Department of Microbiology & Immunology Seminar: “Building Better Models: In Vitro Tissue Vascularization in Human Skin and Brain”

Title: “Building Better Models: In Vitro Tissue Vascularization in Human Skin and Brain”

Speaker: Kyle Divito, PhD
Associate Professor
Department of Biochemistry and Molecular & Cellular Biology
Georgetown University

Abstract:
Two- and three-dimensional in vitro cell and tissue culture models have made significant strides over the past seventy years. However, advanced tissue models and refinements to current techniques are still necessary in order to better replicate single- and multi-cellular human organ systems. In human skin, traditional 2- and 3-dimensional in vitro models are limited to approximately 200-300 µm in depth, yet human skin can reach 5 mm in depth in certain areas. Increased tissue depth in vitro is constrained due to the limitations of passive diffusion which does not permit growth media to enter and waste products to be removed at tissue depths beyond this limitation. More representative skin models would better approximate the 2-3 mm of average depth of human skin and thus would be integral for future basic science and clinical research.

Expectedly, the human blood-brain barrier (BBB) presents a formidable challenge for in vitro modeling due to limited primary cell line availability and a lack of integrated vasculature. BBB in vitro modeling has traditionally relied on endothelial cells seeded onto transwell plates to replicate the barrier. Yet, these models are limited to one or two cell types and often lack appreciable tight cell junctions observed in vivo. Further, the BBB is intimately connected to the periphery via complex vasculature which cannot be easily modeled using traditional 2D or 3D cell culture.

Challenges regarding tissue depth and a lack of perfusion in both human skin and the BBB would be addressed through vascularization. Tissue engineering, microfluidics and 3-dimensional bioprinting have reached a tipping point making these techniques readily accessible and therefore biomimetic devices, such as organ-on-chip, can enhance pre-clinical models by moving them closer to their intended purpose. Here, microfluidic modeling techniques will be presented as a methodology to create robust human blood vessels capable of being integrated into models such as human skin and the BBB. Future directions for these techniques include a discussion on full thickness skin development; cancer modeling; small molecule analytics for use in biomimetic vasculature. The ability to improve in vitro models will help to address multi-organ interfaces and the complexities of human disease.