Biomaterials for MEMS

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

effectiveness.

7.5 BioMEMS IN DRUG DELIVERY: THE REALITY

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.

53

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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