Biorealistic cardiac cell culture platforms with integrated monitoring of extracellular action potentials

Heart-on-a-chip: a revolutionary organ-on-chip platform for cardiovascular disease modeling

Heart-on-a-chip (HoC) devices have emerged as a powerful tool for studying the human heart's intricate functions and dysfunctions in vitro. Traditional preclinical models, such as 2D cell cultures model and animal model, have limitations in accurately predicting human response to cardiovascular diseases and treatments. The HoC approach addresses these shortcomings by recapitulating the microscale anatomy, physiology, and biomechanics of the heart, thereby providing a more clinically relevant platform for drug testing, disease modeling, and personalized therapy. Recent years have seen significant strides in HoC technology, driven by advancements in biomaterials, bioelectronics, and tissue engineering. Here, we first review the construction and on-chip detection in HoC. Then we introduce the current proceedings of in vitro models for studying cardiovascular diseases (CVD) based on the HoC platform, including ischemia and myocardial infarction, cardiac fibrosis, cardiac scar, myocardial hypertrophy and other CVD models. Finally, we discuss the future directions of HoC and related emerging technologies.

Electrochemical Cell-based Biosensors for Biomedical Applications

Abstract:

Electrochemical cell-based biosensors have been showing increasing interest within the last 15 years, with a large number of reports generally dealing with the sensors’ sensitivity, selectivity, stability, signal-to-noise ratio, spatiotemporal resolution, etc. However, only a few of them are now available as commercial products on the market. In this review, technological advances, current challenges and opportunities of electrochemical cell-based biosensors are presented. The article encompasses emerging studies, mainly focusing on the last five years (from 2016 to mid 2021), towards cell-based biological field-effect devices, cell-based impedimetric sensors and cell-based microelectrode arrays. In addition, special attention lies on recent progress in recording at the single-cellular level, including intracellular monitoring with high spatiotemporal resolution as well as integration into microfluidics for lab-on-a-chip applications. Moreover, a comprehensive discussion on challenges and future perspectives will address the future potential of electrochemical cell-based biosensors.

Biocompatibility Study of a Commercial Printed Circuit Board for Biomedical Applications: Lab-on-PCB for Organotypic Retina Cultures

Printed circuit board (PCB) technology is well known, reliable, and low-cost, and its application to biomedicine, which implies the integration of microfluidics and electronics, has led to Lab-on-PCB. However, the biocompatibility of the involved materials has to be examined if they are in contact with biological elements. In this paper, the solder mask (PSR-2000 CD02G/CA-25 CD01, Taiyo Ink (Suzhou) Co., Ltd., Suzhou, China) of a commercial PCB has been studied for retinal cultures. For this purpose, retinal explants have been cultured over this substrate, both on open and closed systems, with successful results. Cell viability data shows that the solder mask has no cytotoxic effect on the culture allowing the application of PCB as the substrate of customized microelectrode arrays (MEAs). Finally, a comparative study of the biocompatibility of the 3D printer Uniz zSG amber resin has also been carried out.

Biomimetic microsystems for cardiovascular studies

Traditional tissue culture platforms have been around for several decades and have enabled key findings in the cardiovascular field. However, these platforms failed to recreate the mechanical and dynamic features found within the body. Organs-on-chips (OOCs) are cellularized microfluidic-based devices that can mimic the basic structure, function, and responses of organs. These systems have been successfully utilized in disease, development, and drug studies. OOCs are designed to recapitulate the mechanical, electrical, chemical, and structural features of the in vivo microenvironment. Here, we review cardiovascular-themed OOC studies, design considerations, and techniques used to generate these cellularized devices. Furthermore, we will highlight the advantages of OOC models over traditional cell culture vessels, discuss implementation challenges, and provide perspectives on the state of the field.

Multiplexing physical stimulation on single human induced pluripotent stem cell-derived cardiomyocytes for phenotype modulation

