Viscoelastic polymer solutions have been widely employed as suspending liquids for a myriad of microfluidic applications including particle and cell focusing, sorting, and encapsulation. It has been recently shown that viscoelastic solutions can drive the formation of equally spaced particles called "particle trains" as a result of the viscoelasticity-mediated hydrodynamic interactions between adjacent particles. Despite their potential impact on applications such as droplet encapsulation and flow cytometry, only limited experimental studies on viscoelastic ordering are currently available. In this work, we demonstrate that a viscoelastic shear-thinning aqueous xanthan gum solution drives the self-assembly of particle trains on the centerline of a serpentine microfluidic device with a nearly circular cross section. After focusing, the flowing particles change their mutual distance and organize in aligned structures characterized by a preferential spacing, quantified in terms of distributions of the interparticle distance. We observe the occurrence of multi-particle strings, mainly doublets and triplets, that interrupt the continuity of the particle train. To account for the fluctuations in the number of flowing particles in the experimental window, we introduce the concept of local particle concentration, observing that an increase of the local particle concentration leads to an increase of doublets and triplets. We also demonstrate that using only a single tube to connect the sample to the microfluidic device results in a drastic reduction of doublets/triplets, thus leading to a more uniform particle train. Our findings establish the foundation for optimized applications such as deterministic droplet encapsulation in viscoelastic liquids and optimized flow cytometry.
Strings of equally spaced particles, also called particle trains, have been employed in several applications, including flow cytometry and particle or cell encapsulation. Recently, the formation of particle trains in viscoelastic liquids has been demonstrated. However, only a few studies have focused on the topic, with several questions remaining unanswered. We here perform numerical simulations and experiments to elucidate the effect of the confinement ratio on the self-ordering dynamics of particles suspended in a viscoelastic liquid and flowing on the centerline of a microfluidic channel. For a fixed channel size, the particles self-order on shorter distances as the particle size increases due to the enhanced hydrodynamic interactions. At relatively low linear concentrations, the relative particle velocities scale with the fourth power of the confinement ratio when plotted as a function of the distance between the particle surfaces normalized by the channel diameter. As the linear concentration increases, the average interparticle spacing reduces and the scaling is lost, with an increasing probability to form strings of particles in contact. To reduce the number of aggregates, a microfluidic device made of an array of trapezoidal elements is fabricated and tested. The particle aggregates reduce down to 5% of the overall particle number, significantly enhancing the ordering efficiency. A good agreement between numerical simulations and experiments is found.
The encapsulation of particles and cells in droplets is highly relevant in biomedical engineering as well as in material science. So far, however, the majority of the studies in this area have focused on the encapsulation of particles or cells suspended in Newtonian liquids. We here studied the particle encapsulation phenomenon in a T-junction microfluidic device, using a non-Newtonian viscoelastic hyaluronic acid solution in phosphate buffer saline as suspending liquid for the particles. We first studied the non-Newtonian droplet formation mechanisms, finding that the data for the normalised droplet length scaled as the Newtonian ones. We then performed viscoelastic encapsulation experiments, where we exploited the fact that particles self-assembled in equally-spaced structures before approaching the encapsulation area, to then identify some experimental conditions for which the single encapsulation efficiency was larger than the stochastic limit predicted by the Poisson statistics.
Viscoelastic polymer solutions have been employed as suspending liquids for a myriad of microfluidic applications including particle or cell focusing and sorting. Very recently viscoelastic liquids have been shown to drive the formation of strings of equally spaced particles called "particle trains". The formation of "particle trains" may have unprecedented benefits on important biomedical applications. For example single cell analysis benefit from encapsulation of a single cell or particle in a droplet for high throughput decoding and sequencing of cellular information. In flow cytometry particle or cell train formation is crucial for analysing their properties without interference from overlapping cells or particles. To date, limited experimental studies are available on viscoelastic particle train formation. In Chapter 4 of the thesis, we demonstrate that a viscoelastic shear thinning aqueous 0.1 wt% xanthan gum XG solution drives the self-assembly of particle trains on channel centerline in a serpentine microfluidic device. In addition, to account for the fluctuations in the number of flowing particles, we introduced the concept of local particle concentration, observing that an increase in local particle concentration led to an increase multi-particle string formation. Thereafter, we simplified the microfluidic configuration to drastically reduce multi-particle string formation. In Chapter 5, we successfully employed a microfluidic device with sixteentrapezoidal elements to reduce multi-particle string formation down to 5 % and studied the effect of confinement ratio on ordering dynamics of particles in 0.2 wt% XG, where larger confinement ratios led to self-assembly at shorter distances. Subsequently, in Chapter 6 we studied the particle encapsulation in a T-junction microfluidic device, using a non-Newtonian viscoelastic 0.1 wt% hyaluronic acid HA solution in phosphate buffer saline as suspending liquid. We first studied the non-Newtonian droplet formation mechanisms, finding that the data for the normalised droplet length scaled as the Newtonian ones. We then performed viscoelastic encapsulation experiments and identified experimental conditions for which the single encapsulation efficiency was larger than the stochastic limit predicted by the Poisson statistics. Overall, our work provides insights into fluid characteristics, experimental conditions and microfluidic devices required to form particle trains and to encapsulate particles in droplets.• This work has not previously been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree.Signed: Anoshanth Jeyasountharan Date: 29/09/2022• This thesis is the result of my own investigations, except where otherwise stated.Other sources are acknowledged by footnotes giving explicit references. A bibliography is appended.
The encapsulation of particles and cells in droplets is highly relevant in biomedical engineering as well as in material science. So far, however, the majority of the studies in this area have focused on the encapsulation of particles or cells suspended in Newtonian liquids. We here studied the particle encapsulation phenomenon in a T-junction microfluidic device, using a non-Newtonian viscoelastic hyaluronic acid solution in phosphate buffer saline as suspending liquid for the particles. We first studied the non-Newtonian droplet formation mechanism, finding that the data for the normalised droplet length scaled as the Newtonian ones. We then performed viscoelastic encapsulation experiments, where we exploited the fact that particles self-assembled in equally-spaced structures before approaching the encapsulation area, to then identify some experimental conditions for which the single encapsulation efficiency was larger than the stochastic limit predicted by the Poisson statistics.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.
Copyright © 2025 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.