Multiarray cell stretching platform for high-magnification real-time imaging

Uniaxial Cyclic Cell Stretching Device for Accelerating Cellular Studies

Cellular response to mechanical stimuli is a crucial factor for maintaining cell homeostasis. The interaction between the extracellular matrix and mechanical stress plays a significant role in organizing the cytoskeleton and aligning cells. Tools that apply mechanical forces to cells and tissues, as well as those capable of measuring the mechanical properties of biological cells, have greatly contributed to our understanding of fundamental mechanobiology. These tools have been extensively employed to unveil the substantial influence of mechanical cues on the development and progression of various diseases. In this report, we present an economical and high-performance uniaxial cell stretching device. This paper reports the detailed operation concept of the device, experimental design, and characterization. The device was tested with MDA-MB-231 breast cancer cells. The experimental results agree well with previously documented morphological changes resulting from stretching forces on cancer cells. Remarkably, our new device demonstrates comparable cellular changes within 30 min compared with the previous 2 h stretching duration. This third-generation device significantly improved the stretching capabilities compared with its previous counterparts, resulting in a remarkable reduction in stretching time and a substantial increase in overall efficiency. Moreover, the device design incorporates an open-source software interface, facilitating convenient parameter adjustments such as strain, stretching speed, frequency, and duration. Its versatility enables seamless integration with various optical microscopes, thereby yielding novel insights into the realm of mechanobiology.

An Easy-to-Fabricate Cell Stretcher Reveals Density-Dependent Mechanical Regulation of Collective Cell Movements in Epithelia

Introduction

Mechanical forces regulate many facets of cell and tissue biology. Studying the effects of forces on cells requires real-time observations of single- and multi-cell dynamics in tissue models during controlled external mechanical input. Many of the existing devices used to conduct these studies are costly and complicated to fabricate, which reduces the availability of these devices to many laboratories.

Methods

We show how to fabricate a simple, low-cost, uniaxial stretching device, with readily available materials and instruments that is compatible with high-resolution time-lapse microscopy of adherent cell monolayers. In addition, we show how to construct a pressure controller that induces a repeatable degree of stretch in monolayers, as well as a custom MATLAB code to quantify individual cell strains.

Results

As an application note using this device, we show that uniaxial stretch slows down cellular movements in a mammalian epithelial monolayer in a cell density-dependent manner. We demonstrate that the effect on cell movement involves the relocalization of myosin downstream of Rho-associated protein kinase (ROCK).

Conclusions

This mechanical device provides a platform for broader involvement of engineers and biologists in this important area of cell and tissue biology. We used this device to demonstrate the mechanical regulation of collective cell movements in epithelia.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-021-00689-6.

Latest Updates on the Advancement of Polymer-Based Biomicroelectromechanical Systems for Animal Cell Studies

Biological sciences have reached the fundamental unit of life: the cell. Ever-growing field of Biological Microelectromechanical Systems (BioMEMSs) is providing new frontiers in both fundamental cell research and various practical applications in cell-related studies. Among various functions of BioMEMS devices, some of the most fundamental processes that can be carried out in such platforms include cell sorting, cell separation, cell isolation or trapping, cell pairing, cell-cell communication, cell differentiation, cell identification, and cell culture. In this article, we review each mentioned application in great details highlighting the latest advancements in fabrication strategy, mechanism of operation, and application of these tools. Moreover, the review article covers the shortcomings of each specific application which can open windows of opportunity for improvement of these devices.

Cytostretch, an Organ-on-Chip Platform

Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in situ by electrical and/or mechanical actuators. These actuations can mimic physiological conditions in real tissue and may include fluid or air flow, or cyclic stretch and strain as they occur in the lung and heart. These conditions similarly affect cultured cells and may influence their ability to respond appropriately to physiological or pathological stimuli. To date, most focus has been on devices specifically designed to culture just one functional unit of a specific organ: lung alveoli, kidney nephrons or blood vessels, for example. In contrast, the modular Cytostretch membrane platform described here allows OOCs to be customized to different OOC applications. The platform utilizes silicon-based micro-fabrication techniques that allow low-cost, high-volume manufacturing. We describe the platform concept and its modules developed to date. Membrane variants include membranes with (i) through-membrane pores that allow biological signaling molecules to pass between two different tissue compartments; (ii) a stretchable micro-electrode array for electrical monitoring and stimulation; (iii) micro-patterning to promote cell alignment; and (iv) strain gauges to measure changes in substrate stress. This paper presents the fabrication and the proof of functionality for each module of the Cytostretch membrane. The assessment of each additional module demonstrate that a wide range of OOCs can be achieved.

