| Poly(vinylidene fluoride)(PVDF)-based ferroelectric polymers own permanent dipole moments,and their spontaneous electric polarization can be changed by externally input energy.They have been applied to a wide variety of energy conversion devices based on electromechanical conversion or pyroelectricity.Flexible bioelectronics have been drawing the attention.Expanding PVDF-based ferroelectric polymers to biosensors,as well as stimulation of neuron or nerve tissue,will bring them new vital energies.Along with the problem of population ageing,retinal degeneration diseases,such as retinitis pigmentosa(RP)and age-related macular degeneration(AMD),severely affect these patients' normal life.Currently,there is no effective medical treatments.Thus,researchers choose to fabricate artificial retina to bypass the damaged photoreceptors,and directly stimulate inner neuron for partially restoration of visual sight.In this thesis,PVDF-based ferroelectric polymers and reduced graphene oxide(RGO)were combined,and then the nanocomposites were fabricated into periodic array with pyramidal sensing units to afford implantable artificial retina.Its photothermoelectric effects were carefully examined.Neuron stimulation and tissue implant were carried out.Detailed contents are listed as follows:1.Due to its excellent photo-thermal effect in the spectrum of near infrared,reduced graphene oxide(RGO)was blended with PVDF-based ferroelectric polymer(FEP)to fabricate nanocomposite films with NIR light response.After the deposition of metal electrodes,the 10×10 sensor array was able to recognize a simulated near infrared image.Photoelectric responses of the RGO/FEP nanocomposite film under the near infrared illumination were collected and vastly improved by means of thermal annealing and electric poling process.After optimization,the nanocomposite film responded quickly to pulsed near infrared laser irradiation with pulse width of 10ms,which was the same time scale as that of nature human retina.To precisely predicate special temperature distribution within the micropatterned RGO/FEP nanocomposite film,finite element analysis was employed for simulation of the temperature change rate,which met well with the experiment results.We also studied the photoelectric responses of RGO/FEP nanocomposites with molybdenum disulfide,polyaniline,lead zirconate titanate ceramics,and so on.In particular,the nanocomposite film of FEP and lead zirconate titanate was highly sensitive to near infrared light and had a very low light detection limit.These outcomes open up a broad road to FEP applications.2.The micropatterned RGO/FEP nanocomposite was prepared by solution casting on a homemade silicon template.The neuron was stained by fluorescent probe of calcium ions.The micropatterned nanocomposite was utilized to stimulate the intimatecontacted neural cells;and apparent fluorescence intensity changes of calcium ion probes was observed by near infrared light.In contrast,red and green light was unable to induce discernable calcium influx.Then,we checked validity of current photosensitive system to identify stylized letter.The micropatterns enabled the artificial retina to accurately stimulate a single cell,presenting the potential to achieve high spatial resolution as the natural retina.3.We then implanted the artificial prosthesis to the retina of a white rabbit and captured visual evoked potentials(VEPs)by light irradiation.The implantation verified biosecurity and long-time stability of this proof-of-concept artificial retina. |
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