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Availableonlineatwww.
sciencedirect.
comSensorsandActuatorsB130(2008)917–942ReviewMEMS-basedmicropumpsindrugdeliveryandbiomedicalapplicationsA.
Nisar,NitinAfzulpurkar,BanchongMahaisavariya,AdisornTuantranontIndustrialSystemsEngineering,SchoolofEngineeringandTechnology(SET),AsianInstituteofTechnology(AIT),P.
O.
Box4,KlongLuang,Pathumthani12120,ThailandReceived21July2007;accepted31October2007Availableonline20December2007AbstractThispaperbrieyoverviewsprogressonthedevelopmentofMEMS-basedmicropumpsandtheirapplicationsindrugdeliveryandotherbiomedicalapplicationssuchasmicrototalanalysissystems(TAS)orlab-on-a-chipandpointofcaretestingsystems(POCT).
Thefocusofthereviewistopresentkeyfeaturesofmicropumpssuchasactuationmethods,workingprinciples,construction,fabricationmethods,performanceparametersandtheirmedicalapplications.
Micropumpshavebeencategorizedasmechanicalornon-mechanicalbasedonthemethodbywhichactuationenergyisobtainedtodriveuidow.
ThesurveyattemptstoprovideacomprehensivereferenceforresearchersworkingondesignanddevelopmentofMEMS-basedmicropumpsandasourceforthoseoutsidetheeldwhowishtoselectthebestavailablemicropumpforaspecicdrugdeliveryorbiomedicalapplication.
Micropumpsfortransdermalinsulindelivery,articialsphincterprosthesis,antithrombogenicmicropumpsforbloodtransportation,micropumpforinjectionofglucosefordiabetespatientsandadministrationofneurotransmitterstoneuronsandmicropumpsforchemicalandbiologicalsensinghavebeenreported.
Variousperformanceparameterssuchasowrate,pressuregeneratedandsizeofthemicropumphavebeencomparedtofacilitateselectionofappropriatemicropumpforaparticularapplication.
Electrowetting,electrochemicalandionconductivepolymerlm(ICPF)actuatormicropumpsappeartobethemostpromisingoneswhichprovideadequateowratesatverylowappliedvoltage.
Electroosmoticmicropumpsconsumehighvoltagesbutexhibithighpressuresandareintendedforapplicationswherecompactnessintermsofsmallsizeisrequiredalongwithhigh-pressuregeneration.
Bimetallicandelectrostaticmicropumpsaresmallerinsizebutexhibithighself-pumpingfrequencyandfurtherresearchontheirdesigncouldimprovetheirperformance.
Micropumpsbasedonpiezoelectricactuationrequirerelativelyhigh-appliedvoltagebutexhibithighowratesandhavegrowntobethedominanttypeofmicropumpsindrugdeliverysystemsandotherbiomedicalapplications.
Althoughalotofprogresshasbeenmadeinmicropumpresearchandperformanceofmicropumpshasbeencontinuouslyincreasing,thereisstillaneedtoincorporatevariouscategoriesofmicropumpsinpracticaldrugdeliveryandbiomedicaldevicesandthiswillcontinuetoprovideasubstantialstimulusformicropumpresearchanddevelopmentinfuture.
2007ElsevierB.
V.
Allrightsreserved.
Keywords:MEMS;Microuidics;Micropump;Drugdelivery;Micrototalanalysissystems(TAS);Pointofcaretesting(POCT);Insulindelivery;Articialsphincterprosthesis;Antithrombogenicmicropump;Ionconductivepolymerlm(ICPF);Electrochemical;EvaporationtypemicropumpContents1.
Introduction9182.
Micropumpsclassication9203.
Basicmicropumpoutputparameters9214.
Mechanicalmicropumps9214.
1.
Electrostatic9214.
2.
Piezoelectric9244.
3.
Thermopneumatic.
9254.
4.
Shapememoryalloy9274.
5.
Bimetallic927Correspondingauthor.
E-mailaddress:st104180@ait.
ac.
th(A.
Nisar).
0925-4005/$–seefrontmatter2007ElsevierB.
V.
Allrightsreserved.
doi:10.
1016/j.
snb.
2007.
10.
064918A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–9424.
6.
Ionconductivepolymerlm9284.
7.
Electromagnetic9294.
8.
Phasechangetype9305.
Non-mechanicalmicropumps.
9305.
1.
Magnetohydrodynamic9305.
2.
Electrohydrodynamic.
9325.
3.
Electroosmotic9335.
4.
Electrowetting9345.
5.
Bubbletype9345.
6.
Flexuralplanarwave(FPW)micropumps.
9355.
7.
Electrochemical9355.
8.
Evaporationtype.
9366.
Discussion.
9377.
Conclusion939Acknowledgements939References9391.
IntroductionMicroelectromechanicalsystems(MEMS)isarapidlygrow-ingeldwhichenablesthemanufactureofsmalldevicesusingmicrofabricationtechniquessimilartotheonesthatareusedtocreateintegratedcircuits.
Inthelasttwodecades,MEMStechnologieshavebeenappliedtotheneedsofbiomedicalindus-trygivingrisetoanewemergingeldcalledMicrouidics.
Microuidicsdealswithdesignanddevelopmentofminia-turedeviceswhichcansense,pump,mix,monitorandcontrolsmallvolumesofuids.
Thedevelopmentofmicrouidicsys-temshasrapidlyexpandedtoawidevarietyofelds.
Principalapplicationsofmicrouidicsystemsareforchemicalanaly-sis,biologicalandchemicalsensing,drugdelivery,molecularseparationsuchasDNAanalysis,amplication,sequencingorsynthesisofnucleicacidsandforenvironmentalmonitoring.
Microuidicsisalsoanessentialpartofprecisioncontrolsys-temsforautomotive,aerospaceandmachinetoolindustries.
TheuseofMEMSforbiologicalpurposes(BioMEMS)hasattractedtheattentionofmanyresearchers.
ThereisagrowingtrendtofabricatemicrodrugdeliverysystemswithnewlywelldevelopedMEMSfabricationtechnologiesandareincreasinglybeingappliedinmedicalelds.
MEMS-basedmicrouidicdrugdeliverydevicesingeneralincludemicroneedlesbasedtransdermaldevices,osmosisbaseddevices,micropumpbaseddevices,microreservoirbaseddevicesandbiodegradableMEMSdevices.
Anintegrateddrugdeliverysystem(DDS)consistsofdrugreservoir,micropumps,valves,microsensors,microchannelsandnecessaryrelatedcircuits.
AsimpliedblockdiagramofadrugdeliverysystemisshowninFig.
1.
Atypicalmicrop-umpisaMEMSdevice,whichprovidestheactuationsourcetotransfertheuid(drug)fromthedrugreservoirtothebody(tissueorbloodvessel)withprecision,accuracyandreliability.
Micropumpsarethereforeanessentialcomponentinthedrugdeliverysystems.
Conventionaldrugdeliverymethodssuchasoralmedica-tions,inhalersandsubcutaneousinjectionsdonotdeliveralldrugsaccuratelyandefcientlywithintheirdesiredtherapeu-ticrange.
Generallymostofthedrugsareeffectiveifdeliveredwithinaspecicrangeofconcentrationbetweenthemaximumandminimumdesiredlevels.
Abovethemaximumrange,theyaretoxicandbelowthatrange,theyhavenotherapeuticbenet[1].
Inconventionaldrugdeliverymethodssuchasoraldelivery,etc.
,thereisasharpinitialincreaseindrugconcentration,fol-lowedbyafastdecreasetoalevelbelowthetherapeuticrange[2,3].
WithcontrolleddrugdeliverysystemsasshowninFig.
1,appropriateandeffectiveamountofdrugcanbepreciselycal-culatedbythecontrollerandreleasedatappropriatetimebythemicroactuatormechanismsuchasmicropump.
Thebenetsofcontrolleddrugreleaseincludesite-specicdrugdelivery,reducedsideeffectsandincreasedtherapeuticeffectiveness.
Micropumpsarealsoanessentialcomponentinuidtrans-portsystemssuchamicrototalanalysissystems(TAS),pointofcaretesting(POCT)systemsorlab-on-a-chip.
Micropumpsareusedasapartofanintegratedlab-on-a-chipconsistingofmicroreservoirs,microchannels,microltersanddetectorsforprecisemovementofchemicalandbiologicaluidsonamicroscale.
Pointofcaretesting(POCT)systemisaTAStoconductdiagnostictestingonsiteclosetopatientstoprovidebetterhealthcareandqualityoflife.
Insuchdiagnosticsystems,MEMSmicropumpsareintegratedwithbiosensorsonasinglechip.
ReviewsonresearchandrecentmethodsofusingBioMEMSformedicineandbiologicalapplicationshavebeenpreviouslyFig.
1.
Schematicillustrationofdrugdeliverysystem.
A.
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/SensorsandActuatorsB130(2008)917–942919published[4–7].
ThesereviewshavereportedintroductoryoverviewsonapplicationsofBioMEMSinbiomedicalengineer-ingsuchassurgicalmicrosystems,therapeuticmicrosystemsanddrugtherapyincludingdevicesbasedonmicroporoussilicon,microneedles,micropumps,andmicroreservoirs,etc.
Reviewsonmicropumpsalonehavealsobeenpublishedprevi-ously[8–10].
ThelastmostcomprehensiveandexcellentreviewonmicropumpswaspublishedbyLaserandSantiago[8].
How-eversomeofthenovelactuationmethodssuchastheuseofpolymerMEMSactuatorslikeionconductivepolymerlm(ICPF)anddevelopmentofevaporationtypemicropumpswerenotcoveredinthereview[8].
Inaddition,someofthemostrecentandpromisingpracticalapplicationsofmicropumpsindrugdeliveryandbiomedicalsystemswerenotmentioned.
ThereviewbyWoias[9]wasabriefoverviewofavarietyofmicrop-umpsandtheirapplications.
Howeverionconductivepolymerlm(ICPF),electrowettingandevaporationtypemicropumpswerenotcoveredinthereview.
ThereviewbyTsaiandSue[10]mentionedaboutthetechnologicalimportanceofmicropumpsintheirmedicalapplicationsuchasdrugdelivery.
Althoughthisfactwasmentionedintheintroductionsectionofthereview,theapplicationofdifferentkindsofmicropumpsindrugdeliveryFig.
2.
Classicationofmicropumpswithdifferentactuationmethods.
920A.
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/SensorsandActuatorsB130(2008)917–942wasnotlinkedandneithermentionedinconclusionstogetaglobalappreciationandoverviewofMEMS-basedmicropumpsandtheirmedicalapplications.
ThisreviewpresentsindepthfocusonsomeofthenovelusesofBioMEMSbasedvariouscategoriesofmicropumpsandtheirpotentialapplicationsindrugdeliveryandotherbiomedicalsystemssuchasmicrototalanalysissystems(TAS)orlab-on-a-chip.
Theemphasisofthereviewwillbetopresentkeyfeaturesofmicropumpssuchasactuationmethods,workingprinciples,construction,fabricationmethods,performanceparametersandtheirmedicalapplicationswherereported.
2.
MicropumpsclassicationAccordingtothedenitionof"MEMS",miniaturizedpump-ingdevicesfabricatedbymicromachiningtechnologiesarecalledmicropumps.
Ingeneral,micropumpscanbeclassiedaseithermechanicalornon-mechanicalmicropumps[11].
Themicropumpsthathavemovingmechanicalpartssuchaspump-ingdiaphragmandcheckvalvesarereferredtoasmechanicalmicropumpswhereasthoseinvolvingnomechanicalmovingpartsarereferredtoasnon-mechanicalmicropumps.
Mechanicaltypemicropumpneedsaphysicalactuatorormechanismtoperformpumpingfunction.
Themostpopularmechanicalmicropumpsdiscussedhereincludeelectrostatic,piezoelectric,thermopneumatic,shapememoryalloy(SMA),bimetallic,ionicconductivepolymerlm(ICPF),electromag-neticandphasechangetype.
Non-mechanicaltypeofmicropumphastotransformcer-tainavailablenon-mechanicalenergyintokineticmomentumsothattheuidinmicrochannelscanbedriven.
Non-mechanicalmicropumpsincludemagnetohydrodynamic(MHD),electro-hydrodynamic(EHD),electroosmotic,electrowetting,bubbletype,exuralplanarwave(FPW),electrochemicalandevap-orationbasedmicropump.
TheclassicationofmicropumpsisshowninFig.
2.
Oneoftheveryrstdocumentsaboutaminiaturizedmicrop-umpisapatentbyThomasandBessman[12]whichdatesbackto1975.
Thedevicewasdesignedforimplantationintothehumanbodyandcomprisedofasolenoidvalveconnectedtoavari-ablepumpingchamberwhichwasactuatedbytwoopposedpiezoelectricdiscbenders.
Thedevicewasfabricatedusingcon-ventionaltechniquesanditwasnotuntil1984thatamicropumpbasedonsiliconmicrofabricationtechnologieswaspatentedbySmits[13].
Smitspublishedhisresultslaterin1990[14].
ThemicropumpdesignedbySmits[13]wasaperistalticpumpcon-sistingofthreeactivevalvesactuatedbypiezoelectricdiscs.
Thedevicewasprimarilydevelopedforuseincontrolledinsulindeliverysystems.
Themostcommontypesofmechanicalmicropumpsaredisplacementpumpsinvolvingapumpchamberwhichisclosedwithaexiblediaphragm.
Aschematicillustra-tionofdiaphragmtypemechanicalmicropumpisshowninFig.
3.
Fluidowisachievedbytheoscillatorymove-mentoftheactuatordiaphragmwhichcreatesunderandoverpressure(p)inthepumpchamber.
UnderpressureinthepumpchamberresultsintheowofuidinsidethepumpFig.
3.
Schematicillustrationofdiaphragmtypemicropump.
chamberthroughtheinletvalve.
Overpressureinthepumpchambertransferstheuidoutofthepumpchamberthroughtheoutletvalve.
Thepressuregeneratedinsidethepumpcham-berisafunctionofstrokevolume(V)producedbytheactuator.
