New mode of drug delivery: long term autonomous rhythmic hormone release across a hydrogel membrane.

This note demonstrates a novel mode of rhythmic drug delivery, which is independent of external modulation or physiological stimulation. Rhythmic behavior is attributed to negative, nonlinear feedback between the swelling state of a hydrogel membrane and the enzymatic conversion of glucose to hydrogen ion. The system pulsates in the presence of a constant level of glucose, thus distinguishing it from insulin delivery devices that respond to changes in glucose concentration. As an example, gonadotropin-releasing hormone (GnRH) was released in short, repetitive pulses over 1 week.