Research Brief
Multidrug-resistant (MDR) bacterial pneumonia poses a major therapeutic challenge due to deep tissue colonization and limited efficacy of antibiotics. This study develops an inhalable piezoelectric nanocatalyst (polarized potassium bismuth titanate, PKBTO) for potent non-antibiotic sonodynamic therapy.
By virtue of its strong ferroelectric polarization, PKBTO exhibits significantly enhanced piezoelectric response under clinically relevant ultrasound stimulation, facilitating efficient charge separation and reactive oxygen species (ROS) generation.
Compared with non-polarized piezoelectric nanocatalysts, PKBTO increases ROS yield by 360.2% against MDR Pseudomonas aeruginosa in vitro and achieves a bactericidal efficiency of over 95%.
In a lethal mouse pneumonia model, aerosolized treatment reduces pulmonary bacterial load by approximately 92%, restores lung tissue structure, normalizes inflammatory markers, elevates the survival rate to 70%, and shows no systemic toxicity.
This study confirms that ferroelectric polarization engineering provides an effective strategy to improve the performance of piezoelectric nanocatalysts, offering a safe and efficient inhalable sonodynamic therapeutic platform for deep respiratory infections refractory to conventional antibiotics.
Highlights
This study develops an inhalable ferroelectrically enhanced piezoelectric nanocatalyst (polarized potassium bismuth titanate, PKBTO) for sonodynamic therapy against lethal multidrug resistant bacterial pneumonia. The core of the research is to significantly improve the piezoelectric performance of nanomaterials through ferroelectric polarization engineering, enabling efficient generation of reactive oxygen species (ROS) under clinically relevant ultrasound stimulation to eliminate deep tissue bacterial infections, providing a noninvasive novel therapeutic strategy to combat antibiotic resistance.
Detailed Analysis
First, the research background addresses the clinical severity of multidrug resistant bacterial pneumonia. Due to deep tissue bacterial colonization and limited efficacy of antibiotics, such infections pose enormous therapeutic challenges and high mortality, creating an urgent need for innovative antibiotic free therapies. Among these, ultrasound represents a promising physical stimulus owing to its favorable tissue penetration and spatiotemporal controllability. Piezoelectric sonodynamic therapy uses ultrasound to activate piezoelectric materials, generating an internal electric field that separates electron–hole pairs, which then react with surrounding substances to produce ROS and kill bacteria. However, the limited mechano electric conversion efficiency of conventional piezoelectric materials restricts their therapeutic efficacy against severe infections in vivo. Therefore, the development of high performance piezoelectric materials is critical to advancing this field.
Second, the innovative solution proposed in this study is the synthesis of the ferroelectric perovskite material KBTO, followed by corona poling to obtain PKBTO. Perovskite materials (ABO₃) inherently possess spontaneous ferroelectric polarization, making them ideal platforms for piezoelectric catalysis. Nevertheless, untreated materials exhibit randomly oriented ferroelectric domains, resulting in very low macroscopic net polarization. Corona poling aligns the macroscopic orientation of ferroelectric domains, thereby substantially enhancing the piezoelectric potential and charge separation efficiency. Material characterizations confirm that polarized PKBTO retains a pure tetragonal perovskite structure, with its piezoelectric coefficient d₃₃ increased remarkably from 5.3 pm V⁻¹ to 54.4 pm V⁻¹, demonstrating that polarization engineering effectively strengthens the intrinsic piezoelectric properties of the material.
