Electroosmotic Micropump Research Articles

A wearable, rapidly manufacturable, stability-enhancing microneedle patch for closed-loop diabetes management

The development of a wearable, easy-to-fabricate, and stable intelligent minisystem is highly desired for the closed-loop management of diabetes. Conventional systems always suffer from large size, high cost, low stability, or complex fabrication. Here, we show for the first time a wearable, rapidly manufacturable, stability-enhancing microneedle patch for diabetes management. The patch consists of a graphene composite ink-printed sensor on hollow microneedles, a polyethylene glycol (PEG)-functionalized electroosmotic micropump integrated with the microneedles, and a printed circuit board for precise and intelligent control of the sensor and pump to detect interstitial glucose and deliver insulin through the hollow channels. Via synthesizing and printing the graphene composite ink, the sensor fabrication process is fast and the sensing electrodes are stable. The PEG functionalization enables the micropump a significantly higher stability in delivering insulin, extending its lifetime from days to weeks. The patch successfully demonstrated excellent blood glucose control in diabetic rats. This work may introduce a new paradigm for building new closed-loop systems and shows great promise for widespread use in patients with diabetes.

A numerical study on applying ion concentration polarization in micropump design

This work focuses on applying the phenomenon of ion concentration polarization to design and investigate a micropump model that is a kind of electroosmotic micropump. Numerical study is conducted for ion concentration polarization in the manner that generates electro-osmosis flow and pumping effect. The formation of the extended space charge layer and the actions of the electric field upon this layer is applied to generate electro-osmosis flow to drive flow in the system. It is clarified that pumping effect can be enhanced by improving the geometry configurations. Multiple simulations are conducted to obtain an optimal micropump design.

A liquid metal based, integrated parallel electroosmotic micropump cluster drive system.

The application of liquid metal in a microfluidic system enables the fabrication of highly integrated on-chip electroosmotic micropumps (EOPs). In this work, a low-voltage driveable integrated parallel EOP cluster drive system is proposed. This system consists of two layers, a branch-channel layer and a trunk-channel layer. The lower branch-channel layer contains separate parallel pumping channels and a pair of comb liquid metal electrodes. The separated branch channels are connected together through the trunk channels in the upper layer. With this structural arrangement, the parallel micropumps form an integrated micropump cluster for larger pumping capacity. The distance between the pumping channel and the electrode next to it is controlled to 20 μm. To guide the pump design, parametric studies are performed and fully discussed. According to the experimental results, the micropump cluster can be driven at a low voltage of 0.5 V, and the flow rate reaches 274 nL min-1 at 5 V. In addition, the paper finally proposes an electrode protection strategy and an integrated pump-valve drive system which is expected to solve the shortcoming of electroosmotic pumps in terms of long-time storage and driving.

Three-dimensional AC electroosmotic micropump with high power density

This paper presents a novel three-dimensional alternating current electroosmosis (ACEO) micropump with high power density. ACEO is a phenomenon to generate a flow of a liquid such as water by applying an AC voltage to the liquid. Using a specific configuration, a net flow due to ACEO becomes unidirectional and an ACEO micropump can be constructed. Many ACEO micropumps have been proposed; however, most of them are of the planar type, and their output power per device volume is not sufficiently high for applications such as micro fluid power sources for micro total analysis systems, lab-on-a-chips, biomedical microelectromechanical systems (bio-MEMSs), soft microactuators, and soft microrobots. To achieve a higher output power density, in this study, we proposed an ACEO micropump using an array of plate-cylinder electrodes, which is called PC-ACEO-MP. To induce unidirectional flow efficiently, a square pole-slit electrodes ACEO micropump called SS-ACEO-MP has been proposed using asymmetrical pillar-shaped electrodes. PC-ACEO-MP is an extension of SS-ACEO-MP with a three-dimensional structure. First, the finite element method simulations were performed and the results showed that PC-ACEO-MP has the potential to realize high output power with a 1 cm3 effective pump volume using large numbers of plate-cylinder electrodes connected in parallel and in series. Second, a fabrication method using MEMS fabrication process, including electroplating, was proposed and developed for a micro-holed electrode plate that forms parallel cylinder electrodes. The validity of the proposed process was confirmed by fabricating large models and micro-models of the micro-holed electrode plate. The diameter and number of microholes were 10 μm and 36 100, respectively, for the large models and 3 μm and 65 500, respectively, for the micro models. Finally, PC-ACEO-MPs were constructed and their promising pumping characteristics were clarified through experiments using deionized water. The estimated power density was approximately 400 times higher than that of the former high output power ACEO micropump.

