Electrohydrodynamic Process Research Articles

Immobilization of calcium oxide onto polyacrylonitrile (PAN) fibers as a heterogeneous catalyst for biodiesel production

We describe the design, creation, and usage of a CaO catalyst immobilized onto polymeric mats for environmentally-friendly biodiesel production. The polyacrylonitrile (PAN) fiber mats were prepared by electrohydrodynamic processing (EHD), commonly known as electrospinning or electrospraying, in which immobilized CaO particles were either physically entrapped on the fibers or chemically bound onto the fiber surface by a dopamine linkage. These two catalyst materials were later successfully used in the transesterification of fresh canola oil into biodiesel. Mechanically entrapped CaO particles in the PAN fibers were able to be re-used up to six times in the conversion of triglycerides into biodiesel, while the chemically immobilized catalyst was found impossible to reuse. The use of EHD processing allows us to create an easily separable, reusable catalyst that could be commonly used in transesterification reactions.

Optimization of Quantum Dot Thin Films using Electrohydrodynamic Jet Spraying for Solution-Processed Quantum Dot Light-Emitting Diodes

The electrohydrodynamic (EHD) jet spraying process is a good method for making quantum dot (QD) layers in light-emitting diodes (LEDs). However, controlling the morphology and large-scale fabrication of the QD layers are critical for realizing all-solution-processed QD-LEDs with high performance. Three spraying techniques were used with the EHD jet spraying technique: a big circular film method, a spiral-line method, and a straight-line method. These techniques were used to obtain QD films with good uniformity. The straight-line spray showed the most promise to obtain a uniform QD layer with large area, and QD-LEDs made with this method showed better performance with a low turn-on voltage of 3.0 V, a luminance of 7801 cd/m2, and a maximum current efficiency of 2.93 cd/A.

Dynamic mechanical analysis of novel cosmeceutical facial creams containing nano-encapsulated natural plant and fruit extracts.

Cosmetic industry following the recent trends in the relative market has turned its interest in the formation of cosmeceutical products containing natural bioactive ingredients. Natural extracts may reveal undesirable sensory characteristics due to their composition. Encapsulation and nanotechnology are the most promising methods to overcome these drawbacks, opening up new perspectives for the future of cosmeceutical industry. The purpose of this study was the use of nano-encapsulated plant and fruit extracts to formulate cosmeceutical facial creams with acceptable rheological characteristics. Electrohydrodynamic process was used to encapsulate pomegranate and tea tree oil extracts and incorporate them in facial cosmetic creams. All the formulations including those without additives, were stored at three different temperatures. Subsequently, rheological oscillatory tests (frequency sweep tests) were performed using the dynamic mechanical analysis method in order to evaluate alterations in storage modulus (G'), loss modulus (G''), and complex viscosity (η*). Dynamic mechanical analysis, showed that all formulations are suitable for application in cosmetic industry, while changes due to storage period or the storage temperature were negligible. The addition of the selected extracts' nanofibers to formulate cosmeceutical facial creams, developed products with acceptable rheological characteristics that could be decisive for the cosmetics industry.

A supercritical CO2 assisted electrohydrodynamic process used to produce microparticles and microfibers of a model polymer

An evolution of traditional electrospray and electrospinning is proposed in this work, adding SC−CO2 in the liquid polymeric solution. This new process arrangement allows to overcome some intrinsic limitations of the traditional processes, namely surface tension and viscosity control. The influence of various process parameters was studied. The increase of electric potential difference did not significantly modify the particle size distributions and the fiber size distributions; but, the distributions became sharper as the electric potential difference increased. At low PVP percentages in the solution, electrospray was favored, forming small particles, due to low solution viscosity. The viscosity of the solution increased with PVP concentration: therefore, first large and very large particles were formed; then, the process was no more able to produce jet break-up, microfibers were obtained and the process was converted to electrospinning, producing microfibers with diameters down to about 1.4 μm. Using lower molecular weight PVP, smaller particles (down to 0.35 μm) were produced and the particles/fibers transition occurred at larger polymer percentages. Pressure and PVP percentage played opposite roles in generating the different morphologies; therefore, electrospray and electrospinning assisted by SC−CO2 are like two faces of the same medal: they could be performed using the same apparatus, properly setting the process conditions and polymer concentration.

