Shape Memory Microneedle to Prevent Risks of Reproductive Hormone Therapy by Switching Sustained to Burst Release Under a Single Transdermal Insertion

ABSTRACT Syringe injections inherently accompany burst inoculation of a defined volume to cover a sustained period of effect. Considering the combinative need for both release patterns, a user‐specified switch between burst and sustained release is required, depending on each therapeutic strategy. Ovarian hyperstimulation syndrome (OHSS) is a representative risk of syringe injections used to stimulate ovulation. Follicle‐stimulating hormone (FSH) is injected repeatedly for sustained effects, followed by a last shot of human chorionic gonadotropin (hCG) for burst effects, which accompanies OHSS risks. Hence, a shape memory microneedle (SMN) is developed by enabling recovery from X to O shape by mild heating, switching from sustained to burst release under a single transdermal insertion. The X shape provides sufficient loading spaces for double hormone layers in gelatin gel from outer FSH to inner hCG onto the SMN. After the 3‐day sustained release of FSH by controlling gelatin degradation in the X shape, the recovery to the O shape pushes out hCG for a 24‐hour burst release with sufficient gelatin breakage in a clinic‐mimetic rabbit model. Despite overdose loading with a single shot, the SMN preserves the injection level of ovulation by suppressing OHSS risks, indicating the SMN's potential to address syringe injection issues.