Stabilization and improved functionality of three-dimensional perfusable microvascular networks in microfluidic devices under macromolecular crowding

BACKGROUND

There is great interest to engineer in vitro models that allow the study of complex biological processes of the microvasculature with high spatiotemporal resolution. Microfluidic systems are currently used to engineer microvasculature in vitro, which consists of perfusable microvascular networks (MVNs). These are formed through spontaneous vasculogenesis and exhibit the closest resemblance to physiological microvasculature. Unfortunately, under standard culture conditions and in the absence of co-culture with auxiliary cells as well as protease inhibitors, pure MVNs suffer from a short-lived stability.

METHODS

Herein, we introduce a strategy for stabilization of MVNs through macromolecular crowding (MMC) based on a previously established mixture of Ficoll macromolecules. The biophysical principle of MMC is based on macromolecules occupying space, thus increasing the effective concentration of other components and thereby accelerating various biological processes, such as extracellular matrix deposition. We thus hypothesized that MMC will promote the accumulation of vascular ECM (basement membrane) components and lead to a stabilization of MVN with improved functionality.

RESULTS

MMC promoted the enrichment of cellular junctions and basement membrane components, while reducing cellular contractility. The resulting advantageous balance of adhesive forces over cellular tension resulted in a significant stabilization of MVNs over time, as well as improved vascular barrier function, closely resembling that of in vivo microvasculature.

CONCLUSION

Application of MMC to MVNs in microfluidic devices provides a reliable, flexible and versatile approach to stabilize engineered microvessels under simulated physiological conditions.

Development of nucleocapsid-specific monoclonal antibodies for SARS-CoV-2 and their ELISA diagnostics on an automatic microfluidic device

Coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has threatened public health globally, and the emergence of viral variants has exacerbated an already precarious situation. To prevent further spread of the virus and determine government action required for virus control, accurate and rapid immunoassays for SARS-CoV-2 diagnosis are urgently needed. In this study, we generated monoclonal antibodies (mAbs) against the SARS-CoV-2 nucleocapsid protein (NP), compared their reactivity using an enzyme-linked immunosorbent assay (ELISA), and selected four mAbs designated 1G6, 3E10, 3F10, and 5B6 which have higher reactivity to NP and viral lysates of SARS-CoV-2 than other mAbs. Using an epitope mapping assay, we identified that 1G6 detected the C-terminal domain of SARS-CoV-2 NP (residues 248-364), while 3E10 and 3F10 bound to the N-terminal domain (residues 47-174) and 3F10 detected the N-arm region (residues 1-46) of SARS-CoV-2 NP. Based on the epitope study and sandwich ELISA, we selected the 1G6 and 3E10 Abs as an optimal Ab pair and applied them for a microfluidics-based point-of-care (POC) ELISA assay to detect the NPs of SARS-CoV-2 and its variants. The integrated and automatic microfluidic system could operate the serial injection of the sample, the washing solution, the HRP-conjugate antibody, and the TMB substrate solution simply by controlling air purge via a single syringe. The proposed Ab pair-equipped microsystem effectively detected the NPs of SARS-CoV-2 variants as well as in clinical samples. Collectively, our proposed platform provides an advanced protein-based diagnostic tool for detecting SARS-CoV-2.

Development of in vitro cardiovascular tissue models within capillary circuit microfluidic devices fabricated with 3D Stereolithography printing

Human cardiovascular tissue and diseases are difficult to study for novel drug discovery and fundamental cellular/molecular processes due to limited availability of physiologically-relevant models in vitro.[1-3] Animal models may resemble human heart structure, however there are significant differences from human cardiovascular physiology including biochemical signaling, and gene expression.[4-6] In vitro microfluidic tissue models provide a less expensive, more controlled, and reproducible platform for better quantification of isolated cellular processes in response to biochemical or biophysical stimulus.[6-12] The capillary driven-flow microfluidic device in this study was manufactured with a 3D stereolithography (SLA) printed mold and is a closed circuit system operating on principles of capillary action allowing continuous fluid movement without external power supply. Human umbilical vein endothelial cells (HUVECs) and human cardiomyocytes (AC16) were encapsulated into a fibrin hydrogel to form vascular (VTM) and cardiac (CTM) tissue models respectively. To determine response to biophysical stimulus, the 3D cardiovascular tissue was directly loaded into the device tissue culture chambers that either had no microposts (DWoP) or microposts (DWPG) for 1, 3 and 5 days. The tissues were analyzed with fluorescent microscopy for morphological differences, average tube length, and cell orientation between tissues cultured in both conditions. In DWPG VTMs displayed capillary-like tube formation with visible cell alignment and orientation, while AC16s continued to elongate around microposts by day 5. VTM and CTM models in devices with posts (DWPG) displayed cell alignment and orientation after 5 days, indicated the microposts induced biophysical cues to guide cell structure and specific organization.

