| The research on hard tissue replacement is one of the most attractive aspects of biomedical engineering. Considering pretty good mechanical properties of the implants are needed, the most prevalent implants are still metallic ones. Bioactive substance such as hydroxyapatite(HA) and bioglass are coated on their surfaces in order to improve the bond between the implants and bone tissue. However, in clinical application these coatings show poor long-term effectiveness due to the relatively large dissolution or resorption rates, which will result in the detachment of the coating or even the failure of the implants. Therefore, the research on coatings with both good bioactivity and long-term effectiveness as well as their behavior will greatly improve the overall performance of the implants.In this dissertation, the research on films with lower dissolution rates and expecting better long-term effectiveness is carried out. The research progress on preparation of HA coatings, especially on sol-gel derived HA thin coatings and fluoridated hydroxyapatite(FHA) coatings and the problems still existed are reviewed. FHA phase obtained is characterized by the means of XRD, FTIR, XPS, NMR and chemical analysis. Different fluorine containing compounds (CF3COOH, HPF6 and NH4PF6) are investigated for the possibility of introducing fluorine and the formation process of FHA phase. Ca(NO3)2-PO(OH)x(OEt)3.x-HPF6-C2H5OH system is selected as precursors after optimizing the dip-coating parameters. Subsequently, the FHA films obtained from dip-coating process and their phase, morphology, interface, bonding strength to the substrate as well as the in vitro behaviors were also investigated by XRD, FTIR, SEM, EDS, TEM, AFM, ICP and chemical analysis.1. The formation processes and mechanisms of FHA phase and fluorapatite(FA) phase in Ca(NO3)2-PO(OH)x(OEt)3-x-C2H5OH system with different fluorine containing compounds are investigated.FA and FHA phase are prepared by the adding of CF3COOH along with N(CH2CH2OH)3. The formation process and mechanism are investigated: The adding of N(CH2CH2OH)3 promoted the dissociation of CF3COOH in the starting solution and some non-volatile, fluorine containing intermediates can be remained after tray-drying of the solution. During the following heat-treatment process, the intermediates decomposed and further react with the rest amorphous calcium phosphate, leading to the final formation of FHA or FA phase. The fluorine content in the FHA phase obtained could be tailored by the content of CF3COOH added..For the first time HPF6 and NH4PF6 are used to synthesize FHA and FA phase. Thephase formation process and mechanism are also investigated: During the refluxing process of the PF6- containing mixture, PF6- reacted with the calcium ion in the mixture and nano-scale particles formed. After tray-drying, these particles remained with amorphous calcium phosphate. During the subsequent heat-treament, CaF2 react with amorphous calcium phosphate and FHA phase or FA phase formed. Varying the amount of HPF6 or NH4PF6 added, the fluorine in the FHA phase could be tailored.According the FTIR results, pOH shifts to higher wavenumbers with increased fluorine content in the FHA phases, which meant in the FHA phase the fluorine existed as F-OH chains, it can be concluded that FHA phase obtained is actually HA/FA solid solution.All the three fluorine-containing compounds can incorporate fluorine into the apatite structure and subsequently form FHA or FA phase. However, only 1/3 of fluorine in CF3COOH can be utilized. In comparison, HPF6 and NH4PF6 have pretty high efficiency in incorporating fluorine.2. The films prepared with different fluorine containing compounds were thoroughly investigated.The quality of the films as well as the film forming ability of the solution of all the three systems are investigated by reflection microscopy and viscosimeter. It is found that the Ca(NO3)2-PO(OH)x(OEt)3-x-C2H5OH system with CF3COOH added gives out much gas during heat-treatment which will result in film... |
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