Nanomedicine - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 129

anode gold membranes

SiO 2

cathode

Si

1 2 3

reservoirs

Fig. 4.1 Controlled release of drugs via MEMS

In what follows, we will describe such bioMEMS starting with a controlled
releasing microchip ( Santini et al. 1999 ), which is a silicon chip that offers
controlled release of a single or of multiple agents on demand. The device is
depicted in Fig. 4.1 . The release of agents contained in one or several reservoirs,
denoted by 1, 2, and 3 in Fig. 4.1 , is done by applying a dc voltage between the
anode, which consists of a 0:3 m thick gold membrane, and the cathode. The
microchip has a dimension of 17 mm 17 mm 310m and incorporates 34
reservoirs, but there is enough space to contain 1,000 reservoirs, thus demonstrating
the immense power of micro/nanotechnologies. This chip was fabricated by a series
of technological processes encompassing optical lithography, CVD, electron beam
evaporation, and RIE.
The reservoir (see Fig. 4.2 ) has the shape of a square pyramid with a volume of
25 nl and releases the agent through the small square opening covered by the anode
membrane. This membrane has dimensions of 50m 50m 300 nm and is made
from gold because gold has low reactivity with many agents in the reservoirs and
is easily processed by micro/nanofabrication techniques. The reservoirs were filled
through the large openings by an ink jet printing method able to deposit 0.2 nl of gel
or liquid solution of desired concentration in each reservoir. Microsyringe pumps
are an alternative solution to fill the reservoirs. The prototype device was able to
release various substances at an applied voltage of 1.04 V. The two situations are
displayed schematically in Fig. 4.3 .
The release of masses of about 250 ng was studied during those days. Each
reservoir can be controlled individually by a dc voltage, and the released agents can
be solid substances, liquids, or gels. This is a lab-on-chip device if the reservoirs are
connected to microfluidic systems, which fill them periodically.
The drug-releasing microchip could be eventually mounted in a biocompatible
case, and it can contain the power source and antenna needed for wireless
communications ( Prescott et al. 2006 ), as shown schematically in Fig. 4.4 .
Such a MEMS-controllable drug delivery was used in vivo to release doses
of several substances using two tracer molecules, fluorescein dye and radiolabel