Light-triggered theranostic hydrogels for real-time imaging and on-demand photodynamic therapy of skin abscesses

The management of wound infection remains the major challenges in real-time diagnosis, effective bac-terial elimination and rapid wound healing. Herein, we developed injectable theranostic hydrogels to achieve long-term visual imaging of infected wounds and possible infection recurrence and to launch an on-demand bactericidal effect without using any antibiotics. Antimicrobial peptide epsilon-polylysine (ePL)-derived hydrogels were prepared through the copolymerization of methacrylated ePL (mPL) and the con-jugates with tetrakis(4-carboxyphenyl) porphyrin (mPL-TCPP) and phenol red (mPL-Pr). Light illumination of mPL-TCPP produces reactive oxidative species (ROS) to initiate free radical crosslinking into PL@Pr-TCPP hydrogels without using any additional photoinitiators and concurrently exhibits antibacterial photody-namic therapy (PDT). PL@Pr-TCPP hydrogels experience quick color changes from yellow to orange and finally to red when pH values change from 5.0 to 9.0. The actual pH and related bacterial levels in the wounds could be read from G/B signal ratios of hydrogel colors captured by a smart phone. The conju-gation of phenol red and TCPP into hydrogels affords a robust bacterial infection diagnosis and persis-tent bactericidal effect after cycled light illumination. The bacterial capture by ePL hydrogels strengthens PDT effect through alleviating the short lifetime and action distance of ROS. On a Staphylococcus aureus-infected abscess model, light illumination of the pregel solutions achieves in situ formation of hydrogel dressings. The synergistic bactericidal performance significantly relieves inflammatory status, accelerates collagen deposition, and promotes neovascularization, leading to full recovery of the infected wounds with regeneration of skin accessories. PL@Pr-TCPP hydrogels on the wound bed show color changes upon the recurrence of bacterial infection, which could also be totally eliminated after light illumination. There-fore, this study demonstrates a feasible strategy to develop theranostic hydrogel dressings for life-cycle diagnosis and on-demand treatment of wound infections.Statement of significance Over 30% of skin and soft tissue infections become chronic even after appropriate antibacterial treat-ment, and recurrent infections are commonly reported after initial infection. Challenges remain in the development of theranostic wound dressings having the capability of point-of-care diagnosis, life-cycle monitoring and on-demand elimination of bacterial infection. Herein, light-triggered gelation is used to develop theranostic hydrogels for reversible naked-eye diagnosis and on-demand photodynamic therapy of wound infections. Light illumination plays a one-stone-two-birds role, i.e., photodynamically pro-duced reactive oxidative species enable bactericidal effect without using any antibiotics, and the gener-ated free radicals initiate crosslinking of hydrogels without using any additional photoinitiators. Bacterial infection-activated color changes of hydrogels could be captured with a smart phone for on-site and per-sistent monitoring of bacterial infection and wound healing process.(c) 2022 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Automated summary

An injectable theranostic hydrogel was developed for long-term imaging of infected wounds, detection of infection recurrence, and on-demand bactericidal effect without antibiotics. The hydrogel exhibited reversible naked-eye diagnosis and photodynamic therapy, utilizing light-triggered gelation and color changes that could be monitored with a smart phone.