Pneumatically actuated cell-stretching array platform for engineering cell patterns in vitro

Development of Cell Culture Platforms for Study of Trabecular Meshwork Cells and Glaucoma Development

BACKGROUND

Various cell culture platforms that could display native environmental cue-mimicking stimuli were developed, and effects of environmental cues on cell behaviors were studied with the cell culture platforms. Likewise, various cell culture platforms mimicking native trabecular meshwork (TM) composed of juxtacanalicular, corneoscleral and uveal meshwork located in internal scleral sulcus were used to study effects of environmental cues and/or drug treatments on TM cells and glaucoma development. Glaucoma is a disease that could cause blindness, and cause of glaucoma is not clearly identified yet. It appears that aqueous humor (AH) outflow resistance increased by damages on pathway of AH outflow can elevate intraocular pressure (IOP). These overall possibly contribute to development of glaucoma.

METHODS

For the study of glaucoma, static and dynamic cell culture platforms were developed. Particularly, the dynamic platforms exploiting AH outflow-mimicking perfusion or increased IOP-mimicking increased pressure were used to study how perfusion or increased pressure could affect TM cells. Overall, potential mechanisms of glaucoma development, TM structures and compositions, TM cell culture platform types and researches on TM cells and glaucoma development with the platforms were described in this review.

RESULTS AND CONCLUSION

This will be useful to improve researches on TM cells and develop enhanced therapies targeting glaucoma.

Advanced Robotics to Address the Translational Gap in Tendon Engineering

Tendon disease is a significant and growing burden to healthcare systems. One strategy to address this challenge is tissue engineering. A widely held view in this field is that mechanical stimulation provided to constructs should replicate the mechanical environment of native tissue as closely as possible. We review recent tendon tissue engineering studies in this article and highlight limitations of conventional uniaxial tensile bioreactors used in current literature. Advanced robotic platforms such as musculoskeletal humanoid robots and soft robotic actuators are promising technologies which may help address translational gaps in tendon tissue engineering. We suggest the proposed benefits of these technologies and identify recent studies which have worked to implement these technologies in tissue engineering. Lastly, key challenges to address in adapting these robotic technologies and proposed future research directions for tendon tissue engineering are discussed.

Pneumatic Cell Stretching Chip to Generate Uniaxial Strain Using an Elastomeric Membrane with Ridge Structure

Cyclic mechanical stretching, including uniaxial strain, has been manifested to regulate the cell morphology and functions directly. In recent years, many techniques have been developed to apply cyclic mechanical stretching to cells in vitro. Pneumatically actuated stretching is one of the extensively used methods owing to its advantages of integration, miniaturization, and long-term stretching. However, the intrinsic difficulty in fabrication and adjusting the strain mode also impedes its development and application. In this study, inspired by the topological defects principle, we incorporated a ridge structure into the membrane surface of a traditional pneumatic cavity stretching chip to regulate the strain mode. Our results showed that the surface ridge structure can directly change the equiaxial stretching mode to the standard uniaxial strain, and it is ridge width-independent. The uniaxial strain mode was further proved by the cell orientation behavior under cyclic stretching stimulation. Moreover, it is easy to realize the multimodal strain fields by controlling the width and height of the ridge and to achieve high-throughput testing by creating a cavity array using microfabrication. Together, we propose a smart method to change the surface strain field and introduce a simple, yet effective, high-throughput pneumatically actuated uniaxial stretching platform, which can not only realize the multimodal mechanical stimulation but also achieve multiscale mechanosensing behaviors of single-cell or multi-cell (tissue and/or organoid) mechanobiology applications.

Studying the Mechanobiology of Aortic Endothelial Cells Under Cyclic Stretch Using a Modular 3D Printed System

Here, we describe a motorized cam-driven system for the cyclic stretch of aortic endothelial cells. Our modular design allows for generating customized spatiotemporal stretch profiles by varying the profile and size of 3D printed cam and follower elements. The system is controllable, compact, inexpensive, and amenable for parallelization and long-term experiments. Experiments using human aortic endothelial cells show significant changes in the cytoskeletal structure and morphology of cells following exposure to 5 and 10% cyclic stretch over 9 and 16 h. The system provides upportunities for exploring the complex molecular and cellular processes governing the response of mechanosensitive cells under cyclic stretch.

