Synopsis
In order to improve bio compatibility and biological function of carbon nanotubes (CNTs), the surface of CNTs was modified by precipitating calcium phosphate compounds in a calcifying solution. To accelerate calcification process and efficacy of modification, a solution containing 6-times higher concentration of calcium and phosphate ions than that of physiological body fluid was used (the 6-times solution). Precipitation of calcium phosphate (Ca-P) upon CNTs was investigated, concerning the incubation time, influence of concentration of CNTs, elemental analyses of products and protein adsorption on the chromatographic column. Time-dependent observation of the reaction products by SEM indicates that the moss-like precipitation of Ca-P at first, then the granular bodies appeared at the beginning of incubation. These moss-like bodies seemed to be replaced gradually by granular bodies, and later, cotton fiber?shaped structures appeared. After 24 hr of incubation, the aggregation of spheroid bodies, composed of hydroxyapatite and CNTs, became the dominant constitute of the products. Ca and P were detected by EDS even when there were no precipitations in SEM image, giving the evidence that the surface CNTs was slightly covered by calcium and phosphate compounds from very early stage. This was further strengthened by a chromatographic result that the chromatography of slightly modified CNTs clearly showed the greater affinity for an acidic protein (albumin) than the unmodified CNT column. Combining with the evidence by EDS for Ca and P contents, this chromatographic result clearly indicates that the presence of calcium phosphates on the surface of CNTs, even though the observation by SEM could not detect it. The improvement of biocompatibility and the functionalization of CNTs could be done using calcification solution and the possible applications were suggested for the adsorption and release of various growth factors and medicines.
Key words: carbon nanotubes, apatite, surface treatment, calcification, nanomaterial
