Could you use DMF or DMSO as solvent? I have been use these solvents and both of them are work well. You can add a little bit triethylolamine when do the experiment.

Thanks for the answer Zhao,

I've seen that people use this solvents as a non-aqueous media for this reaction. I have to find out if they are gonna dissolve the PLA.

Is it not necessary to worry about the pH with this solvents because they are aprotic?

Is the triethanolamine a buffer to keep the pH basic in the second step (amine linkation? Isn't it reduce the effectiveness of the NHS/EDC step which needs to have COOH groups?

How many time needs the reaction? I left the EDC/NHS 0.1M/0.02M for 1h and the APTES (0.1M) for 2h. Is that enough?

I also shake the receptacle where the reaction take place to promote diffusion. But I worry if it's better to left it still to promote interaction between groups.

Thank you very much,

Joan

Hi, Joan.

Here is an protocol which I have been used.

In brief, PLA-COOH (MW~5000) was dissolved in DMSO/DMF.

A total of  EDC and  NHS were gradually added into PLA solution and the mixture was stirred vigorously for 1 h.

After adding the amine group polymers.The solution was stirred at room temperature for 8-12 hours.

The mixture was then subjected to ice-cold water and maintained at 4 C overnight to facilitate precipitation. The precipitation was collected and dried in vacuum.

Acutally, EDC activate carboxyl group at pH=4.5-6 , but it also need higher pH value for Amide bond formation, and the triethanolamine do reduce the effeciveness of the EDC, I think NHS is stable in this situation,so we add more EDC in the experiments.  EDC/NHS>4:1. and  0.2 eq  TEA.

Most of details based on my experience, so I will check the literature make the answer more reasonalbe.

If you have any other question, we could discuss it together.

Thanks for the answer, it's really helpful.

The problem is that I don't want to dissolve the PLA, I want to keep the nanofiber morphology and attach the APTES on the surface. So I'm afraid I cannot use DMSO or DMF.

I guess I have to find a solvent which doesn't dissolve PLA, wets it well and works with the system EDC/NHS.

Thanks

Hi Ruifang,

The pH of DMSO in my lab is ~9.9. How did you buffer the pH at 4.5-6 and later 7-8 for the two-step coupling? Or did you just add acid/base instead of buffers?

# Michelle Wang: I assume that definition of  pH applies only to aqueous solution. In my point, addition of triethanolamine (~ 2 eq) help to convert EDC.HCl to EDC base form which increase activity of EDC in DMSO

Dear Joan,

The reaction you want to do is not feasible because EDC is a catalyst to make amide bond between -COOH and -NH2. You only have -NH2 in APTES and no -COOH in PLA.

I would rather recommend to crosslink APTES through silanization.

1. Plasma treatment PLA nanofiber mat. (or acid treatment)

2. Add 1% APTES in 70% Ethanol , pH4.5~5

3. Put the PLA mat in the APTES solution and wait reaction 2-4h.

4. Rinse

Good luck!

Perhaps try CDI instead of EDC for linking to the -COOH.. It is a carbodiimide linker that can be used in organic solutions.

DMSO works fine for the NHS/EDC chemistry. There are reports on PLA-PEG polymers conjugated to amine with NHS/EDC chemistry in DMSO.