Biomaterial Scaffolds for Corneal Regeneration: Combining human stem cells and biomaterials for tissue engineering of the corneal epithelium and stroma

Cornea is the transparent tissue in the front of the eye essential for our vision. Its normal function requires a constant turnover of new epithelial cells to maintain a healthy ocular surface. Limbal stem cell deficiency (LSCD) is a severe type of corneal blindness where the normal healing capacity of the corneal epithelium is destroyed, for example due to burns or chemical trauma. This painful and debilitating condition cannot be treated with conventional transplantation of donor corneal tissue but requires the introduction of new therapeutic cells to regain the function of the cornea. In addition to the corneal epithelium, the underlying stromal layer is often also affected in LSCD, and the simultaneous delivery of regenerative cells for both corneal layers would be beneficial for treatment of these patients.

Human pluripotent stem cells (hPSCs) have the capacity to differentiate with high efficacy to limbal epithelial stem cells (LESCs), that could provide the therapeutic cells to restore the function of the corneal epithelium. To regenerate the corneal stromal layer, human adipose stem cells (hASCs) provide an attractive cell source because of their immunomodulatory and antiangiogenic properties, relative abundance and ease of isolation, and their capacity to differentiate towards corneal keratocytes. However, for realizing their full therapeutic potential, clinically relevant biomaterial scaffolds are needed for the delivery of these two stem cell types to the cornea.

This dissertation explored the production of hydrogel-based scaffolds for hASCs and hPSC-LESCs in a corneal tissue-mimicking organization and studied their applicability for implantation to corneal wounds in an ex vivo cornea organ culture model. First, hyaluronic acid-based hydrogels were evaluated as suitable cell- encapsulation materials for hASCs. With further modification of the hyaluronic acid with dopamine moieties, tissue adhesive hydrogel implants with encapsulated hASCs and a layer of hPSC-LESCs on the surface were successfully fabricated. Lastly, laser- assisted 3D bioprinting with clinically relevant hydrogel bioinks was used to create corneal structures accurately mimicking the properties of both the stroma and the epithelium.

In conclusion, this dissertation describes innovative methods to produce functional tissue-engineered structures for the regeneration of both the epithelium and stromal layers of the cornea. With the aim of treating patients with stem cell- based therapies in the future, the clinical applicability of both the raw materials and the ready-made structures were considered throughout this work.