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SNF Grand Rounds July 13, 2006

SNF Grand Rounds July 13, 2006. ME342 Jennifer Blundo Gretchen Chua Yong-Lae Park Ali Rastegar. Project Goal. Design a bioMEMs substrate to apply and measure electromechanical forces in the differentiation of human embryonic stem cell-derived (hESC)-cardiac myocytes (CM).

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SNF Grand Rounds July 13, 2006

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  1. SNF Grand RoundsJuly 13, 2006 ME342 Jennifer Blundo Gretchen Chua Yong-Lae Park Ali Rastegar

  2. Project Goal • Design a bioMEMs substrate to apply and measure electromechanical forces in the differentiation of human embryonic stem cell-derived (hESC)-cardiac myocytes (CM) hESC-CMs organized in embryoid body Contractility Electrophysiology Mechanical force Undifferentiated hESCs-Fluc-eGFP (DAPI nuclear stain) bioMEMS device

  3. Current Microscale Devices Thin-film gold strain gauges (200nm) encapsulated in PDMS (50μm). Wen et al, 2005. Thin-film stretchable (0—15%) gold electrodes (25nm) on PDMS. Lacour et al, 2005. 64 Electrode array for extracellular recording, Multi Channel Systems Pressure actuated PDMS membrane (120μm) with S-shaped SiO2 traces. Lee et al, 2004.

  4. BioMEMS: Engineering Specs

  5. BioMEMS: Device Design B. Strained state A. Unstrained state Glass/Quartz: Optically transparent baseplate PDMS: A biocompatible elastomeric polymer PPS: A biocompatible elastomeric polymer Ti: Adhesion layer for electrodes Gold: Biocompatible thin film electrodes SU-8: Transparent polymer

  6. Mechanical Strain—In Vitro Model • Goal: To apply cyclic mechanical strain to hESC precursor cells and observe differentiation

  7. BioMEMS: Stretchable Electrodes C. S. Park, M. Maghribi Characterizing the Material Properties of Polymer-Based Microelectrode Arrays for Retinal Prosthesis

  8. Biaxial Loading—10% Strain • Geometry • PDMS: t = 100μm • Gold: t = 100nm, w = 30μm, L = 240μm, pitch (p) = 120μm • Material Properties • PDMS: E = 500kPa, v = 0.5 • Gold: E = 78GPa, v = 0.44 Stress Contour Plot Strain Contour Plot

  9. PDMS & Gold Electrode Strain

  10. BioMEMS: Loading Curves • Operating pressure < 15psi • Young’s Modulus PDMS E = 500kPa • Thickness = 100um • Membrane diameter = 1cm • Loading post diameter = 0.7cm

  11. Fabrication: Baseplate Step 1:Clean Pyrex 7740 4” glass wafer (300μm thick), dehydrate 5min @ 200°C Equipment: Acetone/Methanol/IPA/DI rinse Location: MERL Glass

  12. Fabrication: SU-8 Processing Step 2: Spin 1st layer SU-8-100(100μm thick), prebake 10min @ 65°C, softbake 30min @ 95°C, expose, postbake 1min @ 65°C, 10 min @ 95°C Equipment: Spin coater, hot plate, exposer Location: MERL Channels to apply vacuum pressure to PDMS membrane Glass Glass Exposed SU-8 Unexposed SU-8

  13. Fabrication: SU-8 Processing Step 3: Spin 2nd layer SU-8(100μm thick), prebake, expose, postbake Equipment: Spin coater, hot plate, exposer Location: MERL Loading post to support PDMS membrane Glass Exposed SU-8 Unexposed SU-8

  14. Fabrication: SU-8 Processing Step 4: Spin 3rd layer SU-8(100μm thick), prebake, expose, postbake Equipment: Spin coater, hot plate, exposer Location: MERL Glass Exposed SU-8 Unexposed SU-8

  15. Fabrication: SU-8 Processing Step 5: Spin 4th layer SU-8(80μm thick), prebake, expose, postbake Equipment: Spin coater, hot plate, exposer Location: MERL Glass Exposed SU-8 Unexposed SU-8

  16. Fabrication: SU-8 Processing Step 6: Develop SU-8, IPA/DI rinse Equipment:Location: MERL Glass Exposed SU-8

  17. Fabrication: SU-8 Processing Step 7:Pipette tetrafluoropolymer (PS200 or T2494) to prevent PDMS membrane stiction Equipment:Location: MERL Glass Exposed SU-8 Tetrafluoropolymer

  18. Fabrication: Baseplate Assembly Step 8: Laser cut Pyrex 7740 4” quartz wafer (300μm thick) and bond quartz over SU-8 Equipment: Laser cutter Location: MERL 20μm clearance between loading post and PDMS membrane Glass/Quartz Exposed SU-8

