Metastructure "Trap" Coating by Acoustic Confinement Effect for Antibacterial Sonothermal Therapy

Antibacterial sonothermal therapy (ASTT) is attractive for treating implant-associated infection, which addresses the limitations of poor penetration of photothermal therapy. However, achieving implant surface-specific ultrasound heating is incredibly challenging. Inspired by the porous acoustic metastructure in noise reduction, the acoustic metastructure would be a new strategy for attaining ASTT. Herein, an "acoustic confinement effect" is proposed to "trap" ultrasound for the metastructure TiO2 porous coating on titanium implants. The metastructure coating accomplishes specific acoustic absorption and efficient acoustic-to-thermal conversion, surpassing the non-specific heating of conventional coatings. The theoretical calculation and experiment of metastructure porous coating prove the acoustic-to-thermal conversion mechanism, which is also validated in metastructure porous coatings on medical polyetheretherketone, indicating it is universal. Excitingly, this acoustic metastructure "trap" can capture bacteria and local sonothermal enhancement, exhibiting superior ASTT antibacterial rates (S. aureus, 99.69%; E. coil, 99.58%) at low-power ultrasound. In addition, the metastructure TiO2 coating mimics human bone and demonstrates outstanding osseointegration. This study sheds substantial light on developing the acoustic responsive surface, broadening a new direction of acoustic metamaterials in medical applications. A strategy of fabricating metastructure coating on implant is proposed, which can act as the "trap" of bacteria and acoustic. Benefiting from the "acoustic confinement effect", the as-prepared porous metastructure TiO2 coating rapidly eliminates bacterial infection by sonothermal effect. This study broadens a new direction of acoustic metamaterials in medical applications. image