Bodin Aase, Gustafsson Lena, Gatenholm Paul
Biopolymer Technology, Department of Chemical and Biological Engineering, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden.
J Biomater Sci Polym Ed. 2006;17(4):435-47. doi: 10.1163/156856206776374106.
Bacterial cellulose (BC), produced by Acetobacter xylinum, and cotton linters as reference were surface modified by ozone-induced graft polymerization of acrylic acid and used as a template for crystallization of calcium phosphate. The grafting was verified using attenuated total reflection-infrared radiation (ATR-IR) and electron spectroscopy for chemical analysis (ESCA). ATR-IR revealed an additional absorption band at 1700 cm(-1), corresponding to the carbonyl group in polyacrylic acid. ESCA figures show, apart from the characteristic peaks for cellulose, additional peaks at 285 eV and 289 eV that correspond to groups in acrylic acid. The grafting yield is higher on cotton linters compared with BC, which most likely has to do with differences in crystallinity and reactivity of the different cellulose materials. No morphology difference directly caused by grafting could be seen with scanning electron microscopy (SEM), which might indicate that acrylic acid was grafted as a thin film on the surface of the cellulose micro fibrils. Calcium phosphate was formed on the surface-modified cellulose by first pre-soaking the materials in a saturated Ca(OH)2 and later in simulated body fluid (SBF). The atomic ratio of calcium phosphate was determined by ESCA to be about 1.5 for the different materials. Energy dispersive spectroscopy (EDS) was used to map and verify that the crystals were calcium phosphate. Secondary ion mass spectroscopy (SIMS) was also used to verify the presence of calcium phosphate complex onto BC. SEM images showed the difference in dimension, distribution and morphology of the crystals depending on the materials. Smaller and a greater number of crystals were obtained on the surface-modified BC and larger and fewer crystals on surface-modified cotton linters. Structural and grafting differences between the celluloses may lead to differences in nucleation sites and possibly differences in the morphology of the Ca-P crystals. The BC-calcium phosphate composite is expected to be useful as a scaffold for bone tissue regeneration.
由木醋杆菌产生的细菌纤维素（BC）以及作为参照的棉短绒通过丙烯酸的臭氧诱导接枝聚合进行表面改性，并用作磷酸钙结晶的模板。使用衰减全反射红外辐射（ATR-IR）和化学分析电子能谱（ESCA）对接枝进行了验证。ATR-IR显示在1700 cm⁻¹处有一个额外的吸收带，对应于聚丙烯酸中的羰基。ESCA数据表明，除了纤维素的特征峰外，在285 eV和289 eV处还有对应于丙烯酸中基团的额外峰。与BC相比，棉短绒上的接枝产率更高，这很可能与不同纤维素材料的结晶度和反应性差异有关。扫描电子显微镜（SEM）未观察到接枝直接导致的形态差异，这可能表明丙烯酸是以薄膜形式接枝在纤维素微纤丝表面。通过先将材料在饱和Ca(OH)₂中预浸泡，然后在模拟体液（SBF）中浸泡，在表面改性的纤维素上形成了磷酸钙。通过ESCA测定，不同材料的磷酸钙原子比约为1.5。使用能量色散光谱（EDS）绘制图谱并验证晶体为磷酸钙。二次离子质谱（SIMS）也用于验证BC上磷酸钙复合物的存在。SEM图像显示，根据材料不同，晶体在尺寸、分布和形态上存在差异。在表面改性的BC上获得的晶体更小且数量更多，而在表面改性的棉短绒上获得的晶体更大且数量更少。纤维素之间的结构和接枝差异可能导致成核位点的差异，进而可能导致钙磷晶体形态的差异。预计BC-磷酸钙复合材料可作为骨组织再生的支架。
