Whitesides Research

Whitesides Group Research

Microfluidics is a field of research that explores the handling of minute amounts of liquids in tiny micrometer scale channels - this approach can reduce sample and reagent consumption, harness benefits from the exquisite micro scale fluid physics, address small objects such as biological cells, but also reduce size and cost of chemical and biological instrumentation and improve overall experimental automation. The potential and vast diversity of design options have driven the expanding field of microfluidics research over the last two decades.

Initial microfluidic devices were fabricated using methods from the microelectronics industry, but cleanrooms, expensive process instrumentation and materials severely restricted access to the technology, especially for chemists and bioscientists, who were not traditional users of cleanrooms. The Whitesides group dramatically changed the field of microfluidics by introducing PDMS-based microfluidics [1]. This simple, robust route to replica mold and seal low-cost elastomeric chips gained widespread popularity in academic communities, unlocking the creativity of researchers to craft their own devices for diverse purposes ranging from studies of fundamental physics, to medical diagnostics.

Paper and threads

We have, more recently, sought to develop even simpler and lower-cost microfluidic technologies based on materials such as paper and threads [2][3]. One class of paper devices is powered by natural occurring wicking, when water wets the hydrophilic cellulose fibers. We have developed a simple method to create fluidic circuits in paper by using a conventional office printer that produces a hydrophobic barrier to selectively block wicking in areas covered with wax ink [4]. Stacking these individual paper sheets into multilayered devices can make even more versatile three-dimensional liquid handling systems [5] (Figure 1) [6]. We are currently working to extend the liquid handling possibilities of these systems, but also to incorporate electrodes [7][8] (Figure 2) and electronics onto the paper substrates and to perform low-cost diagnostic assays needed in the developing World. Similar to paper, cotton threads are ideal at wicking liquids and acting as one-dimensional fluidic channels [3] (Figure 3).

We have also used hydrophobic papers to construct flow channels by cutting, engraving (Figure 4) and embossing (Figure 5) [9][10]. These channels have an open cavity and require external pressure to drive the flow. We have demonstrated, that these channels can be used for multiphase droplet microfluidics, they support gas exchange through porous paper, and the flows can be adjusted by foldable valves.

PDMS microfluidics beyond the microfluidics

We have advanced PDMS device technology into an entirely new field of research - “soft-robotics”[11]. In “soft robotics” elastomeric channels are turned into useful actuators. The field of microfluidics has provided further inspiration, and components, for the newly emerged area of soft robotics. We have, for example, used similar valve-designs to develop integrated control systems for soft actuators (Figure 6) [12], and exploited skin with color-filled channels to create a soft robot capable of camouflage (Figure 7) [13]. Combining same elastomers and manufacturing approaches with ion loaded hydrogels and electricity has allowed us to build fast, transparent and electrically driven actuators (for example, transparent loud-speakers) and stretch and pressure sensors with different electromechanical properties (Figure 8) [14].



[1] Duffy, D.C., McDonald, J.C., Schueller, O.J.A., and Whitesides, G.M., "Rapid Prototyping of Microfluidic Systems in Poly(dimethylsiloxane)", Anal. Chem., 1998, 70, 4974-4984.

[2] Martinez, A.W., Phillips, S.T., Butte, M.J., and Whitesides, G.M., "Patterned Paper as a Platform for Inexpensive, Low Volume, Portable Bioassays", Angewandte Chemie International Edition, 2007, 46, 1318-1320.

[3] Reches, M., Mirica, K.A., Dasgupta, R., Dickey, M.D., Butte, M.J., and Whitesides, G.M., "Thread as a Matrix for Biomedical Assays", ACS Applied Materials & Interfaces, 2010, 2, 1722-1728.

[4] Carrilho, E., Martinez, A.W., and Whitesides, G.M., "Understanding Wax Printing - A Simple Micropatterning Process for Paper-Based Microfluidics", Analytical Chemistry, 2009, 81, 7091-7095.

[5] Martinez, A.W., Phillips, S.T., and Whitesides, G.M., "Three-Dimensional Microfluidic Devices Fabricated in Layered Paper and Tape",  Proc. Natl. Acad. Sci. USA, 2008, 105, 19606-19611.

[6] Martinez, A.W., Phillips, S.T., Nie, Z., Cheng, C., Carrilho, E., Wiley, B.J., and Whitesides, G.M., "Programmable Diagnostic Devices Made from Paper and Tape", Lab on a Chip, 2010, 10, 2499-2504.

[7] Nie, Z., Nijhuis, C.A., Gong, J., Chen, X., Kumachev, A., Martinez, A.W., Narovlyansky, M., and Whitesides, G.M., "Electrochemical Sensing in Paper-Based Microfluidic Devices", Lab on a Chip, 2010, 10, 477-483.

[8] Lan, W., Zou.X.U, Hamedi.M.M, Hu.J., Parolo.C., Maxwell.E.J, Buhlmann.P., and Whitesides.G.M, "Paper-Based Potentiometric Ion Sensing", Analytical Chemistry, 2014, 86.

[9] Glavan, A., Martinez.R.V., Maxwell.E.J., Subramaniam.A.B., Nunes.R.M.D., Soh.S., and Whitesides.G.M., "Rapid Fabrication of Pressure-Driven Open-Channel Microfluidic Devices in Omniphobic RF Paper", Lab on a Chip, 2013, 13, 2922-2930.

[10] Thuo, M.M., Martinez.R.V., Lan.W., Liu.X., Barber.J.R., Atkinson.M.B.J., Bandarage.D.C., Bloch.J., and Whitesides.G.M., "Fabrication of Low-Cost Paper-Based Microfluidic Devices by Embossing or Cut-and-Stack Method", Chem. Mater., 2014, 26, 4230-4237.

[11]  F.Ilievski, A.D.Mazzeo., Shepherd.R.F., X.Chen, and G.M.Whitesides., "Soft Robotics for Chemists", Angewandte Chemie International Edition, 2011, 50, 1890-1895.

[12] Mosadegh, B., Mazzeo.A.D., Shepherd.R.F., Morin.S.A., Gupta.U., Sani.I.Z., Lai.D., Takayama.S., and Whitesides.G.M., "Control of Soft Machines Using Actuators Operated by a Braille Display", Lab on a Chip, 2014, 14, 189-199.

[13] Morin, S.A., Shepherd.R.F., Kwok.S.W., Stokes.A.A., Nemiroski.A., and Whitesides.G.M., "Camouflage and Display for Soft Machines", Science, 2012, 337, 828-832.

[14] Sun, J., Keplinger.C., Whitesides.G.M, and Suo.Z., "Ionic Skin", Adv. Mater., 2014, 26, 7608-7614.

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