Microfluidic and cross-linking methods for encapsulation of living cells and bacteria - A review

Recent trends in nanocellulose: Metabolism-related, gastrointestinal effects, and applications in probiotic delivery

Nanocellulose, a versatile and sustainable nanomaterial derived from cellulose fibers, has attracted considerable attention in various fields due to its unique properties. Similar to dietary fibers, nanocellulose is difficult to digest in the human gastrointestinal tract. The indigestible nanocellulose is fermented by gut microbiota, producing metabolites and potentially exhibiting prebiotic activity in intestinal diseases. Additionally, nanocellulose can serve as a matrix material for probiotic protection and show promising prospects for probiotic delivery. In this review, we summarize the classification of nanocellulose, including cellulose nanocrystals (CNC), cellulose nanofibers (CNF), and bacterial nanocellulose (BNC), highlighting their distinct characteristics and applications. We discuss the metabolism-related characteristics of nanocellulose from oral ingestion to colon fermentation and introduce the prebiotic activity of nanocellulose in intestinal diseases. Furthermore, we provide an overview of commonly used nanocellulose-based encapsulation techniques, such as emulsification, extrusion, freeze drying, and spray drying, as well as the delivery systems employing nanocellulose matrix materials, including microcapsules, emulsions, and hydrogels. Finally, we discuss the challenges associated with nanocellulose metabolism, prebiotic functionality, encapsulation techniques, and delivery systems using nanocellulose matrix material for probiotics. This review will provide new insight into the application of nanocellulose in the treatment of intestinal diseases and probiotic delivery.

Droplet Microfluidic Method for Estimating the Dynamic Interfacial Tension of Ion-Crosslinked Sodium Alginate Microspheres

The research focuses on optimizing the production of hydrogel microspheres using droplet microfluidics for pharmaceutical and bioengineering applications. A semiempirical method has been developed to predict the dynamic interfacial tension at the interface of ion-cross-linked sodium alginate microsphere-sunflower oil modified with glacial acetic acid and Tween 80 surfactant. These microspheres are produced in a small-scale coaxial device that is manufactured using affordable DLP/LCD 3D printing technology with a transparent photopolymer. The method was tested to design the minireactor in the device, which allows for the production of fully cross-linked microspheres that are ready for use at the output of the reactor without additional cross-linking steps in the microsphere collector. The mathematical expression for estimating the interfacial tension at the moment of formation of a hydrogel microsphere includes the Reynolds number for a two-phase liquid, the Ohnesorge number, and the surface tension at the liquid-air interface for continuous medium flow (modified oil). The reliability of the prediction is confirmed for continuous medium and dispersed phase flow rates of 0.8-3.2 and 0.01-0.08 mL/min, respectively. The evolution of the interfacial tension from the moment the microspheres formed and the estimated ultimate interfacial tension in a cross-linked hydrogel-modified oil system contributed to the reliable determination of the linear size of a minireactor. The ultimate interfacial tension of 76.5 ± 0.3 mN/m was determined using the Young-Laplace equation, which is based on measuring the surface free energy of the hydrogel as soft matter using the Owens-Wendt method. Additionally, the equilibrium static contact angle of the fully cross-linked hydrogel surface wetted with oil is measured using the sessile drop method. From a practical perspective, a method for optimizing and streamlining the high-tech manufacturing of cross-linked polymer microspheres and mini- and microchannel devices for use in bioengineering and pharmaceutical applications is suggested.

The use of droplet-based microfluidic technologies for accelerated selection of Yarrowia lipolytica and Phaffia rhodozyma yeast mutants

Microorganisms are widely used for the industrial production of various valuable products, such as pharmaceuticals, food and beverages, biofuels, enzymes, amino acids, vaccines, etc. Research is constantly carried out to improve their properties, mainly to increase their productivity and efficiency and reduce the cost of the processes. The selection of microorganisms with improved qualities takes a lot of time and resources (both human and material); therefore, this process itself needs optimization. In the last two decades, microfluidics technology appeared in bioengineering, which allows for manipulating small particles (from tens of microns to nanometre scale) in the flow of liquid in microchannels. The technology is based on small-volume objects (microdroplets from nano to femtolitres), which are manipulated using a microchip. The chip is made of an optically transparent inert to liquid medium material and contains a series of channels of small size (<1 mm) of certain geometry. Based on the physical and chemical properties of microparticles (like size, weight, optical density, dielectric constant, etc.), they are separated using microsensors. The idea of accelerated selection of microorganisms is the application of microfluidic technologies to separate mutants with improved qualities after mutagenesis. This article discusses the possible application and practical implementation of microfluidic separation of mutants, including yeasts like Yarrowia lipolytica and Phaffia rhodozyma after chemical mutagenesis will be discussed.

