Optogenetic-enhanced Stem Cell Therapy for Neurodegenerative Diseases: A Closed-loop System Integrating Three-dimensional-bioprinted Neural Grafts and Activity-dependent Synaptic Plasticity

Abstract Background: Synaptic connectivity is compromised in neurodegenerative diseases; yet, current stem cell interventions are unable to control graft–host integration. Methods: We propose a closed-loop approach connecting optogenetics, three-dimensional (3D)-bioprinted neural grafts and activity-dependent plasticity for the dynamic restoration of injured circuits. The device utilises patients’ neurons, derived from induced pluripotent stem cells, that express channelrhodopsin-2. These neurons can be optimised to perform optical stimulation in patterns that replicate natural firing patterns, thereby facilitating functional synaptic re-writing. The addition of astrocyte co-cultures is necessary to produce synaptogenic factors, which can stabilize nascent connections. A fibrin-hyaluronic acid hydrogel matrix is used for structural support during the 3D bioprinting process. The graft design includes microfluidic canals for optic probe arrays as well as for real-time readout in the form of calcium imaging and electrophysiology. In addition, magnetic resonance imaging-guided implantation targets degenerated pathways detected by diffusion tensor imaging (DTI) to guarantee that the implantations are anatomically precise. Theta-burst stimulation paradigms induce long-term potentiation in graft-to-host connections, mediated by spike-timing-dependent plasticity rules. This methodology is unique in that it combines optogenetic control with bio-printed tissue engineering, enabling spatiotemporal control of the synaptic repair process. Results: In experiments, we demonstrate the robust survival of grafts in vitro and their functional connectivity with adaptive closed-loop modulation stimulation parameters, as observed in the activity. Conclusions: The system overcomes key deficiencies of current therapies, including the passive integration of grafts and the lack of controlled synaptic formation, and represents a scalable approach towards personalised treatment for neurodegenerative diseases. Its modular architecture makes it compatible with clinical workflow and could accelerate translation.