Hydrogels with Sacrificial Nanofibers for Encapsulated Cell Therapies

Encapsulated cell therapies offer a means to implant living devices within patients capable of sensing and responding to their environment to treat disease. In combination with advances in stem cell research and genetic engineering, applications of cell therapy include type 1 diabetes, liver failure, wound healing, Alzheimers, and Parkinsons. Cell encapsulation devices must protect the delivered cells from the host immune system while enabling sufficient transport of nutrients and waste to maintain cell viability and function. However, current hydrogel microencapsulation approaches are difficult to scale into retrievable devices for applications in large animals, and rigid macroencapsulation devices fail due to thick fibrotic capsule formation. A hydrogel macroencapsulation device could leverage the protective and non-immunogenic properties of hydrogels but would require a high surface area device with efficient transport properties to support a therapeutically relevant population of cells. The objective of this thesis is to develop a 3D printable hydrogel material with nanochannels to increase the rate of transport for small molecules across an immunoprotective barrier while also enabling increased flexibility in device design.

First, I developed a novel method to produce sacrificial nanofibers using a self-assembling dipeptide fmoc-diphenylalanine. The pH sensitive self-assembly of Fmoc-diphenylalanine is leveraged to enable carrier free electrospinning of the small molecule into fibers. Removal of the dipeptide from the hydrogel via pH switch and electric field produces nanochannels within the hydrogel. Next, I characterize the effects of nanochannels on the transport of small molecules and oxygen and demonstrate that my approach significantly improves transport properties while still maintaining immunoisolation capability. As a follow up, I then studied the biological significance of the improved transport properties on spheroids encapsulated in hydrogels with nanochannels produced with my method. Lastly, I adapted the electrospun dipeptide nanofibers to be incorporated into 3D printed hydrogel constructs to increase the diversity of possible sizes and geometries of encapsulation device designs.

The approach presented in this thesis allows for the preparation of a dispersion of peptide nanofibers that are stable in polyacrylamide matrices and are easily dissolved and removed. The resulting highly porous hydrogels have significantly improved transport of oxygen and small molecules while still excluding molecules larger than 70kDa suggesting immunoprotective properties. Further, the improved transport properties, in conjunction with light-induced free radical polymerization, is compatible with 3D printing to obtain a wide range of sizes and shapes for the versatility of artificial organ designs.