Team Four

The Bubbler• Three types• Creates bubbles

from immiscible liquids.

• Various flow rates to control the size of formed bubbles.

http://cdn.iopscience.com/images/0295-5075/94/6/64001/Full/epl13558fig1.jpg

Bubbles and Medicine • Bubbles as a drug delivery

device• Tumor targeting drugs can be

encapsulated in bubbles• Bubbles can be fragmented to

release drug (shown right).

• Bubbles can become trapped in vascular structures

• Delivery of drugs to occluded vessels

Postema, M., Schimtz, G. (2007)

The innovation of LoC bubble makers• Possible to achieve precise

bubble shapes• Nanofabrication allows small

bubbles to be formed• Nano-range bubbles have a

high surface area to volume ratio

• Ideal of drug delivery

• Easy to model the behavior at the microfluidic level

https://pubs.acs.org/cen/multimedia/85/academe/full/6.jpg

This is the basic bubbler design, taken from Garstecki et al. 2006

Objectives• Build a T-junction bubbler with varied channel widths.• Visualize the mechanics of bubble formation• Draw conclusions about the efficacy of our design and methods

Design• The interface between continuous and inlet phases with various

width (w) from a top view. • Qc: continuous phase flow. • Qd: dispersed phase flow

c

d

Design• Cross section showing the dimensions of a channel of height (h) and

width (w).

Design and Fabrication• We decided to test

conditions with various continuous channel widths:

• (1) 50um• (2) 100um• (3) 150um• (4) 200 um

• In all groups: • h = 50um • Wd = 50um.

Design and Fabrication• A close up of the 100um

channel design• Ports allow for the

injection of water and oil, as well as the collection of mixed products.

• The widened section allows the flow to slow so bubbles can be visualized.

Device Gauge

Fabrication• Photolithography:

• Used mask to expose SU-8 coated wafer (50um thickness).• Deposited PDMS, to imprint channels. • Peeled off and used Plasma cleaner to adhere to glass slides.

• Challenges in fabrication:• Gauge didn’t print on mask• Particles and bubbles in Su-8• Exposure times (channel washed off with developer)• Delamination of SU-8 with PDMS peel• Poor adhesion after plasma

Devices produced

A fabricated bubbler device with 100um continuous channel width

Devices – Setup for Testing• Ported for injection, and superglued in place.• Food dye added to water for visualization. Loaded into syringe. • Microinjection apparatus for controlled delivery of water and oil to devices.

Testing methods• Each device was tested for various

flow rates. • The T-junction was visualized to

monitor bubble formation. • Calculations for flow rate

• Capillary number• Shear and pressure driven flow

Figure 5- Vc = velocity of bubble’s neck constriction of continuous phase Vd=velocity of bubble’s elongation before complete neck constriction of dispersion phase Qc= flow rate of continuous phase Qd= flow rate of dispersion phase h= height of channel w= width of channel

Figure 6 - (left) shows the combination of previous figures equations and then the dimensionless reorganization (right). The final length of the bubble is equal to the sum of the initial length at entry (before filling) and the length accumulated during elongation until breakage.

Figure 5- Vc = velocity of bubble’s neck constriction of continuous phase Vd=velocity of bubble’s elongation before complete neck constriction of dispersion phase Qc= flow rate of continuous phase Qd= flow rate of dispersion phase h= height of channel w= width of channel

Figure 6 - (left) shows the combination of previous figures equations and then the dimensionless reorganization (right). The final length of the bubble is equal to the sum of the initial length at entry (before filling) and the length accumulated during elongation until breakage.

Capillary Number

𝐶𝑎=𝜇𝑉𝛾

Determining Flow Rate

Taken from: P. Garstecki et al. 2006

Hypotheses• Test three hypotheses:

• “Can we create liquid droplets of uniform size between two immiscible liquids at a “T” shape junction of a continuous flow channel and a disperse channel?”

• “How does changing the flow rates between the continuous and dispense channel affect the properties of the droplets formed?”

• “How does changing the channel widths of the continuous flow channel affect the properties of the droplets formed?”

Challenges• Poor flow in channels • PDMS and super glue particles clog tubes• Elasticity in pipes

Conclusions and Future Directions• Hypothesis testing:

• 1st: created bubbles with our devices• 2nd and 3rd: unable to fully test these due to device errors

• Future Directions:• Try experiments with less elastic tubing• Use PDMS to adhere ports instead of glue

References • M. L. J. Steegmans et al., “Characterization of emulsification at flat microchannel Y junctions,”

Langmuir, vol. 35, pp. 3396-3401, Feb. 2009.

• “Microfluidic droplet generators,” Micronit MicroFluidics, Enschede., The Netherlands.

• P. Garstecki et al., “Formation of droplets and bubbles in a microfluidic T-junction – scaling and mechanism of break-up,” Lab Chip, vol. 6, pp. 437-446, Jan. 2006.

• What is digital microfluidics? [Web.] Available: http://www.elveflow.com/microfluidic-tutorials/microfluidic-reviews- and-tutorials/what- is-digital- microfluidic/

• M. DE MENECH, P. GARSTECKI, F. JOUSSE and H. STONE. Transition from squeezing to dripping in a microfluidic T-shaped junction, J. Fluid Mech., vol. 595, 2008.