Monitoring of swelling of hydrophilic polymer matrix tablets by ultrasound techniques

The aim of this study was to investigate the ability of ultrasound (US) techniques to monitor the swelling behaviour of hydrophilic polymer matrix tablets. Tablets were prepared from hydroxypropyl methylcellulose (HPMC) and polyethylene oxide (PEO) polymers. The movement of the eroding front was investigated with ultrasound scanning techniques on each tablet's outer interface during tablet immersion in phosphate buffer (PB). In addition, a US window technique was utilized to simultaneously evaluate eroding and swelling front movements during the tablet dissolution process. An optical monitoring was used as the reference method. The focused pulsed echo ultrasound method was found to be applicable for evaluating the swelling process of hydrophilic polymer matrix tablets. Furthermore, it was noted that the sensitivity to follow hydrogel formation and thickening by US monitoring varied depending on the polymer under study. Thus, multifront detection is challenging since the hydrogels formed by different polymers may have totally different acoustic properties. It was found that the microbubbles formed inside the hydrogel were acting as a "contrast agent", characteristic of some polymers during immersion. In spite of these challenges, the US window technique introduced in this study was proven to be a promising method for simultaneous multifront detection.