Organization and differentiation of stem cells on delivery scaffold for retinal tissue engineering

Abstract

Retinal degenerative diseases, including retinitis pigmentosa and age-related macular degeneration, affect more than ten million people in the US. Currently, there is no proven visually beneficial treatment for these types of disease; however, stem cell-based therapy is a recent strategy which has the potential to preserve and restore vision in these conditions. In addition to replacing lost or diseased cells, transplanted cells may be able to rescue dying photoreceptors of the host retina. While studies have shown that retinal progenitor cells (RPCs) delivered by bolus injection can differentiate into retinal specific neurons after subretinal transplantation, they have not been able to maintain morphologic development, lamination, or extensive integration with the host retina. Therefore, a mechanism is needed to confer organization and instructional cues to these grafted cells. In this research, micro and nano-electro-mechanical systems (MEMS/NEMS) processing techniques were used to create biodegradable thin-film scaffolds to guide the differentiation and organization of stem cells for retinal tissue engineering. Through standard MEMS processes, including photolithography and reactive ion etching, a high throughput array of sub-micron features (500 nm to 1 pm) was fabricated into silicon wafers. A novel templating process was developed to then imprint these structures into biodegradable polycaprolactone (PCL) thin films (5 -10 pm) with minimal deformation to the imprinted features. PCL was chosen due to its low melt temperature, adaptability to microfabrication processing, as well as its mechanical and bioresorptive properties. Furthermore, PCL thin films have been shown to be well tolerated long term when transplanted in the subretinal space of mice. RPCs were cultured on PCL thin films, and cell responses to sub-micron topography of varying dimension and geometry were characterized using scanning electron microscopy and immunocytochemistry. Sub-micron features were found to definitively affect cell behavior. For example, while RPCs cultured on post structures demonstrated an early upregulation of differentiation markers, including rhodopsin and recoverin, RPCs cultured on a ridge-groove topography developed substantial elongation and parallel alignment in addition to upregulation. This unique structured PCL thin-film platform therefore provides a means to organize and differentiate RPCs in a controlled manner and offers potential as a clinical treatment for retinal degenerative diseases.