Influence of Humic Compounds on the Crystal Growth of Hydroxyapatite

Abstract

1. ABSTRACT The influence of several natural and synthetic additives containing hydroxy and/or carboxyl groups on the kinetics of crystal growth of hydroxyapatite (HAP) at sustained su-persaturation has been investigated using the constant composition method. Addition of low levels (0.25 to 5 parts per million) of fulvic acid, tannic acid, benzene hexacarboxylic acid, and poly(acrylic acid) to supersaturated calcium phosphate solutions has an inhibi-tory influence upon the rate of crystal growth of HAP. Salicyclic acid, under similar experimental conditions, is an ineffective HAP growth inhibitor. Kinetic analysis suggests Langmuir-type adsorption of added ions on the HAP surfaces with a relatively high affinity for the substrate in the concentration range investigated.