| The demand of artificial scaffolds for bone tissue repair caused by diseases and injuries are increasing with the coming of aging society. Inorganic bone tissue scaffolds based on calcium phosphate have mineral compositions similar to human hard bone,and three dimensiona network structure as well as high porosity, which have been proved to be one of important artificial bone scaffold with excellent quality. However, the scaffolds with high porosity and connectivity, which are prepared by the commonly used method, show low mechanical performance and biological properties. Therefore, the preparation and applications of cancellous bone-like hydroxyapatite scaffolds have attracted more attention.In this paper, Mg2+, Zn2+ doped hydroxyapatite whiskers(Mg&Zn-HA) were prepared by a hydrothermal homogeneous precipitation method and characterized using advanced analytical techniques. Cancellous bone-like scaffold materials with controllable phases, porosity 70-80%, compressive strength 0.2~ 0.75 MPa and pore size 80~240 μm were successfully prepared by freeze-drying casting, using HA powder(D50=13.22 μm) as the basic raw material, Mg&Zn-HA as reinforced material, bioglass as high temperature binder to lower sintering temperature and to promote HA decomposed into β –TCP, in which 1,4-dixane was added as condensation agent, and hydroxyethyl cellulose as binder, sodium polyacrylate as dispersant.The results show that the prepared whiskers were identified as HA when the concentration of the ions doped separately was less than 10mol%. Further increasing its concentration, second phase, identified as Ca18Mg2H2(PO4)14 or CaZn2(PO4)2·2H2O, was appeared in the samples. When a total mixed dopping concentration of 5mol% was conducted in the study, it was found that the XRD diffraction peaks of the product shifted to a smaller angle with the increasing of Zn2+ dopping concentration, and the sample became more agglomerated. The appropriate dopping proportion was Mg2+: Zn2+=1:1 at 5mol% in mixeddopping.During the sintering, glass binder was transformed into liquid phase, and well coverd over the HA powder and HA whiskers. The binding between the HA particles or HA whiskers as well as between HA particles and whiskers promoted the pore formation, obviously increasing the porosity of the scaffold. The optimum ingredients of bioglass melted at 950 ℃ was 46 % P2O5,15% SiO2,14% CaO,8% MgO,11% Na2 O,5 % ZnO,and 1% CaF2. Comprehensive consideration to the porosity, shrinkage and compressive strength of the scaffold, the optimal content of glass binder was 20%. When the sintering temperature was at 950℃ and duration time less than 1h, the phase composition of the samples was composited of HA and β –TCP. In addition, when the sintering temperature was more than 1000℃ and the duration more than 0.5h, the HA was found to decompose thoroughly to β –TCP.Refrigeration process system mainly affect the pore structure of the scaffolds: when the initial cooling temperature was-12℃, the pore size would increase with the lower cooling rate. However, if the cooling rate was too slow,more pore branches would appear. In order to avoid the appearance of branched ice crystals, the optimum cooling rate was-1℃ at the present preparation condition. The effects of final cooling temperature on pore structure was not obvious. According to preparation process, the optimum final temperature was-40 ℃. Solid content in the slurry influenced the mechanical properties, porosity ratio and pore structure of scaffold materials, the optimum solid content was 40 wt%. when 5wt% Mg&Zn-HA whiskers was mixed into scaffold slurry, the mechanical properties of the scaffold were improved when compared with those prepared with pure HA powders, the addion of HA whiskers showed a little influence on the preparation of the cancellous bone-like scaffold with directional pore structure with pore size 80-240μm. |
PDF Full Text Request