Sequential storage and release of microdroplets

A novel method of droplet generation based on the self-propelling of water phase and its potential application in multiplexing continuous flow PCR

Despite the benefits of microfluidic continuous flow PCR (CF-PCR) such as simplified thermal management and expedited heat transfer, challenge remains in processing multiple targets by CF-PCR, particularly regarding spatial multiplexing. The segregation of the target sample into droplets as isolated reactors is an effective method for achieving spatial multiplexing. Nevertheless, conventional techniques for droplet generation necessitate the management of both oil and water phases, thereby augmenting the complexity of channel design and device operation, particularly when parallel channels were needed for manipulating multiple targets. This study presented an innovative technique for droplet formation employing the self-propelling of the aqueous phase through the principles of Laplace pressure and utilizing a time order of fluid loading instead of simultaneous management of fluids. As a result, only a singular type of fluid was necessary for manipulation at one time, thereby streamlining chip design, device configuration, and operations. Spatial multiplexing droplets were generated by multiple microstructures with both functions of the segmentation of the sample target solution and droplet generation. In this study, four types of droplets generated from restoring the preloaded specific primers by target solution with PCR mix completed CF-PCR amplification via the serpentine channel in 10 min. Utilizing the idea of self-propelling of the aqueous phase, this study demonstrated an alternative method for droplet generation and significant promise for a simple way to achieve spatial multiplexing in CF-PCR when detecting multiple targets.

Aggregation of α-synuclein splice isoforms through a phase separation pathway

The aggregation of α-synuclein (αSyn) is associated with Parkinson's disease and other related synucleinopathies. Considerable efforts have thus been directed at understanding this process. However, the recently discovered condensation pathway, which involves the formation of phase-separated liquid intermediate states, has added further complexity. In parallel, it has been reported that different αSyn splice isoforms may be implicated in aggregate formation in disease. In this study, we compare the phase behavior of four αSyn isoforms (αSyn-140, αSyn-126, αSyn-112, and αSyn-98). Using different biophysical tools including confocal microscopy, kinetic assays and microfluidic-based approaches, we find stark differences between the four systems in their propensities to undergo phase separation and aggregation. Furthermore, we show that even small amounts of αSyn-112, one of the predominant isoforms after αSyn-140, can affect the phase separation of αSyn-140. These results highlight the importance of conducting further investigations to elucidate the role of alternative splicing in synucleinopathies.

Aggregation of the amyloid-β peptide (Aβ40) within condensates generated through liquid-liquid phase separation

The deposition of the amyloid-β (Aβ) peptide into amyloid fibrils is a hallmark of Alzheimer's disease. Recently, it has been reported that some proteins can aggregate and form amyloids through an intermediate pathway involving a liquid-like condensed phase. These observations prompted us to investigate the phase space of Aβ. We thus explored the ability of Aβ to undergo liquid-liquid phase separation, and the subsequent liquid-to-solid transition that takes place within the resulting condensates. Through the use of microfluidic approaches, we observed that the 40-residue form of Αβ (Αβ40) can undergo liquid-liquid phase separation, and that accessing a liquid-like intermediate state enables Αβ40 to self-assemble and aggregate into amyloid fibrils through this pathway. These results prompt further studies to investigate the possible role of Αβ liquid-liquid phase separation and its subsequent aggregation in the context of Alzheimer's disease and more generally on neurodegenerative processes.

Inverse Phase Transition in Droplet Clusters Levitating over the Locally Heated Water Layer

Self-assembled microdroplet clusters can levitate above a locally heated water surface. Normally, the temperature of droplets is in the range of 50-95 °C. However, it is possible to generate clusters at lower temperatures. Here, we study the structure and behavior of such cold-stabilized droplet clusters with variable temperature. It has been established that as the temperature decreases, the role of aerodynamic forces decreases, while electrostatic forces, on the contrary, increase. We studied the behavior of droplet clusters at relatively low temperatures down to 28 °C. A chaotic motion of droplets and a phase transition were observed at the surface temperature of the water below a critical value of about Tmax = 35 ± 2 °C. The orderliness of the cluster was quantified with the Shannon/Voronoi entropy. Several stages of cluster evolution were observed and analyzed, and a mechanism of this phenomenon is discussed. An inverse phase transition in which cooling of the cluster decreases its orderliness is discussed. Frequencies of the droplets' oscillations coincide qualitatively with the frequency of the plasma oscillations within the cluster.