Theactuatorhastocontendwiththedeadvolume(V0)presentinthepumpchamber.
Themajordesignparameterofmechanicaldiaphragmtypemicropumpsiscalledthecompressionratio(ε)whichisexpressedasfollows:ε=VV0(1)Mechanicalmicropumpdesignsmaycontainsinglepumpchamberorsequentiallyarrangedmultiplepumpchambersinseriesorinparallel.
Suchtypeofmicropumpsarecalledperi-stalticmicropumps.
Peristalticmovementofdiaphragmsinthesequentiallyarrangedpumpchambers,transferstheuidfromtheinlettotheoutlet.
AschematicillustrationofperistalticmicropumpbasedonthermopneumaticactuationisshowninFig.
4.
Microvalvesareanotherimportantelementofmechanicalmicropumps.
Microvalvesareclassiedaspassiveoractivevalves.
Passivevalvesdonotincludeanyactuation.
Thevalvingeffectofpassivevalvesisobtainedfromadifferenceinpressurebetweentheinletandtheoutletofthevalve.
Mechanicalmicrop-umpsreportedin[15,16,52]havepassivevalves.
Activevalvesareoperatedbyactuatingforceandofferimprovedperformancebutincreasecomplexityandfabricationcost.
Activevalveswithelectrostatic[17],thermopneumatic[18]andpiezoelectric[19]actuationhavebeenreported.
Valvelessmicropumpsaresimilartodiaphragmtypemechan-icalmicropumpsbutdonotusecheckvalvestorectifyow.
Insteadnozzle/diffuserelementsareusedasowrectiers.
AschematicillustrationofvalvelessmicropumpisshowninFig.
5.
Fig.
4.
Schematicillustrationofperistalticmicropump.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942921Fig.
5.
Schematicillustrationofvalvelessmicropump.
Thenozzle/diffuseelementsdirectowsuchthatduringthesup-plymode,moreuidentersthroughtheinletthanexitsattheoutlet.
Thereverseoccursforthepumpmode.
Therstvalvelessminiaturemicropumpusingnozzle/diffuserasowrectifyingelementswaspresentedin1993byStemmeandStemme[20].
Micropumpsfordrugdeliveryapplicationsmustmeetbasicrequirements,whichare[21]:drugbiocompatibility,actuationsafety,desiredandcontrollableowrate,smallchipsizeandlesspowerconsumption.
BiocompatibilityofMEMS-basedmicrop-umpsisbecomingincreasinglyimportantandisregardedasakeyrequirementfordrugdeliverysystems.
Biocompatibilityisdenedas"theabilityofamaterialtoperformwithanappropri-atehostresponseinaspecicapplication"[22].
Asmicropumpsindrugdeliverysystemscanbeimplantedinsidethehumanbody,thereforethematerialsusedforfabricationmustbeabletofullrigorousbiocompatibilityandbiostabilityrequirements[23].
Theimplantedmicropumpbaseddrugdeliverysystemmustbeabletowithstandlongtermexposuretophysiologi-calenvironmentandresisttheadverseimpactofsurroundingtissuesonitsworking[24].
Therefore,biocompatibilityofthematerialsusedtofabricateMEMS-basedmicropumpsanddrugdeliverysystemisanimportantmaterialsselectionparameter.
SiliconbasedMEMStechnologyhasbeensuccessfullyappliedinbiomedicaleldwiththerecentgrowthofimplantabledrugdeliverysystems.
Siliconassubstratematerialhasbeenusedextensivelyasagoodbiocompatiblematerial,howeveratrendtowardstheuseofpolymersassubstratematerialisgrowingaspolymermaterialsarewidelyusedinmedicineandaresuitableforhumanimplantation.
Polymermaterialssuchaspolymethylmethacrylate(PMMA),polydimethylsilox-ane(PDMS),SU-8photoresist,etc.
,possessrelativelybetterbiocompatibilityandareincreasinglybeingusedinfabricationofMEMSmicropumps.
3.
BasicmicropumpoutputparametersAtthedesignstage,severaldesignparametersneedtobecon-sideredtooptimizethemicropumpperformance.
Theseincludemaximumowrate(˙Qmax),maximumbackpressure(hmax),pumppower(Ppump)andpumpefciency(η).
Themaximumowrateisobtainedwhenthepumpisworkingatzerobackpres-sure.
Atthemaximumbackpressure,theowrateofthepumpbecomeszerobecausebackpressureopposestheworkdonebythepump.
Pumphead(h),ornethead,canbederivedfromthesteadyowenergyequationassumingincompressibleowandneglectingviscousworkandheattransfer.
Itistheworkdoneonaunitweightofliquidpassingfromtheinlettotheoutlet[25]:h=pγ+u22g+zoutpγ+u22g+zin(2)wherePisthepressure,γ(=ρg)thepressurehead,gtheaccelerationofgravity,ρtheuiddensity,utheuiddensity,u2/2gthevelocityheadandzistheelevation.
ThisrepresentsanincreaseinBernoulliheadfromtheinlettotheoutlet.
Usually,uoutanduinareaboutthesameandzoutzinisnegligible,sothemaximumpumpheadbecomes:hmax≈poutpinγ=pγ(3)Powerdeliveredtotheuidbythepumpistheproductofthespecicweight,discharge,andnetheadchange.
Itcanbeexpressedas[26]:Ppump=pmax˙Qmax=ρg˙Qmaxhmax(4)IfthepowerrequiredtodrivethepumpactuatorisPactuator,pumpefciencyisexpressedasη=PpumpPactuator(5)Inanidealpump,PpumpandPactuatorisidenticalasnolossesexist.
Efciencyisgovernedbyuidleakagelosses(vol-umetricefciency),frictionallosses(mechanicalefciency),andlossesduetoimperfectpumpconstruction(hydraulicef-ciency).
Therefore,totalefciencyconsistsofthreeparts[25]:η≡ηvηmηh(6)whereηvisthevolumetricefciency,ηmthemechanicalef-ciencyandηhisthehydraulicefciency.
4.
MechanicalmicropumpsMechanicalmicropumpsbasedondifferentactuationschemesalongwiththeirconstruction,fabricationdetailsandapplicationsarediscussed.
Keyfeaturesandperformancechar-acteristicsofmechanicalmicropumpsaresummarizedandreferencedinTable1.
4.
1.
ElectrostaticElectrostaticactuationisbasedontheCoulombattractionforcebetweenoppositelychargedplates.
Byusingtheparal-lelplateapproximationtoCoulomb'slaw,theforcegeneratedbetweentheplateswhenavoltageisappliedcanbeexpressedasF=dWdx=12ε0εrAV2x2(7)whereFistheelectrostaticactuationforce,Wtheenergystored,ε(=ε0εr)thedielectricconstant,Atheelectrodearea,Vthevoltageappliedandxistheelectrodespacing.
Inelectrostaticmicropump,themembraneoftheelectrostaticmicropump[27–30]isforcedtodeectineitherdirectionas922A.
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/SensorsandActuatorsB130(2008)917–942Table1MechanicaldisplacementmicropumpsActuationmechanismReferenceStructureSize(mm)ValvesPumpchambersMembranematerialVoltage(V)Frequency(Hz)Pressure(kPa)Flowrate(l/min)PumpingmediumApplicationreportedinreferenceElectrostaticJudyetal.
[27]Polysiliconn/rActive1Polysilicon50n/rn/rn/rn/rDrugdeliveryZengerleetal.
[28]Si98mm3Cantilevertypepassive1Silicon170252.
570Watern/rZengerleetal.
[29]Si–Si98mm3Cantilevertypepassive1Silicon20030029160WaterChemicalanalysissystemCabuzetal.
[30]Injectionmoldplasticn/rPassive1MetallizedKapton.
160302030GasChemicalandbiologicalsensingMachaufetal.
[33]Si–Si5mm*5mmPassive1Electroplatednickel501830n/r1Watern/rPiezoelectricVanLinteletal.
[34]Glass-Si-glass4100mm3Passive1Glass1250.
1240.
6Watern/rStemmeandStemme[20]Brass2500mm3Nozzle/diffuser1Brass20110214400Watern/rKochetal.
[35]Si–Sin/rPassive1Silicon6002001.
80.
12EthanolDrugdeliverysuchasinsulinSchabmuelleretal.
[36]Si–Si122.
4mm3Nozzle/diffuser1Silicon190240011500Ethanoln/rJunwuetal.
[37]PMMAn/rCantilevertypepassive1Berylliumbronze50800233500WaterDrugdeliveryFengandKim[39]Si–Si160Passive1Silicon8060K0.
123.
2WaterImplantablemicropumpGeipeletal.
[40]Si–Sin/rActive1Silicon100<1104.
5WaterDrugdeliverysystemformetronomictherapyorchronotherapyMaetal.
[41]Si–Si2240mm3Passive1Silicon67.
22083.
431800FluidwithglucoseTransdermalinsulindeliveryDolletal.
[42]Si–Si330mm3Active1Siliconn/r27.
8601800WaterMedicalimplant;SphincterprosthesisHsuetal.
[45]Si-glass24mm*75mmPassive3Glass1404501.
850.
2BloodDrugdelivery/PointofCaretesting(POCT)Suzukietal.
[46]PDMS-glassn/rn/a1PDMS100872.
4k336n/rPointofCareTesting(POCT)ThermopneumaticVanDePoletal.
[52]Glass-Si–Si3000mm3Flap1Silicon61534Watern/rJeongandYang[49]Glass-Si-glassn/rNozzle/diffuser1Silicon84014Watern/rZimmermannetal.
[50]Glass-Sin/rFlap1n/an/r10169IsopropylalcoholCryogenicsystems/DrugDeliveryThermopneumaticHwangetal.
[54]Glass-SU8-Si105.
3mm3Capillarystopvalve1SU-8-210020n/rn/r3.
3WaterDrugdeliverysystems.
Kimetal.
[55]PDMS-glassn/rValveless(nozzle/diffuser)1PDMS556n/r0.
078MethanolDisposableLab-on-a-chipJeongetal.
[56]PDMSn/rActuatorasvalve3PDMS202021.
6WaterDrugdeliverysystemsShapememoryalloyBenardetal.
[57]Si–Sin/rPassivevalves1TiNialloy60.
94.
2349Watern/rBenardetal.
[58]Si–Sin/rPassivevalves1Polyimiden/r0.
90.
536Watern/rXuetal.
[59]Si–Si54mm3Passivevalves1NiTi/Sin/r40-60100kPa340Watern/rShuxiangetal.
[60]Acryl-siliconrubber16mmdia.
*74mmlengthDiffusers1NiTicoilactuator6n/rn/a700SalineIntracavityinterventionBimetallicZhanetal.
[61]Si–Si36mm3n/r1Aluminum-Si5.
50.
51245n/rn/rZouetal.
[63]Si-glass182Checkvalves1Aluminum-Si0.
50.
5336Watern/rICPFGuoetal.
[71]Acryl13mmdia.
*23mmlengthActivevalves2ICPF1.
52.
2n/r37.
8n/rBiomedicalElectromagneticBohmetal.
[74]Plastic800n/rn/rPlastic55002100Watern/rYamahataetal.
[76]PMMAn/rNozzle/diffuser1PDMSn/r120.
02400WaterLab-on-a-chipsystemsYamahataetal.
[77]PMMA4752mm3Checkvalves1n/an/rn/r2.
530WaterPanetal.
[78]PDMS600mm3Ballcheckvalves1PDMSn/rn/r3.
61000WaterLab-on-a-chipsystemsPhasechangeSimetal.
[79]72.
25mm3Passivevalves1silicon100.
506.
1WaterLab-on-a-chipsystemsBodenetal.
[80]Epoxy750mm3Activevalves1Epoxy2n/rn/r0.
074n/rn/rn/r:notreported.
A.
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/SensorsandActuatorsB130(2008)917–942923Fig.
6.
Schematicillustrationofelectrostaticmicropump.
appropriatevoltageisappliedonthetwooppositeelectrostaticplateslocatedonbothsidesasshowninaschematicillustrationinFig.
6.
Thedeectedmembraneisreturnedtoitsinitialposi-tioniftheappliedvoltageiscutoff.
Thechambervolumeinsidethemicropumpvariesbyalternateswitchingofappliedvoltage.
Theuidinreservoirisforcedtoowinthemicrochannelsduetopressuredifferenceinducedbythemembranedeectioninthepumpchamber.
Theadvantagesofelectrostaticmicropumpsarelowpowerconsumptionwhichisoftheorderof1mWandfastresponsetime.
Thedeectionofthediaphragmcanbeeas-ilycontrolledbyappliedvoltage.
Amajordisadvantageisthesmallactuatorstroke,whichisusuallylimitedupto5mwithappliedactuationvoltagesofaround200V.
TherstmicropumpbasedonelectrostaticactuationwasdevelopedbyJudyetal.
[27].
Itwasalsotherstsurfacemicro-machinedmicropumpascomparedtopreviousbulksurfacemicromachinedmicropumps.
Nobulksiliconagentsorwaferbondingtechniqueswereusedinitsfabrication.
Instead,selec-tivedepositionandetchingofsacriciallayerswereusedtofabricatethestructure.
Themicropumpconsistedofanactivecheckvalve,apumpingmembraneandanactiveoutletvalve.
Allpartswereencapsulatedbysiliconnitrideandwereactu-atedbyelectrostaticforce.
Actuationvoltagesofapproximately50Vwererequiredforvalveclosureandmembranedeection.
Howevernopumpingactionwasreported.
Zengerleetal.
[28]developedtherstworkingelectrostaticmicropump.
Themicropumpconsistedofamembranemadeoffoursiliconlayerswhichformedtwocantileverpassivevalves,pumpmembraneandcounterelectrodeforelectrostaticactua-tion.
Themembranehadanareaof4mm*4mmandathicknessof25m.
Thevolumetricstrokeofthemembranewasbetween0.
01and0.
05l.
Theseparationbetweenthemovablemem-braneandtheelectricallyisolatedstatorwas4m.
Thepassivevalveswerecantileversmeasuring1mm*1mmwiththicknessvaryingbetween10and20m.
Duringfabricationallchipsweremadebyanisotropicetchingfromsinglesidepolishedsili-conwafers.
