A microfluidic platform for continuous monitoring of dopamine homeostasis in dopaminergic cells

Localized ultrasonic stimulation using a piezoelectric micromachined ultrasound transducer array for selective neural differentiation of magnetic cell-based robots

Targeted stem cell delivery utilizing a magnetic actuation system is an emerging technology in stem cell engineering that efficiently targets stem cells in specific areas in vitro. However, integrating precise magnetic control systems with selective neural differentiation has not yet been widely considered for building successful neural networks. Challenges arise in creating targeted functional neuronal networks, largely due to difficulties in simultaneously controlling the positions of stem cells and selectively stimulating their differentiation. These challenges often result in suboptimal differentiation rates and abnormalities in transplanted neural stem cells. In contrast, ultrasound stimulation has superior tissue penetration and focusing capability, and represents a promising noninvasive neural stimulation technique capable of modulating neural activity and promoting selective differentiation into neuronal stem cells. In this study, we introduce a method for targeted neural differentiation using localized ultrasonic stimulation with a piezoelectric micromachined ultrasound transducer (pMUT) array. Differentiation was assessed quantitatively by monitoring neurite outgrowth as the ultrasound intensity was increased. The neurite length of cells ultrasonically stimulated for 40 min was found to have increased, compared to the non-stimulated group (119.9 ± 34.3 μm vs. 63.2 ± 17.3 μm, respectively). Targeted differentiation was confirmed by measuring neurite lengths, where selective ultrasound stimulation induced differentiation in cells that were precisely delivered via an electromagnetic system. Magnetic cell-based robots reaching the area of localized ultrasound stimulation were confirmed to have enhanced differentiation. This research demonstrated the potential of the combination of precise stem cell delivery with selective neural differentiation to establish functional neural networks.

Profiling signaling mediators for cell-cell interactions and communications with microfluidics-based single-cell analysis tools

Cell-cell interactions and communication represent the fundamental cornerstone of cells' collaborative efforts in executing diverse biological processes. A profound understanding of how cells interface through various mediators is pivotal across a spectrum of biological systems. Recent strides in microfluidic technologies have significantly bolstered the precision and prowess in capturing and manipulating cells with exceptional spatial and temporal resolution. These advanced methodologies converge with multi-signal mediator detection systems, furnishing potent, high-throughput platforms for dissecting cell-cell interactions at the single-cell level. This approach empowers researchers to delve into intricate cellular dynamics with unprecedented accuracy and efficiency. Here, we present a critical evaluation of the latest advancements in microfluidics-driven techniques for detecting signal mediators involved in cell-cell interactions and communication at the single-cell level. We underscore notable biological applications that have benefited from these technologies and identify pressing challenges that must be addressed in future endeavors leveraging microfluidic tools for single-cell interaction studies.

Brain-on-a-chip: an emerging platform for studying the nanotechnology-biology interface for neurodegenerative disorders

Neurological disorders have for a long time been a global challenge dismissed by drug companies, especially due to the low efficiency of most therapeutic compounds to cross the brain capillary wall, that forms the blood-brain barrier (BBB) and reach the brain. This has boosted an incessant search for novel carriers and methodologies to drive these compounds throughout the BBB. However, it remains a challenge to artificially mimic the physiology and function of the human BBB, allowing a reliable, reproducible and throughput screening of these rapidly growing technologies and nanoformulations (NFs). To surpass these challenges, brain-on-a-chip (BoC) - advanced microphysiological platforms that emulate key features of the brain composition and functionality, with the potential to emulate pathophysiological signatures of neurological disorders, are emerging as a microfluidic tool to screen new brain-targeting drugs, investigate neuropathogenesis and reach personalized medicine. In this review, the advance of BoC as a bioengineered screening tool of new brain-targeting drugs and NFs, enabling to decipher the intricate nanotechnology-biology interface is discussed. Firstly, the main challenges to model the brain are outlined, then, examples of BoC platforms to recapitulate the neurodegenerative diseases and screen NFs are summarized, emphasizing the current most promising nanotechnological-based drug delivery strategies and lastly, the integration of high-throughput screening biosensing systems as possible cutting-edge technologies for an end-use perspective is discussed as future perspective.

In Situ Live Monitoring of Extracellular Acidosis near Cancer Cells Using Digital Microfluidics with an Integrated Optical pH Sensor Film

We demonstrate the live monitoring of extracellular acidification on digital microfluidics using a chip-integrated fluorescent pH sensor film. The metabolism of various types of live cells including cancer and healthy cells were investigated through recording the extracellular pH (pHe) change. An optical pH sensor array was integrated onto a digital microfluidic (DMF) interface with a diameter of 2 mm per pH-sensing spot. Miniaturized, label-free, and noninvasive monitoring of extracellular acidosis on DMF was realized within a pH range of 5.0-8.0 with good sensitivity and rapid response. The pH sensitive probe fluorescein-5-isothiocyanate was covalently bound to poly-2-hydroxyethyl methacrylate and immobilized on a circularly exposed indium tin oxide interface on the DMF top plate. The surface of the fabricated pH sensor spots was modified with polydopamine via self-polymerization. Direct cell attachment on the sensor surfaces enabled rapid pH detection near the cell membranes. Automatic medium exchange on cell-attached pH sensing sites was achieved though solution passive dispensing on DMF. The developed DMF platform was used to monitor the pHe decrease during MCF-7 and A549 cancer cell proliferation due to abnormal glycolysis metabolism. A rapid pH decrease at the pH sensing area in the presence of cancer cells could be detected within 2 min after fresh medium exchange, while no obvious pHe change was observed with HUVEC healthy cells. Real-time detection of cell acidification and cellular response to different metabolic conditions such as higher glucose levels or administered anticancer drugs was possible.

