Optimization of Patterned Surfaces for Improved Superhydrophobicity through Cost-Effective Large-Scale Computations.

The pattern design of superhydrophobic surfaces can be significantly aided by computations that predict the Cassie-Baxter (CB) to Wenzel (W) transition, which is responsible for the break-down of superhydrophobic behavior. We present a computational framework for the optimization of patterned surfaces based on the energy barriers of the CB-W transitions which comprises the following elements: (a) design of structured surface patterns, for example, arrays of pillars, with parameterized geometric features such as size, pitch, slope, and roundness. (b) Computation of the wetting states with a modified Young-Laplace equation that facilitates the introduction of solid/liquid interactions for complex surface patterns and has significantly lower computational cost than other commonly used methods, such as the volume-of-fluid, phase-field, and so forth. (c) Incorporation of the modified Young-Laplace in the simplified string method, allowing the calculation of the minimum energy paths of wetting transitions which, apart from the energy barriers, also reveal the transition mechanisms (CB failure modes). (d) Accommodation of large-scale problems with good parallel performance and scalability on multicore-distributed memory systems using fast iterative solvers and the Message Passing Interface communication protocol. We demonstrate the computational framework with a shape optimization study of inverted conical frustum pillars. The optimization objective function is the resistance to the CB-W transition, which is quantified by the energy barrier-a relatively large energy barrier suggests improved superhydrophobicity. We also report the parallel performance, in terms of parallel speedup for problems ranging from three hundred thousands to 12 million degrees of freedom, solved using up to 40 processing cores.

Concurrent femoral head reduction and periacetabular osteotomies for the treatment of severe femoral head deformities.

AIMS: The aims of this study were to review the surgical technique for a combined femoral head reduction osteotomy (FHRO) and periacetabular osteotomy (PAO), and to report the short-term clinical and radiological results of a combined FHRO/PAO for the treatment of selected severe femoral head deformities. PATIENTS AND METHODS: Between 2011 and 2016, six female patients were treated with a combined FHRO and PAO. The mean patient age was 13.6 years (12.6 to 15.7). Clinical data, including patient demographics and patient-reported outcome scores, were collected prospectively. Radiologicalally, hip morphology was assessed evaluating the Tönnis angle, the lateral centre to edge angle, the medial offset distance, the extrusion index, and the alpha angle. RESULTS: The mean follow-up was 3.3 years (2 to 4.6). The modified Harris Hip Score improved by 33.0 points from 53.5 preoperatively to 83.4 postoperatively (p = 0.03). The Western Ontario McMasters University Osteoarthritic Index score improved by 30 points from 62 preoperatively to 90 postoperatively (p = 0.029). All radiological parameters showed significant improvement. There were no long-term disabilities and none of the hips required early conversion to total hip arthroplasty. CONCLUSION: FHRO combined with a PAO resulted in clinical and radiological improvement at short-term follow-up, suggesting it may serve as an appropriate salvage treatment option for selected young patients with severe symptomatic hip deformities.

Computational investigation of actuation mechanisms of droplets on porous air-permeable substrates.

We study the actuation of droplets on porous substrates by air that permeates through pores. Air pockets are created between the droplets and the substrate which, eventually, incite the droplets to a quasi-moving state. We observe this mechanism computationally and verify it experimentally, using various case studies involving water droplets of different volume that are initially pinned on a porous substrate which has been set to different inclination levels and start to slide down when actuated by permeating air. The computational model employs the continuity equation and the equations of momentum transfer that are coupled with the Volume of Fluid (VOF) method, to track the shape of the droplet. We identify two dominant actuation mechanisms - seen in computations and experiments - that are given the names 'donut' and 'tunnel'. Both of them are characterized by the formation of small air pockets between the droplet and the substrate that coalesce into larger ones that finally escape the droplet, by collapsing its free surface. The two mechanisms differ in the way that the free surface of the droplet collapses. The donut mechanism has the free surface collapsing at its center, thus forming a hole in the middle of the droplet (hence the name, donut), whereas the tunnel mechanism has the free surface collapsing at its rear side, forming a horizontal hole that resembles a tunnel (hence the name). We compare each mechanism in terms of the event (mechanism) occurrence frequency and droplet displacement, and also provide the dependence of the droplet speed with respect to the flow rate of permeating air, substrate inclination and droplet volume.

Droplet Mobility Manipulation on Porous Media Using Backpressure.

Wetting phenomena on hydrophobic surfaces are strongly related to the volume and pressure of gas pockets residing at the solid-liquid interface. In this study, we explore the underlying mechanisms of droplet actuation and mobility manipulation when backpressure is applied through a porous medium under a sessile pinned droplet. Reversible transitions between the initially sticky state and the slippery states are thus incited by modulating the backpressure. The sliding angles of deionized (DI) water and ethanol in DI water droplets of various volumes are presented to quantify the effect of the backpressure on the droplet mobility. For a 50 µL water droplet, the sliding angle decreases from 45 to 0° when the backpressure increases to ca. 0.60 bar. Significantly smaller backpressure levels are required for lower surface energy liquids. We shed light on the droplet actuation and movement mechanisms by means of simulations encompassing the momentum conservation and the continuity equations along with the Cahn-Hilliard phase-field equations in a 2D computational domain. The droplet actuation mechanism entails depinning of the receding contact line and movement by means of forward wave propagation reaching the front of the droplet. Eventually, the droplet skips forward. The contact line depinning is also corroborated by analytical calculations based on the governing vertical force balance, properly modified to incorporate the effect of the backpressure.