Forfabricatingvalves,lithographywasdoneonfrontsideofthewaferforapsandorices.
Pumpingwasachievedforthersttimeatactuationfrequenciesintherangeof1–100Hz.
Atfrequencyof25Hzand170V,aowrateof70l/minatzerobackpressurewasachieved.
Inadditionamaximumpressureheadof2.
5kPawasdeveloped.
Zengerleetal.
[29]laterreportedthedevelopmentofbidirectionalsiliconmicropumpwithelecrostaticallyactuatedmembraneandtwopassivecheckvalves.
Themicropumphaddimensionsof7mm*7mm*2mmandcontainedastackoffourlayers,pumpmembrane,passivecheckvalves,inletandoutlet.
Thebidirectionalpumpingwasdependentonactua-tionfrequencies.
Atlowactuationfrequenciesbetween0.
1and800Hz,themicropumpoperatedintheforwardmode.
Athigheractuationfrequenciesbetween2and6kHz,themicropumpoper-atedinthereversedirection.
Thebidirectionalphenomenonwasduetoaphaseshiftbetweentheresponseofthecheckvalvesandapressuredifferencethatresultedinuidow.
Themaximumpressureachievedbythemicropumpwas31kPa.
Themaximumvolumetricowratewas850l/minatasupplyvoltageof200V.
AdualdiaphragmmicropumpwasintroducedbyCabuzetal.
[30].
Themicropumpconsistedoftwodiaphragmswithseveralthroughholesinpumpchamber.
Thepumpchamberwasmadebyinjectionmolding.
Electrodesweredepositedbyevaporation.
Thindielectricmaterialwasdepositedbyionbeamsputtering.
Themicropumpwasmechanicallyassembled.
Themicropumpachievedowratesof30l/minatfrequencyof30Hzandpowerconsumptionof8mW.
Theoperatingvoltagewas160V.
Themicropumpoperatedinbidirectionalmodebutwasapplicableforgasesonly.
Thistypeofmicropumpwasanidealcandidateinchemicalandbiologicalsensingapplications.
ThedesignandsimulationofanelectrostaticperistalticmicropumpfordrugdeliveryapplicationswasreportedbyTeymooriandSani[31].
Thesizeofthemicropumpwas7mm*4mm*1mm.
Theproposedfabricationprocesscon-sistedofasiliconsubstrateonwhichmembranepartwasconstructedandglasssubstratewhichcontainedinputandout-putports.
Thesimulatedresultforthethresholdvoltageofthemicropumpwas18.
5V.
Theowrateofthedesignedmicropumpwas9.
1l/minwhichwasquitesuitablefordrugdeliveryapplicationssuchaschemotherapy.
Themicropumpwasdesignedtosatisfymajordrugdeliveryrequirementssuchasdrugcompatibility,owratecontrollabilityandlowpowercon-sumptionandsmallchipsize.
Howevertheactualfabricationandtestingofthedesignedmicropumptoverifyperformanceparameterswasnotreported.
Bourouinaetal.
[32]reportedonthedesignandsimulationofalowvoltageelectrostaticmicropumpfordrugdeliveryappli-cations.
Thetotalsizeofthemicropumpwas5mm*5mm.
The924A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942micropumpparameterssuchasmicrochanneldimensionswerechosenfordrugdeliveryapplicationswhereaverysmallowratewasinvolved.
Theworkingvoltagewas10V.
Simulatedowratesintherangeof0.
01–0.
1l/minwerereportedwhichweresuitablefordrugdeliveryapplications.
Thefabricationandtestingofthedeviceforcomparisonwiththeoreticalpredictionswasnotreported.
Machaufetal.
[33]reportedarstattempttofabricateamem-branemicropumpwhichwaselectrostaticallyactuatedacrosstheworkinguid.
Theowrateachievedwas1l/minat50Vactuationvoltage.
Thedesignwasbasedonutilizinghighelec-tricpermittivityoftheworkinguidaswellaslowconductivity.
Theelectrostaticforceactingonthemembranewasproportionaltotheworkinguidelectricpermittivityandhigherthepermit-tivity,thehighertheforceandowrateforagivenappliedvoltage.
ThisconceptwasincontrasttothemicropumpdesigndescribedbyZengerleetal.
[28]wherethevoltagewasappliedacrosstheairgapbetweenelectrodesabovethepumpcham-ber.
TheadvantageoftheapproachadoptedbyZengerleetal.
[28]wasthattheworkinguiddidnotcomeundertheinuenceoftheappliedelectriceldandthusbothconductiveandnon-conductiveuidscouldbepumpedinthisway.
Thelimitation,however,wasthecostandcomplexityofthedeviceduetotherequirementtocreateanairgapabovethepumpchamber.
Itwasaccomplishedwithastackoffoursiliconlayers.
AsthedesigndescribedbyMachaufetal.
[33]involvedapplicationofelec-triceldbetweenthepumpchamberandtheworkinguid,themainadvantageofthedesignwasthesimplicityofconstructionandlowfabricationcostasonlytwosiliconwaferswereused.
Howeverthemicropumpwaslimitedtopumponlyconductiveuids.
Thedevicewasfabricatedinsiliconandthediaphragmwasmadeofelectroplatednickel.
Theassemblywasdoneusingip–chipbonding.
4.
2.
PiezoelectricApiezoelectricmicropumpconsistsofapiezoelectricdiskattachedonadiaphragm,apumpingchamberandvalves.
Thepiezoelectricmicropumpisactuatedbythedeforma-tionofthepiezoelectricmaterials.
PiezoelectricactuationinvolvesthestraininducedbyanappliedelectriceldonthepiezoelectriccrystalasshowninaschematicillustrationinFig.
7.
Typicalcharacteristicsofpiezoelectricactuatorsincludelargeactuationforce,fastresponsetimeandsimplestructure.
However,fabricationiscomplexaspiezoelectricmaterialsarenoteasilyprocessed.
ThecomparativelyhighactuationvoltageFig.
7.
Schematicillustrationofpiezoelectricallyactuatedmicropump.
andsmallstroke,i.
e.
displacementperunitlengthareregardedasthedisadvantages.
VanLinteletal.
[34]reportedarstattempttofabricatesiliconmicropumpbasedonpiezoelectricactuation.
Therecip-rocatingdisplacementtypemicropumpwascomprisedofapumpchamber,athinglasspumpmembraneactuatedbypiezo-electricdiscandpassivesiliconcheckvalvestodirecttheow.
Thepiezoelectricdiscwasattachedbymeansofcyanoacry-lateadhesive.
Itwastherstreportedworkonasuccessfullyfabricatedmicropumpusingmicromachiningtechnologies.
Kochetal.
[35]proposedatypicalpiezoelectricmicropumpbasedonthedeformationofascreen-printedpiezoelectriczir-conatetitanate(PZT)onthesiliconmembrane.
Themicropumpconsistedofastackofthreesiliconchips.
Outletandinletvalveswereformedinthetwolowerlayersandmembraneactuatorformedthetoplayer.
Thedimensionsofthesiliconmembranewere8mm*4mm*70m.
Flowrateofupto120l/minwasachieved.
Amaximumbackpressureof2kPawasmeasuredwhenasupplyvoltageof600Vwasappliedat200Hzacrossa100mthickpiezoelectriclayer.
Themicropumpdesignwassuitabletobeappliedinmedicineascheapdisposablemicrop-umpfordrugdeliverysuchasinsulin.
Schabmuelleretal.
[36]reportedapiezoelectricallyactuatedsiliconmembranemicropumpwithpassivevalves.
Thefabrica-tionofthemicropumpwasbasedondoublesidedprocessingofsiliconandbulkKOHetching.
Thesizeofthemicropumpwas12mm*12mmandtheheightincludingthepiezoelec-triczirconatetitanate(PZT)discwas0.
85mm.
Aowrateof1500l/minandabackpressureof1kPawereachievedwithethanolasthepumpingmedium.
Incaseofairasthepumpingmedium,amaximumowrateof690l/minwasmeasured.
AhighperformancepiezoelectricallyactuatedcantilevervalvemicropumpfordrugdeliveryapplicationwasinvestigatedbyJunwuetal.
[37].
Theoutputvaluesofthemicropumpwereimprovedbythedesignofthecantilevervalves.
Themicrop-umpwithshortercantilevervalvesobtainedhigherowrateof3500l/minandbackpressureof27kPa.
Thesamemicropumpwithlargercantilevervalvesobtainedaowrateof3000l/minandbackpressureof9kPa.
Themicropumpwascomprisedofastructureofstackedlayerswhichweregluedtogether.
ThepumpbodyanduppercoverweremadeofPMMAandmanufacturedbyconventionaltechnology.
Thecantilevervalvesweremadeofprecisionbronzemembrane.
Amaximumbackpressureof27kPaachievedbythemicropumpwashigherthanthenormalbloodpressureof15kPa[38].
Thereforethemicropumpdesignwasapplicablefordrugdelivery.
FengandKim[39]developedapiezoelectricmicropumpwithdomeshapeddiaphragmandonewayparylenevalves.
PiezoelectricZnOlmwithlessthan10mthicknesswasusedtoactuateaparylenediaphragmfabricatedonsiliconsubstrate.
Thesizeofthemicropumpwas10mm*10mm*1.
6mm.
Theowrateof3.
2l/minwasachievedatlowpowerconsumptionof3mW.
Theoperatingvoltagewas80Vandmaximumbackpressurewas0.
12kPa.
ThemicropumpwasfabricatedusingICcompatiblebatchprocessusingbiocompatiblematerials.
Thelowpowerconsumptionofthemicropumpmakesitanidealcandidateforimplantablemicropumppoweredbybattery.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942925Geipeletal.
[40]reportedforthersttimeanoveldesignofmicropumpwithbackowpressureindependentowrateforlowowraterequirementssuchasrequiredindrugdeliv-eryapplications.
Theconceptwasbasedonpiezoelectricallyactuateddiaphragmstoachieveowratesintherangeof1–50l/min.
Themajorlimitationwhichpreventsvolumetricdosingofamicropumpisbackpressuredependency.
Toaddressthisundesiredeffect,thedesignreportedinRef.
[40]workedontheprincipleofperistalticmicropump(micropumpwithmul-tiplechambersinseries)withnomiddlemembranenormallyusedaspumpmembrane.
Twoback-to-backconnectedactivevalvescontrolledtheuidowbyalternateswitchingofthree-phaseactuationscheme.
Theuidwasdrawnfromthereservoirintothepumpchamberuntilanequilibriumpressurewasestab-lished.
Thesimultaneousclosingoftheinletandopeningoftheoutletvalvemovedtheuidinthedesireddirection.
Thesimultaneousswitchingofthevalveswasthekeycharacter-isticofthemicropump.
Themicropumpwasmadefromtwomicromachinedsiliconwafersinabulksiliconprocess.
Backpressureindependencywasprovenupto20kPaforlowfre-quencies.
Thebackpressureindependentmicropumpwithlowpowerconsumptionisidealforapplicationindrugdeliverysystemsformedicaltreatmentsuchasmetronomictherapyorchronotherapy.
Maetal.
[41]presentedthedevelopmentofanovelpiezo-electriczirconatetitanate(PZT)insulinmicropumpintegratedwithmicroneedlearrayfortransdermaldrugdelivery.
Thesizeofsystemwas8mm*8mm*35mm.
Themicroneedlearrayonaexiblesubstratecouldbemountedonnon-planarsur-faceorevenonexibleobjectssuchasahumanngersandarms.
ThepiezoelectricmicropumpdesignwasbasedonthedesignpublishedbyVanLinteletal.
[34].
Flowratesweremea-suredusingdifferentconcentrationsofglucose.
Aowrateupto2400l/minwasachievedatappliedvoltageof67.
2V.
Thematerialsincontactwiththedrugweresilicon,silicondioxide,brassandsiliconepoxywhichareallbiocompatible.
Dolletal.
[42]presentednovelmedicalimplantbasedonbidi-rectionalmicropumpforarticialsphinctersystem.
Thefecalincontinenceisthelossofnaturalandsphinctercontrolandcanleadtounwantedlossoffeces.
Thereareseveraltreatmentoptionssuchasbiofeedbacktraining,strengtheningofthepelvicoorandreconstructivesurgicalmethodswithautologousmate-rialsbutwithlimitedsuccess.
TheGermanarticialsphinctersystem(GASS)isinfactahydraulicmusclefortreatmentoffecalincontinence[43,44].
ThedesignreportedbyDolletal.
[42]wasanintegratedstructurewithallfunctionsinonedevicewithapiezoelectricallyactuatedperistalticmicropumpembed-dedinthesystem.
Themicropumpwasfabricatedinsiliconandthepumpchamberandthevalvelipwerefabricatedbysiliconetchingprocess.
Themicropumpachievedaowrateof1800l/minandwasabletobuildupandmaintainback-pressuresupto60kPa.
Theoverallsizeofthemicropumpwas30mm*11mm*1mm.
Themicropumpfeaturedactivevalveswhichenabledthereversalofthepumpdirectionbyapplyingdifferentactuationschemes.
Hsuetal.
[45]investigateddevelopmentofantithrombo-genicmicropumpsforbloodtransportationtests.
Aperistalticmicropumpbasedonpiezoelectricactuationwasdevelopedtotransportwholeblood.
Themicropumpperformancewaseval-uatedusingdeionisedwaterandwholeblood.
Themicropumpwascomprisedofthreeparts,silicon,pyrexglassandacom-merciallyavailablebulkpiezoelectriczirconatetitanate(PZT)material.
Siliconetchingprocesswasusedtofabricatepumpchambersandchannels.
Threepiecesof12mmsquarebulkpiezoelectriczirconatetitanate(PZT)chipswithathicknessof191mweregluedontothesiliconmembraneusingsilverepoxy.
Thetotalsizeofthemicropumpwas24mm*75mm.
Topreventbloodfromclotting(thrombosis)inthemicrop-ump,twomaterials,polyethyleneoxideurethane(PEOU)andpolyethyleneglycol(PEG)wereusedtoformamonolayeronthesurfaceofthechip.