Farewell to Animal Testing: Innovations on Human Intestinal Microphysiological Systems

The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal disease models have been developed; however, a considerable number of existing models often fail to reproducibly predict human intestinal pathophysiology in response to biological and chemical perturbations or clinical interventions. Intestinal organoid models have provided promising cytodifferentiation and regeneration, but the lack of luminal flow and physical bowel movements seriously hamper mimicking complex host-microbe crosstalk. Here, we discuss recent advances of human intestinal microphysiological systems, such as the biomimetic human "Gut-on-a-Chip" that can employ key intestinal components, such as villus epithelium, gut microbiota, and immune components under peristalsis-like motions and flow, to reconstitute the transmural 3D lumen-capillary tissue interface. By encompassing cutting-edge tools in microfluidics, tissue engineering, and clinical microbiology, gut-on-a-chip has been leveraged not only to recapitulate organ-level intestinal functions, but also emulate the pathophysiology of intestinal disorders, such as chronic inflammation. Finally, we provide potential perspectives of the next generation microphysiological systems as a personalized platform to validate the efficacy, safety, metabolism, and therapeutic responses of new drug compounds in the preclinical stage.

Design, fabrication and characterization of a pure uniaxial microloading system for biologic testing

The field of mechanobiology aims to understand the role the mechanical environment plays in directing cell and tissue development, function and disease. The empirical aspect of the field requires the development of accurate, reproducible and reliable loading platforms that can apply microprecision mechanical load. In this study we designed, fabricated and characterized a pure uniaxial loading platform capable of testing small synthetic and organic specimens along a horizontal axis. The major motivation for platform development was in stimulating bone cells seeded on elastomeric substrates and soft tissue loading. The biological uses required the development of culturing fixtures and environmental chamber. The device utilizes commercial microactuators, load cells and a rail/carriage block system. Following fabrication, acceptable performance was verified by suture tensile testing.

Creased hydrogels as active platforms for mechanical deformation of cultured cells

Cells cultured in vitro using traditional substrates often change their behavior due to the lack of mechanical deformation they would naturally experience in vivo. To mimic the in vivo mechanical environment, we design temperature-responsive hydrogels with patterned surface creases as dynamic cell stretching devices. A one-step photolithographic method is first employed to pattern integrin-binding peptides on the gel, causing single cells or several-cell clusters to adhere to the surface in registry with creases. A variety of crease patterns are prescribed on a single substrate, enabling the mechanical deformation of cultured myoblast cells with different strain states and achieving tensile strain as high as 0.2. As creases provide large amplitude local deformation of the gel surface without the need for macroscopic deformation, can be formed on gels covering a wide range of modulus, and can be actuated using a variety of stimuli, they hold the potential to enable the design of high throughput and versatile platforms for mechano-biological studies.

A polymeric cell stretching device for real-time imaging with optical microscopy

This paper reports the design, fabrication and characterization of a cell stretching device based on the side stretching approach. Numerical simulation using finite element method provides a guideline for optimizing the geometry and maximizing the output strain of the stretched membrane. An unique PDMS-based micro fabrication process was developed for obtaining high parallelization, well controlled membrane thickness and an ultra-thin bottom layer that is crucial for the use with confocal microscopes. The stretching experiments are fully automated with both device actuation and image acquisition. A programmable pneumatic control system was built for simultaneous driving of 24 stretching arrays. The actuation signals are synchronized with the image acquisition system to obtain time-lapse recording of cells grown on the stretched membrane. Experimental results verified the characteristics predicted by the simulation. A platform with 15 stretching units was integrated on a standard 24 mm × 50 mm glass slide. Each unit can achieve a maximum strain of more than 60 %. The platform was tested for cell growth under cyclic stretching. The preliminary results show that the device is compatible with all standard microscopes.

Uniaxial cell stretching device for live-cell imaging of mechanosensitive cellular functions

External mechanical stretch plays an important role in regulating cellular behaviors through intracellular mechanosensitive and mechanotransductive machineries such as the F-actin cytoskeleton (CSK) structures and focal adhesions (FAs) anchoring the F-actin CSK to the extracellular environment. Studying the mechanoresponsive behaviors of the F-actin CSK and FAs in response to cell stretch has great importance for further understanding mechanotransduction and mechanobiology. In this work, we developed a novel cell stretching device combining dynamic directional cell stretch with in situ subcellular live-cell imaging. Using a cam and follower mechanism and applying a standard mathematical model for cam design, we generated different dynamic stretch outputs. By examining stretch-mediated FA dynamics under step-function static stretch and the realignment of cell morphology and the F-actin CSK under cyclic stretch, we demonstrated successful applications of our cell stretching device for mechanobiology studies where external stretch plays an important role in regulating subcellular molecular dynamics and cellular phenotypes.