Design and fabrication of aspiration microfluidic channel for oocyte characterization

The development potential for oocytes can be predicted by their mechanical properties. One important parameter that is measured to calculate oocyte hardness is Cortical Tension (CT). In this work, for the first time, we present the design, simulation, and fabrication of a new aspiration microfluidic chip to measure the CT of oocytes and then predict their maturation capability in the Germinal Vesicle (GV) stage. This high-performance technique facilitates oocyte characterization and is a promising alternative to traditional methods such as MicroPipette Aspiration (MPA). The proposed technique involves considerably simpler operation, less specialized equipment, and less technical skill than MPA. The proposed microfluidic channel also promises faster measurements. It is shown that in order to completely continue the growth process of oocytes in GV stage, the CT should be in a certain range: very low or very high CTs lead to unsuccessful growth. The obtained results show that 79% of oocytes with the CT between 1.5 and 3 nN/μm reach the Metaphase II (MII) stage, whereas the growth for 78% of oocytes with the CT less than 1.5 nN/μm or higher than 3 nN/μm stops at the GV or Germinal Vesicle Break Down (GVBD) stages. Another property, k_vis, that points to the viscous behavior of oocytes is also measured. It is seen that 80% of GV oocytes with the k_vis values between 15 and 30 k Pa s/m reach the MII stage.

Ex-Vivo and In-Vivo Expansion of Spermatogonial Stem Cells Using Cell-Seeded Microfluidic Testis Scaffolds and Animal Model

AIMS

This study was designed to provide both ex-vivo and in-vivo methods for the extraction and expansion of spermatogonial stem cells (SSCs).

METHODS

For in-vivo experiments, azoospermic mouse model was performed with Busulfan. Isolation, culture, and characterization of neonate mouse SSC were also achieved. We performed an in-vivo injection of labeled SSCs to the testes with azoospermia. In ex-vivo experiments, extracted SSCs were seeded on the fabricated scaffold consisting of hyaluronic acid (HA) and decellularized testis tissues (DTT). Immunofluorescence staining with PLZF, TP1, and Tekt 1 was performed for SSCs differentiation and proliferation.

RESULTS

Several studies demonstrated efficient spermatogenic arrest in seminiferous tubules and proved the absence of spermatogenesis. Transplanted SSCs moved and settled in the basement covering the seminiferous tubules. Most of the cells were positive for Dil, after 4 weeks. An epithelium containing spermatogonia-like cells with Sertoli-like, and Leydig cells were evident in the seminiferous tubules of biopsies, and the IHC staining was significantly positive, 4 weeks after injection of SSCs. The results of the ex-vivo experiments showed positive staining for all markers, which was significantly enhanced in scaffolds of ex-vivo experiments compared with in-vitro seeded scaffolds.

CONCLUSION

Ex-vivo SSC differentiation and proliferation using cell-seeded microfluidic testis scaffolds maybe effective for treatment of the azoospermia.

The Applications and Challenges of the Development of In Vitro Tumor Microenvironment Chips

The tumor microenvironment (TME) plays a critical, yet mechanistically elusive role in tumor development and progression, as well as drug resistance. To better understand the pathophysiology of the complex TME, a reductionist approach has been employed to create in vitro microfluidic models called "tumor chips". Herein, we review the fabrication processes, applications, and limitations of the tumor chips currently under development for use in cancer research. Tumor chips afford capabilities for real-time observation, precise control of microenvironment factors (e.g. stromal and cellular components), and application of physiologically relevant fluid shear stresses and perturbations. Applications for tumor chips include drug screening and toxicity testing, assessment of drug delivery modalities, and studies of transport and interactions of immune cells and circulating tumor cells with primary tumor sites. The utility of tumor chips is currently limited by the ability to recapitulate the nuances of tumor physiology, including extracellular matrix composition and stiffness, heterogeneity of cellular components, hypoxic gradients, and inclusion of blood cells and the coagulome in the blood microenvironment. Overcoming these challenges and improving the physiological relevance of in vitro tumor models could provide powerful testing platforms in cancer research and decrease the need for animal and clinical studies.

