a microneedle array , constructed of silicon and silicon dioxide compounds or of a molded plastic material , is provided to penetrate the stratum corneum and epidermis layers of skin , but not into the dermis . the microneedles can be used to either dispense a liquid drug , or to sample a body fluid . the delivery of drugs and sampling of fluids can be performed by way of passive diffusion , instantaneous injection , or iontophoresis . a complete closed - loop system can be manufactured including active elements , such as micro - machined pumps , as well as passive elements such as sensors . a “ smart patch ” can thereby be fabricated that samples body fluids , performs chemistry to decide on the appropriate drug dosage , and then administers the corresponding amount of drug . an electric field may be used to increase transdermal flow rate . such a system can be made disposable , and can be used with medical devices to dispense drugs by iontophoretic / microneedle enhancement , to sample body fluids , and as a closed - loop drug delivery system with fluid sampling feedback using a combination of the other two devices . as a drug dispensing system , the microneedle array includes electrodes that apply an electric potential to the skin between the electrode locations . one of the electrode assemblies is filled with an ionized drug , and the charged drug molecules move into the body due to the applied electric potential . as a body - fluid sampling system , the microneedle array also includes electrodes to assist in moving fluid from the body into a receiving chamber , and which further includes a bioelectrochemical sensor to measure the concentration of a particular substance .