Immobilization of phosphate monomers on collagen induces biomimetic mineralization

Immobilization of phosphoproteins on type-I collagen via covalent binding may induce extra- and intrafibrillar mineralization.

This study tested the hypothesis that methacrylate phosphate esters immobilized on reconstituted type-I collagen can mimic the nucleating role of phosphoproteins.

Three functional monomers (MDP, GPDM and Phenyl-P) that differed in chemical structure and steric hindrances around the phosphate moiety were evaluated. Reconstituted type-I collagen was either left untouched (control) or treated by 5% monomer/ethanol for 20 s. All samples were incubated in simulated dentinal fluid as mineralizing medium at 37°C for 7 or 14 days. The extra- and intrafibrillar mineralization were examined by SEM and TEM/SAED crystallography, respectively.

FT-IR spectroscopy showed that the phosphate groups were incorporated on reconstituted collagen, irrespective of their chemical structure. MDP immobilization induced dense growth of extrafibrillar mineral over time, while with GPDM- and Phenyl-P-immobilized collagen, mineralization was moderate and sparse, respectively. TEM/SAED evidence disclosed that intrafibrillar minerals exclusively occurred in MDP-immobilized collagen.

Immobilization of MDP, which had the lowest steric hindrance, could induce significant biomimetic extra- and intrafibrillar mineralization; resembling the lowest level of hierarchy organization of dentin.