Medical implants and other indwelling medical devices are highly prone to bacterial infections as a result of bacterial attachment and subsequent biofilm formation on their surfaces, which often leads to serious complications and even implant failure. Therefore, surface modification strategies that can effectively prevent bacterial colonization and biofilm formation are of great importance. In recent years, polydopamine (PDA), a bio-inspired polymer derived from the self-polymerization of dopamine, has attracted considerable attention as a versatile surface-modification material due to its excellent adhesive properties and abundant reactive groups. In this study, PDA particles were first prepared via a controlled synthesis route, after which silver nanoparticles (AgNPs) were generated in situ onto the PDA particles through the reduction of silver ions by the catechol groups of PDA, yielding a silver-loaded polydopamine composite (denoted as PDA-Ag). The as-prepared PDA-Ag particles were then deposited onto titanium alloy (TC4) substrates. The effect of silver nitrate concentration on the loading amount of silver on the PDA microspheres was systematically explored, and the optimal concentration was clarified. The surface chemical composition and valence states of the modified TC4 substrates were characterized by X-ray photoelectron spectroscopy (XPS) and energy-dispersive X-ray spectroscopy (EDS), confirming that the PDA-Ag particles were successfully and uniformly deposited onto the TC4 surface. The morphology and microstructure were examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and three-dimensional optical profilometry. The results showed that the PDA particles had a uniform spherical morphology with an average diameter of approximately 150 nm, and the AgNPs anchored on the PDA surface had a diameter of about 25 nm. SEM and TEM images clearly showed the spherical shape of the PDA particles and the uniform distribution of AgNPs on their surfaces, confirming the successful in situ synthesis. After the PDA-Ag coating, the surface roughness of the titanium alloy decreased from 0.357 μm to 25.253 nm, indicating a smoother and more homogeneous surface. In addition, morphological observations revealed that the composite particles were uniformly attached to the substrate, forming a stable functional coating. The antibacterial and anti-biofilm performances of the PDA-Ag modified surfaces were evaluated against the typical Gram-negative bacterium Escherichia coli and Gram-positive bacterium Staphylococcus aureus. The results demonstrated that the modified surface exhibited effective resistance to bacterial attachment, with inhibition rates of 96.14% for E. coli and 85.78% for S. aureus, respectively. Moreover, the biofilm resistance ratios reached 89.83% and 52.80% for E. coli and S. aureus, respectively. These findings indicate that the PDA-Ag coating not only inhibits initial bacterial adhesion but also suppresses subsequent biofilm formation. The excellent antimicrobial activity can be attributed to the sustained release of silver ions and the direct contact-killing effect of the immobilized AgNPs. In conclusion, this study provides a new method and theoretical basis for fabricating antimicrobial surfaces on medical metal materials by using PDA-Ag composite particles. The proposed strategy offers great potential for tackling the surface infection of medical apparatus and implants caused by bacterial accumulation, and can be extended to other metal implant systems.

antimicrobial surface,PDA-Ag NPs,antibacterial performance,reduction in situ