Stepwise neuronal network pattern formation in agarose gel during cultivation using non-destructive microneedle photothermal microfabrication

A micropatterned thermoplasmonic substrate for neuromodulation of in vitro neuronal networks

Understanding how the spatial organization of a neural network affects its activity represents a leading issue in neuroscience. Thanks to their accessibility and easy handling, in vitro studies remain an essential tool to investigate the relationship between the structure and function of a neuronal network. Among all the patterning techniques, ink-jet printing acquired great interest thanks to its direct-write approach, which allows the patterned substrate realization without mold, leading to a considerable saving of both cost and time. However, the inks commonly used give the possibility to control only the structure of a neuronal network, leaving aside the functional aspect. In this work, we synthesize a photosensitive ink combining the rheological and bioadhesive properties of chitosan with the plasmonic properties of gold nanorods, obtaining an ink able to control both the spatial organization of a two-dimensional neuronal network and its activity through photothermal effect. After the ink characterization, we demonstrate that it is possible to print, with high precision, different geometries on a microelectrode array. In this way, it is possible obtaining a patterned device to control the structure of a neuronal network, to record its activity and to modulate it via photothermal effect. Finally, to our knowledge, we report the first evidence of photothermal inhibition of human neurons activity. STATEMENT OF SIGNIFICANCE: Patterned cell cultures remain the most efficient and simple tool for linking structural and functional studies, especially in the neuronal field. Ink-jet printing is the technique with which it is possible to realize patterned structures in the fastest, simple, versatile and low-cost way. However, the inks currently used permit the control only of the neuronal network structure but do not allow the control-modulation of the network activity. In this study, we realize and characterize a photosensitive bioink with which it is possible to drive both the structure and the activity of a neuronal network. Moreover, we report the first evidence of activity inhibition by the photothermal effect on human neurons as far as we know.

In Situ Agarose Microfabrication Technology Using Joule Heating of Micro Ionic Current for On-Chip Cell Network Analysis

Agarose microfabrication technology is one of the micropatterning techniques of cells having advantages of simple and flexible real-time fabrication of three-dimensional confinement microstructures even during cell cultivation. However, the conventional photothermal etching procedure of focused infrared laser on thin agarose layer has several limitations, such as the undesired sudden change of etched width caused by the local change of absorbance of the bottom surface of cultivation plate, especially on the indium-tin-oxide (ITO) wiring on the multi-electrode array (MEA) cultivation chip. To overcome these limitations, we have developed a new agarose etching method exploiting the Joule heating of focused micro ionic current at the tip of the micrometer-sized capillary tube. When 75 V, 1 kHz AC voltage was applied to the tapered microcapillary tube, in which 1 M sodium ion buffer was filled, the formed micro ionic current at the open end of the microcapillary tube melted the thin agarose layer and formed stable 5 μm width microstructures regardless the ITO wiring, and the width was controlled by the change of applied voltage squared. We also found the importance of the higher frequency of applied AC voltage to form the stable microstructures and also minimize the fluctuation of melted width. The results indicate that the focused micro ionic current can create stable local spot heating in the medium buffer as the Joule heating of local ionic current and can perform the same quality of microfabrication as the focused infrared laser absorption procedure with a simple set-up of the system and several advantages.

Biomaterial-based strategies for in vitro neural models

In vitro models have been used as a complementary tool to animal studies in understanding the nervous system's physiological mechanisms and pathological disorders, while also serving as platforms to evaluate the safety and efficiency of therapeutic candidates. Following recent advances in materials science, micro- and nanofabrication techniques and cell culture systems, in vitro technologies have been rapidly gaining the potential to bridge the gap between animal and clinical studies by providing more sophisticated models that recapitulate key aspects of the structure, biochemistry, biomechanics, and functions of human tissues. This was made possible, in large part, by the development of biomaterials that provide cells with physicochemical features that closely mimic the cellular microenvironment of native tissues. Due to the well-known material-driven cellular response and the importance of mimicking the environment of the target tissue, the selection of optimal biomaterials represents an important early step in the design of biomimetic systems to investigate brain structures and functions. This review provides a comprehensive compendium of commonly used biomaterials as well as the different fabrication techniques employed for the design of neural tissue models. Furthermore, the authors discuss the main parameters that need to be considered to develop functional platforms not only for the study of brain physiological functions and pathological processes but also for drug discovery/development and the optimization of biomaterials for neural tissue engineering.

Photothermal Agarose Microfabrication Technology for Collective Cell Migration Analysis

Agarose photothermal microfabrication technology is one of the micropatterning techniques that has the advantage of simple and flexible real-time fabrication even during the cultivation of cells. To examine the ability and limitation of the agarose microstructures, we investigated the collective epithelial cell migration behavior in two-dimensional agarose confined structures. Agarose microchannels from 10 to 211 micrometer width were fabricated with a spot heating of a focused 1480 nm wavelength infrared laser to the thin agarose layer coated on the cultivation dish after the cells occupied the reservoir. The collective cell migration velocity maintained constant regardless of their extension distance, whereas the width dependency of those velocities was maximized around 30 micrometer width and decreased both in the narrower and wider microchannels. The single-cell tracking revealed that the decrease of velocity in the narrower width was caused by the apparent increase of aspect ratio of cell shape (up to 8.9). In contrast, the decrease in the wider channels was mainly caused by the increase of the random walk-like behavior of component cells. The results confirmed the advantages of this method: (1) flexible fabrication without any pre-designing, (2) modification even during cultivation, and (3) the cells were confined in the agarose geometry.