Study On High-Performance Piezoelectric Fibers And Their Applications In Biosensing And Regulation

As a flexible,low-frequency response electromechanical coupling material,organic piezoelectric materials offer broad application prospects for human-machine interfaces,energy harvesters,electronic skin,and nerve/cell/tissue stimulators and biosensors.While polyvinylidene difluoride(PVDF)has been a well-known and broadly used piezoelectric polymer material over years,their weak piezoelectric effect and low ferroelectric stability largely limited their applications as an effective electromechanical coupler for sensing,actuation,and energy harvesting.Recognizing these critical issues,this work is based on electro spinning technology,by combining sheath-gas-assisted technology,self-assembly and in-situ polymerization technology to prepare a series of high-performance piezoelectric nanofibers.This work presented a practical strategy to address the long-standing stability issue in piezoelectric polymers fabrication and opened a door toward the development of flexible electromechanical coupling devices for many biomedical applications.The main research contents and results of this paper are as follows:(1)Sheath-gas-assisted preparation of high-performance piezoelectric nanofibers for biomechanical energy harvestingThe inhomogeneous molecular structure and inherent flexible of organic piezoelectric materials make the improvement on piezoelectric performancebecome an extreme challenge.In this work,a novel sheath-gas-assisted electrospinning method was designed to induce rapid recrystallization by a stretching effect on the PVDF molecular chains.The β-phase content in PVDF/gas nanofibers is as high as 83%,which is about 60%more than PVDF nanofibers.The electromechanical coupling device based on PVDF/gas nanofibers showed outstanding sensitivity and can convert low-frequency femoral and carotid pulsations into a considerable output voltage of 0.4-0.6 V cm-2.The high-performance piezoelectric nanofibers may serve as a powerful tool for developing future flexible force-sensitive microelectric devices and generators for applications in bioelectronics and biomedicine.(2)High-performance piezoelectric nanofibers for real-time micropressure monitoring of cardiovascular wallsImplantable pressure biosensors show great potential for assessment and diagnostics of pressure-related diseases.This work presents a structural design strategy to fabricate core/shell PVDF/hydroxylamine hydrochloride(HHE)organic piezoelectric nanofibers with well-controlled and self-orientated nanocrystals in the spatial uniaxial orientation ofβ-phase-rich fibers,which significantly enhance piezoelectric performance,fatigue resistance,stability,and biocompatibility.Then PVDF/HHE nanofibers soft sensors are developed and used to monitor subtle pressure changes in vivo.Upon implanting into pig,PVDF/HHE nanofiber sensors demonstrate their ultrahigh detecting sensitivity and accuracy to capture micropressure changes at the outside of cardiovascular walls,and output piezoelectric signals can real-time and synchronously reflect and distinguish changes of cardiovascular elasticity and occurrence of atrioventricular heart-block and formation of thrombus.Such biological information can provide a diagnostic basis for early assessment and diagnosis of thrombosis and atherosclerosis,especially for postoperative recrudescence of thrombus deep within the human body.(3)High-performance core/shell piezoelectric nanofiber and its application for biomedical sensorsFabrication of soft piezoelectric nanomaterials is essential for the development of wearable and implantable biomedical devices.However,to achieve high piezoelectric property and long-term stability in biological environment stands a big challenge in this soft functional material development.Here,we report a one-step strategy for fabricating core/shell PVDF/dopamine(DA)nanofibers with a very high β-phase content and self-aligned polarization.The self-assembled core/shell structure is believed essential for the formation and alignment of β-phase PVDF,where strong intermolecular interaction between the-NH2 groups on DA and-CF2 groups on PVDF is responsible for aligning the PVDF chains and promoting β-phase nucleation.As-received PVDF/DA nanofibers exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility.An all-fiber-based soft sensor is fabricated and tested on human skin and in vivo in mice.The devices show a high sensitivity and accuracy for detecting weak physiological mechanical stimulation from diaphragm motions and blood pulsation.This sensing capability offers great diagnostic potential for the early assessment and prevention of cardiovascular diseases and respiratory disorders.(4)Power generation from moisture fluctuations using humidity actuator-driven piezoelectric generatorConverting the chemical energy contained in sweat into electrical energy is of great value for low-power-consumption wearable electronics.This work reported an electromechanical coupling and humidity-actuated two-in-one humidity actuator-driven piezoelectric generator(HAPG)that can yield continuous electric power from fluctuations in the ambient humidity.It is composed of polyvinyl alcohol(PVA)-wrapped highly aligned DA/PVDF shell/core nanofibers(PVA@DA/PVDF).As-received PVA@DA/PVDF nanofibers can exchange water with the ambient humidity to perform expansion and contraction and convert them into electric power.An all-fiber-based portable HAPG is fabricated and tested on human palm skin.The devices show high sensitivity and accuracy for converting the mental sweating-derived continuous moisture fluctuations into electric power.This electric power can be stored in capacitors,which is expected to power micro-and nano-electronic devices or be used in electrotherapy such as electrical stimulation to promote wound healing.Beyond this,the obtained voltage profiles exhibit unique features that can reflect the typical sweat damping oscillation curve features.(5)Cell activity modulation and its specific function maintenance by bio-inspired electromechanical nanogeneratorThis work presents an electromechanical coupling bio-nanogenerator(bio-NG)composed of highly discrete piezoelectric fibers.It can generate surface piezopotential up to millivolts by cell inherent force,and thus provide in situ electrical stimulation for the living cells.Besides,the unique 3D space in the bio-NGs provides an ECM-like growth microenvironment for cells.As a result,when cells were cultured in bio-NGs,the NG-cell interactions in 3D space triggered the opening of ion channels present in the plasma membrane of RGC5 inducing intracellular calcium transients and stimulated the motility of primary hepatocytes to form broad cell aggregates.Besides,it was verified that the 3D cell growth space and NG-interaction can promote cell viability and development,and more importantly,maintain its specific functional expression.This advanced in vitro bio-NGs are expected to fill the gap between the inaccurate 2D systems and the expensive and time-consuming animal models,mimicking the complexity of the ECM and the physiological relevance of an in vivo biological system.More broadly,the in-situ cell-scale stimulation in 3D space can be widely extrapolated to other excitable functional cells,such as glandular or muscle cells,offering a promising strategy for future bioelectronis,where controlled electrical impulses can replace the use of chemical drugs for disease treatment,nerve/tissue repair,and regeneration.