Cell Nanomechanics Based on Dielectric Elastomer Actuator Device

Abstract

As a frontier of biology, mechanobiology plays an important role in tissue and biomedical engineering. It is a common sense that mechanical cues under extracellular microenvironment affect a lot in regulating the behaviors of cells such as proliferation and gene expression, etc. In such an interdisciplinary field, engineering methods like the pneumatic and motor-driven devices have been employed for years. Nevertheless, such techniques usually rely on complex structures, which cost much but not so easy to control. Dielectric elastomer actuators (DEAs) are well known as a kind of soft actuation technology, and their research prospect in biomechanical field is gradually concerned due to their properties just like large deformation (> 100%) and fast response (< 1 ms). In addition, DEAs are usually optically transparent and can be fabricated into small volume, which make them easy to cooperate with regular microscope to realize real-time dynamic imaging of cells. This paper first reviews the basic components, principle, and evaluation of DEAs and then overview some corresponding applications of DEAs for cellular mechanobiology research. We also provide a comparison between DEA-based bioreactors and current custom-built devices and share some opinions about their potential applications in the future according to widely reported results via other methods.

Keywords: Bioreactor; Dielectric elastomer actuator; Mechanical stimulus; Mechanobiology.

Fig. 1

The techniques for creating carbon-based compliant electrodes. a Shadow masking: using a shadow mask to selectively spray the carbon material on target area and then removing the mask to get the final electrodes. b Stamping process: using patterned elastomeric stamp to pick up the carbon material and stamping it on the DEM. Redrawn from Ref. [56] with permission. c Printing: the carbon-based materials can be made into conductive ink; then using printing technology to pattern electrodes. Adapted from Ref. [51] with permission. d Laser ablation: the thick PDMS–carbon composite layers can be patterned by laser ablation and bonded to PDMS membrane by oxygen plasma activation. Adapted from Ref. [58] with permission

Fig. 2

a The schematic picture of FCVA. Adapted from Ref. [59] with permission. A high-voltage (600 V) impulsion initiates the main arc from the cathode, the filter helps to trap the macroparticles and the negatively substrate holder accelerates the positive ions through the plasma sheath. b The schematic of SCB progress. Adapted from Ref. [63] with permission. The Au NPs nanoparticles generated from the cluster source is accelerated by a carrier gas in a supersonic expansion and then focused by aerodynamic lens. The cluster beam can be injected into the deposition chamber and impacted on the surface of a thermo-retractable polystyrene (PS) sheet. c The product of FCVA. Adapted from Ref. [47] with permission. d TEM image of the product of SCB. Adapted form Ref. [63] with permission

Fig. 3

The working principle of dielectric elastomer actuators (DEAs) and the classical DEAs for cellular mechanical stimulus. Adapted from Ref. [71] with permission. a The device consists of a soft dielectric elastomer sandwiched between compliant electrodes on both top and bottom sides; the actuator keeps static without voltage applied, and b the device is motivated when the voltage is applied. Similarly, for cellular mechanical loading, the DEA c keeps the original state without HV applied and d deforms underactuated and then generates two regions as tensile strain area and compressive area

Fig. 4

Example of characterizing DEA system via DIC. The white rectangle is region of interest (ROI) set. Strain distribution of both compressive and tensile mode can be obtained through DIC. Adapted from Ref. [78] with permission

Fig. 5

The schematic of DEA designed for single-cell mechanical stretching. a, b The micro-actuator arrays are designed for single cell; each intersection of vertical lines and horizontal lines forms an individual actuator, where cells can be stretched. Adapted from Ref. [47] with permission; c top view of a small part (four micro-actuators contained) obtained by microscope; the membrane is pre-stretched along y-axis. The bright lines aligned vertically are the ion-implanted electrodes on the top side of PDMS membrane, while the dark lines aligned horizontally are the bottom electrodes. Adapted from Ref. [46] with permission. d Micrograph of one actuator. Adapted from Ref. [84] with permission

Fig. 6

The DEA devices for cellular stimulations. Uniaxial compression was proposed by Alexandre et al. in 2014, which harnesses stress in passive region of the DEA and stimulates the cells on top of the region. Adapted from Ref. [71] with permission. In 2016, they fabricated the DEA for uniaxial stretching of cells, and LECs were used to test the device. Adapted from Ref. [44] with permission. Poulin et al. proposed the active cell culture substrate which can produce complex strain patterns with extremely high-strain rates in 2018. Adapted from Ref. [78] with permission. In 2019, more advanced DEA-based bioreactor providing mechanoelectrical coupling stimulus is proposed. Adapted from Ref. [85] with permission

Fig. 7

a Schematic representation of the measure system proposed by Araromi et al. in 2015: The 24-well cell culture supports are equipped with integrated strain and force measurement sensors that are based on DEA. Besides, the electrical read-out allows for high-throughput parallel measurement in real time. Adapted from Ref. [91] with permission. b Optimization of the DEA-based sensors. Parameters such as R, θ, A, and B are used to model the system. Adapted from Ref. [92] with permission

Fig. 8

Schematic of typical pneumatic, motor-driven, and the DEA-based device. a Side view of classic pneumatic cell stretching devices. An air chamber is formed by combining the membrane, holder, and loading post. Pumping air from the chamber can generate pressure difference that leads to absorption of membrane and stretch the cells. b Side view of motor-driven stretching devices. The membrane with seeded cells is matched with two holders: One is movable, while the other is fixed. The movable holder connects with motor through driven components (gears, track, etc.). Once control signal input to the motor, generated motion drags the holder, causing stretching strain as consequence. c Side and top views of DEA-based cell stretcher. The DEA is sandwiched by biocompatible membrane and then fixed by rigid frame

Fig. 9

Real-time monitor system through DEA devices. a Schematic of the whole system with DEA-based cellular stretcher and inverted microscope. The DEA is motivated and controlled by the high-voltage source, a mini incubator is used to provide the standard environment for living cells (lymphatic endothelial cells (LECs) used), and the microscope is used to monitor the cells. Adapted from Ref. [44] with permission. b Imaging of lung cells A549 during stretching: The DNA and mitochondria are stained as blue and green, respectively. Top picture shows displacement track of the intracellular content of A549 at ×40 magnification; the arrows with different colors and lengths refer to different degrees of displacements. Bottom picture shows the nucleus track of A549, ε_x = 0.12 along the stretch orientation measured through this method, and a line is found to fit the nuclei displacement perfectly. Adapted from Ref. [78] with permission

Fig. 10

Reorientation of the cells. a Cells (REF-52 fibroblast) with random orientations before stretching. b Reorientation after stretching. c The description of strain reference on a polarized cell. Adapted from Ref. [8] with permission

Fig. 11

Effect of membrane tension differences on cellular endocytosis. a Jasplakinolide treatment increases pit lifetime and percentage of arrested pits of stretched cells, adapted from Ref. [104] with permission. b Stretching regulates F-Dex uptake, adapted from Ref. [105] with permission