Clogging of microfluidic constrictions by monoclonal antibody aggregates: role of aggregate shape and deformability

Efficient in-droplet cell culture and cytomechanics measurement for assessment of human cellular responses to alcohol

BACKGROUND

Excessive alcohol consumption poses a significant threat to human health, leading to cellular dehydration, degeneration, and necrosis. Alcohol-induced cellular damage is closely linked to alterations in cellular mechanical properties. However, characterizing these changes following alcohol-related injury remains challenging. Moreover, current research on single-cell mechanics often struggles to culture and measure cells within a controlled microenvironment, leading to complex experimental procedures and imprecise results. (63).

RESULTS

In this study, we developed a novel single cell measurement method that combines cell microculture in alcohol-containing solutions with cytomechanics assessment within microdroplets. This approach integrates key operations, including single-cell encapsulation and culture in droplets, droplet reinjection, and cell deformation analysis within droplets, enabling high-throughput and multi-parameter quantification of single-cell mechanical properties. The use of droplets provides a precisely regulated microculture environment, effectively avoiding channel clogging issues. Additionally, the integration of cytomechanics measurement simplifies the analytical process by eliminating the need for complex techniques within the droplets. Gastric mucosal epithelial cells (GES-1) and human umbilical vein endothelial cells (HUVECs) were selected as models for ethanol-induced injury to validate the proposed technique. The results demonstrate a bidirectional response in cellular deformability following ethanol treatment, with cells becoming stiffer at lower ethanol concentrations and softer at higher concentrations. (136).

SIGNIFICANCE

The integration of droplet microfluidics and cell mechanics offers a powerful platform for investigating the underlying mechanisms of ethanol-induced cellular damage. This approach is also applicable for studying changes in cellular mechanical properties by precisely modulating the microculture environment, providing a reliable tool for drug screening and disease modeling in biochemistry and biomedical engineering. (54).

Does needle clogging change the spatial distribution of injected drug in tissue? New insights by X-ray computed tomography

Prefilled syringes (PFS) are primary packaging materials that offer convenience and safety for subcutaneous injection of parenteral drug solutions. However, an increasingly common problem with the trend towards higher drug concentrations is the clogging of the needle during storage due to evaporative water loss and consequent solidification of the drug. In contrast to all previous studies on this topic, this work focuses on pharmacokinetically relevant aspects and investigates the effects of needle clogging on the spatial distribution of the injected drug in the tissue. X-ray computed tomography (XCT) (both tube-based and synchrotron-based) was used to visualize and analyze the spreading pattern and the fate of the injected liquid in porcine skin. By using controlled injection and force measurement the tissue distribution was correlated with the plunger force profile and the fluid dynamics of the jet. Studies of monoclonal antibody solution demonstrate that clogs, which are formed by evaporation of water and solidification of drug solution in the needle tip, usually dissolve in the flow of the liquid during injection. In the initial injection phase, the liquid jet starts to escape the needle only through a narrow channel in the clog. The resulting high dynamic pressure can alter the distribution of the liquid in the tissue, causing a long tail of liquid that penetrates deep into the fibrous network of the subcutaneous layer. However, the volume of this tail was calculated to be low relative to the overall volume of the injected drug solution (less than 2.4%) and is therefore unlikely to have a significant effect on the absorption kinetics of the injected drug. In addition, it was shown that if a clog were to enter the tissue, it would quickly dissolve.

Clogging transition and anomalous transport in driven suspensions in a disordered medium

We study computationally the dynamics of forced, Brownian particles through a disordered system. As the concentration of mobile particles and/or fixed obstacles increase, we characterize the different regimes of flow and address how clogging develops. We show that clogging is preceded by a wide region of anomalous transport, characterized by a power law decay of intermittent bursts. We analyze the velocity distribution of the moving particles and show that this abnormal flow region is characterized by a coexistence between mobile and arrested particles, and their relative populations change smoothly as clogging is approached. The comparison of the regimes of anomalous transport and clogging with the corresponding scenarios of particles pushed through a single bottleneck show qualitatively the same trends highlighting the generality of the transport regimes leading to clogging.

Structure and flow conditions through a colloidal packed bed formed under flow and confinement

When a colloidal suspension flows in a constriction, particles deposit and are able to clog it entirely, this fouling process being followed by the accumulation of particles. The knowledge of the dynamics of formation of such a dense particle assembly behind the clog head and its structural features is of primary importance in many industrial and environmental processes and especially during filtration. While most studies concentrate on the conditions under which pore clogging occurs, i.e., the pore narrowing up to its complete obstruction, this paper focuses on the accumulation of particles that follows pore obstruction. We determine the relative contribution of the confinement dimensions, the ionic strength and the flow conditions on the permeability and particle volume fraction of the resultant accumulation. In high confinement the irreversible deposition of particles on the channel surfaces controls the structure of the accumulation and the flow through it, irrespective of the other conditions, leading to a Darcy flow. Finally, we show that contrarily to the clog head, in which there is cohesion between particles, those in the subsequent accumulation are held together by the fluid and form a dense suspension of repulsive hard spheres.