Modulating and monitoring the functionality of corticostriatal circuits using an electrostimulable microfluidic device

The central nervous system is organized into different neural circuits, each with particular functions and properties. Studying neural circuits is essential to understanding brain function and neuronal diseases. Microfluidic systems are widely used for reconstructing and studying neural circuits but still need improvement to allow modulation and monitoring of the physiological properties of circuits. In this study, we constructed an improved microfluidic device that supports the electrical modulation of neural circuits and proper reassembly. We demonstrated that our microfluidic device provides a platform for electrically modulating and monitoring the physiological function of neural circuits with genetic indicators for synaptic functionality in corticostriatal (CStr) circuits. In particular, our microfluidic device measures activity-driven Ca²⁺ dynamics using Ca²⁺ indicators (synaptophysin-GCaMP6f and Fluo5F-AM), as well as activity-driven synaptic transmission and retrieval using vGlut-pHluorin. Overall, our findings indicate that the improved microfluidic platform described here is an invaluable tool for studying the physiological properties of specific neural circuits.

DNA Visualization Using Fluorescent Proteins

DNA binding fluorescent proteins are a powerful tool for single-molecule visualization. In this chapter, we discuss a protocol for the synthesis of DNA binding fluorescent proteins and visualization of single DNA molecules. This chapter includes stepwise methods for molecular cloning, reversible staining, two-color staining, sequence-specific staining, and microscopic visualization of single DNA molecules in a microfluidic device. This content will be useful for DNA characterization using DNA binding fluorescent proteins and its visualization at the single-molecule level.

Perfusion culture of endothelial cells under shear stress on microporous membrane in a pressure-driven microphysiological system

This paper reports perfusion culture of human umbilical vein endothelial cells (HUVECs) on a microporous membrane in a pressure-driven microphysiological system (PD-MPS), which we developed previously as a multi-throughput perfusion culture platform. We designed fluidic culture unit with microporous membrane to culture HUVECs under fluidic shear stress and constructed a perfusion culture model in the PD-MPS platform. Four fluidic culture units were arranged in the microplate-sized device, which enables four-throughput assay for characterization of HUVECs under flow. Medium flow was generated above and below the membrane by sequential pneumatic pressure to apply physiological shear stress to HUVECs. HUVECs exhibited aligned morphology to the direction of the flow with shear stress of 11.5-17.7 dyn/cm² under the flow condition, while they randomly aligned under static culture condition in a 6 well plate. We also observed 3.3- and 5.0-fold increase in the expression levels of the thrombomodulin and endothelial nitric oxide synthase mRNAs, respectively, under the flow condition in the PD-MPS compared to the static culture in 6 well plate. We also observed actin filament aligned to the direction of flow in HUVECs cultured under the flow condition.

Affinity-Based Microfluidics Combined with Atomic Force Microscopy for Isolation and Nanomechanical Characterization of Circulating Tumor Cells

In this chapter, we present the materials and methods required to isolate and characterize circulating tumor cells (CTCs) from blood samples of cancer patients based on our newly developed microfluidic technologies. In particular, the devices presented herein are designed to be compatible with at\omic force microscopy (AFM) for post-capture nanomechanical investigation of CTCs. Microfluidics is well-established as a technology for isolating CTCs from the whole blood of cancer patients, and AFM is a gold standard for quantitative biophysical analysis of cells. However, CTCs are very scarce in nature, and those captured using standard closed-channel microfluidic chips are typically inaccessible for AFM procedures. As a result, their nanomechanical properties largely remain unexplored. Thus, given limitations associated with current microfluidic designs, significant efforts are put toward bringing innovative designs for real time characterization of CTCs. In light of this constant endeavor, the scope of this chapter is to compile our recent efforts on two microfluidic technologies, namely, the AFM-Chip and the HB-MFP, which proved to be efficient in isolating CTCs through antibody-antigen interactions, and their subsequent characterization using AFM.

