Electrokinetic microfluidic devices for rapid, low power drug delivery in autonomous microsystems

Electrophoresis of polyelectrolyte-adsorbed soft particle with hydrophobic inner core

This article deals with the electrophoresis of hydrophobic colloids absorbed by a layer of polymers with an exponential distribution of the polymer segments. The functional groups present in the polymer layer further follow the exponential distribution. We made an extensive mathematical study of the electrophoresis of such core-shell structured soft particles considering the combined impact of heterogeneity in polymer segment distribution, ion steric effect, and hydrodynamic slippage of the inner core. The mathematical model is based on the flat-plate formalism and deduced numerical results for electrophoretic mobility are valid for weak to highly charged particles for which the particle size well exceeds the Debye-layer thickness. In addition, we have derived closed form analytical results for electrophoretic mobility of the particle under several electrohydrodynamic limits. We have further illustrated the results for electrophoretic mobility considering a charged and hydrophobic inner core coated with an uncharged polymer layer or a polymer layer that entraps either positive or negatively charged functional groups. The impact of pertinent parameters on the overall electrophoretic motion is further illustrated.

Electrohydrodynamics of diffuse porous colloids

The present article deals with the electrohydrodynamic motion of diffuse porous particles governed by an applied DC electric field. The spatial distribution of monomers as well as the charge distribution across the particle are considered to follow sigmoidal distribution involving decay length. Such a parameter measures the degree of inhomogeneity of the monomer distribution across the particle. The diffuse porous particles resemble several colloidal entities which are often seen in the environment as well as in biological and pharmaceutical industries. Considering the impact of bulk pH and ion steric effects, we modelled the electrohydrodynamics of such porous particulates based on the modified Boltzmann distribution for the spatial distribution of electrolyte ions and the Poisson equation for electric potential as well as the conservation of mass and momentum principles. We adopt regular perturbation analysis with weak field assumption and the perturbed equations are solved numerically to calculate the electrophoretic mobility and neutralization fraction of the particle charge during its motion as well as fluid collection efficiency. We further deduced the closed form relation between the drag force experienced by the charged porous particle and the fluid collection efficiency. In addition to the numerical results, we further derived the closed form analytical results for all the intrinsic parameters indicated above derived within the Debye-Hückel electrostatic framework and homogeneous distribution of monomers within the particle for which the decay length vanishes. The deduced mathematical results as indicated above will be useful to analyze several electrostatic and hydrodynamic features of a wide class of porous particulate and environmental entities.

Implantable microfluidics: methods and applications

Implantable microfluidics involves integrating microfluidic functionalities into implantable devices, such as medical implants or bioelectronic devices, revolutionizing healthcare by enabling personalized and precise diagnostics, targeted drug delivery, and regeneration of targeted tissues or organs. The impact of implantable microfluidics depends heavily on advancements in both methods and applications. Despite significant progress in the past two decades, continuous advancements are still required in fluidic control and manipulation, device miniaturization and integration, biosafety considerations, as well as the development of various application scenarios to address a wide range of healthcare issues. In this review, we discuss advancements in implantable microfluidics, focusing on methods and applications. Regarding methods, we discuss progress made in fluid manipulation, device fabrication, and biosafety considerations in implantable microfluidics. In terms of applications, we review advancements in using implantable microfluidics for drug delivery, diagnostics, tissue engineering, and energy harvesting. The purpose of this review is to expand research ideas for the development of novel implantable microfluidic devices for various healthcare applications.

Manipulation with sound and vibration: A review on the micromanipulation system based on sub-MHz acoustic waves

