Mona Rahbar

Deep-UV patterning of commercial grade PMMA for low-cost, large-scale microfluidics

Although PMMA can be exposed using a variety of exposure sources, deep-UV at 254 nm is of interest because it is relatively inexpensive. Additionally, deep-UV sources can be readily scaled to large area exposures. Moreover, this paper will show that depths of over 100µm can be created in commercial grade PMMA using an uncollimated source. These depths are sufficient for creating microfluidic channels. This paper will provide measurements of the dissolution depth of commercial grade PMMA as a function of the exposure dose and etch time, using an IPA:H2O developer. Additionally, experiments were run to characterize the dependence of the dissolution rate on temperature and agitation. The patterned substrates were thermally bonded to blank PMMA pieces to enclose the channels and ports were drilled into the reservoirs. The resulting fluidic systems were then tested for leakage. The work herein presents the patterning, development and system behaviour of a complete microfluidics system based on commercial grade PMMA.

Microwave-induced, thermally assisted solvent bonding for low-cost PMMA microfluidic devices

We present a low-cost bonding method for polymethylmethacrylate (PMMA) microfluidics that combines elements of solvent bonding, thermal bonding and microwave bonding. Rather than using specialized equipment, we take household equipment and combine it to produce an effective bonding method that borrows from food packaging technologies for selective heating in a microwave. A poor solvent for PMMA is applied between two halves of a microfluidic system and clamped together using miniature binder clips. Excess solvent from the channels is then drawn out via capillary action and avoids channel clogging during the bonding process. Placing the whole apparatus in a commercial microwave will heat up the thin metal clips and cause the solvent to dissolve and bond the PMMA interface. The whole bonding process takes only a few minutes, and results in high bond strengths.

Fabrication Process for Electromagnetic Actuators Compatible with Polymer Based Microfluidic Devices

We demonstrate a new hybrid-soft-lithography micromolding process that results in a mechanically-compliant, magnetically actuated membrane. The new microactuator consists of a thin undoped polydimethylsiloxane (PDMS) membrane with a central magnet feature, which is also micromolded using soft lithography. The central magnet is composed of a magnetic nanocomposite polymer (M-NCP) material, which is achieved by uniformly dispersing rare earth magnetic powder (MQP-12-5) in the PDMS polymer matrix. The hybrid fabrication technique is capable of realizing a highly flexible membrane with the ability of providing bidirectional deflection without sacrificing the transparency of the device, which may be required for many biomedical applications. Furthermore, we show that the hybrid process also yields improved deflection of the membrane using lower magnetic fields than an opaque membrane fabricated entirely in nanocomposite polymer. These lower fields are more suitable to on-chip production of microactuators excited via electronic signals in microcoils.

Design, fabrication and characterization of an arrayable all-polymer microfluidic valve employing highly magnetic rare-earth composite polymer

We present a new magnetically actuated microfluidic valve that employs a highly magnetic composite polymer (M-CP) containing rare-earth hard-magnetic powder for its actuating element and for its valve seat. The M-CP offers much higher magnetization compared to the soft-magnetic, ferrite-based composite polymers typically used in microfluidic applications. Each valve consists of a permanently magnetized M-CP flap and valve seat mounted on a microfluidic channel system fabricated in poly(dimethylsiloxane) (PDMS). Each valve is actuated under a relatively small external magnetic field of 80 mT provided by a small permanent magnet mounted on a miniature linear actuator. The performance of the valve with different flap thicknesses is characterized. In addition, the effect of the magnetic valve seat on the valves performance is also characterized. It is experimentally shown that a valve with a 2.3 mm flap thickness, actuated under an 80 mT magnetic field, is capable of completely blocking liquid flow at a flow rate of 1 ml min−1 for pressures up to 9.65 kPa in microfluidic channels 200 μm wide and 200 μm deep. The valve can also be fabricated into an array for flow switching between multiple microfluidic channels under continuous flow conditions. The performance of arrays of valves for flow routing is demonstrated for flow rates up to 5 ml min−1 with larger microfluidic channels of up to 1 mm wide and 500 μm deep. The design of the valves is compatible with other commonly used polymeric microfluidic components, as well as other components that use the same novel permanently magnetic composite polymer, such as our previously reported cilia-based mixing devices.

Patterning of PMMA Microfluidic Parts using Screen Printing Process

An inexpensive and rapid micro-fabrication process for producing PMMA microfluidic components has been presented. Our proposed technique takes advantages of commercially available economical technologies such as the silk screen printing and UV patterning of PMMA substrates to produce the microfluidic components. As a demonstration of our proposed technique, we had utilized a homemade deep-UV source, λ=254nm, a silk screen mask made using a local screen-printing shop and Isopropyl alcohol - water mixture (IPA-water) as developer to quickly define the microfluidic patterns. The prototyped devices were successfully bonded, sealed, and the device functionality tested and demonstrated. The screen printing based technique can produce microfluidic channels as small as 50 micrometers quite easily, making this technique the most cost-effective, fairly high precision and at the same time an ultra economical plastic microfluidic components fabrication process reported to date.

Microinstrument for optical monitoring of endothelial cell migration under controlled tension/compression via integrated magnetic composite polymer actuation

We present a microfabricated platform that allows simultaneous application of controlled stretch/compression forces and fluid flow shear stresses during endothelial cell (EC) live-cell monitoring. Our device employs a highly flexible magnetic composite polymer (M-CP) for actuation of a flexible microchannel system. We combine our M-CP with micropatterned non-magnetic polydimethylsiloxane (PDMS), resulting in flexible microsystems with integrated actuators and microfluidic channels whereby we can optically visualize cells in order to monitor various aspects of cell behavior including migration, proliferation, and morphological changes. The M-CP can be rendered permanently magnetic, so it can be employed for both substrate tension and compression using the same electro- or permanent magnet with pole reversal. We have demonstrated proof-of-concept of an instrument designed to simultaneously stimulate ECs grown in microfluidic channels with both fluid flow and mechanical stretch/compression using the new M-CP actuators.

High-aspect ratio magnetic nanocomposite polymer cilium

This paper presents a new fabrication technique to achieve ultra high-aspect ratio artificial cilia micro-patterned from flexible highly magnetic rare earth nanoparticle-doped polymers. We have developed a simple, inexpensive and scalable fabrication method to create cilia structures that can be actuated by miniature electromagnets, that are suitable to be used for lab-on-a chip (LOC) and micro-total-analysis-system (μ-TAS) applications such as mixers and flow-control elements. The magnetic cilia are fabricated and magnetically polarized directly in microfluidic channels or reaction chambers, allowing for easy integration with complex microfluidic systems. These cilia structures can be combined on a single chip with other microfluidic components employing the same permanently magnetic nano-composite polymer (MNCP), such as valves or pumps. Rare earth permanent magnetic powder, (Nd0.7Ce0.3)10.5Fe83.9B5.6, is used to dope polydimethylsiloxane (PDMS), resulting in a highly flexible M-NCP of much higher magnetization and remanence [1] than ferromagnetic polymers typically employed in magnetic microfluidics. Sacrificial poly(ethylene-glycol) (PEG) is used to mold the highly magnetic polymer into ultra high-aspect ratio artificial cilia. Cilia structures with aspect ratio exceeding 8:0.13 can be easily fabricated using this technique and are actuated using miniature electromagnets to achieve a high range of motion/vibration.