Ms. Seema Jaffer Profile

Seema Jaffer

R&D Engineer

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Proceedings Article | 13 February 2008 Paper

Mechanical assembly and magnetic actuation of polydimethylsiloxane-iron composite interconnects for microfluidic systems

Seema Jaffer, Bonnie Gray, Derek Sahota, Michael Sjoerdsma

Proceedings Volume 6886, 68860Q (2008) https://doi.org/10.1117/12.764068

KEYWORDS: Magnetism, Microfluidics, Iron, Silicon, Composites, Particles, Actuators, Photography, Polymers, Semiconducting wafers

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We present magnetically-actuated micromechanical interconnects for microfluidic applications fabricated in-house using PDMS-iron elastomer-ferromagnetic composites (EFCs). Interconnects are fluid-tight, interlocking cylindrical posts and holes whose assembly can be made easier by magnetically actuating the EFC cylinders via axial extension and radial contraction. Towards this goal, we demonstrate magnetic actuation of interconnect structures, and quantify the mechanical disassembly of PDMS-iron interconnects without an applied magnetic field. Previously, we showed the mechanical assembly and disassembly of hybrid combinations of non-magnetic SU-8, silicon, and polydimethylsiloxane (PDMS) microfluidic interconnects. We fabricate EFCs for our interconnects by embedding iron microspheres (<63% by weight) in PDMS. We employed permanent magnets to create 0.045-0.065T constant fields, along with an optics test set-up that included a diode laser and magnification to quantify micron-sized deflections. The interconnects exhibited radial contractions of 3-12% and axial elongation of 2-11%. Without the magnetic field, disassembly forces of 36-71mN were measured by a controlled force linear actuator for PDMS-iron cylinders from PDMS and PDMS-iron holes. This work shows promise for radial contraction of cylinders for assembly with lower forces while maintaining high disassembly forces once the interconnects are assembled and the magnetic field is removed.

Proceedings Article | 22 January 2007 Paper

Mechanically assembled polymer interconnects with dead volume analysis for microfluidic systems

Seema Jaffer, Bonnie Gray

Proceedings Volume 6465, 64650P (2007) https://doi.org/10.1117/12.702265

KEYWORDS: Microfluidics, Silicon, Polymers, Actuators, Semiconducting wafers, MATLAB, Photography, Interfaces, Device simulation, Assembly tolerances

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The mechanical and fluidic properties of silicon and polymer peg-in-hole type interconnect structures are analyzed, tested, and compared in this paper. Microfluidic interconnects composed of interlocking cylindrical posts and holes are microfabricated of polydimethylsiloxane (PDMS) and SU-8 polymers and are mechanically tested together with existing silicon interconnects. PDMS cylindrical posts experimentally assemble with lower force (20-81mN) than comparable SU-8 cylindrical posts (44-227mN) for PDMS, SU-8, and silicon holes. In addition to interconnect fabrication and experimental demonstration of substrate-to-substrate attachment, fluidic properties of the interconnects are analyzed via ANSYS simulation to predict whether pressure drop is expected to result in disassembly. Pressures due to simulated fluid flow at 1mL/min are expected to be 383.6Pa at the interconnect interface. Worst-case interconnect dead volume is simulated using ANSYS and Matlab. We estimate the dead volume at maximum fluid flow rates (50µL/min and 1mL/min) to range from 5.8 to 33nL. The fluidic analysis predicts sudden expansions should have larger dead volumes with lower pressure drops, and sudden contractions should have lower dead volumes and higher pressure drops along the interconnect for the same change in channel width.

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