Further studies of calcium phosphate growth on phosphorylated cotton fibres

Abstract

Further studies using scanning electron microscopy/energy dispersive X-ray analysis (SEM/EDX), micro-Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and solid state magic angle spinning nuclear magnetic resonance (MAS NMR) techniques of calcium phosphate growth on Ca(OH)₂-treated urea/H₃PO₃- and urea/H₃PO₄-modified cotton fibres are reported. In the case of the Ca(OH)₂-treated urea/H₃PO₃-modified fibres which have been reported in an earlier paper, further experiments subjecting the urea/H₃PO₃-modified cotton to alternative soaking treatment procedures to Ca(OH)₂ as well as different calcium phosphate growth media such as the alkaline phosphatase-catalysed hydrolysis of disodium p-nitrophenylphosphate to free phosphate have reaffirmed the importance of the Ca(OH)₂ treatment step for the stimulus and growth of calcium phosphate growth on the fibres. Studies on cotton phosphorylated by a slightly different method using urea/H₃PO₄ instead of urea/H₃PO₃ show that a phosphorylated cotton with similar properties to the urea/H₃PO₃-modified fibres can be produced. Soaking of these fibres in saturated Ca(OH)₂ solution leads to cotton coated with thin layers of calcium phosphate formed by partial hydrolysis of the PO₄ functionalities in the phosphorylated cotton which are believed to act as nucleation layers for further calcium phosphate deposition when the fibres are subsequently soaked in 1.5×SBF solution. SEM/EDX studies of the calcium phosphate coatings formed on the Ca(OH)₂-treated urea-H₃PO₄ fibres as a function of soaking time in 1.5 × SBF show that coatings deposit and become noticeably thick after approximately 9 days. XPS studies indicated the presence of carbonate species in the calcium phosphate coating deposited. In common with the calcium phosphate coated Ca(OH)₂-treated urea/H₃PO₃-modified fibres studied earlier, the average EDX-measured Ca: P ratios of the coatings formed on the Ca(OH)₂-treated urea/H₃PO₄ fibres are ∼ 1.60 and give very similar micro-FTIR spectra with evidence of carbonate which suggests that amorphous calcium deficient apatite has deposited.