(b) The photograph of porous sponge (remaining), the SEM image of pore (middle) and the TEM image of dispersed iron powder (right)

(b) The photograph of porous sponge (remaining), the SEM image of pore (middle) and the TEM image of dispersed iron powder (right). and sorting,3cell-containing microsphere generation,4and protein concentration analysis.5More recently, microphysiological systems that incorporate the key functions of individual organs and enable relationships among different microphysiological devices have been successfully applied with microfluidic systems.610These microfluidic-based microphysiological systems provide a novel platform to simulate normal and pathological functions for continuous periods of time, representing human being physiology for the evaluation of drug efficacy and toxicity. It is anticipated the microphysiological systems will eventually enable quick 10074-G5 and high fidelity evaluation of security and effectiveness for various candidate therapeutics. In order to accurately represent human being physiology, it is critical to simulate blood flow patterns in the microfluidic chips of microphysiological systems. For example, physiological pulsatile pressure causes blood vessels to stretch11and the mechanical stress generated from the pulsatile circulation affects the function of vascular cells.1216Despite the importance of physiological flows in microphysiological systems, it has been generally demanding to dynamically control flows in microfluidic chips, due to the lack of tunable pumping systems with suitable dynamic response, the potential of contamination, and the difficulty of generating physiological shear pressure for periods ranging from hours to days.17 Existing microfluidic flow-control mechanisms can be generally divided into two major categories based on methods that use deflection of flexible membranes1723or external pressure pumps,24,25respectively. The flexible-membrane-deflection method uses 10074-G5 mechanical causes, such as those from piezoelectric pin, magnetic disc, or high-pressure compressed air flow, to deform a thin membrane to seal the channel and therefore quit the circulation. However, this method usually creates only on-off circulation patterns, and requires relatively complicated fabrication processes such as multiple-layer assembly. As an alternative method, the pressure-pump systems control circulation patterns with external pressure pump connected to a set of solenoid valves, an 10074-G5 air compressor, a function generator, and a pressure controller.23,24Although the pressure-pump systems can dynamically control flow patterns, applications have been limited due to the complex system configurations and high cost of external supporting equipment. Furthermore, it is not clear whether the pressure-pump systems can generate complicated physiological circulation patterns for microphysiological systems, such as a reverse circulation during diastole stage of heart beating. Here, we demonstrate a simple yet effective method to dynamically control microfluidic flows with a wide variety of rates, frequencies and patterns required by microphysiological systems based on novel magnetoactive sponges.2628The magnetoactive sponge is embedded like a tunable valve across the microfluidic channel (Fig. 1a). A non-uniform magnetic field is definitely applied on the magnetoactive sponge by simply approaching a pub of magnet to the sponge. The magnetic field compresses the magnetoactive sponge, significantly changing its porosity and therefore hydraulic conductivity. As a result, the circulation rate in the 10074-G5 channel can be dynamically assorted by tuning the magnetic field applied on the sponge. Owning to its simple and low-cost fabrication, fast response, and versatility in controlling microfluidic flows, the new flow-control mechanism based on magnetoactive sponges will potentially find important applications in various microphysiological systems. We also display the effect of pulsatile circulation within the response of manufactured blood vessels. == FIGURE 1. == (a) The schematic diagram of the construction of fluidic system. (b) The picture of porous sponge (remaining), the SEM image of pore (middle) and the TEM image of dispersed iron powder (ideal). (c) A photograph of the circulation control system. == Materials and methods == == Fabrication of magnetoactive sponge and microfluidic control device == Polydimethylsiloxane (PDMS) prepolymer and treating agent (Sylgard 184, Dow Corning) were mixed by a excess weight percentage of 20:1. Thereafter, carbonyl-iron powders (Sigma-Aldrich Co., St. Louis, MO) with diameters of 6 9 m and brownish sugar particles with diameters of 100500m were added into the pre-cured PDMS remedy and mixed thoroughly. The excess weight percentage of PDMS, iron IFITM2 powder, and sugars in the resultant combination was 1:3:3. After treating the PDMS.