Balancing the biocompatibility and bacterial resistance of polypyrrole by optimized silver incorporation

Polypyrrole (PPy) which is a conductive polymer with excellent biocompatibility has enormous potential in implantable electronics. However, pristine PPy does not have sufficient bacterial resistance and hence, bacterial infection poses serious threats in vivo. Silver is an excellent antibacterial agent but the optimal concentration is critical because excessive silver is detrimental to human health. In this study, electrochemical polymerization is carried out to fabricate PPy coatings and silver ions (Ag) are introduced by plasma immersion ion implantation (PIII). The optimal Ag ion fluence is determined by monitoring the antibacterial efficiency and cytotoxicity. Our results show that the optimal balance between the antibacterial ability and cytocompatibility can be attained from sample Ti-PPy@Ag-4 implanted with a silver ion fluence of 4 × 10¹⁶ ions cm^-2. In addition to retaining good cytocompatibility, 92% of the bacteria Staphylococcus aureus (S. aureus) can be eliminated. The intricate balance between antibacterial effects and biocompatibility arises from the levels of intracellular reactive oxygen species (ROS) in S. aureus and MC3T3-E1 osteoblasts on Ti-PPy@Ag-4. The antibacterial capability and biocompatibility are verified by the subcutaneous infection model in rats in vivo. The results reveal a simple strategy to improve the bacterial resistance of polymers such as PPy while not compromising the inherent biosafety of the materials. To the best of our knowledge, this is the first attempt to functionalize PPy by Ag PIII to create the proper balance between the antibacterial capacity and biosafety of biomedical implants.