<p>Microfluidics based electroosmotic (EO) micropumps drive fluids without any moving parts. The ease of miniaturization, integration of biocompatible materials, and the simplicity of actuation and control make EO pumps attractive for biomedical applications, analytical chemistry, and several lab-on-a chip applications. While there are several studies in literature about different EO pumps, there is a lack of studies of EO micropumps fabricated with purely biocompatible materials. Such a device could be desirable for in vivo and ex vivo biomedical applications, and for pumping biological fluids in lab-on-chip applications. Biocompatible materials can make microfluidic devices more effective in biological environments. In this study, we report a novel EO micropump made from SU-8 epoxy-based negative photoresist and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate&nbsp;(PEDOT:PSS) conductive polymer. The unique mechanical properties, biocompatibility, and ease of microfabrication make SU-8 a highly desirable material for many applications including microfluidics, diagnostic applications, and implantable devices. PEDOT:PSS is a transparent conductive polymer mainly used as a hole transport layer in organic photodiodes. The tunable conductivity of PEDOT:PSS coupled with its processability make this material desirable for organic electronic applications like thin-film transistors, organic LEDs, and solar cells. PEDOT:PSS can be patterned by laser ablation, microcontact imprinting, and ink-jet printing. These properties make PEDOT:PSS a desirable candidate for microfluidic devices. In this study, we fabricated an EO micropump using SU-8 as the passive material and PEDOT:PSS as the conductive electrodes. The SU-8 passive layer &nbsp;was sandwiched between two conductive surfaces and consisted of a single micropore that functioned as a conduit for fluid transport. Initially, a rectangular SU-8 microstructure without any pore or channel was fabricated. The conductive surfaces were fabricated by spin-coating these SU-8 microstructures with PEDOT:PSS with 5 vol% of Dimethyl sulfoxide (DMSO) solution. DMSO was added to PEDOT:PSS solution to enhance its conductivity. The coated SU-8 microstructure was annealed to esterify the PEDOT:PSS in the presence of SU-8. This process causes PEDOT:PSS to become resistant to DI water. A micropore of 50 µm diameter was created using an infrared laser marking system. &nbsp;We applied a range of electric fields between the two electrodes which resulted in EO flow through the micropore. This controllable fluid flow was visualized by tracking a droplet of DI water deposited on the top and bottom of the micropore. The size of the droplet increased or decreased depending on the polarity of the applied electric field. &nbsp;We also validated the pumping action of a biological fluid with a modified current monitoring technique. For this technique, the EO micropump was connected to two fluidic reservoirs on either side, with each reservoir containing glutamate neurotransmitter of different ionic concentrations. Fluid conductivity measurements were then performed by measuring the change in currents between the electrodes due to the flow of glutamate with different ionic concentrations from one reservoir to the other. These two techniques demonstrated consistent flow visualization caused by the pumping action of the EO micropump. We anticipate that future versions of this device can be used in different in vivo and ex vivo biomedical applications such as drug delivery systems and lab-on-a-chip applications.</p>

An All Polymer Biocompatible Electroosmotic Micropump for Biomedical Applications

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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