The key role of straight fluid jet in predicting the drug dissolution from electrospun nanofibers.

In nanopharmaceutics, a robust manipulation of the preparation process and an accurate prediction of the final product size are very important for developing novel nano drug delivery systems. In the present study, for the first time, a process parameter, i.e. the length of the straight fluid jet, L, is correlated with an experimental parameter, i.e. fluid flow rate, F; a nanofiber property, i.e. diameter, D; and the corresponding drug-sustained release profile. Using a mixed solution consisting of 15% (w/v) polyacrylonitrile and 3% (w/v) ketoprofen in acetone and N,N-dimethylformamide (2:8, v:v) as a spinnable working fluid, a series of medicated nanofibers were prepared under variable F and were characterized. The analysis results disclosed the quantitative relationships among different types of parameters. The process parameter L exhibited a better linear relationship with the nanofibers' diameter (D) than the processing parameter F. These results give a hint that process parameters can be exploited as useful tools for accurately predicting and tailoring the resultant nanofibers' D, and in turn their functional performances. The strategy proposed here presents a new approach to investigate the electrohydrodynamic process and manipulate the functions of nanoproducts through process-property-performance relationships.

Electrohydrodynamic Patterning of Polyethersulfone Membranes.

Microstructuring the surface of membranes is recognized as one of the effective strategies to mitigate the fouling phenomenon. Over the years, significant efforts have been undertaken to develop new techniques for altering the membrane surface topography at the micro- and nanoscale. However, all the previously suggested approaches suffer from some serious drawbacks that impede their widespread implementations, including cost, time, and cumbersomeness. In this study, we show that the electrohydrodynamic (EHD) patterning process can be successfully adopted to form surface patterns on polyethersulfone (PES) microfiltration membranes. The linear stability analysis and nonlinear numerical simulation are performed to theoretically predict the size of the created raised columnar structure (often called pillars). In contrast to the conventional EHD patterning process, the developed method works at room temperature and nonsolvent-induced phase separation is used to solidify the formed structures. An array of pillars was formed on the membrane surface, whose height and width were found to be as low as 31 ± 5 and 98 ± 12 μm, respectively. It is demonstrated that fabricating surface-patterned PES membranes does not require sophisticated facilities and precise control of process condition using this simple moldless method.

High-performance low-voltage soft electrothermal actuator with directly printed micro-heater

Soft actuators are widely studied due to their high flexibility and adaptability. In this paper, a soft electrothermal actuator with directly printed microfilament heater was designed, fabricated, and tested. In this soft actuator, a polyimide (PI) film and a polydimethylsiloxane (PDMS) layer were selected as the two structural layers because of their distinct thermal expansion properties. Embedded between these two layers, a metallic microfilament heater that was made of low-melting-point metal alloy (i.e. Bi58/Sn42) was directly printed with custom-designed pattern using an electrohydrodynamic (EHD) printing process. The pattern of the microfilament heater and the thickness of the soft thermoelectric actuator were carefully designed towards the improved actuation capability. When an electric current was applied, the high temperature generated by the resistive heater causes large mismatch in the thermal expansion of the two structural layers, which bent the actuator. The fabricated soft actuator can achieve a maximum bending curvature of 1.0 cm−1 under an extremely low voltage about 3V. The soft actuator has been demonstrated for potential applications in soft robotics as a soft lifter and a soft gripper. At the full capability, the soft lifter provided a maximum actuation force about 3 mN, and was able to fully lift a load that was twice of its own weight. A four-finger soft gripper was designed and fabricated using four soft actuators to mimic humanoid motions and was implemented for pick-and-place operation for delicate objects.

