1,721,252 research outputs found
Osmosis in aqueous two-phase system and its application in protein encapsulation
No full textEncapsulation is a process where the active pharmaceutical ingredient (API) is preserved in a cage of excipient, such as a polymeric particle. The vulnerable API is protected against degradation before reaching the target site. Conventional encapsulating techniques include emulsion evaporation or spray drying. However, among these techniques, it is inevitable to use an organic solvent to dissolve polymers. Much evidence proves that the oil-water interface denatures proteins once they are adsorbed to and aggregate at the interface. Also, the harsh temperature and pressure change involved could destroy the functional structure of the active ingredients, lending to reduced loading efficiency.
Therefore, the osmo-solidification of the all-aqueous emulsion has been developed to preserve proteins. Enzymes such as beta-galactosidase and alpha-amylase can be well preserved in the osmo-solidified particles. This technique is superior to the other conventional techniques since it is organic solvent-free, and the process takes place under room temperature and pressure. This provides bio-friendly conditions to manipulate the biomolecules. However, the parameters and mechanisms that modulate the size and structure of the particles are unknown. Moreover, factors affecting the encapsulation of biomolecules are still unknown. These unsolved questions greatly hinder the technique from being translated for pharmaceutical applications.
In the present work, we study the mechanism that governs the size and structure of the particles. We report that the size of the particles depends on the spreading of the droplets. Moreover, the formation of skin in the all-aqueous emulsion is induced at a high BSA concentration. To our best knowledge, this is the first report revealing the formation of skin at the aqueous-aqueous interface. The solid layer of the skin significantly affects the size and structure of the particles. We also investigate the partitioning behavior of proteins in the all-aqueous emulsions. The partitioning of proteins governs their encapsulation efficiency in the osmo-solidified particles. Four factors that affect partitioning, including the molecular weight of polyethylene glycol (PEG), the NaCl concentration, the protein charge, and the droplet generating system, are evaluated. Implications for the industry to employ osmo-solidification are discussed. This thesis improves important information on designing an efficient drug carrier via osmo-solidification.published_or_final_versionMechanical EngineeringMasterMaster of Philosoph
Regenerating corneal endothelial functionality by engineering cell construct with aqueous two-phase system (ATPS)
No full textCorneal endothelial transplantation is one of the major surgeries for treating corneal endothelium related corneal dystrophy. Due to the shortage of corneal donor graft, alternatives of full-cornea transplantation need to be developed. In this thesis, we focus on developing scaffold-free cell construct based on aqueous two-phase system (ATPS). With the aid of reducing osmolality difference between the two immiscible phases and centrifugation assisted assembly, the cell construct formed could be applicable in clinical application.
In chapter 2, we investigate different parameters affecting the cell construct formation. Through the process of ATPS equilibration, we can reduce the osmolality difference between the two phases. This reduction of osmolality difference could result in a higher success rate of cell construct formation. By applying centrifugal force at the cell construct formation process, the thickness of the cell construct would be more uniform. The cell construct formed would also be less likely to be fragmented. We also investigate the cell construct formation phenomenon is only applicable on PEG-DEX-based ATPS.