Traditional in vitro bioengineering approaches whereby only individual biophysical cues are manipulated at any one time are highly inefficient, falling short when recapitulating the complexity of the cardiac environment. Multiple biophysical cues are present in the native myocardial niche and are essential during development, as well as in maintenance of adult cardiomyocyte (CM) phenotype in both health and disease. This study establishes a novel biofabrication workflow to study and manipulate hiPSC-CMs and to understand how these cells respond to a multiplexed biophysical environment, namely 3D shape and substrate stiffness, at a single cell level. Silicon masters were fabricated and developed to generate inverse patterns of the desired 3D shapes in bas relief, which then were used to mold the designed microwell arrays into a hydrogel. Polyacrylamide (PAAm) was modified with the incorporation of acrylic acid to provide a carboxylic group conjugation site for adhesion motifs, without compromising capacity to modulate stiffness. In this manner, two individual parameters can be finely tuned independently within the hydrogel: the shape of the 3D microwell and its stiffness. The design allows the platform to isolate single hiPSC-CMs to study solely biophysical cues in the absence of cell-cell physical interaction. Under physiologic-like physical conditions (3D shape resembling that of adult CM and 9.83 kPa substrate stiffness that mimics muscle stiffness), isolated single hiPSC-CMs exhibit increased Cx-43 density, cell membrane stiffness and calcium transient amplitude; co-expression of the subpopulation-related MYL2-MYL7 proteins; and higher anisotropism than cells in pathologic-like conditions (flat surface and 112 kPa substrate stiffness). This demonstrates that supplying a physiologic or pathologic microenvironment to an isolated single hiPSC-CM in the absence of any physical cell-to-cell communication in this biofabricated platform leads to a significantly different set of cellular features, thus presenting a differential phenotype. Importantly, this demonstrates the high plasticity of hiPSC-CMs even in isolation. The ability of multiple biophysical cues to significantly influence isolated single hiPSC-CM phenotype and functionality highlights the importance of fine-tuning such cues for specific applications. This has the potential to produce more fit-for-purpose hiPSC-CMs. Further understanding of human cardiac development is enabled by the robust, versatile and reproducible biofabrication techniques applied here. We envision that this system could be easily applied to other tissues and cell types where the influence of cellular shape and stiffness of the surrounding environment is hypothesized to play an important role in physiology.

Engineering anisotropic cardiac monolayers on microelectrode arrays for non-invasive analyses of electrophysiological properties

Engineering cardiac tissues with physiological architectural and mechanical properties on microelectrode arrays enables long term culture and non-invasive collection of electrophysiological readouts.

Microstructured hybrid scaffolds for aligning neonatal rat ventricular myocytes

In cardiac tissue engineering (TE), in vitro models are essential for the study of healthy and pathological heart tissues in order to understand the underpinning mechanisms. In this scenario, scaffolds are platforms that can realistically mimic the natural architecture of the heart, and they add biorealism to in vitro models. This paper reports a novel and robust technique to fabricate cardiovascular-mimetic scaffolds based on Parylene C and Polydimethylsiloxane (PDMS). Parylene C is employed as a mask material for inducing hybrid and non-hybrid micropatterns to the PDMS layer. Hybrid architectures present striped hydrophobic/hydrophilic surfaces, whereas non-hybrid scaffolds only corrugated topographies. Herein, we demonstrate that wavy features on PDMS can be obtained at the micro- and nanoscale and that PDMS can be integrated into the microfabrication process without changing its intrinsic physical properties. A study of the effects of these scaffolds on the growth of Neonatal Rat Ventricular Myocytes (NRVMs) cultures reveals that cell alignment occurs only for the case of hybrid architectures made of hydrophilic PDMS and hydrophobic Parylene C.

Cell-based biosensors: Recent trends, challenges and future perspectives

Existing at the interface of biology and electronics, living cells have been in use as biorecognition elements (bioreceptors) in biosensors since the early 1970s. They are an interesting choice of bioreceptors as they allow flexibility in determining the sensing strategy, are cheaper than purified enzymes and antibodies and make the fabrication relatively simple and cost-effective. And with advances in the field of synthetic biology, microfluidics and lithography, many exciting developments have been made in the design of cell-based biosensors in the last about five years. 3D cell culture systems integrated with electrodes are now providing new insights into disease pathogenesis and physiology, while cardiomyocyte-integrated microelectrode array (MEA) technology is set to be standardized for the assessment of drug-induced cardiac toxicity. From cell microarrays for high-throughput applications to plasmonic devices for anti-microbial susceptibility testing and advent of microbial fuel cell biosensors, cell-based biosensors have evolved from being mere tools for detection of specific analytes to multi-parametric devices for real time monitoring and assessment. However, despite these advancements, challenges such as regeneration and storage life, heterogeneity in cell populations, high interference and high costs due to accessory instrumentation need to be addressed before the full potential of cell-based biosensors can be realized at a larger scale. This review summarizes results of the studies that have been conducted in the last five years toward the fabrication of cell-based biosensors for different applications with a comprehensive discussion on the challenges, future trends, and potential inputs needed for improving them.

Effect of patterned polyacrylamide hydrogel on morphology and orientation of cultured NRVMs

We recently demonstrated that patterned Parylene C films could be effectively used as a mask for directly copolymerizing proteins on polyacrylamide hydrogel (PAm). In this work, we have proved the applicability of this technique for studying the effect such platforms render on neonatal rat ventricular myocytes (NRVMs). Firstly, we have characterised topographically and mechanically the scaffolds in liquid at the nano-scale level. We thus establish that such platforms have physical properties that closely mimics the in vivo extracellular environment of cells. We have then studied the cell morphology and physiology by comparing cultures on flat uniformly-covered and collagen-patterned scaffolds. We show that micro-patterns promote the elongation of cells along the principal axis of the ridges coated with collagen. In several cases, cells also tend to create bridges across the grooves. We have finally studied cell contraction, monitoring Ca²⁺ cycling at a certain stimulation. Cells seeded on patterned scaffolds present significant responses in comparison to the isotropic ones.