High-throughput bacterial co-encapsulation in microfluidic gel beads for discovery of antibiotic-producing strains

Bacteria with antagonistic activity inhibit the growth of other bacteria through different mechanisms, including the production of antibiotics. As a result, these microorganisms are a prolific source of such compounds. However, searching for antibiotic-producing strains requires high-throughput techniques due to the vast diversity of microorganisms. Here, we screened and isolated bacteria with antagonistic activity against Escherichia coli expressing the green fluorescent protein (E. coli-GFP). We used microfluidics to co-encapsulate and co-culture single cells from different strains within picoliter gel beads and analyzed them using fluorescence-activated cell sorting (FACS). To test the methodology, we used three bacterial isolates obtained from Mexican maize, which exhibit high, moderate, or no antagonistic activity against E. coli-GFP, as determined previously using agar plate assays. Single cells from each strain were separately co-incubated into gel beads with E. coli-GFP. We monitored the development of the maize bacteria microcolonies and tracked the growth or inhibition of E. coli-GFP using bright-field and fluorescent microscopy. We correlated these images with distinctive light scatter and fluorescence signatures of each incubated bead type using FACS. This analysis enabled us to sort gel beads filled with an antagonistic strain, starting from a mixture of the three different types of maize bacteria and E. coli-GFP. Likewise, culturing the FACS-sorted beads on agar plates confirmed the isolation and recovery of the two antagonistic strains. In addition, enrichment assays demonstrated the methodology's effectiveness in isolating rare antibiotic-producer strains (0.01% abundance) present in a mixture of microorganisms. These results show that associating light side scatter and fluorescent flow cytometry signals with microscopy images provides valuable controls to establish successful high-throughput methods for sorting beads in which microbial interaction assays are performed.

Organic functional substance engineered living materials for biomedical applications

Modifying living materials with organic functional substances (OFS) is a convenient and effective strategy to control and monitor the transport, engraftment, and secretion processes in living organisms. OFSs, including small organic molecules and organic polymers, own the merit of design flexibility, satisfying performance, and excellent biocompatibility, which allow for living materials functionalization to realize real-time sensing, controlled drug release, enhanced biocompatibility, accurate diagnosis, and precise treatment. In this review, we discuss the different principles of OFS modification on living materials and demonstrate the applications of engineered living materials in health monitoring, drug delivery, wound healing, and tissue regeneration.

Nanoparticle-Decorated Biomimetic Extracellular Matrix for Cell Nanoencapsulation and Regulation

Cell encapsulation has been studied for various applications ranging from cell transplantation to biological production. However, current encapsulation technologies focus on cell protection rather than cell regulation that is essential to most if not all cell-based applications. Here we report a method for cell nanoencapsulation and regulation using an ultrathin biomimetic extracellular matrix as a cell nanocapsule to carry nanoparticles (CN2 ). This method allows high-capacity nanoparticle retention at the vicinity of cell surfaces. The encapsulated cells maintain high viability and normal metabolism. When gold nanoparticles (AuNPs) are used as a model to decorate the nanocapsule, light irradiation transiently increases the temperature, leading to the activation of the heat shock protein 70 (HSP70) promoter and the regulation of reporter gene expression. As the biomimetic nanocapsule can be decorated with any or multiple NPs, CN2 is a promising platform for advancing cell-based applications.

Microfluidics: Insights into Intestinal Microorganisms

Microfluidics is a system involving the treatment or manipulation of microscale (10^-9 to 10^-18 L) fluids using microchannels (10 to 100 μm) contained on a microfluidic chip. Among the different methodologies used to study intestinal microorganisms, new methods based on microfluidic technology have been receiving increasing attention in recent years. The intestinal tracts of animals are populated by a vast array of microorganisms that have been established to play diverse functional roles beneficial to host physiology. This review is the first comprehensive coverage of the application of microfluidics technology in intestinal microbial research. In this review, we present a brief history of microfluidics technology and describe its applications in gut microbiome research, with a specific emphasis on the microfluidic technology-based intestine-on-a-chip, and also discuss the advantages and application prospects of microfluidic drug delivery systems in intestinal microbial research.

