Transformation of modified brushite to hydroxyapatite in aqueous solution:effects of potassium substitution

Brushite (dicalcium phosphate dihydrate, DCPD, CaHPO4. 2H(2)O) was deposite d electrolytically from calcium dihydrogen phosphate solution with and with out potassium chloride (KCI) as a supporting electrolyte. The kinetics of b rushite transformation to hydroxyapatite (HA, Ca-5(PO4)(3)OH) in the presen ce of calcium and protein free, aqueous body fluid (Hank's balanced salt so lution, HBSS) was investigated. We present evidence that the deposition of brushite in a KCl-supported electrochemical bath yields a modified brushite where some of the calcium is substituted by potassium. Transformation of b oth normal (i.e. potassium free) and modified brushite to hydroxyapatite up on exposure to calcium and protein-free aqueous fluid (HBSS) was followed b y reflectance Fourier Transform Infrared (FTIR) spectroscopy and X-ray diff raction (XRD) techniques. Changes in the morphology of the coatings were st udied using scanning electron microscopy (SEM). Results indicate that modif ied brushite undergoes faster transformation to hydroxyapatite in HBSS in c omparison to normal brushite. Our results show that the presence of potassi um ions in the brushite not only favors the formation of different intermed iate phases but also alters transformation rates to HA. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.