Inversion of Stabilized Large Droplet Clusters

We investigate the spontaneous rearrangement of microdroplets in a self-assembled droplet cluster levitating over a thin locally heated water layer. The center-to-periphery droplet diameter ratio (the "inversion coefficient") controls the onset of the inversion. Larger droplets can squeeze between smaller ones due to increased drag force on them from the air-vapor flow. In smaller clusters, the rotation of the droplets plays an important role since larger droplets rotating with the same angular velocity (dependent on the rotor of the airflow field) have higher viscous friction force with the liquid layer. It is desirable to avoid cluster inversion in experiments where individual droplet positions should be traced.

Pharmacological inhibition of α-synuclein aggregation within liquid condensates

Aggregated forms of α-synuclein constitute the major component of Lewy bodies, the proteinaceous aggregates characteristic of Parkinson's disease. Emerging evidence suggests that α-synuclein aggregation may occur within liquid condensates formed through phase separation. This mechanism of aggregation creates new challenges and opportunities for drug discovery for Parkinson's disease, which is otherwise still incurable. Here we show that the condensation-driven aggregation pathway of α-synuclein can be inhibited using small molecules. We report that the aminosterol claramine stabilizes α-synuclein condensates and inhibits α-synuclein aggregation within the condensates both in vitro and in a Caenorhabditis elegans model of Parkinson's disease. By using a chemical kinetics approach, we show that the mechanism of action of claramine is to inhibit primary nucleation within the condensates. These results illustrate a possible therapeutic route based on the inhibition of protein aggregation within condensates, a phenomenon likely to be relevant in other neurodegenerative disorders.

Programmable Control of Nanoliter Droplet Arrays using Membrane Displacement Traps

A unique droplet microfluidic technology enabling programmable deterministic control over complex droplet operations is presented. The platform provides software control over user-defined combinations of droplet generation, capture, ejection, sorting, splitting, and merging sequences to enable the design of flexible assays employing nanoliter-scale fluid volumes. The system integrates a computer vision system with an array of membrane displacement traps capable of performing selected unit operations with automated feedback control. Sequences of individual droplet handling steps are defined through a robust Python-based scripting language. Bidirectional flow control within the microfluidic chips is provided using an H-bridge channel topology, allowing droplets to be transported to arbitrary trap locations within the array for increased operational flexibility. By enabling automated software control over all droplet operations, the system significantly expands the potential of droplet microfluidics for diverse biological and biochemical applications by combining the functionality of robotic liquid handling with the advantages of droplet-based fluid manipulation.

Dielectrophoresis-Based Selective Droplet Extraction Microfluidic Device for Single-Cell Analysis

We developed a microfluidic device that enables selective droplet extraction from multiple droplet-trapping pockets based on dielectrophoresis. The device consists of a main microchannel, five droplet-trapping pockets with side channels, and drive electrode pairs appropriately located around the trapping pockets. Agarose droplets capable of encapsulating biological samples were successfully trapped in the trapping pockets due to the difference in flow resistance between the main and side channels. Target droplets were selectively extracted from the pockets by the dielectrophoretic force generated between the electrodes under an applied voltage of 500 V. During their extraction from the trapping pockets, the droplets and their contents were exposed to an electric field for 400-800 ms. To evaluate whether the applied voltage could potentially damage the biological samples, the growth rates of Escherichia coli cells in the droplets, with and without a voltage applied, were compared. No significant difference in the growth rate was observed. The developed device enables the screening of encapsulated single cells and the selective extraction of target droplets.