This is the final presentation of our group's bioMEMS course project. We created a "bubbler" with nanofabrication techniques, including photolithography and plasma bonding.

1. Team Four

2. 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

3. 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)

4. 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

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

6. 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

7. 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

8. Design
• Cross section showing the dimensions of a channel of height (h) and
width (w).

9. 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.

10. 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.

11. Device Gauge

12. 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

13. Devices produced
A fabricated bubbler device with 100um continuous channel width

14. 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.

15. 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 di
reorganization (right). The final length of the bubble is equal to the sum of the initial
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.

16. Capillary Number
𝐶 𝑎 =
𝜇𝑉
𝛾

17. Determining Flow Rate
Taken from: P. Garstecki et al. 2006

18. 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?”

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

30. 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

31. 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.