Photo-Enhanced Antimicrobial Activity of Polymers Containing an Embedded Photosensitiser

Fabrication of photo-induced molecular superoxide radical generator for highly efficient therapy against bacterial wound infection

The pressing need for highly efficient antibacterial strategies arises from the prevalence of microbial biofilm infections and the emergence of rapidly evolving antibiotic-resistant strains of pathogenic bacteria. Photodynamic therapy represents a highly efficient and compelling antibacterial approach, offering promising prospects for effective control of the development of bacterial resistance. However, the effectiveness of many photosensitizers is limited due to the reduced generation of reactive oxygen species (ROS) in hypoxic microenvironment, which commonly occur in pathological conditions such as inflammatory and bacteria-infected wounds. Herein, we designed and prepared two phenothiazine-derived photosensitizers (NB-1 and NB-2), which can effectively generate superoxide anion radicals (O2●-) through the type I process. Both photosensitizers demonstrate significant efficacy in vitro for the eradication of broad-spectrum bacteria. Moreover, NB-2 possesses distinct advantages including strong membrane binding and strong generation of O2●-, rendering it an exceptionally efficient antibacterial agent against mature biofilms. In addition, laser activated NB-2 could be applied to treat MRSA-infected wound in vivo, which offers new opportunities for potential practical applications.

AMP-Mimetic Antimicrobial Polymer-Involved Synergic Therapy with Various Coagents for Improved Efficiency

The misuse of antibiotics contributes to the emergence of multidrug-resistant (MDR) bacteria. Infections caused by MDR bacteria are rapidly evolving into a significant threat to global healthcare due to the lack of effective and safe treatments. Antimicrobial peptides (AMPs) with broad-spectrum antibacterial activity kill bacteria generally through a membrane disruption mechanism; hence, they tend not to induce resistance readily. However, AMPs exhibit disadvantages, such as high cost and susceptibility to proteolytic degradation, which limit their clinical application. AMP-mimetic antimicrobial polymers, with low cost, stability to proteolysis, broad-spectrum antimicrobial activity, negligible antimicrobial resistance, and rapid bactericidal effect, have received extensive attention as a new type of antibacterial drugs. Lately, AMP-mimetic polymer-involved synergic therapy provides a superior alternative to combat MDR bacteria by distinct mechanisms. In this Review, we summarize the AMP-mimetic antimicrobial polymers involved in synergic therapy, particularly focusing on the different combinations between the polymers with commercially available antimicrobials, organic small molecule photosensitizers, inorganic nanomaterials, and nitric oxide.

Advancements of Porphyrin-Derived Nanomaterials for Antibacterial Photodynamic Therapy and Biofilm Eradication

The threat posed by antibiotic-resistant bacteria and the challenge of biofilm formation has highlighted the inadequacies of conventional antibacterial therapies, leading to increased interest in antibacterial photodynamic therapy (aPDT) in recent years. This approach offers advantages such as minimal invasiveness, low systemic toxicity, and notable effectiveness against drug-resistant bacterial strains. Porphyrins and their derivatives, known for their high molar extinction coefficients and singlet oxygen quantum yields, have emerged as crucial photosensitizers in aPDT. However, their practical application is hindered by challenges such as poor water solubility and aggregation-induced quenching. To address these limitations, extensive research has focused on the development of porphyrin-based nanomaterials for aPDT, enhancing the efficacy of photodynamic sterilization and broadening the range of antimicrobial activity. This review provides an overview of various porphyrin-based nanomaterials utilized in aPDT and biofilm eradication in recent years, including porphyrin-loaded inorganic nanoparticles, porphyrin-based polymer assemblies, supramolecular assemblies, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs). Additionally, insights into the prospects of aPDT is offered, highlighting its potential for practical implementation.

