Cell mediated remodeling of engineered microvasculature
Calderon, Gisele Amanda
Miller, Jordan S
Doctor of Philosophy
Tissue engineering as a field aims to model and replicate human tissues and organs as substitutes for restoring or improving organ functionality or for studying tightly controlled niches in drug discovery, cancer therapeutics, or fundamental biology. We are in great need of engineered tissues to address the scant availability of organ donors compatible with recipient patients. Further, animal studies are not predictive of human physiology, so there is a tremendous need to quantitatively investigate human cells for drug screening and other therapeutics in a clinically relevant manner. However, current clinical successes have been limited to avascular and simple tissues such as the cornea or bladder. In order to engineer more complex tissue equivalents, we must incorporate essential blood supply or vasculature to provide long-term viability for clinical implantation or for modeled drug screening. Towards engineering more complex, solid organs, bioengineers must identify methods of achieving effective vasculature to permeate the high volume of cells while not compromising the organ’s function. We believe that in order to build solid and complex tissues, we are to include hierarchical vasculature that varies in dimension (ranging from centimeters to micrometers in diameter) to most effectively transport blood and nutrients and remove waste products. Some research groups have historically taken a bottom-up approach to create de novo capillaries by stimulating vascular endothelial cells and support cells to form a provisional capillary plexus in extracellular matrix (ECM) or ECM-like materials. By allowing cells to dictate the vascular organization, we can ensure physiologic relevance, but the technique is currently limited to forming only the smallest vessels found in humans. Further, capillary formation in this bottom-up approach is a slow process that may limit the scope of complexity that can be achieved with organ engineering. Other research groups have also developed top-down, 3D printing (3DP) techniques to control the creation of larger diameter vessels with precise control over every x, y, and z position. With 3DP, open channel geometries can be incorporated into engineered tissues with a high level of control and speed. However, tissue engineers might not design the most optimized architectures and are constrained by the physical limitations of soft material engineering, such as the spatial resolution of the printer and an inability to reach the smallest scale of vessels. Few groups have been able to engineer tissues with vasculature that spans from micro- to macro- scale dimensions, which we identify as a critical step toward the actualization of a multiscale cellularized tissue. Therefore, we propose a combined bottom-up and top-down system that mimics the hierarchy of vasculature within tissues to overcome existing strategies that are limited to either small-scale microvessels or macro-scale physically patterned vessels. We expect this approach may have the capacity to create tissues which could allow rapid anastomosis to an existing vasculature in vivo. We propose to couple cell-based self-assembled capillaries with 3D printed channels to generate a multiscale vascular network which can more adequately approximate living human tissue structure. First, we will assess co-culture pre-vascularization strategies that promote vasculogenesis in our assembled capillaries. Next, we will utilize advanced soft material 3D printing and assess cellular activity in these engineered networks. Finally, we will apply our vascularized networks to therapeutic applications. This setup will allow us to study fundamental questions in vascular biology such as cellular remodeling in response to endothelial cells’ sensed shear stress from convective transport and cell-mediated, angiogenic sprouting and vasculogenic tube formation. We expect that our combined vascular engineering strategy will promote the fluidic union of vascular networks fabricated across multiple length scales. We believe this work will allow researchers to incorporate multi-scale vasculature in vitro for tissue engineered constructs for regenerative medicine or disease modeling applications, and may facilitate the investigation of cellular mechanisms of vascular homeostasis and vascular remodeling in both normal and pathologic settings.
vasculature; endothelial cells; vasculogenesis; 3D printing