The Study Of HA-Glass-α-Al₂O₃ Gradient Composite Biomaterials

α-Al₂O₃ and hydroxyapatite(HA or HAP) ceramics are two kinds of important biomaterials that have been widely studied and used for some time.They have some advantages and disadvantages,but their advantages are complementarity.To compose them by suitable process can prepare novel biomaterials with the both advantages ofα-Al₂O₃ arid HA ceramics,just as high sthrength and excerllent bioactivity.Because of the differences t between their sintering ability and thermal expansion coefficient,it can not get ideal results to compose them strightly or prepare HA coating on the surface ofα-Al₂O₃ ceramics.If the designing idea of gradient fimction materials(GFM) is used for reference,to prepare HA-glass gradient coating onα-Al₂O₃ ceramics,the residual thermal stress in the coating can be reduced effectively and HA-glass-α-Al₂O₃ gradient composite biomaterials with high bonding strength can be got.This kind gradient material has the both advantages of HA andα-Al₂O₃ ceramics and has high value to be studied and applied.In this dissertation,the praperation,structure,properties and apllying bases of HA—Glass—α-Al₂O₃ gradient composite biomaterials were studied.The main works are as following:1.Hydroxyapatite with a particle size 30-50nm was synthesized by wet route in water-alcohol solvent system.The influences of washing-filtrating and drying ways of gel on the particle characteristics of HA were studied.The sintering characteristics of nanometer HA and coarse HA which was fired and ground were researched preliminarily.The CaO-P₂O₅-SiO₂ glass,R₂O-Al₂O₃-B₂O₃-SiO₂ glass,ultrafineα-Al₂O₃,and R₂O-Al₂O₃-B₂O₃-SiO₂ glass—α-Al₂O₃ reinforced HA ceramics were prepared respectively by traditional sintering process.The influnces of the composition of ceramics body on the sintering character and mechanical strength were studied by the tests of bulk shrinkage of the body after sintered,bending strength and fracture toughness(K_IC).The phase transition or reactions between the compostions that taking place during sintering process was analyzed by DTA,XRD and IR,and the microstuctures of the ceramics prepared under diffrent conditions were observed by SEM.These works and results provided a fundamental and experimental basis for preparing HA—Glass—α-Al₂O₃ gradient composite biomaterials.The results show that CaO-P₂O₅-SiO₂ glass can accelerate the sintering of HA and has the reinforcement effect on HA ceramics;The R₂O-Al₂O₃-B₂O₃-SiO₂ glass can decrease the sintering temperature of HA,but it can urge the decomposition of HA when sintered at higher temperature;A suitable amount of ultrafineα-Al₂O₃ can reinforce the HA ceramics but it can block the sintering of HA and raise the sintering temperature when adding amount is more than 10%(wt),the raising of sintering temperature can induce HA decomposing into TCP when it is sintered.The better result was got when R₂O-Al₂O₃-B₂O₃-SiO₂ glass andα-Al₂O₃ was used at same time to reinforce HA ceramics.Glass can accelerate the sintering of HA and lower the sintering temperature.Ultrafineα-Al₂O₃ has reinforcement effect and hinders the glass reacting with HA at some degree,and then prevents HA decomposing.When ultrafineα-Al₂O₃ addition amount is 10%(wt),the glass addition amount is 20%(wt) and sintered at 1200℃,the HA-Glass-α-Al₂O₃ composite biomaterial with average bending strength 105.82Mpa and toughness K_IC 0.84MPa.m^1/2 can be got.2.α-Al₂O₃ cermics substrate was prepared by traditional sintering process when the ultrafineα-Al₂O₃ powder synthesized by low temperature combustion process used as main raw material and CaO-MgO-Al₂O₃-SiO₂ glass used as flux.The HA-Glass-α-Al₂O₃ gradient coatings were prepared onα-Al₂O₃ substrate.Two kinds of glass were used as the compositions of the coatings,i.e.CaO-P₂O₅-SiO₂ glass,R₂O-Al₂O₃-B₂O₃-SiO₂ glass.The influences of the composition and structure of the gradient coating on the combination intensity between the coating and ceramic substrate and the bending strength of the whole gradient composite were studied.The microstructures