Film-Shaped Self-Powered Electro-Osmotic Micropump Array.

This paper reports a new concept of a film-shaped micropump array for biomedical perfusion. The detailed concept, design, fabrication process, and performance evaluation using prototypes are described. In this micropump array, an open circuit potential (OCP) is generated by a planar biofuel cell (BFC), which in turn generates electro-osmotic flows (EOFs) in multiple through-holes arranged perpendicular to the micropump plane. The micropump array is thin and wireless, so it can be cut like postage stamps, easily installed in any small location, and can act as a planar micropump in solutions containing the biofuels glucose and oxygen. Perfusion at local sites are difficult with conventional techniques using multiple separate components such as micropumps and energy sources. This micropump array is expected to be applied to the perfusion of biological fluids in small locations near or inside cultured cells, cultured tissues, living organisms, and so on.

Precision enhanced alignment bonding technique with sacrificial strategy.

This work proposes an "N2-1" sacrificial strategy to help to improve the accuracy of the bonding technique from the existing level. The target micropattern is copied N2 times, and (N2-1) of them are sacrificed to obtain the most accurate alignment. Meanwhile, a method for manufacturing auxiliary solid alignment lines on transparent materials is proposed to visualize auxiliary marks and facilitate the alignment. Though the principle and procedure of alignment are straightforward, the alignment accuracy substantially improved compared to the original method. With this technique, we have successfully fabricated a high-precision 3D electroosmotic micropump just using a conventional desktop aligner. Because of the high precision during the alignment, the flow velocity is up to 435.62 μm/s at a driven voltage of 40 V, which far exceeds the previous similar reports. Thus, we believe that it has great potential for high precision microfluidic device fabrications.

Connected Droplet Shape Analysis for Nanoflow Quantification in Thin Electroosmotic Micropumps and a Tunable Convex Lens Application

Thin electroosmotic flow (EOF) micropumps can generate flow in confined spaces such as lab-on-a-chip microsystems and implantable drug delivery devices. However, status quo methods for quantifying flow and other important parameters in EOF micropumps depend on microfluidic interconnects or fluorescent particle tracking: methods that can be complex and error-prone. Here, we present a novel connected droplet shape analysis (CDSA) technique that simplifies flow rate and zeta potential quantification in thin EOF micropumps. We also show that a pair of droplets connected by an EOF pump can function as a tunable convex lens system (TCLS). We developed a biocompatible and all polymer EOF micropump with an SU-8 substrate and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes. We microdrilled a channel through the electrode/SU-8/electrode layers to realize a monolithic EOF micropump. Then, we deposited a pinned droplet on each end of the microchannel so that it connected them. By controlling the EOF between the droplets and measuring the corresponding change in their shape, we quantified the nanoliter EOF rate and zeta potential at the interface of SU-8 with two liquids (deionized water and a l-glutamate neurotransmitter solution). When the droplet pair and pump were used as a TCLS, CDSA successfully predicted how the focal length would change when the pump drove fluid from one droplet to another. In summary, CDSA is a simple low-cost technique for EOF rate and zeta potential measurement, and a pair of droplets connected by an EOF micropump can function as a TCLS without any moving parts.

Texture-structure-based liquid metal filling for blind-end microchannels and its application on multi-layer chips.

This research work reports a novel method to achieve fast liquid metal (LM) injection in blind-end microchannels which is especially suitable for multi-layer microfluidic chips. This method is based on a texture-like surface bonding technology. The texture-like surface is fabricated on a polydimethylsiloxane (PDMS) slab with standard soft-lithography technology and bonded with another PDMS slab with microelectrode patterns on it. When injected with LM, the texture-like structure can prevent the LM from entering but allows the air inside to be released during the injection to achieve perfect blind-end complex LM electrodes. The experimental results show that it can achieve fast and perfect LM injection in the blind-end pattern and can also prevent the large area of the flat chamber from collapsing during bonding. We also parametrically studied the texture structure's size for bonding strength between the texture structure and the blank PDMS surface. In addition, we integrate three layers of blind-end complex liquid metal patterns into one multi-layer chip using this technology and later use this structure to realize series connection of two LM-based electroosmotic micropumps (EOP). Compared with the conventional LM-based EOP, the structure of the EOP chip was greatly simplified and resulted in a higher level of integration.

