Pancreatic organ transplant availability and compatibility with patients is a major medical issue facing diabetic patients. One emerging method to combat the scarcity of donor pancreases is to bioengineer a pancreas from human pluripotent stem cells. In order to develop an effective bioprinted pancreas, vascular channels must be formed that can facilitate the transportation of oxygen and nutrients throughout the tissue construct. Vascular constructs encounter the challenge of maximizing structural integrity of a hollow channel while also maintaining differentiated islet cell viability and adhesion to 3D printed tissue. A multimaterial 3D bioprinting approach using Pluronic F127 as a sacrificial bioink within a scaffold supportive of islets was designed. Previous research from the lab has generated islet organoids in various alginate scaffolds, by encapsulating hPSCs in alginate. Alginate is favorable for pancreatic islet lineage differentiation, but alone lacks the structural stability needed for bioprinting. In order to meet this requirement,different combinations of gelatin, alginate, and methylcellulose bioinks were tested. Alginate-methylcellulose performed well as a monolayer structure and supported islet culture and differentiation, but could not act as the support for a multilayer construct. To address this issue, methyl-acrylated modified alginate (AlgMA), was chosen as an outer construct because of its biocompatibility and its potential to be UV crosslinked in a layer by layer formation. This allowed for an improvement in structure resolution without significantly affecting viability and functionality of the cells within the printed construct.
AlgMA was synthesized following the protocol outlined by Loessnar, et al. The reaction mixture was dialyzed for 6 days in the dark at 4°C and freeze-dried for one week. A gcode developed for sacrificial blood vessel bioprinting2 was modified using Cellink Heartware software to accommodate the Cellink BioX printer specifications and sizing desired to simulate a pancreatic environment.. 40% w/v Pluronic F127 was printed at 60 kPa and 10mm/s as a solid gel structure at 25 °C. Our results show that 40% w/v Pluronic F127 can successfully function as a printed sacrificial layer, which can be removed from a printed support structure at 4 °C by being dissolved within 3-5 minutes.. Future work will focus on optimizing the AlgMA bioink through ink concentration and photo-crosslinking parameters, for it to successfully serve as a support layer. In addition, the sacrificial 40% w/v Pluronic F127 bioink will be printed with the addition of pancreatic islets, to simulate a more closely aligned pancreatic environment.
