Photoswitchable Micelles for the Control of Singlet-Oxygen Generation in Photodynamic Therapies.

Inadvertent photosensitizer-activation and singlet-oxygen generation hampers clinical application of photodynamic therapies of superficial tumors or subcutaneous infections. Therefore, a reversible photoswitchable system was designed in micellar nanocarriers using ZnTPP as a photosensitizer and BDTE as a photoswitch. Singlet-oxygen generation upon irradiation didnot occur in closed-switch micelles with ZnTPP/BDTE feeding ratios >1:10. Deliberate switch closure/opening within 65-80 min was possible through thin layers of porcine tissue in vitro, increasing for thicker layers. Inadvertent opening of the switch by simulated daylight, took several tens of hours. Creating deliberate cell damage and prevention of inadvertent damage in vitro and in mice could be done at lower ZnTPP/BDTE feeding ratios (1:5) in open-switch micelles and at higher irradiation intensities than inferred from chemical clues to generate singlet-oxygen. The reduction of inadvertent photosensitizer activation in micellar nanocarriers, while maintaining the ability to kill tumor cells and infectious bacteria established here, brings photodynamic therapies closer to clinical application.

Heme-Mimetic Photosensitizer with Iron-Targeting and Internalizing Properties for Enhancing PDT Activity and Promoting Infected Diabetic Wound Healing.

The management of multibacterial infections remains clinically challenging in the care and treatment of chronic diabetic wounds. Photodynamic therapy (PDT) offers a promising approach to addressing bacterial infections. However, the limited target specificity and internalization properties of traditional photosensitizers (PSs) toward Gram-negative bacteria pose significant challenges to their antibacterial efficacy. In this study, we designed an iron heme-mimetic PS (MnO2@Fe-TCPP(Zn)) based on the iron dependence of bacteria that can be assimilated by bacteria and retained in different bacteria strains (Escherichia coli, Staphylococcus aureus, and methicillin-resistant Staphylococcus aureus) and which shows high PDT antibacterial efficacy. For accelerated wound healing after antibacterial treatment, MnO2@Fe-TCPP(Zn) was loaded into a zwitterionic hydrogel with biocompatibility and antifouling properties to form a nanocomposite antibacterial hydrogel (PSB-MnO2@Fe-TCPP(Zn)). In the multibacterial infectious diabetic mouse wound model, the PSB-MnO2@Fe-TCPP(Zn) hydrogel dressing rapidly promoted skin regeneration by effectively inhibiting bacterial infections, eliminating inflammation, and promoting angiogenesis. This study provides an avenue for developing broad-spectrum antibacterial nanomaterials for combating the antibiotic resistance crisis and promoting the healing of complex bacterially infected wounds.

Beyond surface modification strategies to control infections associated with implanted biomaterials and devices - Addressing the opportunities offered by nanotechnology.

Biomaterial-associated infection (BAI) is considered a unique infection due to the presence of a biomaterial yielding frustrated immune-cells, ineffective in clearing local micro-organisms. The involvement of surface-adherent/surface-adapted micro-organisms in BAI, logically points to biomaterial surface-modifications for BAI-control. Biomaterial surface-modification is most suitable for prevention before adhering bacteria have grown into a mature biofilm, while BAI-treatment is virtually impossible through surface-modification. Hundreds of different surface-modifications have been proposed for BAI-control but few have passed clinical trials due to the statistical near-impossibility of benefit-demonstration. Yet, no biomaterial surface-modification forwarded, is clinically embraced. Collectively, this leads us to conclude that surface-modification is a dead-end road. Accepting that BAI is, like most human infections, due to surface-adherent biofilms (though not always to a foreign material), and regarding BAI as a common infection, opens a more-generally-applicable and therewith easier-to-validate road. Pre-clinical models have shown that stimuli-responsive nano-antimicrobials and antibiotic-loaded nanocarriers exhibit prolonged blood-circulation times and can respond to a biofilm's micro-environment to penetrate and accumulate within biofilms, prompt ROS-generation and synergistic killing with antibiotics of antibiotic-resistant pathogens without inducing further antimicrobial-resistance. Moreover, they can boost frustrated immune-cells around a biomaterial reducing the importance of this unique BAI-feature. Time to start exploring the nano-road for BAI-control.

Self-targeting, zwitterionic micellar dispersants enhance antibiotic killing of infectious biofilms-An intravital imaging study in mice.

