by Professor Michelle Khine
The challenge of micro- and nano-fabrication lies in the difficulties and costs associated with patterning at such high resolution. Instead of relying on tradition fabrication techniques -- largely inherited from the semiconductor industry -- for microfluidic applications, we have developed a radically different approach. We pattern at the large scale, which is easy and inexpensive, and rely on the heat-induced relaxation of pre-stressed shape memory polymer sheets (polystyrene and polyolefin) to achieve our desired structures. Using this approach, we have demonstrated that we can create fully functional and complete microfluidic devices with integrated nanostructures within minutes. These devices can be created for only pennies per chip and without any dedicated costly equipment. This enables researchers to make custom microsystems on demand for a range of applications from basic biology studies to stem cell research to point of care diagnostic devices to detect infectious diseases. In this presentation, I will review my lab's approach to each of these areas.
In order for microfluidic technology to fulfill its potential of making a significant impact on fields such as stem cell technologies, systems biology, and point-of-care diagnostics the persistent chasm between academic prototyping and industry-standard devices must be bridged. While most academic labs prototype via soft lithography in polydimethylsiloxane (PDMS), industry is largely intolerant to the inherent materkal drawbacks of PDMS, including: swelling, non-selective absorption, and poor mechanical properties. Industry relies on plastics, including polystyrene (PS) and polyolefins (PO)1. To create such fine features in plastics, however, typically requires either hot embossing or injection molding. Both of these approaches require substantial investments in expensive capital equipment and extensive processing time that largely precludes academic prototyping2,3. We introduce a novel, rapid, and ultra-low-cost strategy to fabricate microsystems with integrated nanostructures using shrink-film techology.
We pattern at the large scale, which is easy and inexpensive, and rely on the heat-induced relaxation of pre-stressed shape memory polymer sheets to achieve our desired structures4-6. Our previous works with shrink films have focused on the applications of a polystyrene toy called "Shrinky-Dinks"7. PS was shown to display a 60% reduction in area upon shrinkage and was used in conjunction with a laser printer to fabricate masters for the fabrication of PDMS microfluidic devices and micro wells for cell culture7,8. Direct patterning of the sheets through etching or deposition was shown to create complete microfluidic devices, and was expanded upon to create a functional biochip that integrated complex microfluidic designs and proteins spots.
Figure 1. Ultra-rapid, low cost manufacturing process of nano-integrated microsystems. Starting with a blank thermoplastic sheet, one can create various micro and nano structures by either applying materials to or removing materials from the plastic. Upon heating, the sheet retracts, causing any stiffer materials (e.g. metals, to buckle). Complete 3D stacked microfluidic chips are achieved within minutes as well as robust substrates for cell studies.
Recently, we demonstrated that a polyolefin shrink thin film exhibits a 95% reduction in area for high-aspect templates for soft lithography9. By combining with a low-cost digital craft cutter, we were able to also achieve relatively uniform and consistent complete microfluidic channels with smooth surfaces, vertical sidewalls, and high aspect ratio channels with lateral resolutions well beyond the tool used to cut them10. The thermal bonding of the layers results in a strongly bonded chip, with leak proof channels, and homogenous surface and bulk properties. Complex microfluidic designs can be easily designed on the fly and protein assays also readily integrated into the device.
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- P. Abgrall, L. N. Low and N. T. Nguyen, Lab Chip, 2007, 7, 520-522.
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- K. Sollier, C. A. Mandon, K. A. Heyries, L. J. Blum and C. A. Marquette, Lab Chip, 2009, 9, 3489-3494.
- M. Long, M. A. Sprague, A. A. Grimes, B. D. Rich and M. Khine, Appl Phys Lett, 2009, 94, -.
- C. S. Chen, D. N. Breslauer, J. I. Luna, A. Grimes, W. C. Chin, L. P. Leeb and M. Khine, Lab Chip, 2008, 8, 622-624.
- A. Grimes, D. N. Breslauer, M. Long, J. Pegan, L. P. Lee and M. Khine, Lab Chip, 2008, 8, 170-172.
- D. Nguyen, S. Sa, J. D. Pegan, B. Rich, G. X. Xiang, K. E. McCloskey, J. O. Manilay and M. Khine, Lab Chip, 2009, 9, 3338-3344.
- D. Nguyen, D. Taylor, K. Qian, N. Norouzi, J. Rasmussen, S. Botzet, K. H. Lehmann, K. Halverson and M. Khine, Lab Chip , 2010, 10, 1623-1626.
- D. Taylor, D. Dyer, V. Lew, M. Khine, Lab Chip, 2010, DOI: 10.1039/c00473.
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