Microfluidic-Based Technologies for Crossing the Blood-Brain Barrier Against Alzheimer's Disease: Novel Strategies and Challenges.

Alzheimer's disease (AD) represents the major cause of dementia worldwide, involving different etiopathogenetic mechanisms, but with no definitive cure. The efficacy of new AD drugs is limited by the multifactorial disease nature that involves several targets, but also by the difficult penetration across the blood-brain barrier (BBB) for reaching the target area at therapeutic doses. Thus, the inability of many compounds to efficiently bypass the BBB makes it arduous to treat the disease. Furthermore, the lack of more representative BBB in vitro models than conventional 2D cultures, and xenogeneic animal models that recapitulate AD pathogenesis, makes it even more difficult to develop definitive cures. In this context, microfluidics has emerged as a promising tool, offering advanced strategies for simulating the BBB, investigating its crossing mechanisms, and developing nanocarriers that successfully pass the BBB for brain-targeting, with particular interest in pathological states. The advantages of microfluidic platforms for studying the BBB role in pathophysiological conditions might herald more tailored and effective approaches based on functionalized nanosystems for treating AD. Here, we provide an overview of the latest advances in microfluidic-based technologies both for the synthesis of nanodrug delivery systems, and for developing advanced models of the BBB-on-a-chip to simulate this biological barrier, facing open challenges in AD, and improving our understanding of the disease.