Application of MEMS in Drug Delivery 163
(c) Evaluate in vivo, in the subcutaneous tissue of a rodent model, the top three
fabrication methods intended for the surface contacting material and select
the method which combines acceptable biocompatibility, reliability, and cost
Biocompatibility and biofunctionality represent the cornerstones onto which med-
ical device development rests. The biological environment is not the culprit,
it represents the defense mechanism which protects the body from harm and
injury. It is time to acknowledge that the present BioMEMS technology is not
developed enough to symbiotically integrate a device, from the perspective of
biocompatibility and biofunctionality, within the body. Yet, the question remains
today, what can be achieved to enhance the clinical success of BioMEMS drug
delivery systems?
The notion of acceptable material biocompatibility and biofunctionality
changes depending on whether a device is employed as a temporary versus a
permanent fixture within the biological environment. Transdermal BioMEMS
represented by drug delivering microneedle array systems (Section 2.2.1) are
attractive for a number of reasons. First, these devices require no surgical pro-
cedure, thus, meeting an increased patient compliance. The simple pressing of
the microneedle array into the epidermis ensures intended location of delivery.
Second, following the suggested treatment, which does not exceed several hours
at most, the device is removed. In such circumstance less aggressive guidelines of
material biocompatibility are considered compared to those in place for the totally
implantable BioMEMS. The short duration that the trandermal BioMEMS are in
contact with the biological environment leads to an abbreviated acute inflamma-
tory and wound healing response, not nearly as developed and prolonged as in the
case of total implantation. Voskerician et al evaluated the in vivo biocompatibility
of silicon based materials and determined that when fully implanted, silicon did
induce an elevated inflammatory response, but, adverse toxicity was excluded.
Thus, in the case of short-term use, such as the concept employed by most of the
microneedle array BioMEMS, MEMS based materials and technologies are still
widely acceptable as a result of the short exposure duration, even though the
exposure is usually repeated (not a one-time use). Third, recognizing and under-
standing the acute inflammatory changes brought into the biological environment
by the presence of the transdermal microneedles could be incorporated into the
drug delivery treatment to ensure that therapeutic levels are not compromised and
the desired biofunctionality maintained.
Disadvantages to the implementation of BioMEMS microneedle array technol-
ogy involve potential fracture of the microneedles during skin penetration, thus,
exposing the biological environment to a permanent foreign body presence of
micro- or nano-scale which will initiate an associated inflammatory and wound
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