Manipulation of micro-objects have been playing an essential role in biochemical analysis or clinical diagnostics. Among the diverse technologies for micromanipulation, acoustic methods show the advantages of good biocompatibility, wide tunability, a label-free and contactless manner. Thus, acoustic micromanipulations have been widely exploited in micro-analysis systems. In this article, we reviewed the acoustic micromanipulation systems that were actuated by sub-MHz acoustic waves. In contrast to the high-frequency range, the acoustic microsystems operating at sub-MHz acoustic frequency are more accessible, whose acoustic sources are at low cost and even available from daily acoustic devices (e.g. buzzers, speakers, piezoelectric plates). The broad availability, with the addition of the advantages of acoustic micromanipulation, make sub-MHz microsystems promising for a variety of biomedical applications. Here, we review recent progresses in sub-MHz acoustic micromanipulation technologies, focusing on their applications in biomedical fields. These technologies are based on the basic acoustic phenomenon, such as cavitation, acoustic radiation force, and acoustic streaming. And categorized by their applications, we introduce these systems for mixing, pumping and droplet generation, separation and enrichment, patterning, rotation, propulsion and actuation. The diverse applications of these systems hold great promise for a wide range of enhancements in biomedicines and attract increasing interest for further investigation.

Recent Advances of Microfluidic Platforms for Controlled Drug Delivery in Nanomedicine

Nanomedicine drug delivery systems hold great potential for the therapy of many diseases, especially cancer. However, the controlled drug delivery systems of nanomedicine bring many challenges to clinical practice. These difficulties can be attributed to the high batch-to-batch variations and insufficient production rate of traditional preparation methods, as well as a lack of technology for fast screening of nanoparticulate drug delivery structures with high correlation to in vivo tests. These problems may be addressed through microfluidic technology. Microfluidics, for example, can not only produce nanoparticles in a well-controlled, reproducible, and high-throughput manner, but it can also continuously create three-dimensional environments to mimic physiological and/or pathological processes. This overview gives a top-level view of the microfluidic devices advanced to put together nanoparticulate drug delivery systems, including drug nanosuspensions, polymer nanoparticles, polyplexes, structured nanoparticles and therapeutic nanoparticles. Additionally, highlighting the current advances of microfluidic systems in fabricating the more and more practical fashions of the in vitro milieus for fast screening of nanoparticles was reviewed. Overall, microfluidic technology provides a promising technique to boost the scientific delivery of nanomedicine and nanoparticulate drug delivery systems. Nonetheless, digital microfluidics with droplets and liquid marbles is the answer to the problems of cumbersome external structures, in addition to the rather big pattern volume. As the latest work is best at the proof-of-idea of liquid-marble-primarily based on totally virtual microfluidics, computerized structures for developing liquid marble, and the controlled manipulation of liquid marble, including coalescence and splitting, are areas of interest for bringing this platform toward realistic use.

Mass transfer of a neutral solute in polyelectrolyte grafted soft nanochannel with porous wall

A soft nanochannel involves a soft interface that contains a polyelectrolyte layer (PEL) sandwiched between a rigid surface and a bulk electrolyte solution. Mass transfer of a neutral solute in a combined electroosmotic and pressure driven flow through a polyelectrolyte grafted charged nanochannel with porous wall is presented in this work. Assuming the PEL as fixed charged layer and PEL-electrolyte interface as a semi-penetrable membrane, analytical solutions were obtained for potential distributions (for small wall potential). Velocity profiles were also derived in the same domains, for both inside and outside the PEL. Convective-diffusive species balance equation was semi-analytically solved inside the PEL. Expression of length averaged Sherwood number was also obtained and effects of different parameters, namely, drag parameter (α), Debye parameter ( κ ¯ ) , and PEL thickness were studied in detail. The variation of permeate concentration and permeation flux across the porous wall was obtained.

A disposable on-chip microvalve and pump for programmable microfluidics

In this work, a low-cost PDMS micro-pump and -valve have been designed and developed to control multiple reagents for enzyme-linked immunosorbent assay (ELISA) on a programmable lab-on-a-chip (LOC) platform. The micro pump and valves were precisely controlled by selectively pressurizing the PDMS channels and chamber to actuate the multiple reagents in a controlled manner. Selective pressurizing of the PDMS structures was initiated by a simple system that maneuvered a single roller bar operated by a programmed microprocessor. The performance of the micro-pump was fully characterized and a minimum fluid volume of 1 μL was controlled. Also, the on-chip microvalves were programmed to flow the multiple reagents to automatically process the multi-step ELISA procedures. By applying the proposed platform, 19.40 pg ml-1 cardiac troponin T (cTnT) was successfully detected on the LOC device by using multiple programmed valves as multiple steps of the enzyme-linked sandwich immunoassay. As a result, the developed micro-pump and -valve, which were successfully applied to actuate a series of solutions in a controlled manner, can be widely applied to lab-on-a-chip based bioassays.