Brick Strex: a robust device built of LEGO bricks for mechanical manipulation of cells

Cellular forces, mechanics and other physical factors are important co-regulators of normal cell and tissue physiology. These cues are often misregulated in diseases such as cancer, where altered tissue mechanics contribute to the disease progression. Furthermore, intercellular tensile and compressive force-related signaling is highlighted in collective cell behavior during development. However, the mechanistic understanding on the role of physical forces in regulation of cellular physiology, including gene expression and signaling, is still lacking. This is partly because studies on the molecular mechanisms of force transmission require easily controllable experimental designs. These approaches should enable both easy mechanical manipulation of cells and, importantly, readouts ranging from microscopy imaging to biochemical assays. To achieve a robust solution for mechanical manipulation of cells, we developed devices built of LEGO bricks allowing manual, motorized and/or cyclic cell stretching and compression studies. By using these devices, we show that [Formula: see text]-catenin responds differentially to epithelial monolayer stretching and lateral compression, either localizing more to the cell nuclei or cell-cell junctions, respectively. In addition, we show that epithelial compression drives cytoplasmic retention and phosphorylation of transcription coregulator YAP1. We provide a complete part listing and video assembly instructions, allowing other researchers to build and use the devices in cellular mechanics-related studies.

Mechanotransduction assays for neural regeneration strategies: A focus on glial cells

Glial cells are mechanosensitive, and thus, engineered systems have taken a step forward to design mechanotransduction platforms in order to impart diverse mechanical stresses to cells. Mechanical strain encountered in the central nervous system can arise from diverse mechanisms, such as tissue reorganization, fluid flow, and axon growth, as well as pathological events including axon swelling or mechanical trauma. Biomechanical relevance of the in vitro mechanical testing requires to be placed in line with the physiological and mechanical changes in central nervous tissues that occur during the progression of neurodegenerative diseases. Mechanotransduction signaling utilized by glial cells and the recent approaches intended to model altered microenvironment adapted to pathological context are discussed in this review. New insights in systems merging substrate's stiffness and topography should be considered for further glial mechanotransduction studies, while testing platforms for drug discoveries promise great advancements in pharmacotherapy. Potential leads and strategies for clinical outcomes are expected to be developed following the exploration of these glial mechanosensitive signaling pathways.

A microdevice platform for characterizing the effect of mechanical strain magnitudes on the maturation of iPSC-Cardiomyocytes

The use of human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) as an in vitro model of the heart is limited by their structurally and functionally immature phenotypes. During heart development, mechanical stimuli from in vivo microenvironments are known to regulate cardiomyocyte gene expression and maturation. Accordingly, protocols for culturing iPSC-CMs have recently incorporated mechanical or electromechanical stimulation to induce cellular maturation in vitro; however, the response of iPSC-CMs to different mechanical strain magnitudes is unknown, and existing techniques lack the capability to dynamically measure changes to iPSC-CM contractility in situ as maturation progresses. We developed a microdevice platform which applies cyclical strains of varying magnitudes (5%, 10%, 15% and 20%) to a monolayer of iPSC-CMs, coincidentally measuring contractile stress during mechanical stimulation using fluorescent nanobeads embedded in the microdevice's suspended membrane. Cyclic strain was found to induce circumferential cell alignment on the actuated membranes. In situ contractility measurements revealed that cyclic stimulation gradually increased cardiomyocyte contractility during a 10-day culture period. The contractile stress of iPSC-CM monolayers was found to increase with a higher strain magnitude and plateaued at 15% strain. Cardiomyocyte contractility positively correlated with the elongation of sarcomeres and an increased expression of β-myosin heavy chain (MYH7) in a strain magnitude-dependent manner, illustrating how mechanical stress can be optimized for the phenotypic and proteomic maturation of the cells. iPSC-CMs with improved maturity have the potential to create a more accurate heart model in vitro for applications in disease modeling and therapeutic discovery.