In chapter 3, we demonstrate the in vitro proliferation, protein expression and ex vivo injection, culture of the corneal endothelial cell construct. Porcine corneal endothelial cell is chosen as the cell type in this study. We show that the porcine corneal endothelial cell harvested is physiologically representative, based on the functionality assay examining the pump and barrier function of the cell construct. The cell construct can also grow and proliferate in vitro with the increase of the cell construct area. Immunocytochemistry is applied to illustrate the physiological markers of the corneal endothelial cell after in vitro culture. After a month of in vitro culture, we find that the cell construct can express ZO-1 and Na+/K+ ATPase, two of the physiological markers of the corneal endothelial cell. It shows its capability to reconstruct the corneal functionality after transplantation. We also demonstrate the feasibility to inject the corneal endothelial cell construct in an ex vivo porcine model using a commercially available intraocular injector. Therefore, the cell construct formed is applicable at clinical context.published_or_final_versionMechanical EngineeringMasterMaster of Philosoph
Elastomeric microsystems with stimuli-responsive actuation : co-doping fabrication and biomimetic applications
No full textElastomeric microsystems are soft devices that employ elastomers as the basic material and integrate various functional micro and nano components, such as mechanical, optical, and fluidic components. With decades of development, elastomeric microsystems have been well applied in the biochemical analysis as microfluidics, health monitoring as soft electronics, and human-machine interaction as soft robotics, respectively. With the demand for precise controllability and environmental responsiveness, stimuli-responsive actuation, referring to mechanical deformation in response to external stimuli such as light, temperature, and humidity, is introduced into elastomeric microsystems. However, disparities in the properties and fabrication methods of stimuli-responsive materials and conventional elastomers lead to the coordinated integration of microstructures, responsive materials, and other functional components into a microsystem remaining a challenge. In addition to developing new micro-processing techniques for responsive materials, modification and functionalization of existing elastomeric microsystems is a compromise between satisfying the well-established micro-processing methods and developing new functions of stimuli-responsiveness. However, endowing an inherently inert elastomer with responsiveness inevitably requires multiple processing steps, raising the threshold of technology and cost. Therefore, a concise and effective method for preparing and functionalizing the stimuli-responsive elastomeric microsystems is urgently required in order to reduce technical barriers and save costs. In addition, although stimuli-responsive microsystems have already proved their practicality in individual fields, many areas with potential translational value are still unexplored. In particular, biomimetic designs inspired by the stimuli-responsive shapes or color variations of natural organisms are promising great applications in biomedicine, optics, and energy.
In this thesis, we propose a co-doping fabrication method to facilitate the integration of stimuli-responsive actuators into elastomeric microsystems. In addition, through biomimetic design, we have developed responsive elastomeric microsystems into novel soft robots, color-changing systems, and microfluidic devices, respectively. In particular, in Chapter 3, we propose the co-doping fabrication method to optimize the preparation and functionalization of the hydrogel-elastomer actuator. Based on this actuator, a series of bio-inspired soft micro-bots are designed, demonstrating their biomimetic motions, such as grabbing, crawling, and jumping. In Chapter 4, we take inspiration from the bi-color of a butterfly’s wing and propose a pixelation method towards solvent-responsive structural coloration via concavity array. Upon solvent stimulation, the prepared array composed of photonic crystal elastomer actuators can form a concavity and thus change color to form letters and patterns, which could be used in dynamic display and camouflage. In Chapter 5, we propose a concept of transformable origami microfluidics inspired by the nastic movement of plants. The designed microfluidic device can change its shape in response to the changes in the environment and can thus be applied to environmentally adaptive photosynthesis.
In summary, the main focus of this thesis is to develop techniques to integrate stimuli-responsive actuation into elastomeric microsystems. The designed stimuli-responsive actuator microsystems are applied in biomimetic applications, such as soft micro-robots, programmable color-changing systems, and transformable origami microfluidics. We believe that the above studies could deepen our understanding of stimuli-responsive microsystems and inspire novel applications in biomedical, optical, and energy engineering.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Instability-driven dynamic behaviors of micro-scale liquid jets
No full textInstability can endow liquid jets with dynamic behaviors that can be either constructive or harmful. For example, the liquid rope coiling effect that happens for a viscous liquid jet may be responsible for the fragility in glass sheets during fabrication due to the inhomogeneity caused by folding and coiling motion of jet. With a moving plate, a coiling jet could draw intricate patterns and been applied to addictive printings with the coiling shape. This instability, termed as buckling instability in a wider context, is an intrinsic tendency for a thin object and will manifest on not only jet, but also elastic rod, elastic rope, viscous liquid bridge, or geological architecture like folded rocks. This widely observed instability is of rich potential to be exploited for manipulating viscous liquid jets.
