Theoretical and Computational Chemistry

Surface Stability and Morphology of Calcium Phosphate Tuned by pH Values and Lactic Acid Additives: Theoretical and Experimental Study

Authors

  • Hongwei Chen Nanjing University & School of Chemistry and Chemical Engineering ,
  • Changchang Lv Nanjing University & School of Chemistry and Chemical Engineering ,
  • Lin Guo Nanjing University & School of Chemistry and Chemical Engineering ,
  • Ming Ma Shanghai Institute of Ceramics, Chinese Academy of Sciences ,
  • Xiangfeng Li Sichuan University & National Engineering Research Center for Biomater ,
  • Zhengyi Lan Shanghai Institute of Ceramics, Chinese Academy of Sciences ,
  • Jun Huo Nanjing University & Kuang Yaming Honors School & Institute for Brain Sciences ,
  • Hao Dong Nanjing University & Kuang Yaming Honors School & Institute for Brain Sciences ,
  • Xiangdong Zhu Sichuan University & National Engineering Research Center for Biomaterials ,
  • Qiang Zhu Nanjing University & School of Chemistry and Chemical Engineering ,
  • Yuming Gu Nanjing University & School of Chemistry and Chemical Engineering ,
  • Ziteng Liu Nanjing University & School of Chemistry and Chemical Engineering ,
  • Jianjun Liu Shanghai Institute of Ceramics, Chinese Academy of Sciences ,
  • Hangrong Chen Shanghai Institute of Ceramics, Chinese Academy of Sciences ,
  • Xuefeng Guo Nanjing University & School of Chemistry and Chemical Engineering ,
  • Jing Ma Nanjing University & School of Chemistry and Chemical Engineering

Abstract

The ubiquitous mineralization of calcium phosphate (CaP) facilitates biological organisms to produce hierarchically structured minerals. The coordination number and strength of Ca2+ ions with phosphate species, oxygen-containing additives, and solvent molecules played a crucial role in tuning nucleation processes and surface stability of CaP under the simulated body fluid (SBF) or aqueous solutions upon the addition of oligomeric lactic acid (LACn, n=1, 8) and changing pH values. As revealed by ab initio molecular dynamics (AIMD), density functional theory (DFT), and molecular dynamics (MD) simulations as well as high-throughput experimentation (HTE), the binding of LAC molecules with Ca2+ ions and phosphate species could stabilize both pre-nucleation clusters and brushite (DCPD, CaHPO4·2H2O) surface through intermolecular electrostatic and hydrogen bonding interactions. When the concentration of Ca2+ ions ([Ca2+]) is very low, the amount of the formed precipitation decreased with the addition of LAC based on UV-Vis spectroscopic analysis due to the reduced chance for the LAC capped Ca2+ ions to coordinate with phosphates and the increased solubility in acid solution. With the increasing [Ca2+] concentration, the kinetically stable DCPD precipitation was obtained with high Ca2+ coordination number and low surface energy. Morphologies of DCPD precipitation are in plate, needle, or rod, depending on the initial pH values that tuned by adding NH3·H2O, HCl, or CH3COOH. The prepared samples at pH ≈ 7.4 with different Ca/P ratios exhibited negative zeta potential values, which were correlated with the surface electrostatic potential distributions and potential biological applications.

Version notes

The new experiments have been supplemented, and thus the corresponding title, introduction and several results have been modified in this manuscript. Additionally, we not only discuss the nucleation process of calcium phosphate, but also the surface stability of calcium phosphate.

Content

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Supplementary material

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Surface Stability and Morphology of Calcium Phosphate Tuned by pH Values and Lactic Acid Additives: Theoretical and Experimental Study
Calculated binding free energies; optimized structures of CaP clusters and DCPD/HA surfaces; surface energies of DCPD/HA surfaces; distribution coefficient δ of carbonate species and LAC; force field parameters of phosphate species, number of ions and water molecules of the CaP systems; ions concentration for high-throughput experimentations in aqueous solution and SBF solution; MD snapshots, SDF and RDF of CaP systems; largest CaP cluster, NCa-contact, number of free Ca2+ ions and phosphate species of CaP systems; contents of Ca and Mg, XRD patterns, TEM images, SEM images and EDS patterns of prepared samples.