Therapeutic drugs administered systematically are evenly distributed to the whole body
through blood circulation and have to cross many biological barriers before reaching the pathological
site. Conventional drug delivery may make drugs inactive or reduce their potency as they may be hydrolyzed
or degraded enzymatically and are rapidly excreted through the urinary system resulting in
suboptimal concentration of drugs at the desired site. Controlled drug delivery aims to localize the pharmacological activity
of the drug to the desired site at desired release rates. The advances made by micro/nanofluidic technologies have provided
new opportunities for better-controlled drug delivery. Various components of a drug delivery system can be integrated
within a single tiny micro/nanofluidic chip. This article reviews recent advances of controlled drug delivery made
by microfluidic/nanofluidic technologies. We first discuss microreservoir-based drug delivery systems. Then we highlight
different kinds of microneedles used for controlled drug delivery, followed with a brief discussion about the current limitations
and the future prospects of controlled drug delivery systems.
Keywords: Controlled/targeted drug delivery, pharmacological activity, micro/nanofluidic technologies, microdevices,
microreservoir, and microneedle.
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