By applying an electric field, a jet could become significantly thinner and would be accelerated, resulting in a buckling jet that otherwise would not buckle. However, the literature relating the electric coiling is limited to assuming a uniform and vertical distribution of the electric field for a needle-to-plate configurated electrodes setup. In our experiment, we found out that this needle-to-plate configuration of electrodes cannot be taken as a uniform and vertical electric field distribution, for a needle-to-plate (commonly used for electric coiling), and plate-to-plate (used as the model when analysis) configuration demonstrates completely different onset conditions for the electric coiling phenomenon. Therefore, we studied the factor of the shape of the electric field on the charged liquid jet and it successively explained the discrepancy observed between a needle-to-plate and plate-to-plate electrode configuration and demonstrate applications with its facile control over coiling onset.
Like an electric field that stretches the jet to tens of micrometers thin and induced coiling, other applications relate to liquid rope coiling are mostly with micro or nanoscale jet, where surface tension is expected to be dominating. We found that if the liquid jet is dispensed from a tiny nozzle with hundreds of micrometers diameter, the onset height of coiling as a function of flow rate is opposite to existing theories. In the existing literature, researchers either ignore the surface tension or shows it only offers minor correction to the onset curve whose experiments are conducted with large orifice and thus surface tension does not play an important role. Nowadays, the most adopted coiling is the coiling in microscale, like high-resolution printing or microfluidic jet folding, where the surface tension becomes dominate and strong enough to alter the slope of an onset curve. Hence, we have identified an unexplored, yet very widely adopted a regime of liquid rope coiling that provides critical guidelines for buckling instability applied in microscale. Our experiments, numerical methods, and linear stability analysis to approach this problem and have obtained well-match results.
In summary, motivated by the discrepancy between our observation and existing theories, we have made our attempts to reveal some new physics and successively accounted for our observation regarding the buckling of micro-scale jets and demonstrate applications initiated by these findings.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Application of droplet reactors with microfluidics
No full textIn droplet microfluidics, droplets act as individual reactors when chemical and biological reactants are encapsulated. To perform reactions and fabricate materials, droplet reactors need to be generated and manipulated. A tremendous amount of droplet generation and manipulation techniques have been developed, such as droplet coalescence and droplet injection, extending the applications of droplet reactors to material fabrication and bio(chemical) analysis. However, few techniques are capable of generating droplets with tunable components in large quantities, this is of great importance in various areas such as reaction condition screening and multi-compartmental particle fabrication. To address this issue, we propose four techniques to generate a large number of droplets with tunable components, contributing to material fabrication and pathogen detection.
Specifically, in Chapter 3, we develop a phase separation-induced droplet generation technique, producing Janus droplets with tunable compartment ratios. The resultant Janus droplets are applied in fabricating non-spherical particles and encapsulating bio-ingredients with preserved bioactivity. In Chapter 4, we propose a segmented picoinjection method to generate droplets with tunable reactants to detect multiple pathogens based on droplet loop mediated-isothermal amplification (dLAMP) technique. In Chapter 5, we propose an electricity-free injection method to inject reactants with tunable volume into flowing droplets, applying in synthesizing nanoparticles and crystals exhibiting narrow size distribution. In Chapter 6, we propose a novel system to generate droplets in large quantities by applying negative pressure. The resultant droplets are applied to simultaneously performing multiple dLAMP reactions to detect pathogens.
In summary, this dissertation focuses on developing techniques to generate droplets with tunable components in large quantities. These developed techniques are applied in material fabrication and bio(chemical) analysis. These advanced techniques extend the application of droplet reactors for tackling real-world issues, such as preserving the bioactivity of the encapsulated ingredients, synthesizing monodispersed materials and detecting pathogens.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Growth dynamics and phase transitions of aqueous phase-separated condensates
No full textBiomolecular condensates are membrane-less organelles that play crucial roles in cellular organization and functions, including RNA transcription [1, 2], stress response [3, 4], and noise buffering [5, 6]. Recent studies have revealed that these condensates form through the liquid-liquid phase separation (LLPS) of biomolecules such as proteins and RNAs, driven by multivalent interactions [7, 8]. In laboratory settings, synthetic systems such as complex coacervates and aqueous two-phase systems (ATPS) are generated through the associative or segregative LLPS [9, 10]. These synthetic systems also lack physical barriers and exhibit physicochemical properties similar to biological condensates, including viscoelasticity, interfacial tension, and surface charges [9, 11]. Consequently, they have been widely used to not only uncover the mechanistic principles that enable biological condensates to concentrate biomolecules and modulate biochemical reactions [9, 12], but also construct artificial cells from basic molecules [13, 14].
