Bioresponsive transcutaneous patches.

Transdermal drug delivery systems that utilize transcutaneous patches of arrayed microneedles have attracted increasing interest in medical practice as an alternative method to hypodermic injection. Over the past ten years, research has focused on leveraging physiological signals associated with diseases or skin-specific tissues to create bioresponsive patches that release drug directly in response to an internally-generated stimulus. This review surveys the recent advances in the development and use of bioresponsive transcutaneous patches for on-demand smart and precise drug delivery, exploiting different physiological signals including pH, serum glucose levels, and enzyme activity. The clinical potential of these devices, including challenges and opportunities, is also discussed.