In vivo evaluation of a microneedle-based miniature syringe for intradermal drug delivery Urs O. Häfeli & Amir Mokhtari & Dorian Liepmann & Boris Stoeber # Springer Science + Business Media, LLC 2009 Abstract A microfabrication process for miniature syrin- ges is described. The MEMS syringes consist of a silicon plate with an array of hollow out-of-plane needles and a flexible poly-dimethylsiloxane (PDMS) reservoir attached to the back of the plate. The PDMS reservoir can be filled with a drug solution or microparticle suspension which is delivered into the skin simply by the pressure of a finger pushing on the miniature syringe. The efficiency of such a syringe for delivering a suspension of microparticles into skin tissue and a radiolabelled protein (albumin) solution into live mice is reported. Such microneedle devices could be used for the intradermal delivery of vaccination agents or for the systemic delivery of highly effective drugs. Keywords Albumin . Drug delivery . MEMS syringe . Microneedles . Protein delivery . Skin 1 Introduction The parenteral route of drug administration via either subcutaneous (s.c.), intramuscular (i.m.) and intravenous (i.v.) injections is crucial when rapid drug absorption is needed (for example in emergency situations when a patient is unconscious or unable to accept oral medication) and in situations when drugs are destroyed, inactivated or poorly absorbed following oral administration. Drug inactivation is a major concern for the newer macromolecular drugs developed in the recent biotechnology revolution, which include peptides, proteins and viral components. For the parenteral delivery of easily inactivated drugs, there is generally negative patient acceptance primarily associated with pain and inconvenience. To get around this perception, developments since the 1990’ s have focused on “needle- free” injection systems (Stoeber 2008). Like typical parenteral injections, they can deliver drugs locally into the different layers of the skin, both as acute or slow release depot systems, where the drug either resides or further distributes through the blood capillaries in the skin to the circulatory system for peripheral and central action. “Needle-free” injection systems are in fact not needle- free, but based on arrays of very small microneedles that can only be seen under the microscope. They are, however, not perceived as needles by patients as they neither induce pain nor result in any bleeding. The needles are in general only a few hundred micrometers long and thus will not reach the sensory nerves in the dermis (see Fig. 1). The microneedle systems have other advantages too. First, as there is no handling of needles involved, the training of the person using these systems is minimal, disposal is simple, and success of drug dosing is expected to be high. Also, the drug reservoir can be built-in and provide a long-term storage function, for example in the form of an oily drug Biomed Microdevices DOI 10.1007/s10544-009-9311-y U. O. Häfeli : A. Mokhtari Faculty of Pharmaceutical Sciences, The University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada D. Liepmann Department of Bioengineering, University of California, Berkeley, CA 94720, USA B. Stoeber (*) Department of Mechanical Engineering and Department of Electrical and Computer Engineering, The University of British Columbia, 2054-6250 Applied Science Lane, Vancouver, British Columbia V6T 1Z4, Canada e-mail: stoeber@mech.ubc.ca URL: http://www.mech.ubc.ca/~stoeber/