The overall goal of this protocol is to enhance axon alignment and myelination of dorsal root ganglion neurons using a static, pre-stretched cell culture system. This method can help answer key question in the nerve tissue engineering field, such as axon alignment and thickness growth. The main advantage of this technique is that this pre-stretched method not only enhances axon alignment but also promotes myelination.
To begin this procedure, pour the mixture of base and curing agent into a tissue culture dish. Keep the gel mixture under vacuum for 20 minutes to remove air bubbles. Then place the gel mixture in the oven at 60 degrees Celsius for overnight curing.
After the PDMS membrane has cured, treat the surface with oxygen plasma in the plasma cleaning and etching system for three minutes. Subsequently, cut a piece of rectangular membrane from the dish. Fix it onto a stretching frame with the oxygen-treated side facing up.
Then place the frame on a stretching stage and evenly stretch it by turning the knob on the stage until it reaches 10%elongation in the longer axis. Next, fix the stretch by tightening the screws on the frame. After that, remove the frame from the stage.
Ensure the membrane surface is dry and free of dust before placing a silicone chamber onto the membrane. Allow the sticky side of the chamber to attach tightly to the membrane. Then sterilize the surface with UV for 10 minutes.
Afterward, add one milliliter of PLL to the PDMS surface in the chamber within six hours of plasma treatment. Next, incubate it for two hours at 37 degrees Celsius prior to seeding the DRG neurons to enhance cell attachment. In this step, prepare the standard grow medium for the DRG neurons.
Prior to isolation, autoclave the isolation equipment and filter reagents. Add five milliliters of isolation buffer into one well of a six-well plate and place the plate on ice. Then prepare 10 milliliters of dissociation medium by adding one milliliter of collagenase A to nine milliliters of 0.05%Trypsin-EDTA.
Filter the solution with a 0.22 micrometer filter and place it on ice. Afterward, sacrifice 10 to 12 five to seven days old SD rats and cut away the skin overlying the spinal cord from the back of each one. Remove any excess tissue around the spine.
Under a surgical magnifier, make the first incision from the neck then make one cut along the spine on both sides with scissors. Detach the spine from the body of the pup and remove excess muscles. Then cut along the long axis of the spine and use tweezers to open the spine completely to extract the spinal cord.
Next, remove the ganglion from the bone pocket. Trim the nerve roots and transfer the ganglia to the ice-cold isolation buffer. Collect approximately 10 to 16 DRGs from both sides.
Repeat the dissection procedure for the rest of the pups. Now, transfer the DRGs with isolation buffer into a sterile 15-milliliter tube. Let the tissue settle to the bottom of the tube and gently remove the isolation buffer on top.
Then add 10 milliliters of dissociation medium into the tube. Incubate the dissected tissues in the dissociation medium in a 37-degree Celsius water bath for one hour while shaking the tube every five to 10 minutes. After the chemical dissociation, centrifuge the ganglia at four degrees Celsius for five minutes.
After five minutes, remove the supernatant, resuspend the pellet in 10 milliliters of standard growth medium and vortex it. Subsequently, centrifuge the dissociated cells once again. Then remove the supernatant, resuspend the pellet in 12 milliliters of standard growth medium and vortex it.
Prior to seeding the cells, remove the PLL solution from the chamber. Rinse the PDMS surface with sterile water and air-dry it. After resuspending the cells, let the suspension sit for one to two minutes to allow the debris to settle to the bottom of the tube.
Next, add 1.5 milliliters of cell suspension into each stretched chamber and incubate it at 37 degrees Celsius with 5%CO2. To eliminate glial cells at one day in vitro, add 10 microliters or 15 microliters of the FDU-U mixture stock solution to each well. After seven hours, replace this medium with fresh standard growth medium and place the pre-stretched culture device in a 37-degree Celsius incubator in 5%CO2.
During the cell culture period, change the medium every two days by replacing half the spent medium with fresh medium. In this procedure, remove the culture medium from the Schwann cells and add five milliliters of 0.05%Trypsin-EDTA into the flask. Incubate the cells at 37 degrees Celsius in 5%CO2 for two to three minutes.
Check the cells under the optical microscope using a 10X objective to see if they lift up from the flask. Then add five milliliters of culture medium to the cells in the flask and mix. Subsequently, add the cell suspension to a 15-milliliter centrifuge tube and centrifuge at 20 degrees Celsius for five minutes.
Then remove the supernatant and resuspend the pellet in seven milliliters of standard DRG growth medium. Following this, transfer 10 microliters of the cell suspension into a 0.5-milliliter microcentrifuge tube. Mix it with 10 microliters of Trypan blue and then count the cell number with a hemocytometer using a 10X objective.
Add the DRG growth medium to dilute the cell suspension to 5, 000 cells per milliliter. Next, remove 0.5 milliliters of the medium from the DRG culture in the stretched chamber and add 0.5 milliliters of Schwann cell suspension to the DRG culture. Culture the cells for one week at 37 degrees Celsius in 5%CO2.
Change the medium every two days by replacing half of the spent medium with fresh standard growth medium. After culturing on the stretched and unstretched surfaces for two weeks, purified Schwann cells were added to the chamber and cultured for another week. Shown here is the beta-III tubulin staining for axons on the stretched surface.
And this is the overlay of beta-III tubulin and P0 staining on the stretched surface, suggesting the Schwann cells are attached to and likely myelinating the axons. This image shows the beta-III tubulin staining for axons on the unstretched surface. And the overlay of beta-III tubulin and P0 staining on the unstretched surface suggests that the Schwann cells are not attached to the axons.
Once mastered, this technique can be done in three to four hours if it is performed properly. While attempting this procedure, it is important to remember to keep the PDMS membrane flat and of homogeneous thickness. Following this procedure, atomizers like pre-stretched microchannels can be performed in order to answer additional questions like axon lens and Schwann cells migration.
After its development, this technique will pave the way for researchers in the field of tissue engineering to explore the role of surface anisotropy on nerve regeneration in spinal cord and sciatic nerve. After watching this video, you should have a good understanding of how to induce axon alignment and myelination using pre-stretched device.
