Liquid Manipulation Research Articles

Gel-based electrochemical DNA synthesis for quasi-solid-state data storage

Chemically synthesized DNA has been considered a promising medium for data storage. Among various methods, electrochemical synthesis is simple and easy to miniaturize, attracting much attention. However, conventional DNA synthesis uses phosphoramidite chemistry involving multi-step liquid-phase reactions and complicated liquid manipulation, restricting scalability and practical application. Here, we report the quasi-solid-state electrochemical DNA synthesis based on gels. All reagents required for different synthesis steps are contained in separate gels without mixing or dilution. Instead of complicated liquid manipulation, DNA synthesis on the electrode requires only relative motion between the electrode and gels. Similarly, blank gels with only acetonitrile are reused to clean the electrode surface without washing with plenty of liquid. We demonstrate our method is scalable using an electrode array for parallel DNA synthesis.

Airflow Triggered Water Film Self-Sculpturing on Femtosecond Laser-Induced Heterogeneously Wetted Micro/Nanostructured Surfaces.

Liquid manipulation is essential for daily life and modern industry, and it is widely used in various fields, including seawater desalination, microfluidic robots, and biomedical engineering. Nevertheless, the current research focuses on the manipulation of individual droplets. There are a few projects for water film management. Here, we proposed a facile method of wind-triggered water film self-sculpturing based on a heterogeneous wettability surface, which is achieved by the femtosecond laser direct writing technology and femtosecond laser deposition. Under the conditions of various airflow velocities and water film thicknesses, three distinct behaviors of the water film were analyzed. As a result, when the water film thickness is lower than 4.9 mm, the self-sculpture process will occur until the whole superhydrophobic surface dewetting. Four potential applications are demonstrated, including encryption, oil containers, reconfigurable patterning, and self-splitting devices. This work provides a new approach for manipulating a water film of fluid control engineering.

Patterned Manipulated Surface Based on Femtosecond Laser with Adjustable Wetting Speed and Directional Fluid Delivery.

Recently, due to the crucial roles of multifunctional liquid manipulation surfaces in biomedical transportation, microfluidics, and chemical engineering, the demand for controllable and functional aspects of directed liquid transportation has increased significantly. However, designing an intelligent manipulation surface that is easy to manufacture and fully functional remains an immense challenge. To address this challenge, a smart surface that can regulate the rate of liquid transport within a patterned channel by temperature is reported. A synergistically controlled approach of poly(N-isopropylacrylamide) and micropillar shape-memory polymers (SMPs) was used to modulate the wetting rate of liquids on surfaces. By femtosecond laser direct writing, temperature-responsive composite surfaces are embedded in the microstructure of shape-memory polymers (SMPs) in a patterned manner, resulting in the preparation of novel programmable liquid manipulation surfaces incorporating boundaries possessing asymmetric wettability. Since the smart surface is based on SMP, the superhydrophobic part in the superhydrophobic/controllable wettability patterning platform is also programmed for droplet directional transport, which takes advantage of the difference in wettability between the rewritable indentation track and the periphery to allow droplets to flow into the temperature-controlled velocity track, enriching the functionality of the surface. In addition, based on its excellent controllability and patterning, the surface has been shown to be used in microfluidic circuit chips with self-cleaning properties, which provides new ideas for circuit timing control. This study provides promising prospects for the effective development of multifunctional liquid steering surfaces, lab-on-a-chip, and microfluidic devices.