Fabrication of β-carotene loaded glucuronoxylan-based nanostructures through electrohydrodynamic processing

Various concentrations of β-carotene (2.5–20% w/w dry mucilage weight) were loaded within Cydonia oblonga mucilage (COM) which further processed through electrohydrodynamic processing (EHP) to attain BC-Loaded nanostructures of high thermochemical stability. The BC loaded COM systems were characterized in terms of droplet size, rheological properties, surface tension, and electrical conductivity and their subsequent impacts on the morphology and physicochemical attributes of the produced nanostructures were studied. Increasing the β-carotene content, increased the viscosity and droplet size of colloidal systems but diminished their conductivity and surface tension. A transition from monomodal to bimodal size distribution was also observed at higher levels of β-carotene incorporation. In the case of EHP-produced nanostructures, scanning electron microscopy observations revealed a transition from nanoparticle to nanofiber by increasing the BC content from 2.5 to 20%. At lower concentrations of BC (2.5 and 5%) electrospraying was the dominant phenomenon that resulted in producing homogenous nanoparticles while the beaded fibers and nanofiber structures were obtained at 10 and 20% concentrations of BC, respectively. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and encapsulation efficiency of the produced nanostructures revealed successful encapsulation of BC into the COM polymer structure through EHP. The results of these assessments showed that the nano-particles comprising BC had more homogenous structure and higher encapsulated BC compared to the BC-loaded nano-fibers. The results of X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements revealed amorphous structure of the produced nanostructures. Thermogravimetric assessments corroborated the higher thermal stability of BC loaded nanostructures compared with the free BC. These results provided novel information on the ability of COM in encapsulating bioactive agents through electrohydrodynamic processing.

Fabrication of PEDOT: PSS conductive patterns on photo paper substrate through electro-hydrodynamic jet printing process

Conductive polymers such as PEDOT: PSS have gained popularity in sensor fabrication and integration. The objective of current work is to investigate the effects of process parameters on the final quality of conductive patterns fabricated through electro-hydrodynamic (EHD) jet printing. Solutions of different concentration of PEDOT: PSS in ethylene glycol and isopropyl alcohol were prepared for printing purpose. Effects of operating parameters such as voltage, frequency, pressure and printing speed on quality of printing patterns were experimentally investigated. Solution with higher concentration of PEDOT: PSS in ethylene glycol has shown better jetting stability even at higher frequencies and printing speeds. Increasing the frequency at high printing speed reduced the size of pattern width. Similarly, higher pulse voltage in the working envelope also reduced the pattern size. However, increasing the pressure increased the size of width of pattern. A drastic decrease in the pattern width was observed with increase in printing speed. A pattern width of approximately 19.6 μm was produced at 500 Hz of frequency and 2000 mm/min of printing speed, the electrical resistance of which is 1.03 × 106 Ω/mm. Finally, these results were compared with the same concentration of PEDOT: PSS in isopropyl alcohol reported in previous studies.

Electrospraying technique under pressurized carbon dioxide for hollow particle production

Fabrication of polyvinylpyrrolidone (PVP) particles by an electrospraying process under pressurized carbon dioxide (CO2) used as an anti-solvent was studied. The process was carried out at a constant temperature with CO2 pressures ranging from 1 to 6 MPa. A fixed applied voltage (17 kV) was employed to generate electric field. PVP powder dissolved in dichloromethane (DCM) at concentrations of 4, 6, and 8 wt% was used as the starting material. Scanning electron microscopy observations indicated that the electrosprayed PVP particles produced at 1–3 MPa using 8 wt% PVP solutions have spherical morphologies. At a similar concentration, increasing the CO2 pressure up to 6 MPa resulted in particle strings and strings as major products. Interestingly, hollow core particles formed when ethanol was added as a secondary solvent for controlling the evaporation rate of DCM during the electrospraying process under pressurized CO2. The FT–IR spectra revealed that the structural properties of PVP did not change after the electrospraying process. This work demonstrates that electrohydrodynamic processes under pressurized CO2 are likely to be fruitful for the fabrication of organic polymers with hollow cores.

