Hardening and reaction mechanism of bioactive cement based on glass

本作者最近发现，当与磷酸铵溶液混合时，CaO、SiO_2基玻璃粉末在几分钟内凝固，并在植入骨缺损时与活骨结合。研究了生物活性玻璃骨水泥的固化硬化机理及其与体液的反应机理，发现当CaO/SiO_2/P_2O_5比值变化不大时，骨水泥的抗压强度变化很大。在CaO-SiO_2-P_2O_5体系中，CaF_2的加入提高了抗压强度，而MgO的加入降低了抗压强度，其中CaO47.1，SiO_235.8，P_2O_517.1，CaF_20.75wt%时抗压强度最高。当玻璃粉的平均粒径大于5 μ m时，其抗压强度降低。水泥的抗压强度随磷酸铵浓度的增加而增加。在pH 7.0-8.3的3.7M磷酸铵溶液中，抗压强度最高。骨水泥的固化归因于在玻璃粉末的颗粒间隙处形成无定形磷酸钙（ACP）。ACP是通过磷酸铵溶液中的P（V）离子与从玻璃中溶解的Ca（II）和Si（IV）离子反应形成的。骨水泥的硬化归因于羟基磷灰石替代ACP的形成及其生长和重结晶。一旦Ca（II）和P（V）离子在浸泡到模拟体液中之前作为磷酸铵钙一水合物固定在骨水泥中，其转化为更大量的羟基磷灰石，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.