Coaxial electrohydrodynamic printing of core–shell microfibrous scaffolds with layer-specific growth factors release for enthesis regeneration

The rotator cuff tear has emerged as a significant global health concern.However,existing therapies fail to fully restore the intricate bone-to-tendon gradients,resulting in compromised biomechanical functionalities of the reconstructed enthesis tissues.Herein,a tri-layered core–shell microfibrous scaffold with layer-specific growth factors(GFs)release is developed using coaxial electrohydrodynamic(EHD)printing for in situ cell recruitment and differentiation to facilitate gradient enthesis tissue repair.Stromal cell-derived factor-1(SDF-1)is loaded in the shell,while basic fibroblast GF,transforming GF-beta,and bone morphogenetic protein-2 are loaded in the core of the EHD-printed microfibrous scaffolds in a layer-specific manner.Correspondingly,the tri-layered microfibrous scaffolds have a core–shell fiber size of(25.7±5.1)μm,with a pore size sequentially increasing from(81.5±4.6)μm to(173.3±6.9)μm,and to(388.9±6.9μm)for the tenogenic,chondrogenic,and osteogenic instructive layers.A rapid release of embedded GFs is observed within the first 2 d,followed by a faster release of SDF-1 and a slightly slower release of differentiation GFs for approximately four weeks.The coaxial EHD-printed microfibrous scaffolds significantly promote stem cell recruitment and direct their differentiation toward tenocyte,chondrocyte,and osteocyte phenotypes in vitro.When implanted in vivo,the tri-layered core–shell microfibrous scaffolds rapidly restored the biomechanical functions and promoted enthesis tissue regeneration with native-like bone-to-tendon gradients.Our findings suggest that the microfibrous scaffolds with layer-specific GFs release may offer a promising clinical solution for enthesis regeneration.

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.

Pulsed electrohydrodynamic printing of conductive silver patterns on demand

Pulsed electrohydrodynamic printing （EHDP） is used to fabricate conductive silver patterns with micrometer resolution. The silver ink pendant experiences swelling, pulsation, and ejection under an applied pulse voltage of 20 Hz. The droplet deposi- tion frequency is equal to the applied voltage frequency so that the EHDP can deposit silver ink on demand. A low applied voltage favors uniform and non-scattering silver patterns while a high applied voltage results in ink scattering. Discrete drop- lets with 45-55 gm in diameter and continuous tracks with 60 gm in width are generated by using a ll0-i.tm-cailber nozzle. The feature size of deposited patterns is about half of the nozzle caliber, and a finer resolution can be achieved with the intro- duction of smaller nozzle calibers. Furthermore, the appropriate curing condition is investigated for sufficient combustion of ink solvent. The minimum resistivity of 3.3 gf~ cm is demonstrated for a continuous track cured at 200~C for 10 min. Eventu- ally, several passive electrical components, such as coated resistors, interdigitated capacitors （6 pF）, and spiral inductors （0.6 gH）, are successfully fabricated.

High-resolution flexible electronic devices by electrohydrodynamic jet printing:From materials toward applications

High-resolution flexible electronic devices are widely used in the fields of soft robotics,smart human-machine interaction,and intelligent e-healthcare monitoring due to their mechanical flexibility,ductility,and compactness.The electrohydrodynamic jet printing(e-jet printing)technique is used for constructing high-resolution and cross-scale flexible electronic devices such as field-effect transistors(FETs),flexible sensors,and flexible displays.As a result,researchers are paying close attention to e-jet printing flexible electronic devices.In this review,we focused on the latest advancements in high-resolution flexible electronics made by e-jet printing technology,including various materials used in e-jet printing inks,the process control of e-jet printing,and their applications.First,we summarized various functional ink materials available for e-jet printing,including organic,inorganic,and hybrid materials.Then,the interface controlling the progress of e-jet printing was discussed in detail,including the physical and chemical properties of the functional ink,the interfacial wettability between the ink and substrate,and the microdroplet injection behavior in a high-voltage field.Additionally,various applications of e-jet printing in the fields of flexible electrodes,FETs,flexible sensors,and flexible displays were demonstrated.Finally,the future problems and potential associated with the development of next generation e-jet printing technology for flexible electronic devices were also 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.