On AC-Field-Induced Nonlinear Electroosmosis next to the Sharp Corner-Field-Singularity of Leaky Dielectric Blocks and Its Application in on-Chip Micro-Mixing

Induced-charge electroosmosis has attracted lots of attention from the microfluidic community over the past decade. Most previous researches on this subject focused on induced-charge electroosmosis (ICEO) vortex streaming actuated on ideally polarizable surfaces immersed in electrolyte solutions. Starting from this point, we conduct herein a linear asymptotic analysis on nonlinear electroosmotic flow next to leaky dielectric blocks of arbitrary electrical conductivity and dielectric permittivity in harmonic AC electric fields, and theoretically demonstrate that observable ICEO fluid motion can be generated at high field frequencies in the vicinity of nearly insulating semiconductors, a very low electrical conductivity, of which can evidently increase the double-layer relaxation frequency (inversely proportional to the solid permittivity) to be much higher than the typical reciprocal RC time constant for induced double-layer charging on ideally polarizable surfaces. A computational model is developed to study the feasibility of this high-frequency vortex flow field of ICEO for sample mixing in microfluidics, in which the usage of AC voltage signal at high field frequencies may be beneficial to suppress electrochemical reactions to some extent. The influence of various parameters for developing an efficient mixer is investigated, and an integrated arrangement of semiconductor block array is suggested for achieving a reliable mixing performance at relatively high sample fluxes. Our physical demonstration with high-frequency ICEO next to leaky dielectric blocks using a simple channel structure offers valuable insights into the design of high-throughput micromixers for a variety of lab-on-a-chip applications.

Microfluidics: innovative approaches for rapid diagnosis of antibiotic-resistant bacteria

The emergence of antibiotic-resistant bacteria has become a major global health concern. Rapid and accurate diagnostic strategies to determine the antibiotic susceptibility profile prior to antibiotic prescription and treatment are critical to control drug resistance. The standard diagnostic procedures for the detection of antibiotic-resistant bacteria, which rely mostly on phenotypic characterization, are time consuming, insensitive and often require skilled personnel, making them unsuitable for point-of-care (POC) diagnosis. Various molecular techniques have therefore been implemented to help speed up the process and increase sensitivity. Over the past decade, microfluidic technology has gained great momentum in medical diagnosis as a series of fluid handling steps in a laboratory can be simplified and miniaturized on to a small platform, allowing marked reduction of sample amount, high portability and tremendous possibility for integration with other detection technologies. These advantages render the microfluidic system a great candidate to be developed into an easy-to-use sample-to-answer POC diagnosis suitable for application in remote clinical settings. This review provides an overview of the current development of microfluidic technologies for the nucleic acid based and phenotypic-based detections of antibiotic resistance.

Acoustofluidic actuation of in situ fabricated microrotors

We have demonstrated in situ fabricated and acoustically actuated microrotors. A polymeric microrotor with predefined oscillating sharp-edge structures is fabricated in situ by applying a patterned UV light to polymerize a photocrosslinkable polyethylene glycol solution inside a microchannel around a polydimethylsiloxane axle. To actuate the microrotors by oscillating the sharp-edge structures, we employed piezoelectric transducers which generate tunable acoustic waves. The resulting acoustic streaming flows rotate the microrotors. The rotation rate is tuned by controlling the peak-to-peak voltage applied to the transducer. A 6-arm microrotor can exceed 1200 revolutions per minute. Our technique is an integration of single-step microfabrication, instant assembly around the axle, and easy acoustic actuation for various applications in microfluidics and microelectromechanical systems (MEMS).

