Is the 1% conc. you want? Or you can dilute it to low concentrations and use 0.22 um filter to sterilize it?

Hyaluronic acid solutions are very problematic in this regard. I do not think diluting will help. Either the hyaluronic acid will end up stuck in the filter or worse you will get solute polarisation at the filter and after a few drops the solution will be just as difficult to pass through as 1%.

The only sensible solution I think is to start with a sterile solution of clinical grade hyaluronan - as used in ophthalmic surgery. (I think there is preparation under the name Hylan but it is a long time since I used this.) You may find this expensive but it may be cheaper than trying to produce your own.

@Jonathan,

But, I am curious, can it be diluted to a relative low concentration for filter sterilization, then re-concentrate it later by applying vacuum to remove water as described in the Patent application "Sterile Hyaluronic Acid Solutions (US 20110195925 A1; year 2011)"?  [http://www.google.com/patents/US20110195925]

See one paragraph from the application:

"Another known method of sterilizing hyaluronic acid is by filtration. Common filtration processes are used in industrial processes for preparing purified hyaluronic acid salts in a concentrated form, usually in the form of dried powder, whereby an aqueous solution is passed through the filter and subsequently dried. Such a filtration processes is described in European patent application EP 867453 and WO 00/44925. U.S. Publication No. 2006/0052336 describes a method of filter sterilizing a high molecular weight hyaluronic acid at a relatively low hyaluronic acid concentration to reduce the viscosity of the solution. Following the filtration step, the concentration of the hyaluronic acid in the solution is concentrated by applying a vacuum and removing the water to obtain a desired more concentrated form of hyaluronic acid."

That sounds fine if you have a factory, some venture capital, and plenty of time. I think Benjamin wants something he can do in an ordinary lab. 

@Jonathan,

Thanks for explanation.

Thanks Jonathan and Yao for all the advises. However, due to my experiment involving extra modification of  hyaluronic acid (with dialysis process as well), purchasing a clinical grade sterile HA does not preserve the sterility of HA along the way.

@ Benjamin,

Well, I am curious, what are you going to do (for sterilization) then?

Dear Yau, 

Recently I had tested the filtration method, by diluting our modified-HA solution.

The result I obtained was, a 10 time dilution of 1% (w/v) into 0.1% (w/v) was able to pass through the 0.22 micrometer filter, but only to a certain extend for lower degree of modification. For your information, several degrees of modification onto HA was performed (10, 20, 30, 40 and 50, degree of modification). 

Meanwhile, there were other opinions regarding the sterilization of HA, such as (1) UV irradiation of lyophilized HA under laminar flow hood, (2) obtained a clinical grade HA and perform the whole modification process under contaminant-free condition, (3) employ a lower molecular weight (ie. 80kDa) HA instead of currently using 2,000kDa HA. (4) High speed centrifugation /  ultracentrifugation of HA solution.

Thanks for your response. I am thinking that if you have to, you can use 'several' syringe filters to finish filtering all of them in several sterile tubes, and then pool them together. Will this work?

I had tested the idea of using several filters, but it was not efficiently and economical friendly. 

Let said 100mL of 1% (w/v) HA, diluted 10 times into 0.1 % (w/v) HA, that will be 1000mL. A single filtration cups was able to filter about 500mL of lower degree of modified HA but  only able to filter less than 50mL for higher degree modified HA. Which mean i would need at least more than 20 filtration cups. 

As Jonathan mentioned earlier, this filtration method probably workable in factory, but not so efficiently and economical friendly with my current lab facility.

Hi Benjamin,

I'm currently facing a similar problem of sterilizing HA solutions in PBS for my cell culture studies. For me it is of high importance to be able to minimize the effect of HA retention on a filter, since I need to know the exact final conc. of HA. That's why I found the data published in this brochure very interesting:

https://www.parker.com/parkerimages/Parker.com/Literature/Process%20Advanced%20Filtration%20Division/PAFD_literature/Life%20Sciences%20Literature/AN_OP_19_10-09_1A-Effective_Filtration_of_Hyaluronic_Acid_Based_Solutions.PDF

Basing on this I learned, that the product with cat. no. ZSHC050-620 may be what we are looking for. Could you please have a look on this and, basing on your experience, comment my suggestion?

Do you have eny experience about HA retention on different filter types?

Best,

Lukasz

Dear Lukasz,

Browsing through the brochure, it seems that this product (ZSHC050-620) may be one of the best option to sterilize HA solution. I can't give any comment on this product until I tested on my HA sample.

Hopefully anyone of us got the chance to give it a try on this product, and then provide some feedback here.  

Did you think out autoclaving? We already know we are going to degrade the product, but it seems to be a solution if you can optimize the ratio temp/time in order to reduce the stay into the machine..? In the US Patent number US 6891035, they specify that by placing the gel in a special container, it was possible to limit this degradation...

Please let me know if you think it could work,

Regards