A Membrane‐Intercalating Conjugated Oligoelectrolyte with High‐Efficiency Photodynamic Antimicrobial Activity

Photosensitizable ZIF-8 BioMOF for Stimuli-Responsive Antimicrobial Phototherapy

Resistant pathogens are increasingly posing a heightened risk to healthcare systems, leading to a growing concern due to the lack of effective antimicrobial treatments. This has prompted the adoption of antimicrobial photodynamic therapy (aPDT), which eradicates microorganisms by generating reactive oxygen species (ROS) through the utilization of a photosensitizer, photons, and molecular oxygen. However, a challenge arises from the inherent characteristics of photosensitizers, including photobleaching, aggregation, and self-quenching. Consequently, a strategy has been devised to adsorb or bind photosensitizers to diverse carriers to facilitate their delivery. Notably, metal-organic frameworks (MOFs) have emerged as a promising means of transporting photosensitizers, even though achieving uniform particle sizes through room-temperature synthesis remains a complex task. In this work, we have tackled the issue of heterogeneous particle size distribution in MOFs, achieving a particle size of 150 ± 50 nm. Subsequently, we harnessed Zeolite Imidazolate Framework 8 (ZIF-8), an excellent subclass of biocompatible MOF, to effectively load two distinct categories of photosensitizers, namely, Rose Bengal (RB) and porphyrin, using a simple, straightforward, and single-step process. Our findings indicate that the prepared RB@ZIF-8 complex generates a more substantial amount of reactive singlet oxygen species when subjected to photoirradiation (using green light-emitting diode (LED)) at low concentrations, in comparison with porphyrin@ZIF-8, as demonstrated in in vitro experiments. Additionally, we investigated the pH-responsive behavior of the complex to ascertain its implications under biological conditions. Correspondingly, the RB@ZIF-8 complex exhibited a more favorable IC50 value against Escherichia coli compared to bare photosensitizers, ZIF-8 alone, and other photosensitizer-loaded ZIF-8 complexes. This underscores the potential of BioMOF as a promising strategy for combatting multidrug-resistant bacteria across a spectrum of infection scenarios, complemented by its responsiveness to stimuli.

Photodynamic therapy for cancer: mechanisms, photosensitizers, nanocarriers, and clinical studies

Photodynamic therapy (PDT) is a temporally and spatially precisely controllable, noninvasive, and potentially highly efficient method of phototherapy. The three components of PDT primarily include photosensitizers, oxygen, and light. PDT employs specific wavelengths of light to active photosensitizers at the tumor site, generating reactive oxygen species that are fatal to tumor cells. Nevertheless, traditional photosensitizers have disadvantages such as poor water solubility, severe oxygen-dependency, and low targetability, and the light is difficult to penetrate the deep tumor tissue, which remains the toughest task in the application of PDT in the clinic. Here, we systematically summarize the development and the molecular mechanisms of photosensitizers, and the challenges of PDT in tumor management, highlighting the advantages of nanocarriers-based PDT against cancer. The development of third generation photosensitizers has opened up new horizons in PDT, and the cooperation between nanocarriers and PDT has attained satisfactory achievements. Finally, the clinical studies of PDT are discussed. Overall, we present an overview and our perspective of PDT in the field of tumor management, and we believe this work will provide a new insight into tumor-based PDT.

In Situ Nanoarchitectonics of a MOF Hydrogel: A Self-Adhesive and pH-Responsive Smart Platform for Phototherapeutic Delivery

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.

Self-Improving Photosensitizer Discovery System via Bayesian Search with First-Principle Simulations

Artificial intelligence (AI) based self-learning or self-improving material discovery system will enable next-generation material discovery. Herein, we demonstrate how to combine accurate prediction of material performance via first-principle calculations and Bayesian optimization-based active learning to realize a self-improving discovery system for high-performance photosensitizers (PSs). Through self-improving cycles, such a system can improve the model prediction accuracy (best mean absolute error of 0.090 eV for singlet-triplet spitting) and high-performance PS search ability, realizing efficient discovery of PSs. From a molecular space with more than 7 million molecules, 5357 potential high-performance PSs were discovered. Four PSs were further synthesized to show performance comparable with or superior to commercial ones. This work highlights the potential of active learning in first-principle-based materials design, and the discovered structures could boost the development of photosensitization related applications.

