What kind of characterization test except measuring the swelling ratio can show the progress in cross-linking?
Hi Azadeh,
Can you explain more about the chemistry of hydrogel you are using?
You can study the reaction kinetics of your hydrogels usong rheometer. Also you might be able to use NMR and check the bonding ratios. This really depends on what you want? do you want to monitor it real time or the end point is important?
Cheers
Most frequently crosslink density is assessed by swelling tests or by analyzing the mechanical behavior. It is, however, only an approximation but is many cases it can be used for comparative purposes. It has a huge literature.
Hi Have a look at Nicholas Peppas books/papers he has published extensively in this area:
His Google Scholar Page: http://scholar.google.com/citations?user=c17D_ggAAAAJ
Crosslinked poly(vinyl alcohol) hydrogels as swollen elastic networks
Nikolaos A. Peppas and Edward W. Merrill
http://onlinelibrary.wiley.com/doi/10.1002/app.1977.070210704/abstract
The structure of highly crosslinked poly(2-hydroxyethyl methacrylate) hydrogels
Nikolaos A. Peppas, Humphrey J. Moynihan and Lucy M. Lucht
http://onlinelibrary.wiley.com/doi/10.1002/jbm.820190405/abstract
You can use Rheometer at a certain temperature, and measure G' and G", if the solution of the polymer forms crosslinking then G' will increase & G" will decrease with the progress of crosslinking. The crossing point of 2 graphs (G'&G") is the crosslinking, now you can work out the rest.
Best wishes.
Ferdous Khan
Thanks everyone. But I think I asked my question not properly. If I go into detail, I want to make a chitosan gel mixed with Genipin for wet-spinning and Because I need to control the swelling for my case, I need the fibre to be semi-crosslinked. I couldn't find anyone who used wet-spinning on a chitosan(+GP). So the other question is that does the GP remains in the structure after being pun in the alkaline bath? I can't recognize any blue color in wet-spun fibres.
You can wash your chitosan derivatives with acid acetic 2% after crosslinking process.
and then you can measure the percentage of crosslinker
Hi what I have done previously is to deactivate and preferably extract any unreacted Xlinker after the crosslinking reaction. For my samples which were GTA-Xlinked samples I used a solvent-H20 system for crosslinking and after my incubation time washed the samples x3 in a solvent-water system containing Glycine and then washed them x3 in solvent-water prior to drying. If I remember correctly unreacted genipin should also be inactivated by glycine.
Papers of interest:
Panzavolta S., Gioffre M., Focarete M.L., Gualandi C., Foroni L., Bigi A. Electrospun gelatin nanofibers: Optimization of genipin cross-linking to preserve fiber morphology after exposure to water. (2011) Acta Biomaterialia, 7 (4) , pp. 1702-1709.
http://www.scopus.com/results/citedbyresults.url?sort=plf-f&cite=2-s2.0-79952189383&src=s&imp=t&sid=DC4C5ABF0509D22D4F5A46C90EE873A2.iqs8TDG0Wy6BURhzD3nFA%3a20&sot=cite&sdt=a&sl=0&origin=inward&editSaveSearch=&txGid=DC4C5ABF0509D22D4F5A46C90EE873A2.iqs8TDG0Wy6BURhzD3nFA%3a1
- useful papers listed on this webpage
http://www.wou.edu/las/physci/ch350/Projects_2006/Vaandering/Genipin.htm
Thanks C. M. Crowley. That was very useful. The other issue is that after I'm mixed aq. chitosan with genipin I'll wet-spin them in an alkaline bath. Most of people previously prepared X-linked fibres using electrospinning. But, I couldn't find anyone who used wet-spinning for this purpose. Using an alkaline bath in wet-spinning makes some salts to be formed in/on the fibre which makes the measurement of X-link density more complicated.
Dear Azadeh Mirabedini, you can also use the MMR spectrum. Select a peak (belonging to a constant group that does not enter the crosslinking reaction) from the cross-linker spectrum and one from the polymer spectrum (the polymer that based on which the hydrogel is made). Then, using software such as MestReNova, calculate the integral of the area below the said peaks. Express the ratio of the peak integral of the cross-linker to the peak of the polymer as a percentage. The higher the percentage, the greater the modification of the polymer, resulting in more crosslinks in the network. A practical example of comparing the cross-link density (degree of modification) of two hydrogels with this method is presented in the following article. Good luck.
Article Temperature-dependent formulation of a hydrogel based on Hya...
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