My lab uses PDMS microfluidic devices for cell culture experiments, however we sometimes get contamination. Currently, we UV them in the cell culture hood for 1-2 hours to sterilize. Is there a UV-box specifically made for this purpose that we can purchase? What do other researchers use to sterilize PDMS devices? Thank you.
Short answer is you cannot reuse PDMS. Since PDMS absorbs certain liquids. It's not possible to achieve "perfect" levels of sterilization. This is especially the case for nucleic acid contamination. But I believe for your application you could use sodium hydroxide & 0.6% hypochlorite washes combined with UV sterilization. There is no special box. You can buy hand held UV light sources and make sure it shining on actual chambers & channels. The thicker the PDMS more would be the UV light loss thru it.
To clarify, I'm not reusing the devices. These are new devices that have water in them to keep the channels open.
We did not do very specific sterilization process, once you keep the fabrication process clean. The only thing we did is perfusing the channel with 70% ethanol (v/v) before loading cell culture medium. After washing the channels with cell culture medium, we start to load the cells. We keep changing medium every day and have no contamination problem for at least two weeks (the longest culture time we did for our experiments).
Using 70% ethanol washing is fine. But we usually do it with sonication for 10-20 min, before thermal bonding the PDMS to glass slides. It takes time for PDMS to dry and might reduce the adhesive properties of PDMS. So we eliminate this step for newly made device.
UV sterilization even just for short time will change the property of PDMS, making it brittle. If you do not care much about the mechanical properties of PDMS, that is fine.
Just curious, why do you need to have water in device to keep channels open? Are these channels having very high aspect ratio?
Thank you for all your replies. For autoclaving, which cycle do you use? Is there liquid in the devices during the autoclave step?
We like to gamma irradiate (available at Vandy) our devices that are used for long term culture. It's the best way to know it's sterile while not putting the devices through a thermal cycle that can change the properties of the device. Our devices have thin membranes and are usually intubated before sterilization. Autoclaving devices that are intubated can cause them to leak at the fluid ports. You are welcome to come by our lab to see how our devices work if you'd like. We are over in Stevenson Center building 6, 8th floor.
http://www.ncbi.nlm.nih.gov/pubmed/26150936
Ozdil B, Onal S, Oruc T, Pesen Okvur D. Fabrication of 3D Controlled in vitro
Microenvironments. MethodsX. 2014 Jul 8;1:60-6. doi: 10.1016/j.mex.2014.06.003.
eCollection 2014. PubMed PMID: 26150936; PubMed Central PMCID: PMC4472850.
UV and Gamma radiations, and thermal treatments could degrade the PDMS after repeated sterilizations. Surely will be better/recommended use a ethylene oxide to esterilize after clean correctly the microchannels with clean solution. I hope you helped. Bye
We also use UV inside the cell culture hood but fungal contamination is still there sometimes. Bacterial contamination does not come after UV treatment. We are currently using autoclave to sterilize microfluidic device.
UV does NOT sterilize. It kills vegetative cells - not spores of bacteria and some fungi and there are bacteria uniquely resistant - even then you should control for light and dark reactivation. Application to fluids and articles like PDMS microfluidic devices is simply ridiculous. UV penetrates fluids poorly and only affects articles at line-of-site surfaces - both with same caveats for limits in efficacy.
Autoclaving , gamma and ethylene oxide may serve your needs, the latter 2 are a pain as you'll need to send it to a supplier for treatment.
I would recommend embedding the PDMS pieces in sterilizable bags in an ethylenoxid (EtO) chamber. You should customize the program to your needs as very complex microfluidic circuits may prevent the EtO from reaching all parts (although PDMS is porous, it will depend on the thickness of the PDMS). Previously, you could use cleaning solutions through the circuit to make sure to clean molecules and microorganisms adhered on the circuit walls, rinse the debris with a long time in flow, dry well by passing filtered air (N2, Argon, etc), and finally sterilize in the EtO chamber with your program.
Note: Gamma radiation has good penetration but maybe is not recomended using several times becasue it can degrade the PDMS chains.
I hope this info will be uselles for you. Good luck, Begum.
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