Synthesis and characterization of Zn-modified hydroxyapatite photoactive composites from eggshell residues for bone regeneration

Photoactive composites based on hydroxyapatite containing zinc (HAp-Zn x%, x = 0, 0.5, 2.5, 5.0, 10.0, 15.0 and 100 mol% Zn2+) were produced by precipitation method and using calcium nitrate converted from eggshell residues. These materials were carefully designed to be used in bone regeneration, and the results demonstrated essential properties to improve the bone repair processes, such as nanometric size, spherical and/or spherocylindrical morphology, negative zeta potential, antioxidant action and ability to scavenger reactive oxygen species (ROS). In addition, antimicrobial tests demonstrated that the modification of HAp with zinc ions induced a photomodulated antibacterial action on HAp, since all tested composites containing zinc exhibited an inhib-itory effect against Staphylococcus aureus (S. aureus) bacteria, which was expressively intensified after irradiation with visible light. This photomodulated antibacterial action is essentially interesting to prevent the occurrence of post-surgical infections common in placement of bone implants. Among these materials, HAp-Zn 15.0% is noteworthy, since it presented the lowest minimum inhibitory concentration (MIC) of 0.12 mg mL-1 in the absence of light, and 0.06 mg mL-1 after 3 h of exposure to the visible light. In this context, our new findings showed that the antibacterial activity of these photoactive composites against S. aureus is not attributed only to the leaching of zinc ions, but also to action of center dot OH and O2 center dot- radicals, which can be generated even in the absence of irradiation. Additionally, our multifunctional composites were able of inhibit S. aureus bacteria and concomitantly stimulate the growth of pre-osteoblastic cells, ensuring its efficient use in regenerative medicine.