A multiphysics model for analysis of droplet formation in electrohydrodynamic 3D printing process

Electrohydrodynamic (EHD) printing is a novel technology used for fabricating high-resolution part features from a wide range of materials. Due to the multiphysics dynamics and the multiphase nature of the microdroplet formation in the EHD printers, modeling of this phenomenon is complicated. In this paper, the formation of a droplet in an EHD printer—under a pulsed electrical field—is simulated using a new numerical model which couples the fluid flow, the electric field distribution and the movement of the electric charges under dynamic and transient conditions. The level-set method is applied to the entire multiphysics domain in order to study the formation of the droplet. The presented model is verified by comparing to the existing experimental results in the literature. In order to find the effective parameters with significant impact, at 95% confidence level, a sensitivity analysis of the process parameters is carried out based on the Plackett-Burman design of experiment approach. It is found that the voltage, the permittivity of ink, the nozzle height above substrate, the density and the conductivity of ink are the most effective parameters.

Influences of electrohydrodynamic time and voltage on extraction of phenolic compounds from orange pomace

Orange pomace, a byproduct of orange juice production, is an important source of phenolic compounds. In this study, the effect of Electrohydrodynamic time (at four levels of 2, 10, 20 and 30 min) and EHD voltage (at four levels of 0, 14, 18 and 22 kV) on the total phenolic compounds (TPC), antioxidant activity (AA), and extraction efficiency (EE) of the extracts from orange pomace powder (OPP) was investigated using Electrohydrodynamic (EHD) process. The results showed that the optimal EHD treatment had the extraction time of 10 min and the voltage level of 18 kV. Under this condition, the TPC, AA, and EE of the extracts were 617.76 ± 6.15 mg/L, 91.97 ± 0.43%, and 64.00 ± 0.00%, respectively. Scanning Electron Microscopy (SEM) pictures illustrated considerable interspaces and pores in the remaining OPP after EHD extraction treatments, compared to the control treatment without EHD process. Moreover, Fourier Transform Infrared (FTIR) spectroscopy of the extracts did not show any destruction of the functional groups of the extracts during EHD process. Therefore, EHD treatment could be an effective method for extraction of natural compounds such as phenolic compounds.

Effect of Process Parameters on Organic Micro Patterns Fabricated on a Flexible Substrate Using the Near-Field Electrohydrodynamic Direct-Writing Method.

A micro pattern is a key component of various functional devices. In the present study, using the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) mixed material as the direct-writing solution and photographic paper as the flexible insulating substrate, the organic micro patterns of various shapes, such as the curve of the second-order self-similar structure, the helical curve, and the wave curve, were fabricated on the flexible insulating substrate by using the near-field electrohydrodynamic direct-writing method. The effects of process parameters, such as the applied voltage, direct-writing height, flow rate of the injection system, and moving velocity of the substrate, on the width and the conductivity of the organic micro patterns were studied in the near-field electrohydrodynamic direct-writing process. The results show that the width of an organic micro pattern increases with the increase of the applied voltage of the high-voltage power supplier and the flow rate of the injection system under the condition where the three other process parameters remained constant, respectively, while the width of an organic micro pattern decreases with the increase of the direct-writing height and the moving velocity of the flexible substrate, respectively. The fabricated organic microcircuit patterns of the natural drying in air at room temperature were tested by a thin film thermoelectric tester at a detection temperature. The results show that the conductivity of a fabricated organic micro pattern decreases with the increase of the electric field intensity, while the effect of moving velocity and the flow rate on the conductivity is small under the condition where the three other process parameters remained constant.

