Skin Perfusion
Summer 2023-Fall 2023
The project focused on further developing, designing, and building a concept given by a plastic surgeon who conducts research on human skin by perfusing it for up to two weeks to simulate a human environment.
Problem Identification
For this project, I worked in the UPMC Adipose Stem Cell laboratory. They had previously created a mechanism of perfusing human skin to keep it alive for up to two weeks. However, the components of the system did not connect with each other to reliably regulate the system and achieve balance perfusion. We started by learning about the current system and the requirements for each component. We set up the entire system in our workspace to first-hand understand the difficulties the researchers had with each component.
Then, I created a high-level systems diagram of all the components and outlined how they are connected. This helped visualize the placement of all the components in the system and tie in the requirements into our search for components that would fit. We spent a few weeks looking at all commercially available products to determine what was available and if anything could be used for our system. I focused on the heating system.
Heating System
Iteration 1:
The initial method of heating the skin and media was using a regular heating pad. However, the researchers could not control the temperature of the pad. Once turned on, the heating pad would heat indefinitely until it was turned off.
To fix this and allow the heating system to self-regulate, we used a PID controller. This system would take input from the system to see how hot it was and turn the heating wire on and off until the desired temperature was reached in order to prevent overheating.
Since the media is flowing in tubing, we used a heating wire to surround the tubing side by side and heat it as it flowed. We wanted to heat it over a distance to allow it to reach the necessary temperature. We covered the lined heating wire and tubing with rubber to help insulate the system and distribute the heat.
When we tested the system, we found the temperature probe we had initially was not able to measure the temperature of the media properly and the heating wire and tubing were not completely flush. This meant that we were losing heat to the surroundings.
Iteration 2:
For our second iteration of designing the heating system, we looked to encapsulate the heating wire and tubing together so that they could remain flush. We achieved this by casting a silicone mold of the heating wire and tubing together. We switched to using a new temperature probe and tested two methods of incorporating it in line with the media to properly read the temperature right before it is inserted into the skin.
When testing this, we found the silicone mold worked better at hearting the system however, it was hard to manage due to the uneven surface. To fix this in our next iteration, we will cast the silicone mold as a two-part mold with a cover so it can lay flat. For the temperature sensor, we found that the method on the left worked better for preventing leakages while adequately measuring the temperature.
Bubble Trap
Initial Design
We found that this bubble trap was inadequate at removing bubbles as the pressure increased faster than the flow rate of the system. This meant that, over time, the liquid level rose and created bubbles in the media. Unfortunately, bubbles in the media are extremely harmful to the skin as they can cause tissue death.
Improved Design
Our improved bubble trap design was based on the desired flow rate of the system. We calculated the optimal height for the system based on the outlined flow requirements. The curved design allowed gravity to assist in achieving the optimal flow rate as well.
Other Components
Gas Exchanger
Currently, the lab is using a tape to secure the gas exchanger to the wall of the fume hood. However, this method is inconvenient as it makes it difficult to replace the gas exchanger every three days. To make the process easier, we have decided to use a commercially available test tube stand that will allow for more straightforward exchange of the gas exchanger.
Pump
This pump is the only one we found that would work for up to three weeks constantly. Initially, the cassettes would stick together and clog the pump. We resolved the issue by dismantling the wheels and carefully cleaning them to remove any media that might have been stuck there. This helped to alleviate the problem and the pump worked more efficiently.
BMES Conference 2023
I was able to present about our work at the 2023 BMES conference. This was an amazing experience where I was able to meet and connect with many other people in this field.
This project is currently in progress.