Graphene-polymer nanofibers enable optically induced electrical maturation in stem cell-derived cardiomyocytes and brain organoids

Pluripotent stem cell (PSC)-derived electrically excitable cells provide a unique window into human disease and development, but they remain electrically immature compared to their in vivo counterparts, partially due to the lack of chronic stimulation. New classes of on-demand, electrically active biomaterials are being employed to enhance cell functions, and here, we fabricated biocompatible, electrospun polymer nanofibers containing light-reactive reduced graphene oxide (rGO). Fiber size, stiffness, and electrical conductivity scaled with rGO concentration which in turn produced conduction-dependent effects in PSC-derived cardiomyocytes and neurons; with acute light stimulation on scaffolds containing rGO, cardiomyocytes exhibited more calcium handling activity and were more synchronous, and neurons showed more peaks with higher frequency. Chronic repetitive, daily light stimulation of nanofibers integrated into mature brain organoids caused organoids to become increasingly more electrically responsive to stimulation over time, mature synapses of excitable neurons, and activate photoreceptor lineage pathways. This work outlines a tunable method where the electrical function of electrically excitable, PSC-derived cells can be titrated with rGO fibers and light stimulation, and it suggests that repetitive light stimulation may provide a novel method for retinal cell differentiation in organoids.