Hydroxyapatite crystallization in the presence of serine, tyrosine and hydroxyproline amino acids with polar side groups

Addition of the amino acids serine, tyrosine and 4-hydroxyproline with pola r uncharged side groups at physiological pH levels to a supersaturated calc ium phosphate solution reduced the crystal growth rate of hydroxyapatite (H AP) at 37 degrees C. Depending on the side group of the amino acid differen t inhibiting activities were observed. The reduction was also found to be r elated to the additive concentration following an expression suggested by t he kinetic Langmuir-type adsorption model. This relationship implies that I -IAP crystallization kinetics was affected through blockage of the active g rowth sites on the crystal surface. In all cases the apparent order of the crystal growth reaction was found to be n = 2, suggesting a surface-diffusi on-controlled spiral growth mechanism. (C) 2000 Elsevier Science B.V. All r ights reserved.