Over the past decade, studies have been primarily focused on identifying and explaining how condensates form and function across different disciplines [15, 16]. However, advances in understanding the dynamics and phase transitions of condensates or coacervates have been limited. For example, while many condensates behave as liquid-like droplets, their growth dynamics often deviate from predictions by classic theories that describe droplet growth via Brownian motion-induced coalescence or Ostwald ripening. In particular, many studies have shown that the growth of biomolecular condensates is significantly suppressed in cells or reconstituted systems [17, 18]. In addition, the material properties of condensates vary in response to environmental stimuli or during the aging process, leading to phase transitions between liquid-like droplets and solid-like aggregates [19-21]. Notably, the liquid-to-solid phase transition (LSPT) of biomolecular condensates is implicated in the pathogenesis of neurodegenerative disease and cancers [22, 23]. The lack of comprehensive understanding of the dynamics and phase transitions of condensates limits our ability to fully appreciate their unique roles in cellular organization and function, as well as hinders the development of condensate-based biomaterials for relevant industrial and biomedical applications.
Given these unresolved questions, we utilize coacervates and ATPS as model systems to study the growth dynamics and phase transitions of condensates, using a combination of experiments, simulations, and theoretical analysis. Chapter 1 provides an overview of phase separation and biomolecular condensates, along with fundamental physical concepts and theoretical models. In Chapters 2 and 3, we study the non-equilibrium coarsening of complex coacervates with varying material properties. Chapter 4 explores how condensates, upon reaching equilibrium, scale their sizes in relation to their surrounding enclosed environments. The chapter 5 focuses on revealing molecular principles that govern phase transitions of condensates, particularly those affected by alcohol molecules. In Chapter 6, I present advancements in creating heterogeneous hydrogels using ATPS systems to mimic the representative features of biological architectures at different length scales. Finally, the concluding chapter summarizes key findings and outlines directions for future research.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Manipulation of liquid marbles by electric field and its applications
No full textTo manipulate liquid marbles by electric field, the fundamental understanding on how liquid marbles response to the electric field is of crucial importance. In this thesis, we mainly focus on the responses of liquid marbles to an externally applied electric field, the realization of manipulating liquid marbles, and the physical mechanism behind the manipulation of liquid marbles. To explore the capacity of our technology, we have also tested some proof-of-concept applications by using liquid marbles as miniature micro-bioreactors.
Chapter 2 focuses on the development of a robust method to manipulate liquid marbles by electric field in a controlled manner. Motivated by the great potential of nonwetting droplets as microreactors for chemical and biological applications, a general and robust method is developed for controlled manipulation of nonwetting droplets. The motion and coalescence of the resulting droplets (termed “liquid marbles”) are actuated at a sufficiently large applied voltage on inkjet-printed devices covered by a dielectric layer. This critical actuation voltage, which determines the driving force and the displacement of actuation, is highly dependent on the initial position of the liquid marble. This finding is ascribed to the fraction of the interfacial area that is electrostatically polarized; as a result, the amount of electrostatic energy released to accelerate the marble to reach peak velocity is position-dependent, as confirmed experimentally. By fine-tuning the driving voltage, individual liquid marbles are actuated and coalesced on demand. Moreover, in our system, cross-contamination between droplets during manipulation is avoided due to the nanoparticle shell, as confirmed by the absence of any trace DNA after amplification using a loop mediated isothermal amplification reaction.