Topologically optimized electrodes for electroosmotic actuation

Electroosmosis is one of the most used actuation mechanisms for the microfluidics in the current active lab-on-chip devices. It is generated on the induced charged microchannel walls in contact with an electrolyte solution. Electrode distribution plays the key role on providing the external electric field for electroosmosis, and determines the performance of electroosmotic microfluidics. Therefore, this paper proposes a topology optimization approach for the electrodes of electroosmotic microfluidics, where the electrode layout on the microchannel wall can be determined to achieve designer desired microfluidic performance. This topology optimization is carried out by implementing the interpolation of electric insulation and electric potential on the specified walls of microchannels. To demonstrate the capability of this approach, one typical electroosmotic device, i.e., electroosmotic micropump, is modeled with several electrode layouts derived. And this approach permits potential applications in chemicals and biochemistry due to its outstanding capability on determining the performance of electrokinetic microfluidics.

Effects of 3D electrodes arrangement in a novel AC electroosmotic micropump: Numerical modeling and experimental validation.

To date, a comprehensive systematic optimization framework, capable of accurately predicting an efficient electrode geometry, is not available. Here, different geometries, including 3D step electrodes, have been designed in order to fabricate AC electroosmosis micropumps. It is essential to optimize both geometrical parameters of electrode, such as width and height of steps on each base electrode and their location in one pair, the size of each base electrode (symmetric or asymmetric), the gap of electrode pairs, and nongeometrical parameters such as fluid flow in a channel and electrical characteristics (e.g., frequency and voltage). The governing equations comprising of electric domain and fluid domain have been coupled using finite element method. The developed model was employed to investigate the effect of electrode geometric parameters on electroosmotic slip velocity and its subsequent effect on pressure and flow rate. Numerical simulation indicates that the optimal performance can be achieved using a design with varying step height and displacement, at a given voltage (2.5V) and frequency (1kHz). Finally, in order to validate the numerical simulation, the optimal microchip was fabricated using a combination of photolithography, electroplating, and a polydimethylsiloxane microchannel. Our results indicate that our micropump is capable of generating a pressure, velocity, and flow rate of 74.2Pa, 1.76mm/s, and 14.8µl/min, respectively. This result reveals that our proposed geometry outperforms the state-of-the-art micropumps previously reported in the literature by improving the fluid velocity by 32%, with 80% less electrodes per unit length, and whereas the channel length is ∼80% shorter.

Development of a microfluidic electroosmosis pump on a chip for steady and continuous fluid delivery

Infusion therapy is the most common form of therapy used in health care. However, the existing infusion devices show higher flow discrepancies as flow rates decrease to a few nLmin-1. As a result, dosing errors can contribute to the morbidity and mortality of patients. In thescope of project 18HLT08 MeDD II- Metrology for drugdelivery, this investigation aims at the development of a silicon microchip flow pump capable of steadily and continuously dispense very low flow rates of a few nLmin-1. The fabrication methodologies explored here use a combination of typical cleanroom micro/nanofabrication techniques and off-the-shelf equipment. Preliminary tests show flow rates as low as 45nLmin-1 can be obtained in this microfluidic electroosmotic pump. The experimental flow rates are in good agreement with results predicted bymultiphysics simulation, with less than 8% deviation ratio. This cost effective electroosmotic micropump has the potential to act as a steady and continuous drug delivery system to neonatal patients as well as to organs on chip (OoC), determining the stability of the shear stress imposed on the cells or the right cell culture medium conditions.

