(7as) Engineering Vascularized Organ-on-Chip Systems to Advance Biological Understanding and Therapeutic Intervention in Human Cancer and Blood Stem Cell Biology

Traditional cell culture based on flat tissue dishes over the last few decades has greatly enhanced our understanding of cellular behaviors in 2D microenvironment. However, these models lack several characteristics of human tissue in 3D, making it challenging to fully recapitulate how cells interact and function in vivo. Organ-on-a-chip models are fantastic platforms that provide additional and controllable parameters (fluid flow, biochemical and mechanical cues) and 3D microenvironment to place cells in a closely resembling native tissue. In a way similar to the human vasculature, organ-on-chip model employs a network of microfluidic channels to establish a ‘circulatory system’ to deliver nutrients, and gases to the cells within the culture. As we strive to better mimic cellular functions in human tissues, these artificial microfluidic networks fail to recapitulate the blood vessels in the human circulatory system largely because the endothelial cells lining the blood vessels function more than just a fluid-carrying conduits. Depending on the organs where the endothelial cells reside, they are also specialized to provide pro-survival, regenerative, and homeostatic cues to the surrounding cells within the tissues. Hence, it is crucial to incorporate organ-specific endothelial cell network in 3D model systems. To fill in the gaps, my graduate and postdoctoral work have offered an approach to engineer vascularized organ-on-a-chip systems to advance our understanding of cellular behaviors in vascularized 3D models in both physiological (angiogenesis, hematopoietic stem cells) and pathological (cancer metastasis, and immune cells) contexts.

Research experience:

My graduate research focused on engineering a biomimetic vessel. During this work, I employed lithography to fabricate a microfluidic platform where the endothelial cell channels were suspended within a 3D extracellular matrix. These endothelial cell channels serve as rudimentary blood vessels and possess properties of in vivo blood vessels. For example, they are surrounded by a thin layer of basement membrane protein and carry fluid flow. Using these rudimentary blood vessels, I further demonstrated that a gradient of chemoattractants could be incorporated into the system to trigger the endothelial cells to migrate and form new blood vessels, a process that is called angiogenesis, which often occurs during wound healing or in tumor progression. Using high resolution confocal microscopy, and imaging processing, I further characterized these newly sprouting vessels and showed that they remarkably displayed many features of in vivo angiogenesis. This biomimetic vessel on a chip also enabled me to perform screening for biochemical factors to identify molecular pathways that influence the morphogenetic processes of collective endothelial cell migration in 3D environment. On the other hand, not only endothelial cells can be seeded into the channel, various other cell types could also be seeded. For example, to model cancer cells and endothelial cell interactions, I successfully seeded pancreatic cancer cells isolated from a genetically engineered mouse pancreatic cancer model into the channel to mimic a malignant pancreatic duct. I discovered that these pancreatic ductal cancer cells invaded into the interstitial matrix towards the blood vessel. Not only did the pancreatic cancer cells invade onto the vessel, they ultimately displaced and replaced the endothelium in the blood vessel, a phenomenon that was similarly reported in human pancreatic cancer patients. Moreover, using molecular biology and genetic approaches (CRISPR/Cas9), I was able to identify the molecular signaling that was involved in vascular invasion of pancreatic ductal adenocarcinoma.

As I experienced the indispensable role of the vascular network in constructing 3D organotypic models during my graduate work, my goal in postdoctoral training is to seek to extend and develop a perfusable vascularized tissue on a chip to allow coculture of the endothelial cells with other cells from different organs such as hematopoietic cells from the bone marrow or hepatocytes from the liver. I am currently being mentored by world-renown scientists: Dr. Shahin Rafii in the field of genetics, vascular biology, hematopoietic stem cells, and Dr. Robert Schwartz in the field of liver and virology. This unique postdoctoral training opportunity has given me a chance to acquire a depth of knowledge in vascular biology, hematopoietic stem cell and organ regeneration in the liver. I am also acquiring additional knowledge and skill sets in RNA sequencing and induced pluripotent stem cells.

Future directions:

The endeavors in my graduate and postgraduate trainings enabled me to travel between different fields and provided me with unique approaches and perspectives to apply in biomedical engineering research. As an independent researcher with the strengths drawn from an engineering perspective during my PhD years and from a molecular biology perspective during my postdoctoral training, my laboratory will seek to reconstitute 3D vascularized mini-organ on a chip to understand human biology in both physiological and pathological contexts. Specifically, we will focus on the three following key areas:

1) Pathological angiogenesis during tumor progression. This work will initially focus on pancreatic cancer but can be extended to other angiogenic tumors such as glioblastoma or hepatocellular adenocarcinoma. We seek to elucidate the molecular mechanisms of tumor-induced angiogenesis. The ultimate goal is to identify new therapeutic targets for tumor angiogenesis as the current angiogenic therapeutics often fail due to an incomplete understanding of tumor angiogenesis.

2) Tumor-endothelial cell communications in tumor-on-a-chip: we are constructing a tumor microenvironment that entails tumor cells and vascular network. We will seek to elucidate the cross-talks between the blood vessel and tumor cells during metastasis.

3) Reconstructing a bone-marrow on a chip: This work will focus on reconstructing a vascularized tissue to coculture endothelial cell network with hematopoietic stem cells (HSCs) and understand the role of endothelial cells in maintenance and expansion of HSCs. Additional work on utilizing differentiated endothelial cells from induced human pluripotent stem cells from patients will also be included to address potential defects in maintaining stemness in hematopoietic stem cells due to genetic defects in endothelial cells.

The exciting proposed research directions above will ensure my lab contribution to the understanding of cellular interactions in human organ on a chip. Given the utility of interconnecting different microfluidic entities, I envision my lab will have an immense potential to address very exciting questions to unravel the cellular communications between different organ-on-a-chip platforms (e.g.: bone-marrow on a chip and tumor on a chip) that, thus far, have remained elusive.

Teaching Interests:

I am interested in teaching courses in the chemical engineering core curriculum such as kinetics and mass transport. With a unique background intertwined between engineering and biology, I am also particularly interested and well-prepared in teaching courses spanning the scopes of two such areas, for example, courses in tissue engineering, biotechnology, and bioengineering.

Successful Proposals:

NIH T32 Interdisciplinary Cardiovascular Training Grant

NSF Graduate Fellowship (Honorable Mentioned)