Targeted Nanotechnology Approaches to Bypass the Blood–brain Barrierin Neurodegenerative Disorders

Neurodegenerative diseases like Alzheimer's disease (AD), Parkinson's disease (PD), Amyotrophic Lateral Sclerosis (ALS), and Huntington's disease (HD) are a growing health burden across the world because of the progressive loss of brain cells and the ineffective nature of the available treatment. One significant challenge in the treatment of these conditions is the Blood- -Brain Barrier (BBB), a highly selective interface that limits the access of most therapeutic molecules to the central nervous system. Nanotechnology has become an attractive approach to addressing this difficulty, as it enables the delivery of drugs with high accuracy and actively engages in the repair of the BBB. This review provides an overall synthesis of focused nanotechnology solutions aimed at both circumventing and restoring BBB function in neurodegenerative illnesses. It discusses various nanoparticle (NP) platforms such as polymeric, lipid-based, micellar, metallic, and carbon-derived systems in the light of their physicochemical aspects, transport across the BBB, and therapeutic efficacy. Particular emphasis is put on the receptor-mediated transcytosis, neurovascular unit modulations, and the regulation of Wnt, Shh, and Tie-2 signalling pathways, which are BBB integrity pathways. The review incorporates mechanisms of BBB repair in combination with neuroprotective nanotherapies, rather than focusing solely on end repair. This review covers the role of targeted nanotechnology in the future of therapeutic approaches for neurodegenerative diseases. By connecting materials science, molecular neuroscience, and clinical innovation, it demonstrates how next-generation brain-targeted therapies can be developed using targeted nanotechnology.