Intracellular Ca2+ imaging for micropatterned cardiac myocytes

Mapping of structural arrangement of cells and collective calcium transients: an integrated framework combining live cell imaging using confocal microscopy and UMAP-assisted HDBSCAN-based approach

Live cell calcium (Ca2+) imaging is one of the important tools to record cellular activity during in vitro and in vivo preclinical studies. Specially, high-resolution microscopy can provide valuable dynamic information at the single cell level. One of the major challenges in the implementation of such imaging schemes is to extract quantitative information in the presence of significant heterogeneity in Ca2+ responses attained due to variation in structural arrangement and drug distribution. To fill this gap, we propose time-lapse imaging using spinning disk confocal microscopy and machine learning-enabled framework for automated grouping of Ca2+ spiking patterns. Time series analysis is performed to correlate the drug induced cellular responses to self-assembly pattern present in multicellular systems. The framework is designed to reduce the large-scale dynamic responses using uniform manifold approximation and projection (UMAP). In particular, we propose the suitability of hierarchical DBSCAN (HDBSCAN) in view of reduced number of hyperparameters. We find UMAP-assisted HDBSCAN outperforms existing approaches in terms of clustering accuracy in segregation of Ca2+ spiking patterns. One of the novelties includes the application of non-linear dimension reduction in segregation of the Ca2+ transients with statistical similarity. The proposed pipeline for automation was also proved to be a reproducible and fast method with minimal user input. The algorithm was used to quantify the effect of cellular arrangement and stimulus level on collective Ca2+ responses induced by GPCR targeting drug. The analysis revealed a significant increase in subpopulation containing sustained oscillation corresponding to higher packing density. In contrast to traditional measurement of rise time and decay ratio from Ca2+ transients, the proposed pipeline was used to classify the complex patterns with longer duration and cluster-wise model fitting. The two-step process has a potential implication in deciphering biophysical mechanisms underlying the Ca2+ oscillations in context of structural arrangement between cells.

Electrohydrodynamic jet 3D printing in biomedical applications

Electrohydrodynamic Jet 3D Printing (e-jetting) is a promising technique developed from electrospinning, which enables precise fiber deposition in a layer-by-layer fashion with customized designs. Several studies have verified that e-jetted scaffolds were able to support cell attachment, proliferation, and extracellular matrix formation, as well as cell infiltration into the scaffold due to the well-defined pores. Besides, e-jetting has also been combined with other techniques to incorporate biomaterials (e.g., hydrogels and cell spheroids) that could not be e-jetted, to promote the biological performance of the scaffold. In the recent decade, applying e-jetting in the fabrication of tissue-engineered scaffolds has drawn a lot of interest. Moreover, efforts have been put to develop varied scaffolds for some specific biomedical applications such as cartilage, tendon, and blood vessel, which exhibited superior mechanical properties and promoted cell behaviors including cellular alignment and differentiation. This review article also provides the reader with some crucial considerations and major limitations of e-jetting, such as scaffold design, printability of large-scale constructs, applicable biomaterials, and cell behaviors. Overall, this review article expounds on perspectives in the context of development and biomedical applications of this technique. STATEMENT OF SIGNIFICANCE: E-jetting technique is able to produce fibers with diameter in micrometer scale, which has been considered as a promising 3D printing technique. This technique has shown promise for regeneration of tissue engineered scaffolds with well-defined structures, which has been reported to apply in regeneration of different tissue types. The superior controllability of the process endows the feasibility of constructing multi-scale scaffolds with great biological mimicry and cellular infiltration. The incorporation of other biomaterials into the e-jetted networks further reinforces the scope of applications as compared to e-jetted scaffolds only. There is no doubt that e-jetting will be a great tool for tissue engineered scaffolding, and this review article will give overall perspectives in this topic.

Surface Chemistry and Microtopography of Parylene C Films Control the Morphology and Microtubule Density of Cardiac Myocytes

Cell micropatterning has certainly proved to improve the morphological and physiological properties of cardiomyocytes in vitro; however, there is little knowledge on the single cell-scaffold interactions that influence the cells' development and differentiation in culture. In this study, we employ hydrophobic/hydrophilic micropatterned Parylene C thin films (2-10 μm) as cell microscaffolds that can control the morphology and microtubule density of neonatal rat ventricular myocytes (NRVM) by regulating their adhesion area on Parylene through a thickness-dependent hydrophobicity. Structured NRVM on thin films tend to bridge across the hydrophobic areas, demonstrating a more spread-out shape and sparser microtubule organization, while cells on thicker films adopt a cylindrical (in vivo-like) shape (contact angles at the level of the nucleus are 64.51° and 84.73°, respectively) and a significantly (p < 0.05) denser microtubule structure. Ion scanning microscopy on NRVM revealed that cells on thicker membranes were significantly (p < 0.05) smaller in volume, but more elongated. The cylindrical shape and a significantly denser microtubule structure indicate the ability to influence cardiomyocyte phenotype using patterning and manipulation of hydrophilicity. These combined bioengineering strategies are promising tools in the generation of more representative cardiomyocytes in culture.

