Modelling the human brain <i>in vitro</i> : biofabrication approaches for neural tissue engineering

The growing demand for physiologically relevant human brain models has driven the development of advanced three-dimensional (3D) systems that can recapitulate key aspects of neural architecture and function. Traditional two-dimensional cultures and animal models fall short in reproducing the structural complexity, cellular diversity, and species-specific characteristics of the human central nervous system. In this review, we provide a comprehensive overview of state-of-the-art scaffold-free and scaffold-based strategies for generating 3D human brain models, with particular emphasis on those derived from pluripotent stem cells. Scaffold-free systems-such as spheroids, organoids, and assembloids-exploit the intrinsic self-organizing capacity of neural cells to recreate spatially and temporally regulated interactions observed during development. Conversely, scaffold-based models utilize biomaterials, including hydrogels and decellularized matrices, to replicate the physical and biochemical properties of the brain microenvironment, providing enhanced control over tissue architecture and reproducibility. A wide range of fabrication methods is discussed, and for each, we assess key features, strengths, and limitations, with particular attention to scalability, reproducibility, and biological relevance. Overall, this review is intended to serve as a practical and well-structured reference for researchers seeking to select or develop the most appropriate<i>in vitro</i>3D brain model for specific applications in neural development and disease modelling.