Extracellular polymeric substances (EPS) hold infectious biofilms together and limit antimicrobial penetration and clinical infection control. Here, we present zwitterionic micelles as a previously unexplored, synthetic self-targeting dispersant. First, a pH-responsive poly(ε-caprolactone)-block-poly(quaternary-amino-ester) was synthesized and self-assembled with poly(ethylene glycol)-block-poly(ε-caprolactone) to form zwitterionic, mixed-shell polymeric micelles (ZW-MSPMs). In the acidic environment of staphylococcal biofilms, ZW-MSPMs became positively charged because of conversion of the zwitterionic poly(quaternary-amino-ester) to a cationic lactone ring. This allowed ZW-MSPMs to self-target, penetrate, and accumulate in staphylococcal biofilms in vitro. In vivo biofilm targeting by ZW-MSPMs was confirmed for staphylococcal biofilms grown underneath an implanted abdominal imaging window through direct imaging in living mice. ZW-MSPMs interacted strongly with important EPS components such as eDNA and protein to disperse biofilm and enhance ciprofloxacin efficacy toward remaining biofilm, both in vitro and in vivo. Zwitterionic micellar dispersants may aid infection control and enhance efficacy of existing antibiotics against remaining biofilm.

Recent Advances and Future Prospects on Adaptive Biomaterials for Antimicrobial Applications.

Bacterial infection is becoming the biggest threat to human health. The scenario is partly due to the ineffectiveness of the conventional antibiotic treatments against the emergence of multidrug-resistant bacteria and partly due to the bacteria living in biofilms or cells. Adaptive biomaterials can change their physicochemical properties in the microenvironment of bacterial infection, thereby facilitating either their interactions with bacteria or drug release. The trends in treating bacterial infections using adaptive biomaterials-based systems are flourishing and generate innumerous possibility to design novel antimicrobial therapeutics. This feature article aims to summarize the recent developments in the formulations, mechanisms, and advances of adaptive materials in bacterial infection diagnosis, contact killing of bacteria, and antimicrobial drug delivery. Also, the challenges and limitations of current antimicrobial treatments based on adaptive materials and their clinical and industrial future prospects are discussed.

Nanocarriers with conjugated antimicrobials to eradicate pathogenic biofilms evaluated in murine in vivo and human ex vivo infection models.

Conventional antimicrobials are becoming increasingly ineffective for treating bacterial infection due to the emergence of multi-drug resistant (MDR) pathogens. In addition, the biofilm-mode-of-growth of infecting bacteria impedes antimicrobial penetration in biofilms. Here, we report on poly(ethylene)glycol-poly(ß-amino esters) (PEG-PAE) micelles with conjugated antimicrobials, that can uniquely penetrate biofilms, target themselves to bacterial cell surfaces once inside the low-pH environment of a biofilm and release conjugated antimicrobials through degradation of their ester-linkage with PAE by bacterial lipases. In vitro, PEG-PAE micelles with conjugated Triclosan (PEG-PAE-Triclosan) yielded no inadvertent leakage of their antimicrobial cargo and better killing of MDR Staphylococcus aureus, Escherichia coli and oral streptococcal biofilms than Triclosan in solution. In mice, PEG-PAE-Triclosan micelles with conjugated Triclosan yielded better eradication efficacy towards a MDR S. aureus-infection compared with Triclosan in solution and Triclosan-loaded micelles at equal Triclosan-equivalent concentrations. Ex vivo exposure of multi-species oral biofilms collected from orthodontic patients to PEG-PAE-Triclosan micelles, demonstrated effective bacterial killing at 30-40 fold lower Triclosan-equivalent concentrations than achieved by Triclosan in solution. Importantly, Streptococcus mutans, the main causative organism of dental caries, was preferentially killed by PEG-PAE-Triclosan micelles. Thus PEG-PAE-Triclosan micelles present a promising addendum to the decreasing armamentarium available to combat infection in diverse sites of the body. STATEMENT OF SIGNIFICANCE: pH-adaptive polymeric micelles with conjugated antimicrobials can efficiently eradicate infectious biofilms from diverse body sites in mice and men. An antimicrobial was conjugated through an ester-linkage to a poly(ethylene glycol) (PEG)/poly(ß-amino ester) block copolymer to create micellar nanocarriers. Stable micelle structures were formed by the hydrophobic poly(ß-amino ester) inner core and a hydrophilic PEG outer shell. Thus formed PEG-PAE-Triclosan micelles do not lose their antimicrobial cargo underway to an infection site through the blood circulation, but penetrate and accumulate in biofilms to release antimicrobials once inside a biofilm through degradation of its ester-linkage by bacterial lipases, to kill biofilm-embedded bacteria at lower antimicrobial concentrations than when applied in solution. PEG-PAE-Triclosan micelles effectively eradicate biofilms of multi-drug-resistant pathogens and oral bacteria, most notably highly cariogenic Streptococcus mutans, in mice and men respectively, and possess excellent clinical translation possibilities.