Characterization and evaluation of the barrier properties of different skin models as an alternative model for human skin
Although human skin is the best in-vitro research model in skin drug delivery, its availability is limited and there is a large variation between different species and even between individuals. So, in this thesis work rat epidermal keratinocyte organotypic culture (ROC) was developed as an alternative model for human skin. This work included ROC epidermis and ROC full-thickness models with and without collagen. Hence, the ROC epidermis model was investigated for morphology by using light microscopy and its barrier properties by measuring differential scanning calorimetry (DSC), transepidermal water loss (TEWL) and permeation of three different solutes (mannitol, corticosterone and tritiated water) and compared with the human epidermal model. This thesis work also sought to improve the morphology and the barrier properties of the ROC epidermal model to resemble as closely as possible the full-thickness human skin model. The ROC models (epidermis and full–thickness) were different from human skin in the thickness of stratum corneum (SC) and viable epidermis. Moreover, these models were devoid of skin appendages. It was noted that, in the case of the full-thickness model with and without collagen, the epidermal layers separated from the underlying dermis particularly after freezing at -80°C. The permeation of tritiated water through human epidermis and ROC epidermis was nearly the same. Also there is no distinct difference in the permeation of tritiated water through full-thickness human skin and the ROC full-thickness with collagen model. However, the permeation of mannitol and corticosterone through human epidermis was different compared to ROC epidermis. The results of the TEWL measurements showed that the ROC full-thickness model without collagen was slightly higher than ROC epidermis. Furthermore, both of them were higher than other models. There is no distinct difference in TEWL between human skin (epidermis and full-thickness) and ROC full-thickness with collagen. The results of the TEWL measurements and the permeation of tritiated water illustrated that collagen increased the barrier properties of the ROC full-thickness model. These results allow us to conclude that the ROC epidermis and the ROC full-thickness with collagen models are promising alternative models for human skin.