Wound infections represent a significant public health concern, often hindering healing and leading to severe complications. Current treatments often rely on antibiotics, but the rise of antibiotic resistance necessitates alternative approaches. This study focuses on developing an injectable wound dressing with biocompatible and antibacterial properties to promote wound healing and reduce antibiotic dependence. The increasing global aging population and escalating healthcare costs exacerbate the burden of healthcare-associated infections, particularly in developing nations. Existing wound dressings frequently lack biocompatibility and fail to adequately stimulate skin regeneration, contributing to further infections. Therefore, the development of hydrogels with moisturizing, biocompatible, and antimicrobial properties is crucial for improving wound healing outcomes. Hydrogels, three-dimensional networks capable of absorbing significant amounts of water, are attractive biomaterials for various biomedical applications. Their high biocompatibility and ability to create a moist healing environment make them ideal for skin wound management, promoting tissue repair and regeneration. While some hydrogels, such as those based on chitosan, possess inherent antibacterial properties, limitations such as limited biodegradability, gel formation challenges, bacterial resistance, and narrow therapeutic windows hinder their widespread clinical use. This research leverages the unique properties of ε-poly-l-lysine (ε-PL), a water-soluble, biocompatible polypeptide with broad-spectrum antibacterial activity, and γ-poly(L-glutamic acid) (γ-PGA), a biocompatible poly-amino acid similar to the extracellular matrix (ECM), to address these limitations. ε-PL's mechanism of action involves disrupting microbial membranes and reducing resistance, while γ-PGA's ECM-like structure supports tissue repair. The combination of these materials offers the potential for a superior wound dressing with enhanced biocompatibility and antimicrobial efficacy.

The literature review section extensively discusses the challenges associated with wound infections and the limitations of current treatment strategies, including the rise of antibiotic resistance. It highlights the advantages of hydrogels as wound dressings, emphasizing their biocompatibility and ability to maintain a moist healing environment. The review also explores existing antimicrobial hydrogels, noting their limitations in terms of biodegradability, gelation properties, bacterial resistance, and therapeutic window. The unique properties of ε-PL and γ-PGA, including their biocompatibility, antimicrobial activity, and tissue-regenerative potential, are thoroughly examined, justifying their selection as the basis for the novel hydrogel developed in this study.

This study involved several key steps: First, ε-PL and γ-PGA were modified with glycidyl methacrylate (GMA) to create ε-PL-GMA and γ-PGA-GMA. The modification introduced methacrylate groups, enabling photopolymerization. Tetrabutylammonium bromide (TBAB) acted as a catalyst during the modification process. The modified polymers were then mixed with the visible light initiator lithium phenyl(2,4,6-trimethylbenzoyl) phosphinate (LAP) and photopolymerized under visible light (405 nm, 60 mW/cm²) to form the hydrogel. Different ratios of γ-PGA-GMA and ε-PL-GMA were used to optimize hydrogel properties. Characterization of the synthesized hydrogels included ¹H-NMR and FT-IR spectroscopy to confirm successful modification and hydrogel formation. Scanning electron microscopy (SEM) was used to visualize the hydrogel morphology. Gelation time and swelling ratio were also determined. Rheological properties were assessed using a rotational rheometer. The in vitro antibacterial activity of the hydrogels was evaluated against Escherichia coli and Staphylococcus aureus using a plate-count method. SEM was employed to visualize the effects of the hydrogels on bacterial morphology. In vitro biocompatibility was assessed using MTT assays and fluorescence microscopy (Calcein-AM/PI staining) with NIH 3T3 cells to determine cytotoxicity and cell viability. Finally, an in vivo study was conducted using a Staphylococcus aureus-infected full-thickness skin defect model in Sprague-Dawley rats. The hydrogels were injected into the wounds, and wound healing was monitored over time by imaging and histological analysis (H&E and Masson's stain). Immunofluorescence staining was used to assess the expression of interleukin-6 (IL-6) and transforming growth factor-beta (TGF-β) in the wound tissues to evaluate the inflammatory response. A control group (untreated wounds) and a group treated with mupirocin ointment were included for comparison.

The study successfully synthesized a novel injectable hydrogel composed of modified ε-PL and γ-PGA via visible light photopolymerization. The resulting hydrogel demonstrated rapid gelation, good biocompatibility, and a wide spectrum of antibacterial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria. In vitro studies showed significant bacterial killing, with kill percentages exceeding 90% for both bacterial species. SEM images revealed morphological changes in bacteria after exposure to the hydrogel, indicative of antimicrobial activity. MTT assays confirmed the hydrogel's biocompatibility, showing no significant cytotoxicity to NIH 3T3 cells. Fluorescence microscopy observations further supported the biocompatibility results, demonstrating normal cell proliferation on the hydrogel. In vivo experiments using a rat model of S. aureus-infected wounds showed that the hydrogel significantly accelerated wound healing. Compared to the untreated control group, the hydrogel-treated group exhibited faster wound closure rates. Histological analysis revealed improved tissue regeneration in the hydrogel-treated wounds. Immunofluorescence staining demonstrated reduced IL-6 expression (an inflammatory marker) and increased TGF-β expression (a marker promoting tissue repair) in the hydrogel-treated group, indicating a reduction in inflammation and enhanced tissue remodeling.

The findings demonstrate the efficacy of the injectable photopolymerized hydrogel in treating infected wounds. The hydrogel's unique combination of biocompatibility and broad-spectrum antimicrobial activity, along with its injectable nature and rapid gelation properties, addresses many limitations of current wound dressings. The accelerated wound healing observed in the in vivo studies confirms the hydrogel's therapeutic potential. The reduced inflammation and enhanced tissue regeneration observed further support its use in promoting efficient wound closure. The results strongly suggest that this hydrogel could serve as a valuable alternative to traditional antibiotic-based treatments for infected wounds, potentially mitigating the problem of antibiotic resistance.

This study successfully developed and characterized a novel injectable, photopolymerized hydrogel with potent antimicrobial and biocompatible properties. The hydrogel's ability to inhibit bacterial infection and promote wound healing in an in vivo model suggests its potential for clinical translation as a safe and effective treatment for infected skin wounds. Future research could focus on optimizing the hydrogel composition for improved performance and exploring its potential in treating other types of wounds and infections. Investigating the long-term effects and potential for large-scale production are also important next steps.

While the study demonstrated promising results, some limitations exist. The in vivo study used a rat model, and the findings may not directly translate to human subjects. Further studies in larger animal models and ultimately clinical trials are needed to confirm the hydrogel's efficacy and safety in humans. The long-term biodegradability and potential for adverse effects after prolonged exposure need further investigation. A more comprehensive investigation of the hydrogel's mechanism of action at the molecular level would also be beneficial.