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Smart Materials in Additive Manufacturing Volume 1: 4D
Printing Principles and Fabrication Mahdi Bodaghi & Ali Zolfagharian
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Editedby
MahdiBodaghi AliZolfagharian
Elsevier
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Notices
Knowledgeandbestpracticeinthisfieldareconstantlychanging.Asnewresearchandexperience broadenourunderstanding,changesinresearchmethods,professionalpractices,ormedical treatmentmaybecomenecessary.
Practitionersandresearchersmustalwaysrelyontheirownexperienceandknowledgeinevaluating andusinganyinformation,methods,compounds,orexperimentsdescribedherein.Inusingsuch informationormethodstheyshouldbemindfuloftheirownsafetyandthesafetyofothers,including partiesforwhomtheyhaveaprofessionalresponsibility.
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Dedication
Thisbookisdedicatedtomygreatparents,MohammadandKokab, whoraisedmewithlove,compassion,andasenseofappreciationfor knowledgeandinnovation;andtomylovelywifeforherpatience, support,andadventurousspirit.
—MahdiBodaghi
Thisbookisdedicatedtomyparentsandsistersfortheirconsistent support,tomywifeforherpatienceandcompany,andtomyson,Alan, formotivatingmetokeepgoing.
—AliZolfagharian
24D-printeddielectricelastomersoftrobots:
andXiaolongWang
44D-printedlow-voltageelectroactivepolymersmodeling
54D-printedstimuli-responsivehydrogelsmodeling andfabrication151
AnaP.PiedadeandAnaC.Pinho
MoqaddasehAfzaliNaniz,MohsenAskari,AliZolfagharian, andMahdiBodaghi
Li-YunHsu,ChristophAlexanderSpiegel,andEvaBlasco
Contributors
KumkumAhmed CollegeofEngineering,ShibauraInstituteofTechnology,Tokyo, Japan
MohammadAlshawabkeh FHKarntenCampusVillach,Villach,Austria
JiaAn SingaporeCentrefor3DPrinting,SchoolofMechanicalandAerospace Engineering,NanyangTechnologicalUniversity,JurongWest,Singapore
Jean-ClaudeAndre LRGP7274UMRCNRS,UniversityofLorraine,Nancy,France
MohsenAskari DepartmentofEngineering,SchoolofScienceandTechnology, NottinghamTrentUniversity,Nottingham,UnitedKingdom;DepartmentofTextile Engineering,SchoolofMaterialEngineering&AdvancedProcesses,Amirkabir UniversityofTechnology,Tehran,Iran
ChangshengBian ShaanxiKeyLaboratoryofIntelligentRobots,Schoolof MechanicalEngineering,Xi’anJiaotongUniversity,Xi’an,Shaanxi,P.R.China
EvaBlasco Organisch-ChemischesInstitut,Ruprecht-Karls-UniversitatHeidelberg, Heidelberg,Germany
MahdiBodaghi DepartmentofEngineering,SchoolofScienceandTechnology, NottinghamTrentUniversity,Nottingham,UnitedKingdom
CheeKaiChua EngineeringProductDevelopmentPillar,SingaporeUniversityof TechnologyandDesign,Tampines,Singapore
DavidCorrea SchoolofArchitecture,UniversityofWaterloo,Cambridge,ON, Canada
FredericDemoly ICBUMR6303CNRS,UniversiteBourgogneFranche-Comte, UTBM,Belfort,France
Lisa-MarieFaller ADMiRELab-AdditiveManufacturing,IntelligentRobotics, SensorsandEngineering,SchoolofEngineeringandIT,CarinthiaUniversityof AppliedSciences,Villach,Austria
RuiGuo StateKeyLaboratoryofSolidLubrication,LanzhouInstituteofChemical Physics,ChineseAcademyofSciences,Lanzhou,People’sRepublicofChina
KhanRajibHossain StateKeyLaboratoryofSolidLubrication,LanzhouInstituteof ChemicalPhysics,ChineseAcademyofSciences,Lanzhou,People’sRepublicof China
Li-YunHsu Organisch-ChemischesInstitut,Ruprecht-Karls-UniversitatHeidelberg, Heidelberg,Germany
WeiMinHuang SchoolofMechanicalandAerospaceEngineering,Nanyang TechnologicalUniversity,JurongWest,Singapore
ZhongyingJi StateKeyLaboratoryofSolidLubrication,LanzhouInstituteof ChemicalPhysics,ChineseAcademyofSciences,Lanzhou,People’sRepublicof China