Particle rotational trapping on a floating electrode by rotating induced-charge electroosmosis

We describe a novel rotating trait of induced-charge electroosmotic slip above a planar metal surface, a phenomenon termed "Rotating induced-charge electro-osmosis" (ROT-ICEO), in the context of a new microfluidic technology for tunable particle rotation or rotational trap. ROT-ICEO has a dynamic flow stagnation line (FSL) that rotates synchronously with a background circularly polarized electric field. We reveal that the rotating FSL of ROT-ICEO gives rise to a net hydrodynamic torque that is responsible for rotating fluids or particles in the direction of the applied rotating electric field either synchronously or asynchronously, the magnitude of which is adjusted by a balance between rotation of FSL and amplitude of angular-direction flow component oscillating at twice the field frequency. Supported by experimental observation, our physical demonstration with ROT-ICEO proves invaluable for the design of flexible electrokinetic framework in modern microfluidic system.

A primary battery-on-a-chip using monolayer graphene

We present here a bottom-up approach for realizing on-chip on-demand batteries starting out with chemical vapor deposition-grown graphene. Single graphene monolayers contacted by electrode lines on a silicon chip serve as electrodes. The anode and cathode are realized by electrodeposition of zinc and copper respectively onto graphene, leading to the realization of a miniature graphene-based Daniell cell on a chip. The electrolyte is housed partly in a gel and partly in liquid form in an on-chip enclosure molded using a 3d printer or made out of poly(dimethylsiloxane). The realized batteries provide a stable voltage (∼1.1 V) for many hours and exhibit capacities as high as 15 μAh, providing enough power to operate a pocket calculator. The realized batteries show promise for deployment as on-chip power sources for autonomous systems in lab-on-a-chip or biomedical applications.

Can Nanofluidic Chemical Release Enable Fast, High Resolution Neurotransmitter-Based Neurostimulation?

Artificial chemical stimulation could provide improvements over electrical neurostimulation. Physiological neurotransmission between neurons relies on the nanoscale release and propagation of specific chemical signals to spatially-localized receptors. Current knowledge of nanoscale fluid dynamics and nanofluidic technology allows us to envision artificial mechanisms to achieve fast, high resolution neurotransmitter release. Substantial technological development is required to reach this goal. Nanofluidic technology—rather than microfluidic—will be necessary; this should come as no surprise given the nanofluidic nature of neurotransmission. This perspective reviews the state of the art of high resolution electrical neuroprostheses and their anticipated limitations. Chemical release rates from nanopores are compared to rates achieved at synapses and with iontophoresis. A review of microfluidic technology justifies the analysis that microfluidic control of chemical release would be insufficient. Novel nanofluidic mechanisms are discussed, and we propose that hydrophobic gating may allow control of chemical release suitable for mimicking neurotransmission. The limited understanding of hydrophobic gating in artificial nanopores and the challenges of fabrication and large-scale integration of nanofluidic components are emphasized. Development of suitable nanofluidic technology will require dedicated, long-term efforts over many years.

New organic–inorganic hybrid material based on a poly(amic acid) oligomer: a promising opportunity to obtain microfluidic devices by a photolithographic process

Miniaturized total analysis systems are becoming a powerful tool for analytical and bioanalytical applications.

Low-cost bioanalysis on paper-based and its hybrid microfluidic platforms

Low-cost assays have broad applications ranging from human health diagnostics and food safety inspection to environmental analysis. Hence, low-cost assays are especially attractive for rural areas and developing countries, where financial resources are limited. Recently, paper-based microfluidic devices have emerged as a low-cost platform which greatly accelerates the point of care (POC) analysis in low-resource settings. This paper reviews recent advances of low-cost bioanalysis on paper-based microfluidic platforms, including fully paper-based and paper hybrid microfluidic platforms. In this review paper, we first summarized the fabrication techniques of fully paper-based microfluidic platforms, followed with their applications in human health diagnostics and food safety analysis. Then we highlighted paper hybrid microfluidic platforms and their applications, because hybrid platforms could draw benefits from multiple device substrates. Finally, we discussed the current limitations and perspective trends of paper-based microfluidic platforms for low-cost assays.

