A novel passive micromixer, called a trapezoidal-zigzag micromixer (TZM), is reported. A TZM is composed of trapezoidal channels in a zigzag and split–recombine arrangement that enables multiple mixing mechanisms, including splitting–recombining, twisting, transversal flows, vortices, and chaotic advection. The effects of geometric parameters of the TZM on mixing performance are systematically investigated by the Taguchi method and numerical simulations in COMSOL Multiphysics. The number of mixing units, the slope angle of the trapezoidal channel, the height of the constriction element, and the width ratio between the middle-trapezoidal channel and the side-trapezoidal channel are the four parameters under study. The mixing performance of the TZM is investigated at three different Reynolds number ( Re ) values of 0.5, 5, and 50. The results showed that a TZM with six mixing units, a trapezoidal slope angle of 75°, a constricting height of 100 µ m, and a width ratio of 0.5 has the highest mixing efficiency. This optimal TZM has a mixing efficiency greater than 85% for Re values from 0.1 to 80. In particular, for Re ⩽ 0.9 and Re ⩾ 20, the mixing efficiency of the optimal TZM is greater than 90%. The proposed TZM has a higher mixing efficiency and a smaller footprint than previously reported micromixers.

In order to produce disposable microneedles for blood-collection devices in smart homecare monitoring systems, we have developed a simple low-cost scalable process for mass fabrication of sharp-tipped microneedle arrays. The key feature in this process is a design of computer numerical control-machined aluminum sample (CAS). The inclined sidewalls on the CAS enable microfabricated traditional-shaped microneedles (TMNs) to be produced in the desired shape. This process provides significant advantages over other methods that use inclined lithography or anisotropic wet etching. TMNs with a length of 1510 μm, a hollow diameter of 120 μm, and the tip radius of 16 μm were successfully fabricated. Theoretical study and practical measurements of fracture force verified the improved mechanical strength of TMNs for safe skin insertion. In addition, the penetration tests on cadaver pork skin demonstrated that the TMNs could pierce the pork skin without breaking, and create the transport conduits through microneedle lumens.

With increasing pressure on food industry to reduce waste while meeting the demand for high food quality and safety, there is a strong motivation for research into sensors for monitoring freshness and general food quality. Degradation of fresh meat and produce is related to metabolic activities of microorganisms which commonly result in formation of gaseous compounds such as CO ₂ . Monitoring the freshness and quality of the food can therefore be accomplished by monitoring the release of these gases in the food package. In this study, an approach to create sensors for detecting gases released by perished food is described. Sensor test is conducted with CO ₂ which is a common gas related to the degradation process of food. The sensor is based on Carbon Nanotubes (CNTs) as sensing elements. A local synthesis technique is used to directly integrate the CNTs onto silicon-based circuits at room temperature. Fabricated CNT-based structures have successfully demonstrated the ability to detect CO ₂ . The sensitivity and selectivity of gas sensors to different gas compounds were also studied. The results indicate that this approach is promising for fabrication of CNT-based gas sensors at low cost for determination of food freshness and quality, making possible complete gas sensors including CNT sensing elements, CMOS signal processing and RF communication on the same chip, manufactured and integrated at the wafer-level scale.