Microfluidic impact printer with interchangeable cartridges for versatile non-contact multiplexed micropatterning

A high-precision automated liquid pipetting device with an interchangeable tip

Liquid handling is a necessary act to deal with liquid samples from scientific labs to industry. However, existing pipetting devices suffer from inaccuracy and low precision when dealing with submicroliter liquids, which significantly affect their applications in low-volume quantitation. In this article, we present an automated liquid pipetting device that can aspirate liquid from microplates and dispense nanoliter droplets with high precision. Liquid aspiration is realized by using a micropump and a solenoid valve, and on-demand nanoliter droplet printing is realized by using a low-cost and interchangeable pipette tip combined with a piezoelectric actuator. Based on the microfluidic printing technology, the volumetric coefficient of variation of the dispensed liquid is less than 2% below 1 µl. A demonstration of concentration dilution for quantitative analysis has been successfully performed using the automated liquid pipetting device, demonstrating its potential in low-volume liquid handling for a wide range of biomedical applications.

High-Throughput Experimentation Using Cell-Free Protein Synthesis Systems

Cell-free protein synthesis can enable the combinatorial screening of many different components and concentrations. However, manual pipetting methods are unfit to handle many cell-free reactions. Here, we describe a microfluidic method that can generate hundreds of unique submicroliter scale reactions. The method is coupled with a high yield cell-free system that can be applied for broad protein screening assays.

Building protein networks in synthetic systems from the bottom-up

The recent development of synthetic biology has expanded the capability to design and construct protein networks outside of living cells from the bottom-up. The new capability has enabled us to assemble protein networks for the basic study of cellular pathways, expression of proteins outside cells, and building tissue materials. Furthermore, the integration of natural and synthetic protein networks has enabled new functions of synthetic or artificial cells. Here, we review the underlying technologies for assembling protein networks in liposomes, water-in-oil droplets, and biomaterials from the bottom-up. We cover the recent applications of protein networks in biological transduction pathways, energy self-supplying systems, cellular environmental sensors, and cell-free protein scaffolds. We also review new technologies for assembling protein networks, including multiprotein purification methods, high-throughput assay screen platforms, and controllable fusion of liposomes. Finally, we present existing challenges towards building protein networks that rival the complexity and dynamic response akin to natural systems. This review addresses the gap in our understanding of synthetic and natural protein networks. It presents a vision towards developing smart and resilient protein networks for various biomedical applications.

Recent progress in creating complex and multiplexed surface-grafted macromolecular architectures

Surface-grafted macromolecules, including polymers, DNA, peptides, etc., are versatile modifications to tailor the interfacial functions in a wide range of fields. In this review, we aim to provide an overview of the most recent progress in engineering surface-grafted chains for the creation of complex and multiplexed surface architectures over micro- to macro-scopic areas. A brief introduction to surface grafting is given first. Then the fabrication of complex surface architectures is summarized with a focus on controlled chain conformations, grafting densities and three-dimensional structures. Furthermore, recent advances are highlighted for the generation of multiplexed arrays with designed chemical composition in both horizontal and vertical dimensions. The applications of such complicated macromolecular architectures are then briefly discussed. Finally, some perspective outlooks for future studies and challenges are suggested. We hope that this review will be helpful to those just entering this field and those in the field requiring quick access to useful reference information about the progress in the properties, processing, performance, and applications of functional surface-grafted architectures.

Low-cost and customizable inkjet printing for microelectrodes fabrication

Microelectrodes for detection of chemicals present several advantages over conventional sized electrodes. However, rapid and low-cost fabrication of microelectrodes is challenging due to high complexity of patterning equipment. We present the development of a low-cost, customizable inkjet printer for printing nanomaterials including carbon nanotubes for the fabrication of microelectrodes. The achieved spatial resolution of the inkjet printer is less than 20 µm, which is comparable to advanced commercially available inkjet printers, with the advantage of being low-cost and easily replicated.

