| 1. |
- Liu, Zhenhua, 1992-
(författare)
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Droplet Acoustofluidics for Biochemical Applications
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Droplet microfluidics is a promising platform for biochemical applications where compartmentalized droplets serve as individual vials. Droplets are formed by using two immiscible phases, the continuous phase and the dispersed phase, making up the droplets. Droplets are interesting because they can provide fast, parallel reactions with low reagent consumption. Microscale particles, such as cells, can be encapsulated in the droplets and chemical reagents can be added via a pico-injector. However, removal of droplet background signal is hard to achieved by conventional methods, especially if you do not want to risk losing the encapsulated cells. In this thesis, I present a droplet microfluidic system that can achieve this, via droplet-internal particle manipulation using acoustophoresis.This droplet microfluidic system contains pico-injection and droplet split with acoustophoresis. The pico-injection is used to add fresh solution into the droplets and the droplet split with acoustophoresis is used to remove the droplet supernatant. With the combination of the pico-injector and the droplet split, the background signal of the droplets can be reduced and the cell medium in the droplets can be exchanged. This droplet microfluidic system can also be used to control timing of enzyme reactions by initiating the reaction by adding enzyme-coupled beads via the pico-injector and taking a sample from the droplets at specific time points via side channels. In this work, I have also investigated how the design of the droplet split could be optimized to obtain high particle recovery and enrichment. Finally, acoustic properties of a selection of oils that can used as the continuous phase were mapped to optimize the droplet system for acoustophoresis.This thesis explores the biochemical applications performed by the droplet acoustofluidics, in-droplet time-controlled enzyme reaction and medium exchange for in-droplet cell culture. Furthermore, the droplet acoustofluidics has the potential to study the reaction kinetics by other enzymes and achieve long-term in-droplet cell culture.
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| 2. |
- Porras Hernández, Ana María
(författare)
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Micropatterning of hyaluronic acid hydrogels for in vitro models
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The human body consist of a vast number of cells, and jointly, the cells, form tissues and organs. The cells interact and respond to their local microenvironment. The cellular microenvironment consists of a highly hydrated and compliant extracellular matrix, neighboring cells and circulating biochemical factors; and jointly, provide chemical and physical cues that regulate cell behaviour However, these cues are often not present in traditional in vitro models, where cells experience a stiff and unstructured environment. An approach to better mimic the in vivo microenvironment in vitro is to use hydrogels. Hydrogels are soft and highly hydrated polymers based on materials naturally found in the extracellular matrix of various tissues. Furthermore, these materials can be chemically functionalized to control the physical, chemical, and mechanical properties of the hydrogels. These functionalities can also be used to prepare micrometre sized cell adhesive regions, or micropatterns, on the hydrogel substrate. The micropatterns guide the cell shape and permit the study of the cell response to these changes in shape and function, which has been observed in e.g., endothelial cells from various origins. Taken all together, the aim of this work was to develop a hydrogel-based cell culture substrate that permits the control of the spatial adhesion of brain endothelial cells in order to study the morphological effects on these cells and contribute to the understanding of the function of brain endothelial cells in health and disease. This thesis demonstrates the functionalization of hyaluronic acid, a naturally occurring extracellular matrix polymer, to prepare photocrosslinkable hydrogels. Then, through photolithography, micropatterns of cell adhesive peptides were prepared on these hydrogels. Brain microvascular endothelial cells, a highly specialized type of endothelial cells, adhered to the micropatterns, and the effect on their alignment and cell chirality depending on the micropatterned sized was studied. Furthermore, changes in their alignment were also observed when exposed to different glucose concentration.
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| 3. |
- Wu, Lulu
(författare)
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Development of Nanocellulose Materials for Nano-filtration and Microfluidic Cell Culture
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nanocellulose, cellulose nanofibrils or nanocrystals, is an interesting material for a wide range of applications. It can be obtained from abundant sources (higher plants, bacteria and algae), and presents many advantages to be used in the biomedical field such as biological safety, high surface area, porosity, and tailorable rheological properties. This thesis selected two different areas to explore the use of nanocellulose materials in life sciences: bioprocessing of biological products and cell culture in microfluidic systems. The production of biopharmaceutical products (e.g. plasma-derived proteins) requires bioactive raw materials of animal or human origin, which present a viral risk. Virus contamination is one of the biggest challenges in the bioprocessing of such biological products, with size-exclusion virus filtration signalled as the preferred method. Commercial virus removal filters tend to have relatively low fluxes, which results in expensive industrial processes and the use of filters based on synthetic polymers is associated with environmental burden. When considering the application of microfluidic devices in cell research, the development of cheap and readily available nano- or micro-biomaterials that are easy to process and integrate is expected to advance the understanding of the relationship between cells and the microenvironment.The first part of the thesis focussed on Cladophora algae-derived cellulose nanofibrils virus removal filters (CCF-VFs) and investigated their application in the bioprocessing of plasma-derived proteins and stem cell differentiation medium. The second part explored the use of wood-derived cellulose nanofibrils (CNFs) as a cell culture substrate in microfluidics. Here, a concentric circular patterned CNF substrate was incorporated into a microfluidic chip to study the role of topography and shear stress in guiding the alignment of human umbilical vein endothelial cells (HUVECs). In conclusion, CCF-VFs show great potential to be integrated into the bioprocessing of plasma-derived products to remove viruses. The first evaluation of CCF-VFs in stem cell culture medium filtration showed promising results. Aligned CNFs were successfully integrated into microfluidic chips as a tool to study the role of mechanical cues on cell alignment.
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