Spatiotemporally controlled navigation of neurite outgrowth in sequential steps on the dynamically photo-patternable surface

Connectivity and network burst properties of in-vitro neuronal networks induced by a clustered structure with alginate hydrogel patterning

Modularity is one of the important structural properties that affect information processing and other functionalities of neuronal networks. Researchers have developed in-vitro clustered network models for reproducing the modularity, but it is still challenging to control the segregation and integration of several sub-populations of them. We cultured clustered networks with alginate patterning and collected the electrophysiological signals to investigate the changes in functional properties during the development. We built inter-connected neuronal clusters using alginate micro-patterning with a circular shape on the surface of the micro-electrode array. The neuronal clusters were enabled to be connected at 3 or 10 days-in-vitro (DIV) by removing the barrier. The neuronal signals from different types of networks were collected from 16 to 34 DIV, and functional characteristics were examined. Connectivity and burst motif analysis were carried out to find out the relation between the structure and function of the networks. Neuronal networks with clustered structure showed different activity properties from the random networks along the development. The clustered networks had more short-range connections compared to the random networks. In the network burst motif analysis, the clustered networks showed more various patterns and a slower propagation of the activation patterns. In this study, we successfully cultured neuronal networks with clustered structure, and the structure affected the functional properties. The network model suggested in this study will be a good solution for observing the effect of structure on function during their development.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-023-00289-5.

Topographical cues of PLGA membranes modulate the behavior of hMSCs, myoblasts and neuronal cells

Biomaterial surface modification through the introduction of defined and repeated patterns of topography helps study cell behavior in response to defined geometrical cues. The lithographic molding technique is widely used for conferring biomaterial surface microscale cues and enhancing the performance of biomedical devices. In this work, different master molds made by UV mask lithography were used to prepare poly (D,L-lactide-co-glycolide) - PLGA micropatterned membranes to present different features of topography at the cellular interface: channels, circular pillars, rectangular pillars, and pits. The effects of geometrical cues were investigated on different cell sources, such as neuronal cells, myoblasts, and stem cells. Morphological evaluation revealed a peculiar cell arrangement in response to a specific topographical stimulus sensed over the membrane surface. Cells seeded on linear-grooved membranes showed that this cue promoted elongated cell morphology. Rectangular and circular pillars act instead as discontinuous cues at the cell-membrane interface, inducing cell growth in multiple directions. The array of pits over the surface also highlighted the precise spatiotemporal organization of the cell; they grew between the interconnected membrane space within the pits, avoiding the microscale hole. The overall approach allowed the evaluation of the responses of different cell types adhered to various surface patterns, build-up on the same polymeric membrane, and disclosing the effect of specific topographical features. We explored how various microtopographic signals play distinct roles in different cells, thus affecting cell adhesion, migration, differentiation, cell-cell interactions, and other metabolic activities.

Neurons-on-a-Chip: In Vitro NeuroTools

Neurons-on-a-Chip technology has been developed to provide diverse in vitro neuro-tools to study neuritogenesis, synaptogensis, axon guidance, and network dynamics. The two core enabling technologies are soft-lithography and microelectrode array technology. Soft lithography technology made it possible to fabricate microstamps and microfluidic channel devices with a simple replica molding method in a biological laboratory and innovatively reduced the turn-around time from assay design to chip fabrication, facilitating various experimental designs. To control nerve cell behaviors at the single cell level via chemical cues, surface biofunctionalization methods and micropatterning techniques were developed. Microelectrode chip technology, which provides a functional readout by measuring the electrophysiological signals from individual neurons, has become a popular platform to investigate neural information processing in networks. Due to these key advances, it is possible to study the relationship between the network structure and functions, and they have opened a new era of neurobiology and will become standard tools in the near future.

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

Conventional neuronal network pattern formation techniques cannot control the arrangement of axons and dendrites because network structures must be fixed before neurite differentiation. To overcome this limitation, we developed a non-destructive stepwise microfabrication technique that can be used to alter microchannels within agarose to guide neurites during elongation. Micropatterns were formed in thin agarose layer coating of a cultivation dish using the tip of a 0.7 [Formula: see text]-diameter platinum-coated glass microneedle heated by a focused 1064-nm wavelength infrared laser, which has no absorbance of water. As the size of the heat source was 0.7 [Formula: see text], which is smaller than the laser wavelength, the temperature fell to 45 [Formula: see text] within a distance of 7.0 [Formula: see text] from the edge of the etched agarose microchannel. We exploited the fast temperature decay property to guide cell-to-cell connection during neuronal network cultivation. The first neurite of a hippocampal cell from a microchamber was guided to a microchannel leading to the target neuron with stepwise etching of the micrometer resolution microchannel in the agarose layer, and the elongated neurites were not damaged by the heat of etching. The results indicate the potential of this new technique for fully direction-controlled on-chip neuronal network studies.

