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BE 167L Lecture 4 General (ppt)

BE 167L Lecture 4 General (ppt) - BE 167L –...

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Unformatted text preview: BE 167L – Bioengineering Lab Lecture 4 Goals for this lecture •  Get a sense for how so; lithography works •  Get a preview of what you’ll be doing in lab •  Get a survey of what types of research could be done using so; lithography as a tool •  Get ideas for what type of experiment you want to do in lab Bioengineering covers a large range of length scales Ostuni et al. Langmuir 2003 Miller et al. Tiss. Eng. 2002 3 •  MicrofabricaFon and So; Lithography – Miniaturize designs – Observe controlled experiments – Change designs quickly •  ApplicaFons to Microfluidics, Microcontact PrinFng Patterned cell growth studies Agarose stamp transfers cells into patterned culture Stevens et al. Biomaterials 2005 Laminin is micro-contact printed with a PDMS stamp to pattern neural cell attachment Lauer et al. Biomaterials 2001 Microfluidic systems •  laminar flow, micromanipulaFons •  lab ­on ­a ­chip •  study individual cells •  sort cells 6 So; Lithography •  Micro ­ and nanofabricaFon techniques based on so;/ elastomeric materials as paRern transfers •  •  •  •  •  •  micro ­contact prinFng replica molding micromolding in capillaries microtransfer molding elastomeric membranes microfluidic devices 7 Microfluidic FabricaFon Overview 2D to 3D Process •  2D drawn mask used to make 3D structures •  Depth controlled by photoresist layer Drawing •  Photomask design creates bas relief features using photoresist on silicon wafer, it “masks” other layers –  negaFve resist cures w/UV –  posiFve resist so;ens w/UV Elastomers can be PDMS, gels, other soft polymers. Elastomer is cured on master mold to make flexible stamp Stamp is used for different applications I. CAD design/Adobe Illustrator Make photomask a. transparency (cheap and fast) high-res commercial printer 5060 dpi = 20 micron res CAD/ART makes 20,000 dpi b. Chrome photomask on quartz ($100s-$1000s, months) 1 micron and below res II. Choose a photoresist and make the master on silicon wafer. note: Masters can be difficult to make and often require a clean room. Both chrome photomasks and completed master molds can be ordered from commercial vendors through the NSFsponsored National Nanotechnology Infrastructure Network (NNIN) Qin et al. Nature Protocols 2010 Using a cleanroom Laminar flow cleanroom Preparing Wafers 4” Silicon Wafers – Previously cleaned with “Piranha” and dehydrated Oxygen plasma to oxidize the silicon surface Spinning Photoresist spreading Photoresist spreading Silicon wafer RotaFon Controlling Photoresist Thickness Viscosity, spin speed, and spin Fme affects final photoresist thickness Photolithography •  Put mask in Fght contact with wafer and expose with UV light for a known Fme period A Completed Mold Molding with Polydimethylsiloxane (PDMS) for a microfluidic device Why PDMS? •  moderately sFff (shear mod.= 0.25 MPa, Young’s = 0.5 MPa) •  conforms to surface with atomic level contact (good seals, microfluidic devices) •  non ­toxic, commercially available (~$80/kg) •  opFcally transparent to 300 nm •  hydrophobic, but can be made hydrophillic with oxygen plasma •  can adhere and seal reversibly, or irreversibly a;er oxidaFon, to many different surfaces 19 PDMS Curing Part B Part A Sylgard is trade name for PDMS, (Dow ­Corning) 1.  Mix vigorously 10:1 Part B:Part A 2.  De ­gas in vacuum chamber 3.  Cure at 65 C for 2 hrs PDMS Bonding Plasma – ionized gas – interacts with the PDMS surface to oxidize it and make it reacFve. 1.  lass and PDMS place in G machine 2.  acuum drawn V 3.  mall amount of O2 or air S introduced into the chamber 4.  adio frequency power supply R turned on 40 WaRs. 5.  ait 30 seconds W O ­ Si O ­ O ­ O ­ Si Si Si PDMS/Glass Surface What is plasma? •  A 4th state of maRer •  A mixture of ionized atomic nuclei (oxygen, nitrogen, etc…) and free electrons. •  Ionized Oxygen is very reacFve, when it bumps into something it will react or bind to it. •  Free electrons are very reacFve and when they recombine with the atomic nuclei, they release energy in the form of light (the halo or corona of blue/pink light) and heat. Final Assembled Device BioPOETS Laboratory Tubing added to punch holes Micro ­contact prinFng •  Stamp molecules that affect weRability and other chemical properFes in paRerns •  proteins or cells can also be stamped Zhao, Xia, and Whitesides, J. Mater. Chem. 1997 Xia and Whitesides, Ann. Rev. Mater. Res. 1998 •  Replica molding – make surfaces with specific designs – change surface properFes – make non ­flat molds Zhao, Xia, and Whitesides, J. Mater. Chem. 1997 Elastomeric membranes for dry li; ­off Whitesides et al. Ann. Rev. Biomed. Eng. 2001 26 •  micromolding in capillaries •  microfluidic devices Chen et al. Proc Natl Acad Sci U S A. 2003 Zhao, Xia, and Whitesides, J. Mater. Chem. 1997 Reminders: •  Case study 1 next Tuesday •  Start thinking about what kind of experiment you want to try in lab ...
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