Microfluidic cap-to-dispense (μCD): a universal microfluidic-robotic interface for automated pipette-free high-precision liquid handling

Microfluidic devices have been increasingly used for low-volume liquid handling operations. However, laboratory automation of such delicate devices has lagged behind due to the lack of world-to-chip (macro-to-micro) interfaces. In this paper, we have presented the first pipette-free robotic-microfluidic interface using a microfluidic-embedded container cap, referred to as a microfluidic cap-to-dispense (μCD), to achieve a seamless integration of liquid handling and robotic automation without any traditional pipetting steps. The μCD liquid handling platform offers a generic and modular way to connect the robotic device to standard liquid containers. It utilizes the high accuracy and high flexibility of the robotic system to recognize, capture and position; and then using microfluidic adaptive printing it can achieve high-precision on-demand volume distribution. With its modular connectivity, nanoliter processability, high adaptability, and multitask capacity, μCD shows great potential as a generic robotic-microfluidic interface for complete pipette-free liquid handling automation.

Miniaturized and Automated Synthesis of Biomolecules-Overview and Perspectives

Chemical synthesis is performed by reacting different chemical building blocks with defined stoichiometry, while meeting additional conditions, such as temperature and reaction time. Such a procedure is especially suited for automation and miniaturization. Life sciences lead the way to synthesizing millions of different oligonucleotides in extremely miniaturized reaction sites, e.g., pinpointing active genes in whole genomes, while chemistry advances different types of automation. Recent progress in matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) imaging could match miniaturized chemical synthesis with a powerful analytical tool to validate the outcome of many different synthesis pathways beyond applications in the life sciences. Thereby, due to the radical miniaturization of chemical synthesis, thousands of molecules can be synthesized. This in turn should allow ambitious research, e.g., finding novel synthesis routes or directly screening for photocatalysts. Herein, different technologies are discussed that might be involved in this endeavor. A special emphasis is given to the obstacles that need to be tackled when depositing tiny amounts of materials to many different extremely miniaturized reaction sites.

Combinatorial Peptide Microarray Synthesis Based on Microfluidic Impact Printing

In this Research Article, a novel inkjet printing technique, micro impact printing (MI printing), is applied for the first time to combinatorial peptide microarray synthesis on amine functionalized microdisc arrays through standard Fmoc chemistry. MI printing shows great advantages in combinatorial peptide microarray synthesis compared with other printing techniques, including (1) a disposable cartridge; (2) a small spot size (80 μm) increases array density; (3) minimal loading volume (0.6 μL) and dead volume (<0.1 μL), reduce chemical waste; and (4) multiplexibility of 5 channels/cartridge and capacity of multiple cartridges. Using this synthesis platform, a tetrapeptide library with 625 permutations was constructed and then applied for the screening of ligands targeting α₄β₁ integrin on Jurkat cells.

High-precision digital droplet pipetting enabled by a plug-and-play microfluidic pipetting chip

Emerging demands for handling minute liquid samples and reagents have been constantly growing in a wide variety of medical and biological areas. This calls for low-volume and high-precision liquid handling solutions with ease-of-use and portability. In this article, a new digital droplet pipetting method is introduced for the first time, derived from the microfluidic impact printing principle. Configured as a conventional handheld pipette, the prototype device consists of a plug-and-play and disposable microfluidic pipetting chip, driven by a programmable electromagnetic actuator for on-demand dispensing of nanoliter droplets. In particular, the impact-driven microfluidic pipetting chip, in place of the traditional disposable pipette tips, offers both liquid loading and droplet generation. The printing nozzle has been micro-fabricated using a femtosecond laser with a super-hydrophobic structure, in order to minimize the dispensing residues. As a result of the high-precision droplet dispensing principle, the variations of the dispensed volume have been successfully reduced from 49.5% to 0.6% at 0.1 μL, as compared to its commercial counterparts. A proof-of-concept study for concentration dilution and quantitative analysis of cell drug resistance has been carried out by using the digital droplet pipetting system, demonstrating its potential in a broad range of biomedical applications which require both high precision and low-volume processing.

