A more effective treatment of bacteremia requires a diagnostic platform that is both sensitive, accurate and rapid. Currently, clinical laboratory techniques require growth of bacteria prior to diagnosis, take days to complete, and leave empiric therapy and broad spectrum antibiotics as the only option at the onset of treatment. In order to bypass this growth requirement, we engineered a system that purifies bacteria from blood to improve performance in a bacteriophage-based luminescence assay. To perform the purification, we used acoustophoresis in plastic microfluidic chips, enabling future development into a low cost point-of-care system. Acoustophoresis achieves differential separation on the basis of size differences between bacteria and blood cells. We show isolation of three known pathogen species, including members of both Gram-negative and positive-bacteria from blood, and show isolation at clinically relevant concentrations. Using the device as a preparation step prior to the bacteriophage-based luminescence assay, we demonstrate a 33-fold improvement in limit of detection, compared with the unpurified sample, achieving a limit of detection of 6 bacteria.
Acoustic manipulation has emerged as a versatile method for microfluidic separation and concentration of particles and cells. Most recent demonstrations of the technology use piezoelectric actuators to excite resonant modes in silicon or glass microchannels. Here, we focus on acoustic manipulation in disposable, plastic microchannels in order to enable a low-cost processing tool for point-of-care diagnostics. Unfortunately, the performance of resonant acoustofluidic devices in plastic is hampered by a lack of a predictive model. In this paper, we build and test a plastic blood-bacteria separation device informed by a design of experiments approach, parametric rapid prototyping, and screening by image-processing. We demonstrate that the new device geometry can separate bacteria from blood while operating at 275% greater flow rate as well as reduce the power requirement by 82%, while maintaining equivalent separation performance and resolution when compared to the previously published plastic acoustofluidic separation device.
The boundary layer ingestion concept has the potential to improve propulsion efficiency that will lead to better fuel economy of commercial aircraft. This design concept has been explored by NASA as the Single-aisle Turboelectric Aircraft with Aft Boundary-Layer propulsor “STARC-ABL.” This paper discusses the 1D-3D aerodynamic design and optimization process as well as the structural analysis of the rotor of a propulsor with incoming distortion. The propulsor is at the tail of the fuselage, and consists of an Inlet Guide Vane (IGV), Rotor, and Outlet Guide Vane (OGV). The design process presented accounts for only the large radial distortion and not the circumferential distortion. The paper also describes a pragmatic way of choosing orthogonal design parameters to proceed with the optimization process using a genetic algorithm. The final optimized design is highly dependent on the objective function to be optimized. A Modified Adiabatic Efficiency (MAE) has been defined to account for the loss of kinetic energy downstream of the propulsor CFD exit plane. This lost kinetic energy is essentially an approximation of the mixing loss of the tangential, axial and radial components of velocity at the OGV exit. The three blade-row adiabatic efficiency and MAE for an intermediate design case was 88.91% and 86.10% respectively. Upon further optimization and a different incoming distortion, using MAE as the objective function improved the MAE by 2.14% and adiabatic efficiency by 0.25% for the final design case presented in this paper. The rotor-only adiabatic efficiency for this case is 94.49%, the IGV-Rotor two blade-row efficiency is 92.71% and the Rotor-OGV two blade-row efficiency is 90.94%. The IGV is necessary to support the nacelle in this configuration. It also allows for the rotor work distribution to be optimized. The resulting rotor blade satisfies the static structural limit of a 1.1 safety factor for titanium at 110% speed. It also includes the pressure loads from the design point. The process uses an open source parametric blade generator whose source and input files for this geometry are on GitHub.
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