Characterization and Surface Properties of Amino-Acid-Modified Carbonate-Containing Hydroxyapatite Particles

Abstract

The surface properties (nature, strength, and stability of interaction of functional groups) and bulk morphologies of a series of amino-acid-functionalized carbonate-containing hydroxyapatite (CHA) particles were investigated. It was found that the amino acids were both occluded in and presented on the surface of the CHA particles. Furthermore, their presence enhanced particle colloidal stability by retardation of Ostwald ripening and in some cases increasing the magnitude of the zeta-potential. Measurements of adsorption isotherms and zeta-potential titrations have shown that the amino-acid-surface interactions are weak and reversible at pH 9 and consistent with a model in which the carboxyl terminus interacts with calcium ions in the CHA lattice. Complexities in adsorption behavior are discussed in terms of different adsorption mechanisms that may be prevalent at different pHs.

The role of amino acids in hydroxyapatite mineralization

“…As is evident from table 2, almost all AAs are able to inhibit both HA particle growth and crystal growth, irrespective of their electrical charges. However, charged AAs, such as Glu, Asp, arginine (Arg) and lysine (Lys), show a significantly stronger effect than non-charged ones [6,7,23]. This is related to the presence of stronger interactions between charged AAs and Ca 2þ and PO 4 32 ions, as well as with the surface of HA particles already formed in solution.…”

“…They showed that a negatively charged AA, Asp, has the highest affinity for HA (table 3). However, Jack et al measured a stronger affinity to HA for a positively charged AA, Lys, and attributed this to the decrease in repulsion between the net negative charges of HA surface and any negatively charged segments on the AA side chains [6]. Despite their differences, both these sets of results imply a stronger effect of charged ( positive or negative) AAs, such as Arg and Asp on inhibiting HA precipitation.…”

“…This includes both the electrostatic interaction between the net charges of AAs and HA surface as well as the interaction between specific segments of the AAs and HA particles. For example, although AAs usually interact through their COOH groups with calcium ions present on HA, a positively charged AA such as Lys shows a high affinity with the HA probably because overall it is less repelled by the negatively charged HA surface [6]. b.…”

“…This is attributed to the ability of these functional groups to attract Ca 2þ and PO 4 32 ions, thus increasing the degree of local supersaturation with respect to calcium phosphate precipitation at regions close to the surfaces [50,53]. While there have been many studies investigating the inhibitory effect of AAs dissolved in solution on HA mineralization [6,[18][19][20][21][22][23][24][25][26][27][28], the effect of AAs bound to surfaces has been subject of just a few studies [8,55,56]. Rautaray et al [8] investigated HA precipitation in the presence of Aspcapped gold nanoparticles (figure 4).…”

Impact of Porosity and Electrolyte Composition on the Surface Charge of Hydroxyapatite Biomaterials

“…values obtained from electrophoretic mobility measurements versus tangential/transversal streaming potential/current measurements). [30][31][32][33][34] In spite of the large variability, it has been gaining consensus that synthetic HA has an isoelectric point (IEP) between pH 5-7. 30,35 The sign of the zeta potential obtained in the present work is negative at pH 6 which is consistent with the IEP.…”