Metal Ion Coordination Polymer-Capped pH-Triggered Drug Release System on Titania Nanotubes for Enhancing...

The current work reports a novel hybrid system with a highly efficient, bioresponsive, and controlled release of antibacterial activity via the metal ion coordination polymer on titania nanotubes (TNTs). These hybrid systems exhibited a self-defense behavior that is triggered by the change of the ambient environment acidity due to bacterial infection with Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). The antibacterial agents, including antibiotics and nanosilver particles, can be loaded into TNTs and then sealed with coordination polymers (CPs) through the attachment of metallic ions such as Zn²⁺ or Ag⁺. The zinc and silver ions work as intermediate coordination bonds, and they are sensitive to the change in H⁺. Because of the strong bonding of CPs, the amount of released antimicrobial agents is maintained at a nonsignificant level when pH is maintained at 7.4. However, the coordination bond of the capped CPs was triggered to open and release antibacterial agents from TNTs once the environment becomes acidic. The release rate gradually increased as the pH value further decreased. Subsequently, the antibacterial efficiency of the hybrid system is accelerated as the local microenvironment becomes more acidic during bacterial infection. In addition, the metal ions that are used for intermediate bond bridging are also favorable for specific biological functions. For example, Zn²⁺ can promote the proliferation of osteoblastic cells, while Ag⁺ can further enhance the antibacterial capability. In conclusion, this smart surface coating system not only demonstrates excellent self-antibacterial properties and biocompatibility but also formulates a controllable delivery system for the long-lasting treatment of biomaterial-related bacterial infections.