Studies On Flexible Polymer Matrix Multifunctional Fibers For Neural Probe

The development of biomedical tools is highly demanded for the exploration of neuroscience,as well as the neuromedical diagnosis and treatment.At present,implantable neural probes are one of the main tools used to study the nervous system.The development of multi-functional flexible neural probes is a powerful tool for brain neuroscience,especially flexible optoelectronic integrated optical fibers with high biocompatibility for optogenetics are still yet to be developed.In addition,optical neural probes combined with advanced imaging technologies(such as multiphoton imaging based on femtosecond lasers)provide a new way to investigate deep living brains.However,few studies have been reported on the combination of multiphoton optical imaging technology and highly biocompatibility optical neural probes.To this end,we here explore the dispersion-controllable focusing fiber(DCFF),which is suitable for the delivering of femtosecond pulses and the optoelectronic integrated flexible fiber(OEF)for optoelectronic operation.The research contents are as follows:(1)Explore the fabrication method of Polydimethylsiloxane(PDMS)optical fiber and its feasibility of biological applications.To achieve total internal reflection in PDMS fiber,the refractive index and light transmission spectrum of PDMS films fabricated with different ratios were measured,and the ratio between the fiber core and cladding materials was determined.To fabricate a PDMS fiber with a complete optical waveguide structure,we explored the fabrication method of the PDMS fiber and determined the fabrication parameters of the PDMS fiber with different core diameters.The fabricated fiber has good optical properties: the transmission loss is about 2-2.5 d B/cm,and the deformed transmission transmittance is about0.72(bend at 180° with 1 mm radius of curvature).The fiber has good mechanical properties:the elongation rate of a fiber with 360 ?m diameter is about 182%;the Young's modulus is only1.46 MPa;the bending stiffness,stress and storage modulus in the frequency range of mammalian movement,respiration and heartbeat(0.01-10 Hz)are 0.35 N/m,0.016 MPa and0.096 GPa,respectively.These experimental results indicate that it is suitable for optical applications in vivo.(2)Design,fabrication and characterization of dispersion-controllable focusing flexible fiber.By fabricating fiber cores with varying diameters along the longitudinal axis,and adjusting the range and period of diameter variation based on the fabrication parameters,a dispersion curve with oscillation landscapes was obtained.The positive and negative dispersion can compensate each other to minimize the net dispersion and thus it reduces the temporal broadening of near-infrared femtosecond pulses.In addition,the endface of fiber was fabricated with a microlens and the curvature of the microlens can be adjusted by changing the fabrication parameters,such that the fiber has a good ability of light focusing,which is especially useful for femtosecond laser scanning/focusing and fluorescence excitation.The fabricated fiber has good optical properties: the transmission loss is about 0.1-0.2 d B/cm(diameter range is 67-110?m),and the deformed transmission transmittance is about 0.61(bend at 180° with 1 mm radius of curvature).The fiber has good mechanical properties: the elongation rate of a fiber(diameter range is 400-660 ?m)is about 148%;Young's modulus is only 1.63 MPa;the bending stiffness,stress and storage modulus in the frequency range of 0.01-10 Hz are 0.53 N/m,0.008 MPa and0.031 GPa,respectively.These experimental results indicate that the fiber has the application potential of being used as an optical neural probe for multiphoton imaging of neurons in vivo.(3)Design,fabrication and characterization of optoelectronic integrated flexible fiber.The fiber was fabricated based on the method of coating deposition.The fabricated fiber has good optical properties: the transmission loss is about 2-3 d B/cm,and the deformed transmission transmittance is about 0.57(bend at 180° with 1 mm radius of curvature).The fiber has good electrical performance: electrochemical impedance(1 k Hz)<10 k?,and the dual-electrode fiber has electrical stimulation capabilities.The impedance is only 20.0 ? 0.9 k?,and good electrical stimulation performance is maintained(tensile strain,80%,).The fiber has good mechanical properties: the elongation rate of fiber with 590 ?m diameter is about 183%:Young's modulus is only 1.36 MPa;the bending stiffness,stress and storage modulus in the frequency range of 0.01-10 Hz are 2.22 N/m,0.03 MPa and 0.107 GPa,respectively.These experimental results indicate that the fiber can be used as an optical electrode for in vivo optogenetics,electrical stimulation,and electrophysiological recording application potential.