Synergistic Photocatalytic and Photothermal Antibacterial Activity of (In, Nb) and (Al, Nb) Co‐Doped TiO₂ Ceramics

Abstract

Biomaterials have been playing a significant role in the replacement and regeneration of nonfunctional or lost bone tissues. [1] With the rapid growth in the usage of implants worldwide, the chances of implant-related infections (IRIs) are also high. [2] Though systemic antibiotic administration is a preferred way to treat such bacteria-induced infections, the abuse of antibiotics leads to the evolution of drug-resistance bacteria, making antibiotic-based infection management a potential threat to clinical healthcare. [3] Therefore, it is necessary to develop alternative antibioticfree treatment strategies that are bacteriaspecific, [4] noninvasive, [5] and do not lead to the evolution of drug resistance. [6] Recently, light-based therapeutic strategies, such as photothermal and photodynamic therapy (PTT and PDT) have received great attention as effective alternative antibacterial therapeutics as they are minimally invasive, requires a shorter treatment period, have negligible chances of resistance development, and exhibit broad-spectrum antibacterial activity to various disease-causing pathogens including the resistant strains. [7][8][9] PTT is characterized by the generation of hyperthermia which induces bacterial death by disrupting their cell membrane and denaturing bacterial proteins. [10][11][12] PDT, on the contrary, takes advantage of the photosensitizers to produce reactive oxygen species (ROS) that subsequently kills bacteria. [13][14][15] However, in many cases, monotherapy using either PTT or PDT is often ineffective, thus demanding the combinatorial actions both techniques with profound bactericidal activity to synergistically treat drug-resistant bacterial infection. [16][17][18][19][20] Moreover, combinatorial therapy can potentially reduce the side effects of monotherapy on bone-forming cells by decreasing the ROS amount for PDT and the temperature for PTT required for efficient bactericidal activity.TiO 2 is widely used as implant material due to its biocompatibility, chemical stability, and photocatalytic capability. [21] TiO 2 can only exhibit photocatalytic activity upon ultraviolet light irradiation ascribed to the wide bandgap, which limits its application as a biomaterial. [22,23] Doping is a prevailing strategy to shift the UV absorption edge of TiO 2 to the visible region or even near infrared (NIR) light. [24] Recently, co-doping has attracted much attention as it can potentially form highly concentrated defect pairs, which can adjust the structure of the energy band, promote optical absorption, and suppress the recombination of electron and hole by charge balance, thus promoting the photocatalytic activity of TiO 2 . [25] Hu et al. [26] produced rutile TiO 2 ceramics co-doped by In and Nb with giant permittivity and observed electron-pinned defect-dipoles (EPDDs) with a low activation energy (%15.6 meV). Subsequently, various types of trivalent