Iontronics

Iontronics is an emerging technology based on sophisticated control of ions as signal carriers that bridges solid-state electronics and biological system. It is found in nature, e.g., information transduction and processing of brain in which neurons are dynamically polarized or depolarized by ion transport across cell membranes. It suggests the operating principle of aqueous circuits made of predesigned structures and functional materials that characteristically interact with ions of various charge, mobility, and affinity. Working in aqueous environments, iontronic devices offer profound implications for biocompatible or biodegradable logic circuits for sensing, ecofriendly monitoring, and brain-machine interfacing. Furthermore, iontronics based on multi-ionic carriers sheds light on futuristic biomimic information processing. In this review, we overview the historical achievements and the current state of iontronics with regard to theory, fabrication, integration, and applications, concluding with comments on where the technology may advance.

Programmable and on-demand drug release using electrical stimulation

Recent advancement in microfabrication has enabled the implementation of implantable drug delivery devices with precise drug administration and fast release rates at specific locations. This article presents a membrane-based drug delivery device, which can be electrically stimulated to release drugs on demand with a fast release rate. Hydrogels with ionic model drugs are sealed in a cylindrical reservoir with a separation membrane. Electrokinetic forces are then utilized to drive ionic drug molecules from the hydrogels into surrounding bulk solutions. The drug release profiles of a model drug show that release rates from the device can be electrically controlled by adjusting the stimulated voltage. When a square voltage wave is applied, the device can be quickly switched between on and off to achieve pulsatile release. The drug dose released is then determined by the duration and amplitude of the applied voltages. In addition, successive on/off cycles can be programmed in the voltage waveforms to generate consistent and repeatable drug release pulses for on-demand drug delivery.

Dynamic radial positioning of a hydrodynamically focused particle stream enabled by a three-dimensional microfluidic nozzle

The ability to confine flows and focus particle streams has become an integral component of the design of microfluidic systems for the analysis of a wide range of samples. Presented here is the implementation of a 3D microfluidic nozzle capable of both focusing particles as well as dynamically positioning those particles in selected flow lamina within the downstream analysis channel. Through the independent adjustment of the three sheath inlet flows, the nozzle controlled the size of a focused stream for 6, 10, and 15 μm polystyrene microparticles. Additional flow adjustment allowed the nozzle to dynamically position the focused particle stream to a specific area within the downstream channel. This unique ability provides additional capability and sample flexibility to the system. In order to gain insight into the fluidic behavior of the system, experimental conditions and results were duplicated within 4.75 μm using a COMSOL Multiphysics(®) model to elucidate the structure, direction, proportion, and fate of fluid lamina throughout the nozzle region. The COMSOL Multiphysics model showed that the position and distribution of particles upon entering the nozzle have negligible influence over its focusing ability, extending the experimental results into a wider range of particle sizes and system flow rates. These results are promising for the application of this design to allow for a relatively simple, fast, fully fluidically controlled nozzle for selective particle focusing and positioning for further particle analysis and sorting.

A versatile PDMS/paper hybrid microfluidic platform for sensitive infectious disease diagnosis

Bacterial meningitis is a serious health concern worldwide. Given that meningitis can be fatal and many meningitis cases occurred in high-poverty areas, a simple, low-cost, highly sensitive method is in great need for immediate and early diagnosis of meningitis. Herein, we report a versatile and cost-effective polydimethylsiloxane (PDMS)/paper hybrid microfluidic device integrated with loop-mediated isothermal amplification (LAMP) for the rapid, sensitive, and instrument-free detection of the main meningitis-causing bacteria, Neisseria meningitidis (N. meningitidis). The introduction of paper into the microfluidic device for LAMP reactions enables stable test results over a much longer period of time than a paper-free microfluidic system. This hybrid system also offers versatile functions, by providing not only on-site qualitative diagnostic analysis (i.e., a yes or no answer), but also confirmatory testing and quantitative analysis in laboratory settings. The limit of detection of N. meningitidis is about 3 copies per LAMP zone within 45 min, close to single-bacterium detection sensitivity. In addition, we have achieved simple pathogenic microorganism detection without a laborious sample preparation process and without the use of centrifuges. This low-cost hybrid microfluidic system provides a simple and highly sensitive approach for fast instrument-free diagnosis of N. meningitidis in resource-limited settings. This versatile PDMS/paper microfluidic platform has great potential for the point of care (POC) diagnosis of a wide range of infectious diseases, especially for developing nations.

