Lignin–Bimetallic Nanoconjugate Doped pH-Responsive Hydrogels for Laser-Assisted Antimicrobial Photodynamic Therapy

Bioinspired nano-antimicrobials stand out in terms of cost effectiveness and scalability when compared to their chemically synthesized counterparts. There is limited efficacy of current antibiotics due to their interference with the immune system as well as development of antibiotic resistance. Lignin, which is a naturally abundant polyphenol-rich biopolymer, can be utilized for the fabrication of sustainable antimicrobial materials. In the present work, development of stable nanocomposite hydrogels embedded with lignin-based photodynamic nanoconjugates has been described. This could lead to complete eradication of microbial infection upon laser exposure. For designing such hydrogels, initially photosensitizer decorated lignin-metallic and lignin-bimetallic nanoconjugates were developed utilizing simple and nontoxic methods. These photodynamic nanoconjugates were then characterized and doped into a poly(acrylic acid)-based hydrogel in order to achieve efficient pH-triggered controlled release. The nanocomposite hydrogels allowed maximum transmission of light, promoting their applicability in antimicrobial photodynamic therapy. Utilization of hydrogel helped in better retention of nanoconjugates, maintaining their antimicrobial photodynamic efficacy as validated via IC₅₀ measurement and live-dead cell imaging. The biocompatible pH-responsive photodynamic antimicrobial hydrogels developed herein could be potentially applicable in controlled drug delivery through the construction of wound dressings, as well as for developing antifungal, antibacterial, or antiviral nanocoatings.