Third, the study systematically evaluates the enhancement of catalytic performance and ROS production by poling treatment. Under ultrasound excitation, PKBTO generates ROS far more efficiently than unpolarized KBTO. Quantitative analysis via electron spin resonance and probe degradation assays shows that the singlet oxygen (¹O₂) yield of PKBTO is increased by 260.2%, with a stronger signal for hydroxyl radical (·OH) generation. This enhancement stems from the optimization of the material’s band structure by polarization engineering: it elevates the valence band maximum, strengthening the oxidation capability of holes and favoring ·OH production; meanwhile, it shifts the conduction band minimum to a more negative potential, enhancing the reduction ability of electrons and promoting the formation of superoxide anions (·O₂) and their subsequent conversion to ¹O₂. Electrochemical measurements further verify that PKBTO produces higher peak potential and current density under ultrasound, with significantly reduced charge transfer resistance, indicating higher mechano-electric energy conversion efficiency and improved charge separation and migration.
Fourth, this work constructs a functionalized nanosystem BKBTO to boost bactericidal efficacy. BKBTO is fabricated by loading the antimicrobial peptide mimetic BriTE onto the surface of PKBTO via electrostatic adsorption. In vitro antibacterial experiments reveal that, under ultrasound, BriTE functionalization endows nanoparticles with specific binding and destructive capabilities toward bacterial cell membranes, establishing a synergistic bactericidal mechanism with piezoelectrically generated ROS. Against multidrug-resistant Pseudomonas aeruginosa, the combined US + BKBTO treatment achieves a bactericidal rate of 95.38%, significantly superior to other control groups, and causes severe damage to bacterial cell membranes and DNA.
Fifth, the in vivo therapeutic efficacy and biosafety of the nanosystem are comprehensively validated in a lethal mouse pneumonia model. The nanocatalyst is delivered via aerosol inhalation, followed by a single ultrasound treatment 1 hour post infection. Results show that US + BKBTO treatment markedly reduces pulmonary bacterial load (inhibition rate of 91.96%) and increases the 7 day survival rate of infected mice from 0% in the control group to 70%. Histopathological analysis demonstrates effective restoration of alveolar structure and reduced inflammatory cell infiltration. Mechanistically, the treatment not only significantly suppresses the overexpression of pro-inflammatory cytokines (TNF-α, IL-6, IFN-β) in the lungs during early infection, alleviating cytokine storm, but also upregulates functional proteins associated with lung tissue repair (e.g., SP-C, α-SMA, VEGF-A), actively promoting tissue repair and angiogenesis. Biosafety assessments reveal excellent biocompatibility of the nanomaterial at both cellular and animal levels, with no toxicity to major organs.
In summary, this work employs a simple post-polarization strategy to successfully enhance the performance of piezoelectric nanocatalysts, establishing a highly efficient and safe inhalable sonodynamic therapeutic platform. Its core lies in using ferroelectric polarization engineering to strengthen the piezoelectric effect and optimize the band structure, thereby greatly improving ultrasound-driven ROS production, and achieving synergistic sterilization combined with antimicrobial peptide functionalization. This strategy offers a promising antibiotic-free, noninvasive approach with high clinical translation potential for treating deep tissue infections, especially antibiotic-resistant respiratory infections.
Conclusion
In summary, we have successfully developed an inhalable ferroelectrically enhanced piezoelectric nanocatalyst that enables highly efficient sonodynamic therapy for multidrug-resistant bacterial pneumonia. By engineering a strong intrinsic polarization, this nanocatalyst exhibits excellent performance in accelerating charge carrier separation and enhancing piezoelectrically induced reactive oxygen species generation, thereby achieving rapid bacterial elimination and comprehensive lung tissue repair in vivo. The aerosol-based delivery ensures deep deposition of the agent in the lungs and minimizes systemic exposure, highlighting the safety of this approach. These findings establish ferroelectric polarization engineering as a versatile strategy for improving piezoelectric catalytic activity, opening new avenues for the treatment of various respiratory infections, including those caused by antibiotic-resistant pathogens, via noninvasive and localized sonodynamic activation. Future research will focus on formulation optimization, evaluation of long-term in vivo fate, scale-up for clinical translation, and expanding its therapeutic scope to other challenging infectious diseases.
Full text link: https://doi.org/10.1016/j.biomaterials.2026.124111