(326a) Biomimitic Hydrogels for Retinal Engineering

Retinal degeneration impacts millions of people and is the leading cause of blindness. Challenges in studying and treating retinal degeneration include: 1. Lack of suitable in vitro models and 2. Lack of therapies to restore lost retinal cells. Retinal organoids have emerged as exciting experimental systems enabling the investigation of retinal development and disease and offering a potential source of retinal cells for transplantation. However, they are limited in reproducibility and robust proper cellular organization (e.g., retinal pigment epithelium presentation adjacent to photoreceptor outer segments). Retinal organoids are traditionally cultured in suspension within Matrigel, a relatively undefined biologically-derived matrix. As spatiotemporal presentation of chemical and mechanical cues are significant in tissue morphogenesis, we have studied the impact of specific extracellular-matrix chemical and physical cues on the development of retinal organoids. In particular, we have explored culturing organoids at an interface between different materials (alginate and PEG-based hydrogel and culture plastic) presenting different cues (e.g., attachment ligands, stiffness), mimicking the directionality of cues presented during development. Optic cup formation and organoid growth were observed in alginate-based gels, even in the absence of the rich chemical cues presented by Matrigel. When cultured within hydrogels of varying stiffness, the evaginations that represent optic cup-like structure formation were limited at higher stiffness levels, as was the overall size of the organoids. Organoids disassembled and spread when cultured adjacent to a hard plastic surface coated with basement membrane proteins.

Cell transplantation has been explored as a promising treatment for retinal degeneration. However, one major limitation to retinal cell transplantation is that the majority (>90%) of transplanted cells do not survive. It is not clear if the cells do not survive due to damage during injection or lack of favorable cues in the bolus injection microenvironment. We have explored the sources of damage to transplanted cells, and have also investigated whether a hydrogel carrier presenting specific chemical and physical cues may 1. Protect retinal cells from damage during transplantation, and 2. Promote retinal cell survival as well as migration and differentiation in the bolus transplantation environment. Alginate-based hydrogels of varying stiffness and chemical composition were explored using a design-of-experiments (DOE) to develop a set of hydrogel formulations. Specifically, the stiffness was controlled using cross-linking with calcium at varying concentration, such that it fell within the range reported for retinal tissue (~1 – 10kPa). Attachment ligands included RGDS peptides mimicking those present in fibronectin and other ECM proteins, as well as laminin and the glycosaminoglycans hyaluronic acid (HA) and chondroitin sulfate (CS). Novel in vitro models of subretinal cell injection and transplantation were developed to test the developed biomaterials. Preliminary data indicate a modest impact of biomaterial properties on cell survival, but a significant effect of chemical cues and stiffness on migration.