PanJiang StateKeyLaboratoryofSolidLubrication,LanzhouInstituteofChemical Physics,ChineseAcademyofSciences,Lanzhou,People’sRepublicofChina
DaewonKim Embry-RiddleAeronauticalUniversity,AerospaceEngineering, DaytonaBeach,FL,UnitedStates
AntoineLeDuigou Univ.BretagneSud,UMRCNRS6027,IRDL,Lorient,France
AmeliaYilinLee EngineeringProductDevelopmentPillar,SingaporeUniversityof TechnologyandDesign,Tampines;HP-NTUDigitalManufacturingCorporateLab, SchoolofMechanicalandAerospaceEngineering,NanyangTechnological University,JurongWest,Singapore
BinLuo ShaanxiKeyLaboratoryofIntelligentRobots,SchoolofMechanical Engineering,Xi’anJiaotongUniversity,Xi’an,Shaanxi;SchoolofMechanicaland ElectricalEngineering,HohaiUniversity,ChangzhouCampus,Changzhou, Jiangsu,P.R.China
MehrshadMehrpouya FacultyofEngineeringTechnology,UniversityofTwente, Enschede,TheNetherlands
MoqaddasehAfzaliNaniz DepartmentofEngineering,SchoolofScienceand Technology,NottinghamTrentUniversity,Nottingham,UnitedKingdom; DepartmentofTextileEngineering,SchoolofMaterialEngineering&Advanced Processes,AmirkabirUniversityofTechnology,Tehran,Iran
AnaP.Piedade UniversityofCoimbra,CEMMPRE,DepartmentofMechanical Engineering,Coimbra,Portugal
AnaC.Pinho UniversityofCoimbra,CEMMPRE,DepartmentofMechanical Engineering,Coimbra,Portugal
MDNahinIslamShiblee DepartmentofMechanicalSystemsEngineering,Graduate SchoolofScienceandEngineering,YamagataUniversity,Yamagata,Japan
StanislavSikulskyi Embry-RiddleAeronauticalUniversity,AerospaceEngineering, DaytonaBeach,FL,UnitedStates
ChristophAlexanderSpiegel Organisch-ChemischesInstitut,Ruprecht-KarlsUniversit€ atHeidelberg,Heidelberg,Germany
XiaolongWang StateKeyLaboratoryofSolidLubrication,LanzhouInstituteof ChemicalPhysics,ChineseAcademyofSciences,Lanzhou,People’sRepublicof China
XuejieXu ShaanxiKeyLaboratoryofIntelligentRobots,SchoolofMechanical Engineering,Xi’anJiaotongUniversity,Xi’an,Shaanxi,P.R.China
YiZhang SingaporeCentrefor3DPrinting,SchoolofMechanicalandAerospace Engineering,NanyangTechnologicalUniversity,JurongWest,Singapore;School ofElectronicScienceandEngineering,UniversityofElectronicScienceand TechnologyofChina,Chengdu,Sichuan,China
ZicaiZhu ShaanxiKeyLaboratoryofIntelligentRobots,SchoolofMechanical Engineering,Xi’anJiaotongUniversity,Xi’an,Shaanxi,P.R.China
AliZolfagharian SchoolofEngineering,DeakinUniversity,Geelong,VIC,Australia
Editorsbiography
Dr.MahdiBodaghi, BSc,MSc,PhD,PGCAP, FHEA,CEng,MIMechE,isSeniorLecturerinthe DepartmentofEngineering,SchoolofScienceand TechnologyatNottinghamTrentUniversity.Mahdi headsthe4DMaterialsandPrintingLaboratory (4DMPL)thathostsabroadportfolioofprojects focusingontheelectro-thermo-mechanical multiscalebehaviorsofsmartmaterials,softrobots, and3D/4Dprintingtechnologies.Intherecent 12years,hehasbeenworkingtowardtheadvancementofstate-of-the-artsmartmaterialsandadditive manufacturing,whichhasledhimtocofoundthe4D PrintingSocietyandtocoedittheSmartMaterialsin AdditiveManufacturingbookseries.Hisresearchhasledtothepublicationofmore than120scientificpapersinprestigiousjournalsonmechanics,manufacturing,and materialsscienceaswellasthepresentationofhisworkatmajorinternationalconferences.MahdihasalsoservedasChairmanandMemberofScientificCommittees for10InternationalConferences,asGuestEditorfor10journals,asEditorialBoard Memberfor8scientificjournals,andasReviewerformorethan130journals.Mahdi’s researchawardsincludetheBestDoctoralThesisAward(2015),theCUHKPostdoctoralFellowship(2016),theAnnualBestPaperAwardinMechanicsandMaterial SystemspresentedbytheAmericanSocietyofMechanicalEngineers(2017),Horizon PostdoctoralFellowshipAward(2018),andtheIJPEM-GTContributionAward (2021)recognizedbytheKoreaSocietyforPrecisionEngineering.
