Microenvironments Matter:Advances in Brain-on-Chip

To highlight the particular needs with respect to modeling the unique and complex organization of the human brain structure, we reviewed the state-of-the-art in devising brain models with engineered instructive microenvironments. To acquire a better perspective on the brain’s working mechanisms, we first summarize the importance of regional stiffness gradients in brain tissue, varying per layer and the cellular diversities of the layers. Through this, one can acquire an understanding of the essential parameters in emulating the brain in vitro. In addition to the brain’s organizational architecture, we addressed also how the mechanical properties have an impact on neuronal cell responses. In this respect, advanced in vitro platforms emerged and profoundly changed the methods of brain modeling efforts from the past, mainly focusing on animal or cell line research. The main challenges in imitating features of the brain in a dish are with regard to composition and functionality. In neurobiological research, there are now methods that aim to cope with such challenges by the self-assembly of human-derived pluripotent stem cells (hPSCs), i.e., brainoids. Alternatively, these brainoids can be used stand-alone or in conjunction with Brain-on-Chip (BoC) platform technology, 3D-printed gels, and other types of engineered guidance features. Currently, advanced in vitro methods have made a giant leap forward regarding cost-effectiveness, ease-of-use, and availability. We bring these recent developments together into one review. We believe our conclusions will give a novel perspective towards advancing instructive microenvironments for BoCs and the understanding of the brain’s cellular functions either in modeling healthy or diseased states of the brain.</p

Production and characterization of miro- and nano-features in biomedical alumina and zirconia ceramics using a tape casting route

A process of micromolding, delivering micro- and nanopatterned ceramic surfaces for biomaterial applications is described in this work. To create the desired structures, tape casting of ceramic slurries on microfabricated silicon mold was used. Several tape casting slurry compositions were tested to evaluate the feasibility of transferring micro- and nano-features from silicon molds. Used ceramics were alumina (α-Al2O3) and yttria stabilized zirconia. Three types of polymeric binders for the green tape (PVB, PES, and PVP) were investigated using three different solvents (ethanol, n-methyl-pyrrolidone, water). Well-defined features in shapes of wells with diameters down to 2.4 μm and a depth of 10 μm and pillars with diameters down to 1.7 μm and a height of 3 μm were obtained. Morphology, grain size and porosity of the sintered bodies were characterized. Finally fibroblast cells were cultured on the surfaces in order to observe their morphology under influence of the microstructured surfaces

Advancing a MEMS-Based 3D Cell Culture System for in vitro Neuro-Electrophysiological Recordings

In this work we present advances in three dimensional (3D) neuronal cell culture systems based on a reversible assembly of a microbioreactor with a microelectrode array (MEA) to create a MEMS-based 3D cell culture system for in vitro neuro-electrophysiological recordings. A batch of six molds were milled in poly (methyl methacrylate). The molds were used for soft lithography of polydimethylsiloxane (PDMS). In the center of the PDMS shape, a porous polyethersulfone (PES) cylindrical tube was press-fitted to form a growth barrier between the culture chamber inside the PES tube and the microfluidic channel surrounding the PES tube. A thin layer of partially cured PDMS was used to seal the bottom of the microbioreactor and provide reversible adhesion with the glass surface of a MEA. SH-SY5Y cells were successfully differentiated inside the microbioreactors in Matrigel and demonstrated extended neuronal networks over a height of at least 184 micrometers within the system. In previous microbioreactor designs visibility was limited due to the closed top with the dispensing holes. The new open top design allows for a better evaluation of the cell culture by optical detection methods during the experiment. Electrophysiological activity was recorded within the microbioreactor using human induced pluripotent stem cell-derived cortical neurons cultured in Matrigel, in 3D, up until 21 days in vitro. In summary, we present advances made in the design, the fabrication process and integration of microbioreactors with MEAs. Optical imaging capabilities improved significantly with an open top and the culture time was further extended from 7 to 21 DIV without leakage or degradation thanks to introducing PES as a barrier material and an enhanced assembly procedure. The latter facilitated a sufficient long-term culture for neurons to mature in an environment free from flow-induced stress and provided a proof of principle for the recording of electrophysiological activity of cortical neurons cultured in 3D

Massively parallel fabrication of repetitive nanostructures: nanolithography for nanoarrays

This topical review provides an overview of nanolithographic techniques for nanoarrays. Using patterning techniques such as lithography, normally we aim for a higher order architecture similarly to functional systems in nature. Inspired by the wealth of complexity in nature, these architectures are translated into technical devices, for example, found in integrated circuitry or other systems in which structural elements work as discrete building blocks in microdevices. Ordered artificial nanostructures (arrays of pillars, holes and wires) have shown particular properties and bring about the opportunity to modify and tune the device operation. Moreover, these nanostructures deliver new applications, for example, the nanoscale control of spin direction within a nanomagnet. Subsequently, we can look for applications where this unique property of the smallest manufactured element is repetitively used such as, for example with respect to spin, in nanopatterned magnetic media for data storage. These nanostructures are generally called nanoarrays. Most of these applications require massively parallel produced nanopatterns which can be directly realized by laser interference (areas up to 4 cm2 are easily achieved with a Lloyd's mirror set-up). In this topical review we will further highlight the application of laser interference as a tool for nanofabrication, its limitations and ultimate advantages towards a variety of devices including nanostructuring for photonic crystal devices, high resolution patterned media and surface modifications of medical implants. The unique properties of nanostructured surfaces have also found applications in biomedical nanoarrays used either for diagnostic or functional assays including catalytic reactions on chip. Bio-inspired templated nanoarrays will be presented in perspective to other massively parallel nanolithography techniques currently discussed in the scientific literature

