Amorphous Calcium Carbonate Stabilized by a Flexible Biomimetic Polymer Inspired by Marine Mussels

Organisms make use of amorphous materials as a certain precursor to form insoluble complex biominerals in the presence of various organic matrices. In this article, we demonstrate that amorphous calcium carbonate (ACC) nanoparticles. can be highly stabilized by a polymerized dopamine (DA), a biomimetic molecule inspired by adhesive proteins in mussels. The cross-linking polydopamine (PDA, a mussel mimicking polymer) flexible chains are adhesively associated with the ACC particles to form ACC@PDA core-shell spheres. We are able to modulate the thickness of PDA shells in the range of a few to several tens of nanometers by adjusting the additive DA amount. The thickness of this mussel mimicking PDA shell significantly influences the stability of ACC nanoparticles; the thicker the PDA shell is, the more stable the ACC core is. The obtained ACC PDA hybrid particles have high stability, partly because the complexing interaction of Ca2+ ions with PDA and encapsulating PDA networks inhibit ACC dissolution and retard subsequent Ostwald ripening, and partly because the PDA coating builds isolated confinement spaces for ACC that prevents contacting and merging of ACC particles which further restrains possible solid-phase transformation. Notably, the protecting effects of PDA endow the obtained ACC PDA composite powder with enough stability to exist for at least one year in the solid state. Our resulting hybrid ACC PDA nanoparticles with tunable size and high stability could serve as a model system for multistep biomineralization, limited space crystallization, and potential biomedical applications as well.