Membrane integration in biomedical microdevices

Abstract

The target of the research presented in this thesis is a design, development and fabrication of a microfluidic device with integrated membrane in the form of a membrane contactor for various biological applications. The microfluidic devices are fabricated and tested for oxygenation of blood and separation of anaesthetic gas. In the first part of the work, the microfluidic system for blood oxygenation, so called lung-on-a-chip, is introduced. In such system, one chamber is devoted to pure oxygen, and the other chamber is designed for blood and they are separated by a dense permeable membrane. Computer modelling is performed in order to design the liquid chamber with homogenous liquid flow, low pressure drop of the system and low shear stress without compensation of high oxygenation. Two different microdevice geometries are proposed: alveolar and meander type design with vertical membrane arrangement. Fabricated devices as well as integrated membranes are made of PDMS by soft-lithography and their surface is modified in order to make them more hydrophilic. The experiments of blood oxygenation are performed and the oxygen concentration is measured by an oximeter electrode and compared to the mathematically modelled values. The parameter sensitivity and the possible improvements of the proposed architectures based on the mathematical simulations are presented as well. The second part of the thesis, introduces the concept of an alveolar microfluidic device as gas-ionic liquid micro-contactor for removal of CO2 from anaesthesia gas, containing Xe. The working principle involves the transport of CO2 through a flat PDMS membrane followed by the capture and enzymatic bioconversion in the ionic liquid solvent. As proof of concept demonstration, simple gas permeability experiments are performed followed by the experiments with ionic liquid and ionic liquid with the enzyme. Finally, an alternative concept of a microfluidic device with an integrated membrane in the form of a fractal geometry with nanonozzles as pores at the vertices of the third-level octahedra for the controlled addition of gaseous species is introduced. Fractal geometry, that is a three-dimensional repetitive unit, is fabricated by a combination of anisotropic etching of silicon and corner lithography. As a proof of concept, simple gas permeation experiments are performed, and the achieved results are compared to the gas permeation obtained by a dense PDMS membrane.