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Introduction to BioMEMS & Medical Microdevices
“Soft” Fabrication and PolymersCompanion lecture to the textbook: Fundamentals of BioMEMS and Medical Microdevices, by Prof. Steven S. Saliterman, http://saliterman.umn.edu/
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Steven S. Saliterman
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).
Steven S. Saliterman
Advantages of Polymers
1. Improved and easier machinability.
2. Optical 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.
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Steven S. Saliterman
“Soft” Fabrication
1. “Soft” lithography.
2. Micromolding.
3. 3-D Photopolymerization.
4. “Smart” polymers and hydrogels.
5. Nanomedicine techniques.
6. Thick-film technologies.
7. Array patterning.
Steven S. Saliterman
Micro-Contact Printing (µCP)
Nguyen, N.T. and S.T. Wereley, Fundamentals and Applications of Microfluidics, Artech House, Boston, MA (2002).
Steven S. Saliterman
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).
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Steven S. Saliterman
Example: PDMS Microfluidic Device
Jaehoon Chung & Euisik Yoon
Steven S. Saliterman
PDMS Molding Station
Steven S. Saliterman
PDMS Castings
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Steven S. Saliterman
UV-Ozone Surface Treatment
Steven S. Saliterman
Inspecting the PDMS casting
Steven S. Saliterman
Alignment on Substrate
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Steven S. Saliterman
Video Inspection of Alignment
Steven S. Saliterman
Inspecting the Final Device
Steven S. Saliterman
Test Apparatus
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Steven S. Saliterman Jaehoon Chung & Euisik Yoon
Steven S. Saliterman
Micromolding
Injection Molding
Reaction Injection Molding
Hot Embossing
Injection Compression Molding
Thermoforming
Atmospheric Molding
AMANDA
Steven S. Saliterman
Injection Molding
Left: Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).
Right: Image courtesy of Thermotech
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Steven S. SalitermanHeckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).
Variotherm Process
Steven S. Saliterman
Hot Embossing
Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).
Steven S. Saliterman
Thermoforming
Heckele, M. and W.K. Schomburg, Review on micro molding of thermoplastic polymers. Journal of Micromechanics and Microengineering 14(3), pp. 1-14 (2004).
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Steven S. Saliterman
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
Steven S. Saliterman
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.
Steven S. Saliterman
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 .
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Steven S. Saliterman
Microstereolithography (MSL)
Suzumori, K. and et al., Microfabrication of integrated FMAs using stereolithography. Proceedings of IEEE MEMS, pp. 136-141 (1994)
Steven S. Saliterman
Dynamic Mask Projection MSL
Bertsch, A. et al., Microsterolithography using a liquid crystal display as dynamic generator. Microsystem Technology 3(2), pp. 42-47 (1997).
Steven S. Saliterman
Clips Car
Gear BoneBertsch A., 1998, 1999, 2001, Personal Correspondence.
MSL Fabricated Parts
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Steven S. Saliterman
Pipe Cup
Gear ScrewBertsch A., 1997, 1999, Personal Correspondence.
Steven S. Saliterman
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.
Steven S. Saliterman
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 methyl-methacrylate polymers; and natural polymers such as alginate and chitosan (polysaccharides).
CH
H2C
C
CH CH3O
NH
*
*
H3C
n
Poly(N-isopropylacrylamide) (PNIPAAm)
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Steven S. Saliterman
O
OO
OO OOH OH
O
OH
OH
O
HO
HO
*
*
HO
COO-
-OOC
-OOC
COO-
H2N
n
Alginate
O
O
OH
O
OHO
**
NH2
NH
C
OH3C
HOH2C
CH2OHn
Chitosan
Natural Polymers
Steven S. Saliterman
Hydrogels
Oosterbroek, R.E. and A. van den Berg, Lab-on-a-Chip: Miniaturized Systems for (Bio)Chemical Analysis and Synthesis, 1st ed. Amsterdam, Elsevier (2003).
Steven S. Saliterman
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.
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Steven S. Saliterman
Synthesis
OH
O
Acrylic Acid (AA)
O
OH
O
2-hydroxyethyl methacrylate (HEMA)
O
O
O
H2O
Ethyleneglyco dimethacrylate (EGDMA)
O
OCH3
Ph
OCH3
2,2'-dimethoxy-2-phenyl acetophenone (DMPA)
Steven S. Saliterman
Synthetic Hydrogels
Steven S. Saliterman
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.
Optical control by fiberoptics at a distance.
Tissue scaffolding devices with selective diffusion.
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Steven S. Saliterman
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).