Implantable microchip: the futuristic controlled drug delivery system

There is no doubt that controlled and pulsatile drug delivery system is an important challenge in medicine over the conventional drug delivery system in case of therapeutic efficacy. However, the conventional drug delivery systems often offer a limited by their inability to drug delivery which consists of systemic toxicity, narrow therapeutic window, complex dosing schedule for long term treatment etc. Therefore, there has been a search for the drug delivery system that exhibit broad enhancing activity for more drugs with less complication. More recently, some elegant study has noted that, a new type of micro-electrochemical system or MEMS-based drug delivery systems called microchip has been improved to overcome the problems related to conventional drug delivery. Moreover, micro-fabrication technology has enabled to develop the implantable controlled released microchip devices with improved drug administration and patient compliance. In this article, we have presented an overview of the investigations on the feasibility and application of microchip as an advanced drug delivery system. Commercial manufacturing materials and methods, related other research works and current advancement of the microchips for controlled drug delivery have also been summarized.

Anisotropic Janus Si nanopillar arrays as a microfluidic one-way valve for gas-liquid separation

In this paper, we demonstrate a facile strategy for the fabrication of a one-way valve for microfluidic (MF) systems. The micro-valve was fabricated by embedding arrays of Janus Si elliptical pillars (Si-EPAs) with anisotropic wettability into a MF channel fabricated in poly(dimethylsiloxane) (PDMS). Two sides of the Janus pillar are functionalized with molecules with distinct surface energies. The ability of the Janus pillar array to act as a valve was proved by investigating the flow behaviour of water in a T-shaped microchannel at different flow rates and pressures. In addition, the one-way valve was used to achieve gas-liquid separation. We believe that the Janus Si-EPAs modified by specific surface functionalization provide a new strategy to control the flow and motion of fluids in MF channels.

Bubble-free and pulse-free fluid delivery into microfluidic devices

The bubble-free and pulse-free fluid delivery is critical to reliable operation of microfluidic devices. In this study, we propose a new method for stable bubble-free and pulse-free fluid delivery in a microfluidic device. Gas bubbles are separated from liquid by using the density difference between liquid and gas in a closed cavity. The pulsatile flow caused by a peristaltic pump is stabilized via gas compressibility. To demonstrate the proposed method, a fluidic chamber which is composed of two needles for inlet and outlet, one needle for a pinch valve and a closed cavity is carefully designed. By manipulating the opening or closing of the pinch valve, fluids fill up the fluidic chamber or are delivered into a microfluidic device through the fluidic chamber in a bubble-free and pulse-free manner. The performance of the proposed method in bubble-free and pulse-free fluid delivery is quantitatively evaluated. The proposed method is then applied to monitor the temporal variations of fluidic flows of rat blood circulating within a complex fluidic network including a rat, a pinch valve, a reservoir, a peristaltic pump, and the microfluidic device. In addition, the deformability of red blood cells and platelet aggregation are quantitatively evaluated from the information on the temporal variations of blood flows in the microfluidic device. These experimental demonstrations confirm that the proposed method is a promising tool for stable, bubble-free, and pulse-free supply of fluids, including whole blood, into a microfluidic device. Furthermore, the proposed method will be used to quantify the biophysical properties of blood circulating within an extracorporeal bypass loop of animal models.

