Electrohydrodynamic printing for high resolution patterning of flexible electronics toward industrial applications

Electrohydrodynamic(EHD)printing technique,which deposits micro/nanostructures through high electric force,has recently attracted significant research interest owing to their fascinating characteristics in high resolution(<1μm),wide material applicability(ink viscosity 1–10000 cps),tunable printing modes(electrospray,electrospinning,and EHD jet printing),and compatibility with flexible/wearable applications.Since the laboratory level of the EHD printed electronics'resolution and efficiency is gradually approaching the commercial application level,an urgent need for developing EHD technique from laboratory into industrialization have been put forward.Herein,we first discuss the EHD printing technique,including the ink design,droplet formation,and key technologies for promoting printing efficiency/accuracy.Then we summarize the recent progress of EHD printing in fabrication of displays,organic field-effect transistors(OFETs),transparent electrodes,and sensors and actuators.Finally,a brief summary and the outlook for future research effort are presented.

Electrohydrodynamic 3D printing of orderly carbon/nickel composite network as supercapacitor electrodes

Electrohydrodynamic(EHD)3D printing of ca rbon-based materials in the form of orderly networks can have various applications.In this work,microscale carbon/nickel(C-Ni)composite electrodes with controlled porosity have been utilized in electrochemical energy storage of supercapacitors.Polyacrylonitrile(PAN)was chosen as the basic material for its excellent carbonization performance and EHD printing property.Nickel nitrate(Ni(NO_(3))_(2))was incorporated to form Ni nanoparticles which can improve the conductivity and the capacitance performance of the electrode.Well-aligned PAN-Ni(NO_(3))_(2) composite structures have been fabricated and carbonized as C-Ni electrodes with the typical diameter of 9.2±2.1μm.The porosity of the as-prepared C-Ni electrode can be controlled during the EHD process.Electrochemical results show the C-Ni network electrode has achieved a 2.3 times higher areal specific capacitance and 1.7 times higher mass specific capacitance than those of a spin-coated electrode.As such,this process offers a facile and scalable strategy for the fabrication of orderly carbon-based conductive structures for various applications such as energy storage devices and printable electronics.

Electrohydrodynamic Fabrication of Triple-layered Polycaprolactone Dura Mater Substitute with Antibacterial and Enhanced Osteogenic Capability

In the field of dura mater repair,it is essential to employ artificial substitutes mimicking the multilayered microar-chitecture and multiple functions of native dura mater for effective neurosurgery.However,existing artificial dura mater substitutes commonly cause complications because of mismatched structural and mechanical properties as well as the lack of antibacterial activity or osteogenic capability.In this study,a triple-layered dura mater substi-tute was fabricated by electrohydrodynamic(EHD)jetting techniques,including electrospinning and melt-based EHD printing processes.Highly aligned polycaprolactone(PCL)nanofibers loaded with gentamicin sulfate(GS)were prepared by electrospinning to form the inner layer,which can mimic the aligned collagen fibers of the native dura mater.Random PCL-GS nanofibers were then deposited by electrospinning to form the middle layer.They were intended to enhance the mechanical properties of the fabricated scaffolds.The outer layer involv-ing PCL microfibers doped with nano-hydroxyapatite(nHA)at various angles was printed by the melting-based EHD method,which can enhance osteogenic capability and promote the fusion between the dura mater substi-tute and the skull.The tensile strength of the triple-layered drug-loaded biomimetic dura mater substitute was 22.42±0.89 MPa,and the elongation at break was 36.43%±2.00%.The addition of GS endowed the substitutes with an anti-infection property without influencing their cytocompatibility.Furthermore,the incorporation of nHA promoted the osteogenic differentiation of MC3T3-E1 cells seeded on the triple-layered scaffolds.This work offers a promising strategy to manufacture multilayered dura mater substitutes with the desired antibacterial and enhanced osteogenic capability performance,possibly providing a novel candidate for dural tissue repair.

Nanoparticle assembly enabled by EHD-printed monolayers

Augmenting existing devices and structures at the nanoscale with unique functionalities is an exciting prospect.So is the ability to eventually enable at the nanoscale,a version of rapid prototyping via additive nanomanufacturing.Achieving this requires a step-up in manufacturing for industrial use of these devices through fast,inexpensive prototyping with nanoscale precision.In this paper,we combine two very promising techniques—self-assembly and printing—to achieve additively nanomanufactured structures.We start by showing that monolayers can drive the assembly of nanoparticles into pre-defined patterns with single-particle resolution;then crucially we demonstrate for the first time that molecular monolayers can be printed using electrohydrodynamic(EHD)-jet printing.The functionality and resolution of such printed monolayers then drives the self-assembly of nanoparticles,demonstrating the integration of EHD with self-assembly.This shows that such process combinations can lead towards more integrated process flows in nanomanufacturing.Furthermore,in-process metrology is a key requirement for any large-scale nanomanufacturing,and we show that Dual-Harmonic Kelvin Probe Microscopy provides a robust metrology technique to characterising these patterned structures through the convolution of geometrical and environmental constraints.These represent a first step toward combining different additive nanomanufacturing techniques and metrology techniques that could in future provide additively nanomanufactured devices and structures.