Dr.AliZolfagharian, BSc,MSc,PhD,ADPRF, GCHE,isSeniorLecturerintheFacultyofScience, EngineeringandBuiltEnvironment,Schoolof EngineeringatDeakinUniversity,Australia.He hasbeenamongthe2%top-citedscientistslisted byStanfordUniversityandElsevier(2020),the AlfredDeakinMedallistforBestDoctoralThesis (2019),andtheAlfredDeakinPostdoctoralFellowshipAwardee(2018).Hehasbeendirectingthe4D PrintingandRoboticMaterialslaboratoryatDeakin Universitysince2018.Aliisthecofounderofthe 4DPrintingSociety,thecoeditoroftheSmart MaterialsinAdditiveManufacturingbookseries publishedbyElsevier,andatechnicalcommitteememberoffiveinternationalconferences.From2020to2022,hehasreceivedmorethanAUD200kresearchfunds fromacademicandindustrialfirms.Ali’sresearchoutputsonflexiblemanipulators, softgrippers,roboticmaterials3D/4Dprinting,andbioprintinginclude71articles, beingeditorof2journals,15specialissues,and5books.
Preface
Wethankyouforchoosingthisbookseriesthatisintendedtocreateanintellectual nicheforsmartmaterialsintheadditivemanufacturingcommunity.Thisbook,the firstintheseries,demonstratestheprinciplesthatfrontlineacademicsandengineers havedevelopedforfour-dimensional(4D)printinginamannerthatwillbeusefulfor studentsandearlycareerresearchersinthefieldatahighereducationlevel.
Duringthepastfewyears,significantprogresshasbeenmadein4Dprintingby researchersintopinstitutionsandlaboratoriesworldwide,combiningadvancesin 3Dprintingofdynamicstructureswithstimuli-responsivematerials,knownassmart materials,tocreateadditivelymanufacturedsmartstructures.However,4Dprinting technologyisonlyintheearlystagesofresearchanddevelopment,soindustrieswill probablylearnmoreaboutitinthecomingyears.WiththeFourthIndustrialRevolutionwellunderway,industriesthattakeadvantageofitsunprecedentedpossibilities willundoubtedlyhaveaneconomicadvantage.Withthisknowledge,institutions, researchers,andstudentsinvestingin4Dprintingtechnologyaretheoneswithradical potential.
Additivemanufacturingtechnologythroughlayeredbuildingofmaterials,also knownas3Dprinting,wasdevelopedinthelate1970sandearly1980sbydifferent scientistsandengineersaroundtheworld.Sincethen,thebasicprocessandtechnologyhaveevolvedfromthetypical3Dprintingprocessestodevelopobjectsandstructuresmainlyusingfunctionalmaterialsindiverseapplicationsbenefitingfromtheir robustmechanicalandgeometricproperties.In2013,theterm“4Dprinting”was introduced,inwhichthefourthdimensionreferstotime-relatedchangesintheshape, properties,color,orfunctionsof3D-printedsmartmaterialsinresponsetoexternal stimuli.Inotherwords,4Dprintingisdefinedasthe3Dprintingofsmartmaterials toworkasdynamicstructuresandmechanismsasopposedtomerelystaticbutfunctionalconstructsconventionallymadevia3Dprinting.