Excitation-contraction coupling of human induced pluripotent stem cell-derived cardiomyocytes

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) hold enormous potential in many fields of cardiovascular research. Overcoming many of the limitations of their embryonic counterparts, the application of iPSC-CMs ranges from facilitating investigation of familial cardiac disease and pharmacological toxicity screening to personalized medicine and autologous cardiac cell therapies. The main factor preventing the full realization of this potential is the limited maturity of iPSC-CMs, which display a number of substantial differences in comparison to adult cardiomyocytes. Excitation–contraction (EC) coupling, a fundamental property of cardiomyocytes, is often described in iPSC-CMs as being more analogous to neonatal than adult cardiomyocytes. With Ca²⁺ handling linked, directly or indirectly, to almost all other properties of cardiomyocytes, a solid understanding of this process will be crucial to fully realizing the potential of this technology. Here, we discuss the implications of differences in EC coupling when considering the potential applications of human iPSC-CMs in a number of areas as well as detailing the current understanding of this fundamental process in these cells.

Adhesion of adipose-derived mesenchymal stem cells to glycosaminoglycan surfaces with different protein patterns

Proteins and glycosaminoglycans (GAGs) are the main constituents of the extracellular matrix (ECM). They act in synergism and are equally critical for the development, growth, function, or survival of an organism. In this work, we developed surfaces that display these two classes of biomacromolecules, namely, GAGs and proteins, in a spatially controlled fashion. The generated surfaces can be used as a minimalistic but straightforward model aiding the elucidation of cell-ECM interactions. GAGs (hyaluronic acid and heparin) were covalently bound to amino functionalized surfaces, and albumin or fibronectin was patterned by microcontact printing on top of them. We demonstrate that adipose-derived stem cells (ASCs) can adhere either on the protein or on the GAG pattern as a function of the patterned molecules. ASCs found on the GAG pattern had different morphology and expressed different surface markers than the cells adhered on the protein pattern. ASCs morphology and spreading were also dependent on the size of the pattern. These results show that the developed supports can also be used for ASCs differentiation into different lineages.

The effect of microgrooved culture substrates on calcium cycling of cardiac myocytes derived from human induced pluripotent stem cells

Induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) have been widely proposed as in vitro models of myocardial physiology and disease. A significant obstacle, however, is their immature phenotype. We hypothesised that Ca(2+) cycling of iPSC-CM is influenced by culture conditions and can be manipulated to obtain a more mature cellular behaviour. To test this hypothesis we seeded iPSC-CM onto fibronectin coated microgrooved polydimethylsiloxane (PDMS) scaffolds fabricated using photolithography, or onto unstructured PDMS membrane. After two weeks in culture, the structure and function of iPSC-CM were studied. PDMS microgrooved culture substrates brought about cellular alignment (p < 0.0001) and more organised sarcomere. The Ca(2+) cycling properties of iPSC-CM cultured on these substrates were significantly altered with a shorter time to peak amplitude (p = 0.0002 at 1 Hz), and more organised sarcoplasmic reticulum (SR) Ca(2+) release in response to caffeine (p < 0.0001), suggesting improved SR Ca(2+) cycling. These changes were not associated with modifications in gene expression. Whilst structured tissue culture may make iPSC-CM more representative of adult myocardium, further construct development and characterisation is required to optimise iPSC-CM as a model of adult myocardium.

Modulating patterned adhesion and repulsion of HEK 293 cells on microengineered parylene-C/SiO(2) substrates

This article describes high resolution patterning of HEK 293 cells on a construct of micropatterned parylene-C and silicon dioxide. Photolithographic patterning of parylene-C on silicon dioxide is an established and consistent process. Activation of patterns by immersion in serum has previously enabled patterning of murine hippocampal neurons and glia, as well as the human hNT cell line. Adapting this protocol we now illustrate high resolution patterning of the HEK 293 cell line. We explore hypotheses that patterning is mediated by transmembrane integrin interactions with differentially absorbed serum proteins, and also by etching the surface substrate with piranha solution. Using rationalized protein activation solutions in place of serum, we show that cell patterning can be modulated or even inverted. These cell-patterning findings assist our wider goal of engineering and interfacing functional neuronal networks via a silicon semiconductor platform.

Vacuum-assisted cell seeding in a microwell cell culture system

We present a simple method to actively pattern individual cells and groups of cells in a polymer-based microdevice using vacuum-assisted cell seeding. Soft lithography is used to mold polymer microwells with various geometries on top of commercially available porous membranes. Cell suspensions are placed in a vacuum filtration setup to pull culture medium through the microdevice, trapping the cells in the microwells. The process is evaluated by determining the number of cells per microwell for a given cell seeding density and microwell geometry. This method is tested with adherent and nonadherent cells (NIH 3T3 fibroblasts, PANC-1 pancreatic ductal epithelial-like cells, and THP-1 monocytic leukemia cells). These devices could find applications in high-throughput cell screening, cell transport studies, guided formation of cell clusters, and tissue engineering.