Theowrateofthemicropumpusingdeionisedwaterwas121.
6l/minat500Hzand140Vandmax-imumbackpressureof3.
2kPa.
Theowrateforbloodwas50.
2l/minat450Hzand140Vandmaximumbackpressureof1.
8kPa.
ThedesignedmicropumpreportedinRef.
[45]hastremendouspotentialinbiomedicalapplicationssuchasdrugdelivery.
Suzukietal.
[46]proposedatravellingwavepiezoelectri-callyactuatedmicropumpforpointofcaretesting(POCT)system.
ThesystemreportedinRef.
[46]comprisedofintegratedtravellingwavemicropumpandminiaturizedsurfaceplasmonresonance(SPR)imagingsensorononechip.
Surfaceplasmonresonance(SPR)imagingisoneofthemostsuitablebiosensorforTAS.
SPRbiosensorisusedtodetectthespecicbiosamplewithrealtimemultisensinganalysis.
ThemicropumpcomprisedofanarrayofpiezoelectricactuatorstoinduceatravellingwaveinaPDMSmicrochannel.
Themaximumowrateachievedbythemicropumpwas336l/min.
TheSPRimagingmeasure-mentswithbovineserumalbuminsolutionswerecarriedoutusingtheprototypediagnosticsystem.
Themajorlimitationofthepiezoelectricallyactuatedmicrop-umpsistherequirementofhighsupplyvoltages.
Inaddition,theapplicationofpiezoelectricdiscsisnotcompatiblewithintegratedfabrication.
Nevertheless,mechanicalmicropumpsbasedonpiezoelectricactuationhavegrowntobethedominanttypeofmicropumpsindrugdeliverysystemsandoptimiza-tionofthegeometricaldesignofpiezoelectricmicropumphasbeendonetoachievehigherstrokesatlowervoltages[47,48].
4.
3.
ThermopneumaticInthermopneumaticmicropump,thechamberwhichisfullofairinside,isexpandedandcompressedperiodicallybyapairofheaterandcoolerasshowninFig.
8.
Theperiodicchangeinvolumeofchamberactuatesthemembranewitharegularmovementforuidow.
Thermopneumaticactuationinvolvesthermallyinducedvol-umechangeand/orphasechangeofuidssealedinacavitywithatleastonecompliantwall.
Forliquids,thepressureincreaseisexpressedasP=EβTVV(8)926A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
8.
Schematicillustrationofthermopneumaticmicropump.
wherePisthepressurechange,Ethebulkmodulusofelas-ticity,βthethermalexpansioncoefcient,TtheemperatureincreaseandV/Visthevolumechangepercentage.
ForsimplicityweassumethatthereisnovolumeexpansionandforwaterastheuidwetakethevalueofE=3.
3*105psiandβ=2.
3*104C1inEq.
(8).
Thus,forwater,thetemper-aturedependentpressurechangecanbeexpressedas76psi/Cfortheaboveconditions.
Suchalargepressuretranslatestolargedeectionsandforcesbutsufferfromhigh-powercon-sumptionandslowresponsetimewhicharecharacteristicofthermalactuationmethods.
Thethermopneumatictypeofmicropumps[49–51]generaterelativelylargeinducedpressureanddisplacementofmem-brane.
However,ontheotherhand,thedrivingpowerhastobeconstantlyretainedaboveacertainlevel.
Until1990,allmicrop-umpdesignsdevelopedwerebasedonpiezoelectricbimorphormonomorphdiscsforactuation.
Inordertofabricatemicropumpusingmicroengineeringtechniquessuchasthinlmtechnol-ogy,photolithographytechniquesandsiliconmicromachining,researcherslookedformicromachinableactuators.
TherstpieceofworkontheutilizationofmicromachinableactuatorswascarriedoutbyVanDePoletal.
[52].
ThethermopneumaticactuationprinciplewasadoptedfromZdelblicketal.
[53]whoreportedtherstthermopneumaticmicropump.
Themicrop-umpwasareciprocatingdisplacementmicropumpwithpassivevalves.
Theactuatorcomprisedofacavitylledwithair,asquaresiliconpumpmembraneandbuiltinaluminummeander,whichservedasaresistiveheater.
Theapplicationofanelectricvolt-agetotheheatercausedatemperatureriseoftheairinsidethecavityandarelatedpressureincreaseinducedadownwarddeectionofthepumpmembranecausingpressureincreaseinthepumpchamber.
Thepressuredifferenceresultedinopen-ingandclosingoftheinletandoutletvalvesrespectively.
Amaximumowrateof34l/minwasreportedat5kPapressureand6V.
Jeongetal.
designedathermopneumaticmicropump[49]withacorrugateddiaphragm.
Thethermopneumaticmicropumphadapairofnozzle/diffuserandanactuatorwithcorrugateddiaphragmandamicroheater.
Thebasematerialforactuatordiaphragmwasdoublesidepolished450mthickn-type(100)siliconwafer.
Theowratesofthemicropumpwiththecorru-gateddiaphragmandthatwiththeatoneweremeasured.
Forthesameinputpower,themaximumowrateofthemicrop-umpwiththecorrugateddiaphragmwas3.
3timesthatwiththeatone.
Themaximumgeneratedpressurereached2.
5kPa.
Themaximumowrateofthemicropumpwithcorrugateddiaphragmreached14l/minat4Hzwhentheinputvoltageanddutyratiowere8Vand40%,respectively.
Zimmermannetal.
[50]developedathermopneumaticmicropumpforhighpressure/highowrateapplicationssuchascryogenicsystemsbutworkedequallywellwherelowowratesandprecisevolumecontrolarenecessarysuchasdrugdeliverysystems.
Themicropumpwasplanarandfabricatedusingawafer-level,four-maskprocess.
Apressureof16kPaandmaximumowrateof9l/minwasachievedatanaveragepowerconsumptionof180mW.
Hwangetal.
[54]reportedasubmicroliterlevelthermopneu-maticmicropumpfortransdermaldrugdelivery.
Themicropumpcomprisingoftwoairchambers,amicrochannelandstopvalve,wasfabricatedbythespincoatingprocess.
Thethermopneu-maticchamberconsistedofohmicheatersontheglasssubstrate.
Thenegativethickphotoresistwasusedtoformthemicrochan-nelsandthetwoairchambersontheglasssubstrate.
Theglassplatewasbondedwithsiliconsubstratebyheating.
Thetotalsizeofthemicropumpwas13mm*9mm*0.
9mmandtheresis-tanceofthemicroheaterwas690.
Thedischargevolumeswere0.
1lfor3sat15Vand0.
1lfor1.
8sat20V.
Thedesignedmicropumpwasfeasibleforsubmicroliterleveldrugdeliverysystems.
Kimetal.
[55]presentedathermopneumaticallyactuatedpolydimethylsiloxane(PDMS)micropumpwithnozzle/diffuserelementsforapplicationsinmicrototalanalysissystems(TAS)andlab-on-a-chip.
Themicropumpconsistedofaglasslayer,anindiumtinoxide(ITO)heater,aPDMSthermopneumaticchamber,aPDMSmembraneandaPDMScavity.
Themicrop-umpwasfabricatedusingspincoatingprocess.
ThethicknessofthePDMSmembranewas770m.
Amaximumowrateof0.
078l/minwasobservedforappliedpulsevoltageof55Vat6Hz.
Theperformanceofthemicropumpisapplicablefordisposablelab-on-a-chipsystems.
Jeongetal.
[56]reportedfabricationandtestofaperistalticthermopneumaticallyactuatedPDMSmicropump.
Themicrop-umpconsistedofmicrochannels,threepumpchambers,inletandoutletportsandthreeactuators.
AllpartsexceptthemicroheaterwerefabricatedwithPDMSelastomer.
Thethermopneumaticactuatorswereoperatedasthedynamicvalvesandcontrolledeasilybysequencingofthreephaseelectricinputpower.
Thusthedesignwassimpliedastherewasnoneedtofabricateaddi-tionalpartssuchascheckvalves.
Backowwasalsoeliminatedasthetwopumpchamberswerealwaysclosedatatime.
Thediameterofthe30m,thickactuatordiaphragmwas2.
5mm.
Themaximumowrateofthemicropumpwas21.
6l/minat2Hzatzeropressuredifference,whenthethree-phaseinputvoltagewas20V.
TheowrateachievedbythemicropumpwasA.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942927applicabletomicroliterleveluidcontrolsystemssuchasdrugdeliverysystems.
4.
4.
Shapememoryalloy(SMA)Shapememoryalloy(SMA)actuatedmicropumpsmakeuseoftheshapememoryeffectinSMAmaterialssuchastitaniumnickel.
Theshapememoryeffectinvolvesaphasetransforma-tionbetweentwosolidphases.
Thesetwophasesarecalledtheaustenitephaseathightemperatureandmartensitephaseatlowtemperature.
InSMAmaterials,themartensiteismuchmoreductilethanausteniteandthislowtemperaturestatecanundergosignicantdeformationbyselectivemigrationofvariantbound-ariesinthemultivariantgrainstructures.
Whenheatedtotheaustenitestarttemperature,thematerialstartstoformsinglevari-antaustenite.
Ifthematerialisnotmechanicallyconstrained,itwillreturntopredeformedshape,whichitretainsifcooledbacktothemartensitephase.
Ifthematerialismechanicallyconstrained,thematerialwillexertalargeforcewhileassum-ingthepre-deformedshape.
Thesephasetransitionsresultinmechanicaldeformationthatisusedforactuation.
Highpowerconsumptionisrequiredandtheresponsetimeisslow.
ShapememoryalloysarespecialalloyssuchasAu/Cu,In/Ti,andNi/Ti.
AschematicillustrationofSMAmicropumpisshowninFig.
9.
ThediaphragmofSMAmicropumps[57–60]isusuallymadeofmaterialtitanium/nickelalloy(TiNi).
TiNiisanattractivematerialasanactuatorformicropumpsbecauseitshighrecov-erablestrainandactuationforcesenablelargepumpingratesandhighoperatingpressures.
Highworkoutputperunitvol-umemakesitsuitableinsizesforMEMSapplications.
TherstSMAmicropumpwasreportedin1997byBenardetal.
[57].
TwoTiNimembraneswereseparatedbyasiliconspacer.
Bothxedandcantilevercheckvalveswerefabricatedtorectifyow.
ThereciprocatingmotionwasgeneratedbyalternatingthejouleheatingtothetwoTiNimembranes.
UponheatingthetopTiNilayer,theactuatorwaspositionedinitsmostdownwardposition.
Fig.
9.
Schematicillustrationofshapememoryalloy(SMA)micropump.
Themaximumowrateachievedwas49l/minatanoper-atingfrequencyof0.
9Hz.
Thebackpressureof4.
23kPawasachieved.
Theoperatingcurrentandvoltagewere0.
9Aand6V,respectively,andpowerconsumptionwas0.
5W.
ApolyimidespringbiasedSMAmicropumpwasreportedbyBenardetal.
[58];howevertheowratewasmuchlowerthantheowratereportedinRef.
[57].
Xuetal.
[59]reportedthestructureofamicroSMApump.
Itsoverallsizewasabout6mm*5mm*1.
5mm.
Themicrop-umpwascomposedofaNiTi/Sicompositedrivingmembrane,apumpchamberandtwoinletandoutletcheckvalves.
Thevolumetricowrateandbackpressureofthemicropumpwere340l/minand100kPa,respectively.
ThemicropumpdesignsreportedinRefs.
[57,58]wereactuatedbyfreestandingSMAthinlmsrequiringspecialbiasstructuretogetSMAeffectandspecialstructuretoseparateworkinguidfromdrivingcircuits.
Thismadethefabricationdifcult.
WhenutilizingaNiTi/SicompositedrivingmembraneasreportedinRef.
[59],nospe-cialbiasstructurewasneededbecausesiliconsubstrateprovidedthebiasingforceandnoisolatedstructurewasneedbecausesiliconstructureseparatedtheworkinguidfromSMAlmcompletely.
SMAeffectwasachievedbycombinedactionofthermalstressandsubstratebiasforce.
Thusthestructureofthemicropumpwassimpliedgivingalargeowrate,excellentdrivingefciencyandlongfatiguelife.
ShuxiangandFukuda[60]developedSMAactuatedmicropumpforbiomedicalapplications.
ThemicropumpwascomprisedofSMAcoilactuatorastheservoactuator,twodif-fusersasone-wayvalves,apumpchambermadeofelastictube,andacasing.
TheSMAcoilactuatorutilizedinthismicropumpwasaTiNiwirewithadiameterof0.
2mm.
Theoverallsizeofthemicropumpwas16mmindiameterand74mminlength.
Thebodyofthemicropumpwasmadefromacrylandchamberwasmadefromsiliconrubber.
Theowrateof500–700l/minwasobtainedbychangingthefrequency.
Thedesignedmicropumpwasabletodemonstratemicroowandwassuitablefortheuseinmedicalapplicationsandinbiotechnologysuchasintracavityinterventioninmedicalpracticefordiagnosisandsurgery.
4.
5.
BimetallicBimetallicactuationisbasedonthedifferenceofthermalexpansioncoefcientsofmaterials.
Whendissimilarmaterialsarebondedtogetherandsubjectedtotemperaturechanges,ther-malstressesareinducedandprovideameansofactuation.
Eventhoughtheforcesgeneratedmaybelargeandtheimplementa-tioncanbeextremelysimple,thedeectionofthediaphragmachievedaresmallbecausethethermalexpansioncoefcientsofmaterialsinvolvedarealsosmall.
Althoughbimetallicmicrop-umpsrequirerelativelylowvoltagescomparedtoothertypesofmicropumps,butarenotsuitabletooperateathighfrequencies.
AschematicillustrationofbimetallicmicropumpisshowninFig.
10.
Thediaphragmismadeoftwodifferentmetalsthatexhibitdifferentdegreesofdeformationduringheating[61,62].
Thedeectionofadiaphragm,madeofbimetallicmaterials,isachievedbythermalalternationbecausethetwochosenmateri-alspossessdifferentthermalexpansioncoefcients.
928A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
10.
Schematicillustrationofbimetallicmicropump.