Impact of bio-mimetic cilia and symmetry breaking wave on double-diffusive radiated magneto Cu-Al2O3/bloodstream in an electroosmotic pump under momentum-thermal slip constraint

Transport of drug/hybrid materials through microfluidic channels requires efficient flow capability, effective mixing, and manipulation. To address this subject, a thermal analysis of double-diffusive stream of hybrid-type radiated bloodstream is considered through an elastic electroosmotic micropump in the presence of a magnetic field. Bio-mimetic cilia are embedded inside the pump surface having momentum-thermal slip effects. The inserted cilia strike and a constant phase difference between the beats of adjacent cilia generate a set of symmetry-breaking metachronal waves along the pump surface. The deemed mathematical model is simplified under the Debye–Hückel linearization and lubrication approach and is solved numerically. The analysis shows that the wall asymmetry and the apt cilia length strengthen the fluid stream and ensure active mixing distributed across significant distances. The radiated blood, the thin EDL, and extended cilia may be regarded as key factors in the cooling process. The entropy formation inside the micropump can be curtailed with the provision of an adequate amount of activation energy and the consideration of velocity-thermal slip effects on the ciliated surface. The intended model may deliver a deep perception of the thermal design of a futuristic drug delivery pump for efficient flow, adequate mixing, and least entropy generation.

A Microtube-Based Wearable Closed-Loop Minisystem for Diabetes Management.

Diabetes is a chronic metabolic disease with a high blood glucose level, leading to both seriously acute and chronic complications. The closed-loop system is an ideal system for diabetes management. However, the large size and high cost of the commercial systems restrict their widespread uses. Here, we present for the first time a microtube-based wearable closed-loop minisystem for diabetes management. The closed-loop minisystem includes a biosensing device, an electroosmotic micropump, and a printed circuit board (PCB) with an algorithm. The microtube-based sensing device coated on the outer surface of the microtube is inserted into subcutaneous tissue for detecting interstitial glucose; the current signal for sensing glucose is processed by the PCB to power the electroosmotic micropump intelligently for the delivery of insulin into the subcutaneous tissue via the microtube channel. The closed-loop minisystem worn on a diabetic SD rat can successfully maintain its blood glucose level within a safe level. It is expected that this new closed-loop paradigm could open up new prospects for clinical diabetes management.

Regulating the aggregation of colloidal particles in an electro-osmotic micropump.

Unrestricted particle transport through microfluidic channels is of paramount importance to a wide range of applications, including lab-on-a-chip devices. In this article, we study via video microscopy the electro-osmotic aggregation of colloidal particles at the opening of a micrometer-sized silica channel in the presence of a salt gradient. Particle aggregation eventually leads to clogging of the channel, which may be undone by a time-adjusted reversal of the applied electric potential. We numerically model our system via the Stokes-Poisson-Nernst-Planck equations in a geometry that approximates the real sample. This allows us to identify the transport processes induced by the electric field and salt gradient and to provide evidence that a balance thereof leads to aggregation. We further demonstrate experimentally that a net flow of colloids through the channel may be achieved by applying a square-waveform electric potential with an appropriately tuned duty cycle. Our results serve to guide the design of microfluidic and nanofluidic pumps that allow for controlled particle transport and provide new insights for anti-fouling in ultra-filtration.

On-Chip CMOS-MEMS-Based Electroosmotic Flow Micropump Integrated With High-Voltage Generator

The rapid development of microfluidic technology has increased the demand for the integration of driving circuits in the microfluidic devices. We have proposed a novel on-chip electroosmotic (EOF) micropump integrated with a high-voltage (HV) generator. The HV (49.8 V) generator is based on a Dickson charge pump, which is fabricated on a silicon-on-insulator (SOI) substrate by the standard CMOS process, and the isolation is achieved by MEMS post-processed deep trench isolation. The size of the 49.8 V generator is $425\times 353\,\,\mu \,\,\text{m}^{2}$ . The HV required for the successful operation of the micropump was generated by the integrated driving circuit with a low-voltage power supply. The maximum flow velocity and flow rate of the proposed EOF micropump were measured as 137 $\mu $ m/s and 167 nL/min, respectively when it was driven by the integrated 49.8 V generator. The efficiency of the micropump is demonstrated by comparing it with the previously reported micropumps. The proposed integration technique is reliable and effective, and potentially boosts the practical applications of lab-on-chip devices. [2019-0206]

Optimization and parametric study of AC electroosmotic micropumping by response surface method

Alternative current electroosmotic micropumps (ACEO) have gained a great interest in microfluidics research due to their low operating potential. In this paper, a parametric study is performed on various geometrical parameters of an ACEO micropump design. The problem is modeled and solved numerically using COMSOL Multiphysics. This micropump relies on the grouping of a periodic electrode array in terms of the applied voltage to create asymmetries in the electrode configuration. The pumping velocity is obtained and investigated for various geometry designs. In addition, the optimal parameters are obtained by employing the response surface methodology (RSM). The RSM could predict the effects of different factors affecting the performance of the system and their interactions. The most important parameters affecting the pumping velocity are identified. It is shown that the pumping velocity is controllable. Three various micropump designs with different cost to benefit ratios are presented. These designs are different due to their fabrication cost and the pumping velocity.

