatase (ALP) data and quantitative polymerase chain reaction (PCR) results also suggested that bone-like p-HAP had better osteogenic ability than t-HAP and n-HAP. Cell bioviability and osteogenic differentiation of MSCs were improved by the platy HAP with (100) faces compared to rod-like HAPs with (001) faces as the main crystal orientation, indicating that MSCs can recognize the crystal face and prefer the (100) HAP faces. This face-specific preference is dependent upon the selective adsorption of fibronectin (FN) on the HAP surface. FN is a plasma protein that plays a central role in cell adhesion. This selective adsorption is further proved by molecule dynamics (MD) simulation. Our results indicate that it is a good choice for cells to use ultrathin HAP with a large (100) face as a basic building block in the hierarchical structure of bone, which is crucial to the promotion of MSCs osteogenic activity during bone formation.In chapter 4, we integrated bone-like p-HAP into polylactic acid (PLA) to fabricate p-HAP/PLA composite scaffold. The pure PLA, t-HAP/PLA and n-HAP/PLA are synthesized as the control groups. We study the bioactivity and osteogenic inducibility of scaffolds by in vitro and in vivo tests. The proliferation and osteogenic differentiation of human mesenchymal stem cells (hMSCs) on different scaffolds were examined in vitro. The results revealed that p-HAP/PLA improved the proliferation and osteogenic ability of hMSCs. And p-HAP/PLA with best cytocompatibility and osteogenic induction as comprated with pure PLA, t-HAP/PLA and n-HAP/PLA scaffolds. Scaffolds were further implanted into SD rat calvarial defect model respectively to evaluate the bone regeneration activity of p-HAP/PLA, using the blank defect as a control. At 8 and 16 weeks post-operation, the micro CT detection and histological analysis were used to investigate the bone repair capacity of scaffolds. All results revealed that p-HAP/PLA composite scaffold had better bone repair effect than other scaffolds. These findings suggesting the bone-like p-HAP could efficiently increase the bone repair quality of scaffolds, and this effect can be used as an advanced strategy to improve material-induced bone repair and hard tissue engineering.In chapter 5, we summarize our study. We have synthesized bone-like p-HAP, and investigated the bioactive effects of bone-like p-HAP. Moreover, bone-like p-HAP has been integrate into PLA to fabricate p-HAP/PLA scaffold for bone repair tests in vitro and in vivo. Finally, we also analysis the shortages of this study and unsolved issues for further research.