Standardizing designed and emergent quantitative features in microphysiological systems

Microphysiological systems (MPSs) are cellular models that replicate aspects of organ and tissue functions in vitro. In contrast with conventional cell cultures, MPSs often provide physiological mechanical cues to cells, include fluid flow and can be interlinked (hence, they are often referred to as microfluidic tissue chips or organs-on-chips). Here, by means of examples of MPSs of the vascular system, intestine, brain and heart, we advocate for the development of standards that allow for comparisons of quantitative physiological features in MPSs and humans. Such standards should ensure that the in vivo relevance and predictive value of MPSs can be properly assessed as fit-for-purpose in specific applications, such as the assessment of drug toxicity, the identification of therapeutics or the understanding of human physiology or disease. Specifically, we distinguish designed features, which can be controlled via the design of the MPS, from emergent features, which describe cellular function, and propose methods for improving MPSs with readouts and sensors for the quantitative monitoring of complex physiology towards enabling wider end-user adoption and regulatory acceptance.

Biosensors integrated 3D organoid/organ-on-a-chip system: A real-time biomechanical, biophysical, and biochemical monitoring and characterization

As a full-fidelity simulation of human cells, tissues, organs, and even systems at the microscopic scale, Organ-on-a-Chip (OOC) has significant ethical advantages and development potential compared to animal experiments. The need for the design of new drug high-throughput screening platforms and the mechanistic study of human tissues/organs under pathological conditions, the evolving advances in 3D cell biology and engineering, etc., have promoted the updating of technologies in this field, such as the iteration of chip materials and 3D printing, which in turn facilitate the connection of complex multi-organs-on-chips for simulation and the further development of technology-composite new drug high-throughput screening platforms. As the most critical part of organ-on-a-chip design and practical application, verifying the success of organ model modeling, i.e., evaluating various biochemical and physical parameters in OOC devices, is crucial. Therefore, this paper provides a logical and comprehensive review and discussion of the advances in organ-on-a-chip detection and evaluation technologies from a broad perspective, covering the directions of tissue engineering scaffolds, microenvironment, single/multi-organ function, and stimulus-based evaluation, and provides a more comprehensive review of the progress in the significant organ-on-a-chip research areas in the physiological state.

A Microfluidic System for Investigating Anticipatory Medication Effects on Dopamine Homeostasis in Dopaminergic Cells

Dopamine (DA) homeostasis influences emotions, neural circuit development, cognition, and the reward system. Dysfunctions in DA regulation can lead to neurological disorders, including depression, developmental disorders, and addiction. DA homeostasis disruption is a primary cause of Parkinson's Disease (PD). Therefore, understanding the relationship between DA homeostasis and PD progression may clarify the mechanisms for pharmacologically treating PD. This study developed a novel in vitro DA homeostasis platform which consists of three main parts: (1) a microfluidic device for culturing DAergic neurons, (2) an optical detection system for reading DA levels, and (3) an automatic closed-loop control system that establishes when and how much medication to infuse; this uses a microfluidic device that can cultivate DAergic neurons, perfuse solutions, perform in vitro PD modeling, and continuously monitor DA concentrations. The automatically controlled closed-loop control system simultaneously monitors pharmacological PD treatment to support long-term monitoring of DA homeostasis. SH-SY5Y neuroblastoma cells were chosen as DAergic neurons. They were cultivated in the microfluidic device, and real-time cellular DA level measurements successfully achieved long-term monitoring and modulation of DA homeostasis. When applied in combination with multiday cell culture, this advanced system can be used for drug screening and fundamental biological studies.

Combining sensors and actuators with electrowetting-on-dielectric (EWOD): advanced digital microfluidic systems for biomedical applications

The concept of digital microfluidics (DMF) enables highly flexible and precise droplet manipulation at a picoliter scale, making DMF a promising approach to realize integrated, miniaturized "lab-on-a-chip" (LOC) systems for research and clinical purposes. Owing to its simplicity and effectiveness, electrowetting-on-dielectric (EWOD) is one of the most commonly studied and applied effects to implement DMF. However, complex biomedical assays usually require more sophisticated sample handling and detection capabilities than basic EWOD manipulation. Alternatively, combined systems integrating EWOD actuators and other fluidic handling techniques are essential for bringing DMF into practical use. In this paper, we briefly review the main approaches for the integration/combination of EWOD with other microfluidic manipulation methods or additional external fields for specified biomedical applications. The form of integration ranges from independently operating sub-systems to fully coupled hybrid actuators. The corresponding biomedical applications of these works are also summarized to illustrate the significance of these innovative combination attempts.

Direct loading of blood for plasma separation and diagnostic assays on a digital microfluidic device

Finger-stick blood sampling is convenient for point of care diagnostics, but whole blood samples are problematic for many assays because of severe matrix effects associated with blood cells and cell debris. We introduce a new digital microfluidic (DMF) diagnostic platform with integrated porous membranes for blood-plasma separation from finger-stick blood volumes, capable of performing complex, multi-step, diagnostic assays. Importantly, the samples can be directly loaded onto the device by a finger "dab" for user-friendly operation. We characterize the platform by comparison to plasma generated via the "gold standard" centrifugation technique, and demonstrate a 21-step rubella virus (RV) IgG immunoassay yielding a detection limit of 1.9 IU mL-1, below the diagnostic cut-off. We propose that this work represents a critical next step in DMF based portable diagnostic assays-allowing the analysis of whole blood samples without pre-processing.