Electrospinning Living Bacteria: A Review of Applications from Agriculture to Health Care

Living bacteria are used in biotechnologies that lead to improvements in health care, agriculture, and energy. Encapsulating bacteria into flexible and modular electrospun polymer fabrics that maintain their viability will further enable their use. This review will first provide a brief overview of electrospinning before examining the impact of electrospinning parameters, such as precursor composition, applied voltage, and environment on the viability of encapsulated bacteria. Currently, the use of nanofiber scaffolds to deliver live probiotics into the gut is the most researched application space; however, several additional applications, including skin probiotics (wound bandages) and menstruation products have also been explored and will be discussed. The use of bacteria-loaded nanofibers as seed coatings that promote plant growth, for the remediation of contaminated wastewaters, and in energy-generating microbial fuel cells are also covered in this review. In summary, electrospinning is an effective method for encapsulating living microorganisms into dry polymer nanofibers. While these living composite scaffolds hold potential for use across many applications, before their use in commercial products can be realized, numerous challenges and further investigations remain.

Engineered Living Materials For Sustainability

Recent advances in synthetic biology and materials science have given rise to a new form of materials, namely engineered living materials (ELMs), which are composed of living matter or cell communities embedded in self-regenerating matrices of their own or artificial scaffolds. Like natural materials such as bone, wood, and skin, ELMs, which possess the functional capabilities of living organisms, can grow, self-organize, and self-repair when needed. They also spontaneously perform programmed biological functions upon sensing external cues. Currently, ELMs show promise for green energy production, bioremediation, disease treatment, and fabricating advanced smart materials. This review first introduces the dynamic features of natural living systems and their potential for developing novel materials. We then summarize the recent research progress on living materials and emerging design strategies from both synthetic biology and materials science perspectives. Finally, we discuss the positive impacts of living materials on promoting sustainability and key future research directions.

Microfabrication of a micron-scale microbial-domestication pod for in situ cultivation of marine bacteria

Through the hyphenation of microfabrication, microfluidics and microbiology, we report the development of a μMicrobial-Domestication Pod (μMD Pod). This in situ cultivation device facilitates cell signaling from neighbouring species and interactions with environmental stimuli for marine bacterial growth to overcome current barriers faced by standard laboratory cultivation methods.

64-channel label-free fluorescence detection and single-particle counting device

A 64-channel detection system for laser-induced fluorescence (LIF) detection at the cell level is established and applied to single event counting. Generally, fluorescence detection at the cellular level requires a dyeing label to enhance the scattered light intensity for the photodetector. However, the dyeing labels, such as fluorophores, probes, and dyes, complicate sample preparation and increase cytotoxicity in the process. Therefore, label-free detection becomes essential for in vivo research. The presented 64-channel detection system is designed for label-free detection with the ability to record feeble emissions. Two linear photodetector devices are included in the system, extending the wavelength detection range to 366-680 nm with an improved spectral resolution at an average of 4.9 nm. The performance of the system was validated by detecting unlabeled human hepatocytes (L-02) and other cell-level biologic samples. In addition, the 64-channel detection system was also used for particle counting with a quartz microfluidic chip. The counting method is based on fluorescence spectra differs from those of other devices (i.e., flow cytometry and cell-sorting equipment), which use isolated irradiance intensities.

Microfluidic droplet-based functional materials for cell manipulation

Functional materials from the microfluidic-based droplet community are emerging as enabling tools for various applications in tissue engineering and cell biology. The innovative micro- and nano-scale materials with diverse sizes, shapes and components can be fabricated without the use of complicated devices, allowing unprecedented control over the cells that interact with them. Here, we review the current development of microfluidic-based droplet techniques for creation of functional materials (i.e., liquid droplet, microcapsule, and microparticle). We also describe their various applications for manipulating cell fate and function.

