Polyvinyl Alcohol Hydrogel Crosslinked By Prepolyurethane For Improving Neural Electrodes

Backgroud:Neural electrodes are the key components of implantable neural devices and foundation of electrical stimulation or electrical signal recording.There are two major problems for developing a long-term interface between neural electrodes and tissue,one is the increase of the electrical impedance in application,the other is the formation of fibrous capsule and neurons apoptosis surrounding the electrodes.Improving the the biocompatibility of neural electrodes is a hotspot of neuroscience research for the effect on decreasing fibre package and neurons apoptosis,and it benefits establishing a stability electrodes-tissue interface.The insulation part of neural electrodes has much bigger contact area with neural tissue than that of the conductive part,so it is very important to improve the biocompatibility of the insulation part.As kind of medical polymer materials,Polydimethylsiloxane(PDMS)is commonly used as the insulation materials for neural electrodes,but PDMS still has some problems such as protein adsorption,fiber sheath formation,and nearby neurons apoptis,which need to be improved.Prepolyurethane/poly polyvinyl alcohol(PPU/PVA)hydrogel is a kind of potential biological materials with good film-forming property,low cytotoxicity,and good biocompatibility and it has been used for the preparation of joint.But PPU/PVA hydrogel has not been researched for application in neural electrodes yet.Objective:To preprare PPU/PVA hydrogel and investigate the feasibility of the synthetic composite as neural electrodes coatings for improving electrodes of PDMS substrate.Methods:(1)PPU/PVA hydrogel was preprared from prepolyurethane(PPU)and polyvinyl alcohol(PVA)by chain extension,and characterized by infrared spectroscopy.The water absorption rate,ionic conductivity,cyclic voltammograms and the safe charge injection were measured to learn the physicochemical properties of composites.Nonspecific protein adsorption on the surface of PDMS after coating by the hydrogels were characterized as well.(2)PC 12 cells were used as a neural model for cytologic evaluation.Cytocompatibility of different materials was investigated by cell proliferation and synapsis differentiation on PPU/PVA hydrogel coated PDMS,PU hydrogel coated PDMS,uncoated PDMS and tissue culture plate.(3)PPU/PVA hydrogel coated PDMS electrodes,PU hydrogel coated PDMS electrodes,uncoated PDMS electrodes were preprared and implanted into the brain of rats for 6 weeks.Neural tissue around the electrodes was dealt with immunohistochemical staining.Evaluation of the PPU/PVA hydrogels,PU hydrogels for astrocyte aggregation and neuron apoptosis was obtained from Immunohistochemical intensity of the neuronal specific marker NeuN and Astrocyte specific marker GFAP around the electrodes.Results:(1)Water absorption rate of PPU/PVA hydrogel was 224%and its ionic conductivity was 5.1 mS/cm.After coating by PPU/PVA,iridium oxide electrodes were used in cyclic voltammograms test,the voltammograms showed a slight decrease of redox peak,the cathodic storage charge of electrodes reduced from54.95 mC/cm2 to 48.26 mC/cm2.The safe charge injection of iridium oxide electrodes decreased just 1.0 mC/cm2 after coating by PPU/PVA,from 4.0 mC/cm2to 3.0 mC/cm2,it indicated that PPU/PVA hydrogels had little impact on the electrochemical properties of electrodes.The Protein adsorption tests indicated that the amount of protein adsorption on the PDMS films was reduced by 92%after coating by PPU/PVA.(2)PC12 cells assay exhibited better attachment,more and longer neurites on PPU/PVA coatings than those on PDMS films(P<0.01),and the growth of PC12 cells on PPU/PVA coatings was similar with PU coating PDMS slide(P>0.05).(3)Coated by PPU/PVA hydrogel and PU hydrogel,NeuN immunohistochemical intensity 30?150?m around electrodes was higher than PDMS electrodes without coating(P<0.05).0?45?m around the implanted electrodes,GFAP intensity was lower in PPU/PVA hydrogels coated PDMS eletrodes than that in PDMS eletrodes without coating(P<0.05),while 50?150?m around the electrodes,the two groups showed no difference(P>0.05).GFAP intensity in PU hydrogel coated PDMS Electrodes was lower than PDMS electrodes without coatings within 0?150 ?m(P<0.05).Conclusion:PPU/PVA hydrogels have applicable electrochemical properties for neural electrodes,it can improve cell proliferation and differentiation on PDMS surface,and reduce fibrous capsule as well as neurons apoptosis aroud the PDMS electrodes,so PPU/PVA hydrogel coatings are promising for improving neural electrodes of PDMS substrate.