Intrafibrillar mineralization of type I collagen with calcium carbonate and strontium carbonate induced by polyelectrolyte–cation complexes

Abstract

Calcium carbonate (CaCO₃), possessing excellent biocompatibility, bioactivity, osteoconductivity and superior biodegradability, may serve as an alternative to hydroxyapatite (HAp), the natural inorganic component of bone and dentin. Intrafibrillar mineralization of collagen with CaCO₃ was achieved through the polymer-induced liquid precursor (PILP) process for at least 2 days. This study aims to propose a novel pathway for rapid intrafibrillar mineralization with CaCO₃ by sequential application of the carbonate–bicarbonate buffer and polyaspartic acid (pAsp)-Ca suspension. Fourier transform infrared (FTIR) spectroscopy, zeta potential measurements, atomic force microscopy/Kelvin probe force microscopy (AFM/KPFM), and three-dimensional stochastic optical reconstruction microscopy (3D STORM) demonstrated that the carbonate–bicarbonate buffer significantly decreased the surface potential of collagen and CO₃²⁻/HCO₃⁻ ions could attach to collagen fibrils via hydrogen bonds. The electropositive pAsp–Ca complexes and free Ca²⁺ ions are attracted to and interact with CO₃²⁻/HCO₃⁻ ions through electrostatic attractions to form amorphous calcium carbonate that crystallizes gradually. Moreover, like CaCO₃, strontium carbonate (SrCO₃) can deposit inside the collagen fibrils through this pathway. The CaCO₃-mineralized collagen gels exhibited better biocompatibility and cell proliferation ability than SrCO₃. This study provides a feasible strategy for rapid collagen mineralization with CaCO₃ and SrCO₃, as well as elucidating the tissue engineering of CaCO₃-based biomineralized materials.