High-aspect-ratio microdevices comprising microneedles, microknives and microblades and their manufacturing methods are disclosed. These devices can be used for the delivery of therapeutic agents across the skin or other tissue barriers to allow chemical and biological molecules getting into the circulation systems. The microneedles can also be used to withdraw body fluids for analysis of clinically relevant species when the device has an integrated body fluid sensor or sensor array in the vicinity of microneedles.