Photo-Enhanced Antimicrobial Activity of Polymers Containing an Embedded Photosensitiser

This work presents the synthesis of a novel photosensitive acrylate monomer for use as both a self-catalyst in the photoinduced electron/energy transfer-reversible addition fragmentation chain transfer (PET-RAFT) polymerisation process and a photosensitiser (PS) for antibacterial applications. Hydrophilic, cationic, and antimicrobial formulations are explored to compare the antibacterial effects between charged and non-charged polymers. Covalent attachment of the catalyst to well-defined linear polymer chains has no effect on polymerisation control or singlet oxygen generation. The addition of the PS to polymers provides activity against S. aureus for all polymer formulations, resulting in up to a 99.99999 % killing efficacy in 30 min. Antimicrobial peptide mimetic polymers previously active against P. aeruginosa, but not S. aureus, gain significant bactericidal activity against S. aureus through the inclusion of PS groups, with 99.998 % killing efficiency after 30 min incubation with light. Thus, a broader spectrum of antimicrobial activity is achieved using two distinct mechanisms of bactericidal activity via the incorporation of a photosensitiser monomer into an antimicrobial polymer.

Tailor-Made Polymer Nano-Assembly with Switchable Function and Amplified Anti-Tumor Therapy

The difficulty in killing tumor cells due to the tendency to metastasis and drug resistance are outstanding and urgent problems for the treatment of cancer. It is imperative to figure out an effective therapy strategy to break the treatment dilemmas. Nano self-assembly has the characteristics of flexible regulation, biological compatibility, and easy access. Herein, an albumin-polymer nano-assembly with switchable cytotoxicity and reactive oxygen species (ROS) amplification capability is developed for anti-tumor therapy. The nano-assembly (PFFBT@HSA) is comprised of conjugated polymer PFFBT and natural protein human serum albumin (HSA) via the hydrophobic and electrostatic interactions. The innovative switchable strategy is proposed and realized by HSA turning off the cytotoxicity of PFFBT and then turning on and enhancing the cytotoxicity by generating massive ROS upon light irradiation. The combination of HSA provides more stable microenvironment to benefit the generation of highly effective anti-tumor model of "0+1>1". These results display that the nanostructured self-assembly and the proposed anti-tumor regulation strategy are effective, which will contribute to the diversified treatment of cancer.

A versatile bacterial membrane-binding chimeric peptide with enhanced photodynamic antimicrobial activity

Photodynamic therapy (PDT) has become an effective antibiosis method for overcoming antibiotic resistance. In this study, we developed a versatile bacterial membrane-binding chimeric peptide PpIX-[PEG₈-(KLAKLAK)₂]₂ (denoted as PPK) by conjugating a photosensitizer protoporphyrin IX (PpIX) with an antimicrobial peptide (KLAKLAK)₂ (KLA) for effective photodynamic inactivation of bacteria. The chimeric peptide PPK with positively charged properties and an α-helical conformation could rapidly bind to microbial cells through electrostatic interactions and membrane insertion. Moreover, PPK could disrupt the bacterial membrane and further elicit lipid bilayer leakage to kill bacteria by toxic reactive oxygen species (ROS) generated by PpIX under 660 nm light. In vitro experiments demonstrated that cationic PPK possessed excellent antimicrobial activity against both Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). Afterward, PPK also exhibited perfect therapeutic effects on S. aureus-infected mice without any systemic side effects. This chimeric peptide PPK will show great potential for photodynamic antibiosis.

Radical Cation Initiated Surface Polymerization on Photothermal Rubber for Smart Antifouling Coatings

Biofouling on surfaces of various materials has attracted considerable attention in biomedical and marine industries. Surface grafting based on covalent surface-initiated polymerization offers a popular route to address this problem by providing diverse robust polymer coatings capable of preventing the biofouling in complex environments. However, the existing methods for synthesizing polymer coatings are complicated and rigorous, or require special catalysts, greatly limiting their practical applications. In this work, a radical-cation-based surface-initiated polymerization protocol to graft the surface of darkened trans-polyisoprene (TPI) rubber with a thermo-responsive smart polymer, poly(N-isopropylacrylamide) (PNIPAM), through a simple iodine doping process is reported. A series of characterizations were performed to provide adequate evidence to confirm the successful grafting. Combining the thermal sensitivity of PNIPAM with the photothermal conversion ability of the darkened rubber, efficient bacteria-killing and antifouling capabilities were successfully achieved as a result of temperature-controlled iodine release and switchable amphiphilicity of PNIPAM.