Calcium Phosphate Bone Cement Preparation Of Biological Materials And Performance

Calcium phosphate cement(CPC) is a new type of artificial hard tissue materials, and can be used in the bone surgery for defect repair and substitution. CPC are composed of powder and liguid. And after stirring the cement powder with liquid, it will self-set and forms hydroxyapatite(HA) which chemical component and structure are similar to the mineral phase of hard tissue. CPC is attractive in a broad range of clinical aplication for repairing bone defects by the virtue of high biocompatibility and self-setting capability.In this thesis, the effect of preparation methods on the purity of beta-calcium phosphate(β-TCP) and tetracalcium phosphate(TTCP) was first investigated. By means of the thermogravimetric analysis(TGA) and differential thermal analysis(DTA) of the mixtue of dicalcium hydrogen phosphate dihydrate(DCPD) and calcium carbonate(CC), it was disclosed that DCPD is dehydrated to DCPA at the range of 180¹97℃ and decomposed to calcium pyrophosphate(CPP) at the range of 197⁶90℃. β-TCP was formed by the reaction between CC and CPP when the temperature is over 691℃. The TGA cure showed that β-TCP is formed fast at the beginning of the reaction and then becomes slow. After long time of ball grinding mill, the mixture of DCPD and CC was heated to 1150℃ for 2h and pure β-TCP was obtained. HA-CC coated powder which has good activity was also fabricated and SEM spectrum showed CC is well coated at the surface of HA. By heating the HA-CC coated powder to 1500℃ for 6h, pure TTCP was obtained. CPC powder was prepared by mixing pure β-TCP and pure TTCP with the molar ratio of 2 and can be stirred with liquid, 0.5mol/L Na_1.8H_1.2PO₄ buffer solution contained citric acid, uniformly.The effect of preparing condition, such as liguid to powder ratio, particle size, HA seed and cement liguid, on initial setting time and compressive strength of CPC were investigated systematically. The relationship between the physical and chemical change, the pastemicrostructure induced by setting reaction and mechanical property were analyzed, providing a basis determination of optimal preparing condition for high performance CPC. The 0.5mol/L Na1.8H1.2PO4 buffer solution contained citric acid can strongly improve the hydration rate of CPC, which shorten the initial setting time and increased the compressive strength of CPC. And with the increase of the concentration of citric acid, the initial setting time becomes short and the compressive strength increase. But when the concentration is over 5.0wt%, the compressive decreased with the increase of the concentration of citric acid.With the increase of CPC powder specific surface area, the initial setting time becomes short and the compressive sthength increases. But when the specific surface area is over 1.1 Om /g, the porosity and imperfection of cement will increase, which decrease the compressive strength. Improving the liquit to powder ratio will increase the porosity of cement, which decreases the compressive strength also. Stirring the cement powder which specific surface area is 1.10m2/g by 0.5mol/L Nai.gHi 2PO4 buffer solution contained 5.0wt% citric acid with the liquit to powder ratio 0.4ml/g, the initial setting time and compressive strength are 3.55min and 34.15MPa respectly. HA seed can accelerate the crystal nucleus to form and grow, which shortens the initial setting time and increase the compressive strength. The chemical processes of CPC hydration was studied. These processes are controlled by dissolution and precipitation chemical reaction. The relative stabilities of the various calcium phosphate salts are the major driving forces for the hydration reaction of CPC slurry at the different pH value. In the ternary system Ca(OH)2-H3PO4-H2O, HA is the least soluble phase at pH value > 4.2, other calcium phosphate salts present in an aqueous solution in this pH range will tend to dissolve and reprecipitate as HA. In the P-TCP and TTCP system, the following two reaction stages' mechanisms are proposed for hydation processes of CPC. In the first stage, hydration reaction rate is controlled by the dissolution rate of CPC powder and the compressive strength increases fast. In the second stage, hydration reaction rate is controlled by the diffusion of solution in the HA production and the compressive strength increases slow.The phase transformation and micrograph of CPC production were studied aslo. If the pH value of the CPC liquit is greater than 4.2, the hydration prodution is HA which is low crystallisty and needle-like crystal is observed by SEM. And if the pH value of the liquit is less than 4.2, the hydration prodution is DCPD. It was indicated that the crystall condition affect the crystal appearance. Low crystalline HA seed decrease the ratio of longitudinal size with latitudinal size of the production and clubed production is formed. High crystalline HA seed makes the lamellar crystal formed. Neutral Na1.gH1.2PO4 buffer solution makes the tiny needle-like crystal formed. If the CPC paste is submersed into the simulated body flaid, crystal partical can be obtained. P-TCP can hydrated and the production is HA while the by-product is H3PO4. TTCP can hydrated and the the by-product is Ca(OH)2. In the 0-TCP+ TTCP system, all the by-production disapear by neutralization reaction, which keeps the pH value of system unchanged.In this thesis, The CPC liquit was improved on by adding citric acid into neutral Na1.gH1.2PO4 buffer solution, and the pH value of which was adjusted purposefully. As a result, the initial setting time and compressive strength is suitably for operation in the surgery, and the crystallography of production was controlled. The crystal form of production can be controlled by various preparation conditions and the materials structure can be designed effectly.