The basic design of the device consists of a piezoelectric transducer which is in contact with a plunger. Voltage-driven displacement of the transducer moves the plunger thereby forcing the drug from a reservoir through an orifice, 20-100 µm in diameter, at a high velocity (>>10 m/s). The volume ejected per pulse can be controlled precisely between 2 to 10 nanoliters by varying voltage across the transducer. The high velocity of the microjets allows their penetration into human skin at depths between 10-100 µm. In essence, this device acts like a printer that prints drugs precisely into the skin. Unlike the current injectors which are limited to discrete injections due to their power mechanisms and the necessity of loading before each use, the microjet device can be used over a long period of time for sustained drug delivery.
Using the typical parameters stated above, the microjet device was successfully tested on human skin in vitro for delivery of mannitol. The amount of mannitol delivered was proportional to the time of injection. Effectiveness of microjets was also confirmed in vivo by testing delivery of insulin in Sprague Dawley rats. Microjets delivered therapeutic doses on insulin in rats and produced hypoglycemia comparable to that obtained by subcutaneous injections. The amount of insulin delivered was proportional to time in accordance with the observations in vitro.
The design described here provides several characteristics desired in a drug delivery device. It allows rapid delivery of drugs without using needles, a feature that is typically seen only in needle-based percutaneous methods. At the same time, the device allows for sustained delivery over a long period of time. The device is capable of providing fine control over dose (~nanoliters), rate of delivery (seconds) and penetration depth (microns).