Browsing by Subject "Viscoelastic focusing"

Now showing 1 - 3 of 3

Open Access
CO2 laser machining for microfluidics mold fabrication from PMMA with applications on viscoelastic focusing, electrospun nanofiber production, and droplet generation
(Elsevier, 2021-03-26) Güler, Mustafa Tahsin; Inal, M.; Bilican, İsmail
In this study, a new method for the fabrication of polydimethylsiloxane (PDMS) microchannels through the replication of plexiglass molds was developed. A plexiglass slab is machined with CO2 laser in the raster mode to produce the mold for the PDMS casting. Then, the PDMS replica of the mold is plasma bonded to a substrate by applying more pressure than standard to overcome the surface roughness inherited from the laser machining process. Depending on the channel complexity, a ready to cast mold in the size of a glass slide can be achieved in 5–20 min, including the design, machining, and cleaning steps. This fully automated and cost-effective mold making method proved to be the fastest among all methods, and it enables up to 2.5 aspect ratio microchannels, down to a width of 60 μm, and a height of 23 μm. The raster mode of the laser provides features lower, in size, then the laser beam waist radius. The produced microchannels were validated using several applications, such as droplet generation, nanofiber production, and viscoelastic microparticle focusing.
Open Access
Fabricating plasma bonded microfluidic chips by CO2 laser machining of PDMS by the application of viscoelastic particle focusing and droplet generation
(Elsevier Ltd, 2021-11-23) Güler, Mustafa Tahsin
In this study, direct CO2 laser machining of microchannels onto PDMS slabs and plasma bonding for sealing have been shown to provide the fastest method to fabricate PDMS microfluidic chips. Due to resolidification, the ashes and dust remains that cover the PDMS slab surface following this ablation process change the surface chemistry and prevent plasma bonding. Removing these remnants on the surface has been shown to be only possible via attaching and detaching a tape to the surface. The effect of laser frequency, speed and power settings has been investigated over the entire possible range with regards to channel geometry. The best laser settings were determined and the resulting output channels were examined under SEM and optical microscopes. PDMS spin coating after laser machining has been proposed as a pre-treatment process to improve the geometrical features of the channel. Water-in-oil droplet generation in the T-junction, as well as microparticle focusing in viscoelastic fluid – used to sample enrichment– have been shown as examples of applications that benefit from precise direct laser machined microchannels.
Open Access
Impedance-based viscoelastic flow cytometry
(WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim, 2019) Serhatlıoğlu, Murat; Asghari, Mohammad; Guler, M. T.; Elbuken, Çağlar
Elastic nature of the viscoelastic fluids induces lateral migration of particles into a single streamline and can be used by microfluidic based flow cytometry devices. In this study, we investigated focusing efficiency of polyethylene oxide based viscoelastic solutions at varying ionic concentration to demonstrate their use in impedimetric particle characterization systems. Rheological properties of the viscoelastic fluid and particle focusing performance are not affected by ionic concentration. We investigated the viscoelastic focusing dynamics using polystyrene (PS) beads and human red blood cells (RBCs) suspended in the viscoelastic fluid. Elasto‐inertial focusing of PS beads was achieved with the combination of inertial and viscoelastic effects. RBCs were aligned along the channel centerline in parachute shape which yielded consistent impedimetric signals. We compared our impedance‐based microfluidic flow cytometry results for RBCs and PS beads by analyzing particle transit time and peak amplitude at varying viscoelastic focusing conditions obtained at different flow rates. We showed that single orientation, single train focusing of nonspherical RBCs can be achieved with polyethylene oxide based viscoelastic solution that has been shown to be a good candidate as a carrier fluid for impedance cytometry.