Numerical modeling of pulsatile blood flow through a mini-oxygenator in artificial lungs.

While previous in vitro studies showed divergent results concerning the influence of pulsatile blood flow on oxygen advection in oxygenators, no study was done to investigate the uncertainty affected by blood flow dynamics. The aim of this study is to utilize a computational fluid dynamics model to clarify the debate concerning the influence of pulsatile blood flow on the oxygen transport. The computer model is based on a validated 2D finite volume approach that predicts oxygen transfer in pulsatile blood flow passing through a 300-micron hollow-fiber membrane bundle with a length of 254 mm, a building block for an artificial lung device. In this study, the flow parameters include the steady Reynolds number (Re = 2, 5, 10 and 20), Womersley parameter (Wo = 0.29, 0.38 and 0.53) and sinusoidal amplitude (A = 0.25, 0.5 and 0.75). Specifically, the computer model is extended to verify, for the first time, the previously measured O2 transport that was observed to be hindered by pulsating flow in the Biolung, developed by Michigan Critical Care Consultants. A comprehensive analysis is carried out on computed profiles and fields of oxygen partial pressure (PO2) and oxygen saturation (SO2) as a function of Re, Wo and A. Based on the present results, we observe the positive and negative effects of pulsatile flow on PO2 at different blood flow rates. Besides, the SO2 variation is not much influenced by the pulsatile flow conditions investigated. While being consistent with a recent experimental study, the computed O2 volume flow rate is found to be increased at high blood flow rates operated with low frequency and high amplitude. Furthermore, the present study qualitatively explains that divergent outcomes reported in previous in vitro experimental studies could be owing to the different blood flow rates adopted. Finally, the contour analysis reveals how the spatial distributions of PO2 and SO2 vary over time.

Multifunctional microchip-based distillation apparatus II - Aerated distillation for sulfur dioxide detection.

A multifunctional microchip-based distillation apparatus is presented for the distilled of sulfur dioxide (SO2) in food products. The microchip is fabricated on poly(methyl methacrylate) (PMMA) substrates, and comprises a sample zone, a buffer zone, a serpentine distillation column, and a collection zone. In the process, the sample is introduced into the sample zone and is heated under carefully controlled temperature and time conditions. The resulting SO2 and water vapor are carried by nitrogen (N2) gas to the distillation column, where the SO2 is separated from the water vapor via the condensing effects of a continuous cold water flow. Finally, the SO2 is transported to the collection zone, where it is collected with hydrogen peroxide (H2O2) and its concentration determined using an alkali-based titration and paper-based detection method. A distillation efficiency of 90.5% is obtained under the optimal distillation conditions at concentrations of 20-4000 ppm. Moreover, a linear correlation (R2 = 0.9997) is observed between the experimental measurements of the SO2 concentration and the known concentration. The validity of the presented microchip-based distillation apparatus is further investigated by distilling the SO2 concentrations of 25 commodity samples. The detection results show that the deviation does not exceed 5.4% compared with the traditional official method.

Multifunctional microchip-based distillation apparatus I - Steam distillation for formaldehyde detection.

A multifunctional microchip-based distillation apparatus for distilling and detecting formaldehyde (CH2O) in food products is developed. The presented apparatus comprises a disposable microchip, a steam supply system, and a recirculating cooling water supply. The microchip is formed on PMMA substrates by laser ablation and includes a sample zone, a flash distillation zone, a cooling zone, a condensation zone, and a collection zone. In the presented method, the CH2O sample is placed in the microchip and is vaporized by the high-throughput vapor supply and driven through the condensed zone. The condensed CH2O liquid is guided into the collection zone of the microchip. Finally, the distilled CH2O solution is determined using an AHMT spectrometry method and a paper-based RGB (red, green and blue) intensity analysis method. A distilled efficiency is as high as 98%, when a vapor stream rate is 0.4 ml/min and a distilled time is 10 min. Moreover, both detection methods show linear relationships of the corresponding CH2O concentrations. The actual sample suitability of the presented multifunctional microchip-based distillation apparatus is confirmed by analyzing the CH2O concentrations of 21 commodities.