The present invention provides high-concentration formulations of opioids such as fentanyl or fentanyl congeners. The selected value is selected from among a voltage and a current of an input signal, and the at least one variable resistance device is configured to memorize the resistance value. The locking and unlocking element comprises a removable slide moving in the groove, the said removable slide including guiding grooves and grooves in the shape of linear cams into which fit rollers fixedly attached to at least one jaw which is removable so as to act on at least one end of the blanket strips.