Hyaluronic acid 3D microenvironments for diabetes treatment

Diabetes mellitus is characterized by hyperglycaemia. The origin of type 1 diabetes mellitus (T1DM) arises from loss of pancreatic β cells in response to an autoimmune reaction. This results in a state of absolute insulin deficiency. The current state of the art research in T1DM involves developing a strategy to protect pancreatic β cells from immune system attack while restoring physiological insulin responsiveness to blood glucose variations for transplantation. This thesis aims to develop a new immunoprotective microenvironment based on hyaluronic acid (HA) for insulin producing cells to treat T1DM. Therefore, biomaterial development is fundamental to the success of creating an immunoprotective microenvironment. This project investigates new routes to chemically modify and crosslink HA. Bis(β-isocyanatoethyl) disulphide (BIED) has been synthesised to crosslink HA of low and high molecular weight (0.1 and 1.2 MDa, respectively) through the formation of urethane bonds. Chemical, physical, mechanical, and biological characterization of the HA hydrogels were performed. Results show that 0.1 MDa gels have higher crosslinking densities and consequently, higher tensile and storage loss moduli. Both high and low molecular weight gels show biocompatibility. Gels maintain cell viability and they do not incite activation of the immune system as observed by low GM-CSF and TNFα cytokine secretion. Moreover, results show that 1.2 MDa gels have increased bacteriostatic activity against Staphylococcus aureus. Subsequently, reduction of the disulphide bond of these hydrogels resulted in new HA derivates bearing thiol groups and pyridine groups. A novel cell encapsulation technique was then developed, utilising the latest cell surface modification methodologies, and conformal multilayer deposition of these HA derivates via a disulphide exchange mechanism in physiological conditions. Pancreatic beta cells from the MIN-6 lineage were encapsulated and displayed normal function with improved immunoprotection in vitro. Female mice from the black 6 (C57BL/6) strain were induced with diabetes by five consecutive low dose streptozotocin (STZ) injections. Following diabetes induction, mice were transplanted with surface engineered MIN-6 and encapsulated MIN-6 cells under the kidney capsule. Due to sex dimorphism and hormonal variances, female mice showed to be more resistant to the inducing effects of STZ, where hyperglycaemia was achieved in 48% of the cohort. Moreover, single-cell encapsulation did not revert hyperglycaemia after transplantation due to the lack of cell-cell interactions Overall, materials research from benchwork to final animal testing showed great potential of HA derivates for cell encapsulation and protection of pancreatic beta cells for T1DM treatment.