Three-dimensional culture of pancreatic precursor cells in poly(ethylene glycol)-based hydrogels: A tissue engineering approach to type 1 diabetes

Islet cell transplantation restores insulin independence to patients with type 1 diabetes; however, access to this potentially curative therapy is limited by a severe shortage of transplantable cells. Renewable cell sources, including embryonic pancreatic precursors and embryonic stem cells, could provide an unlimited supply of transplantable islets if mechanisms can be elucidated to promote their selective in vitro differentiation into functioning beta cells. The primary objective of this thesis is to identify essential signaling cues to manipulate the behavior of embryonic pancreatic precursor cells encapsulated in three-dimensional PEG-based hydrogels toward the design of a tissue engineered scaffold to alleviate type 1 diabetes. PEG-based hydrogels are ideal candidates for the three-dimensional culture of pancreatic precursor cells due to their biocompatibility, resistance to protein and cell adhesion, and effective immunoisolation of encapsulated cells. Because they are bioinert, PEG hydrogels also provide a blank slate culture platform upon which the exposure and duration of individual signaling cues can be controlled. The ability to manipulate the encapsulating culture environment and provide specific and homogeneous signals to the entire cell population offers the opportunity to promote uniform cell differentiation. Within this context, this thesis first explores the differentiation of singly encapsulated pancreatic precursor cells in unmodified PEG hydrogels to determine this cell population's default pathway of differentiation in the absence of external signaling cues. Select soluble and insoluble cues were then added to the culture platform to enhance viability and direct differentiation of pancreatic precursor cells toward a functional, glucose-responsive beta cell fate. Human embryonic stem cells previously differentiated into a pancreatic precursor-like population were then encapsulated in PEG-based hydrogels to determine if beta cell differentiation could be similarly promoted in this clinically relevant cell population. Finally, PEG hydrogels were modified to promote scaffold vascularization, and thus provide a potential mechanism for efficient oxygen and nutrient diffusion to differentiated beta cells if cell-loaded hydrogel discs were implanted in vivo. This research provides a foundation for the tissue engineering of a transplantable beta cell population using PEG-based hydrogels and renewable cell sources.