Calcium alginate elastic capsules with a core-shell structure are versatile spherical solid beads that can be produced in large quantities using various techniques. This type of capsule is a promising platform for cell culture applications, owing to its mechanical elasticity and transparency. This paper reports the production of calcium alginate capsules with high consistency, and for the first time, demonstrates the feasibility of the capsules for microalgal cultivation. Cell growth analysis reveals that the vibrationally-shaken calcium alginate elastic capsule platform yielded a higher maximum cell number (4.86 × 108 cells per mL) during the cultivation period than the control solution platforms. Aquafeed and food supplements for humans are the targeted applications of this novel platform.
We report the fabrication and characterisation of magnetic liquid beads with a solid magnetic shell and liquid core using microfluidic techniques. The liquid beads consist of a fluorinated oil core and a polymer shell with magnetite particles. The beads are generated in a flow-focusing polydimethylsiloxane (PDMS) device and cured by photo polymerisation. We investigated the response of the liquid beads to an external magnetic field by characterising their motion towards a permanent magnet. Magnetic sorting of liquid beads in a channel was achieved with 90% efficiency. The results show that the liquid beads can be controlled magnetically and have potential applications in digital microfluidics including nucleic acid amplification, drug delivery, cell culture, sensing, and tissue engineering. The present paper also discusses the magnetophoretic behaviour of the liquid bead by varying its mass and magnetite concentration in the shell. We also demonstrated the two-dimensional self-assembly of magnetic liquid beads for potential use in digital polymerase chain reaction and digital loop mediated isothermal amplification.
Dimethylpolysiloxanes , Dimethylpolysiloxanes/chemistry , Microfluidic Analytical Techniques/instrumentation , Magnetic Fields , Microspheres
Effective immunotherapies activate natural antitumor immune responses in patients undergoing treatment. The ability to monitor immune activation in response to immunotherapy is critical in measuring treatment efficacy over time and across patient cohorts. Protein arrays are systematically arranged, large collections of annotated proteins on planar surfaces, which can be used for the characterization of disease-specific and treatment-induced antibody repertoires in individuals undergoing immunotherapy. However, the absence of appropriate image analysis and data processing software presents a substantial hurdle, limiting the uptake of this approach in immunotherapy research. We developed a first, automated semiquantitative open-source software package for the analysis of widely used protein macroarrays. The software allows accurate single array and inter-array comparative studies through the tackling of intra-array inconsistencies arising from experimental disparities. The innovative and automated image analysis process includes adaptive positioning, background identification and subtraction, removal of null signals, robust statistical analysis, and protein pair validation. The normalized values allow a convenient semiquantitative data analysis of different samples or timepoints. Enabling accurate characterization of sample series to identify disease-specific immune profiles or their relative changes in response to treatment may serve as a diagnostic or predictive tool of disease.
Droplet-based microfluidics and digital polymerase chain reaction (PCR) hold significant promise for accurately detecting and quantifying pathogens. However, existing droplet-based digital PCR (ddPCR) applications have been relying exclusively on single emulsion droplets. Single emulsion droplets may not be suitable for applications such as identifying the source and pathways of water contamination where the templates must be protected against harsh environmental conditions. In this study, we developed a core-shell particle to serve as a protective framework for DNAs, with potential applications in digital PCR. We employed a high-throughput and facile flow-focusing microfluidic device to generate liquid beads, core-shell particles with liquid cores, which provided precise control over process parameters and consequently particle characteristics. Notably, the interfacial interaction between the core and shell liquids could be adjusted without adding surfactants to either phase. As maintaining stability is essential for ensuring the accuracy of digital PCR (dPCR), we investigated parameters that affect the stability of core-shell droplets, including surfactants in the continuous phase and core density. As a proof of concept, we encapsulated a series of human faecal DNA samples in the core-shell droplets and the subsequent liquid beads. The core-shell particles ensure contamination-free encapsulation of DNA in the core. The volume of the core droplets containing the PCR mixture is only 0.12 nL. Our experimental results indicate that the liquid beads formulated using our technique can amplify the encapsulated DNA and be used for digital PCR without interfering with the fluorescence signal. We successfully demonstrated the ability to detect and quantify DNA under varying concentrations. These findings provide new insights and a step change in digital PCR that could benefit various applications, including the detection and tracking of environmental pollution.