Influence of the solid fraction on the clogging by bridging of suspensions in constricted channels

Clogging can occur whenever a suspension of particles flows through a confined system. The formation of clogs is often correlated to a reduction in the cross-section of the channel. In this study, we consider the clogging by bridging, i.e., through the formation of a stable arch of particles at a constriction that hinders the transport of particles downstream of the clog. To characterize the role of the volume fraction of the suspension on the clogging dynamics, we study the flow of particulate suspensions through 3D-printed millifluidic devices. We systematically characterize the bridging of non-Brownian particles in a quasi-bidimensional system in which we directly visualize and track the particles as they flow and form arches at a constriction. We report the conditions for clogging by bridging when varying the constriction width to particle diameter ratio for different concentrations of the particles in suspension. We then discuss our results using a stochastic model to rationalize the influence of solid fraction on the probability of clogging. Understanding the mechanisms and conditions of clog formation is an important step for optimizing engineering design and developing more reliable dispensing systems.

Effect of Colloidal Interactions and Hydrodynamic Stress on Particle Deposition in a Single Micropore

Clogging is ubiquitous. It happens in a wide range of material processing and causes severe performance degradation or process breakdown. In this study, we investigate clogging dynamics in a single micropore by controlling the surface property of the particle and processing condition. Microfluidic observation is conducted to investigate particle deposition in a contraction microchannel where polystyrene suspension is injected as a feed solution. The particle deposition area is quantified using the images taken using a CCD camera in both upstream and downstream of the microchannel. Pressure drop across the microchannel is also measured. When the particle interaction is repulsive, the deposition occurs mostly in downstream, while an opposite tendency is identified when the particle interaction is attractive. More complex deposition characteristics are found as the flow rate is changed. Particle flux density and the ratio of lift force to colloidal force are introduced to explain the clogging dynamics. This study provides a useful insight to alleviate clogging issues by controlling the colloidal interaction and hydrodynamic stress.

Clog mitigation in a microfluidic array via pulsatile flows

Clogging is a common obstacle encountered during the transport of suspensions and represents a significant energy and material cost across applications, including water purification, irrigation, biopharmaceutical processing, and aquifer recharge. Pulsatile pressure-driven flows can help mitigate clogging when compared to steady flows. Here, we study experimentally the influence of the amplitude of pulsation 0.25P₀ ≤ δP ≤ 1.25P₀, where P₀ is the mean pressure, and of the frequency of pulsation 10^-3 Hz ≤ f ≤ 10^-1 Hz on clog mitigation in a microfluidic array of parallel channels using a dilute suspension of colloidal particles. The array geometry is representative of a classical filter, with parallel pores that clog over time, yielding a filter cake that continues to grow and can interact with other pores. We combine flow rate measurements with direct visualizations at the pore scale to correlate the observed clogging dynamics with the changes in flow rate. We observe that all pulsatile amplitudes at 0.1 Hz yield increased throughput compared to steady flows. The rearrangement of particles when subject to a dynamic shear environment can delay the clogging of a pore or even remove an existing clog. However, this benefit is drastically reduced at 10^-2 Hz and disappears at 10^-3 Hz as the pulsatile timescale becomes too large compared to the timescale associated with the clogging and the growth of the filter cakes in this system. The present study demonstrates that pulsatile flows are a promising method to delay clogging at both the pore and system scale.

Design and Fabrication of Organ-on-Chips: Promises and Challenges

The advent of the miniaturization approach has influenced the research trends in almost all disciplines. Bioengineering is one of the fields benefiting from the new possibilities of microfabrication techniques, especially in cell and tissue culture, disease modeling, and drug discovery. The limitations of existing 2D cell culture techniques, the high time and cost requirements, and the considerable failure rates have led to the idea of 3D cell culture environments capable of providing physiologically relevant tissue functions in vitro. Organ-on-chips are microfluidic devices used in this context as a potential alternative to in vivo animal testing to reduce the cost and time required for drug evaluation. This emerging technology contributes significantly to the development of various research areas, including, but not limited to, tissue engineering and drug discovery. However, it also brings many challenges. Further development of the technology requires interdisciplinary studies as some problems are associated with the materials and their manufacturing techniques. Therefore, in this paper, organ-on-chip technologies are presented, focusing on the design and fabrication requirements. Then, state-of-the-art materials and microfabrication techniques are described in detail to show their advantages and also their limitations. A comparison and identification of gaps for current use and further studies are therefore the subject of the final discussion.

