30-11-2012, 04:49 PM
Er:YAG laser pulse for small-dose splashback-free microjet transdermal drug delivery
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ABSTRACT
The microjet injector system accelerates drugs and delivers them without a needle, which is shown to overcome the
weaknesses of existing jet injectors. A significant increase in the delivered dose of drugs is reported with multiple
pulses of laser beam at lower laser energy than was previously used in a Nd:YAG system. The new injection scheme
uses the beam wavelength best absorbable by water at a longer pulse mode for elongated microjet penetration into a
skin target. A 2.9 μm Er:YAG laser at 250 μs pulse duration is used for fluorescent staining of guinea pig skin and for
injection controllability study. Hydrodynamic theory confirms the nozzle exit jet velocity obtained by the present
microjet system.
INTRODUCTION
The laser-based microjet injection system uses the hydrodynamic
impact of a narrow liquid jet onto skin. The immediate
delivery would enable minimized prescription of
topical drugs intended to work on the outer layers of the
skin, avoiding any skin irritation or allergic reaction and
preventing uncontrolled evaporation of active ingredient
and unpleasant odor associated with noninvasive procedures.
Several types of injection mechanism have been
considered, including spring compression, expansion
of piezoelectric transducer, linear Lorentz-force-driven
piston actuator, and expansion of laser-initiated waves
in water [1–3]. Such mechanisms would eliminate abundant
needle wastes, and they are favored for highly
needle-phobic patients [4].
Anarrow, high-pressure jet of 100 to 200 m∕s velocity is
required to accelerate the drug to penetrate the animal
skin with ∼20 MPa of yield strength [4]. Reducing the
jet diameter to a 100 μm size has shown the advantage
in drug delivery of minimizing damage to the tissue [1].
The present scheme of injection via Er:YAG laser beam
at 250 μs pulse duration generates pressure by the displacement
of liquid via laser-induced vapor bubbles and
the elasticpumping of the drug through a nozzle by amembrane
separating the driving liquid from the drug.