of surface and cross section of the gradient coating were observed by SEM,and the variation of chemical composition along the cross section was analyzed by EDS.The researching results of HA-Glass-α-Al₂O₃ gradient coating show that R₂O-Al₂O₃-B₂O₃-SiO₂ glass is more suitable to be used as the compenent of gradient coating than CaO-P₂O₅-SiO₂ glass.When R₂O-Al₂O₃-B₂O₃-SiO₂ glass is used and suitable amount ultrafineα-Al₂O₃ is added in the coating,the combination intensity between the coating and ceramic substrate increases remarkably.The HA-Glass-α-Al₂O₃ gradient composite biomaterials in which the coating combining withα-Al₂O₃ ceramic substrate tightly,the average combination intensity is about 48.22Mpa,can be prepared under a suitable condition.3.Microwave sintering of HA,HA-Glass and HA-Wollastonite(W)—Glass composite ceramics was studied systematically.The best process of microwave sintering of dense HA and these composite bioceramics was worked out.ZrO₂-Al₂O₃ substrate with high strength was prepared by microwave sintering process,and the HA-W—Glass gradient bioactive coating was prepared on ZrO₂-Al₂O₃ ceramic substrate by microwave sintering.The effects of sintering temperature on the structure,phase trasition and the combination intensity between the coating and ceramic substrate were studied initially,the best sintering temperature was decided.Microwave sintering is beneficial to the compaction of the HA ceramic body,to realize the fast sintering of HA at low temperature and to increase the strength of HA ceramics.The effects of microwave sintering of HA-Glass composite are not as good as that of pure HA. The fast heating and sintering induces the porosity of HA-Glass composite ceramics,and its strength is lower than that of pour HA.Microwave sintering can accelerate HA decomposing, and the decomposing degree of HA will increase with the raising of sintering temperature and the prolonging of sintering period.Microwave sintering process can be used to prepare gradient coatings.HA-W-Glass gradient coating sintered by microwave has similar structure and properties as that of the gradient coating conventional sintered.But microwave sintering can realize fast sintering,shortening the sintering period and saving energy.4.The biomedicine properties of the HA-Glass-α-Al₂O₃ composite biomaterials were evaluated.On the bases of a series of safety evaluation tests,the degradation properties of composite biomaterials were studied by simulative experiments and little rat intramuscular implantation experiment.Simulative body fluid(SBF) immersion test was done and XRD, EDS and SEM techniques were used to study the surface bioactivity of HA-W-Glass gradient coatings.The results of biomedicine properties evaluating show that:The HA-R₂O-Al₂O₃-B₂O₃ -SiO₂ system glass-α-Al₂O₃ composite biomaterials have no toxicity to the organism,and do not induce to hemolysis and pyrogen reaction.The results of intramuscular implantation experiment show that the composite biomaterials have no irritation,and the phagocytosis of mutinucleate cells proves the composite biomaterials are biodegradable in some degree.The results of physics degradation experiment and weight loss analyses after intramuscular implantation show that the composition of the composite biomaterials has effects on the degradation properties of the materials,the HA and glass phase is propitious to the degradation and increase the bioactivity of the biomaterials,and it can increase the durability of the biomaterials to add the ultrafineα-Al₂O₃ in the composite biomaterials.So that the surface of HA-R₂O-Al₂O₃-B₂O₃-SiO₂ system Glass-α-Al₂O₃ gradient coating has better bioactivity and the inter layers of the gradient coating have nice durability.The results of SBF immersion test show that both of HA-W-Glass gradient coatings conventional sintered and microwave sintered at 1150℃have good surface bioactivity.A deposit layer of HA will form on the surface of the gradient coating after it is immersed in SBF for some periods.But the bioactivity of the coating will be lowered when it is sintered at 1200℃.