In Chapter 3, by using liquid marbles as miniature micro-bioreactors, we demonstrate some proof-of-concept applications by combining the manipulation of liquid marbles with conventional detecting technology. Enzymatic colorimetric method is used to quantitatively measure the concentration of glucose in samples, and the results of using microwells as containers are compared with those from using liquid marbles as miniature micro-bioreactors. We find that the linear correlation between absorbance and concentration, which is used to quantify the concentration of glucose, still holds true for liquid marbles. Moreover, liquid marbles encapsulating cells are manipulated by electric field. The experimental results confirm that the cells stay viable after being encapsulated and cultured in liquid marbles for hours. Finally, we demonstrate that, by using our system to manipulate liquid marbles to move, coalesce and mix, we can trigger chemiluminescence reaction in liquid marbles.published_or_final_versionMechanical EngineeringMasterMaster of Philosoph
Interfacial phenomena in all-aqueous systems : dewetting, phase separation, fingering instability, and interfacial emulsification
No full textAqueous two-phase systems (ATPSs), also called as all-aqueous systems, are formed by phase separation of an aqueous solution containing two incompatible additives, such as two incompatible polymers above critical concentrations. Due to the major components of ATPSs are water, the interface between the two immiscible phases possesses some peculiar properties, such as a wide interface (order of 10 nm), an ultralow and a broad range of interfacial tension (less than 1 µN/m to 1 mN/m), as well as the permeability to small molecules (like water and ions). In addition, the all-water nature also enables ATPSs to be excellent platforms in various biomedical applications such as particle synthesis and artificial cell mimicking. Therefore, inspired by these peculiar properties, this thesis explores a wide range of problems involving the interfacial phenomena that highlight the properties of the all-aqueous interface.
In Chapter 4, we systematically study the transformation dynamics of non-equilibrium double emulsions towards their equilibrium state. Two immiscible aqueous phases with a wide range of interfacial tension and viscosity are introduced to form the unstable double droplets in microfluidic channels. After systematically studying the dynamics of these unstable droplets, we conclude a universal scaling law to predict the dewetting velocity of the shell during the transformation of unstable double emulsions. In Chapter 5, by utilizing the permeability of the all-aqueous interface, we successfully achieve multi-layered (up to 4 layers) all-aqueous emulsion droplets from the phase separation of single-layered emulsion droplets in microfluidic channels. In particular, a phase diagram illustrating the complexity of resulting droplet is constructed, where the layer and size of resulting complex droplets are successfully predicted from this phase diagram. In Chapter 6, we report that fingers emerging at the non-equilibrium all-aqueous interface in a vertical Hele-Shaw cell can spontaneously break into an array of droplets. A phase diagram with a wide parameter space where finger breaking occurs or not is concluded. This spontaneous breakup of interfacial fingers suggests a new way to fabricate all-aqueous emulsion droplets. In Chapter 7, by combining spontaneous fragmentation and phase separation of surfactant-laden all-aqueous films on another aqueous substrate, we propose an interfacial emulsification strategy with potential up-scalability to rapidly produce small and uniform all-aqueous droplets. In particular, using the resulting droplets as templates, we successfully fabricate all-aqueous double emulsion droplets and hydrogel microparticles.
To conclude, the main focus of this thesis is utilizing the special properties of ATPSs to study some fundamental interfacial phenomena, including dewetting dynamics in double emulsion droplets, mass-transfer induced phase-separation, fingering instability at the non-equilibrium all-aqueous interface, and interfacial emulsification of thin aqueous films. We believe that the above studies would help add to the understanding of interfacial dynamics as well as inspire some novel applications within ATPSs.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Programmed pressure platform fabrication for ophthalmologic study
No full textGlaucoma, the second leading cause of blindness worldwide, is a neurodegenerative disease characterized by progressive degeneration of retinal ganglion cells (RGCs). Intraocular pressure (IOP) is a well-established risk factor for the development and progression of glaucoma. However, it is still not clear how IOP elevation leads to degeneration of RGCs in glaucoma. Due to the circadian rhythm and pulsatile variation with time, the IOP level is not static throughout the day and is difficult to be monitored and regulated. Therefore, a new platform that has ability to simulate pathological IOP controllably is critically important. Compared to in vivo models, the in vitro models possess higher reproducibility, as well as greater flexibility and more precise control over cell culture environments. In vitro pressure model provides a versatile tool for investigating cellular response and biomolecular changes on glaucomatous problems. In this thesis, we propose new platforms with tunable hydrostatic pressure and programmable dynamic pressure for in vitro ophthalmologic study.