A magnetically controlled microstructured surface for three-dimensional droplet manipulation

The smart manipulation of droplets has received widespread attention due to its potential applications in many fields. However, it is still challenging to realize robust multidimensional, versatile liquid manipulation using magnetically responsive surfaces. Here, a magnetically controlled surface with a dense array of cone-shaped microstructures is developed by the spray self-assembly method using soft nontoxic materials. The effects of the spray volume and material concentrations on the surface morphology and wettability are systematically investigated. The wettability and adhesion properties of the developed surface can be reversibly switched in the presence of an on/off magnetic field. In situ observation indicated that the driving force acted on the droplet is derived from localized deformation of the microstructures. Moreover, theoretical models of droplet manipulation are proposed to demonstrate the underlying mechanism. Under the actuation of the moving magnetic field, the surface can transport droplets of 1–14 μl in the vertical direction, and the modified superhydrophobic surface can transport droplets of 3–30 μl in the horizontal direction and achieve against-gravity droplet climbing with a volume of 10 μl at a climbing angle of 25°. The environmentally friendly and facilely manufacturable surface presents promising applications in liquid microreactors and the transportation of mixed fluids in biological and chemical research.

A hyperbranched-topology-mediated self-roughness approach toward robust all-organic superhydrophobic surfaces

Biomimetic superhydrophobic surfaces (SHSs) have shown promising applications in versatile scenarios. However, due to limitations of complicated templates, expensive instruments, and insufficient adhesion between adhesives and inorganic/organic nanoparticles, simultaneous implementation of facile fabrication and highly robustness of SHSs remains difficult. Here, we demonstrate a hyperbranched-topology-mediated self-roughness approach to construct an all-organic SHS. Because of the stable covalent linkages, the SHS can be applied for versatile surfaces, exhibiting high resistance to mechanical abrasions and chemical corrosions. Additionally, once wetted with alcohol, the surface turns from superhydrophobic to hydrophilic, enabling the manipulation of liquid and gas motion as well as applications as micro-reactors. This topology-mediated self-roughness strategy paves a foundation for future development of liquid-repellent coatings.

Stretchable Superhydrophobic Surfaces: From Basic Fabrication Strategies to Applications

Superhydrophobic surfaces find extensive applications in various fields, including self-cleaning, liquid manipulation, anti-icing, and water harvesting. To achieve superhydrophobicity, the surfaces are designed with hierarchical nano- and/or microscale protrusions. These structures result in a static contact angle above 150° and a sliding/rolling-off angle below 10° when water droplets deposit on the surface. The combination of hierarchical structures and low-surface energy materials contributes to this unique liquid-repellent property. In addition to liquid repellency, the durability of these surfaces is crucial for practical applications, which has prompted the exploration of stretchable superhydrophobic surfaces as a viable solution. The flexibility of these surfaces means that they are effectively safeguarded against mechanical damage and can withstand daily wear and tear. Over the last decade, considerable research has been dedicated to developing stretchable superhydrophobic surfaces to expand their potential applications. This review provides an overview of stretchable superhydrophobic surfaces, specifically emphasizing current processing strategies and their prospective applications. Additionally, we present a forward-looking perspective on future fabrication methods to create robust superhydrophobic surfaces, further enhancing their practicality and versatility.

A sequential liquid dispensing method in a centrifugal microfluidic device operating at a constant rotational speed for the multiplexed genetic detection of foodborne pathogens.

This study proposes a sequential liquid dispensing method using a centrifugal microfluidic device operating at a constant rotational speed for the multiplexed genetic detection of nucleic acid targets across multiple samples in a single operation. A pair of passive valves integrated into each microchamber enabled the liquid to fill towards the center of rotation against the centrifugal force, facilitating the complete removal of air inside the microchamber. Liquid manipulation can be achievable without any surface coating of the device by exploiting the inherent hydrophobicity of the polymer. Furthermore, design guidelines for the optimization of microfluidic devices are clarified. Consequently, our proposed method allows direct liquid dispensing into the reaction chambers without cross-contamination while simultaneously metering the sample/reagent volume for the colorimetric loop-mediated isothermal amplification (LAMP) reaction. In addition, we demonstrated the simultaneous detection of four foodborne pathogens (Salmonella spp., Vibrio parahaemolyticus, Campylobacter spp., and norovirus genogroup II (GII)) across four samples in a centrifugal microfluidic device within 60 min. Furthermore, the device exhibited high quantitation (R 2 > 0.98) of the DNA concentration in the sample. Our proposed method enables a more compact design by eliminating the need for metering chambers and offers a point-of-care testing platform with high simplicity as it operates at a constant rotational speed.