Dependence of the community effect of cultured cardiomyocytes on the cell network pattern

To elucidate the role of the community effect in cardiomyocytes, we developed an on-chip single-cell-based culture system with which the dynamics of the change of beat rate and beat rate fluctuation of cultured cardiomyocytes can be measured at the single-cell level before and after the formation of a cell network. We examined the dependence of the community effect on cell network pattern by culturing cardiomyocytes in differently shaped microchambers and investigated the relation between the network pattern and the stability of the beat rate. We found that beat rate fluctuation tends to decrease as cell-community size increases, irrespective of cell network pattern. This indicates that on-chip single-cell-based cardiomyocyte communities might be able to model a heart tissue accurately enough to be used in practical applications such as drug screening.

Patterning the surface cytophobicity of an albumin-physisorbed substrate by electrochemical means

Spatiotemporal control of surface properties under physiological conditions such as those found in culture media is an important technique in fundamental cell biology, tissue engineering, and cell-based bioelectronics. To this end, we have developed a mild, wet cellular micropatterning technique. The principle of the technique is based on the fact that the cell-repellant property of the albumin-coated substrate rapidly switches to cell-adhesive upon exposure to the reactive oxidizing agent, electrochemically generated hypobromous acid. Herein, we report the effect of the hypobromous acid on serum albumin physisorbed on a hydrophobic substrate. It was found that albumin molecules detach from the substrate by application of the oxidizing agent, resulting in exposure of the underlying hydrophobic surface to the liquid phase. The adsorption of extracellular matrix proteins such as fibronectin onto the hydrophobic surface induces cell adhesion and growth.

In Situ Control of Cellular Growth and Migration on Substrates Using Microelectrodes

We describe an electrochemical method to direct the growth and migration of mammalian cells on a substrate during cultivation in situ. Exposing the albumin-coated substrate to an oxidizing agent, hypobromous acid, electrochemically generated at the tip of the scanning microelectrode, locally switched the substrate from cytophobic to cell-adhesive. This transformation generated the formation of cellular micropatterns. Since the concentration of the oxidizing agent required for the surface processing did not cause significant damage to the cell cultures, we were able to direct in situ cellular proliferation and migration by drawing adhesive micropatterns over the preexisting cellular pattern.

Microelectrochemical approach to induce local cell adhesion and growth on substrates

The nature of an albumin-coated substrate that blocks protein adsorption and cell adhesion was rapidly switched to cell-adhesive by exposure to an oxidizing agent such as HBrO. This finding has enabled cellular pattern drawing even on a single-cell level by closely scanning a microelectrode above the substrate and electrochemically producing the agent at the tip of the electrode. The present microelectrochemical cell patterning is applicable even for a previously cell-patterned substrate and for a grooved substrate. These unique technical features will have impacts on a variety of cell-based studies that require the analysis of heterotypic cell-cell interactions and cellular arrangement on an uneven surface such as semiconductor devices.

Pharmacological characterization of micropatterned cardiac myocytes

The cardiac myocytes patterned on a single cell level were prepared by microcontact printing, and the response to chemical stimuli was studied using confocal fluorescent Ca(2+) imaging. The patterned myocytes were found to conjugate by forming gap junction. It was confirmed for the patterned myocytes that gap junction communication was reversibly inhibited by 1-octanol, but activated by caffeine. Localized stimulation with chemicals was also attempted using a microinjection system for the myocyte patterns formed by single cell alignment. This research was carried out with the objective of developing a bioassay system based on a cellular network.

Biology on a chip: microfabrication for studying the behavior of cultured cells

The ability to culture cells in vitro has revolutionized hypothesis testing in basic cell and molecular biology research and has become a standard methodology in drug screening and toxicology assays. However, the traditional cell culture methodology--consisting essentially of the immersion of a large population of cells in a homogeneous fluid medium--has become increasingly limiting, both from a fundamental point of view (cells in vivo are surrounded by complex spatiotemporal microenvironments) and from a practical perspective (scaling up the number of fluid handling steps and cell manipulations for high-throughput studies in vitro is prohibitively expensive). Microfabrication technologies have enabled researchers to design, with micrometer control, the biochemical composition and topology of the substrate, the medium composition, as well as the type of neighboring cells surrounding the microenvironment of the cell. In addition, microtechnology is conceptually well suited for the development of fast, low-cost in vitro systems that allow for high-throughput culturing and analysis of cells under large numbers of conditions. Here we review a variety of applications of microfabrication in cell culture studies, with an emphasis on the biology of various cell types.