Microtissue-encapsulating devices for hypoxia reduction of cellular therapeutics in diabetes treatment

• Main Author: Chen, Yang
• Other Authors: Dang Thuy Tram
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering; Bioengineering
• Online Access: https://hdl.handle.net/10356/154404
• Institution: Nanyang Technological University

Transplantation of encapsulated islets devoid of immunosuppressants is a potential approach to revive euglycemia in insulin-dependent diabetic patients. However, poor cellular viability impedes the translation of this approach into a clinical treatment due to low oxygen tension at the transplantation site devoid of vasculature. This thesis aims to resolve this issue by designing islet-like microtissues with non-spherical geometries to investigate the role of microtissue geometry in cellular survival and incorporating optimal microtissues in the microtissue-encapsulating devices to prevent rejection from host immune system. First, islet-like microtissues with varying geometries such as toroid, rod and spheroid were designed and fabricated using micromolded non-adhesive hydrogels where monodispersed rat insulinoma β cells assembled into microtissues. We quantitatively demonstrated that with the same volume, microtissues with toroidal geometry had improved cellular survival than microtissues with rod and spheroid geometries. At an equivalent extent of cellular viability, microtissues with toroidal geometry enabled efficacious packing larger group of cells into individual microtissue than microtissues with rod and spheroid geometry. Furthermore, toroid microtissues retained the typical glucose-dependent insulin-secreting function of rat insulinoma β cells. In addition, macroencapsulated toroid microtissues in alginate hydrogel preserved both geometrical and structural integrity. Macrodevices for cell encapsulation have gained increasing attention due to its ease of retrievability and higher loading capacity of therapeutic cells. Next we developed a novel waffle-inspired hydrogel-based macrodevice that enabled both in situ and ex situ encapsulation of spheroidal microtissues in a homogeneous distribution to minimize microtissue aggregation. We optimized device design parameters to maximize homogeneous distribution of encapsulated microtissues in the device. Furthermore, encapsulated microtissues in a homogeneous distribution preserved high cellular viability and glucose-responsive insulin-secreting function. Lastly, we applied this novel waffle-inspired hydrogel-based macrodevice to in situ encapsulate toroid in a homogeneous distribution and investigated the effect of microtissue geometry and distribution on cellular survival and hypoxia. We optimized microwell side length, peg diameter and number of cells seeded per hydrogel template to facilitate formation of toroid microtissues. Microtissues in toroidal geometry retained geometrical, structural integrity and homogeneous distribution following encapsulation in the macrodevice. Confocal microscopy analysis showed that toroid microtissues encapsulated in the macrodevice had decreased cellular hypoxia compared with spheroid microtissues encapsulated in the macrodevice. In addition, encapsulated toroid microtissues in the macrodevice also maintained glucose-responsive insulin-secreting behavior. Overall, the results of this thesis showed that the adoption of toroidal geometry in the design of therapeutical microtissues probably enhances cell survival of cellular grafts. Furthermore, the development of in situ toroid-encapsulating waffle-inspired hydrogel-based macrodevice may offer a new potential strategy to accelerate the clinical translation of cell-based therapy towards cure for insulin-dependent diabetes.