Soft Fabrication and Polymers

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1 Introduction to BioMEMS & Medical Microdevices Soft Fabrication and Polymers Companion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, by Prof., R012408

2 Biomaterials What is a biomaterial? Natural, synthetic and biological materials. Classes of biomaterials: Implanted or have other direct contact with living tissue (in vivo), Transport or containment function (in vitro), Process function (functionalized materials).

3 Advantages of Polymers 1. Improved and easier machinability. 2. ptical transparency for certain detection strategies 3. Biocompatibility. 4. Acceptable thermal and electrical properties. 5. Ability to enclose high-aspect-ratio microstructures. 6. Ability for surface modification and functionalization.

4 Soft Fabrication 1. Soft lithography. 2. Micromolding D Photopolymerization. 4. Smart polymers and hydrogels. 5. Nanomedicine techniques. 6. Thick-film technologies. 7. Array patterning.

5 Micro-Contact Printing (µcp) Nguyen, N.T. and S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA (2002).

6 PDMS (Silicone) Stamp PDMS (Silicone) Stamp PDMS (Silicone) Monomer Nguyen, N.T. and S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA (2002).

7 Example: PDMS Microfluidic Device Jaehoon Chung & Euisik Yoon

8 PDMS Molding Station

9 PDMS Castings

10 UV-zone Surface Treatment

11 Inspecting the PDMS casting

12 Alignment on Substrate

13 Video Inspection of Alignment

14 Inspecting the Final Device

15 Test Apparatus

16 Jaehoon Chung & Euisik Yoon

17 Micromolding Injection Molding Reaction Injection Molding Hot Embossing Injection Compression Molding Thermoforming Atmospheric Molding AMANDA

18 Injection Molding Left: Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp (2004). Right: Image courtesy of Thermotech

19 Variotherm Process Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp (2004).

20 Hot Embossing Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp (2004).

21 Thermoforming Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp (2004).

22 3-D Photopolymerization Three-dimensional photopolymerization is based on layer-by-layer assembly, and is used for rapid production of devices for modeling and prototyping: Stereolithography (SL) Microstereolithography (MSL) Dynamic Projection MSL

23 Photopolymerization UV curing occurs between 225 and 550 nm. Free radical curing: When the photoinitiator is exposed to UV, they break down leaving components with an unpaired electron, or free radicals. Propagation occurs with addition of monomers, and transfer of the free radical down the propagating chain to continue the process of addition of monomers. Termination occurs when the growing chain stops. Acrylates are associated with free radical polymerization.

24 Ionic polymerization: Involves an attack on the π electron pair of a monomer. Cationic curing : Cationic polymerization occurs when the active site has a positive charge (in contrast to anionic polymerization in which the active site has a negative charge). Addition of monomers moves the charge down the chain until termination occurs. Epoxies are associated with cationic curing.

25 Microstereolithography (MSL) Suzumori, K. and et al., Microfabrication of integrated FMAs using stereolithography. Proceedings of IEEE MEMS, pp (1994)

26 Dynamic Mask Projection MSL Bertsch, A. et al., Microsterolithography using a liquid crystal display as dynamic generator. Microsystem Technology 3(2), pp (1997).

27 MSL Fabricated Parts Clips Car Gear Bone Bertsch A., 1998, 1999, 2001, Personal Correspondence.

28 Pipe Cup Gear Screw Bertsch A., 1997, 1999, Personal Correspondence.

29 Smart Polymers and Hydrogels Smart polymeric materials exhibit significant changes in their characteristics with small changes in their environment. These external stimuli include ph, calcium, magnesium, organic solvents, temperature, magnetic field, electrical potential, and IR and UV radiation. Some materials respond to dual stimuli such as calcium and PEG, calcium and temperature, calcium and acetonitrile, ph and temperature, and light and temperature. Electroactive polymers (EAPs) respond to electrical stimulation.

30 Smart polymers are either reversible soluble-insoluble (SIS) in aqueous media or cross-linked in the form of hydrogels. SIS polymers include synthetic polymers such as poly (N-isopropylacrylamide) (PNIPAAm) and methylmethacrylate polymers; and natural polymers such as alginate and chitosan (polysaccharides). * H 2 C CH C n * NH CH CH 3 H 3 C Poly(N-isopropylacrylamide) (PNIPAAm)

31 Natural Polymers * C - H H * n H 2 N H H C - H - C - C H H Alginate * CH 2 H HH 2 C n * NH H NH 2 H 3 C H C Chitosan

32 Hydrogels osterbroek, R.E. and A. van den Berg, Lab-on-a-Chip: Miniaturized Systems for (Bio)Chemical Analysis and Synthesis, 1st ed. Amsterdam, Elsevier (2003).

33 When a stimulus is applied at a critical level, both SIS and hydrogels increase or decrease their overall hydrophilicity and either swell or shrink respectively. Physical hydrogels are held together with noncovalent forces and have hydrophilic and hydrophobic domains. Chemical hydrogels are held together by crosslinking, and have regions of high and low crosslinking. Areas of low crosslinking allow higher swelling.

34 Synthesis H H Acrylic Acid (AA) 2-hydroxyethyl methacrylate (HEMA) H 2 CH 3 Ph CH 3 Ethyleneglyco dimethacrylate (EGDMA) 2,2'-dimethoxy-2-phenyl acetophenone (DMPA)

35 Synthetic Hydrogels

36 Hydrogel Applications Controlled drug delivery. Thermo-responsive microfluidic actuator. Ultrasensitive microcantilever sensor. Combined with optically active nanoparticles, light frequency-dependent optical switching can be accomplished. ptical control by fiberoptics at a distance. Tissue scaffolding devices with selective diffusion.

37 Summary Biomaterials for medical diagnostics and therapeutics include natural, synthetic and biological materials that have contact with humans or human products such as blood, urine, cerebral spinal fluid, organs and other tissue. Soft Fabrication includes: Soft lithography. Micromolding. 3-D Photopolymerization. Smart polymers and hydrogels. Nanomedicine techniques. (see textbook) Thick-film technologies. (see textbook) Array patterning (to be covered later).