DNA , Microfluidics , Humans , Emulsions , Polymerase Chain Reaction/methods , DNA/genetics , Lab-On-A-Chip Devices
Digital droplet reactors have become a valuable tool for the analysis of single cells, organisms, or molecules by discretising reagents into picolitre or nanolitre volumes. However, DNA-based assays typically require processing of samples on the scale of tens of microlitres, with the detection of as few as one or as many as a hundred thousand fragments. Through the present work, we introduce a flow-focusing microfluidic device that produces 120 picolitre core-shell beads, which are assembled into a monolayer in a Petri dish for visualization and analysis. The bead assembly is subjected to polymerase chain reaction (PCR) amplification and fluorescence detection to digitally quantify the DNA concentration of the sample. We use a low-cost 21-megapixel digital camera and macro lens to capture wide-field fluorescence images with a 10-30 mm2 field-of-view at magnifications ranging from 5× to 2.5×. A customised Python script analysed the acquired images. Our study demonstrates the ability to perform digital PCR analysis of the entire bead assembly through end-point imaging and compare the results with those obtained through RT-qPCR.
Polymerase Chain Reaction , DNA/analysis , DNA/genetics , Polymerase Chain Reaction/economics , Polymerase Chain Reaction/methods
Micro elastofluidics is an emerging research field that encompasses characteristics of conventional microfluidics and fluid-structure interactions. Micro elastofluidics is expected to enable practical applications, for instance, where direct contact between biological samples and fluid handling systems is required. Besides design optimization, choosing a proper material is critical to the practical use of micro elastofluidics upon interaction with biological interface and after its functional lifetime. Biodegradable polymers are one of the most studied materials for this purpose. Micro elastofluidic devices made of biodegradable polymers possess exceptional mechanical elasticity, excellent bio compatibility, and structural degradability into non-toxic products. This article provides an insightful and systematic review of the utilization of biodegradable polymers in digital and continuous-flow micro elastofluidics.
Core-shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core-shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core-shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core-shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core-shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail.
We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions.
Liquid marbles are gaining increased attention because of their added advantages such as low evaporation rates, less friction, and ease of manipulation over the pristine liquid drop. Their functionalities could be further enhanced by incorporating different types of particles (size, hydrophobicity, chemical properties, etc.), commonly called Janus liquid marbles (JLMs). However, their fabrication process remains a challenge, especially when we require continuous production. Here, we present a simple and fast approach for the fabrication of JLMs covered with nano- and microparticles in an additive-free environment based on the controlled impact of a water drop over the particle beds. The fabrication process involves collection of polyvinylidene difluoride particles (PVDF, particle type 1) by a water drop followed by its impact over an uncompressed bed of black toner particles (BTP, particle type 2). The whole process takes a time of approximately 30 ms only. The drop impact and the condition of the JLM formation were explained based on the Weber number (We) and maximum spread (ßm) analysis. A theoretical model based on the energy balance analysis is performed to calculate the maximum spreading (ßm), and the experimental and theoretical analyses are found to be in good agreement. Tunability in particle coverage is demonstrated by varying the droplet volume in the range of 5-15 µL. We further extend this strategy for the fast and continuous production of nearly identical JLMs, which could enhance the capabilities of open-surface microfluidic applications.
Extensive research is being devoted to both the fundamental and applied aspects of liquid marbles (LMs). However, influence of the surface tension of the liquid substrate on the stability of the LMs and LM-mediated capillary interaction remains unexplored. In this work, we unveil the role of the surface tension of the liquid substrate on the collapse of multilayered LMs and apply this knowledge for realizing a dense planar assembly of microparticles triggered by LM-mediated capillary interactions. Experiments and analysis show that the required surface tension for the collapse is dependent on the volume of the LMs. The larger LMs are less stable, and thus collapse at a higher surface tension than that required for smaller LMs. The results are explained on the basis of the balance between surface tension forces acting on the LM ( Fs) and its weight ( Fw). Force analysis reveals that the collapse of the LM on the liquid substrate occurs when the surface tension force approaches to its weight, that is, when Fs ≈ Fw. This has been verified for LMs having volume in the range 6-10 µL. The experiments with different surfactants (an anionic and a cationic) lead to similar results which indicate that the collapse condition of the LMs is mainly dependent on their weight and the surface tension of the liquid substrate. Further, we demonstrate the LM-mediated assembly of particles at the liquid surface, and interestingly, the LM can be collapsed once the assembly is completed, leading to a denser well-packed assembled structure. We believe that the presented results could provide new insights in the fields of microfluidics, particle patterning, and assembly.