Zhanetal.
[61]designedasilicon-basedbimetallicmem-brane,foraspecicmicropump.
Amicro-drivingdiaphragmwasmadebydepositinga10mthicklayerofaluminumonthesiliconsubstrate.
Theoverallsizeofthemicropumpwasabout6mm*6mm*1mm.
Theowrateandmaximumbackpressurewereapproximately45l/minand12kPa,respectively,while5.
5Vdrivingvoltageat0.
5Hzwasapplied.
Zouetal.
[63]reportedanovelthermallyactuatedmicrop-ump.
Thismicropumputilizedbothbimetallicthermalactuationandthermalpneumaticactuation.
Thestructureofthemicrop-umpwascomposedoftwochambers(airandwater),abimetallicmicroactuatorandtwo-microcheckvalves.
Theoverallsizeofthemicropumpwas13mm*7mm*2mm.
Thebimetallicactuatorwasmadeofaluminummembraneandasiliconmem-brane.
Whenthebimetallicactuatorwasheated,themembranewasdeformeddownwardstopresstheuid.
Atthesametime,thegasintheairchamberwasheatedandexpandedtostrengthenthebimetallicactuation.
Thepressureowcharacteristicsofmicrocheckvalvewerereported.
Whentheopenpressureofthevalvewas0.
5kPa,theowrateofthevalvereached336l/min.
Pangetal.
[64]utilizedbimetallicandelectrostaticactuationfordrivingandcontrollingofthemicropumpsandmicrovalvesinasingleintegratedmicrouidicsystem.
Themicrouidicchipofthesizeof5.
9mm*6.
4mmwascomprisedofmicrop-umps,valves,channels,cavitiesandotherdifferentsensors.
Bothbimetallicandelectrostaticactuationwasusedtoactuatethemicropumpsandvalves.
Onthevalvemembrane,twoaluminumstructuresweredesignedtoprovidebidirectionaldeformation.
Bimetallicdrivingdeformationofthemicropumpmembraneinonlytheupdirectionwasdesigned.
Bimetallicelementsconsistedofheatingelements,topaluminumlayerandbot-tommechanicalmembrane.
Thedimensionsofthemicropumpdrivingmembranewere1mm*1mm*2m.
Thesizeofthevalvemembranewas6mm*0.
6mm*2m.
Inthemicrou-idicchip,3DstructureswereformedusingsurfaceandbulkmicromachiningfollowedbystandardICcompatibleprocessestofabricatedrivingcircuitsandothersensors.
4.
6.
Ionconductivepolymerlm(ICPF)PolymerMEMSactuatorscanbeactuatedinaqueousenvi-ronmentwithlargedeectionandrequirelesspowerinputthanconventionalMEMSactuators.
Oneofthemostpopularpoly-meractuatorsisionconductivepolymerlmactuator(ICPF)whichisactuatedbystressgradientbyionicmovementduetoelectriceld.
ICPFiscomposedofpolyelectrolytelmwithbothsideschemicallyplatedwithplatinum.
Duetotheapplicationofelectriceld,thecationsincludedinthetwosidesofthepoly-mermoleculechainwillmovetothecathode.
Atthesametime,eachcationwilltakesomewatermoleculestomovetowardsthecathode.
ThisionicmovementcausesthecathodeofICPFtoexpandandanodetoshrink.
Whenthereisanalternatingvoltagesignal,thelmbendsalternately.
AschematicillustrationofthestructureofICPFactuatorisshowninFig.
11A.
ThebendingprincipleofICPFactuatorisshowninFig.
11B.
TheICPFactuatoriscommonlycalledarticialmusclebecauseofitslargebendingdisplacement,lowactuationvoltageandbiocompatibility.
ResearcheshavereportedapplicationsofICPFinrobotic[65],medicaldevices[66]andmicromanipula-tors[67].
Guoetal.
[68–71]reporteddevelopmentofICPFpoly-meractuator-basedmicropumpforbiomedicalapplications.
TheFig.
11.
(A)SchematicillustrationofthestructureofanICPFand(B)schematicillustrationofanICPFbendingprinciple.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942929micropumpcomprisedoftheICPFactuatorasthediaphragm,pumpchamberandtwoonewaycheckvalvesdrivenbyICPFactuators.
ICPFactuatorswereinstalledinseriestoachievehighowrates.
ThesizeofthemicropumpreportedinRef.
[68]was13mmindiameterand23mminlength.
Theowrateofthemicropumpwas4.
5–37.
8l/minat1.
5Vdrivingvoltage.
Themicropumpdesignwithlowpowerconsumption,biocompatibil-ityandadequateowrate,haspotentialapplicationinmedicaleldandbiotechnology.
Guoetal.
havealsoreportedapplicationofICPFactuatorinotherareassuchasarticialshmicrorobot[72,73]withpoten-tialapplicationsinmedicaleldsuchasperformingdelicatesurgicaloperationsupportedbymicrorobottoavoidunneces-saryincisions.
ICPFactuatorhascertainadvantagessuchaslowdrivingvoltage,quickresponse,andbiocompatibility.
Besides,itcanworkinaqueousenvironments.
ThemajorlimitationiscomplexfabricationofICPFactuator.
4.
7.
ElectromagneticMicromagneticdevicesingeneralconsistofsoftmagneticcoresandareactivatedbycurrentsinenergizedcoilsorusepermanentmagnets.
AwirecarryingacurrentinthepresenceofamagneticeldwillexperiencetheLorentzforcegivenbelow:F=(I*B)L(9)whereFistheelectromagnetic(Lorentz)force,Ithecurrentpassingthroughwire,BthemagneticeldandListhelengthofwire.
Theforcegeneratedislarge,however,electromagneticactu-ationrequiresexternalmagneticeldusuallyintheformofapermanentmagnet.
AschematicillustrationofmagneticallyactuatedmicropumpisshowninFig.
12.
Fig.
12.
Schematicillustrationofamagneticallyactuatedmicropump.
Atypicalmagneticallyactuatedmicropumpconsistsofachamberwithinletandoutletvalves,aexiblemembrane,apermanentmagnetandasetofdrivecoils.
Eitherthemagnetorthesetofcoilsmaybeattachedtothemembrane.
Whenacurrentisdriventhroughthecoils,theresultingmagneticeldcreatesanattractionorrepulsionbetweenthecoilsandthepermanentmagnetwhichprovidestheactuationforce.
Electromagneticactuationprovideslargeactuationforceoverlongerdistanceascomparedtoelectrostaticactuation.
Italsorequireslowoperatingvoltage.
However,theelectromagneticactuationdoesnotbenetfromscalingdowninsizebecauseelectrostaticforcereducesbythecubeofscalingfactor.
There-foreitsutilizationformicrofabricatedactuatorsislimitedasonlyafewmagneticmaterialscanbemicromachinedeasily.
Ingeneral,electromagneticmicropumpshavehighpowercon-sumptionandheatdissipation.
AnelectromagneticactuatorwasproposedbyBohmetal.
[74].
Plasticmicropumpwithreasonableperformancewasfabri-catedusingconventionalmicromechanicalproductionmethods.
Themicropumpcomprisedoftwofoldedvalvespartswithathinvalvemembraneinbetween.
Theinletandoutletweresituatedonthebottomsideofthemicropump,whilethemicropumpmembranewasplacedonthetop.
Anelectromagneticactuatorconsistingofapermanentmagnetplacedinacoilwasusedincombinationwithaexiblemicropumpmembrane.
Powercon-sumptionwas0.
5Wandowratesof40,000l/minforairand2100l/minforwaterwereachieved.
Arelativelylargevolumewasoccupiedbytheelectromagneticcoil,thereforethemicrop-umpnaldimensions(10mm*10mm*8mm)wereslightlylarge.
Gongetal.
[75]reporteddesignoptimizationandsimula-tionofafourlayerelectromagneticmicropump.
Thedesignedmicropumpconsistedofelectromagneticactuator,pumpcham-ber,passivemicrovalvesandinletandoutletinterfaces.
Themicroelectromagneticactuatorlocatedonthetopofthemem-brane,wasmadeofplanarcoils.
Thedimensionsoftheactuatorandthepumpingmembranewere6mm*6mmand3mm*3mm,respectively.
Thesimulationresultsshowedthatmaximumowrateupto70l/minwasachievableatafre-quencyof125Hz.
Yamahataetal.
[76]describedthefabricationandcharacter-izationofelectromagneticallyactuatepolymethylmethacrylate(PMMA)valvelessmicropump.
Thecompletemicropumpwasathree-dimensionalstructurecomprisingoffoursheetsofPMMAfabricatedbystandardmicromachiningtechniques.
Themicropumpconsistedoftwodiffuserelements,andapoly-dimethylsiloxane(PDMS)membranewithanintegratedmagnetmadeofNdFeB(neodymium,iron,andboron)magneticpowder.
Alargestrokemembranedeectionupto200mwasobtainedusingexternalactuationbyanexternalmagnet.
Flowrateupto400l/minandbackpressureupto1.
2kPawasmeasuredatresonantfrequenciesof12and200Hz.
Thecombinationofnozzle/diffuserelementswithanelectromagneticallyactuatedPDMSmembraneprovidedlargedeectionamplitudeandade-quateowratesbothforwaterandairandtheconceptcouldbesuccessfullyappliedforlowcostanddisposablelab-on-a-chipsystems.
930A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Yamahataetal.
[77]reporteddevelopmentofnewtypeofmicropumpbasedonmagneticactuationofthemagneticliquid.
Theferrouidwasnotindirectcontactwiththepumpingliq-uid.
ItwasexternallyactuatedbyNdFeB(neodymium,iron,andboron)permanentmagnet.
Themicropumpwasathreedimen-sionalmicrostructurefabricatedbystandardmicromachiningtechniques.
Theworkingprinciplewasbasedontheoscillatorymotionoftheferrouidicliquidinamicrochannel.
Thefer-rouidservedbothasanactuatorandseal.
Thelinearmotionoftheferrouidwasinducedbythecontrolledmechanicalmove-mentoftheexternalmagnetresultinginthepulsedowbyperiodicopeningandclosingofthecheckvalves.
Aowrateof30l/minwasachievedatabackpressureof2.
5kPa.
Panetal.
[78]reportedonthedesign,fabricationandtestofamagneticallyactuatedmicropumpwithPDMSmembraneandtwoonewayballcheckvalvesforlab-on-a-chipandmicrouidicsystems.
ThemicropumpcomprisedoftwofunctionalPDMSlayers.
Onelayerwasusedforholdingballcheckvalvesandanactuatingchamberwhiletheotherlayercontainedaperma-nentmagnetforactuation.
Themicropumpcouldbeactuatedbyexternalmagneticforceprovidedbyanothermagnetorinter-nalmagneticcoil.
Externalactuationofthemembranemountedmagnetprovidedaowrateof774l/minatpowerconsump-tionof13mW.
Alternateactuationofthemicropumpbya10turnplanarmicrocoilfabricatedonaPCboardprovidedaowrateof1000l/min.
Themicrocoildrivewasfullyintegratedandprovidedhigherpumpingratesattheexpenseofmuchhigherpowerconsumption.
4.
8.
PhasechangetypeTheactuatorinphasechangetypeofmicropumpsiscom-posedofaheater,adiaphragmandaworkinguidchamber.
Theactuationofthediaphragmisachievedbythevaporizationandcondensationoftheworkinguid.
AschematicillustrationofphasechangetypemicropumpisshowninFig.
13.
Fig.
13.
Schematicillustrationofaphasechangetypemicropump.
Simetal.
[79]presentedaphasechangetypeofmicrop-umpwithaluminumapvalves.
Themicropumpconsistedofapairofpassivevalvesandaphasechangetypeactuator.
Thedimensionsofthemicropumpwere8.
5mm*5mm*1.
7mm.
Theactuatorwascomposedofaexiblesiliconmembraneonasiliconsubstrateandamicroheateronaglasssubstrate.
Whentheinputpowerwasappliedtothemicroheater,theworkinguidwasheatedandvaporizedcausingpressureincreaseintheworkinguidchamberanddeectionofthemembrane.
Whenthepowersupplywascutoff,themembranewasrestoredduetocondensationoftheworkinguid.
Themaximumowrateofthemicropumpwas6.
1l/minatsupplyvoltageof10Vat0.
5Hz.
Themaximumbackpressureatzeroowratewas68.
9kPa.
Thelowowrateofthistypeofmicropumpwassuitableforappli-cationinlab-on-a-chiprequiringowrateslessthanfewl/minandbackpressureslessthan68.
9kPa.
Bodenetal.
[80]reportedaparafnmicropumpwithactivevalves.
Identicalmembraneactuatorsactivatedthepumpcham-berandactivevalves.
Heaterswereintegratedinsidetheparafn.
Whentheparafnwasmeltedbytheheaters,themembranesealedtheinletandoutletholes.
Themembranereturnedtoitsoriginalshapewhentheparafnsolidied.
Byasequenceofmeltingandsolidicationoftheparafn,thepumpingactionwasachieved.
Aowrateof0.
074l/minwasachievedatanappliedvoltageof2V.
5.
Non-mechanicalmicropumpsNon-mechanicalmicropumpsrequiretheconversionofnon-mechanicalenergytokineticenergytosupplytheuidwithmomentum.
Thesephenomenaarepracticalonlyinthemicroscale.
Incontrasttomechanicalmicropumps,non-mechanicalpumpsgenerallyhaveneithermovingpartsnorvalvessothatgeometrydesignandfabricationtechniquesofthistypeofpumpsarerelativelysimpler.
Howevertheyhavelimitationssuchastheuseofonlylowconductivityuidsinelectrohydrodynamicmicropumps.
Moreovertheactuationmechanismsaresuchthattheyinterferewiththepumpingliquids.
Sincetheearly1990s,manynon-mechanicalmicrop-umpshavebeenreported.
Non-mechanicalmicropumpswithdifferentactuationmethodsarediscussedbelow.
KeyfeaturesandperformancecharacteristicsofmechanicalmicropumpsaresummarizedandreferencedinTable2.
5.
1.