Polysaccharide-Based Hydrogels for Microencapsulation of Stem Cells in Regenerative Medicine

Stem cell-based therapy appears as a promising strategy to induce regeneration of damaged and diseased tissues. However, low survival, poor engraftment and a lack of site-specificity are major drawbacks. Polysaccharide hydrogels can address these issues and offer several advantages as cell delivery vehicles. They have become very popular due to their unique properties such as high-water content, biocompatibility, biodegradability and flexibility. Polysaccharide polymers can be physically or chemically crosslinked to construct biomimetic hydrogels. Their resemblance to living tissues mimics the native three-dimensional extracellular matrix and supports stem cell survival, proliferation and differentiation. Given the intricate nature of communication between hydrogels and stem cells, understanding their interaction is crucial. Cells are incorporated with polysaccharide hydrogels using various microencapsulation techniques, allowing generation of more relevant models and further enhancement of stem cell therapies. This paper provides a comprehensive review of human stem cells and polysaccharide hydrogels most used in regenerative medicine. The recent and advanced stem cell microencapsulation techniques, which include extrusion, emulsion, lithography, microfluidics, superhydrophobic surfaces and bioprinting, are described. This review also discusses current progress in clinical translation of stem-cell encapsulated polysaccharide hydrogels for cell delivery and disease modeling (drug testing and discovery) with focuses on musculoskeletal, nervous, cardiac and cancerous tissues.

How Microgels Can Improve the Impact of Organ-on-Chip and Microfluidic Devices for 3D Culture: Compartmentalization, Single Cell Encapsulation and Control on Cell Fate

The Organ-on-chip (OOC) devices represent the new frontier in biomedical research to produce micro-organoids and tissues for drug testing and regenerative medicine. The development of such miniaturized models requires the 3D culture of multiple cell types in a highly controlled microenvironment, opening new challenges in reproducing the extracellular matrix (ECM) experienced by cells in vivo. In this regard, cell-laden microgels (CLMs) represent a promising tool for 3D cell culturing and on-chip generation of micro-organs. The engineering of hydrogel matrix with properly balanced biochemical and biophysical cues enables the formation of tunable 3D cellular microenvironments and long-term in vitro cultures. This focused review provides an overview of the most recent applications of CLMs in microfluidic devices for organoids formation, highlighting microgels' roles in OOC development as well as insights into future research.

Preparation of Anisotropic Micro-Hydrogels with Tunable Structural and Topographic Features by Compound Interfacial Shearing

We propose a compound interfacial shearing (CIS) process for versatile production of monodisperse Janus emulsions with controllable structural and topographic features. The process induces an active periodic force to decouple material and process parameters, enables independent control of compartmental features in Janus emulsions, and facilitates inline and on-demand generation of various geometric features for a large variety of process parameters and material properties. Janus emulsions of poly(ethylene glycol) diacrylate (PEGDA) with a controlled number of compartments are produced by CIS and photopolymerized to form micro-hydrogels with designated interfacial curvatures. PEGDA micro-hydrogels can be further modified to achieve anisotropy of surface or internal features by the content of an oily dispersed phase. MCF-7 human breast cancer cells are encapsulated in micro-hydrogels for cell proliferation with satisfactory viability. By modifying PEGDA micro-hydrogels with RGDS-conjugated polystyrene microspheres, we have demonstrated the controlled spatial adhesion of MCF-7 cells and human umbilical vein endothelial cells (HUVECs) on the substrates of different three-dimensional (3D) curvatures. Our pilot study suggests a simple and potentially scalable approach to produce 3D substrates with controllable structural and topographic features for 3D guided cell organization.

Microfluidics-based generation of cell encapsulated microbeads in the presence of electric fields and spatio-temporal viability studies

Microfluidics based techniques for generation of cell-laden microbeads are emerging as an attractive route to 3D cell encapsulation due to the precise control provided by microfluidics. However, existing microfluidics based cell encapsulation methods are restricted to 2D planar devices and use of passive methods for droplet generation. In this work, we report the development of a 3D glass-PDMS (polydimethylsiloxane) hybrid device for complete on-chip generation of cell-laden alginate beads in the presence of electric fields. The 3D hybrid device allows application of electric fields for active control of droplet (sodium alginate) size without the need for electrode patterning or liquid electrodes. Chemical gelation is achieved through on-chip coalescence of sodium alginate droplets and calcium chloride plugs, generated using coflow and T-junction geometries respectively. Using this approach, we successfully encapsulate E. coli cells (with viability ∼90 %) into alginate microbeads and perform comprehensive spatio-temporal growth and viability studies. The active control of droplet size coupled with complete on-chip gelation demonstrated here is a promising technology for cell encapsulation with applications such as cell therapy, organ repair, biocatalysis, and microbial fuel cells.

