Review of biomaterial- and organoid-based bioengineering strategies (injectable ECM-mimetic hydrogels, 3D bioprinting, nerve guidance conduits, and vascularized organoids) to recreate permissive neuroregenerative microenvironments for CNS repair and neural circuit reconstruction.

Relevant to Parkinson's for its focus on improving graft survival, modulating neuroinflammation/oxidative stress, and enabling organoid-based cell-replacement or disease-modeling approaches, but it is a conceptual review with limited actionable molecular targets or immediate therapeutic leads.

Neurological injuries and neurodegenerative disorders, including spinal cord injury, traumatic brain injury, stroke, and Parkinson's disease remain largely incurable. In the central nervous system (CNS), a self-reinforcing cascade of neuroinflammation, oxidative stress, blood-brain barrier breakdown, and glial fibrotic scarring restricts long-distance axonal regrowth and graft survival. The peripheral nervous system (PNS) exhibits greater intrinsic regenerative potential, yet critical-length defects remain challenging and have driven the development of clinically relevant conduit designs. This review provides an overview of the microenvironment following CNS injury and summarizes the key design requirements for engineered repair matrices, while highlighting lessons from advanced peripheral nerve guidance conduits. Injectable extracellular matrix (ECM)-mimetic and smart hydrogels can conformally fill CNS cavities, modulate immune and redox cascades, restore vascular function, and provide permissive niches for neural stem/progenitor and endothelial cells. CNS-compatible bioinks and 3D bioprinting enable the fabrication of neurovascular architectures and multicellular constructs with controlled mechanics, topology, and circuit geometry. Advances in nerve guidance conduits inform translation of PNS principles to the brain and spinal cord. Organoid-based strategies, including vascularized organoids, biomaterial-supported grafts, and organoid-neuroelectronic interfaces, suggest routes toward modular biohybrid constructs. Integrating pathology-informed biomaterials, biofabrication, and organoid engineering offers a roadmap for neural circuit reconstruction.