ImplantableEnergyHarvesterforBiomedicalApplication

Abstract

Implantablemedicaldeviceshavebeendevelopedtotreatvariousdiseasesinthebody.Accordingly,ithasbeenincreasingahighinterestofimplantableenergyharvesterthatcancontinuouslysupplypowertoimplantablemedicaldevicesinsidethebody.Theimplantableenergyharvesterisneededforhigherperformancewhilereducingtheirvolumeandweightinordertogenerateenergyinvivoenvironment.Inaddition,sincetheimplantableenergyharvestersarehighlylikelytobeusedinhumansinthefuture,experimentsinanenvironmentsimilartothephysiologicalconditionsofthehumanbodyarerequired.Therefore,inthisthesis,studiesonincreasingtheperformancewhilereducingthevolumeandweightofimplantableenergyharvesters,andapplyingittotheinvivoenvironmentarepresented.First,thefiber-typeenzymaticbiofuelcellwithhighpowerdensitywasfabricatedasaone-bodysystemsuitableforinvivoenvironmentsandimplantedintotheBalb/cmouse.Itwasfabricatedasaone-bodysystembycoatingtheanodeandcathodeoftheenzymaticbiofuelcellwithNafiontopreventashortcircuitbetweenthetwoelectrodes.Thiscanminimizethebiofuelcell'svolumeandincreasetheelectrode'sstability.Thetwo-pliedbiofuelcellsystemwasimplantedintheabdominalcavityofthemouseandgeneratedthehighestpowerdensity(0.3mW/cm)amongpreviouslyreportedbiofuelcellsimplantedinmammals.Sincethetwo-pliedbiofuelcellsystemhasathinfibershape,itcanbeinjectedintothemousethroughasyringewithoutsurgery.Thisinjectablemethodenabledthelowinflammatoryresponseandthehighbiocompatibilityofthetwo-pliedbiofuelcellsystem. Tofurtherimprovetheperformanceoftheimplantableenergyharvesters,thehybridenergyharvesterscombiningthetwistronharvesterusingmechanicalenergyandthebiofuelcellusingchemicalenergyweredeveloped.Sincethishybridenergyharvesterfunctionsasabiofuelcellandatwistronharvesterconcurrently,itcangeneratehigherperformancebythesynergyofbiofuelcellharvestingandtwistronharvesting.Asexpected,thehybridenergyharvestersgeneratedapowerof16.5W/kg,29%higherthanthesumoftheindividualpowers(11.7W/kg).Inaddition,thehybridenergyharvestershowsaremarkableenergypercycleof32.5J/kgandamaximumpowerof14.5W/kgatlowfrequency(0.25Hz). Inordertocompensateinvivoexperimentsforbiomedicalapplications,artificialbloodvesselsthatmimicnativebloodvesselswereimplementedthroughtissueengineering.Thisartificialbloodvesselwasfabricatedwithamechanicalperformancesimilartothatofthenativebloodvesselbyusingatubularknitstructure,andwasimplementedwithanendothelialcellmono-layerandasmoothmusclecellmulti-layers,whicharestructuressimilartonativebloodvessels.Asaresult,theartificialbloodvesselsshowedprominentdurabilitytowithstandmechanicalstress.Inaddition,theartificialbloodvesselsweremanufacturedinvariousstructures(L-structure,Y-structure)andsuccessfullyperformedthefunctionofbloodvessels.|이식형의료기기들은체내여러질병을치료하기위해개발되었고,그에따라체내에서이식형의료기기에전원을공급할수있는이식형에너지하베스터가주목받고있다.이식형에너지하베스터는생체내환경에서에너지를생성하기위해부피와무게는줄이면서더높은성능이요구되고있다.또한,이식형에너지하베스터는미래에인간에게사용될가능성이크기때문에인체의생리학적환경과가까운조건에서의실험이요구되고있다.따라서,본논문에서는이식형에너지하베스터의부피와무게는줄이면서성능을높이는연구와이를생체내환경에적용하기위한방법을제시한다. 첫째로,높은전력을지닌섬유형태의생체연료전지(biofuelcell)를생체내환경에적합한일체형구조로제작하여실험용생쥐(Balb/c)에이식하였다.생체연료전지의양극과음극에나피온(Nafion)을코팅하여두전극의단락을방지함으로써,생체연료전지를일체형으로제조하였다.이는생체연료전지의부피를최소한으로하며,전극의안정성을높일수있다.이일체형생체연료전지는생쥐의복강에이식되어기존에보고된포유류에이식된생체연료전지중최대전력밀도(0.3mW/cm)를보였다.이일체형생체연료전지는얇은섬유형태를가지기때문에주사기를통해생체내에수술없이주입될수있다.이러한주입방법은이식받은쥐들의건강상태가정상쥐와유사함을보여주었고,주입시발생한염증반응은일주일내로40%감소하여생체연료전지의생체적합성을보였다. 또한,이식형에너지하베스터의성능을더욱개선하기위해기계적에너지를사용하는트위스트론(twistron)하베스터와화학적에너지를사용하는생체연료전지를결합한하이브리드에너지하베스터를개발하였다.이하이브리드에너지하베스터는생체연료전지와트위스트론하베스터의역할을동시에할뿐만아니라,두하베스팅이시너지효과를일으켜더높은성능을생성할수있었다.그결과,하이브리드에너지하베스터는개별적인전력의합(11.7W/kg)보다29%더높은16.5W/kg의전력을생성하였고,32.5J/kg의우수한주기당에너지를생성하였다. 마지막으로,체내실험의한계를보완하기위해실제혈관을모방한인공혈관을조직공학적으로구현하였다.이인공혈관은튜브형니트구조를사용하여실제혈관과유사한기계적성능으로제작되었고,실제혈관과유사한구조인내피세포층과평활근세포층으로구현되었다.그결과인공혈관은기계적응력을견딜수있는우수한내구성을보였다.또한,인공혈관을실제혈관의다양한구조(L-구조,Y-구조)로제작할수있었고,이인공혈관들은혈관의기능을성공적으로수행하였다.