Apatite deposition on calcium alginate fibres in simulated body fluid

Calcium alginate fibres with an average diameter of 5 μm were prepared by extruding an aqueous sodium alginate solution through nozzles with holes of 0.1 mm diameter into an aqueous calcium chloride solution, and then through a calcium chloride methanol solution. The ratio of D-mannuronate (M) to L-gluronate (G) subunits in the calcium alginate ranged from 0.7 to 2.0. The fibres were soaked in an aqueous saturated calcium hydroxide solution for 5 d, and then soaked in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Fibres with an M/G ratio of 2.0 had apatite deposited on their surfaces within 7 d in SBF, but fibres with M/G ratios of 0.7 and 1.5 did not. The higher apatite-forming ability of the former fibres was attributed to their release of more calcium ions from the fibres, that is, the formation of a larger number of free carboxyl groups, effective for apatite nucleation and more efficient acceleration of the apatite nucleation by increasing the ionic activity product of the apatite in SBF.