Segmented Microfluidics-Based Packing Technology for Chromatographic Columns

Nanoflow liquid chromatography-mass spectrometry (NanoLC-MS) has become the method of choice for the analysis of complex biological systems, especially when the available sample amount is limited. The preparation of high-performance capillary columns for nanoLC use is still a technical challenge. Here, we report a segmented microfluidic method for the preparation of packed capillary columns, where liquid segments were used as soft, dynamic, and well-dispersed slurry reservoirs for carrying and delivering micrometer packing particles. Based on this microfluidic packing technology, the column bed was assembled layer-by-layer at a 50 μm resolution, and ultralong capillary columns of 3, 5, and 10 m were fabricated in such a manner. The microfluidically packed columns demonstrated excellent separation efficiencies of 116 000 plates/m. The higher efficiencies obtained at higher slurry concentrations also indicate that a high-quality packed bed can be obtained without sacrificing the packing speed. Kinetic performance limit analysis shows that the microfluidic packed columns have higher peak capacity production efficiency in the high-resolution region, presenting an improved separation impedance of 2800, which is significantly better than columns packed with the conventional slurry packing method. In comparison with a commercial nanoLC column, a 5 m long microfluidic packed column was evaluated for proteomic analysis using a standard HeLa protein digest and presented 261% improvement in peptide identification capability, resulting in significantly enhanced protein identification confidence.

Stimuli-responsive engineered living materials

Stimuli-responsive materials are able to undergo controllable changes in materials properties in response to external cues. Increasing efforts have been directed towards building materials that mimic the responsive nature of biological systems. Nevertheless, limitations remain surrounding the way these synthetic materials interact and respond to their environment. In particular, it is difficult to synthesize synthetic materials that respond with specificity to poorly differentiated (bio)chemical and weak physical stimuli. The emerging area of engineered living materials (ELMs) includes composites that combine living cells and synthetic materials. ELMs have yielded promising advances in the creation of stimuli-responsive materials that respond with diverse outputs in response to a broad array of biochemical and physical stimuli. This review describes advances made in the genetic engineering of the living component and the processing-property relationships of stimuli-responsive ELMs. Finally, the implementation of stimuli-responsive ELMs as environmental sensors, biomedical sensors, drug delivery vehicles, and soft robots is discussed.

Development of a microbe domestication pod (MD Pod) for in situ cultivation of micro-encapsulated marine bacteria

Microbial marine natural products hold significant potential for the discovery of new bioactive therapeutics such as antibiotics. Unfortunately, this discovery is hindered by the inability to culture the majority of microbes using traditional laboratory approaches. While many new methods have been developed to increase cultivability, a high-throughput in situ incubation chamber capable of simultaneously isolating individual microbes while allowing cellular communication has not previously been reported. Development of such a device would expedite the discovery of new microbial taxa and, thus, facilitate access to their associated natural products. In this study, this concept is achieved by the development of a new device termed by the authors as the microbe domestication (MD) Pod. The MD Pod enables single-cell cultivation by isolating marine bacterial cells in agarose microbeads produced using microfluidics, while allowing potential transmission of chemical signals between cells during in situ incubation in a chamber, or "Pod," that is deployed in the environment. The design of the MD Pod was optimized to ensure the use of biocompatible materials, allow for simple assembly in a field setting, and maintain sterility throughout incubation. The encapsulation process was designed to ensure that the viability of marine sediment bacteria was not adversely impacted by the encapsulation process. The process was validated using representative bacteria isolated from temperate marine sediment samples: Marinomonas polaris, Psychrobacter aquimaris, and Bacillus licheniformis. The overall process appeared to promote metabolic activity of most representative species. Thus, microfluidic encapsulation of marine bacteria and subsequent in situ incubation in the MD Pod is expected to accelerate marine natural products discovery by increasing the cultivability of marine bacteria.