Electrochemical sensing of oxygen metabolism for a three-dimensional cultured model with biomimetic vascular flow

Microphysiological systems (MPSs) with three-dimensional (3D) cultured models have attracted considerable interest because of their potential to mimic human health and disease conditions. Recent MPSs have shown significant advancements in engineering perfusable vascular networks integrated with 3D culture models, realizing a more physiological environment in vitro; however, a sensing system that can monitor their activity under biomimetic vascular flow is lacking. We designed an open-top microfluidic device with sensor capabilities and demonstrated its application in analyzing oxygen metabolism in vascularized 3D tissue models. We first validated the platform by using human lung fibroblast (hLF) spheroids. Then, we applied the platform to a patient-derived cancer organoid and evaluated the changes in oxygen metabolism during drug administration through the vascular network. We found that the platform could integrate a perfusable vascular network with 3D cultured cells, and the electrochemical sensor could detect the change in oxygen metabolism in a quantitative, non-invasive, and real-time manner. This platform would become a monitoring system for 3D cultured cells integrated with a perfusable vascular network.

Self-homing nanocarriers for mRNA delivery to the activated hepatic stellate cells in liver fibrosis

Herein, we report on the development of a platform for the selective delivery of mRNA to the hard-to-transfect Activated Hepatic Stellate Cells (aHSCs), the fundamental player in the progression of liver fibrosis. Using a microfluidic device (iLiNP), we prepared a series of lipid nanoparticles (LNPs) based on a diverse library of pH-sensitive lipids. After an in-depth in vivo optimization of the LNPs, their mRNA delivery efficiency, selectivity, potency, robustness, and biosafety were confirmed. Furthermore, some mechanistic aspects of their selective delivery to aHSCs were investigated. We identified a promising lipid candidate, CL15A6, that has a high affinity to aHSCs. Tweaking the composition and physico-chemical properties of the LNPs enabled the robust and ligand-free mRNA delivery to aHSCs in vivo post intravenous administration, with a high biosafety at mRNA doses of up to 2 mg/Kg, upon either acute or chronic administrations. The mechanistic investigation suggested that CL15A6 LNPs were taken up by aHSCs via Clathrin-mediated endocytosis through the Platelet-derived growth factor receptor beta (PDGFRβ) and showed a pKa-dependent cellular uptake. The novel and scalable platform reported in this study is highly promising for clinical applications.

Development of experimental microfluidic device and methodology for assessing microrheological properties of blood

BACKGROUND AND OBJECTIVE

Microfluidics is a useful tool for investigating blood microrheology. The study aimed to present the development of a microfluidic device for assessing the microrheological properties of blood cells' suspensions and its application in patients with T2DM.

METHODS

A new microfluidic device was elaborated, connected to a system, including a microscope with a digital camera, a pump with a manometer and a computer with specially developed software. Blood cells' suspensions were investigated in a microchamber between two parallel optical slides within a 100μm distance. The motion of the blood cells in the microchamber was observed by the microscope and it was recorded and visualized by a digital camera. A method for evaluating the deformability of blood cells and a device for its implementation were used [1].

RESULTS

The pressure and flow rate ranges in the microfluidic device were specified by model suspensions of beta-ferroxy-hydroxide and red blood cells (RBC) suspensions. The pressure changes, realized by a pump (micropipette), connected to a manometer were established and the corresponding shear rates in the microfluidic device were determined. Data about the blood microrheological properties like RBC aggregation and deformability, leukocyte adhesion from a group of healthy volunteers and from patients with type 2 diabetes mellitus (T2DM) were obtained.

CONCLUSIONS

The developed device and experimental system is a promising tool for the study of blood microrheology.

Integration of RT-LAMP and Microfluidic Technology for Detection of SARS-CoV-2 in Wastewater as an Advanced Point-of-Care Platform