Amide Modification of Glycolipid Biosurfactants as Promising Biocompatible Antibacterial Agents

Discovering new antibacterial agents is crucial to addressing the increasing risk of bacterial infections induced by antimicrobial resistance in food and agricultural industries. Here, biocompatible acidic-type sophorolipids (ASLs) and glucolipids (GLs) prepared via chemical modification of natural sophorolipids from fermentation were functionalized via amide modification for use as potential antibacterial agents. It was found that the arginine methyl ester derivative of GLs (GLs-d-Arg-OMe) showed excellent antibacterial activity, killing more than 99.99% of Escherichia coli at 200 mg/L. The sterilization dosage of the GLs against Bacillus subtilis, Bacillus cereus, and Staphylococcus aureus was 16-64 mg/L, in contrast to 32-64 mg/L for the fungus Candida albicans. In particular, GLs-d-Arg-OMe showed the best biocompatibility with a therapeutic index of up to 18. It was shown that amide modification of glycolipids can effectively improve antibacterial activity while maintaining biocompatibility, which can be exploited for the development of novel antibiotics in food and agricultural fields.

Spin-state Conversion by Asymmetrical Orbital Hybridization in Ni-doped Co3 O4 to Boost Singlet Oxygen Generation for Microbial Disinfection

Singlet oxygen (1 O2 ) plays a significant role in environmental and biomedical disinfection fields. Electrocatalytic processes hold great potential for 1 O2 generation, but remain challenging. Herein, a facile Ni doping converted spin-state transition approach is reported for boosting 1 O2 production. Magnetic analysis and theoretical calculations reveal that Ni occupied at the octahedral site of Co3 O4 can effectively induce a low-to-high spin-state transition. The high-spin Ni-Co3 O4 generate appropriate binding strength and enhance electron transfer between the Co centers with oxygen intermediates, thereby improving the catalytic activity of Ni-Co3 O4 for effective generating 1 O2 . In neutral conditions, 1×106  CFU mL-1 Gram-negative ESBL-producing Escherichia coli (E. coli) could be inactivated by Ni-Co3 O4 system within 5 min. Further antibacterial mechanisms indicate that 1 O2 can lead to cell membrane damage and DNA degradation so as to irreversible cell death. Additionally, the developed Ni-Co3 O4 system can effectively inactivate bacteria from wastewater and bioaerosols. This work provides an effective strategy for designing high-spin electrocatalysis to boost 1 O2 generation for disinfection process.

Unleashing the Power of PET-RAFT Polymerization: Journey from Porphyrin-Based Photocatalysts to Combinatorial Technologies and Advanced Bioapplications

The emergence of photoinduced energy/electron transfer-reversible addition-fragmentation chain transfer polymerization (PET-RAFT) not only revolutionized the field of photopolymerization but also accelerated the development of porphyrin-based photocatalysts and their analogues. The continual expansion of the monomer family compatible with PET-RAFT polymerization enhances the range of light radiation that can be harnessed, providing increased flexibility in polymerization processes. Furthermore, the versatility of PET-RAFT polymerization extends beyond its inherent capabilities, enabling its integration with various technologies in diverse fields. This integration holds considerable promise for the advancement of biomaterials with satisfactory bioapplications. As researchers delve deeper into the possibilities afforded by PET-RAFT polymerization, the collaborative efforts of individuals from diverse disciplines will prove invaluable in unleashing its full potential. This Review presents a concise introduction to the fundamental principles of PET-RAFT, outlines the progress in photocatalyst development, highlights its primary applications, and offers insights for future advancements in this technique, paving the way for exciting innovations and applications.

Conjugation of antimicrobial peptides to enhance therapeutic efficacy

The growing prevalence of antimicrobial resistance (AMR) has brought with it a continual increase in the numbers of deaths from multidrug-resistant (MDR) infections. Since the current arsenal of antibiotics has become increasingly ineffective, there exists an urgent need for discovery and development of novel antimicrobials. Antimicrobial peptides (AMPs) are considered to be a promising class of molecules due to their broad-spectrum activities and low resistance rates compared with other types of antibiotics. Since AMPs also often play major roles in elevating the host immune response, the molecules may also be called "host defense peptides." Despite the great promise of AMPs, the majority remain unsuitable for clinical use due to issues of structural instability, degradation by proteases, and/or toxicity to host cells. Moreover, AMP activities in vivo can be influenced by many factors, such as interaction with blood and serum biomolecules, physiological salt concentrations or different pH values. To overcome these limitations, structural modifications can be made to the AMP. Among several modifications, physical and chemical conjugation of AMP to other biomolecules is widely considered an effective strategy. In this review, we discuss structural modification strategies related to conjugation of AMPs and their possible effects on mode of action. The conjugation of fatty acids, glycans, antibiotics, photosensitizers, polymers, nucleic acids, nanoparticles, and immobilization to biomaterials are highlighted.

