Biomaterials introduced before are mainly used to repair and replace human bones with wounds, lesions or congenital defects, or repair materials that can be permanently implanted into the body. Recently, an absorbable bioceramic material has been developed rapidly. This material is a form of tricalcium phosphate called “synthos”. This material is made into porous bone blocks and implanted into the damaged parts of the human body. When the adjacent tissues proliferate and grow in the implanted body, the tricalcium phosphate can be slowly replaced by the regenerated bone of animals. This process is called biodegradation process, so this kind of material is also called biodegradation material or bioabsorbent material.
Tricalcium phosphate high artificial bone
1. Preparation of tricalcium phosphate
(1) Synthesis of tricalcium phosphate
Tricalcium phosphate [Ca3 (PO4) 2] is recorded as TCP and has high temperature type α Phase and low temperature type β The two phases are used as bioceramics β Phase. TCP can be synthesized by high-temperature solid-state reaction and wet method at room temperature, that is, aqueous solution reaction. To synthesize pure β- TCP is very difficult. No matter which method is used, there is more or less a second phase α Phase, HAP and Cao exist. The phase transition temperature of high temperature and low temperature is between 1120 ~ 1180 ℃, but the existence of impurities such as Mg and Na will have a great influence on the temperature.
The B-TCP powder synthesized by dry method was milled for a long time and sintered at atmospheric pressure. In order to obtain high-density sintered body, the micro powder synthesized by wet method must be used.
The raw material for synthesizing TCP is similar to hap. During the synthesis, the Ca/P=1.5 should be controlled in batching. The wet method is to add the solution containing phosphorus slowly into the alkaline solution containing calcium to form a white gelatinous precipitate, which is amorphous calcium phosphate. If 1%~2% ammonium sulfate is added to this gelatinous precipitate, a pure TCP close to theoretical density can be obtained at 1100 OC.
(2) Molding and sintering technology of porous calcium phosphate ceramics
Porous calcium phosphate ceramics are made of calcium phosphate powder. After molding, they are fired at about 1150 ℃, the heating rate is 90 ℃ / h, and the heat preservation is 4 5h, the obtained sintered body is β- TCP single phase.
β- The biodegradation characteristics of TCP are closely related to the firing temperature. The research shows that with the decrease of firing temperature, β- The solubility of TCP increases, so the firing temperature should not exceed 1100 ℃. In addition, porous network pores are also conducive to the degradation of materials.
Three molding methods can be used to prepare porous biodegradable materials:
① Add pore forming agent into the powder, such as paraffin, naphthalene and other organic substances. After pressing and forming, burn the pore forming agent in the firing process, leaving uniform connecting pores.
(2) use foaming agent to form, that is, using the fine organic foam molding body to suck the pulp. After drying, the ceramic blank will be uniformly consolidated on the foam skeleton, and the foam will be lost when firing, leaving the porous ceramic body with foam structure. This method requires the existence of no harmful residues after foam burning, and requires a certain strength and slurry to have good wetting and adsorption characteristics.
③ Grouting molding method is used, that is, gypsum mold molding. This method requires strict control of the water content of the gypsum model. After grouting, the mold shall be dried in a constant temperature box with controllable humidity and temperature. For example, it shall be heated to 80 ℃ at the speed of 10 ℃ / h for 10h
2. Structure and properties of tricalcium phosphate
As mentioned earlier, TCP has two crystal forms, high temperature type α Phase and low temperature type β There are two forms of phase. α- TCP is monoclinic system with a density of 2 86g/cm3。 β- TCP is rhombohedral with a density of 3 07g/cm3。 β- The chemical properties of TCP are similar to hydroxyapatite, and the solubility in water is slightly larger.
β- The compressive strength of TCP sintered body is 450 ~ 676mpa, and the flexural strength is 137 ~ 156mpa, which is similar to that of hydroxyapatite.
The solubility of TCP is greater than that of hydroxyapatite. Among them, β- TCP is about twice that of hydroxyapatite, while α- TCP is 10 times that of hydroxyapatite.