Aseriesofbooksonsmartmaterialsinadditivemanufacturinghasbeenannounced tobetterservethepurpose.Thisbook,thefirstintheseries,providesreaderswitha quickoverviewofthecurrentsmartmaterialsandtechniquestoprocessthemvia4D printing.Differenttypesofsmartmaterials,includingshapememorypolymers (SMPs),hydrogels,shapememoryalloys(SMAs),biomaterials,naturalfibers,dielectricelastomers(DEs),liquidcrystalelastomers(LCEs),electroactivepolymers (EAPs),softmaterials,andtheircomposites,usedin4Dprintingbasedontheir responsetostimuli,fabrication,multiphysicsmodeling,controltechniques,andapplications,arediscussed.Afterreadingthechaptersinthisbook,readerswillhopefully learnthebasicsofcurrentsmartmaterialsusedin4Dprintingandtheirprocessing
strategies.SmartMaterialsinAdditiveManufacturing,Volume1issuitablefornew researchers,scientists,industrialdesigners,andstudentsenteringthefieldtofurther familiarizethemselveswiththeconceptsandprinciplesof4Dprintingtechnology. Thisbookistheresultofyearsofcollectiveresearchbyexpertsin4Dprintingand additivemanufacturingofsmartmaterialsandstructures.Theeditorsandauthors hopeyouwillbenefitfromthetimeandeffortittooktoputittogetherandbelieve itwasaworthwhileendeavor.Editingthisbookhasledtotheformationofabigger networkofexpertsin4Dprinting,withwhomwehaveinitiatedcollaborationstofurtheradvancethefield.
MahdiBodaghi AliZolfagharian
Acknowledgments
Thecoeditorsexpresstheirsinceregratitudeanddeepappreciationtoalltheauthors fortheirsignificantandexcellentcontributionstothisbook.Theirenthusiasm,commitment,andtechnicalexpertisehavemadethispioneeringbookpossible.Weare alsogratefultoElsevierforsupportingthisbookproject,andweextendourspecial thankstotheEditorialTeam,Dennis,Mariana,andSurya,fortheirproactivesupport andcooperativeattitude,withboththepublishinginitiativeingeneralandtheeditorial aspects.
4Dprintingprinciples andmanufacturing
MahdiBodaghia andAliZolfagharianb
aDepartmentofEngineering,SchoolofScienceandTechnology,NottinghamTrent University,Nottingham,UnitedKingdom bSchoolofEngineering,DeakinUniversity,Geelong,VIC,Australia
Introduction
Four-dimensional(4D)printingwasinitiallydemonstratedattheTechnology,Entertainment,andDesign(TED)conference(Tibbits,2013)andinajournalarticle(Ge, Qi,&Dunn,2013)in2013.Itisacombinationofthree-dimensional(3D)printing, stimuli-responsivesmartmaterials,design,andamodeling-basedprogrammingtechnology,whichresultsintheevolutioninshape,properties,color,andfunctionalityofa 3D-printedstructureovertime(referredtoasfourthdimension“D”)whenitis exposedtostimuli,suchasheat,light,humidity,magneticfields,stress,andpH. A4D-printedobjectproducedusingsmartmaterialsreactsanddynamicallychanges itsformandsizeasplannedwhenmeetingexternalstimuliovertime(Fig.1.1).