Design, fabrication and characterization of drug delivery systems based on lab-on-a-chip technology

Lab-on-a-chip technology is an emerging field evolving from the recent advances of micro- and nanotechnologies. The technology allows the integration of various components into a single microdevice. Microfluidics, the science and engineering of fluid flow in microscale, is the enabling underlying concept for lab-on-a-chip technology. The present paper reviews the design, fabrication and characterization of drug delivery systems based on this amazing technology. The systems are categorized and discussed according to the scales at which the drug is administered. Starting with the fundamentals on scaling laws of mass transfer and basic fabrication techniques, the paper reviews and discusses drug delivery devices for cellular, tissue and organism levels. At the cellular level, a concentration gradient generator integrated with a cell culture platform is the main drug delivery scheme of interest. At the tissue level, the synthesis of smart particles as drug carriers using lab-on-a-chip technology is the main focus of recent developments. At the organism level, microneedles and implantable devices with fluid-handling components are the main drug delivery systems. For drug delivery to a small organism that can fit into a microchip, devices similar to those of cellular level can be used.

Optic imaging of single and two-phase pressure-driven flows in nano-scale channels

Microfluidic and nanofluidic devices have undergone rapid development in recent years. Functions integrated onto such devices provide lab-on-a-chip solutions for many biomedical, chemical, and engineering applications. In this paper, a lab-on-a-chip technique for direct visualization of the single- and two-phase pressure-driven flows in nano-scale channels was developed. The nanofluidic chip was designed and fabricated; concentration dependent fluorescence signal correlation was developed for the determination of flow rate. Experiments of single and two-phase flow in nano-scale channels with 100 nm depth were conducted. The linearity correlation between flow rate and pressure drop in nanochannels was obtained and fit closely into Poiseuille's Law. Meanwhile, three different flow patterns, single, annular, and stratified, were observed from the two-phase flow in the nanochannel experiments and their special features were described. A two-phase flow regime map for nanochannels is presented. Results are of critical importance to both fundamental study and many applications.

Rapid, multiplexed microfluidic phage display

The development of a method for high-throughput, automated proteomic screening could impact areas ranging from fundamental molecular interactions to the discovery of novel disease markers and therapeutic targets. Surface display techniques allow for efficient handling of large molecular libraries in small volumes. In particular, phage display has emerged as a powerful technology for selecting peptides and proteins with enhanced, target-specific binding affinities. Yet, the process becomes cumbersome and time-consuming when multiple targets are involved. Here we demonstrate for the first time a microfluidic chip capable of identifying high affinity phage-displayed peptides for multiple targets in just a single round and without the need for bacterial infection. The chip is shown to be able to yield well-established control consensus sequences while simultaneously identifying new sequences for clinically important targets. Indeed, the confined parameters of the device allow not only for highly controlled assay conditions but also introduce a significant time-reduction to the phage display process. We anticipate that this easily-fabricated, disposable device has the potential to impact areas ranging from fundamental studies of protein, peptide, and molecular interactions, to applications such as fully automated proteomic screening.

A Microfluidic Approach to Pulsatile Delivery of Drugs for Neurobiological Studies

We present an innovative microfluidic approach to transcranial delivery of small quantities of drugs in brief time pulses for neurobiological studies. The approach is based on a two-stage process of consecutive drug dispensing and delivery, demonstrated by a device featuring a fully planar design in which the microfluidic components are integrated in a single layer. This 2-D configuration offers ease in device fabrication and is compatible to diverse actuation schemes. A compliance-based and normally closed check valve is used to couple the microchannels that are responsible for drug dispensing and delivery. Brief pneumatic pressure pulses are used to mobilize buffer and drug solutions, which are injected via a cannula into brain tissue. Thus, the device can potentially allow transcranial drug delivery and can also be potentially extended to enable transdermal drug delivery. We have characterized the device by measuring the dispensed and delivered volumes under varying pneumatic driving pressures and pulse durations, the standby diffusive leakage, and the repeatability in the delivery of multiple pulses of drug solutions. Results demonstrate that the device is capable of accurately dispensing and delivering drug solutions 5 to 70 nL in volume within time pulses as brief as 50 ms, with negligible diffusive drug leakage over a practically relevant time scale. Furthermore, testing of pulsatile drug delivery into intact mouse brain tissue has been performed to demonstrate the potential application of the device to neurobiology.