Magnetohydrodynamic(MHD)Magnetohydrodynamictheoryisbasedontheinteractionoftheelectricallyconductiveuidswithamagneticeld.
Thecon-ceptofmagnetohydrodynamic(MHD)micropumpisnewandoneoftherstdevelopedMHDmicropumpswasdevelopedbyJangandLee[81]in1999.
MHDreferstotheowofelec-tricallyconductinguidinelectricandmagneticelds.
ThetypicalstructureoftheMHDmicropumpisrelativelysimplewithmicrochannelsandtwowallsboundedbyelectrodestogeneratetheelectriceldwhiletheothertwowallsboundedbypermanentmagnetsofoppositepolarityforgeneratingthemagneticeld.
Inmagnetohydrodynamicmicropumps,LorentzA.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942931Table2MechanicaldisplacementmicropumpsActuationmechanismReferenceFabricatedstructureSize(mm)Voltage(V)Pressure(kPa)Flowrate(l/min)PumpingmediumApplicationreportedinreferenceMHD-DCtypeJangandLee[81]Si–Sin/r600.
1763Seawatern/rHuangetal.
[82]PMMAn/r15n/r1200n/rDrugdelivery,biomedicalstudiesMHD-ACtypeHengetal.
[83]Glass-PMMAn/r15n/r1900n/rn/rLemoffandLee[85]Glass-Si-glassn/rn/a018NaClsolutionn/rEHDRitcherandSandmaier[86]Si–Si3mm*3mm6000.
4314000Ethanoln/rFuhretal.
[87]Si-glassn/r40n/r2Watern/rDarabietal.
[88]Ceramic638.
4mm32500.
78n/r3MHFE-7100n/rElectroosmoticZengetal.
[91]Packedsilicaparticles85mm3200020003.
6Watern/rChenandSantiago[92]Soda–limeglass9000mm310003315Watern/rTakemorietal.
[94]Si-plasticn/r2000100.
1Degassed50mmTrisboratebuffer(pH9.
3)n/rWangetal.
[95]Fusedsilica-glassn/r6000252.
6WaterMicro-analysissystemsElectrowettingYunetal.
[96]Glass-SU8-Si–Sin/r2.
30.
7170Watern/rBubbletypeTsaiandLin[97]Glass-Sin/r200.
384.
5Isopropylalcoholn/rZahnetal.
[99]SOI-quartzdicen/rn/r3.
90.
12WaterContinuousmonitoringDDS/monitorglucoselevelsfrodiabetespatientsFPWLuginbuhletal.
[103].
Silicon-platinum-sol–gel-derivedpiezoelectricceramicn/rn/rn/r0.
255Watern/rNguyenetal.
[104]Aluminum,piezoelectriczincoxide,siliconnitriden/rn/rn/rn/rWaterTAS,cellmanipulatingsystems,anddrugdeliverysystems.
ElectrochemicalSuzukiandYoneyama[107]Glass-Sin/rn/rn/rn/rStandardsolutionofCuSO4DrugdeliveryYoshimietal.
[108]Glass-platinumelectroden/r3n/rn/rNeurotransmittersolutionAdministrationofneurotransmitterstoneurons.
CreateSynapsesinarticialsensoryorgans.
KabataandSuzuki[109]Glass-platinumelectrode-polyimiden/r1.
4n/r13.
8InsulinInjectionofinsulinandmonitoringofglucoseconcentrationEvaporationbasedEffenhauseretal.
[110]Plexiglassn/rn/rn/r0.
35RingerssolutionContinuousmonitoringDDS/continuousglucosemonitoringfordiabetespatientsn/r:notreported.
932A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
14.
SchematicillustrationofMHDmicropump.
forceisthedrivingsourcewhichisperpendiculartobothelectriceldandmagneticeld[82–85].
Theworkinguidtobeusedshouldhaveaconductivity1s/morhigher,inadditiontoexter-nallyprovidingelectricandmagneticelds.
IngeneralMHDmicropumpscanbeusedtopumpuidswithhigherconduc-tivity.
ThisgreatlywidenstheutilizationofMHDmicropumpsinmedicalbiologicalapplications.
ThebubblesgenerationduetoionizationisregardedasamajordrawbackofMHDmicrop-umps.
AschematicillustrationofMHDmicropumpisshowninFig.
14.
JangandLee[81]investigatedperformanceoftheMHDdevicebyvaryingtheappliedvoltagefrom10to60Vwhilethemagneticuxdensitywasretainedat0.
19T.
Theworkinguidusedwasseawater.
Themaximumowratereachedto63l/minwhendrivingcurrentwasretainedat1.
8mA.
Themaximumpressurehead,124kPa,frominlettooutletwasobtainedifthedrivingcurrentwassetandretainedat38mA.
Huangetal.
[82]reporteddesign,microfabricationandtestofDCtypeMHDmicropumpusingLIGAmicrofabricationmethod.
LIGAistheacronymfor"X-rayLithographieGal-vanoformungAbformung,"whichmeansX-raylithography,electrodepositionandmolding.
Adcvoltagesourcewassup-pliedacrosstheelectrodestogeneratethedistributedbodyforceontheuidinthepumpingchamber.
Theexternalmag-neticeldwasappliedusingpermanentmagnets.
Differentconductingsolutionswereusedasthepumpinguids.
Bub-blegenerationaffectedtheowrates.
Bubblegenerationwascausedbyelectrolysisofthepumpinguids.
Bubblegen-erationcouldbereducedbyreversingthedirectionoftheappliedvoltageandacdrivingmechanismwouldimprovetheperformance.
Hengetal.
[83]reportedUV-LIGAmicrofabricationandtestofanac-typemicropumpbasedonthemagnetohydrodynamic(MHD)principle.
Themicrochannelmaterialwasglasssub-stratebasewithPMMAcoverplate.
Aowrateof1900l/minwasachievedwhenacvoltageof15Vwassuppliedat1Hzat75mAcurrent.
Themagneticuxdensity"B"was2.
1T.
LemoffandLee[85]proposedac-typeMHDmicropumpusinganisotropicetchingmicrofabricationprocess.
Flowratesof18.
3and6.
1l/minwereachievedwhenacvoltageof25Vwassuppliedat1kHz.
5.
2.
Electrohydrodynamic(EHD)Themechanismwhichallowsthetransductionofelectricaltomechanicalenergyinanelectrohydrodynamic(EHD)microp-umpisanelectriceldactingoninducedchargesinauid.
TheuidowinEHDmicropumpisthusmanipulatedbyinteractionofelectriceldswiththechargestheyinduceintheuid.
OneoftherequirementsofEHDmicropumpsisthattheuidmustbeoflowconductivityanddielectricinnature.
Theelectricbodyforcedensity→FthatresultsfromanappliedelectriceldwithmagnitudeEisgivenasfollows[86]:→F=q→E+→P·→E12E2E2ερTρ(10)whereqisthechargedensity,εtheuidpermittivity,ρtheuiddensity,Ttheuidtemperatureand→Pisthepolarizationvector.
AschematicgeometryofEHDmicropumpisshowninFig.
15.
ThedrivingforceofDCchargedinjectionEHDmicropumpistheCoulombforceexertedonthechargesbetweenthetwoelec-trodes.
EHDmicropumprequirestwopermeableelectrodesindirectcontactwiththeuidtobepumped.
Ionsareinjectedfromoneorbothelectrodesintotheuidbyelectrochemicalreac-tions.
Apressuregradientdevelopsbetweentheelectrodesandthisleadstouidmotionbetweentheemitterandthecollector.
TherstDCchargedinjectionEHDmicropumpwasdesignedandfabricatedbyRitcheretal.
[86].
Themicropumpconsistedoftwoelectricallyisolatedgrids.
Aowrateof15,000l/minandapressureheadofaround1.
72kPawerereportedat800V.
Thedrivingvoltagecouldbereducedbyreducingthegriddistance.
Fuhretal.
[87]reportedtherstEHDmicropumpbasedontravellingwave-inducedelectroconvection.
Wavesofelectriceldstravellingperpendiculartothetemperatureandconductiv-itygradient,inducechargesintheliquid.
Thesechargesinteractwiththetravellingeldandvolumeforcesaregeneratedtoini-tiateuidtransport.
IntheEHDmicropumpdesignreportedbyFuhretal.
[87],theelectrodearraywasformedonthesub-strateandtheowchannelwasformedacrosstheelectrodes.
ThelimitationsoftheearlierEHDmicropumpswerehighvolt-ageandliquidconductivitywhichmustliebetween1014and109s/cm.
ThemicropumpreportedinRef.
[87]showedthatbyusinghighfrequencybetween100kHzto30MHzandlowvolt-agebetween20and50V,liquidswithconductivitiesbetween104and101s/cmcouldalsobepumped.
Flowintherangeof0.
05–5l/minwasobtained.
Darabietal.
[88]reportedanelectrohydrodynamic(EHD)iondragmicropump.
ThedimensionsofthemicropumpwereFig.
15.
SchematicgeometryofEHDmicropump.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–94293319mm*32mm*1.
05mm.
Thedrivingmechanismwasacombinationofelectricaleld,dielectrophoreticforce,dielectricforceandelectrostrictiveforce.
Theparticlesindielectricuidwerechargedbytheappliedelectricaleldsothattheuidwasconveyedbyinducedelectrostrictiveforces.
Theelectriceldwasdevelopedbyapairofelectrodesconsistingofanemitterandacollector.
Badranetal.
[89]investigatedseveraldesignsofanelectro-hydrodynamic(EHD)iondragmicropump.
Theoveralldimen-sionsofthemicropumpchannelwere500m*80m*60m.
Theeffectofseveraldesignparameterssuchasdiffer-entcombinationsofthegapbetweentheelectrodesonthepressure–voltagerelationshipwerestudiedinthiswork.
DarabiandRhodes[90]reportedonthecomputationaluiddynamics(CFD)modellingofiondragelectrohydrodynamicmicropump.
ThesimulationsweredonetonumericallymodelEHDpump-ingtostudytheeffectsofelectrodegap,stagegap,channelheight,andappliedvoltage.
Itwasfoundthatforagivenchan-nelheighttherewasanoptimumd/gratioatwhichtheowrateismaximumwhere'd'isthestagegapand'g'istheelectrodegap.
5.
3.
Electroosmotic(EO)Electroosmosisalsocalledelectrokineticphenomenon,canbeusedtopumpelectrolytesolutions.
Inelectroosmosis,anionicsolutionmovesrelativetostationary,chargedsurfaceswhenelectriceldisappliedexternally.
Whenanionicsolutioncomesincontactwithsolidsurfaces,instantaneouselectricalchargeisacquiredbythesolidsurfaces.
Forexample,fusedsil-icathatisusedcommonlyinthemanufacturingofmicrochannelsbecomesnegativelychargedwhenanaqueoussolutioncomesincontactwithit.
Thenegativelychargedsurfaceattractsthepositivelychargedionsofthesolution.
Whenanexternalelec-triceldisappliedalongthelengthofthechannel,thethinlayerofcation-richuidadjacenttothesolidsurfacesstartmovingtowardsthecathode.
Thisboundarylayerlikemotioneventuallysetsthebulkliquidintomotionthroughviscousinteraction.
AsketchshowingtheelectroosmoticpumpingofuidinachannelispresentedinFig.
16.
Electroosmotic(EO)micropumpshavecertainadvantages.
Animportantoneisthatelectroosmoticpumpingdoesnotinvolveanymovingpartssuchascheckvalves.
StandardandcheapMEMStechniquescanbeusedforfabrication.
Theoperationofelectroosmoticmicropumpisquite.
Flowdirectioninelectroosmoticmicrop-umpsiscontrolledbyswitchingthedirectionoftheexternalelectriceld.
Themajorlimitationsofelectroosmoticmicrop-umpsarehighvoltagerequiredandelectricallyconductivesolution.
Zengetal.
[91]reportedonthedesignanddevelopmentofelectroosmoticmicropumpfabricatedbypacking3.
5mnon-poroussilicaparticlesinto500–700mdiameterfusedsilicacapillariesusingsilicatefritfabricationprocess.
Themicropumpgeneratedmaximumpressureupto2026.
5kPaandmaximumowrateof3.
6l/minat2kVappliedvoltage.
ChenandSantiago[92]reportedaplanarelectroosmoticmicropump.
ThemicropumpwasfabricatedusingtwopiecesFig.
16.
Schematicillustrationofelectoosmoticowinachannel.
ofsodalimeglasssubstrate.
Standardmicrolithographytech-niqueswereusedtogeneratephotoresistetchmasks.
Chemicalwetetchingwasusedtofabricatethepumpingchannelanduidreservoirs.
Themicropumpgeneratedamaximumpressureof33kPaandamaximumowrateof15l/minat1kV.
Chenetal.
[93]reportedonthedevelopmentandchar-acterizationofmultistageelectroosmoticmicropumps.
A1–3stageselectroosmoticmicropumpswerefabricatedusing100mm*320minternaldiametercolumnspackedwith2mporoussilicaparticles,fused-silicacapillariesandstainlesselec-trodes.
Comparedto1-stageelectroosmoticmicropump,theoutpressuresof2and3stageelectroosmoticmicropumpsweretwotothreetimeshigherandtheowratesof2and3stageelectroosmoticmicropumpswereidenticalwiththatofthe1-stagemicropumpatthesamedrivingvoltage.
Thusn-stageelectroosmoticmicropumpscouldbefabricatedwithpotentialapplicationsinminiaturizeduidbasedsystemssuchasmicro-totalanalysissystems(TAS).
Takemorietal.
[94]reportedanovelhigh-pressureelectroos-moticmicropumppackedwithsilicananospheres.
Aplasticchipwasfabricatedthatconneduniformsilicananosphereswithinthechanneltoproducemoreefcientelectroosmoticowthanthesinglemicrochannelwiththesamecrosssectionalarea.
Themaximumowrateof0.
47l/minandthemaximumpressureof72kPawereachievedwhen3kVwasappliedtotheelectroos-moticpump.
Wangetal.
[95]usedsilica-basedmonolithswithhighchargedensityandhighporosityforahigh-pressureelectroosmoticmicropumphavingadiameterof100m.
