Simple, Cost-Effective Fabrication, and Flow Dynamics Analysis of a Passive Microfluidic Mixer Using 3D Printing and Soft Lithography

Simple and low-cost fabrication of microfluidic devices has attracted considerable attention among researchers. The traditional soft lithography fabrication method requires expensive equipment like a UV exposure system and mask fabrication facility. In this work, an alternative and low-cost UV exposure system was introduced along with an alternative mask fabrication system. A previously reported passive microfluidic mixer was fabricated successfully using this modified soft lithography method. Challenges were presented during this modified fabrication method. Another emerging potential alternative for the fabrication of microfluidic mixers is 3D printing. It was also used in this experiment to fabricate a passive micromixer. This method is well known for rapid prototyping and the creations of complex structures. However, this method has several disadvantages like optical transparency, lower resolution fabrication, difficulties in flow characterization, etc. These problems were addressed, and the solutions were discussed in this work. Comparative analysis between 3D printing and soft lithography fabrication was presented. Flow characterization inside the 3D printed micromixer was carried out using the microparticulate image velocimetry (micro-PIV) system. It explains how the geometrical shape of the micromixer accelerates the natural diffusion process to mix the different fluid streams. Finally, a 3D numerical simulation of the passive micromixer was carried out to visualize the flow dynamics inside the micromixer. The flow pattern found from the numerical simulation and the experimental flow characterization is analogous. These observations could play an important role to design and fabricate cost-effective micromixers for lab-on-a-chip devices.

Compliant Nano-Pliers as a Biomedical Tool at the Nanoscale: Design, Simulation and Fabrication

This paper presents the development of a multi-hinge, multi-DoF (Degrees of Freedom) nanogripper actuated by means of rotary comb drives and equipped with CSFH (Conjugate Surface Flexure Hinges), with the goal of performing complex in-plane movements at the nanoscale. The design approach, the simulation and a specifically conceived single-mask fabrication process are described in detail and the achieved results are illustrated by SEM images. The first prototype presents a total overall area of (550 × 550) μm2, an active clamping area of (2 × 4) μm2, 600 nm-wide circular curved beams as flexible hinges for its motion and an aspect ratio of about 2.5. These features allow the proposed system to grasp objects a few hundred nanometers in size.

Nonmedical Masks in Public for Respiratory Pandemics: Droplet Retention by Two-Layer Textile Barrier Fully Protects Germ-free Mice from Bacteria in Droplets

ABSTRACTDue to the shortage of masks during the pandemic, we recently demonstrated that household textiles are effective environmental droplet barriers (EDBs) with identical droplet retention potential as medical masks. To further promote the implementation of a universal community droplet reduction solution based on a synchronized encouragement/enforcement of mask utilization by the public based on widely available textiles (mask fabrication without the need for sewing machines), here we conducted a study using germ-free mice to determine to what extent textiles were effective in vivo. Using a bacterial-suspension spray simulation model of droplet ejection (mimicking a sneeze), we quantified the extent by which 100% cotton textile prevented the contamination of germ-free animals on the other side of the textile-barrier (simulating a properly worn mask). Of relevance, all mice protected with textiles remained germ-free after two sprays (inoculation dose: >600 bacterial droplet units per 56.75cm2) compared to the contamination of mice not protected by a textile (0/12 vs 6/6, Fisher’s exact, p<0.0001). In a second phase of the experiment with 12 germ-free mice exposed again to 10-fold more droplets remained germ-free, while 100% of mice at 180cm became colonized with a single spray (0/8 vs 4/4, Fisher exact, p=0.002). Collectively, barriers protected all mice (even with low-density textiles, heavy vs. light fabric, T-test, p=0.0028) when using textile-EDB to cover the cages (0/20 vs 10/10, Fisher exact, p<0.0001). This study demonstrated, in vivo, that widely available household textiles are 100% effective at preventing contamination of the environment and the exposed animals by microbe-carrying droplets.

Phase-shift mask fabrication at micrometric scale by ion-exchange in glass for astronomical wavefront sensors

Photolithography combined with ion-exchange in glass is a well-known technology that can be applied to develop many different optical devices. In this work, we present the complete procedure to generate small circular phase-shift masks with diameters of only a few microns and high control in the phase change produced. It is a strategic element in applications such as optical astronomy.