Enhanced single-cell encapsulation in microfluidic devices: From droplet generation to single-cell analysis

Single-cell analysis to investigate cellular heterogeneity and cell-to-cell interactions is a crucial compartment to answer key questions in important biological mechanisms. Droplet-based microfluidics appears to be the ideal platform for such a purpose because the compartmentalization of single cells into microdroplets offers unique advantages of enhancing assay sensitivity, protecting cells against external stresses, allowing versatile and precise manipulations over tested samples, and providing a stable microenvironment for long-term cell proliferation and observation. The present Review aims to give a preliminary guidance for researchers from different backgrounds to explore the field of single-cell encapsulation and analysis. A comprehensive and introductory overview of the droplet formation mechanism, fabrication methods of microchips, and a myriad of passive and active encapsulation techniques to enhance single-cell encapsulation efficiency were presented. Meanwhile, common methods for single-cell analysis, especially for long-term cell proliferation, differentiation, and observation inside microcapsules, are briefly introduced. Finally, the major challenges faced in the field are illustrated, and potential prospects for future work are discussed.

Picoliter agar droplet breakup in microfluidics meets microbiology application: numerical and experimental approaches

Droplet microfluidics has provided lab-on-a-chip platforms with the capability of bacteria encapsulation in biomaterials, controlled culture environments, and live monitoring of growth and proliferation. The droplets are mainly generated from biomaterials with temperature dependent gelation behavior which necessitates stable and size-controlled droplet formation within microfluidics. Here, the biomaterial is agar hydrogel with a non-Newtonian response at operating temperatures below 40 °C, the upper-temperature threshold for cells and pathogens. The size of the produced droplets and the formation regimes are examined when the agar is injected at a constant temperature of 37 °C with agar concentrations of 0.5%, 1%, and 2% and different flow rate ratios of the dispersed phase to the continuous phase (φ: 0.1 to 1). The numerical simulations show that φ and the capillary number (Ca) are the key parameters controlling the agar droplet size and formation regime, from dripping to jetting. Also, increasing the agar concentration produces smaller droplets. The simulation data were validated against experimental agar droplet generation and transport in microfluidics. This work helps to understand the physics of droplet generation in droplet microfluidic systems operating with non-Newtonian fluids. Pathogenic bacteria were successfully cultured and monitored in high resolution in agar droplets for further research in antibiotic susceptibility testing in bacteremia and urinary tract infection.

The Construction and Application of Three-Dimensional Biomaterials

Biomaterials have been widely explored and applied in many areas, especially in the field of tissue engineering. The interface of biomaterials and cells has been deeply investigated. However, it has been demonstrated that conventional 2D biomaterials fail to maintain the 3D structures and phenotypes of cells, which is the result of their limited ability to mimic the latter's complex extracellular matrix. To overcome this challenge, cell cultivation dependent on 3D biomaterials has emerged as an alternative strategy to make the recovery of 3D structures and functions of cells possible. Thus, with the thriving development of 3D cell culture in tissue engineering, a holistic review of the construction and application of 3D biomaterials is desired. Here, recent developments in 3D biomaterials for tissue engineering are reviewed. An overview of various approaches to construct 3D biomaterials, such as electro-jetting/-spinning, micro-molding, microfluidics, and 3D bio-printing, is first presented. Their typical applications in constructing cell sheets, vascular structures, cell spheroids, and macroscopic cellular constructs are described as well. Following these two sections, the current status and challenges are analyzed, as well as the future outlook of 3D biomaterials for tissue engineering.

Tissue Engineering and Regenerative Medicine: Achievements, Future, and Sustainability in Asia

Exploring innovative solutions to improve the healthcare of the aging and diseased population continues to be a global challenge. Among a number of strategies toward this goal, tissue engineering and regenerative medicine (TERM) has gradually evolved into a promising approach to meet future needs of patients. TERM has recently received increasing attention in Asia, as evidenced by the markedly increased number of researchers, publications, clinical trials, and translational products. This review aims to give a brief overview of TERM development in Asia over the last decade by highlighting some of the important advances in this field and featuring major achievements of representative research groups. The development of novel biomaterials and enabling technologies, identification of new cell sources, and applications of TERM in various tissues are briefly introduced. Finally, the achievement of TERM in Asia, including important publications, representative discoveries, clinical trials, and examples of commercial products will be introduced. Discussion on current limitations and future directions in this hot topic will also be provided.