Wetting transitions on patterned surfaces with diffuse interaction potentials embedded in a Young-Laplace formulation.

The Minimum Energy Paths (MEPs) of wetting transitions on pillared surfaces are computed with the Young-Laplace equation, augmented with a pressure term that accounts for liquid-solid interactions. The interactions are smoothed over a short range from the solid phase, therefore facilitating the numerical solution of problems concerning wetting on complex surface patterns. The patterns may include abrupt geometric features, e.g., arrays of rectangular pillars, where the application of the unmodified Young-Laplace is not practical. The MEPs are obtained by coupling the augmented Young-Laplace with the modified string method from which the energy barriers of wetting transitions are eventually extracted. We demonstrate the method on a wetting transition that is associated with the breakdown of superhydrophobic behavior, i.e., the transition from the Cassie-Baxter state to the Wenzel state, taking place on a superhydrophobic pillared surface. The computed energy barriers quantify the resistance of the system to these transitions and therefore, they can be used to evaluate superhydrophobic performance or provide guidelines for optimal pattern design.

Rapid measurement of serum pancreatic amylase.

A simple, rapid assay for the pancreatic isoenzyme of human serum amylase was developed. The assay utilized an immunoabsorbent prepared by coating latex beads with a monoclonal antibody specific for pancreatic amylase. Treatment of patient serum with immunoabsorbent removed pancreatic amylase, and measurement of residual amylase activity with standard total amylase methodology allowed estimation of the pancreatic amylase content. Extraction efficiency of pancreatic amylase was consistent at amylase concentrations up to 1,000 U/L (y = 0.97 x +16.7 U/L; r = 0.9995). The assay was standardized with purified pancreatic amylase added to neonatal serum (low endogenous activity). A comparison of patient specimen results with the results of a standard technique (cellulose acetate electrophoresis) yielded an excellent correlation (immunoabsorption result = 0.96 electrophoresis result + 1.2 U/L; r = 0.987). Salivary amylase did not interfere with the assay until levels exceeded 1,000 U/L. Daily analysis of a frozen serum pool yielded a coefficient of variation of 9.2% at mean pancreatic amylase value of 54 U/L (+/- 5 U/L). A normal range study found a strong influence of age, with pancreatic amylase levels increasing dramatically in the first 3 years of life, to stabilize at a range of 0-66 U/L thereafter.

Macroamylases: differences in activity against various-sized substrates.

Hyperamylasemia caused by macroamylases can lead to the overdiagnosis of acute pancreatitis. We examined whether interference from macroamylase is less in assays that use high-molecular-mass (high-M(r)) substrates rather than oligosaccharide substrates. We hypothesized that high-M(r) substrates would be sterically excluded from macroamylasemic complexes and thus would be hydrolyzed less efficiently. Eighteen macroamylasemic samples were assayed by using red-dyed amylopectin or blue-dyed starch as polysaccharide substrates or by using maltoheptaose or maltotetraose as oligosaccharide substrates. The oligosaccharide substrates gave comparable results (y = 0.81x + 83), but we observed consistently lower activities for amylopectin than for maltotetraose (y = 0.32x + 38). We observed no bias among methods when nonmacroamylasemic specimens were analyzed. The mechanism of this difference was examined by adding antihuman pancreatic amylase antibodies to hyperamylasemic serum samples from patients without macroamylasemia and to purified human pancreatic or salivary isoamylases. In each case, polyclonal and monoclonal antibodies lowered amylase activity more in assays with complex polysaccharides than in those with oligosaccharides. The use of high-M(r) substrates diminishes interference, and detection of suspected macroamylasemia may be possible through comparing activities determined from automated methods that use different substrates.

Macroamylases: differences in activity against various-size substrates.

Hyperamylasemia caused by macroamylases can lead to the overdiagnosis of acute pancreatitis. We examined whether interference from macroamylase is less in assays that use high-molecular-weight rather than oligosaccharide substrates. We hypothesized that high-molecular-weight substrates would be sterically excluded from macroamylasemic complexes and thus would be hydrolyzed less efficiently. Eighteen macroamylasemic samples were assayed by using red-dyed amylopectin or blue-dyed starch as polysaccharide substrates or by using maltoheptaose or maltotetraose as oligosaccharide substrates. The oligosaccharide substrates gave comparable results (y = 0.81x + 83); we observed consistently lower activities for amylopectin than for maltotetraose (y = 0.32x + 38). We observed no bias among methods when nonmacroamylasemic specimens were analyzed. The mechanism of this difference was examined by adding anti-human pancreatic amylase antibodies to hyperamylasemic serum samples from patients without macroamylasemia and purified human pancreatic or salivary isoamylases. In each case, polyclonal and monoclonal antibodies lowered amylase activity more in assays with complex polysaccharides than in those with oligosaccharides. The use of high-molecular-weight substrates diminishes interference, and detection of suspected macroamylasemia may be possible through comparison of activities determined from automated methods that use different substrates.