Editorial for the special issue on microfluidic brain-on-a-chip

A little longer than a decade of Organ-on-Chip (OoC) developments has passed [...

Fabrication technologies for optical scanners based on micromachined cantilevers

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Nanofabricating neural networks: Strategies, advances, and challenges

Nanofabrication can help us to emulate natural intelligence. Forward-engineering brain gained enormous momentum but still falls short in human neurodegenerative disease modeling. Here, organ-on-chip (OoC) implementation of tissue culture concepts in microfluidic formats already progressed with the identification of our knowledge gap in toxicology and drug metabolism studies. We believe that the self-organization of stem cells and chip technology is a key to advance such complex in vitro tissue models, including models of the human nervous system as envisaged in this review. However, current cultured networks of neurons show limited resemblance with the biological functions in the real nervous system or brain tissues. To take full advantage of scaling in the engineering domain of electron-, ion-, and photon beam technology and nanofabrication methods, more research is needed to meet the requirements of this specific field of chip technology applications. So far, surface topographies, microfluidics, and sensor and actuator integration concepts have all contributed to the patterning and control of neural network formation processes in vitro. However, when probing the state of the art for this type of miniaturized three-dimensional tissue models in PubMed, it was realized that there is very little systematic cross-disciplinary research with biomaterials originally formed for tissue engineering purposes translated to on-chip solutions for in vitro modeling. Therefore, this review contributes to the formulation of a sound design concept based on the understanding of the existing knowledge and the technical challenges toward finding better treatments and potential cures for devastating neurodegenerative diseases, like Parkinson's disease. Subsequently, an integration strategy based on a modular approach is proposed for nervous system-on-chip (NoC) models that can yield efficient and informative optical and electronic NoC readouts in validating and optimizing these conceptual choices in the innovative process of a fast growing and exciting new OoC industry

Imprint lithography provides topographical nanocues to guide cell growth in primary cortical cell culture

In this paper, we describe a technology platform to study the effect of nanocues on the cell growth direction in primary cortical cell culture. Topographical cues to cells are provided using nanoscale features created by Jet and Flash Imprint Lithography, coated with polyethylenimine. We investigated nanoscaffolds with periodicities ranging from 200 nm to 2000 nm, and found that the samples with a period between 400 nm and 600 nm and a height of 118 nm showed highly ordered regions of neurites in a newly formed network with a preferential alignment tendency for astrocytes. Live/dead staining results showed that different materials, such as silicon, glass, and imprinted resist are rendered biocompatible by coating with polyethylenimine. This coating therefore allows for a free choice of scaffold materials and promotes good cell-substrate adhesion. From our results we conclude particular length scales of nanoscaffold can impose a degree of order on cell spreading behavior in a complex cellular brain-on-a-chip network, which could thus be used to emulate ordered brain regions and their function in vitr

Stiff-to-soft transition from glass to 3d hydrogel substrates in neuronal cell culture

Over the past decade, hydrogels have shown great potential for mimicking three-dimensional (3D) brain architectures in vitro due to their biocompatibility, biodegradability, and wide range of tunable mechanical properties. To better comprehend in vitro human brain models and the mechanotransduction processes, we generated a 3D hydrogel model by casting photo-polymerized gelatin methacryloyl (GelMA) in comparison to poly (ethylene glycol) diacrylate (PEGDA) atop of SH-SY5Y neuroblastoma cells seeded with 150,000 cells/cm2 according to our previous experience in a microliter-sized polydimethylsiloxane (PDMS) ring serving for confinement. 3D SH-SY5Y neuroblastoma cells in GelMA demonstrated an elongated, branched, and spreading morphology resembling neurons, while the cell survival in cast PEGDA was not supported. Confocal z-stack microscopy confirmed our hypothesis that stiff-to-soft material transitions promoted neuronal migration into the third dimension. Unfortunately, large cell aggregates were also observed. A subsequent cell seeding density study revealed a seeding cell density above 10,000 cells/cm2 started the formation of cell aggregates, and below 1500 cells/cm2 cells still appeared as single cells on day 6. These results allowed us to conclude that the optimum cell seeding density might be between 1500 and 5000 cells/cm2. This type of hydrogel construct is suitable to design a more advanced layered mechanotransduction model toward 3D microfluidic brain-on-a-chip applications