In Chapter 4, we devise a hydrostatic pressure platform to simulate IOP in the eye. By connecting with a liquid column, a monitored hydrostatic pressure is generated inside the cell culture chamber. This platform enables the direct testing of hypotheses related to the role of IOP in primary RGCs degeneration. The morphological changes are recorded under the microscope and then quantified by measuring the total neurite length, axon length, cell body area, and branching complexity. We find that a critical pressure threshold is present at 25 mmHg, beyond which the RGCs become vulnerable. In particular, at pressure above 25 mmHg, the RGCs do not show any neurites extension and begin to degenerate.
In Chapter 5, a new facile programmed pressure platform, that uses the electronic valve to simulate the dynamic pressure, is further designed. Dynamic pressure with convertible profile, programmable amplitude, and frequency can be generated inside a microfluidic PDMS chamber. The output pressure can be calculated by the magnitude of air bubble shrinkage via the ideal gas law, which is identical to that measured by the pressure sensor. Moreover, the ability to generating pulsatile pressures with different amplitude provides great potential to study the mechanism of neurodegeneration under normal IOP. In particular, we find that the expression of ZO-1 between ARPE-19 is increased under dynamic pressure, when compared to that of control group (no pressure).
In summary, we propose a hydrostatic pressure platform and a programmable dynamic pressure platform for in vitro ophthalmologic study in this thesis. The hydrostatic pressure platform can simulate a wide range of physiologically relevant intraocular pressures, and the programmable dynamic pressure platform can generate cyclic and diverse pressure profiles, with tunable amplitude and frequency. Successful establishment of hydrostatic and dynamic pressure platforms will facilitate further studies on the IOP related problems in the eye. We believe that the advancement in this thesis will be beneficial to a variety of research areas, such as drug screening and biomaterials screening in eye care.published_or_final_versionMechanical EngineeringDoctoralDoctor of Philosoph
Impingement of a compound drop on a substrate and emulsification of silicone oil in an eye-on-a-chip
No full textWetting and dewetting are commonly observed processes at solid-liquid interface. In this thesis, we mainly focus on the two specific phenomena at the solid-liquid interface: impact of a compound drop on a solid substrate and adhesion of silicone oil on a cell-lined surface. By studying these two phenomena, we extend the knowledge of understanding of compound droplet impact and reveal a novel mechanism of silicone oil emulsification in ophthalmology.
We study the behavior of a compound drop on a partially wetting surface in Chapter 2. The oil-water compound drop is generated by a coaxial needle at millimeter scale. A compound drop tends to spread slower and rebound higher, which is compared with impact of a single-component drop both qualitatively and quantitatively. The relationship between the maximum spreading diameter of compound drops and Weber Number is investigated. A single-component drop or a compound drop with a small core-shell ratio (0.75) tend to rebound with a small impinging velocity. The spreading and rebounding of a compound drop is not significantly different for different partial wetting surfaces.
We study the emulsification of silicone oil with high-molecule-weight additives in an eye-on-a-chip and in a cell-lined device in Chapter 3. To test the resistance against emulsification, silicone oil is tested in an eye-on-a-chip device with simulated saccadic eye motion for four days. The number of emulsified droplets in high-molecule-weight silicone oil is smaller than that in conventional silicone oil. We find the adhesion of silicone oil is a possible reason of emulsification, and the extensional viscosity increase in high-molecular weight silicone oil increase the resistance against emulsification. Adhesion of silicone oil is demonstrated in a cell-lined microchannel.published_or_final_versionMechanical EngineeringMasterMaster of Philosoph
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