Supramolecular Assemblies based on Polymeric Cyclodextrin Nanosponges and a Cationic Porphyrin with Antimicrobial Photodynamic Therapy Action

Within of the increasing requirement of alternative approaches to fight emerging infections, nano-photosensitisers (nanoPS) are currently designed with the aim to optimize the antimicrobial photodynamic (aPDT) efficacy. The utilize of less expensive nanocarriers prepared by simple and eco-friendly methodologies and commercial photosensitisers are highly desiderable. In this direction, here we propose a novel nanoassembly composed of water soluble anionic polyester β-CD nanosponges (β-CD-PYRO hereafter named βNS) and the cationic 5,10,15,20-tetrakis(1-methylpyridinium-4- yl)porphine (TMPyP). Nanoassemblies were prepared in ultrapure water by mixing PS and βNS, by exploiting their mutual electrostatic interaction, and characterized by various spectroscopic techniques such as UV/Vis, Steady-State and Time Resolved Fluorescence, Dynamic Light Scattering and ζ-potential. NanoPS produce appreciable amount of single oxygen similar to free porphyrin and a prolonged stability after 6 days of incubations in physiological conditions and following photoirradiation. Antimicrobial photodynamic action against fatal hospital-acquired infections such as P. aeruginosa and S. aureus was investigated by pointing out the ability of cationic porphyrin loaded- CD nanosponges to photo-kill bacterial cells at prolonged time of incubation and following irradiation (MBC₉₉ = 3.75 µM, light dose = 54.82 J/cm²).

A metalloporphyrin and hydantoin functionalized nanozyme with synergistically enhanced bacterial inhibition

An elaborate design of multimodal antibacterial agents has been revealed to be a promising strategy to address bacterial resistance, originating from the abuse of antibiotics. In this work, we have developed a positively charged and porous material, FePPOP_Hydantoin, as a disinfectant via introducing 1,3-dibromo-5,5-dimethylhydantoin (Hydantoin) and porphyrin iron units into a polymer framework. The extended π conjugated networks of FePPOP_Hydantoin endowed the material with strong near-infrared (NIR) absorption, high density of surface catalytic active centers, superior stability, and reproducibility. FePPOP_Hydantoin exhibits high peroxidase mimetic and photo-Fenton activity, which can catalyze the biologically allowable maximum concentrations of hydrogen peroxide (100 μM) to produce a vast amount of hydroxyl radicals. Simultaneously, the effective electrostatic interaction between the positively charged FePPOP_Hydantoin and the negatively charged bacteria facilitates the binding of FePPOP_Hydantoin on the bacterial membrane, restricting bacteria within the destruction range of hydroxyl radicals and thus making the bacteria more vulnerable. Finally, further close contact between bacteria and Hydantoin units in FePPOP_Hydantoin gave the material an antibacterial efficiency of over 99.999%. Compared with chemical therapy, photo-Fenton therapy, or peroxidase catalytic therapy alone, FePPOP_Hydantoin had a noteworthy multi-amplified antibacterial efficiency. Furthermore, FePPOP_Hydantoin exhibited good biocompatibility and negligible cytotoxicity. The in vivo antibacterial therapy on the Staphylococcus aureus (S. aureus) infected mouse wound model clearly proved the effectiveness of FePPOP_Hydantoin for fighting bacterial infections. This work highlights opportunities for the design of nanozymes with enhanced bacteriostatic activity, providing a new avenue for the construction of novel antibiotics.

