An overview of methods for the in vivo evaluation of tissue-engineered skin constructs

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.