Three-dimensional continuous particle focusing in a microfluidic channel via standing surface acoustic waves (SSAW)

Three-dimensional (3D) continuous microparticle focusing has been achieved in a single-layer polydimethylsiloxane (PDMS) microfluidic channel using a standing surface acoustic wave (SSAW). The SSAW was generated by the interference of two identical surface acoustic waves (SAWs) created by two parallel interdigital transducers (IDTs) on a piezoelectric substrate with a microchannel precisely bonded between them. To understand the working principle of the SSAW-based 3D focusing and investigate the position of the focal point, we computed longitudinal waves, generated by the SAWs and radiated into the fluid media from opposite sides of the microchannel, and the resultant pressure and velocity fields due to the interference and reflection of the longitudinal waves. Simulation results predict the existence of a focusing point which is in good agreement with our experimental observations. Compared with other 3D focusing techniques, this method is non-invasive, robust, energy-efficient, easy to implement, and applicable to nearly all types of microparticles.

System Integration - A Major Step toward Lab on a Chip

Microfluidics holds great promise to revolutionize various areas of biological engineering, such as single cell analysis, environmental monitoring, regenerative medicine, and point-of-care diagnostics. Despite the fact that intensive efforts have been devoted into the field in the past decades, microfluidics has not yet been adopted widely. It is increasingly realized that an effective system integration strategy that is low cost and broadly applicable to various biological engineering situations is required to fully realize the potential of microfluidics. In this article, we review several promising system integration approaches for microfluidics and discuss their advantages, limitations, and applications. Future advancements of these microfluidic strategies will lead toward translational lab-on-a-chip systems for a wide spectrum of biological engineering applications.

Chemical neurostimulation using pulse code modulation (PCM) microfluidic chips

We report the implementation of a chemical neurostimulation technique using microfluidic devices. The microfluidic chip in this research is used for the in vitro study of the nervous system of Aplysia californica under localized chemical stimulation. The polydimethylsiloxane (PDMS) device is a one-bit pulse code modulator that digitally controls the concentration of the non-hydrolysable cholinergic agonist carbachol injected directly above a ganglion. The chip was successful in repeatedly and controllably inducing bursts of ingestive-like patterns. The ability of the chip to induce rhythmic activity through the sheath of the ganglion suggests that it could serve as the basis for an implantable, in vivo device to control neural activity and motor behavior using chemical stimulation.

Drug delivery for treatment of inner ear disease: current state of knowledge

Delivery of medications to the inner ear has been an area of considerable growth in both the research and clinical realms during the past several decades. Systemic delivery of medication destined for treatment of the inner ear is the foundation on which newer delivery techniques have been developed. Because of systemic side effects, investigators and clinicians have begun developing and using techniques to deliver therapeutic agents locally. Alongside the now commonplace use of intratympanic gentamicin for Meniere's disease and the emerging use of intratympanic steroids for sudden sensorineural hearing loss, novel technologies, such as hydrogels and nanoparticles, are being explored. At the horizon of inner ear drug-delivery techniques, intracochlear devices that leverage recent advances in microsystems technology are being developed to apply medications directly into the inner ear. Potential uses for such devices include neurotrophic factor and steroid delivery with cochlear implantation, RNA interference technologies, and stem-cell therapy. The historical, current, and future delivery techniques and uses of drug delivery for treatment of inner ear disease serve as the basis for this review.

Engineering insect flight metabolics using immature stage implanted microfluidics

Small-scale insect inspired aircraft represent a promising approach to downscaling traditional aircraft designs. Despite advancements in microfabrication, however, it has proven difficult to fully replicate the mechanical complexities that enable these natural systems. As an alternative, recent efforts have used implanted electrical, optical or acoustic microsystems to exert direct control over insect flight. Here we demonstrate, for the first time, a method of directly and reversibly engineering insect flight metabolics using immature stage implanted microfluidics. We present our technique and device for on-command modulation of the internal levels of l-glutamic and l-aspartate acids and quantify the resulting changes in metabolic activity by monitoring respiratory CO(2) output. Microfluidic devices implanted 1 to 2 days prior to insects' emergence achieved survivability and flight-capable rates of 96% and 36%, respectively. Behavior ranging from retarded motion to complete, reversible paralysis, over timescales ranging from minutes to hours is demonstrated.