Biomedical Engineering Reference
In-Depth Information
its polymeric format, they do not constitute a sharp waste biohazard so they can be disposed of
by, for example, incineration.
he microneedle ield has a very interesting history and has produced some of the most
beautiful MEMS images. he irst microneedles were reported in micromachining conferences
by Albert Pisano (University of California at Berkeley) in 1993 and Ken Wise (University of
Michigan at Ann Arbor) in 1994 and were made entirely in single-crystal silicon on the same
plane as the wafer. For 10 years, the ield improved the luidic performance of these “in-plane
microneedles,” introducing other materials such as polysilicon and silicon nitride to produce
better channels (Bruno Frazier from Georgia Tech even produced metallized microneedles by
electroplating in 2003), but no relevant biological data were produced with them. A big concern
was that they were brittle, and if they stayed inside the patient, there would be no easy way
to remove them (except for costly surgery, which would defeat their very existence in the irst
place). An example of an in-plane polysilicon microneedle is shown in
Figure 8.13a
. he ield
made a big turn in 1998, when a team led by Mark R. Prausnitz and Mark G. Allen at Georgia
Institute of Technology was able to produce short microneedles that stuck out of the plane of
the wafer (
Figure 8.13b
). hese “out-of-plane microneedles” were much less brittle and could
a
b
Out-of-plane solid silicon microneedles
In-plane polysilicon microneedle
Microneedle
outlet
100 µm
Blood
stain
c
d
1 mm
Out-of-plane hollow PMMA microneedles
Out-of-plane hollow silicon microneedles
100 µm
500 µm
FIGURE 8.13
In-plane. versus. out-of-plane. microneedles.. (a). Polysilicon. microneedle. fabricated.
with.planar.micromachining..(From.Jeffrey.D..Zahn,.Ajay.Deshmukh,.Albert.P..Pisano,.and.Dorian.
Liepmann,.“Continuous.on-chip.micropumping.for.microneedle.enhanced.drug.delivery,”.
Biomed.
Microdevices
,. 6,. 183-190,. 2004.. Reprinted. with. permission. from. Springer.). (b). First. array. of.
out-of-plane.microneedles.for.transdermal.use..(From.Sebastien.Henry,.Devin.V..McAllister,.Mark.
G..Allen,.and.Mark.R..Prausnitz,.“Microfabricated.microneedles:.A.novel.approach.to.transdermal.
drug.delivery,”.
J. Pharm. Sci.
,.87,.922,.1998..Image.contributed.by.Mark.Allen.).(c).Microarray.of.
out-of-plane.hollow.silicon.microneedles.(inset:.chip.mounted.at.the.end.of.the.syringe)..(From.Raja.
K..Sivamani,.Boris.Stoeber,.Gabriel.C..Wu,.Hongbo.Zhai,.Dorian.Liepmann,.and.Howard.Maibach,.
“Clinical. microneedle. injection. of. methyl. nicotinate:. Stratum. corneum. penetration,”.
Skin Res.
Technol.,
. 11,. 152-156,. 2005.. Reprinted. with. permission. from. John. Wiley. and. Sons.). (d). Array.
of.hollow,.out-of-plane.PMMA.microneedles..The.blood.stains.shown.in.the.inset.(produced.with.
a.three-microneedle.array).demonstrate.the.full.penetration.of.the.stratum.corneum.layer.of.dead.
cells.through.the.skin.of.a.volunteer..(From.Sang.Jun.Moon.and.Seung.S..Lee,.“A.novel.fabrication.
method.of.a.microneedle.array.using.inclined.deep.x-ray.exposure,”.
J. Micromech. Microeng.
,.15,.
903-911,.2005..Figure.contributed.by.Sang.Jun.Moon.)