Vampire bat's tongue-inspired superhydrophilic flexible origami channel for directional and spontaneous liquid manipulation

An improved bat-tongue-inspired superhydrophilic origami channel with liquid manipulation and collecting ability.

Patternable, high-precision, controllable wettability copper layers for 3D resin-based weather-resistant electronics and 3D liquid manipulation.

The realization of 3D patterned metal layers with manipulable surface wettability has significant potential, especially in integrating microelectronics with weather resistance and multifunctional liquid manipulation. However, developing a facile and efficient method to bring it to fruition remains a great challenge. In this work, we proposed a novel 3D selective metallization strategy that combines stereolithography 3D printing with laser-induced selective metallization (LISM). Utilizing 355 nm UV or 1064 nm lasers, this strategy can prepare 3D conductive copper patterns (or circuits) with controlled wettability on various 3D-printed resin parts. The copper layer surface prepared via LISM formed microstructures similar to the papillae on the surface of a lotus leaf, and it spontaneously exhibited superhydrophobicity (156.6°) after aging in the air at room temperature. Superhydrophobic 3D circuits with self-cleaning, corrosion-resistant, and anti-condensation performance were successfully fabricated. By further treating the copper layer with a 355 nm UV laser, we realized the transformation of the superhydrophobic copper layer to a superhydrophilic state, enabling us to prepare high-precision superhydrophilic patterns or channels. A 3D self-driven flow channel was fabricated to successfully realize 3D liquid manipulation and small-scale chemical experiments.

Programming hierarchical anisotropy in microactuators for multimodal actuation.

Microactuators, capable of executing tasks typically repetitive, hazardous, or impossible for humans, hold great promise across fields such as precision medicine, environmental remediation, and swarm intelligence. However, intricate motions of microactuators normally require high complexity in design, making it increasingly challenging to realize at small scales using existing fabrication techniques. Taking inspiration from the hierarchical-anisotropy principle found in nature, we program liquid crystalline elastomer (LCE) microactuators with multimodal actuation tailored to their molecular, shape, and architectural anisotropies at (sub)nanometer, micrometer, and (sub)millimeter scales, respectively. Our strategy enables diverse deformations with individual LCE microstructures, including expanding, contracting, twisting, bending, and unwinding, as well as re-programmable shape transformations of assembled LCE architectures with negative Poisson's ratios, locally adjustable actuation, and changing from two-dimensional (2D) to three-dimensional (3D) structures. Furthermore, we design tetrahedral microactuators with well-controlled mobility and precise manipulation of both solids and liquids in various environments. This study provides a paradigm shift in the development of microactuators, unlocking a vast array of complexities achievable through manipulation at each hierarchical level of anisotropy.

Revolutionizing sample preparation: a novel autonomous microfluidic platform for serial dilution.

Dilution is a standard fluid operation widely employed in the sample preparation process of many bio(chemical) assays. It serves multiple essential functions such as sample mixing with certain reagents at specific dilution ratios, reducing sample matrix effects, bringing target analytes within the linear assay detection range, among many others. Traditionally, sample processing is performed in laboratory settings through manual or automated pipetting. When working in resource-limited settings, however, neither trained personnel nor proper laboratory equipment are available limiting the accessibility to high-quality diagnostic tests. In this work, we present a novel standalone and fully automated microfluidic platform for the stepwise preparation of serial dilutions without the need for any active elements. Stepwise dilution is achieved using the coordinated burst action of hydrophobic burst valves to first isolate a precisely metered volume from an applied sample drop and subsequently merge it with a prefilled diluent liquid. Downstream, expansion chambers are used to mix both reagents into a homogeneous solution. The dilution module was characterized to generate accurate and reproducible (CV < 7%) dilutions for targeted dilution factors of 2, 5 and 10×, respectively. Three dilution modules were coupled in series to generate three-fold logarithmic (log5 or log10) dilutions, with excellent linearity (R2 > 0.99). Its compatibility with whole blood was furthermore illustrated, proving its applicability for automating and downscaling bioassays with complex biological matrices. Finally, autonomous on-chip serial dilution was demonstrated by incorporating the self-powered (i)SIMPLE technology as a passive driving source for liquid manipulation. We believe that the simplicity and modularity of the presented autonomous dilution platform are of interest to many point-of-care applications in which sample dilution and reagent mixing are of importance.

