Real-time monitoring of the dissolution of pH-responsive polymer coatings by capacitive sensing with signal protection mechanism

Accurate assessment of pH-responsive polymer dissolution in vitro is crucial for formula design in drug delivery systems. This study developed a high-performance capacitive sensing system (Cap-S) with a screen-printed carbon electrode (SPCE) for real-time monitoring and evaluating the dissolution rate of EUDRAGIT (R) FL 30 D-55 and L 30 D-55 polymers. The linear detection range of the Cap-S is 1.000-4.000 pF (R-2 = 0.9909) with a sensitivity (0.309 fF/fF). The sensor system exhibited a tri-phasic response with a dual-sigmoidal curve, allowing for accurate measurement of the dissolution time of polymers to reach 50 % capacitance shift (T50 %). The Cap-S showed outstanding temporal resolution (0.1 s) in monitoring polymer dissolution without the need for an electroactive probe commonly used in electrochemistries. It also provides a realistic and discriminative in vitro dissolution assessment of enteric-coated formulations in Hanks' buffer (T50 % = 409 s and > 5.6 h to FL 30 D-55 and L 30 D-55, respectively) versus Sorensen's phosphate-buffered saline (T50 % = 532 s and =1761 s to FL 30 D-55 and L 30 D-55, respectively), among others. The approach is a compact and precise method for real-time monitoring and quantitative assessment of polymer dissolution.