  19. Fabrication: PDMS Membrane Step 1: Clean 4” silicon wafers Equipment:wbnonmetalLocation: SNF Silicon

  20. Fabrication: PDMS Membrane Step 2: Spin sacrificial layer 5% (w/v) poly(acrylic acid) (PAA) (3000 rpm, 15 s) and bake (150C, 2 min) Equipment:Spin coater, Hot plateLocation: MERL Silicon PAA

  21. Sacrificial Layers—PDMS Micromachining • Advantages of water-soluble films • Deposited by spin-coating • The solvent removed at a low temperature (95–150C) • The resulting layer can be dissolved in water • No corrosive reagents or organic solvents • Faster release of features by lift-off • Compatible with a number of fragile materials, such as organic polymers, metal oxides and metals—materials that might be damaged during typical surface micromachining processes

  22. Sacrificial Layers—PAA & Dextran

  23. Fabrication: PDMS Membrane Step 3: Spin 20:1 Sylgard 184 poly(dimethylsiloxane) (PDMS) (40μm thick), bake (60C, 1 hr), O2 plasma Equipment:Location: MERL 2mm gap at edge of wafer to prevent lift-off of PDMS during processing Silicon PAA PDMS

  24. Fabrication: Electrode Array Step 4:Align beryllium copper shadow mask and temporarily bond. Equipment: EV aligner Location: SNF 30μm width tracks for electrode connections Silicon PAA PDMS Shadow Mask Ti Au 20μm diameter electrodes

  25. Fabrication: Electrode Array Step 5: Evaporate Ti adhesion layer (10nm thick) and Au layer (100nm thick) Equipment: Innotec Location: SNF 30μm width tracks for electrode connections Silicon PAA PDMS Shadow Mask Ti Au 20μm diameter electrodes

  26. Fabrication: Electrode Array Step 6: Remove shadow mask, O2 plasma Equipment: Drytek Location: SNF Silicon PAA PDMS Shadow Mask Ti Au

  27. Fabrication: Electrode Array Step 7:Prebake 110°C, spin photo-patternable silicone (PPS) WL5153 30sec @ 2500rpm (6μm thick), expose*, postbake @ 150°C**, develop Equipment: Hot plate, Spin coater, Karl Suss*, BlueM oven**, wbgeneral Silicon PAA PDMS Shadow Mask Ti Au PPS *Proximity exposure **Need to characterize in BlueM Oven

  28. Fabrication: Electrode Array Step 8:Dissolve sacrificial layer PAA in water Equipment: wbgeneral Location: SNF Silicon PAA PDMS Shadow Mask Ti Au PPS

  29. Fabrication: Electrode Array Step 9: Air dry device Equipment: N2 gun Silicon PAA PDMS Shadow Mask Ti Au PPS

  30. Fabrication: Assembly Step 1: O2 plasmaPDMS and quartz surfaces Equipment: Drytek Silicon PDMS PPS Ti Au Glass/Quartz SU-8

  31. Fabrication: Assembly Step 2: Bond PDMS membrane to glass Ti Au SU-8 Glass/Quartz PDMS PPS

  32. Next Steps • Transparency masks SU-8 molding • Laser cutting quartz • Plate electrodes on PDMS • Finish SNF training

  33. Acknowledgements

  34. Sacrificial Layers—PDMS Micromachining • Challenge: etchants may diffuse through PDMS membrane—these traces may ultimately by harmful to cell culture

  35. Sacrificial Layers—PDMS Micromachining • Photoresist—acetone removal through selectively etched holes • Backside etch stop of 4000A thick SiO2—1 mm thick PDMS membrane coated with 540A thick sputtered Cr covers PDMS membrane and a PDMS mold is created to protect the whole PDMS structure. • Water soluble sacrificial layers—dextran and PAA—insoluble in most organic solvents!

  36. Sacrificial Layers—PAA & Dextran • Films were prepared by spin-coating (3000 rpm, 15 s) from a 5% (w/v) polymer solution in water. • Films were then dried by placing the substrates on a hot plate at 150C for 2 min.

  37. Stimulation Electrodes • Goal: To pattern gold electrodes within a flow chamber for selectively stimulating hESCs • Electrodes 100μm x 5000μm (10 per well) • Interelectrode distance 1000μm • Contacts pads 2mm x 2mm (10 per well) • Polished glass wafers 1 mm thick

  38. BioMEMS: Strain gauge • Need a strain gauge and a reference strain gauge for every deformable area.

  39. Strain gauge design • Length (L) • Trace width (w) • Number of turns (t) • Distance between turns (p)

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