Engineered multifunctional biodegradable hybrid microparticles for paclitaxel delivery in cancer therapy

Ovarian cancer is one of the most lethal gynecologic malignancies due to its rapid proliferation, frequent acquisition of chemoresistance, and widespread metastasis within the peritoneal cavity. Intraperitoneal (IP) chemotherapy has demonstrated significant anti-cancer potential but its broad clinical application is hindered by several drug delivery limitations. Herein, we engineer paclitaxel (PTX) laden hybrid microparticles (PTX-Hyb-MPs) for improved delivery of chemotherapy in ovarian cancer. The PTX-Hyb-MPs are comprised of a lipid-coated shell of poly (lactic acid-co-glycolic acid) (PLGA) encapsulating hydrophobic PTX. A co-axial electrohydrodynamic (CEH) process is used for one-step and scalable production of the PTX-Hyb-MP agent with controlled particles size, uniform size distribution, tunable thickness, and high encapsulation rate (92.17 ± 6.9%). The multi-layered structure of the PTX-Hyb-MPs is verified by transmission electron microscopy and confocal fluorescence microscopy. The effect of lipid coating on the enhancement of particle interactions with cancer cells is studied by flow cytometry and confocal fluorescence microscopy. The anti-cancer effect of the PTX-Hyb-MPs is evaluated in SKOV-3 ovarian cancer cells in vitro and a cancer xenograft model in vivo, in comparison with conventional drug delivery methods. Our studies reveal that the PTX-Hyb-MP agent can be potentially used for locoregional treatment of ovarian cancer and other tissue malignancies with sustained drug release, tunable release profiles, enhanced drug uptake, and reduced systemic toxicity.

Electrospinning and electrospraying technologies for food applications.

Electrospinning and electrospraying are versatile techniques for the production of nano- to micro-scale fibers and particles. Over the past 2 decades, significant progresses have been made to advance the fundamental understandings of these electrohydrodynamic processes. Researchers have investigated different polymeric and non-polymeric substrates for producing submicron electrospun/electrosprayed materials of unique morphologies and physicochemical properties. This chapter provides an overview on the basic principles of electrospinning and electrospraying, highlighting the effects of key processing and solution parameters. Electrohydrodynamic phenomena of edible substrates, including polysaccharides (xanthan, alginate, starch, cyclodextrin, pullulan, dextran, modified celluloses, and chitosan), proteins (zein, what gluten, whey protein, soy protein, gelatin, etc.), and phospholipids are reviewed. Selected examples are presented on how ultrafine fibers and particles derived from these substrates are being exploited for food and nutraceutical applications. Finally, the challenges and opportunities of the electrostatic methods are discussed.

Assessing the ex vivo permeation behaviour of functionalised contact lens coatings engineered using an electrohydrodynamic technique

In vitro testing alone is no longer considered sufficient evidence presented solely with respect to drug release and permeation testing. These studies are thought to be more reliable and representative when using tissue or animal models; as opposed to synthetic membranes. The release of anti-glaucoma drug timolol maleate from electrically atomised coatings was assessed here using freshly excised bovine corneal tissue. Electrohydrodynamic processing was utilised to engineer functionalised fibrous polyvinylpyrrolidone-Poly (N-isopropylacrylamide) coatings on the outer side of commercial silicone contact lenses. Benzalkonium chloride, ethylenediaminetetraacetic acid, Brij® 78 and borneol were employed as permeation enhancers to see their effect on ex vivo permeation of timolol maleate through the cornea. Formulations containing permeation enhancers showed a vast improvement with respect to cumulative amount of drug permeating through the cornea as shown by a six fold decrease in lag time compared to enhancer-free formulations. Most drug delivery systems require the drug to pass or permeate through a tissue or biological membrane. This study has shown that to fully appreciate and understand how a novel drug delivery system will behave not only within the device but with the external environment or tissue, it is imperative to have in vitro and ex vivo data in conjunction.