Dotette: Programmable, high-precision, plug-and-play droplet pipetting

Manual micropipettes are the most heavily used liquid handling devices in biological and chemical laboratories; however, they suffer from low precision for volumes under 1 μl and inevitable human errors. For a manual device, the human errors introduced pose potential risks of failed experiments, inaccurate results, and financial costs. Meanwhile, low precision under 1 μl can cause severe quantification errors and high heterogeneity of outcomes, becoming a bottleneck of reaction miniaturization for quantitative research in biochemical labs. Here, we report Dotette, a programmable, plug-and-play microfluidic pipetting device based on nanoliter liquid printing. With automated control, protocols designed on computers can be directly downloaded into Dotette, enabling programmable operation processes. Utilizing continuous nanoliter droplet dispensing, the precision of the volume control has been successfully improved from traditional 20%-50% to less than 5% in the range of 100 nl to 1000 nl. Such a highly automated, plug-and-play add-on to existing pipetting devices not only improves precise quantification in low-volume liquid handling and reduces chemical consumptions but also facilitates and automates a variety of biochemical and biological operations.

Microfluidic Print-to-Synthesis Platform for Efficient Preparation and Screening of Combinatorial Peptide Microarrays

In this paper, we introduce a novel microfluidic combinatorial synthesis platform, referred to as Microfluidic Print-to-Synthesis (MPS), for custom high-throughput and automated synthesis of a large number of unique peptides in a microarray format. The MPS method utilizes standard Fmoc chemistry to link amino acids on a polyethylene glycol (PEG)-functionalized microdisc array. The resulting peptide microarrays permit rapid screening for interactions with molecular targets or live cells, with low nonspecific binding. Such combinatorial peptide microarrays can be reliably prepared at a spot size of 200 μm with 1 mm center-to-center distance, dimensions that require only minimal reagent consumption (less than 30 nL per spot per coupling reaction). The MPS platform has a scalable design for extended multiplexibility, allowing for 12 different building blocks and coupling reagents to be dispensed in one microfluidic cartridge in the current format, and could be further scaled up. As proof of concept for the MPS platform, we designed and constructed a focused tetrapeptide library featuring 2560 synthetic peptide sequences, capped at the N-terminus with 4-[( N'-2-methylphenyl)ureido]phenylacetic acid. We then used live human T lymphocyte Jurkat cells as a probe to screen the peptide microarrays for their interaction with α4β1 integrin overexpressed and activated on these cells. Unlike the one-bead-one-compound approach that requires subsequent decoding of positive beads, each spot in the MPS array is spatially addressable. Therefore, this platform is an ideal tool for rapid optimization of lead compounds found in nature or discovered from diverse combinatorial libraries, using either biochemical or cell-based assays.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Telemedical Wearable Sensing Platform for Management of Chronic Venous Disorder

Enabled by emerging wearable sensors, telemedicine can potentially offer personalized medical services to long-term home care or remote clinics in the future, which can be particularly helpful in the management of chronic diseases. The wireless wearable pressure sensing system reported in this article provides an excellent example of such an innovation, whereby periodic or continuous monitoring of interface pressure can be obtained to guide routine compression therapy, the cornerstone of chronic venous disorder management. By applying a novel capacitive, iontronic sensing technology, a flexible, ultrathin, and highly sensitive pressure sensing array is seamlessly incorporated into compression garments for the monitoring of interface pressure. The linear pressure sensing array assesses pressure distribution along the limb in a real-time manner (up to a scanning rate of 5 kHz), and the measurement data can be processed and displayed on a mobile device locally, as well as transmitted through a Bluetooth communication module to a remote clinical service. The proposed interface pressure measuring system provides real-time interface pressure distribution data and can be utilized for both clinical and self-management of compression therapy, where both treatment efficacy and quality assurance can be ascertained.