Unsteady rotating electroosmotic flow with time-fractional Caputo-Fabrizio derivative

As an effective driven mechanism proved experimentally, rotating electroosmotic (EO) micropump has attracted the attentions of many researchers in recent years. In this article, an exact solution of transient rotating EO flow with time-fractional Caputo-Fabrizio derivative through a slit microchannel is obtained by using Laplace transform method. It is interesting to find from computational results that with the increase of fractional parameter α (0<α<1), the time required to attain steady velocity becomes shorter and the oscillating phenomenon becomes more pronounced.

On-Chip High-Voltage Charge Pump With MEMS Post-Processed Standard 5-V CMOS on SOI for Electroosmotic Flow Micropumps

A novel on-chip integrated high-voltage (HV) generator is realized by our unique MEMS post-processing method with the standard CMOS process on a silicon-on-insulator (SOI). Foundry-made charge-pump elements with standard 5-V transistors on an SOI are isolated with deep reactive ion etching and isotropic etching. This method facilitated the successful operation of a HV-requiring MEMS device, the nominal working voltage of which is greater than 50 V, and by using the silicon device, the driving of an electroosmotic flow micropump was demonstrated. The measured output was proportional to the number of pump stages, and it was observed as 95.2 V with 20 stages. The post-processed CMOS-on-SOI can sustain voltages up to 800 V, and various MEMS with very high voltages can be driven using this technology.

Ultra-fast AC electro-osmotic micropump with arrays of asymmetric ring electrode pairs in 3D cylindrical microchannel

AC electro-osmotic (ACEO) micropumps presently involve the planar or nonplanar electrode pair array in the rectangular microchannel. However, this paper presented a theoretical model of an ultra-fast 3D ring ACEO micropump with arrays of asymmetric ring electrode pairs in the cylindrical microchannel. The theory is on the basis of the interaction between the nonuniform electric field and ions of an electric double layer (EDL) on the surface of ring electrodes. Therefore, we first established the equivalent hollow cylinder capacitance of EDL for ring ACEO micropumps. Then, the 3D Poisson-Boltzmann model by solving the electric field and fluidic flow field with the charge conservation and the slip velocity boundary conditions was numerically calculated. For a dilute strong electrolyte solution, the conductivity as a function of the electrolyte concentration can be obtained by the modified Kohlrausch's dilution empirical equation with the molar conductivity. The results revealed that the flow rate of ring ACEO was higher than the planar ACEO, which agreed well with the experiment. The dependences of the time-averaged pumping velocity on the frequency and concentration have similar bell profiles with a maximal value. Moreover, the optimal velocity with proper geometric parameters was obtained at a given frequency, voltage, concentration, and radius. The high-speed ring ACEO micropump will be significant for the experimental studies to further improve the flow rate and be hopeful for applications of microfluidic mixing, particle manipulation, and so on.

Design and Numerical Study of Micropump Based on Induced Electroosmotic Flow

Induced charge electroosmotic flow is a new electric driving mode. Based on the Navier–Stokes equations and the Poisson–Nernst–Planck (PNP) ion transport equations, the finite volume method is adopted to calculate the equations and boundary conditions of the induced charge electroosmotic flow. In this paper, the formula of the induced zeta potential of the polarized solid surface is proposed, and a UDF program suitable for the simulation of the induced charge electroosmotic is prepared according to this theory. At the same time, on the basis of this theory, a cross micropump driven by induced charge electroosmotic flow is designed, and the voltage, electric potential, charge density, and streamline of the induced electroosmotic micropump are obtained. Studies have shown that when the cross-shaped micropump is energized, in the center of the induction electrode near the formation of a dense electric double layer, there exist four symmetrical vortices at the four corners, and they push the solution towards both outlets; it can be found that the average velocity of the solution in the cross-flow microfluidic pump is nonlinear with the applied electric field, which maybe helpful for the practical application of induced electroosmotic flow in the field of micropump.