RESUMO
Many modern tablet presses have system controls that monitor the force exerted to compress the solid oral dosage forms; however this data provides only limited information about the mechanical state of the tablet due to various process and materials uncertainties. A contact pulse/echo ultrasonic scheme is presented for the determination of the local Young's moduli of the coat and the core materials of enteric-coated and monolayer coated tablets. The Young's modulus of a material compacted into solid dosage can be related to its mechanical hardness and, consequently, its dissolution rate. In the current approach, short ultrasonic pulses are generated by the active element of a delay line transducer and are launched into the tablet. The waveforms reflected from the tablet coat-core interface are captured by the same transducer and are processed for determining the reflection and transmission coefficients of the interface from partially overlapping echoes. The Young's moduli of the coat and the core materials are then extracted from these coefficients. The results are compared to those obtained by an air-coupled acoustic excitation study, and good agreement is found. The described measurement technique provides greater insight into the local physical properties of the solid oral dosage form and, as a result, has the potential to provide better hardness-related performance predictability of compacts.