Brain-on-a-chip (BoC) concepts should consider three-dimensional (3D) scaffolds to mimic the 3D nature of the human brain not accessible by conventional planar cell culturing. Furthermore, the essential key to adequately address drug development for human pathophysiological diseases of the nervous system, such as Parkinson’s or Alzheimer’s, is to employ human induced pluripotent stem cell (iPSC)-derived neurons instead of neurons from animal models. To address both issues, we present electrophysiologically mature human iPSC-derived neurons cultured in BoC applicable microscaffolds prepared by direct laser writing. 3D nanoprinted tailor-made elevated cavities interconnected by freestanding microchannels were used to create defined neuronal networksas a proof of conceptwith two-dimensional topology. The neuronal outgrowth in these nonplanar structures was investigated, among others, in terms of neurite length, size of continuous networks, and branching behavior using z-stacks prepared by confocal microscopy and cross-sectional scanning electron microscopy images prepared by focused ion beam milling. Functionality of the human iPSC-derived neurons was demonstrated with patch clamp measurements in both current- and voltage-clamp mode. Action potentials and spontaneous excitatory postsynaptic currentsfundamental prerequisites for proper network signalingprove full integrity of these artificial neuronal networks. Considering the network formation occurring within only a few days and the versatile nature of direct laser writing to create even more complex scaffolds for 3D network topologies, we believe that our study offers additional approaches in human disease research to mimic the complex interconnectivity of the human brain in BoC studies.

cone. [7,8] Topological cues such as stiffness, [4] hydrophobicity, [9] and modulation of the surrounding surface, for example, through variations in roughness [10,11] or through guiding barriers [12][13][14] and channels, [15][16][17][18][19][20] have also been found to be effective methods to direct the neurite outgrowth on artificial substrates.A significant drawback of classical 2D neuronal in vitro cultures is their inability to sufficiently mimic the distinct 3D connections in a nervous system. [21] Most of the standard lithography techniques are only available in 2D or 2.5D. [22] However, recent advances in micro-and nanoscale fabrication, especially direct laser writing by two-photon polymerization (2PP-DLW), now enable the construction of complex resist-based 3D substrates with feature sizes down to ≈150 nm. [23] Using 2PP-DLW, nearly any mechanically stable structure can be realized as real 3D culturing substrate consisting of a biocompatible polymer within only a few hours. 2PP-DLW has already been utilized for neuronal growth studies. [24][25][26][27][28][29] Note, while most of these applications try to mimic the natural brain environment to a certain structural degree, the adhesions spots of the cell somata and/or the direction of neurite outgrowth on 3D substrates have been statistical so far. As a first step toward 2PP-DLW application for neurite guidance, Turunen et al. used DLW in 2014 to print walls on planar glass substrates to form cavities and channels, and applied laminin with a microinjection system inside the neurocages. [27] The design lacked efficient cell confinement properties, but potential function of printed channels as neurite guides was shown.Other approaches, which enable in vitro neuronal network growth in a 3D environment in different ways, such as synthetic hydrogel platforms, [30][31][32] network growth on micro beads, [21,33] polymer scaffolds fabricated by gaseous salt leaching, [34,35] or microfibrous scaffolds [36] feature only statistically oriented network growth.Here, we present an approach for guided neuronal network growth that features single neurites specifically grown through rectangular tubes in a 3D scaffold. The design we show herein combines the tunability and the precision of a 3D design utilizing 2PP-DLW manufacturing with topologically and chemically predefined adhesion areas as well as guidance paths for While modern day integrated electronic circuits are essentially designed in a 2D fashion, the brain can be regarded as a 3D circuit. The thus enhanced connectivity enables much more complex signal processing as compared to conventional 2D circuits. Recent technological advances in the development of nano/microscale 3D structuring have led to the development of artificial neuron culturing platforms, which surpass the possibilities of classical 2D cultures. In this work, in vitro culturing of neuronal networks is demonstrated by determining predefined pathways through topological and chemical neurite guiding. Tailor-made culturing substrates of microtowers ...

Nanostructured substrates such as nanowire arrays form a powerful tool for building next-generation medical devices.

Approaching integrated hybrid neural circuits: Axon guiding on optically active semiconductor microtube arrays. An array of optically active semiconductor microtubes is utilized to build highly defined neural networks enabling a remote optical detection of action potentials via changing electric field during propagation of action potentials. The axons in the tubes are detected via a confocal microscope.