THE DISRUPTION OF UNSTIRRED LAYERS IN VITRO AND ITS IMPACT ON THE DEVELOPMENT AND MAINTENANCE OF 3D SKIN MODELS

Abstract

Full thickness skin models, generated in vitro, are now a common alternative to ex vivo human skin and animal tissue for testing new active compounds. Although skin models mimic the structure and physiology of both the dermis and epidermis, the culture conditions traditionally lack the dynamic fluid flow associated with vasculature in vivo. Additionally, in vitro static culture generates an unstirred water layer at the media-cell interface, which limits nutrient diffusion. In this study, I aimed to disrupt these unstirred layers by culturing Alvetex® Scaffold skin models in a dynamic bioreactor and subsequently investigating how model development and maintenance is affected. The results show that the time in which perfusion is introduced causes stark differences in model development. On the one hand, early perfusion leads to poor maturation of dermal models and a lack of stratification in the epidermal compartment of full thickness models. On the other hand, delayed perfusion leads to a thicker fibroblast surface layer and a thicker viable epidermis, indicating enhanced tissue development. In full thickness models cultured with delayed perfusion, proliferation of keratinocytes increased in the first week of culture, while early/mid differentiation was more prominent in the first 3 weeks. The barrier function of the delayed perfused models, as identified using trans-epidermal water loss (TEWL), did not change during model development and maintenance. A speed of 100 rpm was found to be suitable for skin models and increasing the stirrer speed led to greater shear stress, which negatively impacted cell morphology. Although this study was limited by great variability in models and reliance on qualitative analysis of relevant biomarkers, the importance of delaying perfusion as an optimisable factor for improving skin models was highlighted. Future work can be conducted, using a larger sample size, on identifying the precise time and speed of perfusion that would generate significant improvements in model structure, physiology, and function.