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

January 16 th, 2007EECE 491C What are hydrogels? Sounds like a weird “glue” or “blob” type of material Network of super-absorbent, natural or synthetic polymer chains

January 16 th, 2007EECE 491C Research Goals Eliminate sensors and/or actuators requiring external power: self-regulated flow control Simplify system construction and assembly by fabricating hydrogels in situ

January 16 th, 2007EECE 491C 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

January 16 th, 2007EECE 491C Fabrication Techniques Combines: Lithography Photopolymerization Microfluidics 1. Flow a mixture of monomers and a photoinitiator into microchannel 2. Place the photomask over the channel, expose to UV light

January 16 th, 2007EECE 491C Fabrication Techniques Con’t 3. Polymerization times can be < 20 seconds 4. Flush the channel with water to remove unpolymerized liquid 250 μm Yeast (Saccharomyces cerevisiae) surrounded by E.Coli (1-2 μm in length)

January 16 th, 2007EECE 491C Results: Flow Sorter Hydrogel objects reversibly expand and contract depending on pH of environment InflowOutflow Time Response 200 Time (seconds) μm

January 16 th, 2007EECE 491C 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

January 16 th, 2007EECE 491C Results: Another Flow Sorter pH

January 16 th, 2007EECE 491C 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

January 16 th, 2007EECE 491C 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