Development and improved fabrication of microfluidic devices for local delivery to investigate properties of healthy and inflamed lymph node tissue in ex vivo slices

Local delivery of chemical analytes to ex vivo tissue slices is a useful mechanism for studying their intrinsic properties, such as diffusivity and tortuosity, which can give new insights into healthy tissue homeostasis and diseased tissue states. Microfluidic devices allow for the manipulation of small volumes of liquid and are well suited to preform local delivery to tissues. Chapter 2 demonstrates the potential of local delivery devices to study tissue properties by investigating the diffusivity of inflamed lymph node tissue after vaccination, and characterizing the diffusion coefficients. Mice were vaccinated with different adjuvants, which are the components of vaccines that promote an immune response. Adjuvant-dependent changes in diffusivity and tortuosity were observed. One of the limitations with previous static delivery port microfluidic devices is the handling of the tissue that is required by the user to target sub-sections of the tissue. Tissue slices are fragile and extraneous handling can cause mechanical damage. Chapter 3 will improve local delivery technology by directly addressing user-handling with a SlipChip design. A SlipChip is a two-phase microfluidic device that consists of two components separated by an oil layer allowing for rearrangement of the fluidic pathway. Using the SlipChip, we can protect the tissue slice from excessive handling by housing the tissue in a chamber and reconfiguring the device to position a port beneath a tissue. The movable microfluidic port device was able to target substructures as small as 200 µm. The first iteration of this movable microfluidic port device required extensive fabrication steps to achieve the design. Digital light processing (DLP) 3D printing is an alternative fabrication method that can simplify the fabrication of the device to make it more accessible for other collaborators and allow for rapid prototyping of more sophisticated designs. Achieving a 3D printed SlipChip movable port device required verification that resin printing can create a fluorinated surface that is flat, smooth and optically clear. Chapter 4, highlights the validation of a versatile and robust method to selectively pattern a fluorinated surface onto a DLP printed component. Utilizing a fluoroalkyl silane, this novel method only requires a simple coating step without prior surface activation. Using this surface modification method, the first SlipChip with DLP 3D printing is fabricated in Chapter 5. First, I investigated the optical transparency, surface smoothness, and biocompatibility of the printed parts, to ensure they were adequate for the movable port device. Then printed movable port SlipChip successfully delivered to sequentially tissue without any leakage. The work in this thesis has focused primarily on improving local delivery to tissue while demonstrating the need for such technology to probe intrinsic properties of tissues. The future of this technology is dependent on the accessibility to collaborators, which has been achieved through 3D printing and is now set up to advance even further.