A simple fabrication method to develop a lignin nanosphere based spray coating which exhibited light assisted diagnostic and antimicrobial potential for the first time.

Metal–organic frameworks (MOFs) have dramatically changed the fundamentals of drug delivery, catalysis, and gas storage as a result of their porous geometry, controlled architecture, and ease of postsynthetic modification. However, the biomedical applications of MOFs still remain a less explored area due to the constraints associated with handling, utilizing, and site-specific delivery. The major drawbacks associated with the synthesis of nano-MOFs are related to the lack of control over particle size and inhomogeneous dispersion during doping. Therefore, a smart strategy for the in situ growth of a nano-metal–organic framework (nMOF) has been devised to incorporate it into a biocompatible polyacrylamide/starch hydrogel (PSH) composite for therapeutic applications. In this study, the post-treatment of zinc metal ion cross-linked PSH with the ligand solution generated the nZIF-8@PAM/starch composites (nZIF-8, nano-zeolitic imidazolate framework-8). The ZIF-8 nanocrystals thus formed have been found to be evenly dispersed throughout the composites. This newly designed nanoarchitectonics of an MOF hydrogel was found to be self-adhesive, which also exhibited improved mechanical strength, a viscoelastic nature, and a pH-responsive behavior. Taking advantage of these properties, it has been utilized as a sustained-release drug delivery platform for a potential photosensitizer drug (Rose Bengal). The drug was initially diffused into the in situ hydrogel, and then the entire scaffold was analyzed for its potential in photodynamic therapy against bacterial strains such as E. coli and B. megaterium. The Rose Bengal loaded nano-MOF hydrogel composite exhibited remarkable IC50 values within the range of 7.37 ± 0.04 and 0.51 ± 0.05 μg/mL for E. coli and B. megaterium. Further, reactive oxygen species (ROS) directed antimicrobial potential was validated using a fluorescence-based assay. This smart in situ nanoarchitectonics hydrogel platform can also serve as a potential biomaterial for topical treatment including wound healing, lesions, and melanoma.

A multifunctional hydrogel that combines the properties of pH-responsiveness as well as controlled release holds enormous potential for antimicrobial photodynamic therapy through the development of wound dressings and coatings. Utilization of lignin (a biodegradable and cost-effective biopolymer) could be advantageous as a sustainable alternative over the conventional hydrogels for photodynamic therapy, which is an underexplored area. In this work, the lignin-based hydrogel was developed, which was found to have remarkable self-healing properties. Moreover, the lignin-based photodynamic hydrogels designed via in situ and ex situ methods were found to be transparent enough (through the variation of lignin concentration) to be utilized for photodynamic therapy applications. The in situ method is an example of lignin hydrogel synthesis which is advantageous as it saves multiple reaction steps of nanoparticle synthesis and incorporation into the hydrogel. However, for the demonstration of photodynamic effect, the lignin-based hydrogels were doped with a photosensitizer (Rose Bengal, RB) and also with RB-conjugated lignin-derived silver nanocomplexes (RB@L-AgNCs). The developed lignin-based nanocomposite hydrogels were characterized through various methods including UV–vis spectroscopy, HRTEM, BET, XRD, FESEM, rheology, and FTIR to determine their material properties. Interestingly, the lignin hydrogels were found to possess pH-responsive properties for controlled release of the incorporated nanoagents. Antimicrobial photodynamic therapy studies were performed using lignin-based nanocomposite hydrogels as well as bare lignin hydrogels through utilization of a green laser for a short time (3 min). Mechanistically, it was observed that the nanocomposite-doped hydrogel worked much better as compared to the native lignin hydrogel due to higher reactive oxygen species (ROS) generation. Furthermore, the antimicrobial photodynamic activity of the developed lignin-based nanocomposite hydrogels was validated through fluorescence microscopy studies (live–dead cell imaging). These developed biodegradable lignin-based nanocomposite hydrogels can be efficiently used for the development of wound dressings and nanocoatings over various surfaces for stimuli responsive antimicrobial effect.