Highly Efficient Transfection of Human Primary T Lymphocytes Using Droplet-Enabled Mechanoporation

Whole-cell-based therapy has been extensively used as an effective disease treatment approach, and it has rapidly changed the therapeutic paradigm. To fully accommodate this shift, advances in genome modification and cell reprogramming methodologies are critical. Traditionally, molecular tools such as viral and polymer nanocarriers and electroporation have been the norm for internalizing external biomolecules into cells for cellular engineering. However, these approaches are not fully satisfactory considering their cytotoxicity, high cost, low scalability, and/or inconsistent and ineffective delivery and transfection. To address these challenges, we present an approach that leverages droplet microfluidics with cell mechanoporation, bringing intracellular delivery to the next level. In our approach, cells and external cargos such as mRNAs and plasmid DNAs are coencapsulated into droplets, and as they pass through a series of narrow constrictions, the cell membrane is mechanically permeabilized where the cargos in the vicinity are internalized via convective solution exchange enhanced by recirculation flows developed in the droplets. Using this principle, we demonstrated a high level of functional macromolecule delivery into various immune cells, including human primary T cells. By utilizing droplets, the cargo consumption was drastically reduced, and near-zero clogging was realized. Furthermore, high scalability without sacrificing cell viability and superior delivery over state-of-the-art methods and benchtop techniques were demonstrated. Notably, the droplet-based intracellular delivery strategy presented here can be further applied to other mechanoporation microfluidic techniques, highlighting its potential for cellular engineering and cell-based therapies.

Optimised hyperbolic microchannels for the mechanical characterisation of bio-particles

The transport of bio-particles in viscous flows exhibits a rich variety of dynamical behaviour, such as morphological transitions, complex orientation dynamics or deformations. Characterising such complex behaviour under well controlled flows is key to understanding the microscopic mechanical properties of biological particles as well as the rheological properties of their suspensions. While generating regions of simple shear flow in microfluidic devices is relatively straightforward, generating straining flows in which the strain rate is maintained constant for a sufficiently long time to observe the objects' morphologic evolution is far from trivial. In this work, we propose an innovative approach based on optimised design of microfluidic converging-diverging channels coupled with a microscope-based tracking method to characterise the dynamic behaviour of individual bio-particles under homogeneous straining flow. The tracking algorithm, combining a motorised stage and a microscopy imaging system controlled by external signals, allows us to follow individual bio-particles transported over long-distances with high-quality images. We demonstrate experimentally the ability of the numerically optimised microchannels to provide linear velocity streamwise gradients along the centreline of the device, allowing for extended consecutive regions of homogeneous elongation and compression. We selected three test cases (DNA, actin filaments and protein aggregates) to highlight the ability of our approach for investigating dynamics of objects with a wide range of sizes, characteristics and behaviours of relevance in the biological world.

Dynamics of progressive pore clogging by colloidal aggregates

The flow of a suspension through a bottleneck often leads to its obstruction. Such a continuous flow to clogging transition has been well characterized when the constriction width to particle size ratio, W/D, is smaller than 3-4. In such cases, the constriction is either blocked by a single particle that is larger than the constriction width (W/D < 1), or there is an arch formed by several particles that try to enter it together (2 < W/D < 4). For larger W/D ratios, 4 < W/D < 10, the blockage of the constriction is presumed to be due to the successive accumulations of particles. Such a clogging mechanism may also apply to wider pores. The dynamics of this progressive obstruction remains largely unexplored since it is difficult to see through the forming clog and we still do not know how particles accumulate inside the constriction. In this paper, we use particle tracking and image analysis to study the clogging of a constriction/pore by stable colloidal particles. These techniques allow us to determine the shape and the size of all the objects, be they single particles or aggregates, captured inside the pore. We show that even with the rather monodisperse colloidal suspension we used individual particles cannot clog a pore alone. These individual particles can only partially cover the pore surface whilst it is the very small fraction of aggregates present in the suspension that can pile up and clog the pore. We analyzed the dynamics of aggregate motion up to the point of capture within the pore, which helps us to elucidate why the probability of aggregate capture inside the pore is high.

Microfluidic In-Situ Measurement of Poisson's Ratio of Hydrogels

Being able to precisely characterize the mechanical properties of soft microparticles is essential for numerous situations, from the understanding of the flow of biological fluids to the development of soft micro-robots. Here, we present a simple measurement technique for determining Poisson's ratio of soft micron-sized hydrogels in the presence of a surrounding liquid. This method relies on the measurement of the deformation, in two orthogonal directions, of a rectangular hydrogel slab compressed uni-axially inside a microfluidic channel. Due to the in situ character of the method, the sample does not need to be dried, allowing for the measurement of the mechanical properties of swollen hydrogels. Using this method, we determined Poisson's ratio of hydrogel particles composed of polyethylene glycol (PEG) and varying solvents fabricated using a lithography technique. The results demonstrate, with high precision, the dependence of the hydrogel compressibility on the solvent fraction and character. The method is easy to implement and can be adapted for the measurement of a variety of soft and biological materials.