Fabrication Of Flexible Electrodes For Implantable Fuel Cells And Their Application In Self-powered Nerve Guidance Conduits

In vivo energy conversion devices are devices that can turn mechanical,thermal or chemical energy in human body into electrical power.The structural design,fabrication and clinical applications of these devices have been the research focus for recent years.Especially,applying these devices in tissue repair has high value in clinical application,but is also challenging.Implantable glucose fuel cells generate electrical power by the consumption of glucose and oxygen in human body,avoiding the problem of power depletion.With the miniaturization and low-power-consumption development of electron devices,implantable glucose fuel cells have attracted wide attention.Flexible and implantable electronic devices are developing rapidly in the last few years.Aiming at the power-supply of these devices,flexible anode and cathode for flexible and implantable glucose fuel cells are prepared by incorporating abiotic glucose oxidation and oxygen reduction catalysts on bacterial cellulose(BC),respectively.BC is chosen as the flexible substrate because of its good biocompatibility and outstanding flexibility.The glucose oxidation and oxygen reduction performance of the electrodes are studied under physiological conditions.Currently,the application of electrical stimulation in peripheral nerve regeneration involves problems such as causing pain or infection,and inaccuracy of the stimulation.To solve these problems,for the first time,nerve scaffolds with self-powered electrical stimulation based on glucose oxidation and oxygen reduction are prepared,which provide a whole-new solution for the application of electrical stimulation in peripheral nerve regeneration.Flexible BC/PtAu electrode for glucose oxidation is prepared by forming PtAu nanoalloy catalyst on the BC substrate.Different loading of PtAu alloy nanoparticles are formed by in-situ reduction of chloroplatinic acid and chloroauric acid with sodium borohydride.The PtAu nanoparticles are uniformly distributed in the nano-network of BC;the average alloy particle size for BC/PtAuⅡ is 23.0 ± 3.2 nm.BC/PtAuⅡ has good catalytic activity towards glucose oxidation,and good resistance against physiological level of oxygen;the cytotoxity of BC/PtAuⅡ is close to that of BC.In addition,BC/PtAuⅡ has outstanding flexibility,with a tensile strength of 56.5 ± 12.7 MPa,and an elongation at break of(17.2 ± 3.5)%.Taken together,the BC/PtAuⅡ electrode holds potential as an anode for flexible and implantable glucose fuel cells.Flexible BC/PDA/Ag electrode for oxygen reduction is prepared by polydopamine(PDA)-aided electroless mentalization on the BC substrate.PDA is uniformly coated on the fibers of BC,which effectively improves the loading of silver nanoparticles.The conductivity of BC/PDA/Ag is 2.72±0.13 s cm-1,which is two orders of magnitude larger than that of BC/Ag.The catalytic activity and stability of BC/PDA/Ag towards oxygen reduction is effectively improved compared with BC/Ag.In addition,The BC/PDA/Ag electrode has good flexibility,as well as good resistance to glucose interference.These facts make BC/PDA/Ag a promising cathode for flexible and implantable glucose fuel cells.Conductive substrate is prepared by incorporating polypyrrole(PPy)on the BC substrate,and then two-dimensional,self-powered nerve scaffold is prepared by further loading cathode and anode catalysts on the conductive substrate.BC/PPy conductive substrate is prepared by the oxidative polymerization of PPy on the nanofibers of BC.The optimized BC/PPy conductive substrate shows tensile strength of 41.2±4.7 MPa,elongation at break of 15.4±1.8%,and conductivity of 1.51±0.05 s cm-1.Next,Pt nanoparticles are incorporated on one end of the BC/PPy conductive substrate by electrochemical deposition to form the anode,and nitrogen-doped carbon nanotubes(N-CNTs)are loaded on the other end by immersion adsorption to form the cathode,forming two-dimensional,self-powered Pt-BC/PPy-NCNTs nerve scaffold.In addition,three-dimensional,self-powered,oriented and conductive Pt-hPCL/PPy-NCNTs nerve conduit is designed and prepared based on oriented polycaprolactone(PCL)fiber membrane formed by electrospinning.In phosphate buffer saline(PBS)containing 5 mM of glucose,the potential difference between the anode and the cathode of Pt-BC/PPy-NCNTs is 350±28 mV;in Dulbecco’s modified eagle medium(DMEM),the potential difference between the anode and the cathode can remain higher than 100 mV for more than 6 h.The effects of the self-powered Pt-BC/PPy-NCNTs nerve scaffold towards axon regeneration are studied in vitro by dorsal root ganglia(DRG)cultivation.The results show that the self-powered Pt-BC/PPy-NCNTs scaffold can effectively promote neurite outgrowth compared with the conductive BC/PPy scaffold.The effects of the self-powered Pt-BC/PPy-NCNTs nerve scaffold are further evaluated in vivo by the rat sciatic nerve defect model.Gait analysis,hematoxylin-eosin(HE)staining,immunofluorescent staining and TEM results indicate that the self-powered Pt-BC/PPy-NCNTs scaffold can promote nerve regeneration compared with the conductive BC/PPy scaffold.