Müller Lenka, Müller Frank A
Department of Materials Science-Biomaterials, University of Erlangen-Nuernberg, Henkestr. 91, 91052 Erlangen, Germany.
Acta Biomater. 2006 Mar;2(2):181-9. doi: 10.1016/j.actbio.2005.11.001. Epub 2006 Jan 4.
The bioactivity of bone and dental implant materials is usually tested in vitro using simulated body fluid (SBF). The composition of common SBF differs from that of blood plasma in that it has a higher Cl- and a lower HCO3- concentration, which affects the composition of in vitro formed bone-like apatite. Five different SBFs with a composition of 142 Na+, 5 K+, 2.5 Ca2+, 1 Mg2+, 1SO4(2-), 1HPO4(2-), and 136 (Cl-+HCO3-) mmol/l were prepared with HCO3- concentrations ranging from 5 to 27 mmol/l. The SBF solutions were prepared by mixing stable concentrated solutions, which increase the reproducibility of in vitro tests due to negligible changes of pH during preparation. The high stability of thus prepared SBF enables the evaluation of hydroxyapatite formation on the surface of bioactive materials without the negative effect of spontaneous precipitation. Furthermore, the use of concentrated solutions offers a facile way to prepare SBF with different ionic contents and thus modify the composition of Ca-P layers precipitated on the surface of the bioactive materials exposed to the SBF solutions. The SBF solutions were shown to be supersaturated with respect to slightly carbonated apatite. The Fourier transform infrared (FT-IR), Raman and X-ray analyses of the precipitated layers indicate that the HCO3- content in SBF influences the composition and structure of the calcium phosphates obtained. It can be supposed that as long as the HCO3- concentration in the testing solutions is lower than 20 mmol/l, only B-type HCA precipitates. At higher HCO3- concentrations, it can be assumed that A-type HCA forms as well considering FT-IR, Raman and X-ray measurements.
骨和牙种植材料的生物活性通常在体外使用模拟体液（SBF）进行测试。常见SBF的成分与血浆不同，其Cl-浓度较高而HCO3-浓度较低，这会影响体外形成的类骨磷灰石的成分。制备了五种不同的SBF，其成分分别为142 mmol/l的Na+、5 mmol/l的K+、2.5 mmol/l的Ca2+、1 mmol/l的Mg2+、1 mmol/l的SO4(2-)、1 mmol/l的HPO4(2-)以及136 mmol/l的（Cl-+HCO3-），其中HCO3-浓度范围为5至27 mmol/l。SBF溶液通过混合稳定的浓缩溶液制备，由于制备过程中pH变化可忽略不计，这提高了体外测试的可重复性。如此制备的SBF的高稳定性使得能够评估生物活性材料表面羟基磷灰石的形成，而不会受到自发沉淀的负面影响。此外，使用浓缩溶液提供了一种简便的方法来制备具有不同离子含量的SBF，从而改变暴露于SBF溶液的生物活性材料表面沉淀的Ca-P层的成分。结果表明，SBF溶液相对于轻度碳酸化磷灰石是过饱和的。对沉淀层的傅里叶变换红外（FT-IR）、拉曼和X射线分析表明，SBF中的HCO3-含量会影响所得磷酸钙的成分和结构。可以推测，只要测试溶液中的HCO3-浓度低于20 mmol/l，就只会沉淀出B型HCA。考虑到FT-IR、拉曼和X射线测量结果，在较高的HCO3-浓度下，可以假设也会形成A型HCA。
