Counterion-mediated Ca2 + accumulation on cationic Langmuir-Blodgett films as template for CaCO3 growth

Abstract

Negatively charged macromolecules play a starring role in Ca2+ saturation at interfaces: they act as organized points for biomineral growth in nature. However, the role positively charged interfaces play in biomineralization remains unknown. Therefore, we decided to use a cationic Langmuir-Blodgett (LB) film composed of dioctadecyldimethylammonium bromide (DOMA) and type-I collagen in the presence of CaCl2 solutions to guide CaCO3 growth on titanium surfaces. Ca2+ was able to interact with DOMA monolayers, leading to impressive cation excess at the film surface, as evidenced by the increased positive zeta potential of the LB films. Additionally, molecular dynamics simulations showed that Ca2+ co-ions were able to accumulate on the positively charged LB interface, especially because configurations like R-N(+)-counterion-Ca2+ existed therein. Counterion-mediated Ca2+ accumulation on the surface was mainly driven by Cl− ions, which were much closer to Ca2+ ions than Br− ions. Ca2+ excess on the surface was sufficient to grow continuous and particulate CaCO3 films on titanium surfaces. In addition, collagen presence induced changes in CaCO3 film morphology and organization. Finally, we were able to confirm that positively charged organic interfaces can act as templates for biomineral growth because counterion-mediated Ca2+ accumulation on these surfaces can drive subsequent crystal growth. This study provides insight into biomineralization templated by positively charged organic matrixes and into the design of bioinspired coatings for metallic surfaces.