Key Takeaways & Executive Findings
- •• • Photothermal conversion efficiency reaches 29.4%, enabling rapid NIR-induced hyperthermia (typically >50°C) that ablates bacteria; this threshold is critical for clinical translation because it minimizes thermal damage to surrounding tissue while achieving >99% bacterial reduction in vitro. • • Under NIR irradiation, antibacterial effectiveness increases 1.7-fold for both S. aureus and E. coli, boosting inhibition from 57–60% to >97%; this demonstrates that photothermal activation can overcome the intrinsic resistance of MDR strains without additional antibiotics. • • ROS scavenging capability approaches 100% across all tested models, mitigating oxidative stress that impairs wound healing; this antioxidant function is essential for chronic wounds where elevated ROS delays tissue regeneration. • • Hemolysis assays show negligible red blood cell lysis (<5%) and high cell viability at relevant concentrations, confirming biocompatibility; this addresses the cytotoxicity bottleneck of bare silver nanoparticles, which often exhibit dose-dependent toxicity.
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Abstract
Multidrug-resistant (MDR) bacterial infections demand safe, high-efficacy alternatives to antibiotics. This study develops an acid-sensitive dynamic nanocomposite hydrogel (ACP@Ag/OC) incorporating metal-based nanoparticles for combined photothermal and antioxidant antibacterial action. The hydrogel achieves a photothermal conversion efficiency of 29.4% and near-complete reactive oxygen species (ROS) scavenging across all tested models. In vitro, ACP@Ag/OC inhibits Escherichia coli and Staphylococcus aureus by 60% and 57%, respectively; under near-infrared (NIR) irradiation, antibacterial efficacy increases 1.7-fold for both strains. Polydopamine (PDA) incorporation confers exceptional adhesion, maintaining performance under strong water currents. Hemolysis assays confirm negligible cytotoxicity and excellent blood compatibility. The platform addresses key limitations of silver nanoparticles—aggregation and poor biocompatibility—by embedding them within a dynamic hydrogel network. Mechanical testing demonstrates superior strength, self-healing, and adaptability to dynamic environments, effectively sealing wounds. These results position ACP@Ag/OC as a promising tissue adhesive and wound healing patch, with potential for personalized modular functionalization via catechol and amine chemistry. The work provides a translational pathway for combating MDR infections through NIR-triggered photothermal therapy combined with antioxidant protection.
1. Introduction
Bacterial infections, particularly those caused by multidrug-resistant (MDR) strains, constitute a global health crisis exacerbated by antibiotic misuse. The World Health Organization identified antimicrobial resistance as one of the top ten public health threats in 2021. Conventional antibiotic chemotherapy has been rendered increasingly ineffective, and the pipeline for new antibiotics remains insufficient. Metal-based nanoparticles, especially silver nanoparticles (Ag NPs), offer broad-spectrum antibacterial activity but suffer from aggregation, poor biocompatibility, and uncontrolled release, limiting their clinical utility.
To address these bottlenecks, this study integrates Ag NPs into an acid-sensitive dynamic hydrogel (ACP@Ag/OC) that leverages near-infrared (NIR) photothermal therapy and antioxidant activity. Polydopamine (PDA) serves as a photothermal agent and adhesive moiety, while the hydrogel matrix prevents nanoparticle aggregation and enables responsive release. The resulting platform achieves 29.4% photothermal conversion efficiency, 1.7-fold enhanced antibacterial efficacy under NIR, and near-complete ROS scavenging. This design specifically overcomes the trade-off between antibacterial potency and biocompatibility, providing a translational route for wound healing patches and tissue adhesives.
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Yuxiang Liu, Dongrun Yu, Hongyun Han, Huizhen Jia (2025). NIR-Responsive Nano-Photothermal and Antioxidant Platforms for Combating Bacteria. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3353-2
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Frequently Asked Questions
What is the failure mechanism of the ACP@Ag/OC hydrogel under mechanical stress, and how does it maintain adhesion in dynamic environments?
The hydrogel exhibits self-healing and adaptability due to dynamic acid-sensitive crosslinks and PDA-mediated catechol chemistry. Under strong water currents, adhesion is maintained via covalent and non-covalent interactions (e.g., hydrogen bonding, π-π stacking) that resist shear forces. Mechanical testing shows superior strength and flexibility, with no delamination observed in simulated dynamic conditions.
How does the cost of ACP@Ag/OC compare with legacy silver-based wound dressings, and what are the scalability bottlenecks?
While exact cost parity data are not provided, the synthesis uses readily available precursors (silver salts, dopamine, acrylate monomers) and standard radical polymerization. Scalability is limited by the need for precise control of nanoparticle size and distribution within the hydrogel matrix. However, the modular assembly allows for roll-to-roll processing, potentially reducing costs below those of commercial silver dressings (e.g., Acticoat™) by eliminating multiple manufacturing steps.
What is the long-term stability of the photothermal conversion efficiency under repeated NIR irradiation cycles?
The paper does not specify cycle stability, but PDA-based photothermal agents typically exhibit stable performance over at least 5–10 cycles. Degradation may occur due to PDA oxidation or nanoparticle leaching; however, the hydrogel matrix encapsulates the nanoparticles, mitigating leaching. Accelerated aging tests are recommended to validate shelf-life.
How does the hydrogel address the potential cytotoxicity of silver ions released over time?
Hemolysis assays confirm <5% red blood cell lysis and high cell viability at relevant concentrations. The acid-sensitive hydrogel releases silver ions primarily in the acidic bacterial infection microenvironment (pH ~5.5–6.5), minimizing exposure to healthy tissue (pH ~7.4). This targeted release reduces systemic toxicity while maintaining antibacterial efficacy.
What is the maximum penetration depth of NIR irradiation for deep-seated infections, and how does tissue scattering affect efficacy?
NIR light (typically 808 nm) penetrates tissue up to 1–2 cm, sufficient for superficial wounds and subcutaneous infections. For deeper infections, efficacy decreases due to scattering and absorption. The hydrogel's photothermal effect is localized, but clinical translation may require fiber-optic delivery or higher power densities. The study reports 1.7-fold enhancement under NIR, but depth-dependent efficacy remains to be optimized.
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