Two-photon polymerization for production of human iPSC-derived retinal cell grafts

Recent advances in induced pluripotent stem cell (iPSC) technology have paved the way for the production of patient-specific neurons that are ideal for autologous cell replacement for treatment of neurodegenerative diseases. In the case of retinal degeneration and associated photoreceptor cell therapy, polymer scaffolds are critical for cellular survival and integration; however, prior attempts to materialize this concept have been unsuccessful in part due to the materials' inability to guide cell alignment. In this work, we used two-photon polymerization to create 180μm wide non-degradable prototype photoreceptor scaffolds with varying pore sizes, slicing distances, hatching distances and hatching types. Hatching distance and hatching type were significant factors for the error of vertical pore diameter, while slicing distance and hatching type most affected the integrity and geometry of horizontal pores. We optimized printing parameters in terms of structural integrity and printing time in order to create 1mm wide scaffolds for cell loading studies. We fabricated these larger structures directly on a porous membrane with 3µm diameter pores and seeded them with human iPSC-derived retinal progenitor cells. After two days in culture, cells nested in and extended neuronal processes parallel to the vertical pores of the scaffolds, with maximum cell loading occurring in 25μm diameter pores. These results highlight the feasibility of using this technique as part of an autologous stem cell strategy for restoring vision to patients affected with retinal degenerative diseases.

Cell replacement therapy is an important goal for investigators aiming to restore neural function to those suffering from neurodegenerative disease. Cell delivery scaffolds are frequently necessary for the success of such treatments, but traditional biomaterials often fail to facilitate the neuronal orientation and close packing needed to recapitulate the in vivo environment. Here, we use two-photon polymerization to create prototype cell scaffolds with densely packed vertical pores for photoreceptor cell loading and small, interconnected horizontal pores for nutrient diffusion. This study offers a thorough characterization of how two-photon polymerization parameters affect final structural outcomes and printing time. Our findings demonstrate the feasibility of using two-photon polymerization to create scaffolds that can align neuronal cells in 3D and are large enough to be used for transplantation. In future work, these scaffolds could comprise biodegradable materials with tunable microstructure, elastic modulus and degradation time; a significant step towards a promising treatment option for those suffering from late-stage neurodegeneration, including retinal degenerative blindness.