Killing Bacteria by Faradaic Processes through Nano-Hydroxyapatite/MoOx Platforms

Following the secular idea of ″restitutio ad integrum″, regeneration is the pursued option to restore bones lost after a disease; accordingly, complementing antibiotic and regeneration capacity to bone grafts represents a great scientific success. This study is a framework proposal for understanding the antimicrobial effect of biocompatible nano-hydroxyapatite/MoOx (nano-HA/MoOx) platforms on the basis of their electroactive behavior. Through cyclic voltammetry and chronoamperometry measurements, the electron transference capacity of nano-HA and nano-HA/MoOx electrodes was determined in the presence of pathogenic organisms: Pseudomonas aeruginosa and Staphylococcus aureus. Faradaic processes were confirmed and related to the switch of MoO42–/PO43– groups in the original hexagonal nano-HA crystal lattice and to the extent of OH vacancies that act as electron acceptors. Microscopic analysis of bacteria’s ultrastructure showed a disruptive effect on the cytoplasmic membrane upon direct contact with the materials, which is not evident in the presence of eukaryotic cells. Experiments support the existence of a type of extracellular electron transfer (EET) process that alters the function of the bacterial cytoplasmic membrane, accelerating their death. Our findings provide strong quantitative support for a drug-independent biocidal physical approach based on EET processes between microorganisms and phosphate ceramics that can be used to combat local orthopedic infections associated with implants.