We have completed testing our first iteration of the payload at Carleton Lab!
Preparation for testing:
In order to attach our payload to the exciter for testing, we had to build one final piece: an interfacing part that would allow us to screw our mount into the exciter. The morning of testing, we used the mill and the drill press to manufacture the piece out of aluminum stock. Despite the tight schedule, we got it done!
After manufacturing the interfacing piece, we headed over to Carleton Lab to test the payload. The outer casing of the payload was able to withstand the vibrational loads we applied to it! The inner compartment though, was not as lucky and cracked.
Our next step is building the next iteration of the payload! We plan to modify many aspects based on testing:
This week we studied the evolution of Pseudomonas aeruginosa and Staphylococcus aerureus mixed colonies over seven days to refine the window of time we plan to grow our CARMEn samples aboard the International Space Station. While our quantitative CFU data will only be available later this week week, our initial morphology data suggests that the biofilms grow close to their maximum size in as little as 5 days at 25°C! These samples were also kept for 3 weeks in the 4°C cold-room to help more accurately simulate the CARMEn samples' growth patterns after kept in cold-stow for approximately 3 weeks aboard the ISS.
Last week we continued our temperature and antibiotic testing and studied the morphology of 14 biofilm colonies under various starting parameters. The goal of this morphology study and subsequent Colony Forming Unit (CFU) analysis is to understand the differences in growth rates of S. aureus and P. aeruginosa when grown separately, next to each other, and mixed together. We hope that studying this collection of colonies can help us establish a baseline of how we expect the colonies to grow under Earth's gravity and help us refine our starting concentrations of each bacteria to allow for optimal growth when CARMEn is flying aboard the ISS!
We are now on week four of cold-stow temperature testing our mixed-species biofilms spotted on agar and then placed in 4°C (the conditions we plan to store our biofilms during transit to Kennedy Space Center and on the SpaceX rocket to the International Space Station.) Our results so far suggest a loss of around 1 order of magnitude of colony forming units (CFUs) each week the biofilms are stored in 4°C. Since we want to maximize the CFUs retrieved from our CARMEn biofilms, this testing provides key evidence that we will need to late-load our biological samples onto the rocket. We will continue our 4°C temperature testing and begin observing the effects of storing fully-grown biofilms (~7 days in 25°C) at 4°C.
Last week we were able to obtain our first antibiotic testing results for our mixed-species biofilms! After isolating individual Staphylococcus aureus and P. aeruginosa colonies from the mixed-species biofilms and conducting antibiotic strip testing, we found that S. aureus grown in a dual-species biofilm develops a dramatic decrease in antibiotic tolerance to both Ciprofloxacin and Tobramycin, while P. aeruginosa grown in a dual-species biofilm persists in its level of antibiotic resistance to both antibiotics. CARMEn will investigate how these antibiotic resistance properties change in microgravity conditions to help us better understand how to better use antibiotics to treat bacterial infections in space!
The first iteration of CARMEn is complete!
Our mechanical build team has been hard at work over the past few weeks manufacturing the components of the payload and last week, we assembled our first prototype. The outer box is made of aluminum and is held together by 3D printed fittings with screws. For a look inside CARMEn, see below!
Above are CAD images of our current design of CARMEn. We have manufactured all the pieces in the diagram above, including the syringe system, inner compartment and fittings, and will continue to improve on our design as we proceed.
See below for some photos of the team manufacturing the payload!
Our next step is testing! We plan to test at Carleton Laboratory, where we will have access to a shake table to test if CARMEn is able to withstand the vibrational loads it will experience during launch and landing. This past week, we finished manufacturing our payload mounting mechanism for testing:
We hope to be able to test next week at Carleton & see how CARMEn holds up! 🤞
After three days of letting our colonies from last week grow, we went back to the lab on Monday to image our first round of biofilms.
Here are some interesting preliminary observations:
This week we started the first round of CARMEn biological testing. The team has spent a long time researching "Pseudomonas take-over"- the effect of P. aeruginosa dominating mixed-species colonies between P. aeruginosa and S. aureus. From the team's research and some helpful advice from Dietrich Lab members, we decided on using TSB (a nutrient rich medium which should help S. aureus grow comfortably) and a 1:1000 starting ratio of P. aeruginosa. We hope this combination of medium and starting concentration ends up a recipe for success!
On Thursday, Swati mixed a 1% Agar 3% TSB medium, and on Friday, she spotted over 50 plates of various sizes with different combinations of P. aeruginosa, S. aureus, dual-species biofilms, and colonies grown next to each other. Several of the plates were placed at 25°C (approximately ambient temperature) and 4°C (cold-stow temperature) where they will be pulled out and harvested in 1-week intervals to determine the length of time the colonies are viable in each of the two temperature conditions. The other plates will be observed periodically for the span of 14 days (while kept at 25°C) to determine what the growth pattern of the bacteria looks like in various sized Petri dishes.
The team has made great progress in our manufacturing timeline this weekend!
On Thursday, we assembled our first fluid system prototype (including successful autonomous dispensing of our syringe!) The prototype includes a 3D printed frame, syringe reservoir, and linear actuator.
On Friday, we toured Columbia University's Carleton Laboratory to visit and learn about the vibration and shake tables which we plan to use for launch/landing simulation testing of our payload prototype.
On Saturday, we completed our second petri dish prototype printed in one of the Columbia Makerspace's Formlabs printer.
Vibration shake table aside, this weekend's manufacturing has given us some pretty good vibes about the coming months of our CARMEn payload preparation!💪 🚀
Bonus: A very important excavation in Carleton Lab conducted by Pol
During this week of payload building, our engineering team 3D printed the petri dishes and fluid system framing that we will be using for our first prototype. After, we will begin running some preliminary structural analysis. Despite the fact that our science equipment is small, the science we gain from it could lead to huge discoveries!