Applying Mechanical Load to Cells in 3D Culture

Introduction
Tension System
Compression System
Equipment, Devices, & Consumables

 

Introduction
Formation of tissues in vitro that are structurally and functionally viable requires several basic conditions, such as 1) cells 2) matrix 3) media and growth factors and 4) mechanical stimulation. These conditions are linked to each other and act in conjunction to form a structurally robust tissue that can withstand biomechanical forces. As a tissue develops, its cells fabricate an extracellular matrix in a given geometry according to developmental pathway cues. Several signal transduction pathways may be involved in generating the composition of the extracellular matrix. Some of these pathways are regulated by mechanical deformation of cell matrix and transmitted into the cell via membrane bound proteins such as integrins, focal adhesion complexes (mechanosensory complex), cell adhesion molecules and ion channels. Cells can also respond to ligands, such as cytokines, hormones or growth factors that are released as a result of matrix deformation.

In order to maintain the integrity and strength of musculoskeletal tissues, the cells may require maintaining a certain level of intrinsic strain. In the absence of this intrinsic strain, the tissue will lose its strength leading to failures or fractures. It is well accepted that immobilization of limbs, bed rest or a reduction in the intrinsic strain level in a tissue leads to bone mineral loss, tissue atrophy, weakness and in general, a reduction in anabolic activity and an increase in catabolic activity. Physical activity, on the other hand, results in anabolic effects including an increase in biomechanical strength and an increase in the intrinsic strain in a tissue.

To generate a tissue in vitro that is more or less equivalent to the native tissues, it is of utmost importance to create an environment that would mimic the in vivo conditions. Culturing cells in a mechanically active environment increases cell metabolism and alters cell shape and other properties. Therefore, it is vital to create and maintain a mechanically active environment (i.e., tension, shear stress or compression) for the cells during the formation of tissues in vitro. In addition to the dynamic environment, culturing cells in 3D environment more closely simulates the native environment than a static 2D culture method.
 

Tension System
Three-dimensional bioartificial tissues (BAT), which have been created with the Tissue Train® Culture System, can be mechanically loaded with the FX-6000™ Tension System. This system is a patented, computerized, pressure-operated instrument that applies a defined controlled, static or variable duration cyclic tension, to cells growing in vitro. This system utilizes regulated vacuum pressure to deform flexible-bottomed culture plates. When used with Tissue Train® culture plates and an Arctangle® loading post, this system can apply up to 20% uniaxial strain to a BAT (Figure 1).


Uniaxial Strain
Figure 1. Uniaxial strain application to a bioartificial tissue construct.

View video Tissue Train® Trapezoidal Construct under Tension with Corresponding Finite Element Strain Values

The StageFlexer® Jr. is designed to allow users to remove a membrane from a Tissue Train® culture plate well and continue observing cellular responses to strain under a microscope in real-time. Strain can be controlled with the FX-6000™ Tension System or the Flex Jr.™ Tension System.
 

Compression System
The FX-5000™ Compression System is a patented, computerized, pressure-operated instrument that applies a defined controlled, static or variable duration cyclic compression, to cells growing in vitro. This system utilizes regulated air pressure to deflect the flexible-bottomed BioPress™ culture plates. A tissue sample or a 3D cell culture is compressed between a piston (attached to the flexible-bottomed membrane) and a stationary platen (Figure 2). This system can apply an unconfined compressed of up to 14 pounds of applied force.

Compression Schematic
Figure 2. Schemcatic of how compression is applied to tissue samples in a BioPress™ well.


The StagePresser™ is designed to compress a single tissue sample or cells in a gel while viewing the cellular activity under a microscope. The StagePresser™ uses a piston adhered to a rubber membrane to apply force to a sample in culture. The piston is moved upward by positive air pressure applied to the silicone membrane. A FX-5000™ Compression System controls the compression frequency, amplitude, waveform, and cycles (or time period).
 

Equipment, Devices, & Consumables

 

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