Bioengineered Wound Healing Skin Models: The Role of Immune Response and Endogenous ECM to Fully Replicate the Dynamic of Scar Tissue Formation In Vitro

Experimental Approaches to Scar Modeling through Mechanical Skin Damage and Chemical Burn in Sprague Dawley Rats

Creating of a scar model in laboratory animals is the most acceptable option for the preclinical search of scar treatment. However, due to high skin regeneration rate in laboratory rodents, creating an optimal animal model of scar formation is a challenge. Here we describe five methods for modeling a scar tissue in rats that we have tested. These methods allowed achieving different histopathological features and different stages of skin scar formation.

Copper-based dressing: Efficacy in a wound infection of ex vivo human skin

This study aimed to evaluate the wound healing and antibacterial effects of two experimental copper dressings compared to a commercial silver dressing. Burn wounds were created in the ex vivo human skin biopsies, then were infected by Staphylococcus aureus. Tissues were treated with copper dressings, silver dressing, or a dressing without any antibacterial component. An infected wound tissue without treatment was considered as the control group. Three days after treatments, tissues were analyzed by bacterial count and histology staining, while their media was used to assess the expression of cytokines and chemokines. Histology staining confirmed the presence of second-degree burn wounds and colonization of bacteria in the surface and superficial layer of tissues. The results demonstrated a higher antibacterial effect, improved epithelium formation, and decreased wound area in one of the copper dressings compared to other dressings. Markers associated with infection control increased in both the copper and silver-treated groups. The cytokine profiling analysis revealed increased expression of markers related to angiogenesis and anti-inflammatory responses and decreased pro-inflammatory cytokine responses in the infected wound treated with one of the copper dressings. Our results confirmed the efficacy of the experimental copper dressing in reducing bacteria and promoting wound healing.

Design and Evaluation of Liposomal Sulforaphane-Loaded Polyvinyl Alcohol/Polyethylene Glycol (PVA/PEG) Hydrogels as a Novel Drug Delivery System for Wound Healing

Hydrogel scaffold has been widely applied as drug delivery systems for treating skin injuries. However, the poor drug loading and rapid drug release of hydrogel restricted their application. In the current study, we present a nanoliposome containing sulforaphane (SF) as a nano-drug delivery system that is encapsulated within the scaffold hydrogel system to overcome these limitations and improve wound healing. The hydrogel substrate consisting of 10% polyvinyl alcohol (PVA)/5% polyethylene glycol 400 (PEG400) was prepared by the freeze-thaw method, and the nanoliposomal system was manufactured by the thin film hydration method at different molar ratios of cholesterol: SPC: DPPC: DSPE-PEG2000. The nanoliposome and hydrogel system was characterized by physicochemical analyses. The findings achieved from the optimization of the sulforaphane-loaded nanoliposome (SFNL) displayed an increase in the molar ratio of SPC, leading to a higher entrapment efficiency and a gradual release profile. Narrow size distribution, optimal electrical charge, and the lack of molecular interactions between SF and nanoliposome components in the FTIR analysis make SFNL a suitable drug delivery system for the wound healing process. The obtained SFNL-encapsulated freeze-thawed hydrogel system has sufficient and specific swelling ability at different pH values and increased mechanical strength and elongation. Additionally, the release pattern of SFNL at different pH values showed that the release of SF from liposomes depends on the pH value of the environment and accelerates in line with decreasing pH values. Encapsulation of nanoliposomal SF in the hydrogel structure provides a sustained release pattern of SF compared to its free form and increased as the pH environments continued to raise. The cytotoxicity and cell uptake of SFNL-loaded hydrogels against human skin fibroblasts (HFF cell line) were investigated. The in vitro analyses displayed that the toxicity properties of SF and SFNL were dose-dependent, and SFNL exhibited lower toxicity compared to free SF. Furthermore, the proper cell compatibility of the prepared hydrogel against the HFF cell line was confirmed by the MTT assay. These findings imply that the hydrogel scaffold loaded with SFNL may have wound-healing potential.

In vitro strategies for mimicking dynamic cell-ECM reciprocity in 3D culture models

The extracellular microenvironment regulates cell decisions through the accurate presentation at the cell surface of a complex array of biochemical and biophysical signals that are mediated by the structure and composition of the extracellular matrix (ECM). On the one hand, the cells actively remodel the ECM, which on the other hand affects cell functions. This cell-ECM dynamic reciprocity is central in regulating and controlling morphogenetic and histogenetic processes. Misregulation within the extracellular space can cause aberrant bidirectional interactions between cells and ECM, resulting in dysfunctional tissues and pathological states. Therefore, tissue engineering approaches, aiming at reproducing organs and tissues in vitro, should realistically recapitulate the native cell-microenvironment crosstalk that is central for the correct functionality of tissue-engineered constructs. In this review, we will describe the most updated bioengineering approaches to recapitulate the native cell microenvironment and reproduce functional tissues and organs in vitro. We have highlighted the limitations of the use of exogenous scaffolds in recapitulating the regulatory/instructive and signal repository role of the native cell microenvironment. By contrast, strategies to reproduce human tissues and organs by inducing cells to synthetize their own ECM acting as a provisional scaffold to control and guide further tissue development and maturation hold the potential to allow the engineering of fully functional histologically competent three-dimensional (3D) tissues.

Chronic Wound Healing Models

In this paper, we review and analyze the commonly available wound healing models reported in the literature and discuss their advantages and issues, considering their relevance and translational potential to humans. Our analysis includes different in vitro and in silico as well as in vivo models and experimental techniques. We further explore the new technologies in the study of wound healing to provide an all encompassing review of the most efficient ways to proceed with wound healing experiments. We revealed that there is not one model of wound healing that is superior and can give translatable results to human research. Rather, there are many different models that have specific uses for studying certain processes or stages of wound healing. Our analysis suggests that when performing an experiment to assess stages of wound healing or different therapies to enhance healing, one must consider not only the species that will be used but also the type of model and how this can best replicate the physiology or pathophysiology in humans.

Full Skin Equivalent Models for Simulation of Burn Wound Healing, Exploring Skin Regeneration and Cytokine Response

Healing of burn injury is a complex process that often leads to the development of functional and aesthetic complications. To study skin regeneration in more detail, organotypic skin models, such as full skin equivalents (FSEs) generated from dermal matrices, can be used. Here, FSEs were generated using de-epidermalized dermis (DED) and collagen matrices MatriDerm^® and Mucomaix^®. Our aim was to validate the MatriDerm- and Mucomaix-based FSEs for the use as in vitro models of wound healing. Therefore, we first characterized the FSEs in terms of skin development and cell proliferation. Proper dermal and epidermal morphogenesis was established in all FSEs and was comparable to ex vivo human skin models. Extension of culture time improved the organization of the epidermal layers and the basement membrane in MatriDerm-based FSE but resulted in rapid degradation of the Mucomaix-based FSE. After applying a standardized burn injury to the models, re-epithelization occurred in the DED- and MatriDerm-based FSEs at 2 weeks after injury, similar to ex vivo human skin. High levels of pro-inflammatory cytokines were present in the culture media of all models, but no significant differences were observed between models. We anticipate that these animal-free in vitro models can facilitate research on skin regeneration and can be used to test therapeutic interventions in a preclinical setting to improve wound healing.