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On-line pH detection of cell culture environment is necessary in a bioprocess or tissue engineering. Devices by means of electrochemical mechanisms for this purpose have been reported to be less suitable compared with optical-based sensing principles. More recently, some non-invasive optical sensing systems have been proposed for online pH monitoring of cell culture environment. However, these devices are not for multi-target pH monitoring purpose, and are large in scale and thus not appropriate for the pH monitoring at a micro scale such as in microbioreactor or microfluidic-based cell culture platform. To tackle these issues, an optical fiber sensor array for on-line pH monitoring was proposed using microfluidic technology. The working principle is based on the optical absorption of phenol red normally contained in culture medium. Different from other device of the similar working principle, the proposed device requires less liquid volume (less than 0.8 microl), is non-invasive, and particularly can be configured as an array for high throughput pH monitoring. The present device has been optimized for the shape of detection chamber in a microfluidic chip with the aid of computational fluid dynamics (CFD) simulation, to avoid flow dead zone and thus to reduce the response time of detection. Both simulation and experimental results revealed that the design of oval detection chamber (axis, 1.5 and 2.0 mm) can considerably reduce the response time. Preliminary test has proved that the optical pH detection device is able to detect pH with average detection sensitivity of 0.83 V/pH in the pH range of 6.8-7.8, which is normally experienced in mammalian cell culture.

In this study, we successfully designed and tested a new micropump that utilizes an active check valve and bottom-protruding structure to achieve sample transportation. We performed theoretical analyses and numerical simulations to determine the optimal location of the active check valve. We also experimentally analyzed variations in the generated flow rate with respect to the pneumatic frequencies, actuated air pressures, and locations of the active check valve. The experimental results indicate the optimum air pressure, driving frequency, and location of the active check valve to be 68.9 kPa, 26.0 Hz, and 2.0 mm, respectively. We obtained a maximum pumping rate of 488 μL/min and a maximum pumping efficiency of 35.4%. The proposed micropump could perform a crucial function in the transportation of microfluids and could be incorporated into micro total analysis systems. [ABSTRACT FROM AUTHOR]

This study aimed to design and fabricate planar constricted–expanded structures that are integrated into paper-based channels in order to enhance their chaotic advection and improve their mixing performance. Chromatography papers were used to print paper-based microfluidics using a solid-wax printer. Three different constricted–expanded structures—i.e., zigzag, crossed, and curved channels—were designed in order to evaluate their mixing performance in comparison with that of straight channels. A numerical simulation was performed in order to investigate the mixing mechanism, and to examine the ways in which the planar constricted–expanded structures affected the flow patterns. The experimental and numerical results indicated that the proposed structures can successfully mix confluents. The experimental results revealed that the mixing indices (σ) rose from the initial 20.1% (unmixed) to 34.5%, 84.3%, 87.3%, and 92.4% for the straight, zigzag, curved, and cross-shaped channels, respectively. In addition, the numerical calculations showed a reasonable agreement with the experimental results, with a variation in the range of 1.0–11.0%. In future, we hope that the proposed passive paper-based mixers will be a crucial component in the application of paper-based microfluidic devices. [ABSTRACT FROM AUTHOR]

In this study, a valveless pump was successfully designed and fabricated for the purpose of medium transportation. Different from traditional pumps, the newly designed pump utilizes an actuated or a deflected membrane, and it serves as the function of a check valve at the same time. For achieving the valveless property, an inlet or outlet port positioned in an upper- or lower-layer thin membrane was designed to be connected to an entrance or exit channel. Theoretical analysis and numerical simulation were conducted simultaneously to investigate the large deformation characteristics of the membranes and to determine the proper location of the inlet or outlet port on the proposed pump. Then, the valveless pump was fabricated on the basis of the proposed design. In the experiment, the maximum flow rate of the proposed pump exceeded 12.47 mL/min at a driving frequency of 5.0 Hz and driving pressure of 68.95 kPa. [ABSTRACT FROM AUTHOR]