Themaximumowratesandmaximumpressuregeneratedbythemicropumpusingdeionisedwaterwere2.
9l/minand304kParespectively,at6kVappliedvoltage.
934A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
17.
Continuouselectrowetting.
5.
4.
Electrowetting(EW)Electrowettinginvolveswettabilitychangeduetoappliedelectricpotential.
Inelectrowetting,theuidistransportedusingsurfacetension.
Surfacetensionisaninterfacialforcewhichdominatesatmicroscale.
Voltageisappliedonthedielectriclayer,decreasingtheinterfacialenergyofthesolidandliquidsurfacewhichresultsinuidow.
Continuouselectrowetting(EW)isusuallyappliedtoadjustthesurfacetensionbetweentwoimmiscibleliquidssuchasliquid-phasedmetal(e.
g.
mercury)andelectrolyte.
Itsinter-faceisreferredtoas"electricdoublelayer"(EDL)asshowninFig.
17.
Duetoprotonationeffectonthemercurysurface,theelectricpotentialbetweenrightendofmercurydropletandthecathodeofelectrodepairishigherthanthecounterelectricpotentialontheleftside.
Thesurfacetensiondifferencebesideamercurydropletthuspushesthedroplettowardright.
Continu-ouselectrowettinginvolvesnoheatingoftheliquid,demonstratefasterspeedandlowpowerconsumptioncomparedtothermocapillary.
Yunetal.
[96]reportedacontinuouselectrowetting(EW)micropump.
Surfacetensioninducedmotionofmercurydropinamicrochannellledwithelectrolytewasusedastheactuationenergyforthemicropump.
Themicropumpwascomprisedofastackofthreewafersbondedtogether.
Themicrochannelwasformedonaglasswaferandlledwithanelectrolytewherethemercurydropwasinserted.
Themovementofthemercurydropdraggedtheelectrolytewhichdeectedthemembraneformedonthesecondsiliconwafer.
Thevolumetricowratereachedupto70l/minatdrivingvoltage2.
3Vandpowerconsumptionof170W.
Themaximumpressurewasabout0.
8kPabyapplyingvoltageof2.
3Vat25Hzfrequency.
5.
5.
BubbletypeThepumpingeffectinbubbletypemicropumpsisbasedontheperiodicexpansionandcollapseofbubblegeneratedinmicrochannel.
Aschematicillustrationofexpandingandcol-lapsingbubbletypemicropumpisshowninFig.
18.
Fig.
18.
Abubblemicropump.
Thebubbletypemicropumpsalwaysneedtobeheatedsothattheirapplicationscopeislimitedincaseheatingprocessisnotallowedorpreferred.
TsaiandLin[97]reportedavalvelessmicropumpbasedonthermalbubbleactuationandnozzle/diffuserowregulation.
Microbubblewasgeneratedinthemicrochambertocreatepumpingchamber.
Duetoexpansionofthebubble,theowrateatthediffuser,Qdwaslargerthantheoneatthenozzle,Qn.
Whenthepumpingbubblecollapsed,QdwassmallerthanQn.
Thusanetowwasgeneratedfromnozzletodiffuserbyperiodicallycontrolledvoltageinputduringeachcycleconsistingofbubbleexpansionandcollapse.
Thepumpingchamber,nozzle/diffuserowregulatorsandchannelswerefabricatedonasiliconsubstrate.
Themaximumvalueoftheowrateofthebubbletypemicropumpwas5l/minastheappliedvoltagewasexertedperiodicallyat250Hzwith10%dutycycleandpowerconsumptionof1W.
Gengetal.
[98]reportedabubble-basedmicropumpforelec-tricallyconductingliquids.
Thedevicedevelopedaheadofafewmillimetersofwaterwithtypicalowratesintherangeof100l/min.
HoweverhighlocaltemperaturewasobservedduetoahighACvoltageappliedbetweentwochannels.
Zahnetal.
[99]reportedmicroneedlesintegratedwithanon-chipMEMSbubblemicropumpforcontinuousdrugdeliveryapplications.
Theexpansionandcollapseofthermallygeneratedbubbleswithowrectifyingcheckvalveswereusedtoachievethenetowratethroughthedevice.
Themicropumpwasfab-ricatedusingsilicononinsulator(SOI)fabricationprocessandquartzdice.
Visualmethodswereusedtorecordowratesandnetowrateofwateroutofthemicroneedleswasapproximately0.
12l/minwithapressureof3.
9kPa.
DrugdeliverysystemsuchasreportedinRef.
[99]withmicroneedlesintegratedwithmicropump,offersverytightcontroloverinjectionowratesatgivendrugconcentrations.
Inadditionsuchdevicescanalsobeusedforsamplecollectionforanalysis.
Theowdirectioncanbereversedbyreversingthevalvedirectionanduidcanbeextractedviamicropumpthroughmicroneedles.
Thussuchanintegrateddevicecanbeusedtodetermineglucoselevelsfordiabetespatients.
YinandProsperetti[100]reporteddataobtainedonasim-plemicropumpbasedontheperiodicgrowthandcollapseofasinglevapourbubbleinamicrochannel.
Themicropumpwasfabricatedbylasermachiningofmicrochannelof150mdiam-eteronacrylicplate.
Thebottomplatewascoveredbyanotherequalsizedacrylicplate.
Platinumwireswereembeddedinthegroovesinthetopplatetoprovidetheheatingsource.
Forachanneldiameterintherangeof100m,pumpingratesofsev-eraltensofl/minandpressuredifferencesofseveralkPawereA.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942935achievedbythesystem.
Thedesignofsuchtypeofmicrop-umpswassuitableforpumpingelectricallyconductinguidssuchassaltsinsomebiomedicalapplicationsforwhichjouleheatingcanbeusedtogeneratethebubble.
Non-conductinguidsontheotherhandrequiretheuseofheatersembeddedinthemicrochannel.
ApreliminarydemonstrationofmixingeffectwasalsopresentedbyoperatingthemicropumpinparallelintwomicrochannelsjoinedataY-junction.
Thiscouldbepotentiallyusefulwheretwoormorekindsofdosesarerequiredtobemixedupduringtheexpanding/collapsingcycles.
JungandKwak[101]fabricatedandtestedabubble-basedmicropumpwithembeddedmicroheater.
Themicropumpwhichconsistedofapairofvalvelessnozzle/diffuserelementsandapumpchamber,wasfabricatedbyembeddingmicroheatersinasilicondioxidelayeronasiliconwaferwhichservedasthebaseplate.
Thetopplateofthemicropumpwithinletandoutletportswasmadeofglasswafer.
Theperformanceofthemicropumpwasmeasuredusingdeionisedwater.
Theappliedsquarewavevoltagepulsetotheheaterwas30V.
Volumeowratesweremeasuredat40,50,60,70,and80%dutyratiosoverthesevendifferentoperationfrequenciesfrom0.
5to2.
0Hz.
Anoptimalowrateof6l/minat60%dutyratioforthecircularcham-berand8l/minat40%dutyratioforthesquarechamberwasmeasuredwhichindicatedthatmicropumpowratedecreasedasthedutyratioincreased.
5.
6.
Flexuralplanarwave(FPW)micropumpsInultrasonicallydrivenorexuralplatewave(FPW)microp-umps,aphenomenoncalledacousticstreamingoccursinwhichaniteamplitudeacousticeldisutilizedtoinitiatetheuidow.
Anarrayofpiezoelectricactuatorssettheacousticeldbygeneratingexuralplanarwaveswhichpropagatealongathinplate.
ThethinplateformsonewalloftheowchannelasshowninFig.
19.
Thereismomentumtransferfromchannelwalltotheuid.
Fluidmotionbytravellingexuralwaveisusedforthetrans-portofliquidsinanultrasonicallydrivenmicropump.
Flexuralplatewave(FPW)micropumprequireslowoperatingvoltageandthereisnorequirementsofvalvesorheating.
IncontrastFig.
19.
Schematicillustrationofacousticstreaming.
totheEHDmicropumps,thereisnolimitationontheconduc-tivityofliquidsorgases.
FPWpumpingeffectwasreportedbyMoroneyetal.
[102].
Fluidmotionwasdemonstratedwhenultrasonicexuralwavespropagatedinthinmembrane.
Zincoxidewasusedaspiezoelectriclayertogeneratewave.
AFPWmicropumpwasreportedbyLuginbuhletal.
[103].
Piezoelec-triczirconatetitanate(PZT)sol–gelthinlmswereusedasthepiezoelectriclayer.
Thedeviceconsistedofdualtransducerspat-ternedonathinlmcompositemembraneofsiliconnitrideandasol–gelderivedpiezoelectricthinlm.
FPWactuatorwasusedtopumpliquidsinsilicontubeswithaowrateof0.
255l/min.
Nguyenetal.
[104]proposedmicrouidicsystembasedonFPWmicropump.
Themicropumpwasmadeofanaluminum,piezo-electriczincoxide,polysilicon,andlow-stresssiliconnitridemembranewithatypicalthicknessof1–3m.
Themicrouidicsystemhavingasizeof10mm*10mmwasfabricatedusingcommonfabricationtechniques.
TheFPWmicropumprequiredlowoperatingvoltageandlesspowerconsumption(lessthan10mW).
Themicropumpwassuitablefordeliveringsensitivebiomaterials.
Potentialapplicationsincludemicrototalanalysissystem(TAS),cellmanipulatingsystems,anddrugdeliverysystems.
Mengetal.
[105]reportedamicromachinedmicropumpusingultrasonicexuralwaveplatewavetravellingalongathinmembranetoexciteanacousticeldintheuidincon-tactwiththemembrane.
Theacousticeldgeneratedtheuidow.
Bidirectionalandfocusedowwasachievedbyanovelcombinationofradialtransducers.
Potentialapplicationsofthistypeofmicropumpsincludemicrototalanalysissystemsanddrugdeliverydevices.
5.
7.
ElectrochemicalInelectrochemicalmicropumps,theelectrochemicalgen-erationofgasbubblesbytheelectrolysisofwater,providesthedrivingforcetodispenseliquids.
Thuselectrochemicalmicropumputilizesthebubbleforcethatisgeneratedbyelec-trochemicalreactionduringelectrolysis.
Thestructureofthemicropumpiscomposedofelectrodesforsupplyingelectric-ity,uidchannels,chamberforelectrolysis(bubblegeneration)andinletandoutletreservoirs.
AschematicillustrationofelectrochemicalactuationisshowninFig.
20.
Thedesignandconstructionoftheelectrochemicalmicropumpisrel-ativelysimpleanditcanbeeasilyintegratedwithothermicrouidicsystems.
Thelimitationoftheelectrochemicalmicropumpisthatthegeneratedbubblemightcollapseandbecomewaterleadingtounsteadyandunreliablereleaseofdrug.
Bohmetal.
[106]reportedanelectrochemicallyactuatedmicropumpforclosedloopcontrolledmicrodosingsystem.
Electrochemicalgenerationofgasbubblesbyelectrolysisofwaterprovidedthedrivingforcetodispensetheuid.
Thedos-ingsystemcomprisedofamicromachinedchannelandreservoirstructuremadeofsiliconandpyrexcoveronwhichasetofplat-inumelectrodeswerepatterned.
Theelectrodeswereusedforelectrochemicalgasgeneration.
Therateofbubblegenerationwasabout0.
0012l/min.
936A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
20.
Schematicillustrationofelectrochemicalactuation.
SuzukiandYoneyama[107]proposedareversibleelectro-chemicalnanosyringepump.
Themicropumpwasfabricatedbymicromachining.
Thinlmthreeelectrodesystemforactuationandsensingwasformedonaglasssubstrate.
Microchannelandreservoirforelectrolytewereformedonthesiliconsubstrate.
Themicropumpoperatedatconstantpotentialusinghydrogenbubbleastheworkingmedium.
Pumpingratewascontrolledbysettingtheappliedpotentialoftheworkingelectrodetoanappro-priatevalue.
Themicropumpcouldbeusedtopumpexternalsolutionintoandoutofthesystemaswellaspumpinginternalsolutionoutofthesystemasrequiredindrugdeliverysystems.
Yoshimietal.
[108]developedamethodofchemicalstim-ulationofneuronsusinganeurotransmittercontaininganelectrochemicalmicropump.
Theelectrochemicalmicropumpwaspoweredbythebubblegeneratedduringwaterelectrolysis.
Themicropumpconsistedofaglassnozzlewith10mdiame-tertip.
Twoplatinumelectrodesforelectrolysiswereembeddedinthepumpbodywhichwaslledwithneurotransmittersolu-tion.
Apotentialdifferenceof3Vwasappliedtotheelectrodestodirectthesolutiontoowtowardstheneurons.
Themicrop-umpwascapableofrapidadministrationofneurotransmitterstoneurons.
Themicropumpdesigncouldbeminiaturizedtocreate"synapses"inarticialsensoryorgans.
KabataandSuzuki[109]developedamicropumpbasedonelectrochemicalprincipleformicroinsulininjectionsystem.
Majorcomponentsofthemicropumpwereathinlmtwo-electrodesysteminaclosedcompartment,asiliconerubberdiaphragmtoseparateanelectrolytesolutionfromaninsulinsolution,andareservoirforinsulin.
Amicroneedlewasattachedtotheoutlet.
Thehydrogenbubblesaregeneratedontheworkingelectrode.
Thisresultedindeformationofthediaphragm,andtheinsulinsolutionwaspumpedoutthroughthemicroneedle.
5.
8.
EvaporationtypeThepumpingprincipleofanevaporation-basedmicropumpissimilartothexylemtransportsystemintrees.
Thedesignprincipleofthemicropumpinvolvescontrolledevaporationofaliquidthroughamembraneintoagasspacecontainingasorptionagent.
AschematicillustrationofthemicropumpisshowninFig.
21.
Effenhauseretal.
[110]reportedanevaporation-baseddis-posablemicropumpconceptthathaspotentialapplicationsincontinuouspatientmonitoringsystems.
Thevapourpressureinthegaschamberwaskeptbelowsaturationandduringthisphase,uidevaporationfromthemembranewasreplacedbycapillaryforceswhichinducedowfromthereservoir.
