Synthetic lipid vesicles have served as important model systems to study cellular membrane biology. Research has shown that the mechanical properties of bilayer membranes significantly affects their biological behavior. The properties of a lipid bilayer are governed by lipid acyl chain length, headgroup type, and the presence of membrane proteins. However, few studies have explored how membrane architecture, in particular trans-bilayer lipid asymmetry, influences membrane mechanical properties. In this study, we investigated the effects of lipid bilayer architecture (i.e. asymmetry) on the mechanical properties of biological membranes. This was achieved using a customized micropipette aspiration system and a novel microfluidic technique previously developed by our team for building asymmetric phospholipid vesicles with tailored bilayer architecture. We found that the bending modulus and area expansion modulus of the synthetic asymmetric bilayers were up to 50% larger than the values acquired for symmetric bilayers. This was caused by the dissimilar lipid distribution in each leaflet of the bilayer for the asymmetric membrane. To the best of our knowledge, this is the first report on the impact of trans-bilayer asymmetry on the area expansion modulus of synthetic bilayer membranes. Since the mechanical properties of bilayer membranes play an important role in numerous cellular processes, these results have significant implications for membrane biology studies.

A flexible and reliable approach to continuously fabricate monodisperse, asymmetric vesicles that provides simultaneous control over the membrane unilamellarity, vesicle size, and luminal content.

Data center energy usage keeps growing every year and will continue to increase with rising demand for ecommerce, scientific research, social networking, and use of streaming video services. The miniaturization of microelectronic devices and an increasing demand for clock speed result in high heat flux systems. By adopting direct liquid cooling, the high heat flux and high power demands can be met, while the reliability of the electronic devices is greatly improved. Cold plates which are mounted directly on to the chips facilitate a lower thermal resistance path originating from the chip to the incoming coolant. An attempt was made in the current study to characterize a commercially available cold plate which uses warm water in carrying the heat away from the chip. A mock package mimicking a processor chip with an effective heat transfer area of 6.45 cm2 was developed for this study using a copper block heater arrangement. The thermo-hydraulic performance of the cold plates was investigated by conducting experiments at varying chip power, coolant flow rates, and coolant temperature. The pressure drop (ΔP) and the temperature rise (ΔT) across the cold plates were measured, and the results were presented as flow resistance and thermal resistance curves. A maximum heat flux of 31 W/cm2 was dissipated at a flow rate of 13 cm3/s. A resistance network model was used to calculate an effective heat transfer coefficient by revealing different elements contributing to the total resistance. The study extended to different coolant temperatures ranging from 25 °C to 45 °C addresses the effect of coolant viscosity on the overall performance of the cold plate, and the results were presented as coefficient of performance (COP) curves. A numerical model developed using 6SigmaET was validated against the experimental findings for the flow and thermal performance with minimal percentage difference.

Optimization of liquid-cooled heatsinks (cold plates) is of critical importance due to their wide-spread application in high-performance electronic packages consisting of heterogeneous integrated systems, field programmable gate arrays (FPGAs), and on-chip hotspots. In this study, the thermo-hydraulic performance of a commercial microchannel impingement cold plate is analyzed in detail. Impingement cold plates are preferred over parallel flow cold plates due to their lower pressure drop where there is no restriction on space (i.e. where flow can enter perpendicular to the electronic board.). Splitting the flow into two branches cuts the flow rate and path in half, which leads to a lower pressure drop through the channels. Since the fins of the present commercial cold plate (considered as the baseline design) are tilted, the effect of fin tilt angle on the hydraulic and thermal performance of the cold plate is also studied. Response surface method is used to optimize the geometry of the fins and impinging inlet. The results of optimization show that hydraulic resistance can be reduced by 50% without a remarkable change in thermal resistance. The effect of geometric parameters on the cold plate thermo-hydraulic performance is studied by using the computational fluid dynamics results at response surface method design points. The variation of the cold plate coefficient of performance with the coolant flow rate and inlet temperature is compared for the baseline design and a selected optimal design. Finally, the effect of impinging inlet geometry on the chip temperature profile is also examined.