Undergraduate Student Grove City College Lancaster, Pennsylvania, United States
Introduction: A large portion of Americans have Gastroenterology (GI) issues. With a significant portion of the population being affected by these issues, studying the GI tract has become increasingly important. The GI tract includes the colon which contains epithelial cells on its interior surface. These cells live in an environment where fluid and particle movement places various stresses on the cells, which affect their gene expression. Two of the most common types of laboratory test subjects are live animal models (in vivo) and isolated cultured cells (in vitro). With in vitro testing, cells sit in a static environment that does not simulate the stresses that cells see inside the body. While animal testing does expose cells to a dynamic environment that stresses the cells, this testing environment is very difficult to control making it difficult to isolate variables.
Organ-on-Chips (OoC) have been introduced as a new technology that addresses this laboratory testing problem. OoCs are microfluidic devices that contain areas for cells to grow and channels for media input and output. Fluids are pushed through these channels to the cells, providing nutrients and fluid stress in a way that simulates the body. Since chip design affects the channel-cell interaction, OoCs must be uniquely designed and altered to simulate the desired environment of the cells they are testing. Gut-on-a-chip (GOC) is a type of OoC that replicates the environment of the gut. This paper examines chip fabrication methods, with the end goal of creating a Gut-on-a-chip.
Materials and
Methods: To simulate the desired environment for epithelial cells in the colon, our lab aimed to design a chip with two channels that have a membrane sandwiched in between where the cells can be plated to mimic distinct microenvironments. Molds for the channels were printed with CADworks3D Profluidics 285D using a polydimethylsiloxane (PDMS) compatible resin, CADworks3d Master Mold resin. PDMS was then poured in the two molds and cured. An ElveFlow Plasma Bonding Pen was used to plasma bond one half of the chip to a PDMS membrane which was then plasma bonded to the other half of the chip. A challenge with this fabrication method is getting successful bonding.
When molds come out of the printer, they must be cleaned. The post-printing cleaning process affects the molds’ surface quality which affects the PDMS’s bonding surface. To determine the best cleaning method, molds were cleaned in isopropyl alcohol (IPA) baths, wiped with IPA covered cleanroom wipes, or sprayed with an IPA filled airbrush. The molds were used to create chips that were then tested for successful bonding.
PDMS is hydrophobic, but when successfully treated by the plasma bonding pen, it becomes hydrophilic. The success of the pen’s treatment can be observed by watching water's reaction to treated PDMS. Experiments were conducted to test the effect that different pen to PDMS distances (2 to 10 millimeters with a 2 millimeter increment) and different pen time exposures (1 to 10 seconds with a 1 second increment) had on the success of the treatment.
Results, Conclusions, and Discussions: From experimentation, it was determined that the best post-printing process was a combination of the initial cleaning methods. The molds treated with just the IPA bath were shiny but had many bumps on the surface from excess resin that was not cleaned off. The chips made from these molds rarely bonded. The molds treated with a cleanroom wipe had a dull, scratched up surface and created chips that would not bond. The molds treated with just the airbrush had a shiny, clean surface but only bonded half of the time. The IPA bath and airbrush were finally combined into a cleaning process because the bath can first remove a large amount of the excess resin, thus making the cleaning process easier, and then the airbrush can easily and quickly be used to remove any of the remaining resin. The best process for treating the PDMS pieces with the plasma bonding pen is for the treatment to be 6 seconds long and 4 millimeters away from the surface of the PDMS. In the time experiment, the water droplet at one second did not spread out much. With each second up until 6 seconds, the water spread out more and more. After 6 seconds, there was no observable difference in how much the water spread out. For the distance experiment, the water droplets spread out the same amount at 2 millimeters and 4 millimeters. After 4 millimeters, for each successive distance, the water droplet spread out less. 4 millimeters was chosen as the correct distance because the further away the pen is held, the more of the surface that the pen can treat at once. At this phase in experimentation, successful bonding is still not consistent. The next area of exploration is the post-plasma bonding pen treatment. It is recommended that after the two halves have been stuck together, that the chip be heat-treated. Future experimentation will look at the effect the different temperatures and times have on the success of the bond.
