Hardening and reaction mechanism of bioactive cement based on glass

作者最近发现，CaO、SiO_2基玻璃粉末与磷酸铵溶液混合后，几分钟内就会凝固，并在植入骨缺损处时与活骨粘结。研究了生物活性玻璃水泥的凝结硬化机理及其与体液的反应机理。生物活性玻璃水泥的抗压强度变化很大，CaO/SiO_2/P_2O_5的变化很小。CaO-SiO_2-P_2O_5组成中添加CaF_2可提高抗压强度，而添加MgO可降低抗压强度。CaO 47.1、SiO_2 35.8、P_2O_5 17.1、CaF_2 0.75wt比的抗压强度最高。当玻璃粉的平均粒径大于5微米时，其抗压强度下降。水泥的抗压强度随溶液中磷酸铵浓度的增加而增加。3.7M磷酸二氢铵溶液在pH 7.0~8.3范围内抗压强度最高。水泥的凝结是由于无定形磷酸钙(ACP)在玻璃粉的晶间空间形成的。磷酸铵溶液中的P(V)离子与玻璃中溶解的Ca(II)、Si(IV)离子反应生成ACP。水泥的硬化归因于取代ACP的羟基磷灰石的形成以及它的生长和再结晶。一旦Ca(II)和P(V)离子以一水磷酸铵钙的形式固定在水泥中，然后浸泡到模拟体液中，它就会转化为更多的羟基磷灰石，并提供更高的抗压强度。

The present authors recently found that a Cao,SiO_2-based glass powder sets in a few minutes, when mixed with an ammonium phosphate solution, and bonds to living bone when implanted into bone defect. Such type of bioactive cement is useful for bone filler, drug carriers in the drug delivery system etc. In the present study, setting and hardening mechanism of the bioactive glass cement and its reaction mechanism with a body fluid were investigated.The compressive strength of the cement largely varied with small changes in the CaO/SiO_2/P_2O_5 ratios. Addition of the CaF_2 to CaO-SiO_2-P_2O_5 composition increased the compressive strength, whereas that of the MgO decreased it. The composition of CaO 47.1, SiO_2 35.8, P_2O_5 17.1, CaF_2 0.75 wt ratio gave the highest compressive strength among the examined compositions. Its compressive strength decreases when average particle size of the glass powders was above 5 mum. The compressive strength of the cement increased with increasing the concentration of ammonium phosphate in the solution. The solution of 3.7M ammonium phosphate at pH 7.0-8.3 gave the highest compressive strength. The setting of the cement is attributed to the formation of amorphous calcium phosphate(ACP) at the intergranular spaces of the glass powders. The ACP is formed by the reaction of P(V) ion in the ammonium phosphate solution with Ca(II) and Si(IV) ions dissolved from the glass. The hardening of the cement is attributed to the formation of the hydroxyapatite in place of ACP and to its growth and recrystallization. Once the Ca(II) and P(V) ions are fixed in the cement as calcium ammonium phosphate monohydrate before soaking into the simulated body fluid, it converts to a larger amounts of hydroxyapatite, and gives a higher compressive strength.