JOURNAL OF MATERIALS SCIENCE: MATERIALS IN MEDICINE 6 (1995) 658-669 Further studies of calcium phosphate growth on phosphorylated cotton fibres M. R. MUCALO, Y. YOKOGAWA, T. SUZUKI, Y. KAWAMOTO, F. NAGATA, K. NISHIZAWA Bioceramics Group, National Industrial Research Institute of Nagoya, 1-1 Hirate-cho, Kita-ku, Nagoya 462, Japan 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)rtreated urea/H3PO3- and urea/H3PO4-modified cotton fibres are reported. In the case of the Ca(OH)2-treated urea/HaPO3-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 x 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 x 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. 1. Introduction Earlier, a study was reported [1] in which the growth of calcium phosphate on cotton modified via treat- ment with urea/phosphorous acid (H3PO3) was described. Studies of the stimulation of growth of calcium phosphate (hydroxyapatite) on pre-treated or specially designed substrates are of potential value in the design of biomaterials which more closely re- semble the natural tissues in which they come into contact with. However, another potential use of the cotton/hydroxyapatite system is as a virus filter given the adsorptive properties of hydroxyapatite [-2] which may allow the attachment of drugs for any future treatment of serious viral diseases. In the previous study [1], it was found that amorph- ous calcium phosphate material could be stimulated to form on cotton fibres phosphorylated by the urea/phosphorous acid method after soaking in saturated Ca(OH)2 for approximately one week. The 658 prior Ca(OH)2 treatment was found to produce highly crystalline clusters lodged in the fibres which were confirmed by micro-FTIR to be calcium phosphite monohydrate (CaHPO3.H20). These are believed to slowly dissolve upon introduction of the cotton sam- ples in 1.5 x SBF (1.5 x concentration of simulated body fluid solution) so elevating the Ca 2 ÷ ion concen- tration in the vicinity of the fibres and stimulating calcium phosphate formation. In the present study, results on the calcium phos- phate growth on cotton fibres phosphorylated in a dif- ferent manner (i.e. by urea/phosphoric acid) from the previous investigation [1] will be presented. In addi- tion, continuing investigations on the urea/phosphor- ous acid modified cotton system are reported. These studies were carried out in order to see whether the Ca(OH)2 treatment step (necessary for the stimulation of calcium phosphate growth on the fibres) could be avoided since soaking in this highly alkaline medium 09574530 © 1995 Chapman & Hall