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Wound cleansing agents are routine in wound care and preoperative preparation. Antiseptic activity intends to prevent contaminating microbes from establishing an infection while also raising concerns of cytotoxicity and delayed wound healing. We evaluated the cytotoxicity of five clinically used wound cleaning agents (saline, povidone iodine, Dove® and Dial® soaps, and chlorhexidine gluconate [CHG]) using both an ex vivo and in vivo human skin xenograft mouse model, in contrast to classical in vitro models that lack the structural and compositional heterogeneity of human skin. We further established an ex vivo wound contamination model inoculated with ~100 cells of Pseudomonas aeruginosa or Staphylococcus aureus to evaluate antimicrobial efficacy. Scanning electron microscopy and confocal microscopy were used to evaluate phenotypic and spatial characteristics of bacterial cells in wound tissue. CHG significantly reduced metabolic activity of the skin explants, while all treatments except saline affected local cellular viability. CHG cytotoxicity persisted and progressed over 14 days, impairing wound healing in vivo. Within the contamination model, CHG treatment resulted in a significant reduction of P. aeruginosa wound surface counts at 24 h post‐treatment. However, this effect was transient and serial application of CHG had no effect on both P. aeruginosa or S. aureus microbial growth. Microscopy revealed that viable cells of P. aeruginosa reside deep within wound tissue post‐CHG application, likely serving as a reservoir to re‐populate the tissue to a high bioburden. We reveal concerning cytotoxicity and limited antimicrobial activity of CHG in human skin using clinically relevant models, with the ability to resolve spatial localization and temporal dynamics of tissue viability and microbial growth. [ABSTRACT FROM AUTHOR]

Translation of wound healing research is limited by the lack of an appropriate animal model, due to the anatomic and wound healing differences in animals and humans. Here, we characterize healing of grafted, full‐thickness human skin in an in vivo model of wound healing. Full‐thickness human skin, obtained from reconstructive operations, was grafted onto the dorsal flank of NOD.Cg‐KitW41JTyr + PrkdcscidIl2rgtm1Wjl/ThomJ mice. The xenografts were harvested 1 to 12 weeks after grafting, and histologic analyses were completed for viability, neovascularization, and hypoxia. Visual inspection of the xenograft shows drying and sloughing of the epidermis starting at week four. By week 12, the xenograft appears healed but has lost 63.05 ± 0.24% of the initial graft size. There is histologic evidence of epidermolysis as early as 2 weeks, which progresses until week 4, when new epidermis appears from the wound edges. Epidermal regeneration is complete by week 12, although the epidermis appears hypertrophied. An initial increase of infiltrating immune mouse cells into the xenograft normalizes to baseline 6 months after grafting. Neovascularization, as evidenced by positive staining for the proteins human CD31 and alpha smooth muscle actin, is present as early as 2 weeks after grafting at the interface between the xenograft and the mouse tissue. CD31 and alpha smooth muscle actin staining increased throughout the xenograft over the 12 weeks, leading to greater viability of the tissue. Likewise, there is increased Hypoxia Inducible Factor 1‐alpha expression at the interface of viable and nonviable tissue, which suggest a hypoxia‐driven process causing early graft loss. These findings illustrate human skin wound healing in an ischemic environment, providing a timeline for use of full thickness human skin after grafting in a murine model to study mechanisms underlying human skin wound healing. [ABSTRACT FROM AUTHOR]

BACKGROUND: No objective technique exists to distinguish necrotic from viable tissue, risking over-excision in burns and loss of wound healing potential. Second window indocyanine green (SWIG) is a novel fluorescence-imaging modality being studied to identify residual solid tumors during oncological surgery. SWIG has also been shown to have avidity for necrosis in animal models, but translation of these findings to humans is lacking. The objective of this study was to evaluate SWIG in the identification of burn wound necrosis and compare it with previously published indocyanine green angiography (ICGA) techniques. STUDY DESIGN: This study used mouse, human skin xenograft and human patient burn models. Brightfield and SWIG near-infrared imaging were performed on macroscopic tissue samples, which were then cryopreserved, sectioned, and analyzed for microscopic fluorescence. SWIG fluorescence findings were correlated to visual assessment of the burn wound as well as histological markers of necrosis using hematoxylin and eosin and lactate dehydrogenase stains. RESULTS: We found that SWIG identified burn necrosis in a manner dependent on the dose and timing of indocyanine green (ICG) administration and had an inverse fluorescence signal compared with ICGA. Furthermore, SWIG fluorescence identified the interface of viable and nonviable tissue. CONCLUSION: Our study confirmed that ICGA is an inconsistent and nonstandardized modality to evaluate burn injuries. In contrast, SWIG imaging is a potential imaging modality to objectively prognosticate burn wound healing potential and guide intraoperative burn excision. Further studies are needed to define ratios of fluorescence intensity values to guide surgical decision-making in burn excision and to better define how ICG is retained in necrotic tissue to enhance utility of SWIG in other disease processes. [ABSTRACT FROM AUTHOR]