The problem is not wavelength but rather the intensity of your UV source and the concentration of the irgacure. I will recommend to increase the concentration of irgacure to at least 0.2% in the final solution or else you need to find other system that has higher intensity. 36W is relative low to crosslink irgacure at 0.05%, you may need to look for the system that work at 400W to crosslink it.

You make consider lower pH, sometimes things work out in acidic.

Ratima Suntornnond I was worried that it would be something like that... I'd can't really go above a 0.1% solution of I2959, because it's quite cytotoxic and would kill the cells I'm planning on adding to the gel. At this point I'm resigned to finding a new light source. Do you have any suggestions as to what I can use, that's not too expensive? Every paper I've read state that they use ~4mw/cm2 UV light, but never actually state what the light is (as in, what the device is that produces it), so I'm a bit stuck there.

Ahmed Nada I pH balance everything to 7.4 before I use it, so I don't think that's the problem.

Thanks :)

For irgacure 2959, you need the UV light that has 365 nm wavelenght or lower (UVA or UVV light).

Depends on how fast you want to crosslink, if you don't mind longer curing time, 3-10 mW/cm2 light intensity from normal LED array handheld lamp can be used.

How old is your initiator? Might be the bottle is too old and the initiator is off. You can also try to recrystallize it if you feel the I2959 is dirty.

Irgacure for cell culture works well at 0.05% w/v and around 10 mW/cm2. The intensity is not so bad for the cells as is the heat that these lamps often produce.

We used the Blackray lamps http://ftp.uvp.com/blakraylamps.html for many of our cell culture experiments and never had much issues with cell death.

A good alternative to Irgacure is LAP which is more water soluble so you dont need to solubilize it first in ethanol, which is also nice

Michael Müller The initiator is brand new, we only got it in a few months ago.

I've sourced out this lamp:

https://www.aliexpress.com/item/replace-120w-Handle-protable-LOCA-uv-curing-machine-365NM-light-for-curing-Screen-repair-curing-lights/32774957989.html

It's a little bit more powerful than what's usually used, but I can just use blackout tape on a few of the LEDs to reduce the intensity.

I haven't had any problems with I2959's solubility, I just dissolve it in PBS by sonication and leaving in an incubator over a weekend.

Hi Lachlan

Not sure if this is the case for I2959 as well, but if you take for example initiators such as ACVA you can actually set them off by ultrasonication, so you might actually "use up" your I2959 with your dissolution process.

My suggestion is to do a 5% solution of I2959 in ethanol (store in fridge and under the exclusion of light), then dilute 1:100 when you mix it with your hydrogel. The little amount of ethanol does not bother the cells at all in my experience.

Hi Lachlan

as it is reported in papers, you can use solutions up to 0.5% concentration of I2959. I had problems with curing the GelMA hydrogel. I found 2 reasons; firstly, the intensity of the UV. and secondly, the degree of degree of substitution of gelatin by methacrylate. if you synthesize the hydrogels yourself, make sure about DoF.

Light absorbance is depending on the concentration of PI to your solution for IC2959. At the datasheet of this photoinitiator, you'll find out that in the light absorbtion at 365nm light source is so low, that it may cannot create free radicals. I use 2% IC2959 with 365nm light source and have excellent results. I have solutions with 0,5% PI and have very good polymer link as well. Keep in mind that except for the wavelength, the concentration of PI in your solution is critical, as to low concentrations ends to unreacted products. The free radicals are so few that cannot create adequate polymer network.

Ali Mokhtarzade Hi Ali,

I have modified my hydrogel with Glycidyle methacrylate as well. What intensity, concentration and gel/initiator ratio do you recommend?

Hi Fariba,

The used initiator indicates the intensity of the UV, not the hydrogel itself or the synthesis ingredients. So if you are using Irgacure2959, you must use 362 nm UV source light with an intensity of 9 mW/cm2 (which I employed). About the concentration, I cannot precisely help you, as I have no experience working with the mentioned Gelating-baed hydrogel. I suggest you read this article: Article Synthesis and characterization of site selective photo-cross...

Good luck with your research.