Piezoelectric-driven droplet impact printing with an interchangeable microfluidic cartridge

Microfluidic impact printing has been recently introduced, utilizing its nature of simple device architecture, low cost, non-contamination, and scalable multiplexability and high throughput. In this paper, we have introduced an impact-based droplet printing platform utilizing a simple plug-and-play microfluidic cartridge driven by piezoelectric actuators. Such a customizable printing system allows for ultrafine control of droplet volume from picoliters (∼23 pl) to nanoliters (∼10 nl), a 500 fold variation. The high flexibility of droplet generation can be simply achieved by controlling the magnitude of actuation (e.g., driving voltage) and the waveform shape of actuation pulses, in addition to nozzle size restrictions. Detailed printing characterizations on these parameters have been conducted consecutively. A multiplexed impact printing system has been prototyped and demonstrated to provide the functions of single-droplet jetting and droplet multiplexing as well as concentration gradient generation. Moreover, a generic biological assay has also been tested and validated on this printing platform. Therefore, the microfluidic droplet printing system could be of potential value to establish multiplexed micro reactors for high-throughput life science applications.

Microfluidic tactile sensors for three-dimensional contact force measurements

A microfluidic tactile sensing device has been first reported for three-dimensional contact force measurement utilizing the microfluidic interfacial capacitive sensing (MICS) principle. Consisting of common and differential microfluidic sensing elements and topologically micro-textured surfaces, the microfluidic sensing devices are intended not only to resolve normal mechanical loads but also to measure forces tangent to the surface upon contact. In response to normal or shear loads, the membrane surface deforms the underlying sensing elements uniformly or differentially. The corresponding variation in interfacial capacitance can be detected from each sensing unit, from which the direction and magnitude of the original load can be determined. Benefiting from the highly sensitive and adaptive MICS principle, the microfluidic sensor is capable of detecting normal forces with a device sensitivity of 29.8 nF N(-1) in a 7 mm × 7 mm × 0.52 mm package, which is at least a thousand times higher than its solid-state counterparts to our best knowledge. In addition, the microfluidic sensing elements enable facilitated relaxation response/time in the millisecond range (up to 12 ms). To demonstrate the utility and flexibility of the three-dimensional microfluidic sensor, it has been successfully configured into a fingertip-amounted setting for continuous tracing of the fingertip movement and contact force measurement.

Iontronic microdroplet array for flexible ultrasensitive tactile sensing

An iontronic microdroplet array (IMA) device, using an ultra-large interfacial capacitance at the highly elastic droplet-electrode contact, has been proposed for flexible tactile sensing applications. The transparent IMA sensors consist of an array of nanoliter droplets sandwiched between two polymeric membranes with patterned transparent electrodes, forming the electrical double layers with remarkable unit-area capacitance. Under external loading, the membrane deformation results in the circumferential expansion at the highly elastic droplet-electrode contact, which offers a completely new capacitive sensing scheme with a dramatic increase in sensitivity. Under the simple device architecture, the IMA has achieved device sensitivity of 0.43 nF kPa(-1) and a minimal detectable pressure of 33 Pa, the highest reported values for its dimension. In addition, the hysteresis of the droplet deformation has been reduced by introducing a layer of hydrophobic coating to the conductive electrode surface, ensuring a fast mechanical response (on the order of several milliseconds). To demonstrate the utility of the transparent flexible IMA sensor, it has been successfully mounted onto a fingertip setting to map different surface topologies and embedded into a wristband to resolve dynamic pressure waves throughout cardiovascular cycles.

Photopatternable and photoactive hydrogel for on-demand generation of hydrogen peroxide in cell culture

Oxidative stress, largely mediated by reactive oxygen species (ROS), is a nearly ubiquitous component in complex biological processes such as aging and disease. Optimal in vitro methods used in elucidating disease mechanisms would deliver of low levels of hydrogen peroxide, emulating the in vivo pathological state, but current methods are limited by kinetic stability or accurate measurement of the dose administered. Here we present an in vitro platform that exploits anthraquinone catalysts for the photocatalytic production of hydrogen peroxide. This system can be dynamically tuned to provide constant generation of hydrogen peroxide at a desired physiologic rate over at least 14 days and is described using a kinetic model. Material characterization and stability is discussed along with a proof-of-concept in vitro study that assessed the viability of cells as they were oxidatively challenged over 24 h at different ROS generation rates.