Neurite Guidance and Three-Dimensional ConfinementviaCompliant Semiconductor Scaffolds

Abstract

Neurons are often cultured in vitro on a flat, open, and rigid substrate, a platform that does not reflect well the native microenvironment of the brain. To address this concern, we have developed a culturing platform containing arrays of microchannels, formed in a crystalline-silicon nanomembrane (NM) resting on polydimethylsiloxane; this platform will additionally enable active sensing and stimulation at the local scale, via devices fabricated in the silicon. The mechanical properties of the composite Si/compliant substrate nanomaterial approximate those of neural tissue. The microchannels, created in the NM by strain engineering, demonstrate strong guidance of neurite outgrowth. Using plasma techniques, we developed a means to coat just the inside surface of these channels with an adhesion promoter (poly-d-lysine). For NM channels with openings larger than the cross-sectional area of a single axon, strong physical confinement and guidance of axons through the channels are observed. Imaging of axons that grow in channels with openings that approximate the size of an axon suggests that a tight seal exists between the cell membrane and the inner surface of the channel, mimicking a myelin sheath. Such a tight seal of the cell membrane with the channel surface would make this platform an attractive candidate for future neuronal repair. Results of measurements of impedance and photoluminescence of bare NM channels are comparable to those on a flat NM, demonstrating electrical and optical modalities of our platform and suggesting that this scaffold can be expanded for active sensing and monitoring of neuron cellular processes in conditions in which they exist naturally.

Buckling-Induced Kirigami

“…Our buckling-induced strategy not only provides a simple route for manufacturing kirigami sheets, but can also be combined with optimization techniques to design perforated patterns capable of generating desired complex 3D surfaces under external loading [9,11,41]. Finally, since the response of our perforated sheets is essentially scale-free, the proposed pop-up strategy can be used to fabricate kirigami sheets over a wide range of scales, from transformable meterscale architectures to tunable nano-scale surfaces [24,40].…”

Vertically-Aligned Functionalized Silicon Micropillars for 3D Culture of Human Pluripotent Stem Cell-Derived Cortical Progenitors

“…Other scaffold-based methods have been reported for the biofabrication of in vitro 3D tissue-like models [15][16][17]. In particular, some of these systems, especially the ones based on 3D polymeric materials, i.e., microfibres and hydrogel scaffolds, offer a highly useful and strong method for creating large-scale 3D tissue cultures.…”

“…Both scaffold-free organoid-based technologies and natural or synthetic scaffold-based culture systems have been developed [7]. In particular, since different tissue types show definite assemblies associated with their functional organization, scaffold-based methods allow assisted mimicking of complex tissue geometrical topographies, such as cerebral cortex, thus facilitating effective biofabrication of in vitro 3D tissue-like models [15][16][17]. With this purpose, silicon-based micro-fabricated culture substrates with well-defined continuous and discontinuous topographies, including the development of surfaces patterned with grooves, nanopillars or nanowires for the study of neural guidance and polarity, have been extensively developed in order to create scaffolds for a variety of applications [18][19][20][21][22][23][24].…”

Assembly and Self‐Assembly of Nanomembrane Materials—From 2D to 3D

“…It is worth noting that chemical treatments of the surface may not be a precondition for sufficient adhesion although the van der Waals force is relatively weak compared to covalent linkage. Some experiment work demonstrated the possibility of producing complex 3D structures without surface chemical treatment . A typical 3D helical structure fabricated by this self‐assembly process, as an example, is shown in Figure a.…”

“…Some experiment work demonstrated the possibility of producing complex 3D structures without surface chemical treatment. [219] A typical 3D helical structure fabricated by this self-assembly process, as an example, is shown in Figure 6a. Experimental observations proved that during the self-assembly, in-plane bending is energetically unfavorable compared with out-ofplane bending or twisting, and therefore translational motion and out-of-plane bending or twisting were dominant in self-assembly.…”