is 20kDa PEGDA ((10% wt) 100mg in 800ul pbs) + 2kDa PEG-dithiol (10mg in 200ul PBS) stoichiometricly balanced? is the molar ratio (1:1) for DA:SH
I attend to make the gels by michael type addition
I want to measure the mesh size of the PEG DA gel and i want to use the Flory - Rehner equation. searching the literature, most papers have used a ratio of 1:1 of the peg monomer and peg crosslinker.
Does the molar ratio of the reaction need to be 1:1 if i want to use the flory - rehner equation?
I will not be using PBS (as stated in the question) but 4 mM Triethanolamine of the same volume.
Simply enter the values in the following online calculator
http://www.graphpad.com/quickcalcs/Molarityform.cfm
The rest is very simple mathematical calculation. Hope you are able to work it out.
You won't get a cross linked gel from a Michael addition reaction of two di functional molecules, you'll only get a higher molecular weight linear polymer. You need a multifunctional molecule to get a gel by Michael addition reactions only (e.g. use a PEGtriacrylate or a PEG trithiol or yet higher functionality, tetra-PEGs are most common). Perhaps you have seen papers that use free-radical copolymerization of PEGDA which can give gels without a multifunctional crosslinker but that is not Michael addition cross linking.
Flory-Rehner has an 'effective' crosslink density term since it is not possible to get 100% elastically effective crosslinks (plus there will be entanglements). So the cross linker stoichiometry doesn't matter in terms of applicability of F-R, though when possible it can be insightful to calculate a theoretical cross linking efficiency based on stoichiometry. Mesh size found from crosslink density is a highly idealized parameter, of primarily qualitative value.
I did not mention this in the question but i'm actually using multifunctional 4 arm PEG acrylate purchased from laysan bio. Can cross linked gels be created via Micheal type reaction?
Yes, if you are using a tetra functional PEG-acrylate (PEG-tetra-acrylate) it should be possible to get a gel by this route,
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