Lignin Nanoparticles Containing Cobalt‐Cyanine Complexes: Potential Multifunctional Platforms for Photoacoustic Imaging and Photothermal Treatment of Bacterial Biofilms in Chronic Wounds

Chronic wounds (CWs) are characterized by persistent inflammation and bacterial biofilms, which hinder healing and contribute to antibiotic resistance. Therefore, innovative treatments with both anti-inflammatory and antibiofilm properties are urgently needed. Here, cobalt phthalocyanine (CoPc), a photo-excitable dye, is combined with polyphenolic lignin to develop CoPc-Lig nanoparticles (NPs). These NPs demonstrate antioxidant activity by scavenging reactive oxygen species and inhibiting key enzymes implicated in CW pathophysiology. Moreover, they are internalized into Staphylococcus aureus and Pseudomonas aeruginosa biofilms, a critical feature for enhancing antibacterial effects. Upon near-infrared light excitation, CoPc-Lig NPs produce a thermal increase, which reduces bacterial viability and disrupts biofilm integrity. This mild photothermal effect is particularly advantageous in CW treatment, as excessive temperatures can damage newly formed tissue. Additionally, the NPs exhibit strong photoacoustic (PA) properties, enabling their use in PA imaging, an emerging non-invasive technique for real-time monitoring. The PA signal remains stable over time and is detected in ex vivo tissue phantoms. These findings highlight the potential of CoPc-Lig NPs as a theragnostic platform for CW management, integrating antimicrobial cobalt, antioxidant polyphenols, and photo-excitable phthalocyanines. Future studies will focus on optimizing photothermal treatment conditions and exploring synergies with debridement and antibacterial agents to enhance therapeutic outcomes.