Development of lab-on-a-chip (LOC) system based on integration of reverse transcription loop-mediated isothermal amplification (RT-LAMP) and microfluidic technology is expected to speed up SARS-CoV-2 diagnostics allowing early intervention. In the current work, reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) and RT-LAMP assays were performed on extracted RNA of seven wastewater samples from COVID-19 hotspots. RT‑LAMP assay was also performed on wastewater samples without RNA extraction. Current detection of SARS-CoV-2 is mainly by RT-qPCR of ORF (ORF1ab) and N genes so we targeted both to find the best target gene for SARS-CoV-2 detection. We also performed RT-LAMP with/without RNA extraction inside microfluidic device to target both genes. Positivity rates of RT-qPCR and RT-LAMP performed on extracted RNA were 100.0% (7/7) and 85.7% (6/7), respectively. RT-qPCR results revealed that all 7 wastewater samples were positive for N gene (Ct range 37-39), and negative for ORF1ab, suggesting that N gene could be the best target gene for SARS-CoV-2 detection. RT-LAMP of N and ORF (ORF1a) genes performed on wastewater samples without RNA extraction indicated that all 7 samples remains pink (negative). The color remains pink in all microchannels except microchannels which subjected to RT-LAMP for targeting N region after RNA extraction (yellow color) in 6 out of 7 samples. This study shows that SARS-CoV-2 was successfully detected from wastewater samples using RT-LAMP in microfluidic chips. This study brings the novelty involving the use of wastewater samples for detection of SARS-CoV-2 without previous virus concentration and with/without RNA extraction.

Microfluidic devices as model platforms of CNS injury-ischemia to study axonal regeneration by regulating mitochondrial transport and bioenergetic metabolism

Central nervous system (CNS) neurons typically fail to regenerate their axons after injury leading to neurological impairment. Axonal regeneration is a highly energy-demanding cellular program that requires local mitochondria to supply most energy within injured axons. Recent emerging lines of evidence have started to reveal that injury-triggered acute mitochondrial damage and local energy crisis contribute to the intrinsic energetic restriction that accounts for axon regeneration failure in the CNS. Characterizing and reprogramming bioenergetic signaling and mitochondrial maintenance after axon injury-ischemia is fundamental for developing therapeutic strategies that can restore local energy metabolism and thus facilitate axon regeneration. Therefore, establishing reliable and reproducible neuronal model platforms is critical for assessing axonal energetic metabolism and regeneration capacity after injury-ischemia. In this focused methodology article, we discuss recent advances in applying cutting-edge microfluidic chamber devices in combination with state-of-the-art live-neuron imaging tools to monitor axonal regeneration, mitochondrial transport, bioenergetic metabolism, and local protein synthesis in response to injury-ischemic stress in mature CNS neurons.

Bridging the electrode-neuron gap: finite element modeling of in vitro neurotrophin gradients to optimize neuroelectronic interfaces in the inner ear

Although cochlear implant (CI) technology has allowed for the partial restoration of hearing over the last few decades, persistent challenges (e.g., poor performance in noisy environments and limited ability to decode intonation and music) remain. The "electrode-neuron gap" is inherent to these challenges and poses the most significant obstacle to advancing past the current plateau in CI performance. We propose the development of a "neuro-regenerative nexus"-a biological interface that doubly preserves native spiral ganglion neurons (SGNs) while precisely directing the growth of neurites arising from transplanted human pluripotent stem cell (hPSC)-derived otic neuronal progenitors (ONPs) toward the native SGN population. We hypothesized that the Polyhedrin Delivery System (PODS®-recombinant human brain-derived neurotrophic factor [rhBDNF]) could stably provide the adequate BDNF concentration gradient to hPSC-derived late-stage ONPs to facilitate otic neuronal differentiation and directional neurite outgrowth. To test this hypothesis, a finite element model (FEM) was constructed to simulate BDNF concentration profiles generated by PODS®-rhBDNF based on initial concentration and culture device geometry. For biological validation of the FEM, cell culture experiments assessing survival, differentiation, neurite growth direction, and synaptic connections were conducted using a multi-chamber microfluidic device. We were able to successfully generate the optimal BDNF concentration gradient to enable survival, neuronal differentiation toward SGNs, directed neurite extension of hPSC-derived SGNs, and synaptogenesis between two hPSC-derived SGN populations. This proof-of-concept study provides a step toward the next generation of CI technology. STATEMENT OF SIGNIFICANCE: Our study demonstrates that the generation of in vitro neurotrophin concentration gradients facilitates survival, neuronal differentiation toward auditory neurons, and directed neurite extension of human pluripotent stem cell-derived auditory neurons. These findings are indispensable to designing a bioactive cochlear implant, in which stem cell-derived neurons are integrated into a cochlear implant electrode strip, as the strategy will confer directional neurite growth from the transplanted cells in the inner ear. This study is the first to present the concept of a "neuro-regenerative nexus" congruent with a bioactive cochlear implant to eliminate the electrode-neuron gapthe most significant barrier to next-generation cochlear implant technology.

