[jadeelk]

Hi all,

(This is my first post, so please forgive me if this is not the right forum.)

I am looking for a material (rigid sheet or film), that is highly gas permeable and preferably transparent. Can anyone suggest any good options?

Here are more details.

I have a rare eye disease, and I am doing this sort of research project with my eye doctor that might help me improve my eyesight. The key idea is to get swimming goggles, drill two holes in them and fill them with saline solution, so that the eyes are essentially underwater in tear-like liquid for an extended period of time. The problem with this approach is that the eyes consume oxygen not from the blood, but directly from the air through the tear film (mostly). The material of swimming goggles is typically not gas permeable or has very low permeability, so the eyes essentially "suffocate" after a few minutes. So I am looking to replace part of the goggle material with gas permeable material to restore the flow of oxygen to the eyes. I plan to remove the front panel of the goggles and replace it with gas permeable material, that's why I prefer transparent one. If the material is not transparent, then I am thinking of making some sort of tubes made out of gas permeable material, that would protrude from the outside into the goggles delivering oxygen from the air to the water inside the goggles.

You would ask me, why is it even possible? Well, there are so called rigid gas-permeable (RGP) contact lenses, that are made of rigid transparent material, that can let enough oxygen to the eyes, exactly what I needBut I talked to a few manufactureres about buying it, with not much luck. Their  material comes in a form of a "button", this is something in between a cyllinder and a cone, that later will be molded in a lens of right shape. This is too hard for me to work with, and besides, they cvan only sekll me a large party of 500 buttons, which would cost me way more than I can afford.

So I am looking for a material available in small quantities and highly gas permeable. The permeability should be similar to those of RGP contact lenses, or at least same order of magnitude. From
http://www.contamac.com/Products/Gas-Permeable/
we can learn that lowest the permeability of one of the materials for RGP contact lenses is 26 * 10^-11 = 2.6 * 10^-10 cm^2/sec. In my understanding the effective rate of oxygen permeation will depend on the size and thickness of the gas permeable material, but anyhow this gives us some sort of a baseline. So I am looking for a material with gas permeability close to this baseline number or higher.

I've spent quite some time on the internet trying to find a good candidate. One of the materials I found is Polymethylpentene  or PMP. But its permeability to oxygen according to
http://www.goodfellow.com/E/Polymethylpentene.html
is only 2 * 10^-12 cm^2/sec, which is 100 times lower than RGP contact lens material. Also I don't like that it comes in a form of a film: I am planning to remove the front plate of my swimming goggles and replace it with gas permeable material. If it is going to be film, then the water inside the goggles will press and deform it and introduce optical distortion. PMP also comes as a rigid sheet, but the thickness is 4mm, which is too thick for me. If there are no better candidates, I will probably try PMP film.

Another material I found is polydimethylsiloxane (PDMS). According to:
https://www.permselect.com/membranes
it has great permeability to oxygen: 6 * 10^-8 cm^2/sec, so only a small patch of it on the goggles  should be enough. It is not transparent, but I can probably tolerate this. However I couldn't find where I can order it in sheet or as a film; I could only find web sites that sell it as a liquid. Does anyone know if I can order film or sheet of PDMS?

So I am wondering if anyone knows any good candidates for me to try and where to order them? Just to reiterate: I am looking for a material that has oxygen permeability similar to 2.6 * 10^-10 cm^2/sec or higher, and comes in form of a sheet or film, preferably transparent and available to order in small quantities.

Also please forgive me if I missed some obvious piece of information on the wegbsites about the materials. Due to my eye condition, I use computer essentialy as a blind person using screenreaders and sometimes they miss some crucial piece of information that is obvious to the sighted people.

Any suggestions will be appreciated. Thank you,
Tony

[Enthalpy]

Hi jadeelk,

Pmp is rather expensive and not very common, but I see hope that you find some flat part of proper thickness among finished items. Pmp is often used in medical equipment that must be sterilized, so you could get a catalogue for syringes and the like and check if some has the proper shape and size, get a sample and cut youfilm out of it.

One producer of Pmp is Mitsui
http://www.mitsuichemicals.com/tpx_cha.htm
maybe they give you a sample if the film exists there.

