Amorphous Calcium Phosphate and Amorphous Calcium Phosphate Carboxylate: Synthesis and Characterization

Abstract

Amorphous calcium phosphate (ACP) is the first solid phase precipitated from a supersaturated calcium phosphate solution. Naturally, ACP is formed during the initial stages of biomineralization and stabilized by an organic compound. Carboxylic groups containing organic compounds are known to regulate the nucleation and crystallization of hydroxyapatite. Therefore, from a biomimetic point of view, the synthesis of carboxylate ions containing ACP (ACPC) is valuable. Usually, ACP is synthesized with fewer steps than ACPC. The precipitation reaction of ACP is rapid and influenced by pH, temperature, precursor concentration, stirring conditions, and reaction time. Due to phosphates triprotic nature, controlling pH in a multistep approach becomes tedious. Here, we developed a new ACP and ACPC synthesis approach and thoroughly characterized the obtained materials. Results from vibration spectroscopy, nuclear magnetic resonance (NMR), X-ray photoelectron spectroscopy (XPS), true density, specific surface area, and ion release studies have shown a difference in the physiochemical properties of the ACP and ACPC. Additionally, the effect of a carboxylic ion type on the physiochemical properties of ACPC was characterized. All of the ACPs and ACPCs were synthesized in sterile conditions, and in vitro analysis was performed using MC-3T3E1 cells, revealing the cytocompatibility of the synthesized ACPs and ACPCs, of which the ACPC synthesized with citrate showed the highest cell viability.

Small organic molecules containing amorphous calcium phosphate: synthesis, characterization and transformation

“…The 31 P NMR spectra of ACP show characteristic broad Gaussian peaks between −15 and 15 ppm centered from 2.2 to 6.5 ppm (Indurkar et al, 2023b). As shown in Figure 4B, the broad peak was observed in all the synthesized ACPs centered at 3.03 ppm (ASP_ASC), 3.89 ppm (ACP_GLU), and 4.07 ppm (ACP_ITN) respectively.…”

“…The invitro biomineralization experiments were performed with six types of ACP (pure ACP, ACP_ACE, ACP_GLU, ACP_ITN, ACP_ASC, and ACP_CIT). The ACP variants, such as pure ACP, ACP with citrate (ACP_CIT), and acetate (ACP_ACE), were synthesized, and characterization was reported in our previous study (Indurkar et al, 2023b). On the other hand, ACP variants such as ACP_GLU, ACP_ITN, and ACP_ASC were synthesized and characterized in the current study.…”

“…Later, the centrifuge tube containing the precipitate was immersed in liquid nitrogen for 15 min, followed by freeze-drying for 72 h. The obtained power was stored in airtight containers until further characterization. Similarly, pure ACP, ACP_ACE and ACP_CIT were synthesized and characterized previously (Indurkar et al, 2023b).…”

“…However, Becher et al have identified that many biological ubiquitous small organic molecules can inhibit the conversion of ACP to HAp at their respective tissue concentration (Becker, 1977). Considering these findings, ACP composites were developed using small organic molecules of polycarboxylate (such as citrate, succinate, acetate, and several amino acids), pyrophosphate, phosphocitric acid, polyphosphates as well as di-and-triphosphate nucleotide (Ikawa et al, 2009;Chinopoulos and Adam-Vizi, 2010;Grover et al, 2013;Stipniece et al, 2016;Feng et al, 2020;Indurkar et al, 2023b).…”

“…The novel direction of incorporation of mitochondrial organic molecules in ACP offers a unique strategy to address bone-related disorders, potentially leading to innovative therapeutic interventions. Previously, we have developed ACP and its composite with citrate (ACP_CIT) and acetate (ACP_ACE) (Indurkar et al, 2023b). In this study, the ACP was synthesized with ascorbate (ACP_ASC), glutamate (ACP_GLU), and itaconate (ACP_ITN), were thoroughly characterized, and their cytocompatibility was evaluated.…”