An Engineered Infected Epidermis Model for In Vitro Study of the Skin’s Pro-Inflammatory Response

Abstract

Wound infection is a major clinical challenge that can significantly delay the healing process, can create pain, and requires prolonged hospital stays. Pre-clinical research to evaluate new drugs normally involves animals. However, ethical concerns, cost, and the challenges associated with interspecies variation remain major obstacles. Tissue engineering enables the development of in vitro human skin models for drug testing. However, existing engineered skin models are representative of healthy human skin and its normal functions. This paper presents a functional infected epidermis model that consists of a multilayer epidermis structure formed at an air-liquid interface on a hydrogel matrix and a three-dimensionally (3D) printed vascular-like network. The function of the engineered epidermis is evaluated by the expression of the terminal differentiation marker, filaggrin, and the barrier function of the epidermis model using the electrical resistance and permeability across the epidermal layer. The results showed that the multilayer structure enhances the electrical resistance by 40% and decreased the drug permeation by 16.9% in the epidermis model compared to the monolayer cell culture on gelatin. We infect the model with Escherichia coli to study the inflammatory response of keratinocytes by measuring the expression level of pro-inflammatory cytokines (interleukin 1 beta and tumor necrosis factor alpha). After 24 h of exposure to Escherichia coli, the level of IL-1β and TNF-α in control samples were 125 ± 78 and 920 ± 187 pg/mL respectively, while in infected samples, they were 1429 ± 101 and 2155.5 ± 279 pg/mL respectively. However, in ciprofloxacin-treated samples the levels of IL-1β and TNF-α without significant difference with respect to the control reached to 246 ± 87 and 1141.5 ± 97 pg/mL respectively. The robust fabrication procedure and functionality of this model suggest that the model has great potential for modeling wound infections and drug testing.

Challenges in exploring and manipulating the human skin microbiome

“…When the epidermis is locally removed, either by punching or thermal injury, these models can reproduce a skin wound environment by making the dermis accessible to bacteria. These models have been widely used to study the infection process by following microbial growth and tissue damage [ 119 – 126 ]. These infection models have mostly been used to identify potential antibacterial treatments.…”

Evolution of Biochip Technology: A Review from Lab-on-a-Chip to Organ-on-a-Chip

“…The skin is considered as the largest organ with several specific functions including regulation of body temperature, prevention of dehydration and acting as the first protection shield to protect other organs against environmental stressors (biological, physical and chemical). For toxicology testing of new compounds, physiologically relevant skin models are of crucial importance for pharmaceutical, chemical and cosmetic industries to identify potential hazards on the skin [128]. In this section, we highlight the current developments on skin-on-a-chip models.…”

“…More recently, a simplified gelatin-based skin-on-a-chip model has been developed by Jahanshahi et al [128] for studying wound infection, skin's pro-inflammatory response and drug screening. In this platform, keratinocytes have been cultured on the microchannels which have been embedded in a gelatin matrix.…”

Evaluation of in vitro human skin models for studying effects of external stressors and stimuli and developing treatment modalities

“…Mechanical breaches in the skin barrier present an opportunity for pathogens to enter the body and impede the wound healing process, as demonstrated in Figure 2. [23] An infected skin model was formed by scratching a reconstructed epidermis to enable the entry of E. coli bacteria into the epidermis (Figure 2A). Wound healing progression of a control model, the infected model, and a model treated with an antibiotic (ciprofloxacin) was monitored at 0 h, 24 h, and 48 h intervals via bright field microscopy (Figure 2B).…”

“…coli colony-forming units (CFU) after 8 and 24 h. Reproduced with permission. [23] Copyright 2020, MPDI ments and therapeutics. [37] In addition, physiologically relevant mechanical forces can be leveraged to improve the biomimicry of in vitro skin models.…”