Biomedical Engineering Reference
In-Depth Information
Fig. 4.15
A CNT optical
antenna
antenna
exciton energy
transfer
shell CNT
core CNT
through the opening on the front side. The surface and the cross section of the
chip are displayed in Fig. 4.16 a, b, respectively. The negatively charged L -glutamate
molecules in a buffer solution are introduced in the reservoir. The front surface of
the chip consists of a pair of Pt electrodes separated by typical distances of 10m
and patterned over a SiO 2 =Si substrate, in which a releasing opening is etched.
This structure is placed over a plexiglas flow cell, which contains the reservoir, and
the resulting device is sealed with polydimethylsiloxane (PDMS) such that another
Pt wire is trapped at the interface between the flow cell and the top structure. To
release the L -glutamate, a voltage is applied between the Pt electrodes, charged
positively, and the Pt wire, which is charged negatively. As a result, the L -glutamate
molecules tend to move away from the Pt wire and toward the Pt electrodes, being
released through the opening on the top surface. The device was tested using a
solution of 10 mM L -glutamate diluted in a phosphate buffer solution (PBS), which
was introduced in the minireservoir, and the neurotransmitter fluorescence was
monitored during actuation experiments. The electrokinetic actuation voltage on the
Pt wire is able to release the drug starting at a value of -200 mV. At a higher actuation
voltage of -500 mV, applied for during 1 s, the device is able to spread glutamate
molecules in a region with a diameter of 100m; the glutamate molecules stimulate
neuron cells in the environment. Also, the diffusion of the glutamate is suppressed
by applying and inverse voltage.
Neuronal drug delivery is related also to the implantable neuronal probes which
initially, in the 1980s, contained a recording array consisting of ten channel
microelectrodes integrated with the signal processing chip ( Najafi and Wise 1986 ;
Wang and Soper 2007 ). In Fig. 4.17 , we have represented such a microneural probe.
The probe has a length of 4.7 mm, a width of 15m at the tip and 160m near
the base, and has a thickness of 15m. More sophisticated neural probes were
developed.
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