1. Poly(D,L-lactide-co-glycolide) (PLGA) with terminal carboxylate groups (PLGA-carboxylate) is dissolved in any solvent for PLGA (as

mentioned in materials section) at a concentration of 5mM. PLGA can be dissolved at this concentration with gentle stirring.

2. Both NHS (molecular weight 115.09) and EDC (molecular weight 191.7) are dissolved in the PLGA solution at a concentration of 25mM. (Both

EDC and NHS are added in a stoichiometric excess of 5 times compared to PLGA). PLGA-carboxylate is converted into PLGA-NHS by

adding EDC and NHS to PLGA-carboxylate solution with gentle stirring for about 1 hour.

3. The reaction product PLGA-NHS is precipitated out by adding the washing solution methanol. Approximately 10 times volume excess of

methanol is added to the solution. The solution is centrifuged at 2000 x g to precipitate out the PLGA-NHS and discard the supernatant

(removes the traces of EDC and NHS. This procedure of washing with methanol is repeated at least three times.

4. The PLGA-NHS pellet is dried under a vacuum for 30 minutes to remove any traces of the washing solution.

5. The PLGA-NHS pellet is now re-dissolved in the same solvent at the same concentration that was used initially to dissolve PLGA. The

heterobifunctional PEG (amine-PEG-carboxylate) is then added to the PLGA solution at a concentration of 5mM (stoichiometric ratio of 1:1).

The mixture solution is incubated for 24 hours with constant stirring.

6. After 24 hours, the reaction product PLGA-b-PEG block copolymer is precipitated out by adding the washing solution methanol in excess.

Repeat the washing and centrifugation process as mentioned above three times. This will remove all excess unreacted PEG.

7. The PLGA-b-PEG block copolymer is dried under vacuum.

Reference :URL: http://www.jove.com/details.php?id=3398

DOI: 10.3791/3398

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