BIOE Honors Program Defense: Tolulope Awosika
Thursday, April 18, 2019
A. James Clark Hall, Room 4104
Dr. Kim Stroka
Cellular and Biomaterial Approaches to Vascular Tissue Engineering and Oxygen Delivery
Engineered organs, tissues, and scaffolds are designed for the treatment of lost or diseased tissues by implantation in a host. Their clinical success could reduce the dire need for organ and tissue donors, accelerate wound healing, and improve outcomes for patients. However, the clinical translation of tissue engineered constructs has been limited by their lack of vasculature. Specifically, cells in the interior regions of large avascular scaffolds, eventually, undergo hypoxia-induced cell death since they are more than 200mm, the diffusion limit of oxygen, from the peripheral vessels. Current wisdom holds that a functional scaffold, of clinically relevant size, must be pre-vascularized; that is, it must be designed to contain a pre-existing vascular network that can connect with the host vasculature upon implantation and deliver oxygen to all cells within the scaffold.
Pre-vascularization requires in vitro recapitulation of angiogenesis and, as a result, is driven by interactions between endothelial cells (ECs) and mural cells. Mesenchymal stem cells (MSCs), a popular mural cell source, are known to have dichotomous effects on the angiogenic activity of ECs, being pro-angiogenic in some contexts and anti-angiogenic in others. For pre-vascularization, this dichotomy necessitates the maximization of the pro-angiogenic benefits of MSCs and the minimization of their anti-angiogenic effects. To this end, we describe efforts to optimize MSC-mediated regulation of angiogenesis by varying EC:MSC co-culture ratio in 3D-printed scaffolds and monitoring the resultant angiogenic gene expression over 14 days. We find that the expression of key angiogenic genes is upregulated in the 3:1 EC:MSC ratio relative to others, and, thus, recommend the 3:1 ratio for pre-vascularization designs.
Additionally, we explore the use of perfluorocarbons, organic molecules known to have high oxygen solubility, as an alternative to the pre-vascularization paradigm. Studies have shown that functionalization of chitosan scaffolds with a perfluorocarbon moiety can enhance oxygen solubility and, thus, enhances cell viability within the scaffold relative to non-fluorinated scaffolds. Here, we report the covalent functionalization of gelatin with pentadecafluorooctanoyl chloride and the mixing of this fluorinated gelatin with methacrylated gelatin to produce a polymer blend of fluorinated and photo-crosslinkable gelatin in which cells can be encapsulated.