SF₆ Optimized O₂ Plasma Etching of Parylene C

Parylene C is a widely used polymer material in microfabrication because of its excellent properties such as chemical inertness, biocompatibility and flexibility. It has been commonly adopted as a structural material for a variety of microfluidics and bio-MEMS (micro-electro-mechanical system) applications. However, it is still difficult to achieve a controllable Parylene C pattern, especially on film thicker than a couple of micrometers. Here, we proposed an SF₆ optimized O₂ plasma etching (SOOE) of Parylene C, with titanium as the etching mask. Without the SF₆, noticeable nanoforest residuals were found on the O₂ plasma etched Parylene C film, which was supposed to arise from the micro-masking effect of the sputtered titanium metal mask. By introducing a 5-sccm SF₆ flow, the residuals were effectively removed during the O₂ plasma etching. This optimized etching strategy achieved a 10 μm-thick Parylene C etching with the feature size down to 2 μm. The advanced SOOE recipes will further facilitate the controllable fabrication of Parylene C microstructures for broader applications.

Microcontact printing of polydopamine on thermally expandable hydrogels for controlled cell adhesion and delivery of geometrically defined microtissues

Scaffold-free harvest of microtissue with a defined structure has received a great deal of interest in cell-based assay and regenerative medicine. In this study, we developed thermally expandable hydrogels with spatially controlled cell adhesive patterns for rapid harvest of geometrically controlled microtissue. We patterned polydopamine (PD) on to the hydrogel via microcontact printing (μCP), in linear shapes with widths of 50, 100 and 200μm. The hydrogels facilitated formation of spatially controlled strip-like microtissue of human dermal fibroblasts (HDFBs). It was possible to harvest and translocate microtissues with controlled widths of 61.4±14.7, 104.3±15.6, and 186.6±22.3μm from the hydrogel to glass substrates by conformal contact upon expansion of the hydrogel in response to a temperature change from 37 to 4°C, preserving high viability, extracellular matrix, and junction proteins. Microtissues were readily translocated in vivo to the subcutaneous tissue of mouse. The microtissues were further utilized as a simple assay model for monitoring of contraction in response to ROCK1 inhibitor. Collectively, micro-sized patterning of PD on the thermally expandable hydrogels via μCP holds promise for the development of microtissue harvesting systems that can be employed to ex vivo tissue assay and cell-based therapy.

STATEMENT OF SIGNIFICANCE

Harvest of artificial tissue with controlled cellular arrangement independently from external materials has been widely studied in cell-based assay and regenerative medicine. In this study, we developed scaffold-free harvest system of microtissues with anisotropic arrangement and controlled width by exploiting thermally expandable hydrogels with cell-adhesive patterns of polydopamine formed by simple microcontact printing. Cultured strips of human dermal fibroblasts on the hydrogels were rapidly delivered to various targets ranging from flat coverglass to mice subcutaneous tissue by thermal expansion of the hydrogel at 4°C for 10min. These were further utilized as a drug screening model responding to ROCK1 inhibitor, which imply its versatile applicability.

Regulation of the microenvironment for cardiac tissue engineering

The microenvironment of myocardium plays an important role in the fate and function of cardiomyocytes (CMs). Cardiovascular tissue engineering strategies commonly utilize stem cell sources in conjunction with microenvironmental cues that often include biochemical, electrical, spatial and biomechanical factors. Microenvironmental stimulation of CMs, in addition to the incorporation of intercellular interactions from non-CMs, results in the generation of engineered cardiac constructs. Current studies suggest that use of these factors when engineering cardiac constructs improve cardiac function when implanted in vivo. In this review, we summarize the approaches to modulate biochemical, electrical, biomechanical and spatial factors to induce CM differentiation and their subsequent organization for cardiac tissue engineering application.

On-chip, multisite extracellular and intracellular recordings from primary cultured skeletal myotubes

In contrast to the extensive use of microelectrode array (MEA) technology in electrophysiological studies of cultured neurons and cardiac muscles, the vast field of skeletal muscle research has yet to adopt the technology. Here we demonstrate an empowering MEA technology for high quality, multisite, long-term electrophysiological recordings from cultured skeletal myotubes. Individual rat skeletal myotubes cultured on micrometer sized gold mushroom-shaped microelectrode (gMμE) based MEA tightly engulf the gMμEs, forming a high seal resistance between the myotubes and the gMμEs. As a consequence, spontaneous action potentials generated by the contracting myotubes are recorded as extracellular field potentials with amplitudes of up to 10 mV for over 14 days. Application of a 10 ms, 0.5-0.9 V voltage pulse through the gMμEs electroporated the myotube membrane, and transiently converted the extracellular to intracellular recording mode for 10-30 min. In a fraction of the cultures stable attenuated intracellular recordings were spontaneously produced. In these cases or after electroporation, subthreshold spontaneous potentials were also recorded. The introduction of the gMμE-MEA as a simple-to-use, high-quality electrophysiological tool together with the progress made in the use of cultured human myotubes opens up new venues for basic and clinical skeletal muscle research, preclinical drug screening, and personalized medicine.

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.