Early molecular responses of mangrove oysters to nanoplastics using a microfluidic device to mimic environmental exposure

This study assessed the effects of nanoplastics (NPs) using for the very first time microfluidic devices (chip) mimicking transition waters. Three kinds of NPs were tested: crushed NPs from polystyrene pellets (NP-PS), or from Guadeloupe beaches (NP-G); and latex PS (PSL-COOH). The eluted fractions from the microfluidic device showed a low aggregation of NPs. They remained stable over time in the exposure media, with a stabilization of NPs of small sizes (< 500 nm). These chips were thus used for the toxicological assessment of NPs on swamp oysters, Isognomon alatus. Oysters were exposed for 7 days to the chip elution fraction of either NP-G, NP-PS or PSL-COOH (0.34-333 µg.L^-1). Gene transcription analyses showed that the tested NPs triggered responses on genes involved in endocytosis, mitochondrial metabolism disruption, oxidative stress, DNA repair, and detoxification. Highest responses were observed after NP-G exposure at low concentrations (1 µg.L^-1), as they are originated from the natural environment and accumulated contaminants, enhancing toxicological effects. As salinity influences aggregation and then the bioavailability of NPs, our results demonstrated the importance of using microfluidic devices for ecotoxicological studies on swamp or estuarine species.

Perfusion culture of multi-layered HepG2 hepatocellular carcinoma cells in a pressure-driven microphysiological system

Here we report the perfusion culture of a multi-layered tissue composed of HepG2 cells (a human hepatoma line) in a pressure-driven microphysiological system (PD-MPS), which we developed previously as a multi-throughput perfusion culture platform. The perfusion culture of multi-layered tissue model was constructed by inserting a modified commercially available permeable membrane insert into the PD-MPS. HepG2 cells were layered on the membrane, and culture medium was perfused both through and below the membrane. The seeded density (number of cells/cm²) of the culture model is 70 times that of static culture in a conventional 35-mm culture dish. Pressure-driven circulation of the medium in our compact device (8.6 × 7.0 × 4.5 cm³), which comprised two perfusion-culture modules and a pneumatic connection port, enabled perfusion culture of two multi-layered tissues (initially 1 × 10⁵ cells). To obtain insight into the basic functionality of the multi-layered tissues as hepatocytes, we compared albumin production and urea synthesis between perfusion cultures and static cultures. The HepG2 cells grew and secreted increasing amounts of albumin throughout 20 days of perfusion culture, whereas albumin secretion did not increase under static culture conditions. In addition, on day 20, the amount of albumin secreted by the HepG2 cells in the microfluidic device was 68% of that in the conventional culture dish, which was seeded with the same number of cells but had a 70 times larger culture area. These features of high-density culture of functioning cells in a compact device support the application of PD-MPS in single- and multi-organ MPS.

Tumor-on-a-chip model for advancement of anti-cancer nano drug delivery system

Despite explosive growth in the development of nano-drug delivery systems (NDDS) targeting tumors in the last few decades, clinical translation rates are low owing to the lack of efficient models for evaluating and predicting responses. Microfluidics-based tumor-on-a-chip (TOC) systems provide a promising approach to address these challenges. The integrated engineered platforms can recapitulate complex in vivo tumor features at a microscale level, such as the tumor microenvironment, three-dimensional tissue structure, and dynamic culture conditions, thus improving the correlation between results derived from preclinical and clinical trials in evaluating anticancer nanomedicines. The specific focus of this review is to describe recent advances in TOCs for the evaluation of nanomedicine, categorized into six sections based on the drug delivery process: circulation behavior after infusion, endothelial and matrix barriers, tumor uptake, therapeutic efficacy, safety, and resistance. We also discuss current issues and future directions for an end-use perspective of TOCs.