Thermoplasmonic neural chip platform for in situ manipulation of neuronal connections in vitro

Cultured neuronal networks with a controlled structure have been widely studied as an in vitro model system to investigate the relationship between network structure and function. However, most cell culture techniques lack the ability to control network structures during cell cultivation, making it difficult to assess functional changes induced by specific structural changes. In this study, we present an in situ manipulation platform based on gold-nanorod-mediated thermoplasmonics to interrogate an in vitro network model. We find that it is possible to induce new neurite outgrowths, eliminate interconnecting neurites, and estimate functional relationships in matured neuronal networks. This method is expected to be useful for studying functional dynamics of neural networks under controlled structural changes.

Cultured neuron networks provide insight into network structure and function, but the ability to control network topology is a challenge. Here the authors develop a nanorod-mediated thermoplasmonics platform that enables the formation of new connections, the abolishment of existing connections, and the modulation of network activity during cultivation.

A photoresponsive soft interface reversibly controls wettability and cell adhesion by conformational changes in a spiropyran-conjugated amphiphilic block copolymer

The functionalities of soft interfaces including cell adhesion can be enhanced by dynamic conversion of polymer properties and movement via external stimuli. Light is a superior stimulus, and various surfaces modified with photoreactive molecules have been prepared. However, in most of these studies, the surface properties are irreversibly changed due to photo-degradation, and reversible adhesion and collection of cells is not feasible. In this study, we developed a photoresponsive polymer soft interface that was able to spatiotemporally control wettability, cell adhesion, and detachment in a reversible manner. Spiropyran molecules were introduced into the hydrophobic block of an amphiphilic diblock copolymer consisting of poly(methyl methacrylate) and polyethylene glycol, and the monomer unit numbers of these components were optimized. The copolymer was immobilized on a glass substrate as a nanofilm. With alternating irradiation using UV and visible light, the surface exhibited reversible changes in hydrophobicity and hydrophilicity, and the direction of change was opposite to the polarity change in photo-isomerization of spiropyran. We also achieved photo-control of effective cell adhesion and detachment with sequential irradiation with UV and visible light. These remarkable functions could be ascribed to conformational changes triggered by photo-isomerization of spiropyran. This photoresponsive polymer soft interface may have applications as a powerful tool in biological studies by facilitating sequential changes in wettability and bioaffinity.

STATEMENT OF SIGNIFICANCE

We developed a photoresponsive polymer soft interface, which was able to spatiotemporally control wettability and cell adhesion/detachment in a reversible manner, by introducing spiropyran into the hydrophobic block of an amphiphilic diblock copolymer. With alternating irradiation using UV and visible light, the surface exhibited unique reversible wettability changes; the direction of hydrophobicity and hydrophilicity change was opposite to the polarity change in spiropyran photo-isomerization. Light-dependent reversible control of spatiotemporal cell adhesion and detachment was also achieved with sequential UV (adhesion) and visible light irradiation (detachment). Cell detachment using noncytotoxic visible light was realized for the first time. Cell-patterning capability stably lasted for 25days. This photoresponsive surface could be applied to fabrication of engineered tissues comprised of several cellular species.

Packing polymorphism in the crystal structure of 4,5-dimeth-oxy-2-nitro-benzyl acetate

The title compound shows two packing polymorphs, in which the mol­ecular structures are planar and essentially similar. One crystal shows inter­molecular C—H⋯O and π–π inter­actions, while the other crystal exhibits several modes of inter­molecular C—H⋯O inter­actions.

The title compound, C₁₁H₁₃NO₆, shows two polymorphs, orange and yellow forms, both of which crystallize in the space group P2₁/c. The mol­ecular structures in the two polymorphs are essentially similar and adopt a planar structure, the maximum deviations for the non-H atoms being 0.1836 (13) and 0.1276 (13) Å, respectively, for the orange and yellow forms. In the orange crystal, mol­ecules are linked by an inter­molecular C—H⋯O inter­action into a helical chain along the b-axis direction. The chains are stacked along the c axis through a π–π inter­action [centroid–centroid distance = 3.6087 (11) Å], forming a layer parallel to the bc plane. In the yellow crystal, mol­ecules are connected through C—H⋯O inter­actions into a sheet structure parallel to (-302). No significant π–π inter­action is observed. The unit-cell volume of the orange crystal is larger than that of the yellow one, and this accounts for the predominant growth of the yellow crystal.

Collagen surfaces modified with photo-cleavable polyethylene glycol-lipid support versatile single-cell arrays of both non-adherent and adherent cells

Cell patterning on photo-responsive materials are a promising tool for preparing unique single-cell arrays. However, most conventional single-cell arrays on such smart materials can be applied only to adherent cells and limit cellular functions such as extension and migration within the patterned adhesive surfaces. In this study, a versatile single cell array that works with both non-adherent and adherent cells was constructed using a photo-cleavable polyethylene glycol (PEG)-lipid/collagen surface. On this single-cell array, cells behaved similar to their native functions without limitation from the patterned surface. Furthermore, quantitative imaging analyses of cellular motility and morphological changes were performed in a high-throughput manner.

