Biomedical Engineering Reference
In-Depth Information
FIGURE 10.8
Silicon dioxide microneedle array.
1.
Increased Permeability—
The self-sealing properties of SC are poorly understood. It
is probable that SC seals holes spontaneously up to a given magnitude, but
beyond that limit it cannot close itself. This property can be used by micronee-
dles to increase the permeability of skin by orders of magnitude, making it pos-
sible to diffuse macromolecules across the skin. Thus in some cases, the
microneedles may not themselves deliver the drug. Unmedicated microneedles
may simply puncture the skin and then medicines may be smeared on and left to
be rapidly absorbed through the holes.
2.
Application customization
—Microneedles can be fabricated in various shapes
(cylindrical, pyramidal, and polyhedral) or sizes and may be hollow or solid.
Such geometrical flexibility allows for fabrication of microneedle arrays
customized for the type and volume of drug and the duration of use. This feature
also translates to flexibility in method of drug delivery. For example, medicines
may be delivered the way a regular hypodermic needle does so, or microneedles
may be coated with medication which would be absorbed on contact.
3.
Material flexibility
—Microneedles can be fabricated using a variety of materials
such as silicon, glass, carbon nanotubes, biodegradable polymers, and metals.
The choice of material would depend on the application. For example, metal-
lic microneedles are the most popular because they have high strength and
biocompatibility. Polymer needles have the advantage of being biodegradable,
and thus if the tips snap off during insertion, the body would simply absorb
the remains.
4.
Minimal medical training requirements
—Microneedles are expected to become
a boon for immunization programs in developing countries as they could
be applied by people with minimal medical training. Drugs could similarly be
administered at home instead of presently compulsory clinical visits. The signif-
icance of such capability is further enhanced due to possibility of mass vaccina-
tion or antidote administration in bioterrorism incidents. The cause is further
helped by the fact that microneedle fabrication promises to be less expensive
than any other reported technology.
5.
Site specific therapy—
Highly targeted drug administration to individual cells is
possible using microneedles. A potential application is to modulate the immune
system by administering drugs precisely into the area where special immune
cells reside. Langerhans cells, for example, are the major immunomodulatory
cells that modify delivery of HIV particles from the epidermis to the lymph