Study on a Noncontact Microdroplet Separation Method under the Action of Corona Discharge.

Precision manipulation of various liquids is essential in many fields such as various thermal, optical, and medical applications. This paper proposes an effective noncontact microdroplet separation method that is based on the action of corona discharge. A blade-plate electrode is constructed to generate an ionic wind, thereby enabling the droplet to be separated according to the shape of the blade electrode. Line, curve, S-shape, and parallel separation of the droplet can be realized in the experiment setup. Furthermore, experiment parameters, including the driving voltage, cutting speed, the distance of the upper and lower electrodes, cutting depth, etc., are discussed. Experimental results show that the proposed method is feasible and effective and can be used in application scenarios that require precise manipulation of droplets.

(Invited) Confined Electrodeposition Enables Additive Manufacturing of Metals at Micro- and Nanoscale

Additive manufacturing, also commonly known as 3D printing, is rapidly becoming a part of our everyday life: from DIY use by hobbyists to industrial manufacturing, 3D printing is experiencing a booming success. The technologies advance quickly with faster print rates, broader choice of materials and a constantly increasing accuracy and printing resolution. Impressively, state-of-the-art techniques take the printed feature sizes to the extreme: multiphoton optical stereolithography and focused electron or ion beams are now capable to produce objects with nanoscale resolution. Although at the cutting edge to printing finest details, these advanced manufacturing methods lack the capacity to process dense and pure electrical conductors – materials very much needed to push the limits of the technologies of the future – sensors, energy storage devices, logical gates and memory interfaces.Electrochemical methods, which have an advantage to process a wider range of materials – conductors and semiconductors, bulk materials and colloids, at a first glance, have little to do with additive manufacturing. Electrodeposition, a well-established approach traditionally used to produce metallic coatings or thin films, is often integrated in microfabrication process but is limited to planar two-dimensional designs. However, when combined with state-of-the-art nanoelectrochemical approaches, electrodeposition can be taken into a three-dimensional realm, where it can be used to produce complex structures with micro- and nanoscale dimensions [1]. The key to achieve this is nanoscale confinement of precursor delivery that is combined with layer-by-layer additive processing. Liquid manipulation by pressure driven flow through nanoscale cantilevers [2] or intermittent meniscus formation using droplet cells [3] – a variety of nanoelectrochemical techniques can be used to fabricate metallic structures with various morphologies. The recent advances in these technologies including instrumental aspects, performance metrics such as resolution and print rates, as well as some materials characteristics are highlighted in this talk.

(Invited) Electrocatalytic Syntheses with Interfacial Control

Synthesis driven by renewable electricity offers a sustainable, scalable, decentralized, and energy-efficient route to furnish value-added products. As all electrocatalytic reactions occur at the phase boundary between conductive solids and liquid electrolytes, the discovery, design, and manipulation of selective electricity-driven reactivity demands new methods to probe and tune this interface and predict how interfacial structural changes influence reaction selectivity.The functionalization of aldehydes and ketones with organic halide electrophiles remains a privileged reaction class to construct C(sp3)‒C(sp3) bonds. Translation to molecular catalytic strategies remains challenging due to competitive side reactivity imposed by radical intermediates following sp3 organic halide activation. Our group has uncovered an alternative paradigm that deploys catalytic electrode surfaces to develop reductive fragment-based electrophile coupling reactions. Using in-situ spectroscopy and electrochemical analyses, we reveal the “black box” of the catalytic interface. The addition of Lewis acids pre-organizes the surface, enabling a carbon-centered radical (obtained via electrocatalytic activation) to efficiently add to the carbonyl. Our studies lay a foundation to develop sustainable synthetic methodologies by tuning the interfacial structure at catalytic, reusable electrodes at the molecular level.

