Functional hydrogel structures for autonomous flow control inside microfluidic channels

1
Functional hydrogel structures for autonomous
flow control inside microfluidic channels

• D. J. Beebe, J. S. Moore, J. M. Bauer, Q. Yu, R.
  H. Liu, C. Devadoss B-H Jo
• Presented by Gabriel Man
• EECE 491C

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What are hydrogels?

• Sounds like a weird glue or blob type of
  material
• Network of super-absorbent, natural or synthetic
  polymer chains

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Research Goals

• Eliminate sensors and/or actuators requiring
  external power self-regulated flow control
• Simplify system construction and assembly by
  fabricating hydrogels in situ

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Applications

• Combined sensor and actuator (sense chemical
  environment in one channel, regulate flow in
  adjacent channel) pH-sensitive throttle valve
• Self-regulated drug delivery or biosensors
  featuring antigen-responsive hydrogels

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Fabrication Techniques

• Combines
• Lithography
• Photopolymerization
• Microfluidics
• Flow a mixture of monomers and a photoinitiator
  into microchannel
• Place the photomask over the channel, expose to
  UV light

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Fabrication Techniques Cont

1. Polymerization times can be lt 20 seconds
2. Flush the channel with water to remove
   unpolymerized liquid

250 µm
Yeast (Saccharomyces cerevisiae) surrounded by
E.Coli (1-2 µm in length)
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Results Flow Sorter

• Hydrogel objects reversibly expand and contract
  depending on pH of environment

Inflow
Outflow
Outflow
Time Response
1.0
0.0
200
400
600
800
1000
1200
Time (seconds)
300 µm
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Results Throttle Valve

• Pressure drop of 0.09 PSI to 0.72 PSI in top
  channel
• Force associated with volumetric changes
  sufficient to deform membrane and control flow in
  lower channel

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Results Another Flow Sorter
1.0
0.8
0.6
0.4
0.2
pH
1
3
5
7
9
11
13
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Conclusions

• Approach can be extended to build
  multifunctional microfluidic systems, allowing
  complex fluidic processes to be performed
  autonomously
• Eliminates microscale assembly and external
  electronics for sensing/actuation
• Scaling down hydrogel structures to the
  micro-scale improves response time

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Critique Summary
ve -ve
Major In situ fabrication ease and explanation of fabrication procedure Combining sensing and actuation functions No external power required Application antigen-responsive hydrogels used in drug-delivery No discussion of weaknesses (i.e. response time, contamination, possible leakage, tapered cylindrical structures Not sure what larger cylindrical structure being compared in Figure 2 is
Minor Explanation of methods, device fabrication and characterization Figures clear and easy to understand Dimensions should be put alongside scale bars Factor that triggers expansion/contraction (pH) should be mentioned earlier Fluid in Figure 3 is dyed, but not Figure 2? Figure 2e, 0.0 point on y-axis labeled 1