If polyoxometalate (anion) is electro-statically binded with the a cationic polymer using acrylic acid as a monomer.
what will be the release mechanism of the drug and what will be the effect of pH on drug release?
Normally a drug is loaded in free form in polymeric network (hydrogel) and release mechanism is by diffusion process. Here the drug by itself is the part of hydrogel system and is electro-statically binded with the polymer.
Dear Sir;
since you are using a weak carboxylic acid for the binding of the drug, one can expect a high release of the drug by lowering the pH, since carboxylic acid groups tend to converge towards their neutral state when approaching a pH around 3. If this is the situation, the binding of the drug is reduced and it becomes free to diffuse out of the matrix. Regards
Dear Sir,
I tried to ilustrate what Mr. Abdelkader has explained.
considering the pKa of acrylic acid is 4,25 it´s means that in pH lower than 4,25 the carboxylic group of acrylic acid will be a neutral specie, in this case, the cation will be released from polymeric matrix. This mechanism is usually aplied to drugs in oral administration, since the stomach pH is very low (about 1,5). So inicially you have your drug attached to your polymeric matrix (forma A) so when this polymeric matrix arrives to your stomach the drug is released (Form B).
Please look the attached figure, hope it help you.
Dear Shafi,
I agree with everyone's comments above. However, when you drop the pH to evaluate the release I suggest doing a control in your standard release media (maybe PBS, pH 7.4?). This way you can say more or less release as well. From my experience, just dropping the pH to below the pKa of carboxylic acid groups did not instantly dump the drug off from my polymer. The drug binding happens in hours so this is unlikely explained by diffusion limitations of my drug out of the polymer network. Dropping the pH did increase how much came off, but not all came off immediately. This may be due to (1) my system itself and yours could behave differently, (2) strong ionic interaction that slows protonation, (3) or something else (opinions, thoughts, etc. would be great).
Dear all,
Thanks Dr. Jeannine Coburn for the nice contribution and coments. I would add a small concerning another factor that will contribute to the release, is the osmosis effect which operates and help in diffusion ones the drug is released first from the binding sites of the matrix towards another environment. As you have said, things sometimes do not go along with our thinking, but the experience is the only witness about any result and explanation. Regards
Thanks Alot Raphael Henrique Marques Marcilli,Jeannine Coburn and Abdelkader BOUAZIZ
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