micrIO: an open-source autosampler and fraction collector for automated microfluidic input-output

Microfluidic devices are an enabling technology for many labs, facilitating a wide range of applications spanning high-throughput encapsulation, molecular separations, and long-term cell culture. In many cases, however, their utility is limited by a 'world-to-chip' barrier that makes it difficult to serially interface samples with these devices. As a result, many researchers are forced to rely on low-throughput, manual approaches for managing device input and output (IO) of samples, reagents, and effluent. Here, we present a hardware-software platform for automated microfluidic IO (micrIO). The platform, which is uniquely compatible with positive-pressure microfluidics, comprises an 'AutoSipper' for input and a 'Fraction Collector' for output. To facilitate widespread adoption, both are open-source builds constructed from components that are readily purchased online or fabricated from included design files. The software control library, written in Python, allows the platform to be integrated with existing experimental setups and to coordinate IO with other functions such as valve actuation and assay imaging. We demonstrate these capabilities by coupling both the AutoSipper and Fraction Collector to two microfluidic devices: a simple, valved inlet manifold and a microfluidic droplet generator that produces beads with distinct spectral codes. Analysis of the collected materials in each case establishes the ability of the platform to draw from and output to specific wells of multiwell plates with negligible cross-contamination between samples.

Chitosan Microbeads Produced by One-Step Scalable Stirred Emulsification: A Promising Process for Cell Therapy Applications

Cell microencapsulation is a promising approach to improve cell therapy outcomes by protecting injected cells from rapid dispersion and allowing bidirectional diffusion of nutrients, oxygen, and waste that promote cell survival in the target tissues. Here, we describe a simple and scalable emulsification method to encapsulate animal cells in chitosan microbeads using thermosensitive gel formulations without any chemical modification and cross-linker. The process consists of a water-in-oil emulsion where the aqueous phase droplets contain cells (L929 fibroblasts or human mesenchymal stromal cells), chitosan acidic solution and gelling agents (sodium hydrogen carbonate and phosphate buffer or beta-glycerophosphate). The oil temperature is maintained at 37 °C, allowing rapid physical gelation of the microbeads. Alginate beads prepared with the same method were used as a control. Microbeads with a diameter of 300-450 μm were successfully produced. Chitosan and alginate (2% w/v) microbeads presented similar rigidity in compression, but chitosan microbeads endured >80% strain without rupture, while alginate microbeads presented fragile breakage at <50% strain. High cell viability and metabolic activity were observed after up to 7 days in culture for encapsulated cells. Mesenchymal stromal cells encapsulated in chitosan microbeads released higher amounts of the vascular endothelial growth factor after 24 h compared to the cells encapsulated in manually cast macrogels. Moreover, microbeads were injectable through 23G needles without significant deformation or rupture. The emulsion-generated chitosan microbeads are a promising delivery vehicle for therapeutic cells because of their cytocompatibility, biodegradation, mechanical strength, and injectability. Clinical-scale encapsulation of therapeutic cells such as mesenchymal stromal cells in chitosan microbeads can readily be achieved using this simple and scalable emulsion-based process.

Geometry Effects of Axisymmetric Flow-Focusing Microchannels for Single Cell Encapsulation

Cell microencapsulation is a promising technique to protect living cells in biomedical applications. Microfluidic devices can be utilized to control the production of high-throughput cell-laden droplets. This paper demonstrates the effects of flow-focusing geometry on the droplet size, frequency of droplet generation, and number of cells per droplet. Orifice radius, orifice length, and nozzle-to-orifice distance can significantly influence the flow-field and manipulate droplet formation. This paper analyzes these geometry effects using a numerical front-tracking method for the three fluid phases. It is found that as the orifice radius increases, the drop size and the number of cells in the droplet increase. For a short orifice radius, increasing the orifice length results in the generation of smaller droplets at higher frequency and fewer cells per droplet. On the other hand, for a longer orifice, droplet production is invariant with respect to orifice length. It is also found that shorter distances between the nozzle and the orifice lead to a more controlled and uniform production of droplets. When the nozzle-to-orifice length is increased, the droplet formation becomes non-uniform and unpredictable. Probability charts are plotted with respect to the orifice length and orifice radius, which show that a greater than 50 % probability of single cell encapsulation can be achieved consistently.