Bioinspired Quercitrin Nanocoatings: A Fluorescence-Based Method for Their Surface Quantification, and Their Effect on Stem Cell Adhesion and Differentiation to the Osteoblastic Lineage

Polyphenol-based coatings have several potential applications in medical devices, such as cardiovascular stents, contrast agents, drug delivery systems, or bone implants, due to the multiple bioactive functionalities of these compounds. In a previous study, we fabricated titanium surfaces functionalized with flavonoids through covalent chemistry, and observed their osteogenic, anti-inflammatory, and antifibrotic properties in vitro. In this work, we report a fluorescence-based method for the quantification of the amount of flavonoid grafted onto the surfaces, using 2-aminoethyl diphenylborinate, a boronic ester that spontaneously forms a fluorescent complex with flavonoids. The method is sensitive, simple, rapid, and easy to perform with routine equipment, and could be applied to determine the surface coverage of other plant-derived polyphenol-based coatings. Besides, we evaluated an approach based on reductive amination to covalently graft the flavonoid quercitrin to Ti substrates, and optimized the grafting conditions. Depending on the reaction conditions, the amount of quercitrin grafted was between 64 +/- 10 and 842 +/- 361 nmol on 6.2 mm Ti coins. Finally, we evaluated the in vitro behavior of bone-marrow-derived human mesenchymal stem cells cultured on the quercitrin nanocoated Ti surfaces. The surfaces functionalized with quercitrin showed a faster stem cell adhesion than control surfaces, probably due to the presence of the catechol groups of quercitrin on the surfaces. A rapid cell adhesion is crucial for the successful performance of an implant. Furthermore, quercitrin-nanocoated surfaces enhanced the mineralization of the cells after 21 days of cell culture. These results indicate that quercitrin nanocoatings could promote the rapid osteointegration of bone implants.