Evaporatedliq-uidwascontinuouslyreplacedbyowofliquidthroughthemicrouidicsystemsuchasmicrodialysiscatheter.
Theaverageowrateof0.
35l/minwasachieved.
Lowfabricationcost,nomovingpartsandlackofexternalenergysourcewereimpor-tantfeaturesofthistypeofmicropump.
Themaindrawbackofthepumpwasthatitworkedonlyinsuctionmode.
Suchtypeofmicropumpscanbeusedforcontinuousglucosemonitoringwhereadialysissolutionispumpedinaconstantfashionatsmallowratesthroughamicrouidicsystemsuchasmicrodialysiscatheter.
Namasivayametal.
[111]investigatedtranspiration-basedmicropumpfordeliveringcontinuousultralowowrates.
Thepumpingconceptwasbasedonthecommonlyobservedphe-nomenonoftranspirationinplantleaves.
Whentheliquidwasheatedatthemeniscus,thevapourpressureincreasedresultinginenhancedevaporation.
Asthevapourdiffusedout,afreshliquidsupplywasdrawnintothechannelfromareservoirforsteadystateoperation.
Thecapillaryforceaidedimbibitionpro-cess(absorptionoradsorptionofliquid)continueduntilthereservoirwasdepletedafterwhichthemeniscusbegantodrawback.
Fig.
21.
Schematicillustrationofevaporationbasedmicropump.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–9429376.
DiscussionThefabricatedstructureofmostofthemechanicalandnon-mechanicalmicropumpsreportedaboveiscomposedofglass,siliconorplastic.
HoweverinviewoftheincreaseduseofMEMS-basedmicropumpsinimplantabledrugdeliverysystemsandemphasisonloweringthemanufacturingcosts,sil-iconisnowbeingreplacedwithpolymerbasedmaterialssuchaspolydimethylsiloxane(PDMS)andpolymethylmethacrylate(PMMA),etc.
Theuseofpolymerbasedmaterialsisrapidlygrowingbecauseoftheirgoodbiocompatibility,excellentphys-icalandmechanicalproperties,lowcostandsimpleandfastfabrication.
Variousfactorsotherthanpressureandowratearerele-vanttotheselectionofmechanicalmicropump.
Themagnitudeofappliedvoltagerequiredforthesemicropumpsisoneoftheimportantfactorswhichcanbecompareddirectlyandwhichvarieswidely.
Voltageisanimportantparameterofmicropumpasitdeterminestheelectronicsandothercomponentstooper-atethemicropump.
InFig.
22,graphicalrepresentationofowratesandoperatingvoltagesforreportedmechanicalmicrop-umpsisshown.
Thevaluesofowrateandvoltageareplottedonalogscaletofacilitatecomparison.
Electrostatic,piezo-electricandthermopneumaticmicropumpsproducehigherowratesattheexpenseofhigh-appliedvoltagevalues.
MicropumpswithconductingpolymerlmactuatorssuchasICPFappeartobethemostpromisingmechanicalmicropumpswhichpro-videadequateowratesatverylowappliedvoltage.
Bimetallicmicropumpsalsorequirelessvoltageandprovidehigherowrates.
Aswithmechanicalmicropumps,performanceofnon-mechanicalmicropumpsisalsodependentonvariousotherfactorsinadditiontopressureandowrate.
InFig.
23,graphicalrepresentationofowratesandoperatingvoltagesforreportednon-mechanicalmicropumpsisshown.
Thevaluesofowrateandvoltageareplottedonalogscaletofacilitatecomparison.
Electroosmoticmicropumpsrequirehighoperatingvoltagesandproducelowowrates.
Electroosmoticmicropumpsaregen-erallyusedinmicroanalysissystemswherelowowratesarerequired.
MHDandEHDmicropumpsproducehighowratesattheexpenseofhighoperatingvoltages.
Electrowettingandelec-trochemicaltypeofmicropumparethemostpromisingoneswhichexhibithighowrateatlowappliedvoltage.
Workinguidpropertiesalsoinuencetheowratesandmustbetakenintoaccountinchoosingnon-mechanicalmicropumps.
Elec-troosmoticandmagnetohydrodynamicmicropumpscanhandlemanyworkinguidswhicharewidelyusedinchemicalandbiologicalanalysis.
Electrochemicalmicropumpscanalsohan-dleavarietyofsolutionssuchasinsulinandneurotransmittersolutionindrugdeliveryapplication.
Flowrate,pressuregeneratedandsizeofthemicropumpsareimportantparametersofmicropumps.
Anotherimportantparameteristheratioofmicropumpowratetoitssizewhichisreferredtoasselfpumpingfrequency[8].
Tocomparemechanicalandnon-mechanicalmicropumps,self-pumpingfre-quencywascalculatedformicropumpswhereboththesizeandowrateswereavailableinadditiontopressure.
InFig.
24,comparisonofmechanicalandnon-mechanicalmicropumpsintermsofsize,self-pumpingfrequencyandowratesispresented.
PressurevaluesofthemicropumpsareplottedinFig.
25.
Sizeofthemicropumpisanimportantparameterasitinu-encestheparticularapplicationofamicropump.
Thedifferentmanufacturingprocessesandoperationalnatureofmechani-Fig.
22.
Comparisonofvoltagevs.
owrateformechanicalmicropumps.
938A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942Fig.
23.
Comparisonofvoltagevs.
owratefornon-mechanicalmicropumps.
calandnon-mechanicalmicropumpsgenerallydictatewhichmicropumpissuitableforaparticularapplication.
Electroos-moticpumpreportedbyZengetal.
[91]whichissmallerinsizeascomparedtoelectroosmoticmicropumpreportedbyChenandSantiago[92],performsbetterintermsofpressuregenerationasshowninFigs.
24and25,respectively.
ThereforeelectroosmoticpumpreportedbyZengetal.
[91]isintendedforapplicationswherecompactnessintermsofsizeisrequiredalongwithhigh-pressuregeneration.
ThermopneumaticmicropumpssuchastheonereportedbyVanDePoletal.
[52]tendtoproducelowowratesandlowpressuresrelativetotheirsize.
Howevertheirperformancemustbemeasuredagainstlowcostmanufactur-ingassociatedwiththesemicropumps.
PiezoelectricmicropumpreportedbyStemmeandStemme[20]performsbetterintermsofowrateachievedwithrelativelybetterself-pumpingfrequencyandsmallersizeascomparedtothepiezoelectricmicropumpreportedbyVanLinteletal.
[34].
AmongallmicropumpscomparedinFig.
24,piezoelectricmicropumpreportedbySch-abmuelleretal.
[36]exhibitsthehighestself-pumpingfrequencyandadequateowratewithrespecttoitssmallsize.
Bimetal-licmicropumpssuchastheonereportedbyZouetal.
[63]exhibithigherself-pumpingfrequencyandhighowrateatrel-Fig.
24.
Comparisonofmechanicalandnon-micropumpsintermsofsize,owrateandselfpumpingfrequency.
A.
Nisaretal.
/SensorsandActuatorsB130(2008)917–942939Fig.
25.
Comparisonofmechanicalandnon-micropumpsintermsofsizeandpressure.
ativelysmallersizeofthemicropump.
Similarly,electrostaticmicropumpreportedbyR.
Zengerleetal.
[28]exhibitshighself-pumpingfrequencyatasmallsizeofthemicropump.
There-forefurtherresearchonbimetallicandelectrostaticallyactuatedmicropumpsissuggestedtofurtherimprovetheperformanceofmechanicalmicropumps.
Non-mechanicalElectroosmotic[91]andmechanicalelectrostatic[27–28]andpiezoelectricmicrop-umps[39]ofcomparablesizesshowcomparableperformanceintermsofowrates.
7.
ConclusionThepioneeringworkonmicropumpsstartedin1975.
Howeverresearchanddevelopmentonmicropumpsusingmicrofabricationtechnologystartedin1980sandshiftedtowardsMEMSareaaround1990.
Sincethen,MEMStech-nologieshavebeenappliedtotheneedsofbiomedicalindustry,resultingindevelopmentofvariouscategoriesofmicropumpconcepts,fabricationtechnologies,devicesandapplications.
Micropumpsforvariousbiomedicalapplicationssuchastransdermalinsulindelivery,articialsphincterpros-thesis,antithrombogenicmicropumpsforbloodtransportation,micropumpforinjectionofglucosefordiabetespatientsandadministrationofneurotransmitterstoneuronsandmicrop-umpsforchemicalandbiologicalsensinghavebeenreported.
BiocompatibilityofMEMS-basedmicropumpsisbecomingincreasinglyimportantanduseofbiocompatiblepolymerbasedmaterialssuchaspolydimethylsiloxane(PDMS)andpoly-methylmethacrylate(PMMA),etc.
isgrowing.
Piezoelectricallyactuatedmechanicaldisplacementmicropumpshavebeenthefocusofparticularattentionandhavebeenwidelyusedindrugdeliveryandpointofcaretesting(POCT)systems.
Theappliedvoltageisakeyconstraintfactorfordrugdeliverydrivingpower.
Inotherwords,themicropumpshavetobelimitedbylowappliedvoltagebecauseoftheircriticalappli-cationindrugdeliverysystems.
Electrostaticandpiezoelectricmicropumpsrequirehighdrivingvoltage.
MicropumpswithconductingpolymerlmactuatorssuchasICPFappeartobethemostpromisingmechanicalmicropumpswhichprovideade-quateowratesatverylowappliedvoltages.
Howevertheirperformancemustbeweighedagainstcomplexanddifcultbatchfabrication.
Amongnon-mechanicalmicropumps,elec-trowettingandelectrochemicaltypeofmicropumparesuitableforlowvoltageandhighowrateapplications.
Electroosmoticmicropumpsrequirehighoperatingvoltagesandexhibitlowowrates.
Suchtypesofmicropumpsaresuitableforapplica-tionsinmicro-analysissystems.
Basedontheextensiveliteraturereview,theauthorsconcludethatoverallcommercializationofMEMSmicropumpsindrugdeliveryandbiomedicalappli-cationisstillinitsbeginning.
Alotoftechnicalinformationisavailableforanumberofmicropumpconcepts.
Howevermanyofthenovelmicropumpsreportedinliteraturefordrugdeliveryandotherbiomedicalapplicationsstillneedtobeincor-poratedintopracticaldevices.
Tondamicropumpsuitableforaparticularapplicationisachallengeandthiswillcontinuetomotivateresearcherstoworkondevelopingmicropumpsandincorporatingtheminpracticaldrugdeliveryandbiomedicalsystems.
AcknowledgementsTheauthorswouldliketothankandacknowledgeNationalElectronicsandComputerTechnologyCenter,Thailandforpro-vidingthegrantundertheMEMSproject.
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BiographiesA.
NisariscurrentlyPhDcandidateinthedepartmentofdesignandmanufac-turingengineeringattheSchoolofEngineeringandTechnology,AsianInstituteofTechnology,AIT,Bangkok,Thailand.
HisPhDresearchdealswithdesignandfabricationofMEMSbasedmicrouidicdeviceforbiomedicalapplica-tions.
PreviouslyhehasdonehismasterofscienceinadvancedmanufacturingtechnologyfromUniversityofManchester,UnitedKingdomin2002.
Hispostgraduateresearchworkhasbeenpublishedinreferredjournalsandconferenceproceedings.
Hisresearchinterestsareniteelementmodellingofmaterials,micro/nanoelectromechancialsystemsandmicrouidics.
Dr.
NitinAfzulpurkariscurrentlyanassociateprofessorandthecoordinatoroftheMechatronicsandtheMicroelectronicsProgram,AsianInstituteofTechnol-ogy,Thailand.
HeobtainedPhDfromUniversityofCanterbury,NewZealandinmechanicalengineeringwithspecializationinRobotics.
HehaspreviouslyworkedinIndia,NewZealand,JapanandHongKong.
Hehasauthoredoversev-entyveresearchpapersintheeldofRobotics,MechatronicsandMEMS.
Hiscurrentresearchinterestsarecomputervision,MEMSandmechatronicsystems.
HeisamemberofIEEE.
Prof.
BanchongMahaisavariyaiscurrentlyprofessorofOrthopaedicSurgery,DepartmentofOrthopaedicSurgery,FacultyofMedicine,SirirajHospital,MahidolUniversity,Bangkok,Thailand.
HeisalsodeputydeanforAcademicaffairs,FacultyofGraduateStudies,MahidolUniversity,Bangkok,Thailand.
HeobtainedhismedicaldegreefromFacultyofMedicine,SirirajHospital,MahidolUniversityin1979.
HewasobservingFellowatAOTraumaCenteratKarlsruhe,Tubingenin1990.
HewasalsoavisitingFellowinDepartmentofTrauma,Uni-versityofInnsbruck,Austriain2002.
PreviouslyhehasservedasChairman,subcommitteeresearchmethodology,RoyalCollegeofOrthopaedicSurgeonofThailand.
Heiscouncilmember,RoyalCollegeofOrthopaedicSurgeonofThailand.
HeisalsoeditoroftheJournalofThaiOrthopaedicSurgeon.
Dr.
AdisornTuantranontiscurrentlyLabdirectorofNanoelectronicsandMEMSLaboratory,NationalElectronicsandComputerTechnologyCenter(NECTEC),underNationalScienceandTechnologyDevelopmentAgency(NSTDA),Thailand.
HeisamemberofthefoundingcommitteeofNationalNanotechnologyCenter(NANOTEC),ThailandandChairmanofThailand'sNanoelectronicsSeminarandTrainingCommittee.
HehasalsoservedasanadjunctseniorresearchscientistandlectureratAsianInstituteofTechnology(AIT),Bangkok,Thailand.
HeobtainedPhDin2001fromUniversityofCol-oradoatBoulder,Colorado,USA,inelectricalengineeringwithspecializationinOpticalMEMSandLaserandOpticsSystem.
HiscurrentresearchinterestsareopticalMEMS,MicrouidicLab-on-a-chipandoptoelectronicspackaging.
Hehasover100paperspublishedinrefereedjournalsandconferenceproceedings.
HereceivedThailandYoungTechnologistAwardin2004.