Biomedical Engineering Reference
In-Depth Information
are. critically. different. from. the. conventional. electronic. system. designs. and. accordingly.
require.new.design.methodology.at.every.design.level..Clearly,.integration.and.miniatur-
ization.of.the.implants.become.essential.and.require.solutions.from.many.fronts—device,.
circuit,.architecture,.system,.algorithm,.design,.testing,.packaging,.and.technology.
Nanotechnology. plays. a. critical. role. in. the. integration. and. miniaturization. of. the.
implants,.especially.in.the.areas.of.electrode.and.packaging.designs..Both.recording.and.
stimulation. functions. critically. depend. on. the. eficacy,. eficiency,. safety,. and. reliability.
of.the.electrodes..The.electrodes.provide.the.contact.to.the.tissues.of.nerves.or.muscles.
in.the.fashion.of.“rubber.meeting.the.road”.in.car.driving..The.physical.properties.and.
dimensions. strongly. correlate. the. characteristics. of. an. electrode. and. its. applications.
accordingly.. The. core. requirements. for. stimulation. and. recording. lie. in. the. high. efi-
ciency.of.charge.transferring,.biocompatibility,.and.durability..Signal-to-noise.ratio.(SNR).
is.a.critical.factor.in.recording.electrode.design..The.factor.that.most.affects.the.charge.
transferring.mechanism.is.the.area.that,.in.turn,.impacts.on.selectivity..The.electrode.is.
made.of.metal,.which.directly.affects.biocompatibility..The.prosthesis.systems.are.often.
operated. in. continuously. dynamic. excitation. (stimulation. or. recording). via. electrodes.
by. current,. and. thus. charge,. whose. long-term. reliability. and. safety. effect. in. terms. of.
electrochemical.properties.must.be.carefully.studied..One.of.the.great.challenges.is.the.
inlammatory. response. resulting. in. the. generation. of. glial. cells. around. the. implanted.
electrodes,. which,. in. turn,. degrades. the. effectiveness. of. the. recording. and. stimulation.
operations.
1
.Nanotechnology.provides.ways.of.surface.modiications.to.precisely.control.
both. chemical. and. biological. reactions,. as. well. as. the. transition. mechanisms. of. physi-
cal.property..For.example,.an.anti-inlammatory.surface.modiication.could.attenuate.the.
formation.of.glial.cells.
2
In. order. to. improve. an. electrode's. SNR,. and. thus. the. sensitivity,. surface. modiication.
techniques.using.nanotechnology,.to.increase.the.surface.area.of.an.electrode.and.reduce.
the.electrode.impedance.accordingly,.have.been.reported,
3,4
.as.shown.in.Figure 16.1..The.
report.shows.that.a.carbon.nanotube.(CNT)-coated.electrode.achieves.25.times.the.imped-
ance.reduction,.a.45-fold.charge.transfer.rate,.and.65%.noise.reduction.
5
.This.performance.
improvement.has.a.direct.impact.on.the.future.neural.implant.if.it.requires.a.high.density.
of.electrodes,.which.in.turn.reduce.the.geometry.size.of.each.electrode.
FIGURE 16.1
Electrodes.after.surface.modiication.techniques..Such.techniques.reduce.the.impedance,.interface.noise,.and.
increase.the.charging.capacity..(From.Keefer,.E.,.et.al.,.
Nat. Nanotech.
,.3,.434-439,.2008.)
