This paper reports on an exemplary study of the performance of commercial computational fluid dynamic (CFD) software programs when applied as engineering tool for microfluidic applications. Four commercial finite volume codes (CFD-ACE+, CFX, Flow-3D and Fluent) have been evaluated by performing CFD-simulations of typical microfluidic engineering problems being relevant for a large variety of lab-on-a-chip (LOAC) applications. Following problems are considered as examples: multi lamination by a split and recombine mixer, flow patterning on a rotating platform (sometimes termed “lab-on-a-disk”), bubble dynamics in micro channels and the so called TopSpot® droplet generator for micro array printing. Hereby mainly the capability of the software programs to deal with free surface flows including surface tension and flow patterning of two fluids has been studied. In all investigated programs the free surfaces are treated by the volume-of-fluid (VOF) method and flow patterning is visualised with a scalar marker method. The study assesses the simulation results obtained by the different programs for the mentioned application cases in terms of consistency of results, computational speed and comparison with experimental data if available.

We demonstrate that Multi-Body Dissipative Particle Dynamics (MDPD) can be used as an efficient computational tool for the investigation of nanoscale capillary impregnation of confined geometries. As an essential prerequisite, a novel model for a solid-liquid interface in the framework of MDPD is introduced, with tunable wetting behaviour and thermal roughening to reduce artificial density- and temperature oscillations. Within this model, the impregnation dynamics of a water-like fluid into a nanoscale slit pore has been studied. Despite the coarse graining implied with the model fluid, a sufficient amount of non-equilibrium averaging can be achieved allowing for the extraction of useful information even from transient simulations, such as the dynamic apparent contact angle. Although it is found to determine the capillary driving completely, it cannot be intepreted as a simple function of the capillary number.

We describe a new multilamination technique to accelerated mixing of centrifugally pumped flows through a simple network of preferentially radial, low-aspect-ratio microchannels. Mixing by multilamination is enforced by planar split-and-recombine structures, consisting of a common inlet for two concurrent centrifugal flows, and a transient region of parallel microchannels which merge again into one common outlet. A repatterning of flow is observed in each parallel channel which is induced by the Coriolis pseudo force. In a distinct regime of the parameter space spanned by the speed of rotation, the channel geometry as the viscosity (and density) of the liquids, a multilamination of flow is achieved at the entrance of the common outlet channel. We also present parallelization and cascading strategies to further enhance the homogeneity and throughput of mixing by multilamination.

Human metapneumovirus (hMPV) is a recently discovered pathogen in respiratory tract infection. The published literature suggests milder illness severity in hMPV compared with respiratory syncytial virus (RSV) infection. In two consecutive seasons, 637 nasopharyngeal aspirates from pediatric patients were tested by hMPV polymerase chain reaction, and risk factors and clinical and laboratory items were analyzed. The hMPV patients were compared with hMPV-negative but RSV-positive patients by matched pair analysis. HMPV was detected in 17.9% of all samples. In total, 88 hMPV-infected patients with complete datasets were considered. More than half of all hMPV patients were older than 12 months, 45.5% had at least one risk factor for a severe course of viral respiratory tract infection, and 27.3% were born prematurely, 15.9% with a birth weight <1,500 g. At least one other virus was also detected in 39 patients (44.3%; RSV in 29.5%). Coinfection did not result in greater severity of illness. On matched pair analysis (hMPV-positive/RSV-negative vs. hMPV-negative/RSV-positive), the epidemiological and clinical features of hMPV infection were similar to those of RSV infection, as in the hMPV group higher proportions of patients with hypoxemia on admission (33% vs. 21%) and of intensive care treatment (20.8% vs. 10.4%) were observed. More hMPV patients showed lobar infiltrates in radiological chest examination. In 60% of all hMPV infections, the attending physicians prescribed antimicrobial chemotherapy. We conclude that in hospitalized children, hMPV infection is as serious as RSV infection and therefore deserves the same attention. Virologic diagnosis from respiratory secretions is mandatory because clinical, laboratory, and radiological signs cannot sufficiently discriminate between viral and bacterial respiratory tract infection in infants and children.

We demonstrate how the speed of mixing under laminar conditions can be appreciably enhanced in concurrent centrifugal flows through straight, low-aspect-ratio microchannels pointing in radial direction in the plane of rotation. The convective mixing is driven by the inhomogeneous distribution of the velocity-dependent Coriolis pseudo force and the interaction of the so-induced transverse currents with the side walls. By investigating the key impact parameters, which are the geometry of the channels and the speed of rotation, it is shown that the contact surface between two laminar flows can be folded to shorten mixing times by up to two orders of magnitude!

We describe a fatal case of encephalitis that might be correlated with primary human metapneumovirus (HMPV) encephalitis. Postmortem HMPV RNA was detected in brain and lung tissue samples from the patient. Furthermore, HMPV RNA was found in culture fluids from cells coincubated with lung tissue.

Recently, an increasing number of studies demonstrated that the human metapneumovirus (HMPV) causes mild to severe respiratory infections in children and immunosuppressed adults, and may be a frequent but somewhat undervalued pathogen. Here, we report the detection of a new variant of HMPV that is not closely related to the HMPV strains described until now. The strain was detected in a 6.5-year-old girl with an acute and severe exacerbation of asthma bronchiale triggered by an infection with a newly detected HMPV variant. The presented data provide new information on genetic heterogeneity of HMPV and necessitate an optimization of diagnostic procedures for the detection of HMPV infection.

This work presents a novel flow switch for centrifugal microfluidic platforms which is solely controlled by the Coriolis pseudo force. This Coriolis switch consists of an inverse Y-structure with one common upstream channel and two symmetric outlets on a rotating disk. Above a certain threshold frequency, the Coriolis force becomes dominant that the entire flow is diverted into one of the outlets which is selected by the direction of rotation. The threshold frequency has been measured to be 350 rad s(-1) (similar to55.7 Hz) for a channel width of 360 mm and a depth of 125 mum. The results are supported by extensive CFD simulations.

This paper shows for the first time a flow switch which is controlled by the Coriolis force on a centrifugal Jab-on-a-disk" platform. The Coriolis switch consists of an inverse Y- structure with one common upstream channel and two symmetric outlets. Above a certain threshold frequency coo, the Coriolis force becomes dominant to direct nearly 100% of the flotv in one of the outlets which is selected by the direction of rotation. The threshold fre- quency has been measured to be 350 rad s-l for a channel width of 360 urn and a depth of 125 ym. The results are supported by extensive CFD simulations.

We investigate how the pseudo-Coriolis force can be employed for the hydrodynamic control of flow through straight and radial microchannels of rectangular cross section on a rotating disk. The key impact parameters are the channel geometry, the angular velocity and the radial downstream position. On the basis of the Coriolis eect, we demonstrate two novel types of hydrodynamically controlled devices for lab-on-a-disk platforms which do neither require hydrophobic structuring of the substrate nor ex- ternal actuators other than a fixed rotational drive unit. The first device is a flow switch constituted by a symmetric fork structure. Above a certain threshold frequency, the flow is diverted into one particular outlet selected by the sense of rotation. The second device is a hydrodynamically con- trolled split-and-recombine mixer represented by a simple, 2-dimensional network of low-aspect-ratio channels in parallel. The multilamination of flow which is required to enable rapid mixing under laminar conditions is enforced by the transversal currents resulting from the Coriolis force. By cascading a sequence of such laminators, mixing times can be reduced by more than one order of magnitude!