On the size-regulation of RNA-loaded lipid nanoparticles synthesized by microfluidic device

The use of lipid nanoparticles (LNPs) for nucleic acid delivery is now becoming a promising strategy with a number of clinical trials as vaccines or as novel therapies against a variety of genetic and infectious diseases. The use of microfluidics for the synthesis of the LNPs has attracted interest because of its considerable advantages over other conventional synthetic methods including scalability, reproducibility, and speed. However, despite the potential usefulness of large particles for nucleic acid delivery to dendritic cells (DCs) as a vaccine, the particle size of the LNPs prepared using microfluidics is typically limited to approximately from 30 to 100 nm. In this study, focusing on Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, the effect of some synthetic parameters, including total flow rate, flow rate ratio, buffer pH, lipid concentration, molar ratio of PEG-lipid as well as salt concentration, on particle size was systematically examined by means of the design of experiment approaches. The findings indicated that the simple addition of salt (e.g. NaCl) to a buffer containing nucleic acids contributed greatly to the synthesis of large LNPs over 200 nm and this effect was concentration-dependent with respect to the salt. The effect of salt on particle size was consistent with a Hofmeister series. The systemic injection of larger mRNA-loaded LNPs resulted in a higher transgene expression in mouse splenic DCs, a higher activation of various splenic immune cells, and had a superior effect as a therapeutic cancer vaccine in a syngeneic mouse model compared to the smaller-sized counterpart with constant lipid composition prepared with lower NaCl concentration. Collectively, size-regulation by the simple addition of salt is a promising strategy for developing potent LNPs.

A real-time monitoring system for automatic morphology analysis of yeast cultivation in a jar fermenter

The monitoring of microbial cultivation in real time and controlling their cultivation aid in increasing the production yield of useful material in a jar fermenter. Common sensors such as dissolved oxygen (DO) and pH can easily provide general-purpose indexes but do not reveal the physiological states of microbes because of the complexity of measuring them in culture conditions. It is well known from microscopic observations that the microbial morphology changes in response to the intracellular state or extracellular environment. Recently, studies have focused on rapid and quantitative image analysis techniques using machine learning or deep learning for gleaning insights into the morphological, physiological or gene expression information in microbes. During image analysis, it is necessary to retrieve high-definition images to analyze the microbial morphology in detail. In this study, we have developed a microfluidic device with a high-speed camera for the microscopic observation of yeast, and have constructed a system capable of generating their morphological information in real-time and at high definition. This system was connected to a jar fermenter, which enabled the automatic sampling for monitoring the cultivation. We successfully acquired high-definition images of over 10,000 yeast cells in about 2.2 s during ethanol fermentation automatically for over 168 h. We recorded 33,600 captures containing over 1,680,000 cell images. By analyzing these images, the morphological changes of yeast cells through ethanol fermentation could be captured, suggesting the expansion of the application of this system in controlling microbial fermentation using the morphological information generated. KEY POINTS: • Enables real-time visualization of microbes in a jar fermenter using microscopy. • Microfluidic device for acquiring high-definition images. • Generates a large amount of image data by using a high-speed camera.

Microfluidic chips as a method for sperm selection improve fertilization rate in couples with fertilization failure

PURPOSE

Sperm quality plays a vital role in successful fertilization and pregnancy. Patients with fertilization failure (total failure or low-fertilization rate) despite having normal semen parameters are a challenging group whose sperm cannot fertilize the oocyte via the intracytoplasmic sperm injection (ICSI) technique. Microfluidics is offered as a new method for proper sperm sorting.

METHODS

This study aimed to evaluate sperm parameters, DNA fragmentation index (DFI), expression of phospholipase C zeta 1 (PLCZ1), and transition nuclear proteins 1 (TNP1) mRNAs in sperm selected by microfluidic sperm sorting (MSS) chip compared with conventional density gradient centrifugation technique in patients with fertilization failure following ICSI. Subsequence fertilization rate and embryo quality were assayed.

RESULTS

Normal morphology and total motility were significantly higher, and DFI was significantly lower in sperm selected by the MSS chip in fertilization failure and control groups. The RT-PCR results demonstrated a significant increase in the expression of PLCZ1 and TNP1 genes in sperm of both groups selected by MSS chips compared to the DGC method. In addition, with the selected sperm by MSS chip, an increase in fertilization rate and improvement of embryo quality was obtained.

CONCLUSION

The present study findings show that sperm sorting by the microfluidic method improves fertilization rate in patients with poor fertilization outcomes following ICSI.

