Controlled Syringe Pump Extrusion to Create Hydrogel Gradients

The primary objective of this project is to build upon my previous research where I developed a method to create hydrogel gradients. Hydrogels are comprised of polymer(s) suspended in water. A gradient is the change from one concentration of to another. I used 10% gelatin weight ratio to deionized water mixed with dye. The gelatin was heated and stirred until dissolved and then was split into two portions and dyed two different colors and then placed into syringes while at around 45 degrees. By using a specialized nozzle, I could feed two syringes into one nozzle that has a static mixer at the tip to ensure the gelatin was evenly mixed. Gelatin is a liquid at higher temps (40-50 degrees C) and sets at lower temperatures so the gradients were extruded on a chilled metal plate so the gelatin would set almost immediately. Depending on how fast one syringe extruded versus the other I could change the color and even mix them. After creating several gradients by hand I utilized a syringe pump to have even extrusion rates. The syringe pump was utilized by alternating which pump was extruding so a colleague had to move the plate. This has applications in bioprinters and rather than having somebody move the plate manually the bioprinter will move the plate or the extruder. These results build on the potential of bioprinting gradients for use in bioprinters in regenerative medicine and other bioengineering applications.

Hello, my name is Elizabeth Clark and I’m a bioengineering student and my research project was built up on my previous research project which is creating hydrogen gradient as many cellular functions and processes utilize gradient in the human body.

So for keywords and background, hydrogels are comprises a polymers in water a gradient is the change of concentration so in this case in a line and will be represented by the changing color. Gelatin is the hydrogel I used. I use the 10% concentration so 10 mL of water I would use 1 g of gelatin and a syringe pump is the tool that I use that allows for the extrusion rate and you can program different extrusion rates.

So this slide just shows briefly the set up I used in my previous research project and I modified it slightly for the gelatin. Two syringes are being fed into a custom static mixer and extruded by hand. I only did this a few times just to ensure that a different hydrogel would work. Gelatin is a liquid at warmer temperatures so around 40 to 50°C and when placed on a cooler surface, in this case of metal plate that is chilled, it would sit almost immediately set.
I have with the syringe pump and it will alter the color by which one is extruded.

Here’s a video of that. When I wanted to change the color I would just pause one syringe pump and start to extrude on the other and then flip it. And as you can see on the right is the gradient that was just created from the video

Special thanks to Oscar for funding this project as well as my mentor Dr. Remi Veneziano, as well as the other people listed. Thank you.