In situ modification of cell-culture scaffolds by photocatalytic decomposition of organosilane monolayers

We demonstrate a novel application of TiO2 photocatalysis for modifying the cell affinity of a scaffold surface in a cell-culture environment. An as-deposited octadecyltrichlorosilane self-assembled monolayer (OTS SAM) on TiO2 was found to be hydrophobic and stably adsorbed serum albumins that blocked subsequent adsorption of other proteins and cells. Upon irradiation of ultraviolet (UV) light, OTS molecules were decomposed and became permissive to the adhesion of PC12 cells via adsorption of an extracellular matrix protein, collagen. Optimal UV dose was 200 J cm(-2) for OTS SAM on TiO2. The amount of collagen adsorption decreased when excessive UV light was irradiated, most likely due to the surface being too hydrophilic to support its adsorption. This UV-induced modification required TiO2 to be present under the SAM and hence is a result of TiO2 photocatalysis. The UV irradiation for surface modification can be performed before cell plating or during cell culture. We also demonstrate that poly(ethylene glycol) SAM can also be patterned with this method, indicating that it is applicable to both hydrophobic and hydrophilic SAMs. This method provides a unique tool for fabricating cell microarrays and studying dynamical properties of living cells.

Local polymer replacement for neuron patterning and in situ neurite guidance

By locally dispensing poly-L-lysine (PLL) molecules with a FluidFM onto a protein and cell resistant poly-L-lysine-graft-polyethylene glycol (PLL-g-PEG) coated substrate, the antifouling layer can be replaced under the tip aperture by the cell adhesive PLL. We used this approach for guiding the adhesion and axonal outgrowth of embryonic hippocampal neurons in situ. Cultures of hippocampal neurons were chosen because they mostly contain pyramidal neurons. The hippocampus is known to be involved in memory formation, and the stages of network development are well characterized, which is an asset to fundamental research. After fabricating diffuse PLL spots with 10-250 μm diameter, seeded hippocampal cells stick preferentially onto the spots migrating toward the spot center along the PLL gradient. Cell clusters were formed depending on the lateral size of the PLL dots and the density of seeded cells. In a second step of this protocol, the FluidFM is used to connect in situ the obtained clusters. The outgrowth of neurites, which are known to grow preferentially on adhesive substrates, is tailored by writing PLL lines. Antibody staining confirms that the outgrowing neurites are mostly axons, while the activity of the neurons is assessed by a calcium indicator, proving cell viability. The calcium signal intensity of two actively interconnected clusters showed to be correlated, corroborating the formation of vectored and polarized interconnections.

Rapid Prototyping of Heterotypic Cell-Cell Contacts

Disparities in cellular behaviour between cultures of a single cell type and heterogeneous co-cultures require constructing spatially-defined arrays of multiple cell types. Such arrays are critical for investigating cellular properties as they exist in vivo. Current methods rely upon covalent surface modification or external physical micromanipulation to control cellular organization on a limited range of substrates. Here, we report a direct approach for creating co-cultures of different cell types by microcontact printing a photosensitive cell resist. The cell-resistant polymer converts to cell adhesive 0 with light exposure, thus the initial copolymer pattern dictates the position of both cell types. This strategy enables straightforward preparation of tailored heterotypic cell-cell contacts on materials ranging from polymers to metallic substrates.

Dynamic substrate based on photocleavable poly(ethylene glycol): zeta potential determines the capability of geometrical cell confinement

Dynamic substrates whose cell adhesiveness changes in response to an external stimulus are useful not only for patterning cells in various geometries but also for inducing cell migration or arraying heterotypic cells. The requirements for such applications are high switching efficiency in cell adhesiveness and long-term persistence of the created cellular patterns. In this study, we prepared a dynamic substrate bearing photocleavable poly(ethylene glycol) (PEG) and examined the effect of the surface PEG density and the charge of cationic base materials on the above-mentioned key requirements. An amino-terminated substrate with a certain amino group density and charge was functionalized with photocleavable PEG5K, with and without subsequent backfilling of photocleavable PEG2K. The PEG chains made the surface non-cell-adhesive, but subsequent near-UV irradiation of the substrate induced photocleavage of the PEG, eventually making the surface cell-adhesive. The substrates were analyzed by atomic force microscopy, contact angle measurements, ellipsometry, and zeta potential measurements, complemented with protein adsorption observations. Although the density of amino group in the base material affected both the grafting efficiency of the backfilling PEG and the electrokinetic potential mainly in the positive range, the latter mainly determined the protein- and cell-repelling abilities of the substrates. Furthermore, varying the surface compositions had almost no effect on the switching efficiency in the early stage of the culture, but it became more significant after culturing cells for a longer time; the cells fouled the nonirradiated PEGylated regions earlier on the surfaces with higher positive zeta potentials. These results indicate that the zeta potential is an essential factor in the long-term persistence of cellular patterns on photoactivatable substrates. This study not only provides a recipe for the development of a dynamic substrate with an adequate time frame but also clarifies how the interfacial nanoarchitectures, composed of the nanometer-scale PEG brushes and charged base materials, affect the biocompatibility.