Biomimetic apatites functionalized with antioxidant phytotherapeutics: The case of chlorogenic and sinapic phenolic compounds

Synthetic bone-like apatites (i.e. biomimetic apatites) increasingly attract attention in the field of bone substitutes due to their similarity to natural bone mineral and their intrinsic surface reactivity, as opposed to conventional hydroxyapatite. Associations with a range of bioactive species can be a way to further tailor their properties after implantation. In the present work, we have focused on the preparation of hybrid materials combining biomimetic apatites, doped or not with antibacterial Ag⁺ ions for added antimicrobial pertinence, and two biophenolic compounds, namely chlorogenic acid (CA) and sinapic acid (SA). Using complementary characterization techniques, especially FTIR and Raman spectroscopies, as well as Monte Carlo computational simulations, we elucidate the possible interaction between such biophenolic molecules and apatite. The follow-up of isotherms of adsorption also pointed out the quantitative sorption of CA and SA onto biomimetic apatites, potentially up to larger extents than reported so far in the literature for apatitic substrates. Finally, antioxidant properties of prepared hybrids were measured via free radical scavenging tests using DPPH as reactant, showing that the studied phytotherapeutic agents retained antioxidant properties after the adsorption process. This work thus evidences that bone-like apatites can be quantitatively associated to biophenolic bioactive agents to further modulate their properties as smart bone substitutes, providing them additional antioxidant features, among others.