Balabani, S

Huck, WTS

Ma, S

Sherwood, JM

UCL Discovery

Motivation: Cell encapsulation and flow cytometry Experimental Methods Flow topology in single droplets Conclusions and Outlook Flow patterns in w/o & w/o/w droplets Shear stress distribution Engineering single and double droplets for flow cytometry Shaohua MA 1, Joseph SHERWOOD2, Wilhelm T. S. HUCK 3, Stavroula BALABANI 4,*  1 Chemistry Research Laboratory, University of Oxford, UK 2 Department of Bioengineering, Imperial College London, UK  3 Institute for Molecules and Materials, Radboud University Nijmegen, The Netherlands 4 Department of Mechanical Engineering, University College London, UK.  *s.balabani@ucl.ac.uk This  work is a collaboration between the Fluid Mechanics Group of Dr. Stavroula Balabani in the Department of Mechanical Engineering at UCL and the Microdroplets Group of Prof. Wilhelm Huck at the University of Cambridge, now at Radboud Univesrity. Part of the work appeared in LabChip cover.    Ma et (2015) Deformation of double emulsions under sheath flow focusing, Lab Chip, 15(22):4291-30; Ma et al (2015) The microenvironment of double emulsions in rectangular microchannel. Lab Chip, 15(10):2327-34; Ma et al (2014) On the flow topology inside droplets formed in rectangular microchannels, Lab Chip, 14, 3611-3620.  •  Cell encapsulation applications require a low shear droplet environment  •  Single microdroplets typically not compatible with flow cytometry because carrier fluid is oil. •  Double emulsions could provide a milder environment and protect fragile cells being damaged by harsh shear conditions. •  Internal flows and deformation of compound droplets  are studied to assess cell viability and suitability for flow cytometry applications such as fluorescence activated cell sorting (FACS)   Velocity distributions  are similar for fluids used –i.e. viscosity ratios used (approaching 1) •  Viscosity ratio alters typical droplet flow pattern •  Increasing viscosity ratio from 0.12 to 0.80 eliminates recirculation patterns  •  Role of viscosity more prominent than interfacial tension •  Double emulsions: •  exhibit low shear stresses ensuring cell viability •  deform less under sheath flow conditions •  hence, good candidates for cell screening applications Flow cytometry 1  Single droplets: refractive index matching liquids  as well as fluorinated oil HFE7500 (297730-93-9, 3M, 0.77cSt), Pico-SurfTM 1 (PS-1).  Double emulsions: deionised water, 1.5 wt% PS-1 surfactant in HFE7500, and water with 0.5 wt% sodium dodecyl sulphate (SDS) surfactant   µPIV setup Sample Images Inner core Single droplet ū/vd ῡ/vd  Droplet deformation under sheath flow conditions •  w/o single droplets deform more than w/o/w double emulsions under certain aqueous sheath flow focusing •  deformed single droplets cannot recover their non-deformed morphologies as they remain in confinement longer,  •  double emulsions recover their non-deformed morphology rapidly downstream of the sheath focusing point.  Droplet deformation was studied in a hydrodynamic focusing setup designed using COMSOL.  Deformation index (D) quantified from images of deforming droplets.   Contours and frequency distribution of shear rate magnitude |γ*|.   Droplets result in a narrow distribution of shear rate magnitude values compared to the microfluidic channel flow with a mean value which is an order of magnitude lower.    inner core a/b=1.4 y-z plane of microchannel-  Values normalised  With nominal shear,   vc/w 30-50 image pairs acquired  Centroid location to  estimate droplet velocity 3 pass correlation used to obtain velocity field Spatial resolution: 6.4 um Droplet formation	Micro Particle Image Velocimetry (µPIV) HFE7500 ( λ=0.8) Higher velocity along the oil-water interface  and low velocity in the bulk volume. Lower focal plane Middle focal plane Lower focal plane Middle focal plane Silicon oil and water/glycerol mixture  (λ=0.12) Typical recirculating patterns seen. Inner-outer viscosity ratio plays a key role in determining topology 1http://www.assay-protocol.com/cell-biology/flow-cytometry

Engineering single and double droplets for flow cytometry applications

http://discovery.ucl.ac.uk/1526512/1/Balabani_Engineering_droplets_cytometry_poster.pdf

Engineering single and double droplets for flow cytometry applications

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