Self-sufficient microfluidic systems using highly porous elastomeric sponges
Creators: name: Thurgood, Peter
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 310199
subject: Biochemistry and cell biology not elsewhere classified
classificationCode: 400399
subject: Biomedical engineering not elsewhere classified
classificationCode: 400899
subject: Electrical engineering not elsewhere classified

description: Conventional microfluidic systems enable the manipulation of liquids in micro- scale structures. However, the majority of microfluidic systems rely on external off-chip equipment, such as pumps, tubes and valves for driving and control of flow. This in turn increases the overall costs, and dimensions of the system while decreases their utility for point-of-care purposes, and importantly their widespread application in biological laboratories.<br><br>Chapter 1 presents a brief overview of self-sufficient microfluidic devices, and explores self-sufficient microfluidic components made of polydimethylsiloxane (PDMS) capable of storage and release of aqueous solutions into fluidic environments, which can be operated without the need for external off-chip equipment, and specialised training in microfluidics. This review identified a clear gap in the current body of knowledge and motivated me to develop PDMS sponges as a building block of self-sufficient lab-on-a-chip structures.<br><br>Chapter 2 presents my first research contribution. Here, I fabricated a highly porous sponge by templating microscale droplets of water in PDMS using a microfluidic T-junction system. Scanning electron microscopy revealed the unique structure of the sponge, consisting of large pores which were only interconnected by small holes. This unique structure allowed for storage of aqueous solutions and their slow release into fluidic environments. Experiments indicated that the release characteristics of the sponge can be tuned by varying the size of the pores and interconnecting holes.<br><br>I further demonstrated the capability of the highly porous PDMS sponge for the chemical stimulation of cultured cells. As a proof-of-concept, the sponge was<br><br>loaded with ionomycin and placed into a well pre-coated with human umbilical vein endothelial cells. This enabled me to monitor the intracellular calcium signaling of cells in response to releasing ionomycin using a simple setup.<br><br>I also demonstrated the ability of the PDMS sponge for the active release of stored chemicals into a microfluidic system. A PDMS sponge was loaded with an aqueous solution, and squeezed using a simple screw mechanism. This enabled me to release the stored solution in a controlled manner over consequent cycles into the surrounding flow.<br><br>Chapter 3 presents my second research contribution. Here I demonstrated the capability of the highly porous PDMS sponge for the generation of micro- droplets of aqueous solutions in oil by simply squeezing the sponge. The small interconnecting holes located at the interface of the sponge and the surrounding oil acted as microscale orifices, enabling the generation of hundreds of droplets, with the majority of them ranging from 10 to 200 μm.<br><br>I demonstrated the ability of sponge-based droplet generation for the encapsulation of cells. As a proof-of-concept, monocytic leukaemia cells were encapsulated in droplets containing cell culture medium. The density of encapsulated cells was proportional to the volume of droplets as well as the concentration of cells, enabling me to produce hundreds of isolated droplets with various cell populations.<br><br>I further investigated the ability of produced droplets for studying the response of cells to chemical stimulation. As a proof-of-concept, the leukaemia cells were stimulated with hydrogen peroxide prior to encapsulation. The quick settling of encapsulated cells facilitated monitoring their responses using fluorescent<br><br>microscopy. Investigation of cell viability yielded similar results compared to off-chip experiments in the absence and presence of hydrogen peroxide. Experiments indicated the ability for conducting parallel experiments using multiple isolated cell clusters simultaneously.<br><br>Chapter 4 presents a summary of the key findings of this thesis. overall, the highly porous PDMS sponges developed during this research creates unprecedented opportunities for generation of self-sufficient microfluidic systems for various cellular assays.