I'm preparing Heparin hydrogel using PEGDA as crosslinker. I know there are two main method 1)Michael addition: which need long time and 2)Radical addition : which need photoinitiator and UV . Is it possible to produce this Gel with UV alone without the photoinitiator ?
Adel,
the real problem of Michael addition is not the long time, indeed in case of crosslinking of diacrylate, by addition of tiny amount of diamines, it can take less than 10 seconds to cross-link. The real problem of this reaction is the chemical stability of the newly formed cemical group, which degrades in aqueous media after less than 2 days, due to the scarce stability of the functional group: beta-aminoester.
Actually I don't understand why you prefer to cross-link Heparin with PEGdA, I think it is NOT the right choice. Heparin, being a polisacchride, containing carboxylic groups, can be easily cross-linked, even at very low concentrations, usibg the couple EDC/NHS. So I recommend you to use equimolar ratio between EDC and the carboxylic groups of Heparin, and use a molar ratio between EDC/NHS= 3:1
You can dissolve Heparin in buffer solution having pH= 5-5,5, even at the concentration of 5-10% w/w, keep temperature range between 40-50°C, and you will obtain a chemically stable and firm gel after few seconds.
If you find my answer useful, I will appreciate upvoting it,
Regards,
Irini
First of all Irini thanks a lot for your detailed answer. ...Actually there was a misunderstanding in what I meant ....I'mean using EDC/HOBT/Cysteamine in the beginning to for the O-acyl active compound, then I used DTT to break the disulfide ,finally I use PEGDA as cross linker. ....So based on my experience and literature forming hydrogen in room temp is taking more than one day. ...Other option is to use temperature between 40 and 50 ...my question was ...Is it possible to use UV. ..What do you think????
What I understood is that you want to exploit the electrophilic character of acrylate to couple it to -SH groups of cysteine moities. You can push the reactio by adding tiny amount of tertiary amines, as the pH push the kinetics towards the poliaddition reaction.
In alternative, if you want to proceed by radical polimerization by UV, you have to add a photo initiator, Irgacur, for exampe. but without adding the photoinitiator, the reaction will not start.
In this case, the reaction will involve any unsaturate -C=C- group, so PEGdA will cross-link with each other, and Heparin will be physically trapped as an intrapenetrated mesh, but not covalently bound to the polymeric network.
I think that you may investigate approaches for increasing the kinetics of Michael addition, such as by adjusting the concentrations of the reactive species. Being a second-order kinetics, the higher the concentration of the reacting species, very the faster the reaction
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