Theemergenceof4Dprintingtechnology isexpectedtorevolutionizeindustrial manufacturingwiththerapidadvancement ofthebasicchemicalindustry,materials science,computerscience,andenginee ringdesignandmodeling.Theglobal4D printingmarketisexpectedtoreachacompoundannualgrowthrate(CAGR)of 42.95%by2025(https://www.marketsandmarkets.com/Market-Reports/4d-print ing-market-3084180.html).Aerospace,automotive,clothing,artwork,defense andmilitary,andhealthcareareamongtheend-userindustriesfor4Dprintingtechnology,withvaryingratesofdemandandtranslation.Inrenewableenergy,4Dprintingcanimproveenergyharvestingeff iciencyandreducecarbonemissions(Luetal., 2021).Inthefieldoftheintelligentoptimizationofvehicles,achievementsinaircraft,automobiles,andshipsarerapidlyemerging(Hanetal.,2020)withthecapabilityoffabricatingitemsevenbiggerthan printersviashape-shiftingcapability.In thefieldoftextilesandcivi lproducts,skirts,shoes,andprogrammabletextilesare alreadyonthemarket(Schmelzeisen,Koch,Pastore,&Gries,2018 ),inclinical medicineapplications,4D-printedscaffolds,knownas4Dbioprinting,cellmodels ( Askarietal.,2021),drugreleaseandmedicaldevices( Bodaghi,Damanpack,& Liao,2016 ; Bodaghi,Noroozi,Zolfagharian,Fotouhi,&Norouzi,2019; Xiao& Huang,2020; Zolfagharian,Gregory,Bodaghi,Gharaie,&Fay,2020),andinthe fieldofsoftrobotics,avarietyofnovelmec hanicalstructuresandactuatorshave beendeveloped( Zolfagharianetal.,2020; Zolfagharian,Kaynak,&Kouzani, 2019; Zolfagharian,Kouzani,Khoo,Gibson,&Kaynak,2016).4Dprintingalone
Fig.1.1 4Dprintingconceptincomparisonwith3Dprinting.
isamajorstepforwardsinceitisinnovative tousesmartmaterialstocreatedynamic structuresthatthetraditionalmanufacturingmethodcouldnotreadilyachieve.
4Dprintingtechnologymakesuseofsmartmaterialssuchasshapememorypolymers(SMPs),hydrogels,shapememoryalloys(SMAs),liquidcrystalelastomers (LCEs),hydrophilicmaterials,composites,andothermultifunctionalmaterials becauseoftheirstimuli-responsivepropertiesandshaperecoveryfeatures.Smart materialsfor4Dprintingareoneoftheemergingfieldsofresearchinwhichvarious materialsaresynthesizedfordynamicmechanismsaccordingtotheirreactionstovariousexternalstimuli.Byintegrating3Dprintingtechnologyandsmartmaterials,a 4D-printedsmartstructurewillresultinlowerproduction,transport,andhandling costs,leadingtosavingmoneyandeffortsupportingtheecosystem(Haleem, Javaid,Singh,&Suman,2021).Thefutureapplicationsofsuchstructuresinthebuilding,transportation,textiles,healthcare,defense,andaerospaceindustriesarevast (Ahmed,Arya,Gupta,Furukawa,&Khosla,2021; Haleemetal.,2021; Kuang etal.,2019). SeriesI:Smartmaterialsandstructure:4Dprinting
Thematerialsusedfor4Dprintingaregenerallycalled“SmartMaterials”asthey couldchangetheirpropertiesovertime.Thesematerialscanrespondtoexternalstimuliandpossessautonomousbehaviors,likeshapememory,self-assembly,color change,andself-healing.Eventhoughstimuli-responsivematerialshavebeen
4Dprintingprinciplesandmanufacturing3
employedinvariousapplications,onlyasubsetofthemcouldbeusedfor4Dprinting basedonwhetherasmartmaterialcouldbeprintedbyitselforrequiresothermaterials toachievetemporalchanges(Shen,Erol,Fang,&Kang,2020).Hence,thesmart materialsusedin4Dprintingessentiallypossessdualkeyabilities,whicharestimuli responsiveandprintability.Theselectionofthematerialsfor4Dprintingishighly dependentontheintendedapplicationsandtheprintingmethod.Inthepresentbook, differenttypesofsmartmaterialsusedin4Dprintingbasedontheirresponseto stimuli,manufacturingtechniques,andapplicationswillbediscussed.