Pneumatic unidirectional cell stretching device for mechanobiological studies of cardiomyocytes

In this paper, we present a transparent mechanical stimulation device capable of uniaxial stimulation, which is compatible with standard bioanalytical methods used in cellular mechanobiology. We validate the functionality of the uniaxial stimulation system using human-induced pluripotent stem cells-derived cardiomyocytes (hiPSC-CMs). The pneumatically controlled device is fabricated from polydimethylsiloxane (PDMS) and provides uniaxial strain and superior optical performance compatible with standard inverted microscopy techniques used for bioanalytics (e.g., fluorescence microscopy and calcium imaging). Therefore, it allows for a continuous investigation of the cell state during stretching experiments. The paper introduces design and fabrication of the device, characterizes the mechanical performance of the device and demonstrates the compatibility with standard bioanalytical analysis tools. Imaging modalities, such as high-resolution live cell phase contrast imaging and video recordings, fluorescent imaging and calcium imaging are possible to perform in the device. Utilizing the different imaging modalities and proposed stretching device, we demonstrate the capability of the device for extensive further studies of hiPSC-CMs. We also demonstrate that sarcomere structures of hiPSC-CMs organize and orient perpendicular to uniaxial strain axis and thus express more maturated nature of cardiomyocytes.

Integrated elastomer-based device for measuring the mechanics of adherent cell monolayers

Cells in the body collectively sustain mechanical deformations in almost all physiological functions. From the morphogenesis stage, cells' ability to sustain stress is essential for the body's well-being. Several pathologies have been associated with abnormal mechanical properties, thus suggesting the Young's modulus as a biomarker to diagnose diseases and determine their progression. Advancements in the field are quite slow because current techniques for measuring cell and tissue mechanics rely on complex and bulky measurement platforms that have low repeatability rates and limited measurement time-scales. We present the first miniaturized system that allows accurate quantification of the Young's modulus of adherent cell monolayers over a longer time (1-2 days). Our approach is based on tensile testing and optical read-out. Thanks to a thoughtful design and material choice, we are able to miniaturize tensile testing platforms into a 1 cm × 2 cm device. We provide highly repeatable Young's modulus measurements in the relevant range between 3 kPa and 300 kPa, over time and under physiological conditions, thus representing an interesting alternative to existing measurement platforms. Furthermore, the compatibility with standard biological equipment, continuous optical imaging and measurements on all types of adherent cells make this device highly versatile. Measurements on human sarcoma osteogenic (SaOS2) and Madin-Darby canine kidney cells (MDCK) are reported. The demonstrated capability to measure real-time changes in mechanical properties, such as after chemical treatment, opens the door for investigating the effects of drugs on cell mechanics.

Self-Renewal and Differentiation of Adipose-Derived Stem Cells (ADSCs) Stimulated by Multi-Axial Tensile Strain in a Pneumatic Microdevice

Adipose-derived stem cells (ADSCs) were suggested for treating degenerative osteoarthritis, suppressing inflammatory responses, and repairing damaged soft tissues. Moreover, the ADSCs have the potential to undergo self-renewal and differentiate into bone, tendon, cartilage, and ligament. Recently, investigation of the self-renewal and differentiation of the ADSCs has become an attractive area. In this work, a pneumatic microdevice has been developed to study the gene expression of the ADSCs after the stimulation of multi-axial tensile strain. The ADSCs were cultured on the microdevice and experienced multi-axial tensile strain during a three-day culture course. Self-renewal and differentiation abilities were investigated by mRNA expressions of NANOG, sex determining region Y-box 2 (SOX2), octamer-binding transcription factor 4 (OCT4), sex determining region Y-box9 (SOX9), peroxisome proliferator-activated receptor gamma (PPAR-γ), and runt-related transcription factor 2 (RUNX2). The result showed that the genes related self-renewal were significantly up-regulated after the tensile stimulation. Higher proliferation ratio of the ADSCs was also shown by cell viability assay. The microdevice provides a promising platform for cell-based study under mechanical tensile stimulation.