Generation of transmitochondrial cybrids using a microfluidic device

Mitochondrial cloning is a promising approach to achieve homoplasmic mitochondrial DNA (mtDNA) mutations. We previously developed a microfluidic device that performs single mitochondrion transfer from a mtDNA-intact cell to a mtDNA-less (ρ⁰) cell by promoting cytoplasmic connection through a microtunnel between them. In the present study, we described a method for generating transmitochondrial cybrids using the microfluidic device. After achieving mitochondrial transfer between HeLa cells and thymidine kinase-deficient ρ⁰143B cells using the microfluidic device, selective culture was carried out using a pyruvate and uridine (PU)-absent and 5-bromo-2'-deoxyuridine-supplemented culture medium. The resulting cells contained HeLa mtDNA and 143B nuclei, but both 143B mtDNA and HeLa nuclei were absent in these cells. Additionally, these cells showed lower lactate production than parent ρ⁰143B cells and disappearance of PU auxotrophy for cell growth. These results suggest successful generation of transmitochondrial cybrids using the microfluidic device. Furthermore, we succeeded in selective harvest of generated transmitochondrial cybrids under a PU-supplemented condition by removing unfused ρ⁰ cells with puromycin-based selection in the microfluidic device.

A micro-channel array in a tissue engineered vessel graft guides vascular morphogenesis for anastomosis with self-assembled vascular networks

Vascularization of 3D engineered tissues poses a great challenge in the field of tissue engineering. One promising approach for vascularizing engineered tissue is cocultivation with endothelial cells (ECs), which spontaneously self-assemble into a natural capillary network in the presence of supportive cells. However, the ECs do not self-assemble according to physiological hierarchy which is required to support blood supply. This work describes the design and fabrication of an AngioTube, a biodegradable engineered macro-vessel surrounded by cylindrical micro-channel array, which is designed to support physiological flow distribution and enable the integration with living capillaries. The well-defined geometry of the engineered micro-channels guides endothelial cells to form patent micro-vessels which sprouted in accordance with the channel orientation. Three different in-vitro models were used to demonstrate anastomosis of these engineered micro-vessels with self-assembled vascular networks. Finally, in-vivo functionality was demonstrated by direct anastomosis with the femoral artery in a rat hindlimb model. This unique approach proposes a new micro-fabrication strategy which introduces uncompromised micro-fluidic device geometrical accuracy at the tissue-scale level. STATEMENT OF SIGNIFICANCE: This study proposes a micro-fabrication strategy suitable for processing real-scale cylindrical implants with very high accuracy, which will enable translation of the high-resolution geometry of micro-fluidic devices to clinically relevant implants containing functional multi-scale vascular networks. Moreover, this approach promises to advance the field of tissue engineering by opening new opportunities to explore the impact of well controlled and uncompromised 3D micro-geometry on cellular behavior.

Microfluidic one-directional interstitial flow generation from cancer to cancer associated fibroblast

Tumors, unlike normal tissue, have vascular anomalies and create interstitial flow (IF), which allows soluble substances from cancer cells to be transported directionally toward the tumor stroma. In the stroma, IF activates fibroblasts. Cancer-associated fibroblasts (CAFs) are formed from stimulated cells and aid cancer growth. A microfluidic device was designed to generate a one-directional flow of a small volume mimicking IF from donor cells to recipient at steady-state conditions only based on the medium evaporation from reservoirs with different diameter. The IF carried substances from donor cells, which stimulated the activation of fibroblasts on the receiving side, as well as their migration and stellate formation. Matrix metallopeptidases 9 and 14 as well as CAF markers such as fibroblast activation protein alpha, vimentin, and alpha-smooth muscle actin are abundantly expressed in the migrating fibroblasts. The created platform mimicked one-directional delivery in tumor stroma. This will allow researchers to investigate how cancer cells activate and differentiate stromal cells. STATEMENT OF SIGNIFICANCE: We show how to provide continuous one-directional interstitial flow (IF) in a microfluidic device without using any power source and instrumentation. This microfluidic technology was used to simulate the tumor microenvironment. Fibroblasts in the tumor stroma are activated and migrated toward cancer cells, as recapitulated by co-culture of cancer cells as donor and fibroblasts as recipient under the one-directional IF. We believe that soluble substances from cancerous cells delivered by the one-directional IF efficiently regulated the development of cancer-associated fibroblasts (CAFs),  as shown by increasing roundness and decreased circularity, taking on a stellate morphology, and by enhanced invasion into a type I collagen hydrogel. Migrating fibroblasts into the hydrogel had significant levels of MMP-9, MMP-14, FAP, vimentin, and αSMA, all of which are CAF markers, bearing a capacity to form hot stroma affecting tumor malignancy.