Safe Energy Source in Battery-operated Toys for Children.

OBJECTIVES: Serious and even fatal consequences of disk batteries ingestion in children are well known. Among other applications, disk batteries are used to power small toys, from which they can be unexpectedly extracted and swallowed. METHODS: We tested a new cell intended for little toys (green cell [GC]), after 6 and 12 hours of in vitro close contact with esophageal swine mucosa. The GC was compared with lithium and silver button batteries under the same experimental conditions. RESULTS: Tissues in contact with the GC did not show pH variations nor histological alterations after 6 and 12 hours. In such conditions, statistically significant differences were found between the GC and the lithium and silver batteries. CONCLUSIONS: So far, multidisciplinary medical effort has been driven to both emergency approach and subsequent operative strategies in children with ingested batteries. Our trial demonstrates the possibility to primarily prevent battery-induced damages by designing new-generation safe cells with no tissue toxicity to power little toys intended for children.

Computational modeling of passive furrowed channel micromixers for lab-on-a-chip applications.

BACKGROUND: Effective micromixers represent essential components for micro total analysis systems or lab-on-a-chip. Indeed, mixing is a key process for the success of all chemical or biochemical reactions. Most microfluidic systems operate in a laminar flow regime dominated by molecular diffusion, which is not favorable to mixing. In the present work, numerical analyses of mixing in 3-dimensional channels with obstacles on the walls were performed to investigate mixing behavior and flow characteristics with geometric parameters as well as Reynolds number. METHODS: Several channel wall geometries were numerically modeled, and the influence of obstacle height, phase shift between the walls, channel cross-section shape (aspect ratio) and Reynolds number on mixer performances was investigated. Wall geometries were evaluated comparatively in terms of index of mixing and pressure drops caused. RESULTS: Results indicated that furrowed channels with proper triangle-shaped obstacles show good performances in terms of achieving complete mixing in a very short length of channel, and at the same time offer low pressure losses. Convective motions are the main influences responsible for successful mixing, and micromixers with triangle-shaped obstacles show an improvement in the mixing performances for increasing Reynolds numbers. Moreover, short times are required for the mixing process. Finally, depending on the Reynolds number that one works at, there is also some flexibility in the choice of the channel geometry, as the occurrence of effective chaotic advection was obtained for several conformations of the channels proposed in this study. CONCLUSIONS: Mixing enhancement can be achieved by optimizing the shape of the furrowed channel.

Geometrical effects in microfluidic-based microarrays for rapid, efficient single-cell capture of mammalian stem cells and plant cells.

In this paper, a detailed numerical and experimental investigation into the optimisation of hydrodynamic micro-trapping arrays for high-throughput capture of single polystyrene (PS) microparticles and three different types of live cells at trapping times of 30 min or less is described. Four different trap geometries (triangular, square, conical, and elliptical) were investigated within three different device generations, in which device architecture, channel geometry, inter-trap spacing, trap size, and trap density were varied. Numerical simulation confirmed that (1) the calculated device dimensions permitted partitioned flow between the main channel and the trap channel, and further, preferential flow through the trap channel in the absence of any obstruction; (2) different trap shapes, all having the same dimensional parameters in terms of depth, trapping channel lengths and widths, main channel lengths and widths, produce contrasting streamline plots and that the interaction of the fluid with the different geometries can produce areas of stagnated flow or distorted field lines; and (3) that once trapped, any motion of the trapped particle or cell or a shift in its configuration within the trap can result in significant increases in pressures on the cell surface and variations in the shear stress distribution across the cell's surface. Numerical outcomes were then validated experimentally in terms of the impact of these variations in device design elements on the percent occupancy of the trapping array (with one or more particles or cells) within these targeted short timeframes. Limitations on obtaining high trap occupancies in the devices were shown to be primarily a result of particle aggregation, channel clogging and the trap aperture size. These limitations could be overcome somewhat by optimisation of these device design elements and other operational variables, such as the average carrier fluid velocity. For example, for the 20 µm polystyrene microparticles, the number of filled traps increased from 32% to 42% during 5-10 min experiments in devices with smaller apertures. Similarly, a 40%-60% reduction in trapping channel size resulted in an increase in the amount of filled traps, from 0% to almost 90% in 10 min, for the human bone marrow derived mesenchymal stem cells, and 15%-85% in 15 min for the human embryonic stem cells. Last, a reduction of the average carrier fluid velocity by 50% resulted in an increase from 80% to 92% occupancy of single algae cells in traps. Interestingly, changes in the physical properties of the species being trapped also had a substantial impact, as regardless of the trap shape, higher percent occupancies were observed with cells compared to single PS microparticles in the same device, even though they are of approximately the same size. This investigation showed that in microfluidic single cell capture arrays, the trap shape that maximizes cell viability is not necessarily the most efficient for high-speed single cell capture. However, high-speed trapping configurations for delicate mammalian cells are possible but must be optimised for each cell type and designed principally in accordance with the trap size to cell size ratio.