Polydimethylsiloxane is the most common silicone. About every silicone is polydimethylsiloxane - but silicones are very varied in hardness, curing method, which leaves different impurities in it that you don't want in your eyes. Some silicones are allowed as implants in the human body.

What I don't grasp: silicones are rubbers, very soft ones. You worried about the Pmp film deforming itself (supposedly because you have water inside the swimming goggles and air outside), but a silicone film will deform hugely more.

I have already used a silicone that was perfectly transparent. It served to glue glass on solar cells for satellites. This particular one cost a true fortune, like 2k€/kg, because Wacker made it on demand for satellites, hence the exorbitant price, but it's just a standard product from them where the silica filling is removed.

Wacker is strong on silicones and has certainly many answers. They put documentation online, for instance:
Solid and liquid silicone rubber, material and processing guidelines

Natural rubber too is knowingly permeable to gas. Other rubbers too?

Do you already know how to replace the goggles' film with Pmp and hold the Pmp in a way that releases no toxic material? For instance, I wouldn't want glue in my eyes, nor compounds left over by plastic welding.

Did you try to evaluate if the water will transport the oxygen well enough?

[Corribus]

A misleading figure, Enthalpy, because for many polymers, the oxygen permeability value is extremely sensitive to moisture/humidity.

[Borek]

This is close to self medication, which is against forum rules, but I am going to let it go for now.

Why do you want to replace front of the goggles? Why not leave the front hard and flat, but replace sections of the goggle side walls? Then you don't have to worry about transparency of the material.

You are aware of the fact you will need a very strong glasses in front of the goggles? Human eye works OK in air, but not in water, because of different refraction coefficient. That's why we can't see well under water and you will face exactly the same problem with your goggles on.

[jadeelk]

Borek,
With all my respect to the forum rules, I am doing this project together with my eye doctor. In fact this was his idea that we need to somehow deliver oxygen to the water inside the goggles.
Replacing the front plate of the goggles seems to be the easiest thing to do, also it's surface area is large, which should in theory let more oxygen in.
I am fully aware that  I'll need a strong lens to correct the effect of the water. My eye doctor can get me the lens and I'll just glue it on top, but that'll be much later, if if I can solve the oxygen problem. I will be fine even without the lens, since I don't currently have much useful vision left anyways.


Enthalpy,
Thanks for your response. I will try to talk to both Mitsui and Wacker.
If there is a good candidate that is flexible like rubber, I am considering buying a tube made out of it, 3-5mm in diameter . Then I can drill two holes on the top and bottom parts of the goggle and make the tube to connect these two holes, so that the air can go inside the tube and through the tube into the water. This might block my vision some, but that's not a big deal for me.

If I decide to replace the front panel of the goggles with gas permeable material, I was planning on using a water resistant glue. I am aware that it is toxic, but in my understanding, I can wash it in the water 10/100/1000 times and that will wash away all the loose particles. And I am discussing every step with my eye doctor, so he will not let me do anything to hurt my eyes.
>> Did you try to evaluate if the water will transport the oxygen well enough?
I haven't. Well, there are rigid gas permeable contact lenses, that work on a similar principle, but the water layer is much thinner. And my eye doctor thinks that this idea is worth trying.

[Enthalpy]

I like the idea of a tube, because it separates the two functions which are individually demanding hence difficult to combine: the good windows and the permeable part.

Instead of air in the tube and the tube in the goggle, maybe you could replace some side part of the goggles by a permeable material - for instance by a contact lens.

I have no data about their permeability, but in electrical engineering we use heat-shrink tubing
https://en.wikipedia.org/wiki/Heat-shrink_tubing
which consists of irradiated polyethylene. Somehow the arrangement of the molecules is so strongly disrupted that these sleeves shrink irreversibly their diameter by a factor-of-3 at heat. My instinct suggests that the disrupted arrangement is more permeable to air. The other advantage is that shrinking such a sleeve over a normal tube makes a watertight connection.

I wonder: how much oxygen is necessary, and would one water filling contain enough for a day without any refill by the atmosphere?