Xanthate-supported photo-iniferter (XPI)-RAFT polymerization: facile and rapid access to complex macromolecules

Xanthate-supported photo-iniferter (XPI)-reversible addition-fragmentation chain-transfer (RAFT) polymerization is introduced as a fast and versatile photo-polymerization strategy. Small amounts of xanthate are added to conventional RAFT polymerizations to act as a photo-iniferter under light irradiation. Radical exchange is facilitated by the main CTA ensuring control over the molecular weight distribution, while xanthate enables an efficient photo-(re)activation. The photo-active moiety is thus introduced into the polymer as an end group, which makes chain extension of the produced polymers possible directly by irradiation. This is in sharp contrast to conventional photo-initiators, or photo electron transfer (PET)-RAFT polymerizations, where radical generation depends on the added small molecules. In contrast to regular photo-iniferter-RAFT polymerization, photo-activation is decoupled from polymerization control, rendering XPI-RAFT an elegant tool for the fabrication of defined and complex macromolecules. The method is oxygen tolerant and robust and was used to perform screenings in a well-plate format, and it was even possible to produce multiblock copolymers in a coffee mug under open-to-air conditions. XPI-RAFT does not rely on highly specialized equipment and qualifies as a universal tool for the straightforward synthesis of complex macromolecules. The method is user-friendly and broadens the scope of what can be achieved with photo-polymerization techniques.

Peptide–Polymer Conjugates: A Promising Therapeutic Solution for Drug-Resistant Bacteria

By 2050, it is estimated that 10 million people will die of drug-resistant bacterial infection caused by antibiotic abuse. Antimicrobial peptide (AMP) is widely used to prevent such circumstances, for the positively charged AMPs can kill drug-resistant bacteria by destroying negatively charged bacterial cell membrane, and has excellent antibacterial efficiency and low drug resistance. However, due to the defects in low in vivo stability, easy degradation, and certain cytotoxicity, its practical clinical application is limited. The emergence of peptide–polymer conjugates (PPC) helps AMPs overcome these shortcomings. By combining with functional polymers, the positive charge of AMPs is partially shielded, and its stability and water solubility are improved, so as to prolong the in vivo circulation time of AMPs and reduce its cytotoxicity. At the same time, the self-assembly ability of PPC enables it to assemble into different nanostructures to undertake specific antibacterial tasks. At present, PPC is mainly used in wound dressing, bone tissue repair, antibacterial coating of medical devices, nerve repair, tumor treatment, and oral health maintenance. In this study, we summarize the structure, synthesis methods, and the clinical applications of PPC, so as to present the current challenges and discuss the future prospects of antibacterial therapeutic materials.

Regulating the bacterial oxygen microenvironment via a perfluorocarbon-conjugated bacteriochlorin for enhanced photodynamic antibacterial efficacy

Photodynamic therapy (PDT) has attracted considerable attention, since it could effectively kill bacteria and prevent the development of multi-drug resistance. However, PDT currently suffers from oxygen limitation and hypoxia is a prominent feature of pathological states encountered in inflammation, wounds, and bacterial infections. Herein, an oxygen-tunable nanoplatform based on perfluorocarbon-conjugated tetrafluorophenyl bacteriochlorin (FBC-F) was designed for effective antimicrobial therapy. The introduction of fluorine atoms can not only increase the reactive oxygen species (ROS) production capacity of FBC-F by facilitating the intersystem crossing (ISC) process of FBC photosensitizers, but also make FBC-F deliver more oxygen into the treatment sites benefiting from the outstanding oxygen-dissolving capability of perfluorocarbon. As a consequence, the FBC-F nanoplatform was able to efficiently generate singlet oxygens for type II PDT, as well as superoxide anions and hydroxyl radicals for type I PDT, and significantly improve antibacterial efficacy in vitro. In vivo experiments further proved that the FBC-F with a powerful antibacterial capability could well promote wound healing and destroy biofilm. Thus, this FBC-F nanoplatform may open a new path in photodynamic antibacterial therapy. STATEMENT OF SIGNIFICANCE: Photodynamic therapy is a promising antibacterial treatment, but its efficacy is severely compromised by hypoxia. To overcome such a limitation, we constructed an oxygen-regulated nanoplatform (FBC-F) by attaching perfluorocarbons (PFC) to the NIR photosensitizer (FBC). As an analogue of bacteriochlorin, FBC could generate ¹O₂ through energy transfer , as well as O₂^-· and ·OH through electron transfer for synergistic type I and type II photodynamic antibacterial therapy. Benefiting from the oxygen-dissolving capability of PFC, FBC-F could efficiently deliver more oxygen into the treatment site and alleviate the hypoxic environment. As a consequence, FBC-F could effectively generate large amounts of reactive oxygen species to achieve improved antibacterial efficacy and provide a promising approach for eliminating biofilms.