Thedevelopmentofadvancedsmartmaterialswithintegratedshapeactuationand multi-stimuli-responsivecapabilityischallengingandhighlydesiredin4Dprinting. Thepropertiesofstimuli-responsivematerialsdeterminethestimulusandmethodof actuation(Kuang,2021).SMPsandhydrogelsarethemostrecentsmartmaterials usedfor4Dprinting,mainlyresponsivetoheatstimulus.However,compositesof thesematerialsarefocusedondeveloping4D-printedstructuresresponsivetoother stimuli,suchaslight,electric,andmagneticfields,whicharehighlydesirablefor remote-controlledactuations(Hippleretal.,2020).Despitethisadvance,4Dprinting ofSMPsstillfaceschallengesinachievingadesirablereversibleactuation(Kuang, 2021).Bycontrast,hydrogelcompositesenablereversibleshapeshiftingduetoa stimulus-responsiveswellinganddeswellingprocess(Zolfagharian,Kouzani, Khoo,Gibson,&Kaynak,2016).Yet,hydrogelsaremechanicallysoftmaterials, andtheiractuationinvolvestime-consumingdiffusionandmasstransportofwater orotherchemicals,whichlimitstheirapplications.LCEsalsoenablereversibleshape actuationwithrelativelyenhancedmechanicalproperties(Barnesetal.,2020).Both photo-andthermal-responsiveLCEshavebeenusedfor4Dprintingtoenablelarge strainreversibleactuations.Recently,magnetoactivematerialshavebeenusedfor4D printingwithremote-controlledandfastactuation(Zhangetal.,2021).Other multifunctionalmaterials,suchasself-healingmaterialsandbiomaterials,havealso beendevelopedfor4D-printedstructuresforbroadapplicationsinrobotics (Zolfagharianetal.,2019)andbiomedicine(Askarietal.,2021).
However,themostexisting3Dprintingmethodsmaynotbeapplicabletosmart materials.Therefore,thedevelopmentofnewmaterialsfor4Dprintingwillrequire themodificationofexisting3Dprintingmethodstoo.Externalfield-assisted3Dprovidesanewmethodtofabricatehigh-performanceandstimulus-responsivematerials. Anelectricfield,forexample,canbeusedtoalignconductivematerials,suchas graphiteorliquidmetal,forprintingfunctionalcomposites(Yang,Kim,Kim,& Kim,2021),andamagneticfieldcanbeusedtoassistprintingofanisotropiccompositesforcontrolledshapeshifting(Rastogi&Kandasubramanian,2019).Moresophisticatedmulti-material4Dprintingtechnologiesareespeciallydesirabletofabricate morecomplexstructureanddeviceswithshapeshiftingandotherfunctional properties.
Thisbookhaspresentedtheprinciplesof4Dprintingcommonmaterialsand manufacturingtechniques,fromanengineeringpointofviews.Thefollowingintroducethechapters,presentedinthebook,whichintroducebasicelementsandadvancementof4Dprintingwithafocusonsmartmaterialsand4Dprintingtechniques (Fig.1.2).
Fig.1.2 4D-printedsmart materialsdiscussedinthisbook.
4D-printeddielectricelastomersoftrobotsmodeling andfabrications
Adielectricelastomeractuator(DEA)isasmartmaterialwiththecapabilityofgeneratinghighbendingmotioninresponsetoanappliedelectricalstimulus(ElAtrache, Kim,Divo,&Drakunov,2019).Amongthematerialsusedforsoftrobots,dielectric elastomers(DEs)areintrinsicallycompliant,fastresponse,andhigh-energydensity polymersthatcanoperateasbothsoftactuatorsandsoftsensors(Mahmudetal., 2021).However,DEs’layeredstructureandsoftnaturemaketheirmanufacturability challenging,especiallyfornon-trivialbiomimeticgeometriestypicalforsoftrobotics. TofacilitateeffectiveDEsoftrobots’fabrication,thischapterprovidesacomprehensiveanalysisofDEmaterials’transitionintoafinalproductbymeansof4Dprinting. Thisunveilsnewpossibilitiesfortrulybiomimeticsoftrobotswithembeddedanddistributedactuation-sensingsystems(Zolfagharianetal.,2020).DEAsarepromising smartmaterialsdrivingsoftroboticstechnologyduetotheirsuperiorperformance. Duetothehard-to-fabricatelayeredstructuresusingdifferentmaterials,DEAs’transitionfromconventionaltoadditivemanufacturingisnotaneasytask.Nevertheless, asarecognizedmanufacturingapproachforfabricatingthestate-of-the-artDEA devices,4Dprintinghasrecentlyexperiencedextensivedevelopment.Propermaterial selection,technologicalaspects,andDEAdesignconsiderationsareimportantto avoidtypicalDEAdefects,especiallyinstackedconfigurations(Sikulskyi, Mekonnen,ElAtrache,Divo,&Kim,2021).
