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

Abstract

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/MoO x (nano-HA/MoO x ) platforms on the basis of their electroactive behavior. Through cyclic voltammetry and chronoamperometry measurements, the electron transference capacity of nano-HA and nano-HA/MoO x electrodes was determined in the presence of pathogenic organisms: Pseudomonas aeruginosa and Staphylococcus aureus. Faradaic processes were confirmed and related to the switch of MoO4 2–/PO4 3– 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.

Electroactive Biomaterials Regulate the Electrophysiological Microenvironment to Promote Bone and Cartilage Tissue Regeneration

“…Abnormal osteoclast activation is one of the major causes of bone repair failure. [ 242 ] It has been reported that the exposure of osteoclasts to ES results in voltage‐gated Ca 2+ channels mediating the influx of Ca 2+ ions, leading to the disruption of actin ring formation and subsequent alterations in the cell cytoskeleton, ultimately impeding the formation of osteoclast podosomes (specific adhesive structures), and, in turn, inhibiting the bone‐resorbing activity of these cells. [ 243 ] The application of electroactive biomaterials to inhibit osteoclast activation and promote bone tissue repair could be a feasible strategy.…”

“…In another study, Sieben et al. [ 242 ] designed an electroactive biomaterial based on nano‐HAp and MoOx, which was observed to mediate extracellular electron transfer, altering the function of bacterial cell membranes and accelerating the death of pathogens. Furthermore, hydroxyapatite demonstrated favorable biocompatibility, mechanical characteristics, and osteoinductive properties, thereby further enhancing bone tissue regeneration.…”