2.2 Neurology
Neurology is another field which is being explored for MF applications. MF is
employed for bothin vivodeliveries of drug solutions from on-chip reservoirs
situated on neural implants as well asin vitrostudies of neuronal cells via highly
precise delivery growth and inhibitory factors by the use of gradient-generating
devices [ 15 ]. It is tough to probe the complex interactions that actually occur among
neural cells using conventional methods of analysis. In this context, MF has proved
to be the most suitable technique for neurology experiments. For instance, rapid,
highly sensitive determination of trans-membrane potential has been possible in
MF devices utilizing charged membrane-permeable, potential- sensitive dyes, with
minimal use of reagents [ 16 ]. The LoC system consists of a quartz sipper chip
containing microchannels connected to a sipper capillary, a fluorescence reader, a
vacuum pump, and a computer. The flow rate in the detection channel is controlled
by pressure driven pumps and could be varied from 2 to 10 nLs^1 by varying the
applied pressure from 21 to 25 psig. Cells and samples were first mixed on the chip
and then the dyes are added to the mixture. After a short incubation in a detection
channel, the fluorescence of individual cells was detected. The membrane potential
was determined by monitoring the dye uptake rate of the cells and modulated either
by opening or blocking K+channels by varying cytoplasmic free Ca2+. NMR
(nuclear magnetic resonance) micro coils have been efficiently used to study single
non-perfused neurons [ 17 ], where NMR probes have been micro-fabricated on the
glass substrate MF platforms and sucrose solutions are used for their testing
[ 18 ]. Besides this MF principle and techniques have been applied in the isolation
of brain tissue culture studies. The separation of brain tissue specimens under
in vitroconditions is a very complicated task as it requires exquisite control over
experimental conditions and access to neural networks and synapses [ 19 ]. Scott
et al. designed a MF chip for simultaneous recording of electrical signals and
optical characterization of brain tissue slice preparations [ 20 ]. The device was
utilized to record waves of spontaneous activity in developing cortical slices and
to perform multisite extracellular recordings during simultaneous calcium imaging
of activity. The device consists of an array of MF channels and a perfusion chamber
(Fig.8.2A). Each channel consists a well at one end, an aperture which is in contact
with the perfusion chamber in the middle, and pressure and electronic controls at
the other end is connected to port. The apertures are 20 or 50μm in diameter with a
spacing of 300μm and are designed to probe an array of anatomically relevant sites.
The relatively large aperture size and spacing were chosen because they are
appropriate for the anatomical features in the particular study. The work paved a
way to develop devices of different geometric configurations for other studies also.
The use of microchips may overcome the limitations of reduced oxygen and
nutrient supply while using conventional interface and submerged slice chambers
to the brain slices allow the neuroscientists to design complex experiments to have a
better insight into neuroprocesses [ 15 ]. Mauleon et al. developed an MF system that
allows diffusion of oxygen throughout a thin membrane and directly to the brain
196 S. Solanki and C.M. Pandey