Laser Direct Writing of Microchannels for Artificial Lungs.

This research describes laser machining of microchannel branching networks into silicon. The branching network is designed to serve as gas exchangers for use in artificial lungs and simulates physiological flow; mimicking the tree-like vascular structure of natural lung. In the development of such micro-fluidic structures, the flexibility of laser direct writing facilitates creation of three-dimensional multi-level structure. And, the maskless process will reduce time and cost compared to that of conventional photolithography technique. First, near-IR nanosecond ablation of silicon is studied. An emphasis has been placed on the improvement of the surface quality of nanosecond ablation. An acid etching post process step is introduced to clean out debris-buildup caused by strong thermal reaction of the irradiated silicon. Influences of processing parameters on the depth and the surface morphology of laser ablation followed by acid etching are investigated. Combinations of laser processing parameters are optimized to create a wide range of microchannel sizes with reasonable surface quality. Second, femtosecond ablation of silicon is experimentally and numerically studied. While providing better surface quality and resolution than nanosecond pulses, relatively low productivity of femtosecond pulses has limited its contribution in practical applications. Investigations on the effect of processing parameters are conducted to improve processing speed and to achieve a wide range of microchannel sizes with reasonable surface quality. Optimized processing condition provides macroscopic material removal as well as micron scale precision. To understand the non-thermal process of femtosecond ablation of silicon, a numerical model is simulated. The modeling considers two characteristic mechanisms: free electron (or electron-hole pair) generation and electron-phonon interaction before thermal equilibrium. Finally, the blood flow and the oxygen transfer in the microchannel networks are characterized by both experiments and numerical simulations. In the simulation, the shear thinning non-Newtonian characteristic of the blood viscosity and the oxygen-hemoglobin binding are taken into account. The simulation results demonstrate the benefit of gas exchangers designed using Murray’s law. The laser technique developed in this study provides the ability to mimic the feature of the natural vasculature in development of artificial lungs. The physiological features are expected to contribute to further development of artificial lungs.PhDMechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/64584/1/kamdong_1.pd