P18081: Mechanical Bioreactor
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Exhibit Description

How does flexing affect the cells in your body? Our device, which repeatedly stretches cells, shows how movement causes cells to behave differently and provides a dynamic environment closer to conditions in the body.

Why do we flex cells?

In biology, the cell is commonly defined as the smallest building block making up all living things. There are trillions of cells in our bodies, each performing specific "jobs" to sustain life. So, how do these cells know how and when to act? Our bodies communicate with our cells by utilizing varied stimuli (mechanical, chemical, electrical, etc.) that help to inform our cells how to "behave". Essentially the environment in which the cells develop determine what type of cells they will become and how they will function. With our device, we want to see how the mechanical cues of strain affect the cells' performance in culture.

How do we accomplish this?

In order to flex cells in culture, the team had to develop a device that was both "biofriendly" and had the capacity to deliver externally supplied strain to the cells.

Sterile "Biofriendly" Environment

In order for the device to be considered "biofriendly", it had to maintain a sterile environment of 37oC, 100% humidity, 5% CO2, and pH 7.4. To do this, the team decided to design the bioreactor to be placed inside of a standard lab incubator (which will externally regulate these parameters).

Strain Application

In order to apply strain to the cells, it was decided that a flexible cell chamber (where the cells are growing!) would be repeatably stretched by an external force. Polymethylsiloxane (PDMS) was selected to make the flexible chamber. PDMS is a custom-moldable, flexible substrate that is clear to allow viewing of the cells with a microscope. The PDMS is molded by mixing an elastomer and curing agent and pouring into a mold. Both elastomer and curing agent start as gels, mixing them together activates cross-linking and solidifies the substrate.This chamber is where cell culture will take place! Cells will attach to the bottom of the chamber and experience any strain/stress applied to the chamber.
Figure 1: Outline of the PDMS molding process. You will notice the translucent properties of PDMS in the final chamber. This property is one of the main factors for choosing PDMS as a substrate; we can see through it, and therefore easily image our cells.

Figure 1: Outline of the PDMS molding process. You will notice the translucent properties of PDMS in the final chamber. This property is one of the main factors for choosing PDMS as a substrate; we can see through it, and therefore easily image our cells.

A hole-and-peg system was selected to attach the PDMS cell chamber to the mechanical strain apparatus. The key strength of this system is ease of assembly, portability, and analysis for the student.

Figure 2: This is the SolidWorks CAD Model design for the hole and peg set up. There are a total of four pegs in the system; two stationary pins fixed to the base of the device, and two pins attached to the actuating arm that will cyclically strain (pull) the mold. The PDMS chamber contains 4 hollow channels for the pegs to attach.

Figure 2: This is the SolidWorks CAD Model design for the hole and peg set up. There are a total of four pegs in the system; two stationary pins fixed to the base of the device, and two pins attached to the actuating arm that will cyclically strain (pull) the mold. The PDMS chamber contains 4 hollow channels for the pegs to attach.

The chamber will stretch utilizing a ServoCity Linear Actuator. The actuator will pull on one side of the chamber, while the other side of the chamber remains anchored to a stationary plate. This action will strain the chamber, and since the cells are attached to the bottom of this chamber, they will also experience this strain. This actuator will continuously move in and out, to apply cyclic strain. A program has been set-up to control frequency and displacement of the actuator motion; as well as, control the duration of cyclic strain application. Over time, cells put under mechanical strain will change from random orientation to perpendicular orientation.

What does a flexed cell look like?

Unfortunately, due to time delays and cell attachment issues, no images have been captured to show realignment of cells with our system. However, several scholarly articles have established that when put under cyclic mechanical strain, adherent cells are known to change structure and orientation by modifying their focal adhesions (their method of attaching and interacting with the substrate) [1]. Goldyn et al. found that cells put under mechanical stress changed from random orientation to perpendicular orientation [2].
Figure 3: Cell orientation change from random to perpendicular to mechanical strain over a course of eight hours.Goldyn et al.

Figure 3: Cell orientation change from random to perpendicular to mechanical strain over a course of eight hours.Goldyn et al.

[1] Vining, Kyle H., and David J. Mooney. “Mechanical Forces Direct Stem Cell Behaviour in Development and Regeneration.” Nature Reviews Molecular Cell Biology, vol. 18, no. 12, 2017, pp.728–742., doi:10.1038/nrm.2017.108.

[2] Goldyn, A. M., et al. “Force-Induced Cell Polarisation Is Linked to RhoA-Driven MicrotubuleIndependent Focal-Adhesion Sliding.” Journal of Cell Science, vol. 122, no. 20, 2009, pp. 3644–3651.,doi:10.1242/jcs.054866.

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