Porous micropillar structures for retaining low surface tension liquids.

The ability to manipulate fluid interfaces, e.g., to retain liquid behind or within porous structures, can be beneficial in multiple applications, including microfluidics, biochemical analysis, and the thermal management of electronic systems. While there are a variety of strategies for controlling the disposition of liquid water via capillarity, such as the use of chemically modified porous adhesive structures and capillary stop valves or surface geometric features, methods that work well for low surface tension liquids are far more difficult to implement. This study demonstrates the microfabrication of a silicon membrane that can retain exceptionally low surface tension fluorinated liquids against a significant pressure difference across the membrane via an array of porous micropillar structures. The membrane uses capillary forces along the triple phase contact line to maintain stable liquid menisci that yield positive working Laplace pressures. The micropillars have inner diameters and thicknesses of 1.5-3 µm and ∼1 µm, respectively, sustaining Laplace pressures up to 39 kPa for water and 9 kPa for Fluorinert™ (FC-40). A theoretical model for predicting the change in pressure as the liquid advances along the porous micropillar structure is derived based on a free energy analysis of the liquid meniscus with capped spherical geometry. The theoretical prediction was found to overestimate the burst pressure compared with the experimental measurements. To elucidate this deviation, transient numerical simulations based on the Volume of Fluid (VOF) were performed to explore the liquid pressure and evolution of meniscus shape under different flow rates (i.e., Capillary numbers). The results from VOF simulations reveal strong dynamic effects where the anisotropic expansion of liquid along the outer micropillar edge leads to an irregular meniscus shape before the liquid spills along the micropillar edge. These findings suggest that the analytical prediction of burst Laplace pressure obtained under quasi-static condition (i.e., equilibrium thermodynamic analysis under low capillary number) is not applicable to highly dynamic flow conditions, where the liquid meniscus shape deformation by flow perturbation cannot be restored by surface tension force instantaneously. Therefore, the critical burst pressure is dependent on the liquid velocity and viscosity under dynamic flow conditions. A numerical simulation using Surface Evolver also predicts that surface defects along the outer micropillar edge can yield up to 50% lower Laplace pressures than those predicted with ideal feature geometries. The liquid retention strategy developed here can facilitate the routing and phase management of dielectric working fluids for application in heat exchangers. Further improvements in the retention performance can be realized by optimizing the fabrication process to reduce surface defects.

Delay to curative surgery greater than 12 weeks is associated with increased mortality in patients with colorectal and breast cancer but not lung or thyroid cancer.

BACKGROUND: Surgery for cancer is often delayed due to variety of patient-, provider-, and health system-related factors. However, impact of delayed surgery is not clear, and may vary among cancer types. We aimed to determine the impact of the delay from cancer diagnosis to potentially curative surgery on survival. METHODS: Cohort study based on representative sample of patients (n = 7,529) with colorectal, breast, lung and thyroid cancer with local or regional disease who underwent potentially curative surgery as their first therapeutic modality within 1 year of cancer diagnosis. They were diagnosed in 2006 and followed for mortality until April 2011, a median follow-up of 4.7 years. RESULTS: For colorectal and breast cancers, the adjusted hazard ratios (95 % confidence intervals) for all-cause mortality comparing a surgical delay beyond 12 weeks to performing surgery within weeks 1-4 after diagnosis were 2.65 (1.50-4.70) and 1.91 (1.06-3.49), respectively. No clear pattern of increased risk was observed with delays between 4 and 12 weeks, or for any delay in lung and thyroid cancers. Concordance between the area of the patient's residence and the hospital performing surgery, and the patient's income status were associated with delayed surgery. CONCLUSIONS: Delays to curative surgery beyond 12 weeks were associated with increased mortality in colorectal and breast cancers, suggesting that health provision services should be organized to avoid unnecessary treatment delays. Health care systems should also aim to reduce socioeconomic and geographic disparities and to guarantee equitable access to high quality cancer care.