Development of Electrochemical Paper-Based Devices for Field Assays

The birth of the modern field of paper-based analytical devices (PADs) was marked by the pioneering work by the Whitesides’ group which demonstrated that it was possible to perform complex manipulation of liquids within hydrophilic paper channels delimited by hydrophobic barriers [1]. The key features of paper as a platform are: a) flexibility; b) low thickness and lightness; c) absorbency; d) high surface-to-volume ratio; e) hydrophilicity and capillary action; f) chemical and biological inertness; g) disposability and biodegradability, and; h) low cost and wide availability. Among the various detection modes that are compatible with PADs, electrochemical detection is very attractive since electrochemical transducers can be readily and rapidly patterned on paper using various approaches. Combined with low-cost and portable instrumentation, electrochemical PADs (ePADs) are well suited to on-site assays and point-of-care testing and relevant applications have been developed in various fields such as clinical diagnostics, environmental monitoring and food quality control [2-4].The methods of patterning of the hydrophobic barriers and of depositing the electrodes are critical in the fabrication of ePADs and several approaches have been proposed in the literature [2-4]. Τhe aim of this work was the development of different approaches for the fabrication of ePADs. For this purpose, hydrophobic barriers were delimited using: x-y plotting with commercial hydrophobic marker pens, wax printing and thermal printing. Electrodes were deposited on the PADs using x-y plotting with commercial writing pencils and conductive inks formulated in-house and screen-printing. Different fabrication parameters were optimized including the selection of the paper substrate, the conditions for the formation of the hydrophobic barriers and the electrode deposition parameters. Applicability of the ePADs was demonstrated for different applications for on-site assays including the enzymatic amperometric detection of glucose, the determination of trace metals by stripping analysis and the voltammetric detection of organic compounds.

A portable all-in-one microfluidic device with real-time colorimetric LAMP for HPV16 and HPV18 DNA point-of-care testing

Screening for high-risk human papillomavirus (HPV) infection is one of the most important preventative measures for cervical cancer. However, fast, convenient, and low-cost HPV detection remains challenging, especially in resource-limited settings. Here, we report a portable all-in-one device (PAD) for point-of-care testing (POCT) for HPV16 and HPV18 DNA in cervical swabs. The PAD was engineered to integrate modules for extraction-free sample lysis, loop-mediated isothermal amplification (LAMP) with lyophilized reagent beads, and real-time colorimetric signal sensing into a single miniaturized device, considerably shortening the sample-to-result time to 15 min. The precision liquid handling in the completely sealed microfluidic chip is achieved by a uniquely designed pressure-balanced automatic liquid flow mechanism, thereby eliminating the need for manual manipulation of liquids and thus the risk of biohazards. The PAD employs an improved real-time colorimetric LAMP (rcLAMP) assay with a limit of detection (LOD) of 1 copy/μL, enabled by enhanced assay chemistry to maximize the reaction kinetics. To validate this device for clinical application, we tested 206 clinical cervical swab samples and obtained a sensitivity of 92.1% and a specificity of 99.0%. This custom PAD enabled by microfluidic and electronic engineering techniques can be configured for the simultaneous detection of HPV16 and HPV18 or other pathogens in point-of-care applications.

