pH-Sensitive poly (acrylic acid-co-acrylamide) anionic hydrogels for jejunum targeted drug delivery systems

Ionic hydrogels are favorable for drug delivery applications, and fluorescence probes have been employed to analyze drug carriers. In this work, we studied swelling properties of pH-sensitive poly (acrylic acid-co-acrylamide) P(AAc-co-AAm) hydrogels in the presence of 30 vol% AAc at different pH values by steady-state fluorescence technique. We introduced a hydrophilic fluorescence probe, pyranine 4 (4sPy), due to its emission spectrum independent of pH. 4sPy molecules were trapped in the P(AAc-co-AAm) hydrogel network during the gelation before the swelling process. We monitored the effect of pH on fluorescence intensities of 4sPy during in situ swelling processes and also compared the behavior of trapped 4sPy molecules with the behavior of trapped drug carriers in a controlled drug delivery system. Most of the 4sPy molecules were released out from the hydrogels at high pH, such as drug molecules in the drug delivery system. Our results indicated that these hydrogels reached the maximum swelling ratio at pH = 9. The cooperative diffusion coefficient, D, was found using in situ fluorescence and gravimetric results as nearly 10⁻⁸ m²/s for different pH values that are comparable to the diffusion coefficient of drug molecules in drug delivery systems in the literature. Scanning electron microscope results indicated the change in morphology of anionic hydrogels swollen at different pH values. These results showed that P(AAc-co-AAm) hydrogels could be applicable for jejunum targeted drug delivery systems, and the 4sPy can be a candidate probe to monitor the drug carriers.