Electrohydrodynamic printing process monitoring by microscopic image identification.

Electrohydrodynamic printing (EHDP) is able to precisely manipulate the position, size, and morphology of micro-/nano-fibers and fabricate high-resolution scaffolds using viscous biopolymer solutions. However, less attention has been paid to the influence of EHDP jet characteristics and key process parameters on deposited fiber patterns. To ensure the printing quality, it is very necessary to establish the relationship between the cone shapes and the stability of scaffold fabrication process. In this work, we used a digital microscopic imaging technique to monitor EHDP cones during printing, with subsequent image processing algorithms to extract related features, and a recognition algorithm to determine the suitability of Taylor cones for EHDP scaffold fabrication. Based on the experimental data, it has been concluded that the images of EHDP cone modes and the extracted features (centroid, jet diameter) are affected by their process parameters such as nozzle-substrate distance, the applied voltage, and stage moving speed. A convolutional neural network is then developed to classify these EHDP cone modes with the consideration of training time consumption and testing accuracy. A control algorithm will be developed to regulate the process parameters at the next stage for effective scaffold fabrication.

Preparation of monodisperse charged droplets via electrohydrodynamic device for the removal of fine dust particles smaller than 10 μm

Electrohydrodynamic (EHD) device is utilized in various applications and could be useful for the suppression of particulate matter in ambient conditions. In this study, we focused on the ejection of charged droplets containing electrolytes in a microdripping mode and with high charge density. Several different electrolytes with different physical and electrical properties were tested for our EHD process in order to produce the charged droplets stably. Results from series images by high-speed camera represented that droplet size and frequency were dependent on the applied voltage and flow rate, and showed different behaviors in various EHD modes such as dripping, microdripping, mixed dripping, and unstable dripping. Consecutive experimental data for charge density showed that 15 wt% KCl solution was proper to obtain highly charged droplets with the size from 50 to 100 μm. For this solution, the suppression of the fine dust particle was tested for the removal of PM10, PM2.5, and PM1 at various applied voltages. The droplet formation in microdripping mode was effective for the removal of smaller dust particles and could be applicable for the air remediation in indoor or domestic environment.

Food-grade gliadin microstructures obtained by electrohydrodynamic processing

This paper presents a comprehensive study on the electrohydrodynamic processing of gliadin to develop food-grade delivery systems with different morphologies. The effects of biopolymer concentration, applied voltage and solution flow-rate on particle morphology, molecular organisation, crystallinity and thermal properties were investigated. Gliadin concentration influenced the apparent viscosity and conductivity of the solutions, giving raise to particle morphologies at 10 wt% gliadin and beaded-free fibers above 25 wt% gliadin. In general, increasing the voltage resulted in smaller average sizes of the obtained structures, while no significant differences in morphology were observed among the tested flow rates. Interestingly, the amide I position in the FTIR reflected changes in protein conformation which could be correlated with the final morphology attained. Moreover, the acetic acid used for solution preparation disrupted the original amino acid chain packing of the gliadin fraction, being the electrospun/electrosprayed samples amorphous. These gliadin-based microparticles and microfibers obtained could serve as food-grade delivery vehicles.

Current characteristics of stable cone–jet in electrohydrodynamic printing process

Electrohydrodynamic printing (EHDP) may produce micro-/nano-patterns for various applications using an external electric field to drive a charged polymer jet. This paper investigates both current characteristics and governing parameters at stable cone–jet mode in EHDP process. Experimental results show that the current increases with increasing applied voltage, flow rate, fluidic conductivity, and even concentration. The convection current Ic dominates the EHDP process of extremely low-conductivity solution by Ic ∝ Q1/2, while the conduction current Io dominates the EHDP process of high-conductivity solution by Io ∝ QV, where Q is the flow rate of solution and V is the applied voltage.