Functionalized chitosan based antibacterial hydrogel sealant for simultaneous infection eradication and tissue closure in ocular injuries

Management of infections at ocular injury often requires prolonged and high dose of antibiotic, which is associated with challenges of antibiotic resistance and bacterial biofilm formation. Tissue glues are commonly used for repairing ocular tissue defects and tissue regeneration, but they are ineffective in curing infection. There is a critical need for antibacterial ocular bio-adhesives capable of both curing infection and aiding wound closure. Herein, we present the development of an imine crosslinked N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC)‑silver chloride nanocomposites (QAm1-Agx) and poly-dextran aldehyde (PDA) based bactericidal sealant (BacSeal). BacSeal exhibited potent bactericidal activity against a broad spectrum of bacteria including their planktonic and stationary phase within a short duration of 4 h. BacSeal effectively reduced biofilm-embedded MRSA and Pseudomonas aeruginosa by ∼99.99 %. In ex-vivo human cornea infection model, BacSeal displayed ∼99 % reduction of ocular infection. Furthermore, the hydrogel exhibited excellent sealing properties by maintaining ocular pressure up to 75 mm-Hg when applied to human corneal trauma. Cytotoxicity assessment and hydrogel-treated human cornea with a retained tissue structure, indicate its non-toxic nature. Collectively, BacSeal represents a promising candidate for the development of an ocular sealant that can effectively mitigate infections and may assist in tissue regeneration by sealing ocular wounds.

Bacterial Nosocomial Infections: Multidrug Resistance as a Trigger for the Development of Novel Antimicrobials

Nosocomial bacterial infections are associated with high morbidity and mortality, posing a huge burden to healthcare systems worldwide. The ongoing COVID-19 pandemic, with the raised hospitalization of patients and the increased use of antimicrobial agents, boosted the emergence of difficult-to-treat multidrug-resistant (MDR) bacteria in hospital settings. Therefore, current available antibiotic treatments often have limited or no efficacy against nosocomial bacterial infections, and novel therapeutic approaches need to be considered. In this review, we analyze current antibacterial alternatives under investigation, focusing on metal-based complexes, antimicrobial peptides, and antisense antimicrobial therapeutics. The association of new compounds with older, commercially available antibiotics and the repurposing of existing drugs are also revised in this work.

Discovery of metal-based complexes as promising antimicrobial agents

The antimicrobial resistance (AMR) is an intractable problem for the world. Metal ions are essential for the cell process and biological function in microorganisms. Many metal-based complexes with the potential for releasing ions are more likely to be absorbed for their higher lipid solubility. Hence, this review highlights the clinical potential of organometallic compounds for the treatment of infections caused by bacteria or fungi in recent five years. The common scaffolds, including antimicrobial peptides, N-heterocyclic carbenes, Schiff bases, photosensitive-grand-cycle skeleton structures, aliphatic amines-based ligands, and special metal-based complexes are summarized here. We also discuss their therapeutic targets and the risks that should be paid attention to in the future studies, aiming to provide information for researchers on metal-based complexes as antimicrobial agents and inspire the design and synthesis of new antimicrobial drugs.

Copper(ii) complexes of N-propargyl cyclam ligands reveal a range of coordination modes and colours, and unexpected reactivity

The coordination chemistry of N-functionalised cyclam ligands has a rich history, yet cyclam derivatives with pendant alkynes are largely unexplored. This is despite the significant potential and burgeoning application of N-propargyl cyclams and related compounds in the creation of diversely functionalised cyclam derivatives via copper-catalysed azide-alkyne 'click' reactions. Herein we describe single crystal X-ray diffraction and spectroscopic investigations of the coordination chemistry of copper(ii) complexes of cyclam derivatives with between 1 and 4 pendant alkynes. The crystal structures of these copper complexes unexpectedly reveal a range of coordination modes, and the surprising occurrence of five unique complexes within a single recrystallisation of the tetra-N-propargyl cyclam ligand. One of these species exhibits weak intramolecular copper-alkyne coordination, and another is formed by a surprising intramolecular copper-mediated hydroalkoxylation reaction with the solvent methanol, transforming one of the pendant alkynes to an enol ether. Multiple functionalisation of the tetra-N-propargyl ligand is demonstrated via a 'tetra-click' reaction with benzyl azide, and the copper-binding behaviour of the resulting tetra-triazole ligand is characterised spectroscopically.

Carbon dots-releasing hydrogels with antibacterial activity, high biocompatibility, and fluorescence performance as candidate materials for wound healing

Antibacterial hydrogels have received attention for preventing infections and for their biomedical applications. However, traditional antibiotics-containing and metal nanoparticle-containing hydrogels often cause bacterial resistance, exhibit low biocompatibility, and lack real-time monitoring capability. Here, a fluorescent antibacterial hydrogel with antibacterial ability, excellent optical performance, and high biocompatibility was developed based on cationic carbon dots (CDs), pectin, and acrylic acid triggered construction of the hydrogel network by cross-linker. The antibacterial high-cationic CDs (+51.20 mV) were synthesized by a simple hydrothermal method and released from hydrogel in response to broken hydrogen bonds due to a change in the ambient environment caused by the growing bacteria. The hydrogel showed long-term potent broad-spectrum antibacterial ability (even drug-resistant bacteria) due to the bacterial membrane seriously damaged by the released CDs. The inhibitory capability of this hydrogel was 108.5-fold higher than the other hydrogel. After implantation or incubation with cells, no obvious cytotoxicity or tissue toxicity was observed for the antibacterial hydrogel. This hydrogel enhanced both the application of CDs in vivo and the biosafety of hydrogel. Furthermore, the multicolor fluorescence emission produced by CD provides a potential idea for the development of dual-function hydrogels with in situ monitoring and prevention of bacterial infections to treat wounds.