Oneofthemainadvantagesof4D-printedDEAsoftrobotsisthesimplificationof themanufacturingprocessbyminimizingproductionstageswhileincreasingprecision.Asamethodoffabricatingfinisheddeviceswithoutintermediatemanualsteps, 4Dprintingfocusesonfullyprinted,non-prestretchedDEAs.Thus,unimorphDEAs areoftenemployedduetotheirabilitytogeneratelargebendingdeformationsat
4Dprintingprinciplesandmanufacturing5
relativelylowstrainswithoutprestretch.Asdiscussed,theabsenceofprestretchand lowactuationstrainallowsasimplematerialmodeltofitexperimentalresults.Meanwhile,geometricalnonlinearitiesshouldbeconsideredinthemodelingofDEAsoft robotsduetotheirlargedeflectionandthickness.Thus,thereisstillconsiderableroom forimprovementtoenableaccuratemodelingofthemulti-morphactuatorwithdifferentsoftrobotbodies.
Meanwhile,4D-printedDEAisstillinitsinitialstagecomparedtoothermonomaterialsoftactuatorsandnecessitatesfurtherinvestigation.Therefore,thischapter aimstohelpthereaderunderstandthemajorchallengesonthewayto4D-printedDEA softrobots.Differentfabricationtechniques,materialproperties,andDEgeometries areanalyzedtoestablishafundamentalunderstandingofhowtoimplementhighqualityDEsoftrobots.Moreover,recentmodelingapproachessuitableforDEsoft robotsarestructuredintoeasy-to-useguides.Usingthisknowledge,thereaderwill beabletoutilizeanddevelopappropriateadditivemanufacturing(AM)methods,sensiblyselectmaterials,altertheirpropertiesasneeded,andaccuratelypredictfinalperformancebasedonDEsoftrobotdesignandapplication.
4D-printedlight-responsivestructures
Withtheadvancementsinthearenaof4D-printedlight-responsivestructures,more andmoresmartdevicesareappearingwithcomprehensiveproperties.Lightasan excellentstimulusenablesremotecontrol,rapidlyswitchingonandoff,easytunability,andpreciselocalareaprojectionin4D-printedstructures.Light-responsive4D printinghasalsogainedpopularityduetoitsexcellentpropertiesoftheabundant sourceofenergy,non-contactmode,clean,andeasycontrolofintrinsiccharacteristics suchasthetunablewavelengthandintensity(Zhu,Zhang,Yang,Liu,&Liu,2020). Accordingly,light-responsive4Dprintingisdependentontheconversionofphotochemicalorphotothermaleffectsandthenresultsinmechanicalbehaviors (Browne,Redondo,&Pumera,2020).Thusfar,4Dprintingoflight-responsivestructureshasbeenachievedbydifferentfunctionalmaterials,includingliquidcrystalline polymericmaterials,hydrogels,andSMPs,whichcanbeeithersemi-crystallineor amorphous(Zolfagharian,Kaynak,etal.,2020).
Thischapterfocusesontheessentialcomp onentsof4D-printedlight-responsive structuressystems.Themajoradvancesin light-responsive4D-printedstructures, includinginnovativedesignprinciplesandactivationmechanismsoflightactivatedsmartmaterials,arediscussed.Potentialemergingapplicationsinencryptionandanti-counterfeiting,self-healing,softrobotics,andphoto-controlled microfluidicsarefurtheroverviewed.Furthermore,typicalm aterialsusedfor light-responsivestructures,including SMPs,liquidcrystallinematerials,and hydrogels,aresummarizedsystematically,andeachofthemisstatedbyitsunique strengthsandweaknesses.Thecurrentchallengesandoutlooktoward4D-printed light-responsivestructuresarealsopointedouttoleaveasignificantspacefor futureinnovationopen.
