Surface functional group dependence on apatite formation on self-assembled monolayers in a simulated body fluid

Abstract

Self-assembled monolayers (SAMs) of alkanethiols having CH3, PO4H2, COOH, CONH2, OH, and NH2 terminal groups formed on a gold surface via sulfur attachment were soaked in a simulated body fluid (SBF), whose ion concentrations were nearly equal to those of human blood plasma, at 37 degrees C for up to 40 days. The effect of their terminal functional groups on apatite formation was assessed using X-ray photo-electron spectroscopic (XPS) measurement and a quartz crystal microbalance (QCM) technique. The Ca and P atoms were detected, of which element intensities increased with time, on SAMs except for the alkanethiol having the methyl terminal group. The Ca/P atomic ratios of the apatites formed on the SAMs ranged from around 1.0 to around 1.3. The most potent inducer for apatite formation, judged from the growth rate (micrometers per day) calculated from the weight change during QCM measurement, was the SAM of the alkanethiol with the PO4H2 group, followed by that of the alkanethiol with the COOH group. The SAMs of the alkanethiols with the CONH2, OH, and NH2 groups possessed much weaker inducing powers than the former two SAMs. Little weight change was observed for the methyl-group-terminated alkanethiol SAM. The growth rates increased with time, irrespective of the terminal group species among apatite formation-inducing groups. During the experimental observation period, the following relationship held. The growth rate decreased in the order PO4H2 > COOH >> CONH2 approximately equal to OH > NH2 >> CH3 approximately equal to 0. Some negatively charged groups strongly induced apatite formation but the positively charged group did not, it can be said that the apatite formation initiated via calcium ion-absorption upon complexation with a negative surface-charged group may be dominant in biomaterial calcification where ionic species directly contact the biomaterial surface in body fluids.

Dietary L-Lysine Prevents Arterial Calcification in Adenine-Induced Uremic Rats

“…Using self-assembled monolayers that have CH 3 , PO 4 H 2 , COOH, CONH 2 , OH, or NH 2 terminal functional groups, Tanahashi et al revealed that the negatively charged groups strongly promote hydroxyapatite formation. 42 The results of Tanahashi et al suggest that the electrical adsorption of calcium ions on the negatively charged surface, but not the adsorption of phosphate ions on the positively charged surface, promotes hydroxyapatite formation. 42 Indeed, Tanase et al demonstrated that the growth of hydroxyapatite on the c-plane of crystallographically aligned hydroxyapatite is faster than that on the a-plane.…”

“…42 The results of Tanahashi et al suggest that the electrical adsorption of calcium ions on the negatively charged surface, but not the adsorption of phosphate ions on the positively charged surface, promotes hydroxyapatite formation. 42 Indeed, Tanase et al demonstrated that the growth of hydroxyapatite on the c-plane of crystallographically aligned hydroxyapatite is faster than that on the a-plane. 43 In this study, we revealed that L-Lys, L-Arg, and L-homoarginine, but not Gly, L-Ala, or L-Pro, attenuated mineral precipitations in supersaturated calcium/ phosphate solutions ( Figure 8A).…”

Synthetic Alginate is a Carrier of OP-1 for Bone Induction

“…It is also known the number of carboxyl residues in DC alginate is larger than that in CB alginate. The carboxyl residues induce apatite nucleation followed by the deposition of hydroxyapatite crystals on the alginate [35]. Furthermore, the Ca 2+ contained in DC alginate can be utilized for new calcified bone, which is an advantage compared with CB alginate.…”

Preparation and biological evaluation of hydroxyapatite-coated nickel-free high-nitrogen stainless steel

“…We predicted that the carboxyl groups of the glutamic acid would interact with the Ca ions in the treatment solution, which would lead to nucleation of calcium phosphate [45]. After the immobilization of glutamic acid on the TSC-i-HNS surface, the HNS surface properties were analyzed through contact angle measurement and XPS.…”

“…Tanahashi and Matsuda reported that phosphate or carboxyl groups in self-assembled monolayer on substrate ions was weak [45]. These results suggest that the interaction between the glutamic acid carboxyl groups and the Ca ions released from Ca-EDTA promoted the nucleation of calcium phosphate on the HNS surface.…”