UV sterilization will definitely oxidize the surface of the PDMS (nearly the same as plasma treatment only slower). This is sometimes used to activate the surface of the PDMS for bonding or silanization. When PDMS is exposed to UV the methyl side chains go through hydrolysis which results in a hydroxyl group replacing the methyl entirely or just forming an alcohol group on the methyl. These hydroxyls are quite reactive and will cause the surface of the PDMS to start to crosslink. Eventually, you end up with something that resembles a crust of SiO2 on the surface of the PDMS with cracks in between exposing some of the other reaction products which may include aldehydes and ketones.

I agree with John that ethanol sterilization is your best bet if you don't want to deal with the modified surface of the PDMS.

On the other hand, a quick treatment with APTES may improve the surface performance of the PDMS with the cells and that UV surface modification is just the ticket to getting the APTES to covalently bond to the surface of the PDMS. Even better, add a layer of glutaraldehyde and then fibronectin or collagen.

UV sterilization will definitely oxidize the surface of the PDMS (nearly the same as plasma treatment only slower). This is sometimes used to activate the surface of the PDMS for bonding or silanization. When PDMS is exposed to UV the methyl side chains go through hydrolysis which results in a hydroxyl group replacing the methyl entirely or just forming an alcohol group on the methyl. These hydroxyls are quite reactive and will cause the surface of the PDMS to start to crosslink. Eventually, you end up with something that resembles a crust of SiO2 on the surface of the PDMS with cracks in between exposing some of the other reaction products which may include aldehydes and ketones.

I agree with John that ethanol sterilization is your best bet if you don't want to deal with the modified surface of the PDMS.

On the other hand, a quick treatment with APTES may improve the surface performance of the PDMS with the cells and that UV surface modification is just the ticket to getting the APTES to covalently bond to the surface of the PDMS. Even better, add a layer of glutaraldehyde and then fibronectin or collagen.

Cheers for both of your answers, I've certainly been using a plasma etcher to bond the device and wet it, prior to UV sterilisation, and following this, cell culture.

The only problem with ethanol sterilisation is that I can't merely spray the device excessively with the stuff; the internal chambers which I grow the neurons in will need to be sterilised which would require flowing ethanol through the device. That isn't itself difficult to do, however the ethanol will become absorbed within the PDMS so even after flushing repeatedly with water, there's no guarantee it wont diffuse into the media...

Think I'll test sterilising the devices with plasma oxygen, and hurrying over to the bio lab to wet the device with sterile water before the surface of the PDMS de-activates and returns to it's hydrophobic state. Thanks once again for both of your help :)

Regards

Chris

So you are UV treating a device that has been plasma bonded to glass? There is some possibility that you are experiencing O3 poisoning of the PDMS. If you are using something like the Jelight or Bioforce UV/Ozine cleaners, they generate a large amount of O3 which can remain in the bulk for a long time and form free radicals with a considerable time delay. If you do you device assembly in a cleanroom, then you can load the sterile water while still in the cleanroom (a walk-in biosafety cabinet) and then put the device into an air tight container. We actually put our devices into a wide mouth mason jar submerged in sterile water for transport to the cell culture suite. The jars are easily cleaned before putting them in the biosafety cabinet and come out bubble free and sterile.

Have you ever thought about steam sterilization for the PDMS itself or tested it? PDMS is water vapour permeable and often used for gas separation membranes. Also ethyleneoxide sterilization might work.

Ethanol will swell the PDMS it is hard to be removed from it.

Ethanol will swell the PDMS only during a few  hours.  

Elena you are right but one has to remove EtOH completely before bringing cells in contact with the treated PDMS....

Use EtOH 1 minute, remove EtOH in vacuo,  and then fill up inert gas

If you afterwards perform a TGA measurement you will see how much EtOH is still in the PDMS.