Interface-driven Sr-morin complexation at Langmuir monolayers for bioactive coating design.

Flavonoid-metal complexes are widely studied because of their interesting luminescent behavior and biological activity. Despite the extensive exploration of flavonoid-metal coordination processes in solution, the formation of complexes using the flavonoid molecule inserted in a lipid membrane has been little investigated. This effect could provide important insight into the biological activity of flavonoids at lipid membranes and could represent an attractive strategy to design supramolecular structures. Here, we studied the complexation between Sr2+ and morin inserted in an octadecylphosphonic acid (OPA) Langmuir monolayer. This is a relevant system due to the synergism imposed by the association of the Sr2+ ability to control bone formation/resorption with the morin antioxidative effect. Morin incorporation into the OPA monolayers and further Sr2+ complexation were monitored by surface pressure isotherms. Electronic absorption spectroscopy and fluorescence techniques showed Sr-morin complexation both in solution and at the air-liquid interface. Although morin complexation has been described to occur only at basic pH, the specific thermodynamic properties at the air-liquid interface drove metal complexation. LB films were deposited on Ti surfaces, and the resulting OPA/Sr-morin coatings exhibited high surface free energy and increase on its polar component. This optimized surface feature supported further serum protein adsorption and osteoblast growth and differentiation, indicating that these lipid-based coatings are promising for bioactive coating design. This study paves the way for the use of this lipid-based coating in the design of implants for faster osteointegration. Moreover, flavonoid-metal complexation at membranes could also help to shed light on the biological role played by flavonoids.

Lipid-mediated growth of SrCO3/CaCO3 hybrid films as bioactive coatings for Ti surfaces.

SrCO3 is frequently used as Sr2+ source in ceramic cements, but its application as bioactive coating for metallic implants has not been explored yet. Aiming at rapid osteointegration and because of the well-known Sr2+ effects on bone metabolism, researchers have sought to design Sr2+-containing biomaterials. In this context, developing simple techniques to prepare Sr2+-based coatings is a must nowadays. Here, we describe the use of a bioinspired lipid-mediated approach to grow SrCO3 hybrid films on Ti surfaces at room temperature. To obtain these coatings, we applied the Langmuir-Blodgett technique to deposit phospholipid films with high degree of organization on Ti. In this way, we expected that controlled SrCO3 crystal growth could be templated by the array of nucleation points arising from electrostatic interaction between Sr2+ and the phospholipid polar heads. To control surface composition and the amount of Sr2+ released from the coatings, we also promoted CaCO3 co-precipitation in the hybrid films. We characterized the hybrid coatings in terms of morphology, chemical structure, wettability, and ability to release Sr2+ upon immersion in biological medium. In vitro osteoblast culture on mixed SrCO3/CaCO3 films revealed that the osteogenic response depended on surface composition, as indicated by alkaline phosphatase activity overexpression, which is an early indicator of osteoblast differentiation. Results showed that the mixed SrCO3/CaCO3 hybrid film created a synergic environment for osteoblasts, and that proper Sr2+ release associated with a Ca2+-rich environment might have optimized the Sr2+ anabolic effect. In conclusion, we have proposed a bioinspired and versatile technique to grow hybrid films that can control surface composition and Sr2+ release. Our results open an opportunity to explore the use of SrCO3-based coatings for rapid metallic implant osteointegration.