PhD Oral Exam - Mostapha Marzban, Mechanical Engineering
When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.
Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.
A 3D suspended polymeric microfluidics (SPMF3) for sensitive diagnosis is reported in this study. Design, simulation, fabrication and experimental validations for different applications are presented. Using this innovative lab on a chip platform, variety of biophysical measurements can be done on bioparticles and cells such as detection, counting, flexibility and sizing without any external excitation.
Study of cells and bioparticles have been one of the main foci of microsystems due to their advantages such as simplicity, low price and portability. These microsystems can be categorized in two main groups based on their design which are either microcantilevers or micofluidics. Biodiagnostic microsystems employ different transduction principles to study cells and bioparticles. Microcantilevers work based on mechanical principles such as deflection or frequency variation. However, Microfluidics work based on optical and electrical techniques such as light detection and impedance variation.
Microcantilever systems have shown a broad range of cells and bioparticles detection with a relatively low analysis time in comparison with other methods. This has brought more focus and studies towards this technique. The most innovative microsystem for biophysical study is Suspended Microchannel Resonator (SMR) which has overcome the main issue of microcantilever based systems that have low quality factor imposed by damping effect of surrounding liquid medium.
The first SMR was micromachined in silicon wafer and was actuated using electrostatic excitation electrodes. The microcantilever movements applied by external excitation was captured by an optical laser method. It means that, bioparticles passing through suspended microchannel with a weight in the order of nanogram cannot deflect the highly stiff silicon microcantilever. To overcome this issue, new SMR suspended microfluidics has been investigated which is made of Polydimethylsiloxane (PDMS). This innovation has decreased microchannel stiffness enough to detect bioparticles. In other words, the necessity of integration of external excitation electrodes has been removed by using PDMS instead of silicon material.
In this study, a 3D suspended polymeric microfluidic platform was designed and fabricated for sensitive biodiagnostic applications. To improve the sensitivity of the former suspended microfluidic systems, microchannel plane was modified from microcantilever plane by 90 degrees. This innovative design was simulated and fabricated to validate the concept. Detection of variations in fluid properties which results in diagnosis of bioelements modification during a process has been completely done using SPMF3. It is shown in this thesis that kinematic viscosity is the only fluid parameter that can be used to monitor the variations of fluid properties. Finally, detection and diagnosis of bioelements have been performed and validated using polystyrene microbeads and air bubbles inside the suspended microchannel. In this experiment, 60μm-polystyrene beads were detected using the SPMF3. Moreover, different air bubbles with multiple dimensions and flow rates were detected and studied while passing through the suspended microfluidics.
This thesis also presents a simple theoretical model along with finite element analysis and experimental validation on the effect of fluid properties of both Newtonian and non-Newtonian fluids on the static behavior of suspended 3D microfluidic platforms.