Preventing the harmful biofilm increase on the polylactic-acid/Mg surface by the addition of quercetin

Biodegradable composites with antimicrobials properties designed to reduce biofilm formation can sometimes produce the opposite effect to that expected. This is what happened with the antibacterial response of the biomaterial polylactic acid (PLA) doped with Mg: previous studies have shown that Mg is excellent for reducing early biofilm but enhances biofilm after 24 h. For this reason, a natural dopant, quercetin (Qr) is proposed in this work to prepare PLA/Mg/Qr matrices which not only prevent the increase in biofilm formation but also reduce it effectively. PLA crystallinity affects both the mechanical properties and the distribution of dopants inside the matrix and influences the degradation and release rate of the embedded compounds: a semicrystalline state places the dopants closer to the surface, it hardens less with time than the amorphous one, and it results in a higher release of the active compounds and a greater reduction of biofilm. The antibacterial character of Qr comes from its degradation products since, due to its high chemical instability, these derivatives are the ones that appear in the physiological-like environment after releasement. Exposure of the PLA/Mg/Qr matrix to physiological environments also alters its surface physicochemical properties, thus disfavouring bacterial colonization on the material. Therefore, the new sustainable antimicrobial biocomposite PLA/Mg/Qr is able to combine mechanical enhancement with antimicrobial performance.