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

Calcium carbonate (CaCO 3 ), 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 CaCO 3 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 CaCO 3 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 CO 3 2- /HCO 3 - ions could attach to collagen fibrils via hydrogen bonds. The electropositive pAsp-Ca complexes and free Ca 2+ ions are attracted to and interact with CO 3 2- /HCO 3 - ions through electrostatic attractions to form amorphous calcium carbonate that crystallizes gradually. Moreover, like CaCO 3 , strontium carbonate (SrCO 3 ) can deposit inside the collagen fibrils through this pathway. The CaCO 3 -mineralized collagen gels exhibited better biocompatibility and cell proliferation ability than SrCO 3 . This study provides a feasible strategy for rapid collagen mineralization with CaCO 3 and SrCO 3 , as well as elucidating the tissue engineering of CaCO 3 -based biomineralized materials.