Controlled synthesis of metal-organic frameworks via AC electrokinetic mixing-assisted microfluidics: A case study of ZIF-8

Metal-organic frameworks (MOFs) have great potential for a wide range of applications given their flexible structures and pore networks. Morphology control directly affects the properties and applications of MOFs. Unfortunately, governing the desired dimension and shape of MOFs is often limited by macrosystems that require organic solvents and additives while including time-consuming treatments. Microfluidics as a practical alternative provides precise manipulation of microscale liquid, has the potential to be a superior platform for directed crystal generation. Here we reported an AC electrokinetic (EK) mixing-assisted micro-synthesis method, which allowed the actively controlled synthesis of MOFs in aqueous phase. The effects of flow rate, molar-ratio of precursors, electric field intensity, and frequency on the synthesis of zeolitic imidazolate framework-8 (ZIF-8) were investigated. Using this method, the particle size of ZIF-8 were varied, and the geometry were changed between flower-like polyhedra, cubes, spheres, and rhombic dodecahedra. Furthermore, the synthesized various ZIF-8 provide different levels of immobilization sites based on their morphological deviations. The flower-like cubic ZIF-8 had defect structures and exhibited a maximum horseradish peroxidase (HRP) loading of about 16%. The study provides a simple, green and reliable tuning strategy for breaking the single morphological form of MOFs to enhance their physicochemical properties.

Topical sevoflurane: a galenic experience

Sevoflurane is a volatile liquid from the family of ether-derived halogenated hydrocarbons that is approved for the induction and maintenance of inhalational general anesthesia in the hospital setting. This review describes the pioneering experience of a Spanish Pain Unit in the home treatment of complicated painful wounds using topical sevoflurane instillations according to a protocol approved for off-label use. Aspects of safety and efficacy, both analgesic, antimicrobial and pro-healing are addressed, and some future lines of research are discussed in terms of new formulations for topical use. After more than seven years of use of the protocol, an experience of over 70,000 applications of topical sevoflurane has been gained. In general terms, the analgesic effect appears quickly, is highly intense and persists for several hours. As a result, patients can reduce their consumption of systemic analgesics and benefit from an improvement in their quality of life. In addition, there are signs that suggest sevoflurane also possesses antimicrobial and pro-healing properties. Regarding safety, pruritus at the level of the periulcerous skin is the most frequently reported adverse effect, although it is usually transient and well-tolerated, and no systemic toxicity has been reported. Overall, the risk-benefit balance of the drug has so far been very favorable. To avoid manipulation of this volatile liquid, we have developed a new formulation of sevoflurane in gel form, which has made it possible to successfully apply sevoflurane in the context of painful pathologies where the skin remains intact. Furthermore, these types of new formulations, including sevoflurane microspheres, which we have also developed, could improve the efficacy and safety of topical sevoflurane while reducing the occupational exposure of healthcare staff. This means that the development of new formulations is a field with a very promising future.

A facile and scalable approach to tear-and-use polyethylene (PE) tape with adjustable hydrophobicity for water transferring

Despite the refined microstructures for liquid manipulation materials is hard to be readily and massively fabricate, the damage and abrasion during storage and transportation is still a main factor limiting its service life. Herein, a facile, scalable, and eco-friendly approach to superhydrophobic polyethylene (PE) tape via constructing polypropylene (PP)-PE-PP sandwiched structures with multi-melt multi-injection molding was reported. The PE tape can be long-term protected by PP layer before use. By peeling the protective PP layers from the PE tape, the hydrophobicity can be instantly endowed to the peeled PE surface, which should give credit is the failure of the interphase layer between PE and PP, followed by in-situ formation of multi-tier microstructures of the peeled PE surface during the peeling process. The hydrophobic performance can be regulated up to 154.0 ± 8.99° by optimizing PE chain structure. Moreover, by simply tunning the peeling temperature from −198 °C to 110 °C, the PE tunable water contact angle (WCA) ranges from 133.6 ± 4.39° to utmost 156.3 ± 3.57°, owing to the transformation of hierarchical multi-tier surface topography around the transition temperature (EP). Ultimately, the as-prepared hydrophobic PE tapes were successfully utilized for loss-free manipulation and transferring of the water droplet, which provides a significant prospect of eco-friendly and continuous production for durable hydrophobic materials.

Friction Manipulation of Ionic Liquids under Boundary Lubrication by Controlling the Surface Potential

Friction Manipulation of Ionic Liquids under Boundary Lubrication by Controlling the Surface Potential