Biomedical Engineering Reference
In-Depth Information
8
Implantable Microdevices
Engineers and doctors foresaw very early
the need for miniaturizing devices that
penetrate the human body, recognizing that any amount of penetration would be an invasion
of a foreign body. hese penetrating devices would range from “passive implants,” such as den-
tal implants, to “active implants,” such as microelectrodes. As a result, the ield of BioMEMS
produced early on a plethora of implantable microdevices using traditional silicon microma-
chining. Not all the envisioned devices were as useful as doctors would have liked them to be
because, as it turned out, the materials that were used in their development were not biocompat-
ible for long-term human use. It would require a few more decades of research to ine-tune or
redesign most of these processes.
Note that, for obvious reasons of space, we do not cover here the vast body of literature on
drug delivery, a ield that has oten resorted to clever microfabrication and microluidics tricks
to produce nanoparticles that encapsulate drugs and that are then implanted into the body;
although it can be argued that the nanoparticles are, in fact, implantable nanodevices—and we
agree that they have extremely interesting biophysical properties and an enormous therapeutic
potential—we do not have space to cover them here.
he reader should note that, this being the inal chapter, it tends to contain less details on pro-
cessing and microfabrication (referring to earlier chapters whenever possible) and tries to focus
on the inal goal of these studies: the use of these devices inside the human body (skin included).
Paradoxically, for several decades, the ield of implantable microdevices struggled to produce
biomedically relevant data because it was technologically behind in its vision. his is no longer
the case, and the ield is now (as we speak) blooming like a desert ater a rainfall. Here is a short
chapter with very exciting developments.
8.1 Dental Implants
Donald Brunette, from the University of British Columbia in Vancouver (Canada), envisioned
early in the 1980s the importance of exploiting
contact guidance
, the tendency of cells to
align to edges such as those present on micromachined groove substrates (see Section 6.2.2).
Brunette's laboratory was housed in the Department of Oral Biology, so he was deeply interested
in controlling the migration and penetration into dental implants of epithelial cells (which form
a seal with the implants) and gingival ibroblasts; this critical process determines the success
of the implantation procedure in the long term. Translation of the early in vitro studies into
animal studies took more than a decade, but eventually it was possible to produce implants con-
taining microtopographies in the form of titanium-coated micromolded tapered pits (
Figure
8.1a
through
c
). It was shown that these topographies can stimulate connective tissue and bone