Use of Photodynamic Therapy Associated with Antimicrobial Peptides for Bacterial Control: A Systematic Review and Meta-Analysis

Considering the challenges related to antimicrobial resistance, other strategies for controlling infections have been suggested, such as antimicrobial photodynamic therapy (aPDT) and antimicrobial peptides (AMP). This study aims to perform a systematic review and meta-analysis to obtain evidence on the antimicrobial effectiveness of aPDT associated with AMP and establish in vitro knowledge on this topic for further study designs. The PubMed, Scopus, Web of Science, Science Direct, Scielo, and Cochrane Library databases were searched. Two independent and calibrated researchers (Kappa = 0.88) performed all the systematic steps according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The odds ratio (OR) was used as the effect measure. The Peto method was used to perform the meta-analysis due to the sparse data. Twenty studies were included in the present review. The result was significant (OR = 0.14/p = 0.0235/I-squared = 0%), showing better outcomes of aPDT associated with peptides than those of aPDT alone for controlling the microbial load. Only 20% of the studies included evaluated this approach in a biofilm culture. Combined treatment with aPDT and AMP highly increased the ability of microbial reduction of Gram-positive and Gram-negative bacteria. However, additional blind studies are required to evaluate the efficacy of this therapy on microbial biofilms.

Contributions of photochemistry to bio-based antibacterial polymer materials

Surgical site infections constitute a major health concern that may be addressed by conferring antibacterial properties to surgical tools and medical devices via functional coatings. Bio-sourced polymers are particularly well-suited to prepare such coatings as they are usually safe and can exhibit intrinsic antibacterial properties or serve as hosts for bactericidal agents. The goal of this Review is to highlight the unique contribution of photochemistry as a green and mild methodology for the development of such bio-based antibacterial materials. Photo-generation and photo-activation of bactericidal materials are illustrated. Recent efforts and current challenges to optimize the sustainability of the process, improve the safety of the materials and extend these strategies to 3D biomaterials are also emphasized.

Poly(l-ornithine)-Grafted Zinc Phthalocyanines as Dual-Functional Antimicrobial Agents with Intrinsic Membrane Damage and Photothermal Ablation Capacity

Multifunctional antimicrobial peptides that combine the intrinsic microbicidal property of cationic polypeptide chains and additional antibacterial strategy hold promising applications for the treatment of infections caused by antibiotic-resistant bacteria, especially "superbugs". In the present study, star-shaped copolymers ZnPc-g-PLO with a zinc phthalocyanine (ZnPc) core and four poly(l-ornithine) (PLO) arms were designed, synthesized, and evaluated as dual-functional antimicrobial agents, that is, intrinsic membrane damage and photothermal ablation capacity. In an aqueous solution, amphiphilic ZnPc-g-PLO molecules self-assemble into nanosized polymeric micelles with an aggregated ZnPc core and star-shaped PLO periphery, where the ZnPc core exhibits appreciable aggregation-induced photothermal conversion efficiency. In the absence of laser irradiation, ZnPc-g-PLO micelles display potent and broad-spectrum antibacterial activities via physical bacterial membrane disruption as a result of the high cationic charge density of the star-shaped PLO. Upon laser irradiation, significant improvement in bactericidal potency was realized due to the efficacious photothermal sterilization from the ZnPc core. Notably, ZnPc-g-PLO micelles did not induce drug-resistance upon subinhibitory passages. In summary, dual-functional ZnPc-g-PLO copolymers can serve as promising antibacterial agents for the treatment of infectious diseases caused by antibiotic-resistant bacteria.