Controlled Cavitation and Sonoporation in Microfluidics

Claus-Dieter OhlFaculty of Science and TechnologyPhysics of FluidsUniversity of TwentePostbus 217, 7500 AE EnschedeThe Netherlands.Email: c.d.ohl@utwente.nlSeverine Le Gac´BIOS the Lab-on-a-Chip groupMESA+ Institute for NanotechnologyUniversity of TwentePostbus 217, 7500 AE EnschedeThe Netherlands.Email: S.LeGac@ewi.utwente.nlEd ZwaanFaculty of Science and TechnologyPhysics of FluidsUniversity of TwentePostbus 217, 7500 AE EnschedeThe Netherlands.Email: e.v.zwaan@casema.nlKinko TsujiShimadzu Europa GmbHAlbert-Hahn-Strasse 6-10,D-47269 Duisburg, Germany.Email: kts@shimadzu.deAlbert van den BergBIOS the Lab-on-a-Chip groupMESA+ Institute for NanotechnologyUniversity of TwentePostbus 217, 7500 AE EnschedeThe Netherlands.Email: A.vandenBerg@ewi.utwente.nlINTRODUCTIONCavitation – the growth and collapse of mostly empty bub-bles – is commonly attributed to large scale or very rapid flows,e.g. at ship propellors or at fuel injection nozzles. Cavitation isvery aggressive to materials and one reason is its ability to fo-cus fluid flows to very small scales; the bubbles concentrate theenergy from the fluid during their shrinkage. Only recently theattention from largely free cavitation bubbles has shifted towardsthe study of more confined bubbles [1–5]. Here we report onan experiment to exploit cavitation in microfluidic systems or socalled lab-on-a-chip devices for flow handling and biological cellmanipulation. In microfluidics generally due to the small scaleslow Reynolds number flows are observed. Yet, cavitation bubble-induced flows allow to reach a high Reynolds number regimealso on these small scales. By exploiting this rarely studied flowregime new techniques for liquid and cell handling become fea-sible. Here, we will report first on the effect of a channel wallon the bubble dynamics and then present an application for cellhandling and membrane poration.EXPERIMENTAL SETUPA single and well controlled cavitation bubble is generatedwith an expanded beam from a pulsed and frequency-doubledNd:YAG laser (Solo PIV, New Wave, USA) focused into a lightabsorbing liquid (water or cell growth medium supplementedwith Direct Red 81 or Trypan Blue, respectively). The energiesof the laser pulses are in the range 5−50µJ and have a durationof 6ns. The focus of the laser beam and the image plane of the40x objective of the inverted microscope superimpose, thus al-low to take in-focus images with a high-speed camera (up to 1million frames/s, HPV-1, Shimadzu Corp., Japan) of the bubbleoutline. A filter block reflects only the green laser light and letspass all other wavelengths for proper illumination with a fiberlamp. The microfluidic chambers are first designed with a CADsoftware, transfered onto a lithographic mask, and then etchedinto a silicon wafer. The microsystems are then fabricated from apolymeric material PDMS (polydimethylsiloxane, Sylguard 184,Dow Corning, USA) using conventional molding technique andbonded to a glass cover slip or polypropylene foil.1 Copyright c 2007 by ASMEProceedings of IMECE2007 2007 ASME International Mechanical Engineering Congress and Exposition November 11-15, 2007, Seattle, Washington, USA