An Overview of Methods for theIn VivoEvaluation of Tissue-Engineered Skin Constructs

Abstract

Cutaneous wounding often leads to contraction and scarring, which may result in a range of functional, cosmetic, and psychological complications. Tissue-engineered skin substitutes are being developed to enhance restoration of the skin and improve the quality of wound healing. The aim of this review is to provide researchers in the field of tissue engineering an overview of the methods that are currently used to clinically evaluate skin wound healing, and methods that are used to evaluate tissue-engineered constructs in animal models. Clinically, the quality of wound healing is assessed by noninvasive subjective scar assessment scales and objective techniques to measure individual scar features. Alternatively, invasive technologies are used. In animal models, most tissue-engineered skin constructs studied are at least evaluated macroscopically and by using conventional histology (hematoxylin-eosin staining). Planimetry and immunohistochemistry are also often applied. An overview of antibodies used is provided. In addition, some studies used methods to assess gene expression levels and mRNA location, transillumination for blood vessel observation, in situ/in vivo imaging, electron microscopy, mechanical strength assessment, and microbiological sampling. A more systematic evaluation of tissue-engineered skin constructs in animal models is recommended to enhance the comparison of different constructs, thereby accelerating the trajectory to application in human patients. This would be further enhanced by the embracement of more clinically relevant objective evaluation methods. In addition, fundamental knowledge on construct-mediated wound healing may be increased by new developments in, for example, gene expression analysis and noninvasive imaging.

Strategies Demonstrating Efficacy in Reducing Wound ContractionIn Vivo

“…4 A representative data set should therefore indicate the original wound size and how this size has decreased over time (Fig. 2).…”

“…Measurements of reepithelialization and restoration of barrier function should be separate from measurements of contraction as measured by contracting wound area. 4 No animal model perfectly replicates the effect that any treatment has on wound contraction in humans. However, important information can be inferred from studies in animal models, and the most commonly used models in this field of research are small rodents, rabbits, and pigs.…”

“…However, important information can be inferred from studies in animal models, and the most commonly used models in this field of research are small rodents, rabbits, and pigs. 4 Mice and rats are loose-skinned animals; thus, their dermis contracts much more readily than that of humans. This results in faster wound closure times, the mechanism being primarily through contraction.…”

“…27 A number of promising treatments utilizing tissue-engineering strategies with biomaterials and cells have been reported in recent years, which have shown a reduction in wound contraction, primarily at early time points. 4 Some of these studies have further reported delayed or reduced appearance of myofibroblasts and collagen deposition more closely resembling uninjured skin. However, the exact mechanisms by which these treatments reduce contraction remain unclear at this time, and it thus remains to be seen to what extent they will reduce contraction and scarring in patients.…”

Recellularizing of human acellular dermal matrices imaged by high‐definition optical coherence tomography

“…used to evaluate the performance of tissue-engineered constructs in animal wound models. 28 Non-invasive, in/ex vivo 2-D optical imaging technologies such as conventional OCT (vertical imaging) and confocal microscopy (horizontal imaging) may be of benefit in the quality assurance of skin constructs. 29,30,11 Recent progress in three-dimensional tissue engineering have simultaneously generated a need for new techniques to visualize and assess tissues in three dimensions.…”