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The effect of O2plasma treatment on the surface property of exposed and unexposed SU8 photoresist has been investigated for the fabrication of a monolithic MEMS microstructure. It can solve the non-uniformity problem of second resist coating on the SU8 with high intrinsic shrinkage after exposure and post-exposure baking (PEB) in the fabrication of the stacked polymer-metal or polymer-polymer structure, which was used in the application of microfluid, bio and chemistry. The thickness difference of untreated SU8 before PEB between the exposed and unexposed SU8 was about 0.3% while that after PEB increased to about 6%. It could result in large non-uniformity of about 18 µm thickness difference for the following second resist coating on the hydrophobic surface without plasma treatment. The surface property of SU8 in terms of the contact angle and surface energy can be adjusted by O2plasma treatment for enhancing the coating uniformity of the following resist. The measured contact angles of the exposed and unexposed SU8 decrease with O2plasma time, corresponding to the increased surface energy determined by the Lifshitz-van der Waals/Lewis acid-base approach. It displayed that the similar hydrophilic surface property can minimize the thickness difference of second resist coating on the first shrunken SU8. A monolithic nozzle plate with a physical resolution of 600 dpi in a single column was demonstrated for an inkjet application based on the improved uniformity. [ABSTRACT FROM AUTHOR]

In this article, a Ti/Al thin film with Ti as an adhesive layer that merits high conductivity, excellent adhesion and low cost is used as the electrode in a biomedical blood separation chip instead of the conventional biomedical electrode mostly made of expensive Au and/or Pt. The design and fabrication of the meander-shaped Ti/Al thin-film electrode are studied for the application to promote the capillary-driven dielectrophoresis (DEP) blood separation chip. The meandered electrode with a castellated profile of 0.6 and 0.2 mm spacing instead of the flat one is designed on the glass substrate to produce an asymmetric electric field for the DEP force to separate the blood. The meander-with-castellated electrode shape and gap affects the electric field gradient on the separation performance. The patterning of the electrode was performed by the low-cost CO2 laser-ablated polymer tape rather than an expensive-complex photolithography process and then followed by sputtering together with lift-off process. The Ti/Al thin film is coated on the channel backside rather than inside for contactless DEP to avoid the contact pollution of the sample as well to reduce the operation voltage. The COMSOL Multiphysics® simulation of the electric field and the blood separation test were done for verifying the design and experiment. In the simulation, the 0.2 mm castellated electrode can greatly enhance the asymmetric electric field peak of 24000 V m−1 compared to the flat electrode of about 12000 V m−1. Also, the 0.2 mm gap castellated electrode with three-time electric-field-gradient-pulse frequency can enhance the DEP force compared to the 0.6 mm gap electrode. In the experiment, the blood chip of 0.2 mm castellated electrode with the highly increased electric field and DEP force can shorten the starting separation time from 533 s to 253 s and enhance the separation efficiency from 20.0% to 51.7% at the applied voltage of 5 V and 1 MHz. [ABSTRACT FROM AUTHOR]

The traditional closed-channel polydimethylsiloxane (PDMS) capillary mixer without a delay valve generally encounters backflow problems. In this article, the design of a polyethylene glycol (PEG) coated PDMS mixing meander channel for long-term capillary-actuating with a delay valve and open surface is investigated using numerical analysis and flow-visualization experiments. The self-driven open-surface PEG-PDMS meander mixer exhibits a high mixing extent of more than 90%. The simulation and experiments of the triggering delay valve evidence that two fluids can merge together before the meander channel and then flow into the mixing unit to eliminate the backflow problem. It also enhances an efficient mixing. In addition, the open-surface channel shows a lower channel depth for self-actuating compared to the closed one. In terms of simulation, the mixing extent of both blue and red inks at the position just after the delay valve is about 43% and enhanced to 92% at about 10 mm mixing length after the delay valve. In terms of experiments, the ImageJ analyzed mixing extent is enhanced from about 57% to 96% of mixing extent within the meander channel at the same position. The experiment is in a good agreement with the simulation result. [ABSTRACT FROM AUTHOR]

An integrated technology of CO2 laser processing and polymer molding has been demonstrated for the rapid prototyping of biodegradable poly-lactic-co-glycolic acid (PLGA) microneedle arrays. Rapid and low-cost CO2 laser processing was used for the fabrication of a high-aspect-ratio microneedle master mold instead of conventional time-consuming and expensive photolithography and etching processes. It is crucial to use flexible polydimethylsiloxane (PDMS) to detach PLGA. However, the direct CO2 laser-ablated PDMS could generate poor surfaces with bulges, scorches, re-solidification and shrinkage. Here, we have combined the polymethyl methacrylate (PMMA) ablation and two-step PDMS casting process to form a PDMS female microneedle mold to eliminate the problem of direct ablation. A self-assembled monolayer polyethylene glycol was coated to prevent stiction between the two PDMS layers during the peeling-off step in the PDMS-to-PDMS replication. Then the PLGA microneedle array was successfully released by bending the second-cast PDMS mold with flexibility and hydrophobic property. The depth of the polymer microneedles can range from hundreds of micrometers to millimeters. It is linked to the PMMA pattern profile and can be adjusted by CO2 laser power and scanning speed. The proposed integration process is maskless, simple and low-cost for rapid prototyping with a reusable mold. [ABSTRACT FROM AUTHOR]